Marwan Al Heib

Pascal Bigarre

Jean-Pierre Josien

Yves Guise

Détente

Détente par saignée de voies profondes : une méthode efficace pour la lutte contre les coups de terrains

RESUME

Dans cet articie, nous avons cherche ä apprecier l'efficacite de cette methode par la modelisation numerique. Nous avons utilise le code UDEC base sur l'approche des elements disdncts. Cette modelisation valide la methode et met en evidence son efficacite confirme par les observations et mesures m situ. Elle permet egalement de comprendre le röle positive du procede employe. Les resultats sont tres encourageants. Nous avons mis en evidence que l'efficacite de la saignee est d'autant plus importante que les contraintes initiales horizontales sont tres fortes. ABSTRACT Dynamic floor heavage m deep coal mines may be alleviated using extensive floor slottmg before mining operadons Start. Cleariy identified äs efficient from in situ observations, this method has been tested on numerical simulations of the fractured rock mass. Stress/strain relief in the floor has been qualified and compared with measurements.

Results show that floor slotting is an attracdve method for Rockbursting alleviadon äs well äs safe and economical to work out. l.

INTRODÜCTION

The management of the Provence Operations ünit of the Houilleres du Bassin du Centre et du Midi (Charbonnages de France Group) has drawn up a geological engineering scheme to control dynamic phenomena.

This programme introduces a coherent approach tailored to the development of workings m the mine. It is based essentially on methods of relieving Stresses around roadways. In principle, the different methods involve eüminating original and induced stress concentradons and modifying the brittle character of the rock mass. If this objective is not achieved, the slot would make it possible to inidate the phenomenon at an appropriate dme.

Stress relief holes have been known and used for a very long dme. A new method was recendy introduced which involves simply making a slot in roadway floors.

In this artide, we shall begin by describing the principle of the method and the resources necessary for its applicadon. We shall then give a comparison between a zone to which this method has been applied and one to which it has not.

A numerical simuladon using the disdnct element method has been carried out to determtne the role of the slot and the mechanisms this type of stress relief m volves.

PRINCIPLE OF THE METHOD

A slot is made parallel to the centre line of the roadway. This allows controüed operadon with regard dynamic phenomena in the wall and dissipadon of die stored energy. Figure l shows die roadways in which slots were made. The slot can be produced by a machine fitted widi a disk cutter (Fig. 2). The slots currently used by HBCM are 90 cm deep and 15 cm wide. For sadsfactory operadon, die slot must be produced before the seam is worked. Subsequently die slot is monitored over dme to assess its effecdveness.

Figure 3 shows how die widdi of die slot changes äs a funcdon of distance from the cutdng face.

After die first pass, die measured widdi is only 7 to 8 cm on the average instead of 15, indicädng a closure of the order of 8 cm, virtually half the inidal widdi. It may also be noted that slip between strata is fostered because the measurements and the follow-up observadons have often shown a stepped shape. Since 1992 all roadways have been treated with this method.

COMPARISON OF TREATED AND UNTREÄTED ZONES

A number of faces distributed through all districts were systemadcally monitored. Table l shows that no floor heave was recorded in the treated zones. In the main roadway, no suspicious event was recorded in the treated zones but two suspicious events were recorded in the nontreated zones. Comparison is more difficult in the auxiliary roadways.

NUMERICAL SIMULATION

The aim of numerical sünuladon is mainly to understand the stress relief mechanism introduced by the slot in the roadway wall. It is also possible to evaluate the efficiency of the slot in eüminadng any danger of wall bowing. The quesdon arises äs to whether cutdng the slot in the wall of the roadway does not also modify the behaviour and Stresses in the roadway facing.

Many parameters influence behaviour, and numerical modelling will also make it possible to determine the influence of each. The UDEC code (ITASCA, 1994) was used. The choice of numerical method (distinct elements) was determined by the substantial stratificaüon for the Operation of the slot.

4.l Descripüon of a model * Geometry

The roadways excavated in Provence are virtually rectangular in section, 6 m wide and 3 m high. The woridngs involve altemate seams of coal and beds of liniestone.

* Geological characterisücs

The strata in the Provence mine mainly consist of very hard rocics (Rc> 100 MPa).

INERIS carried out laboratory tests to charactedse the coal and the strata in the roof and walls (TRITSCH, 1993 andGHOREYCffl, 1982). Areducing coefficient of 0.5 was adopted so äs to take fracturing and the real characteristics of the rock into account (BIENAWSKI, 1989).

The rocky strata behave in an elastic-plastic manner. The Mohr-Coulomb plasticity cntenon was chosen. However the stratification joints were not characterised owing to the difficuldes of sampling and testing the joints. The joints were therefore modelled on the basis of theoretical and pracdcal considerations and a number of observations.

* Loading

The inidal Stresses have been measured over a long penod. The results showed that the Provence mine was characterised by major horizontal Stresses between l and 3 dmes the vertical stress.

Two loadings were used, one with the vertical stress and a horizontal stress twice äs high, the other with die same vertical stress but a horizontal stress of 0.5 dmes the verdcal stress.

The phases of caiculation were äs follows:

-the roadway excavation phase;

-the slot production phase;

-the advance of the cutting face.

Results and interpretadon

By analysing the parameters it is possible to quantify and analyse the behaviour of the roadway. These parameters are the defonnadon, the movements of joints and the new stress distribudon.

The displacements induced by the producdon of the slot are found to be in the roadway wall. The displacement caused is equal to a third of the displacement induced by the gallery (Fig. 4).

Changes in the slot depend on the inidal horizontal Stresses -It can be seen (Fig. 5) that the slot begins to funcdon äs soon äs it is cut with mobilisadon of the joints. The slot is deformed by a greater amount for the simuladon of a cutdng face.K*)

The final closure state is of the same order of magnitude äs that obtained by the in situ measurements after the cutdng pass. The joints in the roadway wall undergo slippage induced by shear Stresses. Joint shearing also occurs in the roof Supports, which agrees with the observed process of roof damage.

Comparison of the two simuladons with and without slots show the value of the slot The extension of the slip zones due to shear is much greater when no slot is present (Figs. 6 and7).

» t l l I l

1 I l l l i i l l 1 1 1 l 1 ! I i ! J l i li l The high horizontal Stresses are localised at the introduced is of the Order of 30%. This relief is bottom and middle of the wall (60 MPa).

I l i \ \ \ \ \ F .

I l i l i \ \ \ I I 1 1 l ! \ \ \ \

not limited only to the wall. The facings are also Following cutdng of the slot, these stresses fall stress relieved over a considerable distance (Figs. significantly (40 MPa). The stress relief 8 and 9).

Hg. 5 : Slot section äs a funcdon of distance frorn cutting face

CONCLUSION

In this arücle we have analysed the behaviour of the rock mass in the vicinity of roadways treated by slots. Comparison of in situ observations in the treated zones with those made in untreated zones demonstrated the efficiency of this method and led to its being incorporated in the geological scheme for controlling dynamic phenomena.

The numerical modelling approach was used to analyse and quantify the role played by the slot.

The results show that the slot makes an effecdve contribution to stress relieving the wall in the case of high initial horizontal stresses and to stress relieving the roadway facing.

The deformations and displacements obtained by the caiculation are comparable with the in situ measurements.

6.

Joints Mifch FH or SH = 0.0 shear displacements on Joinfcs max shear disp = 2.263E-02

eaoh Une thick = 8.922E-03

. '1.300 . 4,200 Flg. 5 : Slot section äs a funcdon of distance from cutting face

-.1.600 -4. «100 -4.200 -î 1 1 1 1 1 1-i ] 1-i 1 1 1 1 1 r-[-i f 4,
T 1-7--1-1 1-1-1-|-1-1-1-1-r~]-1-

CONCLUSION

In this ardcle we have analysed the behaviour of the rock mass in the vicinity of roadways treated by slots. Comparison of in situ observations in the treated zones with those made in untreated zones demonstrated the efficiency of this method and led to its being incorporated in the geological scheme for controlling dynamic phenomena.

The numerical modelling approach was used to analyse and quantify the role played by the slot The results show that the slot makes an effective contriburion to stress relieving the wall in the case of high initial horizontal Stresses and to stress relieving the roadway facing.

The deformations and displacements obtainedby the caiculation are comparable with the in situ measurements.

  DETENTE PAR SAIGNEE DE VOffiS PROFONDES: UNE METHODE EFFICACE POUR LA LUTTE CONTRE LES COUPS DE TERRAINS A SIMPLE METHOD FOR THE ALLEVIATION OF DYNAMIC PHENOMENA IN MINE STRÜCTÜRES ALHEIB M. 1 *, BIGARREP.*, JOSIEN J. P. 2 **, GU1SE Y. 3 ***

  Fig. 2 : UNAC cutting machine

  Slot changes äs a funcüon of distance from the cutting face 17 measured at metric points 3340 and 3342

Fig. 4 :

 4 Fig. 4 : Displacements induced only by production of tne slot

Fig. 6 :

 6 Fig. 6 : Shear displacements of joints after slotting with a vertical loading of 30 MPa

Table l :

 l Effecüveness of the slot

Rg. l : Location of slots


A D Jones

Z Pokryszka

S Lowrie

C Tauziede

P-M Dupond

A PHYSICAL SCALE MODEL OF FLOWS IN THE WASTE OF A RETREAT LONGWALL COALFACE

A physical model has been developed to simulate the flows and mixing of gases in the waste of a longwall retreat coalface. The model is used in conjunction with computational modelling, and the distributions of permeability and gas emission in the model waste fotlow those in Computer simulations (Pokryszka et al 1996). The physical model represents at 1/70th scale a 200 m long, 3 m high coalface with a waste extending up to 280 m to the face start line. The model is tilted to the same seam slopes äs the real face, e.g. 22° ascensional Ventilation along the face and 7° slope to the dip. The purpose is to investigate the flow of three components: Ventilation seepage flow through the waste; methane; and nitrogen injected to quell spontaneous combustion. A heavier-than-airSurrogate gas (SF g ) is used in place of methane, and therefore the model is inverted so that gas layers form along the "rooP. The main forces driving the flows in the waste (pressure gradients due to Ventilation and the density difference of gas layers) are kept in proportion by appropriate scaling of the permeability. Calibration and validation used data from a coalface at a mine in the Lorraine coalfield. The model is now in operational use.

INTRODUCTION

Background Both physical and Computer modeis are dependent on data from the real mine for calibration and validation. The two types of modelling also assist each other. For example, measurements of Ventilation flows in the roadways and face are evidence of the seepage flow through the waste and these data are interpreted by the Computer model to produce estimates of the permeability of the waste; these estimates serve, in the present catibration of the physical model, äs the specification for the distribution of permeability. Conversely, physical modeis have traditionally been used to lest and develop Computer modeis, e.g., Sorbie et al (1990). Once consistency between the two types of model has been demonstrated (or differences satisfactorily explained), then greater confidence can be placed in results (rom modelling changes in mining or Ventilation conditions. The Computer simulations may be more readily suited to varying some Parameters such äs face length. Conversely, there may be situations where the results of the physicat model appear more realistic.

The mines in the Lorraine coalfield have faces with steep stopes, significant gas emission from the waste, and are prone to spontaneous combustion; hence the importance of effective control of the circulation of gases (air, methane, and nitrogen used to quell combustion) within the waste. As part of a Programme of studies intended to provide information which will aid Ventilation engineers to make optimal use of the resources at their disposal, an aerodynamically scaled model has been developed, calibrated and validated in conjunction with a Computer model used at INERIS to simulate the flows through the waste (Pokryszka, 1996).

This paper describes the aerodynamic scaling, the structure of the physical model, results of tests to calibrate the modet to the conditions on a particular French coalface (DORA 1 SUD), and initial tests using the model to examine the consequences of changes in the techniques used for control of gas or spontaneous combustion. The validation included measurements of transit times across the waste for comparison of the model with the real waste Underground, thereby indicating whether similar distributions of velocities apply across the model and real wastes.

Objectives The objectives were to design, construct, calibrate, validate a physical model representing the entire zone of the waste, with aerodynamic scaling of the forces included in the Computer simulations (ie., pressure gradients due to Ventilation and gas density differences, and the resistance öf the face and waste). The model was intended to be small enough so that important features (e.g., seam slopes) could be changed to represent different situations. This is possible with a 1/70th scale model, äs described below, although it unavoidably involves sacrificing the completeness of the aerodynamic scaling of the flows on the face (Jones and Lowrie, 1995).

SCALING RELATIONSHIPS Physical Processes Controlling the Plow and Dispersion

The flow and mixing of gases within the waste are controlled by: • inertiat dispersion -a function of the Reynolds number (R s =udyv a ) and occurs at R " > about 2; • dispersion by molecular diffusion -a function of the Peclet number (P^ud^/D); • pressure gradients -produced by the main Ventilation and by differences in the density of the gases (due to both temperature and composition).

The Reynolds number and Peclet number are functions of the velocity of the seepage airflow through the waste (u), the nominal grain diameter (d), and respectively, the kinematic viscosity v a of air and the coefficient of diffusion of the emitted gas (D).

The structure of the waste affects the relative importance of these processes; in principle, the model waste could represent a real waste where there are either fissures between large blocks of rock or a relatively homogenous bed of crushed granulär material. In the first instance, the latter was chosen because it aids straightforward comparison with the Computer models which treat the waste äs a permeable material.

Similitude of Flows for the Seventieth Scale Model

Since the internal structure of the real waste cannot be specified exactiy, only indirect estimates were available for the nominal diameter of grain or fissure; hence the Peclet and Reynolds numbers also could only be order-of-magnitude estimates. Consequently, the main conditions for attaining similar flow in the model were (hat:

• the pressure gradients due to Ventilation or gas density should be scaled by the same factor; • the relative locations in the waste where inertial and diffusive mixing dominate should be similar; and • the effect of molecular dispersion should not become disproportionately large in the reduced scale model. Scaling factors fulfilling these requirements were derived (Jones and Lowrie, 1995) and are summarised in Table 1. This scaling includes the effects of density due to gas composition (e.g. methane vs air), but not temperature differences; äs was the case for the Computer model (Tauziede et al, 1993). The scaling of the flows between füll scale and model by x 4.3 x 10-4 (äs in Table 1 ) means that a flow of 10 m 3 s' in the füll scale becomes 4.3 litre per second, or 260 litres min -1 in the model. A typical district Ventilation flow of 30 m 3 s"' becomes 774 litres min-'.

With these scaling factors for the geometry, permeability and velocity, the Reynolds number (defined in terms of the nominal grain diameter) is kept constant. (The permeability is dependent on the grain size, Dullien (1975)). In principle, this constant Reynolds number should preserve the contribution made by inertial mixing to the dispersion at any given location in the waste. The above specification also maintains the pressure gradients, due to the difference in density (either between methane and air or between SF g and air) and due to the Ventilation respectively, in correct proportion. The transit time through the model is scaled down with both the change in velocity (x 2.1 ) and the reduction in geometrical scale. Le., by 6.8 x 10 -3 . Thus, for example, a transit time for flow though the waste of 10 hours in the füll scale becomes approximately 4 minutes in the model. The effect of molecular dif-fusion, although not kept fully in proportion to this transit time, remains relatively insignificant during transit times äs low äs this. In the waste, the product ud is kept constant in preserving the Reynolds number for the Ventilation flow through the waste. Therefore, the Peclet number udg/D (relevant to comparing the significance of molecular diffusion to the inertial mixing) changes in proportion to D which becomes the value for the Surrogate gas (SP g ). This means that the Peclet number (based on the nominal grain diameter) is larger in the model waste than in the füll scale waste by a factor of about 3. So the relative locations in the waste where the mixing of gases becomes dominated by either inertial or diffusive processes should be similar for the model and the füll scale.

The Peclet number based on the grain size is informative about the relative locations of inertial and diffusive mixing. However, a Peclet number can also be caiculated f rom the dimensions (i.e. length L or height h) of the coalface (which are scaled down by a factor of 1/70th) äs a basis for comparing the rate of transport by the flow with that by molecular diffusion. This gives a Peclet number uL/D which is approximately ten times smaller in the model than in the füll scale. So the effect of the seventy fold reduction in geometric scale (which would tend to increase the significance of molecular diffusion) has been ameliorated by the increase in velocity and the use of the Surrogate gas (with a lower diffusion coefficient). Consequently, mixing by molecular diffusion is still relatively slow in the small scale model.

Given the various uncertainties involved in estimating the conditions in the real waste, there appears to be sufficient resemblance between the flows in the füll scale and in the model.

MODELL1NG THE FLOW OF THREE GASES

Densities of Surrogate gases With SF g äs a Surrogate gas for methane, the density difference and the consequent pressure gradients are scaled by x 9.3. A Surrogate gas can also be used in place of the nitrogen in order to produce a proportionale increase in density difference. For example, the difference (0.04 kg m -3 ) between the densities of air (1.29 kg m -3 ) and nitrogen (1.25 kg m' 3 ) could be scaled up approximately by x 9.3 (and inverted) with the selection of argon (1.70 kg m-3 ). However, it has been reported by INERIS that the nitrogen at the point of injection is typically 10°C cooler than the ambient air temperature. This temperature difference is sufficient to reduce the density difference between air and nitrogen to zero, near the point of injection at least! In this Situation, the model could be used with one and then the other in order to investigate the effect of this order of difference in density.

Measurement of Gas Concentrations

The experimental procedures developed for determining the concentrations of 3 components (Ventilation air, injected nitrogen/ argon, and the emitted SF g ) used infra red absorption to measure the concentrations of the two injected/emitted components. However, neither nitrogen (N 2 ) nor argon (Ar) are detectable with the infra red gas analyzer; Consequently, a tracer gas mixed with the nitrogen/argon was used äs a marker of the gas concentration. Ethane (C 2 H 6 ) was chosen äs the tracer because: • its molecular weight of 36, and therefore its coefficient of molecular diffusion, are of the same order äs those for N ; , (molecular weight 28) or Ar (molecular weight 40); • it is measurable at an infra red wavelength which does not interfere with the measurement of SF " . At a concentration of approximatefy 3% in nitrogen or argon,

Retum Roadway Return Roadway

Abandoned Intake Roadway

Abandoned Intake Roadway the level of tracer is high enough for the gas analyzer to yield the measurements of interest but also low enough to ensure that the ethane does not create any risk of explosions (or the constraints associated with working with flammable gases).

DESIGN AND CONSTRUCTION OFTHE MODEL

The model comprised a rectangular box structure with an open channel representing the face and the (4 m x 3 m) zone representing the waste filled with granulär material of appropriate permeability, and with gas injection lines.

The 1/70th scale model required a tilting support table similar to that built for a 1/30th scale model (Jones and Lowrie, 1993). The tilting System consisted of two large hydraulic pistons which could raise one or the other end of a lower frame to produce angles of up to 35°; this lower frame held four smaller pistons acting in pairs to produce a transverse slope for the upper frame holding the model.

Consistency with the Computer Simulation

Preparation of the physical model to represent the distributions of permeability and gas emission for DORA 1 SUD äs estimated from the Computer Simulation involved: • approximating the continuous distribution of permeability (of the Computer Simulation) by zones ot selected materials of fixed (different) permeabilities; • obtaining the ränge of permeabilities by preparation and measurement (of the permeability) of a ränge of suitable materials; • approximating the continuous distribution of gas emission by point sources from the smallest practicable orifices in pipelines in the base of the waste; • spacing the orifices in the injection pipes to produce approximately the same Variation with distance from the face; • placing the injection pipes parallel to the roadways, and at intervals caiculated to give the specified distribution of emission with distance from the roadways; • supplying gas (SFJ injection flows to 17 zones of the waste, with each zone monitored independently by rotameters; • injecting gas along the coal face, simulating emission from the uncut coal seam.

EXPERIMENTAL MEASUREMENTS

Experimental measurements on the model comprised: • Ventilation flow, total and on the face, by pitot static tube and dilution of tracer gas; • pressure differences across the waste and face, with a micromanometer attached to an array of needle probes; • injection flows, with calibrated flow meters; • gas samples, collected from the waste using an array of 50 needle probes; • transit times for the flow across the waste, with helium äs a tracer gas (Pokryszka and Tauziede, 1995); • after calibration and validation, gas concentrations illustrating the model's use in simulating nitrogen injection at two alternative sites and three flows.

L«w

RESULTS

Flows and Pressure Gradients

The model was operated at the target flows for the Ventilation, gas emission, and drainage. The pressure gradient along the face was consistent with the estimated approximate target.

Concentration Distributions

With the model operating at the specified flows, the concentrations were measured at the array of sampling points in three lest runs, giving repeat samples at some of the sample points. Consistency appeared reasonably good between runs; therefore, the concentrations in Figure 1a are averages (where available). Figure 1a show the data for each sampling point and the curves indicate the main trends. Figure 1b illustrates the comparable trends caiculated from the Computer Simulation of the same face. The Computer simulations are readily adjusted to the real face length (of 240 m), whereas the physical model was equivalent to 200 m. Nevertheless, the main trends in the concentrations can still be compared between Figure 1a and Figure 1b. Importantly, the general trends appear sensibly consistent.

Characteristics of Velocity Distributions

Transit Times The transit time measurements were used to characterise the distribution of velocities around the face and waste. Depending on where the tracer pulse was injected and where the passirig pulse detected, the Signals either characterised the distribution of velocities for the entire ensemble of face and waste, or gave a direct estimate of velocity across the waste at a given distance from the face. Figure 2 shows the deformation of a rectangular pulse of tracer due to the ränge of different transit times involved in the passage of a pulse of tracer across the ensemble of face and waste. The data points indicate the measurements taken Underground (with observation points at finite inten/als äs samples were taken and subsequently analyzed); the curve of continuous readings taken from the experiment in the model follow a very similar shape; and the CFD Simulation also gives a similar predicted response.

Velocity Distribution for Flow in the Waste The transit times measured with injection and sampling points respectively in the abandoned intake and abandoned return roadways, and each at the same distance from the face, were used to estimate velocities across the waste at given distance from the face. The values estimated from measurements Underground, from measurements on the model, and from CFD simulations, are shown in Figure 3. The two sets of experimental data show similar dependence on distance from the face. The CFD Simulation shows the dependence äs a continuous function with velocity diminishing with distance from the face , eventually reaching a minimum level at about 80 m from the face where the waste is expected to be fully compacted. Near the face Start line, the compaction of the waste is less complete, and the velocity above the minimum level. This form of the dependence for the CFD Simulation was supported by comparisons with other experimental data from the real face at a later stage in its working when the waste had extended further, and from other faces investigated.

Example of Application of the Model Once the above results had supported the consistency of the model with the füll scale, a series of simulations (Jones et al, 1995) were undertaken to assess how the effectiveness of nitrogen injection would depend on site and rate of injection. This included injection at two alternative points in the intake abandoned roadway: (equivalent at füll scale to) 25 m or 90 m from the face; and each at three flow rates (0.3, 0.6 and 1.2 m 3 s 1 ). The results showed that the increase from the lowest flow rate produced a large increase in the area of the waste where the nitrogen injection reduced the air (and hence oxygen) concentrations to below the level needed to support combustion. However, further increase in nitrogen flow had relatively little effect on the concentration profiles. The concentration profiles fitted to the data (for concentrations at the array of sampling points) from the tests at the lower flows (0.3 and 0.6 m 3 s 1 ) are shown in Figure 4. The form of the dependence estimated from the CFD simulations is also very similar (Pokryszka et al, in press).

DISCUSSION

Calibration and Validation

The main points for comment concem the physical effects which have been taken into account in the scaling, the Information on which the 1/70th scale physical model is based, its consistency with both the real mine and the Computer Simulation, and the scope for its application.

The flows have been scaled for the effects of the Ventilation pressure, pressure due to the density difference of gas layers associated with differences in gas composition, the inertial and molecular dispersion in the waste, the permeability of the waste, and the resistance of the face.

The information from a Computer Simulation (Pokryszka et al, 1996;Tauziede et al, 1993) provided the best available definition of the distribution across the real waste of both gas emission and permeability and the model was prepared to match these specifications. The resultant pressure gradient across the model was shown to be consistent with pressure gradients estimated from Underground data (from ERNA 3 NORD and DORA 1 SUD).

The proportion of flow entering the model waste was similar to (hat in the füll scale (approximately 85% of the Ventilation on the face at its mid-point).

The data for the gas concentrations in the model showed satisfactory repeatability between repeat tests.

Comparison of the concentrations in the waste between Computer and physical model is affected by the way the Computer model treats the seam äs being two dimensional whereas the physical model Das a finite depth, so that data from the Computer are always average concentrations whereas data from the physi-cal modef are mid-seam concentrations. Nevertheless, the form of the concentration distributions in the waste were qualitatively similar for the physical model and the Computer Simulation (Pokryszka'et al 1996, Tauziede et al, 1994).

Probably the main limitation of the 70th scale model is that the flows on the 1/70th scale model face were not scaled for the effects of gas layering, and the model face was a simple open duct with the resistance to give the right balance of flows between face and waste. The exchange of gas between model waste and model face produced a relatively slower increase in concentration towards the return end of the face. However, such interchanges would be more suitable for modelling at the 1/30th scale: calibration and validation a thirtieth scale model is in progress.

In summary, the Operation of the model has shown that with permeabilities spanning a thousand fold ränge (10 -° to 10 -5 m 2 ) and gas emission flux varying over a 7 fold ränge, the concentrations obtained in the model were of similar magnitude to those in the füll scale and the transit times for flows through the waste were shown to be consistent with the scaling of the transit times for the füll scale waste.

The Example of Application

The nitrogen injection simulations show some marked differences between injection rates and injection sites. For example, it appears that injection of a low (0.3 m 3 ^1) nitrogen flow at 25 m from the (füll scale) face will probably be inefficient äs the concentration of air is reduced only in a relatively small zone. With injection at 95 m from the face, the low injection rate produced a larger area of high nitrogen concentration (and low air concentration) in the low permeability core of the waste. With injection at 0.6 m 3 s"', the area of low air concentrations became larger, and the critical zone of rapid change occurred near the periphery of the lowest permeability zone (äquivalent to about 70 m from the füll scale face). Further increase in nitrogen flow caused relatively little change in the zone of ihertisation.

CONCLUSIONS

The main conclusions are:

• an aerodynamically scaled physical model of the flows in the waste has been successfully designed, calibrated and validated in comparison with data from a real coalface and with consistency with a Computer Simulation of the same face; • simulations in the model have indicated how the effectiveness of nitrogen injection depends on the site of injection and the ftow used; and, again, the predicted trends showed consistency with those predicted from the Computer simulations; • the model is suitable for use in further simulations;

• the results of these initial simulations illustrate the use of the model in providing information to help engineers make optimal use of available resources.

THE FUTURE

The model described above was designed and constructed at the Institute of Occupational Medtoine (IOM), following a related Programme of work for the European Coal and Steel Community (ECSC) and British Coal which had produced the design and construction of a similar model representing the flows on the face in more detai), including the effect of gas density on dispersion of gas (Jones, 1994;Jones andLowrie 1994a, 1994b). This earlier model is designed for use äs a twentieth or thirtieth scale representation of a coalface and waste.

After the measurements described above, the seventieth scale model has been transferred to Charbonnages de France and is now utilized for simulations. For example, recent simulations have further examined the dependence of the effectiveness of nitrogen injection on the site of injection; these conf irmed (hat, for the conditions at DORA 1 SUD äs investigated above, injection at 25 m from the face is less effective than at approximately 100 m, and have indicated that injection at 50 m is äs efficacious äs at 100 m. The gas concentrations in the 1/70th scale model are now sampled from 64 sampling points with an automatic sequencing system, and the concentrations are measured directiy on line.

The thirtieth scale model remains at the IOM and has recently been calibrated to operate äs a physical analogue of Computer simulations.

Further investigations using both these physical modeis and the linking element of the CFD simulations are in progress and will be reported in due course. The available results of the CFD simulations are also currently being reported, e.g. (Pokryszka et al, in press).

Figure 1 :

 1 Figure 1:1a Concentrations Measured in the Physical Model; 1b Concentrations in the CFD Simulation.

  PREPARATION OF THE 1/70TH SCALE MODELTO REPRESENT DORA 1 SUD Main Characteristics of the face to be simulatedThe Characteristics of the face to be simulated were defined by measurements made at DORA 1 SUD; this specification included: (i) face on a slope of 22° and mining at 7° to the dip, and with ascensional Ventilation; (ii) drainage (of 0.306 rrvV 1 ) from a chamber on the intersection of face Start line and return roadway; (iii) Ventilation flow of 31.5 m 3 s'; (iii) gas emission into the waste of 0.68 m's-'; (iv) (ace at approximately 220 m from the face start line; (v) face-length treated äs approximately 200 m (actually 240 m); and (vi) a pressure gradient along the face estimated from data from a similar face.

Figure 2 .

 2 Figure 2. Deformation of a rectangular pulse of tracer by the ensemble of the face and waste.

Figure 3 .

 3 Figure 3. Order of magnitude of velocity across the waste äs a function of distance from the face, äs estimated frpm transrt time measurements in tha real mine, in the model, and by CFD Simulation.

Figure 4 .

 4 Figure 4. Map of the concentrations ot air in the waste by fitting contours to the data from experiments with nitrogen injection in the seventieth scale model.

Table 1

 1

	. Summary of the scaling factors for the 1/70th scale model
	with SF, used äs a Surrogate for methane
	PROPERTY	SCALING
	Reynolds number ud g /V g	constant
	Peclet number ud g /D	3 times larger
	nominal grain size d g	x 0.48
	velocity u	x 2.1
	permeability K	x 0.23
	geometry, face length L and	x 1/70
	face height h
	transit time Llu	x 0.0068
	Peclet number U/./D	10 times
		smaller
	flow ui. 2	x 4.3 x 10 -4

ACKNOWLEDGEMENTS This Programme of studies was funded by the French Coal Industry (Charbonnages de France), INERIS and the European Coal and Steel Community (ECSC). REFERENCES Dullien FAL. 1975. "Single phase flow through porous media and pore structure". Chemical Engineering Journal; 10: p 1-34. Jones AD, Lowrie SJ. 1995. "Construction and validation of modeis for the study of the circulation of gas in French longwal! retreat coalfaces," Edinburgh: Institute of Occupational Medicine. (IOM Report TM/95/04). Jones AD, Lowrie SJR, Crawford NP. 1995. "Initial application of the seventieth scale model of the flows through the waste," Final report on project for Charbonnages de France. Edinburgh: Institute of Occupational Medicine. Jones AD. (1994). "Aerodynamic scale model simulations for predicting methane gas concentrations in retreat longwall coal • faces," Ph.D. Thesis, Nottingham: University of Nottingham. Jones AD and Lowrie SJR. 1994. "An aerodynamic scale model for simulations of methane control at the retum end of longwall retreat coalfaces," The Mining Engineer; 154: p 43-49. Jones AD and Lowrie SJR. 1994. "Laboratory simulations of the effects of changes in mining conditions on methane control for longwall coalfaces," The Mining Engineer; 154: p 95-100. Jones AD and Lowrie SJR. 1994. "Small Scale Model Simulations of Methane Gas in Coalmines," In: Ventilation '94. Proceedings of the 4th International Symposium on Ventilation for Contaminant Control, September 5-9,1994, Stockholm, Sweden : p 411 -416. Jones AD, Lowrie SJR 1993. "Applications of aerodynamic scale model simulations to predicting the accumulation of methane gas and airborne pollutants in modern coalmines," Final report on CEC Contract 7262/32/229/08. Edinburgh: Institute of Occupational Medicine. (IOM Report TM/93/08). Jones AD, Lowrie S 1992. "Feasibility of using small scale modeis to study the circulation of gas in French longwall retreat coal faces," Final report no. P613/92/2. Edinburgh. Institute of Occupational Medicine. Pokryszka Z, Tauziede C, Carrau A, Bouet R, Saraux E. In Press. "Application of Numerical, Gas-Plow Modelling to Optimisation of Nitrogen Injections in the Goaf," 27th International Conference of Safety on Mines Research Institutes, New Delhi, India. Pokryszka Z, Tauziede C, Jodart A,, Marion C, Bouet R, Mouilleau Y, Carrau A, Jones A, Lowrie S. 1995. "Modelisation des Circulations des Gaz en Taille Rabattante," Final report on CEC Contract 7262/03/277 Institut National de l'Environnement tndustriel et des Risques (INERIS), Verneuilen-Halatte, France. Pokryszka Z, Tauziede C. 1995. "Resultats des tests de calage de la maquette d'une taille rabattante ä l'echelle au 1/70eme," Report number SSE-ZPo/BS 23EP03/R07. Institut National de l'Environnement Industriel et des Risques (INERIS). Sorbie KS, Sheb M, Hosseini A, Wat, RMS 1990. "Scaled miscible flows in layered beadpacks investigating viscous crossftow, the effects of gravity, and the dynamics of viscous slug breakdown" Society of Petroleum Engineers, 65th Annual Technical Conference and Exhibition, September 23-26 1990, New Orleans, USA. Tauziede C, Pokryszka Z, Bouet R, Jones A. 1994 "Ecoulements des gaz dans ta zone de foudroyage des tailles rabattantes," Journee d'exposes des resultats des recherches de I'INERIS à CdF ä Homboug-Haut, le 2 juin 1994. Institut National de l'Environnement Industriel et des Risques (INERIS). Tauziede C, Mouilleau Y, Bouet R. 1993. "Modelling of gas flows in the goaf of retreating faces," Presented at the 25*' International Conference on Safety in Mines Research Institutes, Pretoria, South Africa.


Guy Marlairc'

Sabine Fernandez-Garcin <"•

HEALTHCARE FIRE SAFETY IN FRANCE

Fire prcvenrion and protecdon reguladons for Public Access Buildings (PAB)cxist m France nnoe 1906.Since diät timc they have bcen regularly updated or fully reviewcd in Order to improve fire safety. Tbc spcdfic mcasurcs applying today to healthcare fadlides are derivcd from a set of general fire safety reguladons diät covers all Public Access Buildings (PAB) induding highrise bulldings, t This ardde bricfly reviews die current technical and organisadonal measures which are cnforccable by law and are aimed at controlling and rcdudng nie risk in public and pnvate Frcndi hcaldicaie fadlides. Healdicare fadlides located in France are dassified äs building occupandes for designated use and äs sudi must comply with eidler one or bodi (if relevant) of die following sets of safety ruies induded in offidal acts under die ddes : 'Regulation against Fire and Panic in Public Access Buildings, tatest füll text rdease dacedOctober 1980 'Regulation regardingsafety in High Rise Buildings (HRB) and. protection against ßre and panic in such structwvs, tatest füll text release dated October 1977

These ofFidal documents, in addidon to more general prescriptive codes, such äs the 'Building Construction andDiuelling Code, describe die measures diät must be sadsfied while designing die building (e.g. selecdon of fire resistant walls...), dudng implementadon of other technical measures (such äs availability and distribudon of fire fighdng devices) or by operadonal procedures during the use of the building (implementadon of a fire safety service, training of the stafF, informadon for the padents, maintenance of safety devices...).

The paper also briefly describes the regulacory scene in France, providing pracdcal examples of requirements and commencs in the light of the experdse of the authors.

Introduction

In France, the first genuine prevcndon policy in Public Access Buildings (PAB) widi linuced applicadon was enforced by legislation äs early äs 1906. PAB are designated in France by the Acronym ERP for Etablissements Recevant du Public. Indced, a spccial attcndon is obviously needed to prcvent fire disasters in PAB, whcrc safety impcding drcumstances may be systemadcally feared. In fact, die members of the Public are very often unfamiliar widi die building structures and widi die related possiblc cscape routes diät could be uscd in die event of a fire.

Healdicare fadlides have to cope • wid i a soll moie cridcal background for die management of fire safety dian in odier types of PAB, since die members of die Public involving padents or visitors are most of the dme highiy so-essed or deeply affecicd by emodon according to die medical reasons of their stay. Moreover, they generally have a vcry poor knowledge of the inner configuradon of the building housing die healdicare occupancy and naturally, many padents have limited mobility. They may thus be confronted to huge difficulties for escaping by their own in case of cmergency. In addidon some areas in hospitals present special fire hazards (storage of flammable drugs, laundries...) and padents under heavy treatment in intense dierapy units are nearly impossible to evacuate [l]. Therefore, healdicare fadlides in France have for long been considered äs a designated occupancy in PAB from a regularory point of view, which has lead to reinforcement of general fire safety measures applying to PAB, taking account of the pardcular scene of hospitals.

Turning towards facts and figures, let us quote some statisdcal figures regarding healthcare bedding capadry in France and related firedeaths siadstics that also stress the requirement of a good fire safety policy in this kind of building occupancy.

There is about 3500 healthcare institutions in France (exclusive of ambulatory care units) some 30% of them being State insticurions and the other 70% private establishmenis [START_REF]Data issued from OCDE statistics (31'Public Acccss Buildings -Panicular or Spedal Establishments, Fransel Publishcr[END_REF].

These healthcare facilities represent an overall hosting capacity of some 552,800 beds. This figure is to be compared to the overall capacity of some 2,500,000 beds in the EU, among which 265,000 beds in the UK, 660,700 beds in Germany or 412,100 beds in Italy (figures from 1994).

Even if the exisdng acddentology records in France seem to reveal limited single fire disasters in healthcare compared to some other Nations, table l shows if necessary that the fire hazard in French healthcare facilities is also a reality. Regarding frequency of fire occurrences in the sector, annual statistics from the BSPP (Rrc brigades operating in the Paris sector) present 54 records of fire-fighting operations in healthcare premises in the Paris region duringyear 1995 only [START_REF] Jeanroy | Fire Safety in High-Risc Buildings[END_REF].

General f ramework of the actual legislation pertaining to fire safety in french health care premises

A first observarion must be srated that concerns the prescripcive approach of the official current text, even if the pcrformance-based approach has never been totally crased by application of the special ruie described in ;micle <7/Wof [START_REF]Safety Rcgulation of June 1980, -Special prescripdons applying to PAB of the first group ( l erc a 4e categorie)[END_REF].

Dcspirc of the existence of some other minor official texts to be considered for a complete regulatory analysis of fire safety in French healthcare premises, detailed prescriptions in matter of fire safety in healthcaie premises are issued from the French Ministry ofinterior (cquivalent to UK Home Office) in regulatory texts summarised with their references in table 2.

A schemadc broader view of the scope of those texts with their legislative origin is given in figure l.

The French readers who would like to learn more about what is the real regulatory Status applying to French care units, are invited to refer to documents [3] to [START_REF] Dirmcr | Hie safety in High-Rise Buildings (so-callcd • IGH')[END_REF] which give füll details induding comprehensive official and private comments.

The following are some main features of the regulatory scene regarding all types of French healthcare premises.

Types and categories of Public Access buildings and High-Rise Buildings

A general classification of PAB, into size classes (categories) valid to healthcare insritudons, according to the importance of potenrial public simultaiicously present in the premises is a basic consideradon of the legislation for selecung die appropriate measures in terms of general fire safety philosophy, kinds of measures and level of soength. Table 3 oudines the main facts regarding this classification.

Oassificadon of a complex insritudon comprising several buildings open to the public is operated by totalling the number of people in the larger 'non isolated' structures : basically, two strucnires arc considered isolated from one another whcn a safe distance of min 8 mcters bctwcen them is provided by construcrion or by use of adcquate fire resistant walls, floors or ceilings to separate reladve occupandes in neighboured structures.

Besides, tables 4 and 5 present the administrative distribudon of various PAB according to main possible occupancies involving Public.

As can be seen, healthcare fadlides are idendfied äs designaied « type U » PAB in the general case and 'G.H.U.' establishments when the acdvity is housed in a high-rise structure. About 10 such 'G.H.U. insdtudons are numbered in the sole Ile-de-France administrative region [START_REF]Data issued from OCDE statistics (31'Public Acccss Buildings -Panicular or Spedal Establishments, Fransel Publishcr[END_REF]. Several ochers are existing in other regions.

Of course, measures regarding fire safety in healthcare premises are taldng account of the size (i.e. category) of the facility and are basically more stringent, for equal category in a high-rise building than in a Standard one. Moreover, some important measures of ehe current regulation (1977) up to 300 but (arger than specific limit for classification into 5th category limit specific to each type of PAB

General philosophy of fire safety policy in hospitals

Concepts derived from general fire safety concerns in PABs As in all PAB, another basic considerarion is that the fire safety policy of healthcare premises in France is directed uniquely to life safety. As a result, property loss prevention -unless specially demanded by the insurers-is not dircctiy aimed at by the tcxts which explains the very limited implementation of auromated fire extinguishing Systems in such areas in France.

As outlined by Orr [lO], safe evacuarion of the parients, visitors, medical and administrative staff either from the building itself or for the damaged 'zone' in complex structures is considered äs the unique fire safety challenge in French hospitals and other care units.

To achieve such an operational result in case of emergency, basic measures comprising consiruction mcasures, additional various cechnical safety devices ;ind organisacional measures, have co be foreseen ai die vcry beginning of a new hcalchcarc projecr nud tluly implementcd and maintaincd dunng all life of ihc nctivirv. according ro vcry dcciilcd rcquircmcm.s i;ivcn bv the tcxt.s.

Examples of technical measures for compllance with the fire regulation in healthcare premises

To

A (an 'A' type System is the most powerfui exisdng one).

A fire safety system according to set of French standaids NF S 61-931 to NF S 61-940 [11] is a fuüy integrated firc protecdon system of decrcasing complexity acoording to categories A to E. Category A type oomprises two main sub-systems caüed : 'SDI' (Category A only) automated Fire detecdon system, SMSTautomated safety procedures activaoon system. The equipment basically collecis all usefül informarion or orclers regarding firc safety only (e.g. the gesdon of other technical informarion usefui for healthcarc units monitoring arc not allowed here), treats them and consequently operaces and monitors all elemental safety (unctions like closing fire doors orshucters, management of evacuation procedures (alarm message diffusion, technical gestion of emergency exits...), activarion of smoke venring, automaric firc fighting system -if any, and so on...

Administrative and organisational measures applying for healthcare units in France

A good human Organisation in hospitals and other care units is a key facror to get sure that the fire safety goals will be preserved in any fire occurrence. The regulalory Status in the field is thus very important and stringent in terms of composition and qualificadon of the staff belonging to the fire safecy service, in terms of information and Simulation exerdses of evacuation and fire fighting techniques and procedures. Provisions are also given to organise the external monitoring of the compliance of the regulatory texts by both external controls opcrated by agreed technical Services and by inspecdons carried out by various safeiy commission on behalf of the authorities. At last but not least, the French regulatory scene also outlines the duty which is belonging primarily to the general manager of the healthcare unit who shall be aware of his Obligation in terms of fire safety strategy äs stressed recendy by Charters talking about the related Situation in the UK [START_REF] Charters | Tire safety challenges (adng NHS Trusts[END_REF].

Organisation ofthe infernal fire safety forces

New important features were brought into die fidd by official amendments in 1995. The scopc of diese amcndments covcrs the Organisation itself and qualificadons required to become mcmbcrs of dic fite safety service, in healthcaie units äs well äs in odier PAB.

For healthcare units, die regulation siates that a fire safety service, independent to the external fire brigades forces, must be implemcnted according to specific ruics in agrcemcnt with tablc 7.

As can be seen from tablc 7, particular attcntion has bcen brought on the allowcd duües to fire safety service members in addidon to normal fire safety conccrns in ordcr to prcvent any deviadon of dic main duty ofthc fire safety forces that must obviously focus on fire safecy purposes. The detailcd duties in correspondcncc to the global fire safety mission assigned to fire safety Services have also bccn given a regulatory rramcwork.

Morc The fire safety service must, among odier mendoned duties, assure a permanent presence into the Central Safety Room located in the lower storeys where a permanent phonc communication line is connected to the fire brigades. They must also go the warching rounds and organise fire fighting tralning for die staff and evacuadon exercises.

Maintenance, repairs and checking operafions

The pcrtalning regulation is very prcscriptive in die field and Stares who (staff members of the healthcare institutions or external agreed Services) may do what, and at what given frcqucncy. These rcquircments covers for instance the SSI, the lifts, die fire doors, the fire or flame-proof shutters, the rescue mcans, die conu-ol ofthe allowed fire load...).

Survey of the safety records of fhe occupancy through fhe safety logbook

A 'log book' must be implemented and regularly updatcd which contains all records in reladon of fire safety of thc building. This document must even bc initiated whcn the official application for a new healthcare occupancy is prcsented to die Authorities. It must contains the building construction liccnce, the nominarivc list of fire safety staff, all records regarding requested maintenance and checking operations, safety instructions prepared for emcrgcncy planning purposes, accident records and so on. Thcre is an cvidcnce thac this rcgulatory rcquirement is primarily lived äs a constraint (among others) which may just help the Authoriries to get a quick insight of the fire safety performance of the viskcd cstablishment. The authors' fceling is that this log-book, if corrccdy fed with the requested data should normally be at first a very usefill tool for the proper validation of the fire safety policy by the management staff kself, since it is intended to contain the csscntial pari of thc Information needed by thcm for provision of in-housc monitoring of the opcrations.

Periodical visits of Safety Commissions

Safety Commissions is the extcrnal official body which has to rcport on the actual compliancc of regulaüons that pertain to healthcare premiscs. A revision of their competencc and their duries has been issued in 1996 which aims at increasing their cfficiency. As a result, surprisingly, the planned periodidty of inspcction visits of PABs and Highrisc buildings that are parc of their missions were slightly rcduccd in 1997, evcn in largc hospitals of first category. The actual Situation of periodical visits äs requested by the new amendmcnt follow ruies expressed in table 8.

Formerly, Ist category hospitals were stated to be visited cvery year, which in pracdcc was nearly never the real scenario, due to technical and organisational constraints. The new periodicity remains howcver at the highest level compared to other types of PABs [START_REF] Granjcan | Fire safety -Collecdon of Offidal Aas with expertisc and comments guidance for design and prevention (in Fiench)[END_REF]. In addition, unexpected visits may also be decided and operated by safety Commissions.

Discussions on fire safety level in French healthcare premises

Lessons from some recenr accidenfs

(öfter [3])

Fire scenario at the Barbotan baths.

21 persons died from Inhalation of fire gases inside the eure unit. The enquiry revealed that poorly controlled repairs on the roof using hot bituminous sheets were at the origin of fire. Fire propagation to ceiling of the swimmingpool over the patienis under treatment. Human error äs well äs major non compliance of the regulation (no escape route, no fire detector, no extinguisher...!) associaced with the absence of regulatory visits of the concerncd Safety Commission were found 10 be the main reasons of the sinister. A sinister still discussed for penalty setting at the concerned French Court.

F/re /n fhe Bruz psychiafric unit

This took place in 1993. As a result of voluntary intended fire by ayoung paricnt in an isoladon room, 20 people were killed, 32 injured, the building nearly fully destroyed. Once again, major non compliance with the fire regulation was quickly oudined by the enquiry such äs non encascd stairways, no smoke vendng, last visit of the Safety Commission dating from 9 years, no fire training offcred to the medical staff of thc cstablishment...

The Amarylis fire

This accidcnt took placc in a home for aged people with care facilides, end of 1996. Place of ongin is a room at the floor IcveL Heavy smoke quiddy filled in the nearby rooms still occupied. 18 persons were rescucd by the fire brigadcs but three finally died a litde later. Invesdgadons rcvcalcd that doors remained opcned, evacuadon procedure operated with the Public was not appropriate, staff membcrs were very limited in numbers.

For sure, it would be abusive to conclude that füll compliance of the concerncd fire regulation would have prevented from any occurrence of those fire disasiers in healthcare units. But observed non conformides are so fundamental that they have obviously emphasised dramadcally the role played by the human factor in the management of the evacuadon.

Fire safety in hospitals housed in high rise buildings

M.M. Jeanroy claimed in [START_REF] Jeanroy | Fire Safety in High-Risc Buildings[END_REF] that no firedeath with the exception of one fire-fighter has ever been deplored in any of those construcdons since the beginning of high-rise building French history. Available stadstics tend to show that a very small propordon of fires occurrences are taking place in HRB compared to total figures relared co all PABs including those housed in convendonal buildings. The expertise of the authors leads to a less enthusiastic conclusion regarding the fire safety performance in healthcare occupancies in such type of buildings. Wc have been told by other experts of the medical sccne that this type of building make the overall safety issues required for this type of occupancy quite difficult and expensive to manage : äs a consequence, new healthcarc unks in project in France are iikely to reject this kind of architectural design.

Concluding comments

AH information provided in the paper regarding the regulatory Status of fire safety requirements shall be considered äs non exhaustive : to achieve exhausdveness, hundred of official text pages should be compiled and fully analysed and interprcted, not forgetting to seek for regulär (somerimes monthly) Updates ! In parricular few consideration has been given here to special requirements in healthcare housed in high-rise buildings. However, degree of complexity äs regards fire safety in healthcare in France seems to be less difficult to cope with than the general fire regulatory scene in the UK, äs dcscribed by Andrew [START_REF] Prof | Fir e Law and Regulanon, written support of course Fire & Explosion, University of Lccds, Ccntrc for Combustion and Energy Studics[END_REF] Moreover, die authors would like to express the feeling, in confirmation to othcr views cxprcssed elsewhere [START_REF] Jeanroy | Fire Safety in High-Risc Buildings[END_REF] that the French regulatory fiamcworkthough somedmes boring to analyse and get use of-is one of the best and more efficient in the worid, provided it is properly during all life of a givcn healthcare Institution. Some improvement »s expected in the near füture in terms of needed provisions together with simplification of the texts [15], and anyway, the interpretadon of obscure prescripdons may always bc requested by the Cennal safeiy Commission m chaigc of daboration of the official documents. French priority users of the regulatory scene, that is to say architeos, fire officers and chief execurives of hospitals have the opportunity to organise (hemselves in a profcssional associarion [16/17] that may hdp in making rruitfui discussions with the authorities.

The relative satisraction that may be drawn out to some extent from the firedeath statistics in French healthcare shall be balanced by other technical considerations on the current background. For instance, we must also take account of the important ageing of many healthcare premises, including much Public escablishments in Paris of very good medical reputarion. There, technical consrraints make it often nearly impossible to refurbish the building in Order to bring it in line with the current strucrural fire protection quality level. In such old buildings, the professionalism of the fire safety teams and adequate measures of compensation (increased inspection procedures...) are of prime iinportance.

Indeed, the fire safety policy success rclies in all cascs on (he efficiency of men and in the same time the human factor is very often a cause of worry [l 8]. Above all, the fire safety policy must be directed and supported by the management board itself.

The duties are very broad and heavy in healthcare units. In parricular, the fire safety concern must be properly inregrated in a more global safety approach which comprises many other topics [START_REF] Marchani | Hospital Safety', comments on the Conference Hospital[END_REF] (electrical safety, constant availability of medical gases, arson prevention, occupational safety...) : a very huge task indeed.

  Charge of fire safety service, min. of 3 persons simultaneousfy present, including one captain and one fire safety officer. captain and fire safety officer are not allowed to perform technical tasks without relationship with fire safety targets Classified in other categories, but less than 1500 persons in total (by addition of all members of the Public in all buildings) Designated staff members in Charge of fire safety service in addition to normal medical duty, trained to use of rescue and escape means, head of task force may also be a designated staff member Same classification äs above, but more than 1500 people in several PABs of the establishment Designated staff members or Specialised staff, in any case under the management of a fire safety officer (whose duty is fire safety only)

Table l : A selection of firedeaths records in hospitals in various countries (from [3])

 l

Table 2 :

 2 Main reguhtion texts (successive releases.actual in bold ) ebborated by the French Ministry of the lnterior to applkation a) the BuHding Construction and Dwelling Code CCCH • An. 122/123)

	in high-rise healthcare
	institurions have been given recrospective eflects in 1982
	for application in previously crecred conscructions.
	Large healrhcare institutions like Centres

Table 3 :

 3 Distribution of PABs into size classes according to the irnpoitance of the public.

l a groufl ofPAßs Nature of activity invotving public in buildings (conventional PABs) Cod'rfied ctass of PABs (French so-called 'type') (n

buildings Speciol types Auditoriums, lecture rooms, meeting rooms and show rooms Stores, supermarkets. shopping malls Restaurants, pubs Hotels, boarding houses Dance halb, gaming-rooms Education institutions, children's holiday camp Libraries, documentation centres Exhibidon halls

		L
		M
		N
		0
		P
		R
		S
		T
	Healthcare facilities	U
	Places of worship	V
	Administrations, Banks, Offices	w
	Covered places of Sport	X
	Museums

y Floatings structures. railway stations. mountain inns.open-air institutions, covered car parks. Inflated structures, big tops or tents. refuges EF, GA, OA, PA, PS, SG. CTS, REF

Table 4 : Distribution of PAB according 10 the oature of building use

 4 Occupancy nature of buildings Type of HRB criteria for classification äs HRB Residential accomodation (flats) 1 G.HA floor level of upper storey more than 50 m up the highest ground platform accessible to the fire brigades trucks .H.O. floor level of upper storey more than 28 m up the highest ground platform accessible to the fire brigades trucks G.H.R. floor level of upper storey more than 28 m up the highest ground platform accessible to the fire brigades trucks G.H.S. floor level of upper storey more than 28 m up the highest ground platform accessible to the fire brigades trucks '

	Hotels
	Institutions
	for Education
	Places for
	archive storage
	Healthcare premises	G.H.U. floor level of upper storey more than 28 m up the highest ground platform accessible
		to the fire brigades trucks
	Offices	G.H.W. l floor level of upper storey between 28 m and SO m up the highest ground
		platform accessible to the fire brigades trucks
	Offices	G.H.W 2 floor level of upper storey more than 50 m up the highest ground platform
		accessible tö the fire brigades trucks
	Combined use of more than
	one aforementioned activity

G

G.H.Z. floor level of upper storey more than 28 m up the highest ground platform accessible to the fire brigades trucks Table

5

: Definition criteria and classification of High-Rise Buildings (HRB) including healthcare premises Hospitaliers Universitaires (C.H. U.) have to cope wich prescriprions of type U (and possibly ro type G.H.U. high-rise buildings) but may also bc subject in related areas to requircments applying for institutions of types L (mecting and lecture rooms), Af restaurants), R (Education arcas for undergraduate physicians) , or V (areas of worship)

[START_REF] Vincent | Protecrion against nie and panic hazards in care insdtutions[END_REF]

  Maintenancc and checking requirements are included in each of the aforemencioned cacegory of measures. Ruies for external control and survey of the actual applicacion of die legislation by the Authorities have also been implemented by law enforcement, äs well äs penalty sei out in case of non observance of duties by general managers and chief execudves.

		Customised features to take account of spedal fire
	risk typology in healthcare units
		In French healthcare prcmises, the classification
	into the relevant categories of PABs results fi-om die
	following caiculation procedure of die public capadty:
	•	l person per bed
	•	l other person for three beds accounring for
		medical staff
	•	l other person per bed accounting for the
		paticnt visitors (l per two beds in small
		cstablishments)
	•	8 persons per consulting units or internal
		exploratory unit		These measures can be classified into the
	•	other membersofthe public size in other rooms	following classes 2 :
		of the Institution under declaration of the	•	general administration ('(Wand 'Gf'articies);
		healthcare General Manager.	•	construction requirements -CO art. (in matter
	The customised fundamental fire safety philosophy		of soructural fire resistance, Isolation from other
	in terms of evacuation procedure consists in		buildings, internal distribution of rooms
	horizontal transfer of invalid patienis towards a		(traditional wall partition, compartmentauon
	nearby fire protected zone and thercaftcr vertical		or sectorisation according to accurate mcanings
	transfer Strictiy limitcd to extreme emcrgency cases,		and technical observance of outlet routes,
	valid people arc however planned to bc vertically		temporary refuges areas and building
	evacuated (if required) to get out of the building.		accessibility), stairways protecrion, sizing of
				evacuarion routes, limkation of fire sprcad
				along front walls ('C+D' technical ruie) or by
				ducts and cable trays...) ;
			•	limitation of fire loads and flame and smoke
				spread by use of adequate floor coverings,
				ceiling and wall linings and furniture (AM),
			•	smoke venting measures (DP),
				dcsign of HVAC Systems (CH), steam and hot
				water production Systems,
			•	requirement for gas necwork (GZ),
			•	specifications for electrical sysrems and lighting
				Systems (EL & EQ,
			•	design and Operation of lifts and escalators (AS)
			•	safeiy requirements regarding cooking devices
				and main kitchens (GC)
			•	implementation of rescue means (Active fire
				protection Systems, mobile fire extinguishers,
				orher fire-fighting facilities like hose-reels,
				buckcts, in-house fire safety service, fire
				.Simulation exerciscs...) (MS)
			Figurcs 2 and 3 illustrate (wo basic technical
			principics applying for fire snfcty considcrations m
			.ill PAß.

Table 6 :

 6 size requirements for fire resistant compartments in hospkals compared to those apptying for other PABs

	satisfy the general firc safety policy previously
	explained, a set of technical measures apply involving for
	instance :
	reinforced structural fire resistance of inner
	distriburion of rooms and medical wards (Division
	of medical wards into 'zones' -2 at least by
	hospitalisation level-, restricted use of
	compartments in terms of configuration, size -see
	table 6),
	increased accessibility of the building facades to
	the fire brigades motor trucks,
	increased severiry regarding reaction to Fire
	performance of inner linings,
	increased number and oversized dimensions of
	escapes routcs and issues (rooms door of min 1.10
	m of width, horizontal pathways of min. 1.40 m
	of width).

System (Systeme de Sicurite Incendie or 'SSI) of category

Table 7 : basic ruies for the implementation of the inner fire safety service according to the relevant category class of the healthcare occupancy I st & 2nd categories 2years 3rd & 4th categories 3years 5jh category no scheduted visits at current stateTable 8 :Periodidty of Safety Commission Visits äs requested since 1997

 78


Guy Mariair

Archibald Tewarson'

EVALUATION OF THE PERFORMANCE OF THREE ASTM E 2058 AND NFPA 287 FIRE PROPAGATION APPARATUSES

As a result of a fruitfui collaboration initiated in 1994 between

Factory Mutual Research and MERIS, round robin tests have been carried out m three Fire Propagation Apparatuses (FPAs), previousiy known äs FMRC ßammability apparatuses m the USA or 'Tewarson' calorimeters in Europe. The apparatuses ftwo operated by Factory Mutual Research and Approvals in Norwood in USA and the more recent one by INERIS m Verneuil-en-Halatte in France) are all meeting the requirements of recently issued American Standards ASTM E 2058 and NFPA 287. This posier briefly describes the development of the FPA, followed by the description of the round-robin testing programme carried out so far that includes ignition, combustion and propagation tests for seven commercially-important plastics. The materials have been characterised carefuily from the thermo-chemistry point of view. Round robin results for the global ßammability parameters such äs CHF, TRP and FPl, äs defined in the Standards, are very encouraging, both in terms of repeatability of measurements in each laboratory and reproducibility of data from one lab to the other.

INTRODUCTION

Factory Mutual Research is historically the first user of the polyvalent Fire Propagation Apparatus in U.S.A. described in both recently issued Standards ASTM E 2058' and NFPA 287 2 In Europe, INERIS commissioned in 1997 [START_REF] Nomine | Thermal and Toxic Effects of Fire : Investigation of the Laboratory Calorimeter[END_REF] the first FPA meeting the mentioned Standards, although early use of previous versions of equipment was there identified, in particular in France 4 ' 5 ' [START_REF] Chapman | Fire behaviour of MD1 and TDI", part 5.5 (Supporting sciences) of 'MD] and TDI : Safety, Health and the Environment[END_REF] . Factory Mutual Research was responsible for the original design and has clearly shown the polyvalence of the apparatus for both material performance approvals and research purposes regarding flammability properties 7 ' 8 ' [START_REF]Factory Mutual, Approval Standard Class l Conveyor Belting[END_REF] . INERIS on the other end has mainly contributed thus far to the promotion of the equipment in leaming about the fire behaviour of materials and chemicals in both well and under-ventilated conditions [START_REF] Adam | Experimentai Evaluation of the Pire Hazard of Organophosphorous Insecticides By Use of Various Test Methods[END_REF] '"' 12 .

Towards the end of year 2000, a new collaborative work was agreed between Factory Mutual Research and INERIS to study the reproducibility of data. We hereafter give the background of work, description of FPAs used in the study and materials selected for the comparisons, äs well äs preliminary results. The study is expected to be completed by the end of this year.

FROM EARLY 'FMRC' FLAMMABILITY APPARATUS TO FIRE PROPAGATION APPARATUS (FPA) OF TODAY

Considerable efforts were made by the pactory Mutual Research to refine the design of the 50kW labscale flammability apparatus äs it is referred to in early technical papers. So doing the evolution through 25 years of development have led to a very mature and polyvalent concept. The reader may appreciate the importance of the underlying technological evolution by comparing early drawings of the equipment provided by first users (see for instance references' 3 ' 14 ) to upgraded version of the FPA that was issued in the mid 90's (see figure l).

The effbrts have continued for the last five years to promote the recognition and the use of the Fire Propagation Apparatus in a collaborative way for important purposes such äs for testing materials (figure 2) for clean rooms' 5 by Factory Mutual Researeh and Approvals or for the qualification of under-ventilated fires of chemicals 12 by INERIS (figure 3).

ROÜND ROBIN TESTS PROGRAMME

For the round robin testing, a first series of seven commercially available plastics were selected : 1. Polymethylmethacrylate (PMMA) (FP1 > 20) 2.. Polyoxymethylene (POM), Deirin® (FPI of the order of 14) 3.

Polycarbonate (PC), (FPI in the ränge between 12 and 14) 4.

Polysulfone (POS) (FPI « 11) 5.

Rigid Polyvinyl Chloride (PVC) (FPI in the ränge between 7 and 8) 6.

Polyetherimide (PEI) 7.

Nylon (PA 6-6)

All 7 selected polymers are listed in table l with information on commercial designation of the materials and their suppliers. 4 that also includes predicted values äs given by the Bote 's and Garvin's correlations [START_REF] Mariair | An Analysis of practicai Methods for Estimating Heats of Combustion in Fire Safety Studies[END_REF] . The comparison between predicted and measured values shows good agreement, except for rigid PVC where the measured value is somewhat higher than expected. The agreement for the heats of combustion is consistent with the true elemental analysis of the materials (table 3). The data show that except for rigid PVC, the commercial products selected are very dose in tenns of chemical composition to the parent pure polymers. Rigid PVC sample contains some non identified oxygenated additive, that results in lower content of the chlorine element compared to pure PVC and thus in slightly more energetic product.

PMMA

One may notice the presence of minor amount of nitrogen in the POM sample (eonfinned during the combustion tests of POM samples though the detection of nitrogen oxides in the INERIS FPA (see figure 3), which is equipped with some additional on-line chemical analysis capabilities 1 9). Some sulfar (in addition to oxygen) in also present in the PVC sample.

Basic findings froin preliniinai-y comparisons of round robin tests

Ignition tests

Time-to-ignition for sustained ignition is mcasured visually by a stop watch. Its measurement was folind to be remarkably similar between various operators (rarely more than l second of difference between two operators monitoring a single test run in one lab), although recording of the time is not always easy.

From preliminary comparisons of data, a reasonable agreement was found between the raw data and data derived for the flammability parameters CHF (critical heat flux) and TRP (Thermal Response Parameter). A potential improvement of ignition test procedure was identified for fürther tightening the agreement. The improvement consisted of repeating each measurement at least three times for each heat flux applied during the test and do the relevant statistical treatment of the data. This would be essentially usefui for difficult heavily charring materials or when "transient" ignition processes occur prior to sustainable ignition. in the case of PMMA Propagation and combustion tests Combustion tests were performed in normal air with samples exposed to 50 kW/m 2 to quantify yield o smoke, Fire propagation tests were performed in 40% oxygen concentration for 300 mm long vertical samples with bottom exposed to 50 kW/m 2 to quantify the heat release rate during upward fire propagation. The measured heat release rate was combined with the TRP value from ignition test to caiculate the Fire Propagation Index (FPI). The value of FPI was multiplied by the smoke yield to determine the Smoke Development Index (SDI).

In the round robin testing, rate of heat release was in remarkably dose agreement between the three labs. The agreement was excellent for non chairing materials (both peak values of HRR and HRR profile versus time) and in good agreement for charring materials (at least peak values). In the latter case, the very complex charring process causes minor discrepancies in the detailed evolution of rate of heat release versus time, but not the peak value and the final ranking of the material, in terms of FPI.

CONCLUSIONS AND PERSPECTIVES

A series of round robin tests on a selection of seven plastics have been successfülly carried out by three laboratories operating a Fire Propagation Apparatus meeting the technical requirements of the recently issued ASTM E 2058 and NFPA 287 Standards. A detailed characterisation of the materials has been performed and recorded. Basic observations confinn satisfactory repeatability of measurements in each lab and the analysis of the results for the appraisal of reproducibility of data from one lab to the other looks very encouraging. The reproducibility of the ignition, propagation and combustion test procedures is reasonable, in particular in terms of the time to ignition measurements, and caiculated rate of heat release for all samples. However, improvements of test protocols such äs using cross wires for the sample conditioning whenever the material to be tested is charring or not and repeating at least three times the time to ignition measurement protoeol (to eliminate isolated aberrant data plot) for each heat flux increment in the series of ignition tests have been identified äs immediate simple things having clear positive impacts.

It is intended to analyse the data fürther in tenns or reproducibility (according for instance to Standard ISO 5755) and reiated caiculated flammability parameters such äs CHF (critical heat flux), TRP (thermal response parameter), FPI (fire propagation index) or SDI values (smoke development index). Further testing on samples of 2 foam plastics (PUR and PIR) and fire retarded polyester is also planned. Once the work is completed, the results will be published in the open literature.

Figure l :

 l Figure l : Sketch of the current Version of the FPA. äs finalised by FMR. Research division Figure 2 : view of the FPA of FMR. Approvals division

Figure 4 :

 4 Figure 4 : graphical determination of TRP (slope of the curves)

Table l : technical identification of test materials

 l Table 2 lists the theoretical composition of each polymer.Enough samples had been ordered in a single procedure in the fonn of sheets such that the tests could be performed in at least four apparatuses. Indeed, a fourth apparatus which is the prototype of the The testing procedures described in ASTM E 2058 were followed by all laboratories involved in the study to perförm consistently ignition, combustion and propagation tests.

			Manufacturer /supplier			Commercial designation
	Polymethylmethacrylate	Polycast technology (USA)		Poly 76 polycast acrylic sheet
	(PMMA)
	Polycarbonate (PC)		Sheffield Plastics, Ine, Sheffield,		Hyzop GP polycarbonate sheet
			MA (USA)
	Polyoxymethylene (POM)	A.L. Hyde Company (supplier)		Deirin® acetal resin
			E.I. Dupont de Nemours & Co
			(Ine), Wilmington, DE, (USA)
	Polysulfone (POS)		Scientific Polymer Products (USA),	Polysulfone resin 046-C
			Ontario, NY (USA)
	Rigid PVC		Vycom (Pa) USA			Polyvinyl Chloride sheet
	Polyetherimide (PEI)	DSM Engineering Plastic products	Ultem product, natural (1000)
			Ine Reading, PA (USA)
	Nylon (PA 6-6)		A.L. Hyde Company (supplier)	Zyte!® nylon resin
			E.I. Dupont de Nemours & Co
			(Ine), Wilmington, DE, (USA)
			mass % of overall sample weight
	polymers	C%	H%	0%	N%	'	S%	Cl%
	PMMA	60	8.0	32.025	0			0	0
	PC	75.6	5.5	18.9	0			0.	0
	POM	40.0	6.7	53.3	0			0	0
	POS	73.3	5.0	14.5	0			7.2	0
	PVC	38.4	4.8	0	0			0	56.8
	PEI	75.0	4.05	16.2	4.73			0	0
	PA 66	63.7	9.73	14.2	12.4		0	0

commercial Version delivered by the UK Company F.T.T. Ltd to Factory Mutual Approvals was also available. This latter apparatus was not used in the overall round-robin tests, äs a separate evaluation process was in progress". The samples (about 100 mm by 100 mm by 25 mm thick slabs for ignition and combustion tests, and 100 mm wide, 300 mm high and 25 mm thick slabs for propagation tests) were prepared at Factory Mutual Research by a single operator according to requirements of FM 4910 testing Standard

[START_REF] Mutual | Test Standard FMRC Clean Room Materials Flammability Test Protoeol[END_REF]

and distributed to all operators involved. All samples were blackened using a Thermalox 250 spray paint.

Table 2 : theoretical chemical comnosition of selected polymers (no additives) RESÜLTS Detailed characterisation of the fest s.iniples

 2 Table3summarises the results from cheroieal analysis performed by [NERIS to accurately qualify the chemical nature of the plastics selected for the round-robin tests. A comparison with the theoretical composition in table2shows that all the polymers are relatively pure except PVC. Also POM contains some nitrogen compound äs an iinpurity.

					mass % of overall sample weight
	materials	C%		H%	0%	N%	S%	Cl%
	PMMA	60.1 ±0.1		8.56 ±0.04	32.14 ±0.25	<0.1	<0.04	<0.02
	PC	75.7 ±0.1		5.50 ±0.05	18.40 ±0.25	<0.i	<0.04	<0.02
	POM	41.4 ±0.1		6.91 ±0.09	51.40 ±0.25	0.15 ±0.05	<0.04	<0.02
	POS	72.9 ±0.1		4.82 ±0.04	14.39 ±0.25	<0.1	8.2±0.1	0.02±0.1
	PVC	38.9 ±0.1		4.77 ±0.04	4.33 ±0.25	<0.1	0.36 ± 0.02	49
	PEI	73.83	4	4.07	17.98	4.89	<0.02	<0.02
	PA 66	61.86		10.24	17.82	11.96	<0.02	<0.02

Table 3 : Results of the eleroental analysis of test samples performed by INERIS INERIS

 3 also measured the complete heats of combustion of all plastic samples selected for the round robin tests using an oxygen bomb calorimeter by INERIS following the French Standard AFNOR NF M 03-005. Results are reported in table

Table 4 : Net heats of combustion (all valnes in MJ/kp)

 4

		Predicted values for pure polymers(a) 18	Measured values
				on samples
		Boie's correlation	Garvin's correlation
		25.14	25.57	24.76 ±0.03
	PC	29.71	30.35	29.88 ±0.02
	POM	14.48	14.88	15.72±0.02
	POS	29.64	30.27	30.42±0.02
	PVC	18.07	17.1	19.31 ±0.04
	PEI	28.72	29.48	28.27 ±0.02
	PA 66	30.84	31.36	29.17 ±0.03
	(a) with use of the theoretical elemental composition of pure polymers for the caiculations)


Norbert Gonzalez-Flesca
email: norbert.gonzalez.flesca@ineris.fr

Sotiris Vardoulakis

Andre Cicolella

Assessment of BTX Concentrations Near a Petrol Station Using Diffusive Samplers

Keywords: Air quality, population exposure, benzene, service Station, petrol, vapour recovery, Stage l & 2 control, displacement loss, spillage loss, wind conditions, dispersion modelling

A combined monitoring and dispersion modelling methodology was applied for assessing air quality related to concentration levels of benzene, toluene and xylenes (BTX) at three different levels of proximity to a petrol selected service Station: (I) next to the füel pumps, (II) in the surrounding environment, and (III) m the background. A Gaussian dispersion model (CALINE4) was used for assessing the road traffic contribution to the local concentrarions under different meteorological conditions. It was established that Stage 2 vapour recovery reduces BTX concentrarions not only near the pumps but also in their surrounding environment. However, there is evidence that the efficiency of the System is wind speed dependent. The modelling Simulation of the worst case wind scenario revealed the significance of local traffic emissions. It was shown that the traffic contribution to the local BTX levels even from a single road in the vicinity of the Station can be, under certain conditions, higher than the contribution of the Station itself. Finally, after comparison with previous studies, the concentrations measured near the service Station (which was situated in a rural environment) appear to be lower than those observed in busy street canyons in city centres. It can be concluded that although Stage 2 recovery System effectively reduces working VOC losses in service stations, it will only have a limited positive impact on local air quality if the service Station is located in a heavily polluted area.

Introduction

From a toxicological point of view benzene is the most notorious petrol component. It has been classified in the group l of IARC [l]. Furthermore, according to the Worid Health Organisation (WHO) [START_REF] Who | Proposition de directive du Conseil concemant les valeurs limites du benzene et du monoxyde de carbone dans Fair ambiant[END_REF], there is no single threshold value for benzene below which there is no danger for human health. WHO proposes a unit risk excess of 6 x lO' 6 per ug/m 3 for leukaemia based on a linear extrapolation model without threshold. From a regulatory point of view a limit value of 5 Hg/m 3 has been proposed for benzene by the European Commission (EC) [3]. For France the Loi sur l'Air [4] determines an air quality objective value of 2 ug/m 3 . Fuel storage and delivery activities in service stations have also been subject of EC regulation [5].

Tanks containing petrol can emit VOC vapours due to filling and emptying activities (displacement losses) äs well äs changes in temperature and atmospheric pressure (breathing losses). Every time an empty tank is filled, the corresponding air volume saturated with petrol vapour is displaced into the atmosphere. Displacement losses can increase both occupational exposure to VOC in the immediate proximity of the pumps (for people working m the Station, car drivers and passengers), and population exposure in the surroundings of the Station [6,7]. For the reduction of these emissions vapour recovery devices can be put in place. These Systems return the VOC saturated volume of air which has been displaced from the tank being filled to the tank being emptied during the delivery of the füel. The equipment used for vapour recovery during the loading of a storage tank is called Stage l control, while the System used for the same purpose during the remelling of a vehicie tank is called Stage 2 control. A two week monitoring campaign was carried out in a modern service Station by the RN 10 motorway near the small town of Prunay in the south of Rambouillet (Yvelines, France) in November 1999. During the first week the vapour recovery system of the Station was operating, while during the second week it was disconnected. The adopted methodology, presented below, was based on real measurements and model simulations.

2 Methods

Site description

The specific service Station was selected for the campaign because of the availability of modern refüelling facilities and vapour recovery Systems (which could be switched on and off), the flat topography of the site (which increases confidence in modelling results), the good natural Ventilation of the area (which makes simple Gaussian modeis applicable), the existence of only one traffic axis (RN 10, a good linear source), the easily measured background contribution, and the relatively constant quantities of petrol sold in the Station.

Sampling methodology

The concentration of a pollutant at a given location and time is fhe summation of the contributions from different emission sources. The major factor determining the dispersion of gaseous pollutants in the atmosphere is the wind (speed and direction) and its related turbulent effects. Considering the case of the service Station the concentration Ci of a pollutant at a given location can be expressed in the following way:

Ci = C o + C g + C r (l)
where C o is the background concentration of the pollutant C g is the concentration due to emissions released within the Station C r is the contribution from vehicie traffic in the proximity of fhe Station.

C r and C § are expected to vary with time and distance from the source. The total concentration Q of the pollutant äs well äs the background contribution CO can be measured using adequate equipment. By contrast, the other two independent contributions C § and Cr need to be caiculated.

In order to study the efficiency of the vapour recovery system, the Variation of VOC releases within the Station needs to be quantified and attributed to different factors (vapour recovery, traffic volume, accidental spillage, weather conditions, composition of the füel, etc.) In addition, the variations of C s should be significant compared to CO and Q values.

A mobile monitoring unit (trailer-lab) and diffusive samplers were used for taking measurements at 20 sampling locations (Fig. l), which can be classified in three different "levels" of proximity to the source: (I) next to the füel pumps, (11) within their surrounding environment, and (III) in the background. The samplers placed nearer the source (level I) were located in pairs at two different heights (hi = 0.2 m, h ; = 2.0 m).

Measurement techniques

Two anemometers, one 3-D ultrasonic (WindMaster, Gill Instruments, Hampshire, UK) and one mechanieal (microvane and three-cup), were used for monitoring local wind speed and direction. This equipment was sheltered in the weather-proof trailer-lab parked next to the Service Station. Perkin Ebner (PE) diffusive samplers (adsorbent: Carbotrap B) were used for the multisite BTX measurements. The PE tubes were sheltered in specially designed aluminium boxes, and regularly replaced. Field notes were taken for traffic volume and vehicie speed. The quantity of petrol sold in the Station was controlled by the füel pump meters.

Analysis of the samples

BTX samples were analysed using thermal desorption and gas chromatography / flame ionisation detection. A quality assurance (QA/QC) programme, including sampling duplicates, blanks and instrument calibration with Standard gases was followed during the sampling and analytical work. Ambient BTX concentrations were caiculated from the relationship:

1 m (2)
Where C is the ambient concentration of the gas, L/S is a constant depending on the dimensions of the sampling tube, D is the diffüsion coefficient of the gas in ambient air, m is the mass of the pollutant sampled, and t the time of exposure [8]

Cartography and modelling

The cartography of the pollutants (i.e. the plotting of iso-concentration lines on a site map) is an efficient means of visualising sampling results and interpolated values. Amongst the different interpolation methods applicable to this case, kriging was considered äs the most appropriate because of the irregulär distribution of the sampling points and the possibility of using variogram modeis [9]. Carbon monoxide and benzene concentrations were modelled using CALINE4, the last version of the Gaussian dispersion model developed by the California Department of Transportation [START_REF] Benson | Office of Transportation Laboratory[END_REF]. Model input requirements include emission factors, description of the site topography, meteorological and traffic data. CALINE4 caiculates the pollutant concentrations for multiple receptors at distances up to 500 m from the source (see Fig. l).

Results and discussion

Measurements were taken for two different time periods. During the first period the Stage 2 recovery System was operating, during the second period it was disconnected. General meteorological, traffic and füel data were averaged during the different periods. Weekly mean BTX concentrations for all locations were measured (with and without vapour recovery) are given m Fig. 2 (stage 2 desconnected). The concentrations detected nearer the ground (at 0.2 m height) at proxinüty level I were significantly higher than the others and were considered separately

Displacement and spillage losses

The dose to tite ground WCTC significaritly higher than those measured at 2 m height TSas eould be explained by the short distance between samplers and car exhausts, äs well äs by the occurrence of accidental spillage losses of fuel on the ground.

Dispersion conditions

In order to establish the influence of wind speed on the ambient pollution levels, BTX concentrations were plotted against the reciprocal of the wind speed (see fig. 3 below) for the two different periods of the campaign. Only the measurements of higher temporal resolution were used.

Benins

Fig. 3. Concentrations plotted versus wind speed

These corresponded to the sampling points near the pumps (level I), where difiüsive tubes were replaced every 48 hours, thus covering a wider ränge of meteorological conditions. The observed concentration variations could be attributed maüily to the changes in wind speed since the Station was constantly upwind with respect to the RN 10 and the quantity of füel sold remained ahnost constant. It can be seen that for a given wind speed benzene äs well äs total BTX concentrations were lower when the Stage 2 control was operating, suggesting that the System works efficiently. The efficiency of the System, however, varies with the wind speed, äs it is shown in Table 2. Furthermore, it appears that there is a critical wind speed value above which the system is no longer effective. While vapour recovery is taking place, benzene reduction is generally higher than total BTX reduction, possibly due to the higher volatility of benzene. Nevertheless, it should be remembered that measurements are not only affected by evaporative emissions, but also by combustion releases from vehides using the Station.

Table 2: Impact of Stage 2 control on BTX concentrations for dijferent wind conditions

Road traffic contribution

CALINE4 was used to estimate the possible contribution from road traffic (RN 10) to the BTX levels occurring at the level II sampling locations. The meteorological input parameters were: wind speed = 2.5 m/s, ambient temperature = 7°C. The model was run for the most unfavourable wind conditions (i.e. worst case mode). CO emission factors were taken from the literature [11] and were adapted to the site specific car fleet composition before being introduced into the model. The outcome of the Simulation was used to caiculate benzene concentrations by applying an empirically established CO/benzene relationship [START_REF] Vardoulakis | Monitoring and modelling techniques for assessing air quality in urban micro-environments[END_REF]. This approach was adopted in order to avoid the use of benzene emission factors, which would have introduced a higher uncertainty component in the caiculations. The results are presented in Table 3. As expected, NNE and SSE wind directions represented the worst case meteorological scenario. Under these conditions, winds blowing almost parallel to the road axis accumulate the pollutants emitted along the upwind segments of what can be considered äs a linear source (i.e. RN 10). As far äs the receptors of level II are concemed, under worst case wind conditions tfae emissions from RN 10 contribute more strongly than the petrol Station itself to the total benzene levels. Finally, comparing the benzene concentrations observed during this study with levels usually occurring in urban environments, it can be concluded that the average benzene concentrations to which pedestrians may be exposed in busy street canyons are generally higher than those occurring in the surroundings (level II) of a Stage 1& 2 implemented service Station located in a rural area [START_REF] Vardoulakis | Monitoring and modelling techniques for assessing air quality in urban micro-environments[END_REF][START_REF] Hartle | [END_REF].

Conclusions

The adopted mefhodology of using multisite difiüsive sampling combined with dispersion modelling allowed a first evaluation of the benefits of Stage 2 control in a motorway service Station. This deterministic approach gave reliable results without requiring excessive measurements or caiculations. It has been demonstrated that Stage 2 vapour recovery reduces BTX and especially benzene levels near the fael pumps and in the surrounding environment of tfae Service Station. Consequently, population exposure to these substances is expected to be reduced during the Operation of the System. Although vapour recovery reduces VOC emissions due to displacement losses, the effectiveness of the control device is proved to be inversely proportional to the local wind speed. Fuel spillage losses in a Service Station should be taken into consideration when evaporative emissions are caiculated in personal exposure studies. Under unfavourable wind conditions, the contribution from vehicie traffic in adjacent streets to the pollution levels near the Station can be very significant and even higher man the contribution of the Station itself. More detaüed information of these campaigns can be found on [16]

Fig

  Fig.l. Concentration mapping using the kriging methodwith a linear variogram model.

D

  Fig. 2 Example of BTX concentrations proßles for sites l to 19

Table 3 :

 3 Road traffic contribution to the CO and benzene levels in the surroundings ofthe service Station (under worst case wind conditions)

	Site n°1	Wind Dir (deg)	CO (ppm)	Benz. (ug/m3)
		169	0.4	4.8
	2	12	0.4	4.8
	3	12	0.4	4.8
	4	11	0.4	4.8
	5	11	0.4	4.8
	9	19	0.2	2.4
	10	161	0.2	2.4
	11	161	0.2	2.4
	12	161	0.2	2.4

Acknowledgements

This study was carried out in coUaboration with TOTAL RAFFINAGE DISTRIBUTION, which made available one Service Station. The appreciation of the authors is extended to Jean-Claude Pinard (INERIS) for bis technical support, and Armelle Frezier (INERIS) for the chemical analysis of the samples.