S Daëron

E Ruffin

CALCULATIONS OF FIRE SMOKE BEHAVIOUR IN LONG RAIL TUNNELS

In order to simulate fire consequences in complex underground networks, we want to implement a coupling between a ID ventilation code and a CFD model or a zone model. The project consists in 3 main steps: the development of a ID ventilation code whose programming structure will support a coupling with another code, the definition of exchange of boundary conditions between the 2 codes and the validation of this exchange. In this paper we present our new ID code developed in this framework. A case study shows the global reaction of the flow to afire and proves the interest of keeping into account the whole network instead limiting the calculation domain to a zone closed to the accident.

INTRODUCTION

Accurate knowledge of accidental phenomena in long rail tunnel such as fire and release of toxic or inflammable gases constitutes an important goal for safety management. This knowledge will, on the one hand, provide for better planning of the operation and the calculation of the dimensions of ventilation systems and other safety measures while on the other hand can be used to define procedures to limit the consequences of an accident. The various techniques presently used to predict the effect caused by fires or accidental gas leaks can only be applied to the simplest ventilation systems or network geometry. Regarding modelling, the CPU calculation time needed by a field code to model a fire in a whole network is prohibitive. Thus generally the calculation domain is limited to a small zone close to the accident for fixed boundary conditions. As a result, overall effects of an accident in a complex tunnel (e.g. Channel Tunnel) or in a network of suburban tunnels (e. g. underground) are practically impossible to predict with a satisfying accuracy. This is mainly due to the fact that one cannot simultaneously take into account the global and environmental parameters of a ventilation network and the local physical effects of an accident.

The INERIS project aims at carrying out a numerical simulation tool designed to predict the global behaviour of the heat or smoke in a tunnel. There are different families of numerical codes available. There are mono-dimensional codes, which allow the calculation of ventilation systems in complex networks. It's possible to implement in those codes models for heat and mass transfer. However this kind of model cannot take into account some physical effects like stratification or backlayering. Another family is the field model family (Computational Fluid Dynamics), which allows a rather good modelling of various physical process if appropriate models are used (turbulence, buoyancy, combustion...), see for example [START_REF] Ruffin | Numerical simulations of locomotive fires in the Lyon-Turin tunnel[END_REF]. But this kind of code cannot be used for the calculation of a complete network because of the CPU calculation time, as said above.

So, in order to use the complementarity of these families we want to implement a coupling between a ventilation code (network model) and a CFD model. Each code will use the boundary conditions provided by the other one. The transfer of boundary conditions will be validated through theory, well known case study and numerical comparison as well as experiments. Experiments will be carried out by means of a cold mock-up facility, which has been purpose-built in INERIS.

1D CODE BRIEF DESCRIPTION

Main features

A new version of our existing ventilation code VENDIS (VENtilation Dispersion), including new major capabilities, has been already achieved [START_REF] Ruffin | Development of a tool for simulation of accidental situations in underground networks[END_REF]. This program now includes a mesh builder (definition of network geometry), a tool which helps the user to define various accidental scenarios, a new calculation model of the transient network flow taking into account density variations and a post-processor for results' display (cf. Figure 1). The mesh builder allows the user to define the network in terms of several geometry elements, which represent the whole network of galleries. A particular effort focused on the automatic calculation of connections existing between the geometry elements. This allows the user to easily delete or add an element or to modify the network geometry.

Figure 1: A ventilation network example, a twin rail tunnel

Modelling the air/smoke/gas flow in an underground network is complex because many environmental parameters have to be taken into account during an accidental situation. Each phenomenon in a gallery has an effect on the overall flow, which is translated into equations. Among all effects, which can occur in underground networks, let's notice: • natural and mechanical ventilation (fans, jet fans) • piston effect • singularities of the network • fire, gaseous emissions • buoyancy A particular attention has devoted to modular program structure in order to make easier further developments like implementation of the different phenomena. Each transient phenomenon is bound with a so-called scenario-file, which groups all the parameters necessary for the modelling and of course the scenario describing phenomenon evolution.

Calculations

The Hardy-Cross Algorithm (HCA) [START_REF] Cross | Analysis of flow on networks of conduits or conductors[END_REF] gives the different flow rates and the pressure losses for all the branches. This algorithm is based on two kinds of equations. First it uses the Kirchoff's law applied to the flow rates and pressure losses. Then the Ventilation Network Theory makes it possible to choose independent equations among them in order to calculate the unknown variables. The detailed method is described in [START_REF] Ruffin | Development of a tool for simulation of accidental situations in underground networks[END_REF]. Secondly, HCA uses equations characterising the branches of the network. Accidental and environmental effects are also modelled at this step and linked with their pressure effects in the network. A good taking into account of phenomena requires necessarily a fine description of the effect in the branch. Consequently, we can refine the concerned branch by cutting it into several branches. This can strongly increase the total number of branch in the HCA. The calculation time will then also increase. To avoid the increase of number of branches while preserving a good description of the effects, we developed a near field model. Our idea was to include internal points in the different branches that need a local refinement. These points will never define any intersection but just segments of the branch, on which local equations are solved to estimate the parameters on each segment. As a result the so defined portions contribute numerically to the overall evaluation of the branch but don't appear in the resolution of the HCA. Of course, according to the branch we can use or not this near field model. So we developed a first lD/lD-coupled model where the ID-coupled model gives a refined description of the accidental source (heat and mass transfer). This is the first step to a 1D/3D coupling since we hope that various kind of existing field models can be coupled in the same way in the future.

Particular models used in our code

Our aim is essentially the modelling of transient heat and mass transfer phenomena. Thus, it's necessary to take into account the inertia of air mass and to model heat and mass transfer. All effects are translated in pressure terms and included in the characteristic equations of the branches. For example to model the resistance of the galleries we use the well-known RQ 2 model. We wrote a model for pressure losses induced by inertia kP inertia , which is inspired from the fundamental principle of mechanic. If we applied this principle to the air mass contained in a branch, we can write that this inertia force F inertia equals the product of Af^e rt/a with the section of the branch:

* Inertia model

F in
In this way we obtain the model representing inertia of air mass.

Q t+1 -Q' tia =PL---- S At
We made a first validation with on the basis of tests carried out in the Norwegian Fodness tunnel (cf. [START_REF]Rescue in case of tunnel fire. Work group managed by the 'Direction de la Défense et de la Sécurité Civiles[END_REF]). Because of missing data, we made some simplifying hypothesis. The data taken into consideration were:

Length =6565 m Density = 1.30 kg/m 3 Natural ventilation velocity = 1 m/s Section=52 m 2
With these hypotheses, the whole tunnel contains about 400 t of air. This mass is accelerated through groups of jet fans at different sections, until a velocity of 4.5 m/s is reached. The ventilation stops after 360 s. This simulation needs transient scenarios to simulate the fans.

Figure 2 shows the air velocity variation in the tunnel. We see that in our calculations the stable airflow is not completely reached. This could be explained by our simplifying hypotheses and/or by bad adjustments of parameters (density, fan characteristics...). The come back to the initial flow seems to be well predicted by our model.

Heat transfer model

The model is based on the fact that time step is small enough to ensure that a quantity of heat cannot "jump" a complete branch of the network. We suppose that the heat transfer is homogeneous in a branch. The algorithm treats successively all intersections of the network. At an intersection, writing the heat flux conservation, we calculate a mixture temperature while supposing that the mixture is instantaneously achieved. The model convects this temperature in the concerned branches respecting convection length. The remaining part of the branch is gradually treated in the same manner. The mass transfer is modelled in the same way and won't be further treated here. Note that the smoke is associated with the heat front and propagates with the same velocity.

A SIMPLE RAIL TUNNEL CASE STUDY

Presentation

The following figure shows the geometry of the case study. The geometry points and the internal points necessary for a good description of the accidental effect are represented on Figure 3. All sections of the branches are supposed to be circular. Table 1 gives the other parameters. We supposed that a piston effect (due to a train) causes a fixed flow rate equal to either 400 kg/s or 600 kg/s in the upstream tunnel. We supposed that a burning train is stopped in an underground station (the deviation) 300 m before an exhaust shaft. The convected firepower is fixed constant to 20 MW. The refinement points were added all ten meters in the whole deviation, after the fire location, in the shaft and in the first half of the downstream tunnel. This refinement procures a good description of the heat transfer. Note that in all cases we supposed that the wall and the ambient temperature are equal to 273 K. The aim of this case study is to point out the global reaction rather than a precise study of the temperature field. This example shows that only a fire can strongly disturb an established flow. Figure 4 shows the different points where we follow the transient effects. These points are used to represent the time variations of temperature and mass flow-rates at different locations.

-• ©• I

Figure 4 : points of observation of transient effects

Transient accidental situations

• Fire with closed exhaust shaft

In this case we suppose that the shaft is closed. The fire starts 20 s after the beginning of simulation. A steady situation for the temperature field is reached after about 8 min (cf. Figure 5). In this case the heat transfer does practically not affect the flow rate. Downstream from the fire, in the deviation, the temperature rapidly exceeds the maximum temperature (about 60°C) that people can support without protection (cf. Figure 7). Even rescue service with protection cannot intervene in the deviation downstream the fire (cf. Figure 6). The smoke progresses with a velocity of about 3 m/s. Figure 8 shows that after 10 min half of the downstream tunnel is invaded by the heat and that after about 20 min all the downstream tunnel is concerned. • Fire with exhaust shaft and a main flow rate equal to 400 kg/s

This case is the same as above but with the shaft opened. We let the flow establish by itself. We can see (cf. Figure 9) rather important variations in the flow rates after the ignition of fire.

In the shaft (point 2) the flow rate increases (+200 kg/s) whereas in the downstream deviation (point 4), we note an important decreasing (-160 kg/s) that causes an inversion of the flow direction. The inversion of the flow occurs after 174 s. That's early enough to prevent the apparition of smoke in the downstream tunnel. At this time the smoke occupies the whole shaft and the temperature are quite high (cf. Figure 12). 200 m of the downstream deviation is touched by a smoke front with a high temperature gradient (cf. Figure 13). If we suppose that 60°C is the limit that passengers can support, this limit is overstepped along 350 m in the downstream deviation. This situation is transient (cf. Figure 10, point 3) and because of the inversion of the flow at the time 174 s in the downstream deviation, all the smoke is evacuated in the shaft. The portion of deviation between the fire and the shaft stays as for it inaccessible for rescue services. The stable situation is reached after about 300 s for the flow rate (cf. Figure 9) and 350 s for the temperature (cf. Figure 10). In the upstream deviation (cf. Figure 9, point 1), we note small variations of the flow rate that causes small variations in the maximum temperature of the fire(cf. Figure 11, abscissa 1700) whereas the power of the fire heat release rate is fixed constant. • --,.,,,,,". .

'""• • -• • • • """" • • "- .
-"20 s after

Space variations of temperature in the downstream deviation

-h- I ! ^^ i ,-.--:;S5ss^--' : 1 1 : % x \ . , • • • • -, . • • -• ---• - • • • ""• • • • • """"• • point 2,
Fire with exhaust shaft and a main flow rate equal to 600 kg/s

The value of the main flow rate upstream the fire plays an important role. We suppose now that the piston effect in the upstream tunnel causes a mass flow rate of 600 kg/s that corresponds to a velocity equal to 9 m/s. Figure 14 shows the decreasing of value of flow-rate (-120 kg/s) in the downstream deviation and the augmentation of the flow-rate in the shaft (+120 kg/s) due to the chimney force. This flow rate variation is sufficient to prevent the inversion of the flow in the downstream deviation observed in the previous case. The smoke is therefore distributed in the shaft and in the downstream deviation (cf. Figure 17, 700 s) and later in the downstream tunnel (cf. Figure 18, 1400 s). In the downstream tunnel, the apparition of heat and smoke occurs after 1200 s (cf. Figure 15, point 4). ... 1 .

""""point 1, near fire

• • • point 2, in shaft • • • • • • '
• point 4, after shaft junction ation 330 320

' • * ' ' • ' • " • • • • • • • • • > -> . • . • . , , ""XC'"-"'-'» \ \ V -*•
-50 s after ignition ""'

""'• '• • • • • • • • • • • • • • • • • .....• ... .

Abscissa (m)

Concluding remarks

We represent on the following figures the steady airflow repartitions before and after fire ignition. Figure 19 clearly shows the inversion of the flow in the downstream deviation when the main flow rate is equal to 400 kg/s. Figure 20 shows also the important variations of the value of the flow rates for a main flow rate of 600 kg/s. We insist on the fact that these flow variations are only due to the occurrence of a fire since all other parameters stay constant. In a more realistic aspect, this main flow variation can be induced by movements of trains in the tunnel, which may induce uncontrolled displacement of smoke around the accidental source. Then, the interest of accurate previsions of global accidental scenarios is obvious. The good response to an accident is strongly bound to the knowledge acquired from these scenarios and the previsions of the temporal evolution of accidental sources. These conclusions have been also expressed by a French Government commission which was created after the 'Mont-Blanc' catastrophe (cf. [START_REF]Rescue in case of tunnel fire. Work group managed by the 'Direction de la Défense et de la Sécurité Civiles[END_REF]).

PERSPECTIVES

INERIS further work will be devoted to a more accurate modelling of the accidental zone. In order to do that, we are going to extend the work regarding models coupling procedures to others kinds of model like zone-model and CFD model. The aim of the coupling is to provide precise transient boundary conditions for the field code while the global network also depend on the phenomena, which occur in the 3D zone. The coupling will be then completely interactive. This coupling will need an important validation phase. We will use well known cases to validate our results but we will also carry out some experiments to validate the transient aspects, the boundary condition problems and the exchange of data between the coupled codes. A reduced scale model has been specially built at INERIS in order to carry out experimental validations (cf. Figure 21).

It will mainly consist to connect simple network (some branches and one or two fans) to a three-dimensional geometry. This three-dimensional geometry will be a parallelepiped rectangle representing for example:

a ventilated room (office, small building scale 1/10,1/2), a section of gallery (road tunnel, covered section scale 1/30,1/10).

Figure 21

The simulation of accidental sources will be obtained by using air-helium mixtures. The helium proportion will characterise a hot gas source (e.g. an air-helium mixture with 84% of helium has a density equal to that of products of combustion at 800 °C). Using SFÔ mixtures the behaviour of heavy gas can also be studied.

Figure 2 :

 2 Figure 2: Time evolution of the velocity in the tunnel

Figure 3 :

 3 Figure 3: case configuration

  Figure 5Figure7Space variations of temperature in upstream deviation

"

  Figure 9Time variations of temperature

  Figure10

  Figure 14Time variations of temperature

Figure 19 :

 19 Figure 19: repartition of the flow rates, for a main flow rate equal to 400 kg/s

Table 1 :

 1 Parameters for the different branches

ACKNOWLEDGEMENTS

The financial support provided by the French Ministry of the Environment, for both the numerical and the experimental aspects of this project, is gratefully acknowledged.


Isabelle Zdanevitch
email: isabeue.zcicinevitch@ineris.fr

Norbert Gonzalez-Flesca

Emmanuelle Bastin

Influence of vehide traffic reduction in a town centre on BTX polhition

Keywords: urban atmospheric pollution, vehicular traffic reduction, BTX cles ; pollution atmospherique urbaine, reduction de la circulation automobile, BTX

French towns took part in a pilot experiment consisting m drastically reducing the vehicie traffic in the town centres. According to that scheine, WERIS, m association wifh the local Air Qualily Moniforing Nefwork A1RLOR, carried out a BTX sampling campaign over 3 days, in order to quantify the impact of the traffic restrictions on dir quality. This campaign was carried out in the centre of Nancy, where traffic restrictions viere imposed on an extensive wea. Sampling sites viere chosen dose to the busiesi traffic roules. Sampling was carried out using passive samplers, on 10 hours on each day of the campaign. Measurements show clearly that, over the 3 days, the traffic flow reduction led to a decrease in BTX roadside comentrations by between 30 to 80 %. These measurements correlate 'well with CO levels monitored at one of the sampling sites, and with the volume of traffic in circulation each day. The correlation between BTX and CO clearly indicates traffic äs the main source of atmospheric pollution. Measured benzene levels over the 3 days are compared • with statutory limit values in France and in Europe.

Introduction

In 1997, the City of La Rochelle, concerned with urban pollution problems, decided to restrict the flow of traffic in its town centre for one day. This Operation is now repeated on an annual basis each 22'"' of September, with an increasing number of French towns involved (35 in 1998, more than 60 in 1999). This Operation is managed by the French Ministry of Environment.

The aims of this Operation are « to give the town back to pedestrians and cyclists, to develop public transport facilities, and to improve the air quality in town centres. » (Press release of the French Ministry of Environment, 1998).

Objectives

It seems obvious that with limited traffic or even no traffic at all, travelling is easier for pedestrians, cyclists and buses. However, assessment of any real improvement in air quality has to be carefülly carried out by appropriate means. Therefore, in the different participating towns, the local Air Quality Monitoring Networks have set up additional monitormg stations. The role of INERIS was to quantify the reduction of pollution related to vehicular trafiBc by measuring BTX (benzene, toluene, xylenes) levels. The sampling campaign was carried out in collaboration with AIRLOR (the Air Quality Monitoring Network for the Lorraine region, France), with whom a previous study of personal, indoor and outdoor exposure to VOC had been carried out [START_REF] Gonzalez-Flesca | Pilot Study of Personal, Indoor and Outdoor Exposure to Benzene, Fonnaldebyde and Acetaldehyde[END_REF] Samples were taken over three days, staning the day before (September 21" identified äs day "A") and ending the day after (day "C"), the "traffic-free" day (day "B"), in order to evaluate the changes in BTX levels due to the restriction of traffic, and taking into account the influence of meteorological variations.

The results of the BTX analysis could then be completed with the following data supplied by AIRLOR : CO concentrations at different points in the town centre, and volume of traffic circulating in the centre during those days.

Experimental

Out of the 15 sites reviewed, the 10 retained were chosen because they came forward äs good candidates for high roadside pollution levels : crossroads or busy streets, roads where the trafßc was slowed down due to comers or bends... One of the sites was situated beside an AIRLOR monitoring Station.

Each day, sampling was carried out using axial difiüsion tubes loaded with "Carbotrap B", previously described [START_REF] Bates | Ambient Volatile Organic Compound Monitoring by Diffüsive Sampiing. Compatibility of High Uptake Rate Samplers with Thermal Desorption[END_REF]. The tubes were placed inside purpose built aluminium shelters to prevent vandalism. Thermal desorption followed by GC analysis of the tubes was perförmed at INERIS.

Results and discussion

Comparison of BTX concentrations over the three days BTX concentrations have been determined for all sites. Results are shown in The wind direction : E-NE, was steady over the three days, whereas the mean wind speed was higher on days A and B : around 4 m/s, than on day C : below 2 m/s, resulting in a greater dispersion of pollutants. In order to eompare the concentrations measured over the three days, we have plotted "normalised" values for each compound, expressed äs {[concentration, p.g/r n 'jxwind speed}. These results are shown m Figures l to 4 It should be noted that sampling site n° l, which was situated beside the AIRLOR monitoring Station "Henri Poincare", always exhibited the highest BTX concentrations. At this site, wind direction was parallel to the street axis over the three days.

BTX concentrations for day B have been compared with those of days A and C. The decrease in concentrations has been caiculated äs follows :

Where C g = concentration, in ii g/m 3 , of the compound i, measured in the site s, on day B, and

C \ c = idem but on days A or C.
The reduction in concentration, d, varied between 30 to 80 %, depending on the site and compound, äs shown in Table 2. The greatest differences were observed for the heavier compounds. For some sites, o-xylene concentrations on the « traffic-fi-ee » day were below the GC quantification limit : this gives an apparent "100 %" decrease.

Pecrease of concentration relateJ to the day betöre, %

Siten"

Correlation of BTX concentrations with other data

Carbon monoxide concentrations over 4 days are reported in Figure 5, volume of traffic in Table 3 [START_REF] Bourdet | Proposition de Directive du Conseil concemant les valeurs limites du benzene et du monoxyde de carbone dans l'air ambiant[END_REF]. The decrease in BTX concentrations in the traffic restriction zone of the centre of Nancy, correlates well with CO levels monitored by AIRLOR at site n°l, and with the volume of traffic recorded at two points, in Lafayette Street (between sites n° 6 and 8) and Stanislas Street (near site n° 5).

Though data are missing between 9 a.m. and 2 p.m. (7 to 12 a.m, GMT) due to a monitonng failure, it can be seen that CO concentrations recorded on the « traffic-free » day does not show the morning rush hour peak, äs the traffic was restricted frorn 7 am (5 a.m, GMT äs indicated on Fig. 5). The sudden increase in concentration at 5 p.m. GMT (7 p.m. local time) corresponds to the end of the restriction : we saw the traffic retuming to normal within a few minutes after 7 p.m. Nevertheless, the integrated CO concentration for this day is, according to AIRLOR, 5 to 7 times smaller than usual. Likewise, the decrease in BTX concentrations, by 60 to 70 %, is comparable to the trends in the volume of traffic. Correlation between BTX concentraüons and CO levels are typical of roadside pollution [START_REF] Gonzalez-Flesca | Pollution urbaine de proximite sur un site parisien. Mesures et modelisation[END_REF]. The ratio of toluene/benzene has a mean value of 2 for the days having normal traffic and l.4 for the « traffic-free » day. Likewise, benzene/xylenes ratios show a decrease in the heavier compounds on the day with restricted traffic. This is typical of an aged air mass, when the major pollution source is the traffic. Oxidation of hydrocarbons in the troposphere involves mainly "OH during the day, and NO'3 at night. Reactivities of oxidation vary from one hydrocarbon to another, in the following sequence : m-xylene > (o, p)-xylene > toluene > benzene (Academie des Sciences, 1993) Near a source like a busy street, the benzene/toluene ratio will be given directiy by the source itself, e. g. füel and exhaust composition. During the « traffic-free » day, when the direct source was limited, the BTX levels came from either older or remote emissions. In this way, tropospheric oxidation could occur, and cover the local diffusion or dispersion effects. Therefore, the BTX ratios are modified according to reactivities.

Nearly all the roadside benzene levels measured at the 10 sites in the centre of Nancy, under light wind conditions, exceed the EC proposed limit value of 5 ug/m 3 (Proposed Directive COM 1998, 591). All of them exceed the French target value for air quality of 2 ug/m 3 (Decret Francais n° 1998). With traffic restrictions, all the sites show a benzene concentration below 5 ug/m 3 , and nearly all the sites are dose to the French target for air quality, the greatest value being 2.7 ug/m 3 .

Conclusion

This roadside BTX study carried out in the centre of Nancy shows that passive sampling is a usefül method for measuring hydrocarbons even for periods äs short äs 10 hours. Direct comparison between pollution levels at different traffic volumes is possible, provided little changes in the meteorological conditions are involved. We have shown a good con-elation between BTX concentrations, CO levels and the volume of traffic over the 3 days of the campaign, which is typical of a roadside pollution.

Traffic restrictions greatly improve the air quality, especially under light wind conditions : with a normal flow of traffic, roadside benzene levels are always higher than the French Target value for Air Quality, of 2 ug/m 3 , and exceeds, in most places, the proposed European Limit Value of 5 ug/m 3 , With a limited flow of traffic, all sites show a benzene concentration smaller than the European Limit Value, and the French Target value is only slightly exceeded.

  .

FigureFigure 3 Figure 4 :

 34 Figure l : normalised benzene levels over the 3 days Figure l : concentrations normalisees en hemme (m+p)-Xylene

Figure 5 :

 5 Figure 5 : CO concentrations at site ?1 ("Poinoare") during the sampling days Fig. 5 : profils de CO ä la Station POINCARE (site n°]} lors des jours de prelevements

Table l .

 l

	Day A, site n°B 1	2	3	4	5	6	7	8	9	10
	ENZENE	7.4	3.4	3.1	4.2	3.6	2.4	4.7	2.5	2.4	2.3
	TOLUENE	15.9	4.7	6.2	8.7	6.9	6.0	6.2	4.4	4.3	2.6
	m+p-XYLENE	11.7	3.7	4.6	6.5	5.0	3.6	4.5	3.2	4.6	1.5
	o-XYLENE	4,0	1.4	1.6	2.4	1.7	1.2	1.8	1.5	1.1	0.6
	Day B, site n°B 1	2	3	4	5	6	7	8	9	10
	ENZENE	2.7	0.8	2.1	1.0	2.3	0.7	2.0	1.1	1.3	1.4
	TOLUENE	2.9	1.3	2.7	1.7	1.7	1.6	3.2	1.1	1.2	1.7
	m+p-XYLENE	2.0	1.1	1.4	0.5	1.4	1.0	1.1	0.8	0.9	1.1
	o-XYLENE	0.8	0.0	0.6	0.0	0.6	0.0	0.7	0.6	0.5	0.3
	Day C, site n"	1	2	3	4	5	6	7	8	9	10
	BENZENE	8.0	3.5	6.0	6.7	6.1	5.3	6.9	3.7	5.6	3.0
	TOLUENE	20.2	7.3	8.6	15.4	14.1	12.2	16.9	9.0	13.1	5.5
	m+p-XYLENE	16.2	5.1	5.9	11.7	9.9	8.6	11.6	6.5	9.6	4.0
	o-XYLENE	5.6	1.7	2.5	4.1	3.6	3.2	4.1	2.5	3.6	1.6

Table l :

 l BTX concentrations in |J.g/m 3 for each site, for each day of the campaign Tableau l : concentrations des BTX en ng/m 3 par site, pour chacun des 3 jours

Table 2 :

 2 Concentration ratios between the days « with » and « without » cars Tableau 2 : rapports de concentrations en BTX entre les jours « avec » et « sans » voitures

Table 3 :

 3 Number of vehides[START_REF] Bourdet | Proposition de Directive du Conseil concemant les valeurs limites du benzene et du monoxyde de carbone dans l'air ambiant[END_REF] Tableau 3 : complage des vehiculesBTX ratiosThe daily ratios of toluene and xylenes over benzene were caiculated for each site : the values are shown in Table4.

	Tolnene/benzene ratio for the sampling sites
	Date	1	2	3	4	5	6	7	g	9	10	Mean	St devinlion
	09/21/1998	2.1	1.4	2.0	2.1	1.9	2.5	1.3	1.8	1.8	1.1	1.8	0.4
	09/22/1998	1.1	1.6	1.3	1.7	0.7	2.4	1.6	1.0	0.9	1.2	1.4	0.5
	09/23/1998	2.5	2.1	1.4	2.3	2.3	2.3	2.4	2.4	2.3	1.8	2.2	0.3
	(m+p)-Xylene/benxene ratio for the sampting sites
	Date	1	2	3	4	5	6	7	8	9	10	Mean	St deviation
	09/21/1998	1.6	1.1	1.5	1.5	1.4	1.5	0.9	1.3	1.9	0.7	1.3	0.4
	09/22/1998	0.7	1.4	0.7	0.5	0.6	1.5	0.5	0.7	0.7	0.8	0.8	0.3
	09/23/1998	2.0	1.4	1.0	1.7	1.6	1.6	1.7	1.8	1.7	1.3	1.6	0.3
	o-Xyigne/benzene ratio for the samplJBg sites
	Date	1	|__2_	3	4	5	6	7	8	9	10	Meau	St deviation
	09/21/1998 09/22/1998	0.5 0.3	0.4 **	0.5 0.3	0.6	0.5 0.3	0.5 **	0.4 0.4	0.6 0.5	0.4 0.4	0.3 0.2	0.5 0.3	0.1 0.1
	09/23/1998	0.7	0.5	0.4	0.6	0.6	0.6	0.6	0.7	0.6	0.5	0.6	0.1
		** : HO ratio available, o-xylene concentration was below quantification limits

Table 4 :

 4 BTX ratios for the different sampling days Tableau 4 : rapports des BTX entre evx, selon le jour de prelevement

Acknowledgements : authors thank S. Bourdet, P. Lavrilloux, A. Frezier and J. C. Pinard for technical assistance.


Marc Caumont

Sylvie Ponthieu

V'B SAFETY PROVISIONS AND LPG

Keywords: L, P, G, , safety device

The safety of an industrial site depends in particular on the characteristics of the safety devices employed and the equipment installed. In France, the safety evaluation of an installation is carried out, in particular, through hazard analysis. However, the absence of objective criteria for safety device evaluation makes the task difficult. Different pieces of equipment that assure the, same function don't necessarily have the same safety level. Consequently, INERIS undertook a study including: -an outline of the various practices based on an inventory of French regulation and a comparison with regulations applied in other European countries, -an accidentology allowing one to focus on some important safety devices, -a description of the various devices that can be encountered on a L.P.G site, accompanied by a collection of descriptive boards of safety devices used with L.P.G., -a presentation of the concept of devices that are " Important For Safety ", with definitions of commonly-used terms, -a presentation of some approaches for taking into account safety devices in the evaluation of the risks or specific methods used for the evaluation of a L.P.G. site.

INTRODUCTION

In 1997 there were 95 establishments in France storing at least 300 cubic metres (m 3 ) of LPG (exclusively butane and propane) not including the underground storage sites. Some 90% of these 95 sites were created between 1956 and 1975. These sites have over 300,000 m 3 of storage capacity made up as follows :

• Mounded tanks : 23,600 m 3 (10 sites),

• Above ground spherical tanks : 220,000 m 3 (68 sites),

• Cylindrical tanks : 27,000 m 3 (49 sites),

• Cryogenic tanks : 60,000 m 3 (3 tanks on a single site).

Four operators account for 54 of these sites ; chemical firms and refineries operate 15 of them.

The remaining 26 sites are where LPG is used as a utility for heating plants, industrial furnaces, and so on, for a variety of activities.

There are at least about 182 spheres (100 containing butane and 82 propane), 200 horizontal tanks and 2 vertical cryogenic tanks (35,000 and 20,000 m 3 ). The capacity of the spheres varies from 300 to 5.000 m 3 . Mounded tanks include horizontal tanks some of which have substantial capacity (3,000 m 3 ) and spheres (from 1,000 to 3,500 m 3 ). In France there are also 23 industrial sites (essentially in the chemical industry) storing products similar to LPG (for example, butadiene) with tank capacities ranging from 80 to 9,000 m 3 .

In the current situation of technological change INERIS is undertaking a study for the French Ministry of Environment (MATE) in the following five areas :

• A description of the different types of industrial facilities in France using LPG, specifying the different industrial practices involved, • An inventory of the principal current regulatory requirements in different European countries (notably the UK, the Netherlands, Belgium and Italy) and a comparison with French requirements, • The feedback of experience based upon an analysis of industrial accidents involving LPG, • Identifying systems which are important to safety, • An evaluation of the consequences of various accident scenarios according to the safety systems present on the installation.

This study is still in progress. Hereafter some extracts of the sections covering an overview of French LPG sites, the comparison of regulations and the feedback of experience are briefly presented.

OVERVIEW OF FRENCH INDUSTRIAL SITES UTILISING LPG

The French sites utilising LPG can be subdivided into 7 main categories :

• Refineries (producing and storing LPG and distributing it to "buffer" and/or operating sites) ; • "Buffer" sites (receiving and storing LPG and distributing it to operating sites) ; • Operating sites (receiving and storing LPG and distributing to clients and to "local depots") consisting of :

•> filling centres (distributing LPG in bulk, "packaging" and distributing cylinders) ;

• intermediate depots (distributing only bulk LPG) ; • So-called "local depots" (receiving and storing LPG and distributing it in bulk to clients), which are similar to the intermediate depots but store smaller quantities (storage capacity < 120 m 3 ). • Industrial sites employing LPG as a utility for an industrial process (for example, heating plants, industrial furnaces, and so on). • Chemical sites employing LPG as a raw material.

• The cosmetic industry employing LPG as a propellant gas (aerosols).

In the following we shall disregard industrial sites employing LPG as a raw material, utility or propellant gas. Some characteristics of the different types of French industrial site where activities are entirely or partly focused on LPG are given in the following

TANK EQUIPMENT

For the tanks themselves, French regulations require to mound them (for capacity greater then 500 m J ). This makes it possible to reduce safety distances for major accident scenarios. Quite a number of the existing spheres have been "mounded" by being covered with "TEXSOL" (special blend of sand and synthetic fibres). Use of this technique has allowed continued use of sites that were threatened by housing developments. More than a dozen industrial .sites have used this technique for protecting their spheres.

Apart from the safety fundamentals -proper pressure vessel design, provision for hydraulic and seismic loading, and so on -the strategies applied with respect to tank auxiliaries have the following objectives :

• to limit any spread of product,

• to protect the tanks against any thermal effects,

• to a lesser degree, to protect the tanks from impact missiles. The safe state for tanks is attained by remote controlled safety valves on each connections that close automatically if gas or a flame is detected on site. In addition, the liquid outlet connections are fitted with internal remote controlled safety valves (usually hydraulically operated). Bunds are the rule around above ground tanks. Thermal and mechanical protection is attained by adding one metre of earth or an equivalent thickness of TEXSOL (60 centimetres). For above ground tanks, protection against thermal effects is provided by a spray system (10 Iitres/m 2 .min). Regarding the protection against missile impact, mounded tanks (under earth or TEXSOL). are inherently safe. Above ground tanks -most French LPG tanks are of this type -do not meet this safety objective apart from a few rare exceptions (when tanks are protected by a concrete wall or dome)

INVENTORY AND COMPARISON OF LPG REGULATIONS

GENERAL

The different regulations or '"reference documents" specific to LPG facilities were summarised for five countries : the Netherlands, the United Kingdom, Italy, Belgium and France. Of the five countries considered, only Belgium( 1) , Italy( 2) and France( j) have specific regulations for LPG facilities. The respective sources are given in chapter referneces. In the Netherlands, the directive "LPG distribution depots" (4) serves as the basis for defining the regulatory requirements governing the issue and renewal of licences for operating such installations. In the United Kingdom, two reference documents* 5 * may be used, one from the Health & Safety Executive, and the other from the British Institute of Petroleum. However these two documents provide guidance and do not have the force of law. It may be noted that general or particular legislation not specific to LPG facilities may contain requirements that also apply to such facilities. Such legislation is disregarded in this study. Our inventory was drawn up using, first, the above documents and, secondly, information obtained from industry and government representatives in the countries concerned. Notwithstanding this, the inventory should not be regarded as exhaustive. Apart from the classification of products, the main items dealt with in these regulations are :

• Rules for the location of tanks

Summary of regulatory requirements for valves on liquid outlets

This comparison reveals appreciable differences in approach between the different countries considered. In France for example, internal valves are required on liquid outlets while the other countries considered have opted for safety devices outside the tank.

LPG ACCIDENTS

Accidents are unfortunately a prime consideration from the safety standpoint, whether in terms of prevention, protection or control. The accident analysis performed is based mainly on information available in the "ARIA" database (6 ). It was done for each zone of activity -for example storage, transfer (loading/unloading), cylinder filling, etc., and also for each type of phenomenon : BLEVE (Boiling Liquid Expanding Vapour Explosion), explosion and fire. The following summary refers only to the analysis of accidents occurring during LPG transfer operations involving tanker trucks or w7agons.

REVIEW OF ACCIDENTS OCCURRING DURING LPG LOADING OR UNLOADING

Statistical analysis

The statistical analysis of LPG accidents occurring during loading or unloading covers a sample of 33 events, most of the data being taken from the ARIA database. These events took place in the period 1951 to 1998. Although the sample is on the small side, we shall try to deduce the main trends. A breakdown of where the accidents took place is shown below.

Distribution of accidents by type of location

It will be seen that the processes of unloading LPG on private premises and industrial sites (in bulk) alone account for over half (53%) of the events listed. In both these circumstances, transfer is practically always done using equipment carried on the tanker trucks (pumps, hoses on reels ; etc.). It should be borne in mind that a truck serving private clients (capacity limited to 6 or 9 tonnes) fills up at the filling centre or depot and then delivers supplies to an average of 10 clients. The number of unloading operations by these trucks at private premises far exceeds the number of their loading operations at LPG centres. Ten accident events are listed in connection with operations at these LPG centres. The two earliest events (Port Newmark in 1951 andBrinkley in 1957) shown in the "others" category could probably be included with them. No particular analysis of the geographical location of the accidents was done since those reported by the different sources are strongly influenced by the availability of information. In fact the proportion of the accidents taking place in Europe and North America is very high compared with other parts of the world. Here it is interesting to note that countries, like Russia, apparently had very few accidents. As a result the list is not exhaustive since a number of accidents probably took place with no report being published either by the media or the international organisations. As to the time distribution of the events, the number of cases reported appears to rise steadily as time passes : 50% of the accidents have been in the last 10 years. This observation is probably related to the growth of safety policies and the enhanced media attention for accidents and incidents that impose a wider circulation of information.

Phenomena observed

These have been classified into five categories : Phenomenon 1. Liquid spreading on the ground 2. Gas phase leak without ignition Jet (or pool) fire 4. Gas or vapour explosion 5. BLEVEofatank Phenomena used as a basis for classifying accidents It is worth noting that phenomena 1 and 2 can be precursors of 3 or 4, while the flare (or pool) fire can be the precursor of 5 (a BLEVE). In other words, a leak of flammable product (whether liquefied or not) may ignite well after it spreads. The following figure shows the different phenomena involved. The phenomenon shown in the following classification is the most significant one noted during the accident (for a leak followed by a fire, this type of accident is placed in the fire category).

Gas leak

Spreading liquid 0% without ignition 20%

Jet or pool fire 20%

Explosion 24%

BLEVE 36%

Distribution of events by observed phenomena Thus it can be seen that the main phenomenon characterising accidents during LPG transfer operations is a leak followed by ignition of the cloud formed, which in most cases (60%) leads to the effect of overpressure (24%) or a fireball (BLEVE : 36%). However ignition didn't occurred in 20% of the cases reported.

The two phenomena of fire and explosion (including BLEVE). which of course regularly occur together, account for more than two thirds of the accidents (80%). I -or the cases listed it will be seen that a leak is usually accompanied by the formation of a cloud that drifts with the prevailing wind. The ignition of this cloud at a distance (possibly at a considerable distance) is followed by a "flame return" that can cause fire under the road or rail tanker or tankers or its immediate vicinity.

The known BLEVEs listed in the literature result, in all the cases listed above, from a fire heating the tank, leading to an increase in pressure and mechanical failure. This phenomenon therefore affects ordinary above ground tanks, i.e., those where the shell has little or no protection from thermal effects. Among the accidents listed, inadequate means of protection are regularly identified as decisive in the development of an accident sequence towards a BLEVE.

Explosions of flammable gases are the result of a gas leak followed by ignition of the cloud if this is wholly or partly enclosed in a confined space. A large number of experiments have shown that the ignition of a gas cloud in free space, in the case of LPG, does not generate significant overpressure that is harmful to the environment. This is confirmed by accident reports. Indeed this condition of partial containment is probably the reason why most explosions of combustible gas (with the appearance of overpressure effects) concern production units, where there is usually a high density of equipment (with seals, valves, etc.) in a small volume, or leaks on customer's premises, for example when the cloud has entered a dwelling. Of course in these cases the explosion of the cloud could cause damage and leaks to the other tanks or mobile tankers (the domino effect).

Finally we may note that only one of the listed events mentions an incident that did not give rise to a leak and that no report mentions the presence of LPG in the liquid phase on the " r ound.

The severity of accidents

This was evaluated simply by dividing the accidents into two categories :

• Accidents not resulting in casualties.

• Accidents resulting in casualties.

Some 55% of the accidents did not result in casualties. In 15 of the listed cases there were casualties (injury or death) and the phenomena responsible are shown in the figure below.

BLEVE Others 13% 33%

Fire 34%

Causes of injury or death Fire (excluding fireballs) is the main cause of casualties with 5 accidents. The victims were people present in the gas cloud when it ignited. The "other"" category (5 cases) mainly contains accidents for which there is no information as to the cause of casualties (4 cases) and. in the 5 th case, the operator had a fall following a leakage of LPG. These 1 5 accidents were responsible for a total of 236 victims with 26 deaths and 210 injured. It is worth pointing out that two events resulting in a BLEVE alone accounted for 14 deaths and 144 injured.

However accidents occurring at LPG loading or unloading points do not always lead to loss of life. Thus on 1 April 1990 an accident occurred in an LPG filling centre at SYDNEY (Australia) during a process where the product was being transferred from a road tanker to a storage tank. A fire started and led to a BLEVE in a cylindrical 50 tonne LPG tank and a tanker truck. About 10,000 people were evacuated and the neighbouring airport temporarily closed, but there were no victims.

The causes of accidents As to the causes and circumstances of the 33 accidents listed, we identified the following seven causes set out in the table :   1.

2.

4. 5.

7.

Hose failure Failure of mobile tanker component Failure of connecting Failure in break away Truck departed while Human error Other causes system coupler connected Types of causes-circumstances considered Any accident, even if it affects a whole area, is "usually caused by a particular action or system. In the present case therefore, we looked into the nature of the causes and separated the main groups of causes-circumstances occurring. Their distribution is shown in the following figure.

Others 43%

Breakdown by type of cause-circumstance

The classification is based upon the precursor event. Lots of causes are identified. However the relatively large number of accidents (6 cases) involving the failure of systems on road or rail tankers will be noted. Hose failures account for 6% of cases (2 events) as do the failures of connecting systems or a breakaway coupler, or leaks resulting from the road tanker's leaving while still connected to the fixed installations. As regards failures of connecting systems, it is worth noting that the two events reported concern the operations of filling clients' tanks for which the connecting systems are much smaller (V A ") than those used on LPG sites (2" and 3").

Human error, which could also have been identified as a major cause in the case of tankers departing when still connected, covers two types of error in this classification :

• Opening the wrong line, allowing product to discharge to atmosphere (2 accidents in Germany). • Operator error leading to the bursting of a hose, for example the accident at Divonnesles-Bains or the discharge of product when liquid was being taken from a client's tank (the accident at Mouans-Sartoux).

Feedback of experience

In view of the small number of accidents listed, and taking into consideration the variety of possible scenarios, we must point out that the preventive, protective or control measures referred to in this paragraph are not the only ones taken at loading or unloading facilities on French LPG sites.

The accidents listed are usually characterised :

• by a leak either from the road or rail tanker or from the fixed installation,

• by the ignition of the cloud, often outside the site,

• by the means of control, notably spray systems, frequently inoperative either through their design or as a result of damage when the accident sequence began.

From these facts it is clear that the objectives as regards measures of prevention, protection and control should be :

• to employ high quality and reliable systems,

• to minimise any accidental releases of product,

• to cool tanks to prevent their bursting in the event of ignition.

The measures described below are guided by these objectives.

For the fixed installation

Hoses A few accidents have occurred on site during the transfer of liquefied gases. A good number of these involved hoses, a technique no longer employed on French LPG sites except for one or two where they are used for the gas phase. For both loading and unloading operations on LPG sites, articulated metal arms are the rule both for road and rail tankers. Each transfer arm is usually fitted with two automatic isolating devices and the transfer zones are under continuous surveillance for gas leaks or heat sources. These aspects are described below. It will be noted that hoses are still used for the operations of loading and unloading liquefied toxic gases such as ammonia, chlorine, and so on.

One-wax valves

These are useful only when tanker trucks or wagons are being unloaded. In these circumstances the one-way valve can substantially limit the quantities of product discharged to the atmosphere from the fixed installations. This passive system has the advantage of a short response time but serves no purpose in the case of fire or increased temperature. To be effective, it should be fitted as close as possible to the base of the arm. just before or after the motorisée! valve at that point.

Brcakaw'ay coupler

The causes of accidents include the unexpected movement of the road or rail tanker during loading or unloading. Whatever the cause of the movement of the tanker whose product is being transferred, the presence of breakaway coupler ensures that the mechanically weak point of the system consisting of the road or rail tanker, its pipework, the articulated arm and the fixed installation, lies between two automatic isolating valves. The breakaway coupler should have the following two characteristics :

• It should create a weak point in the transfer arm that will fail under abnormal stress.

• An automatically closing isolating valve is positioned at both sides of this weak point.

This arrangement can limit the amount of LPG discharged to the atmosphere, if the valve is open, to a few hundred grammes.

It will be noted that two accidents arising from malfunctions of such breakaway coupler are listed in this study. They occured before the system has been modified.

Gas and fire detectors Product transfer systems should be located in areas where there is continuous detection of :

• gas -flame • heat
It is of course extremely difficult to determine the best detection positions particularly for flames and gas.

Gas detection

Gases are usually detected using sensors with two alarm concentration levels : 20% and 50% of the Lower Flammable Limit for the gases, and which generally lead to :

• 20% LFL : audible and visible alarm, • 50% LFL : audible and visible alarm, with the site setup in safe condition by closing the motorised safety valves at the base of the arms and all motorised safety valves of all types on the site, and possibly automatic spraying of the installations.

Flame detection This can involve flame detectors (of the infrared or other type). Detection of flames by a sensor should, besides raising an alarm, at least put the site in a safe condition and possibly initiate automatic spraying of the installations.

Detection of heat

Due consideration should be given to the potential ignition of a flammable gas cloud, as indicated by the accidents listed in this study. To limit the consequences of such an event each motorised valve at the base of the arm (and indeed all the motorised valves on the site) should be placed in a safe position automatically in the event of any rise in temperature in their immediate vicinity. If the valves are operated pneumatically, this objective can be achieved by introducing a compressed air supply pipe which, over the last few metres before the actuator, is made of a meltable material. Then any substantial rise in temperature (about 80°C) in the vicinity of the valve will melt its supply pipe and lead to the automatic closure of the motorised valve.

For mobile tankers

Railway tankers

Rail tankers have two nozzles at the bottom of the tank, one for the liquid phase and one for the gas phase (fitted with an extension tube opening into the gas phase). Each nozzle has :

• a stop valve, inside the tanker, which can only be opened and kept open by pulling on the operating lever ; this is done by introducing a hook secured to the valve operating lever (or to the extension cable) and to the rail track, in order to maintain a continuous pull on the valve operating lever ; • a manual valve.

Removal of the hook, for any reason, leads to the automatic closure of the stop valve under the effect of the closure springs it contains. Three types of hook may be encountered :

• mechanical, • pneumatic.

• electromagnetic.

The hooks, whether of mechanical or other design, are automatically released if the rail tanker should be accidentally moved, causing the automatic closure of the valves at the bottom of the rail tanker. However the motorised hooks (pneumatic or electromagnetic) have the advantage that they can be operated by gas or fire detectors and by pressing an emergency stop button, which means that the placing of the rail tankers being loaded or unloaded in a safe condition can be incorporated in the general process of placing the site in a safe condition. Mechanical hooks on the other hand, if a leak should occur without wagon movement, can only be operated by a cable some 30 metres in length (usually) and on condition that the cable is not in the gas cloud. Finally, we should mention an original technique-which, instead of fixing up the hook on the rail, employs a pneumatic hook-retaining bar, a technique that has been systematically applied to sites. The system consists of a bar parallel to the rail and near to it, held in this position by being clamped axially by a pneumatic jack. The hook is then secured to this bar rather than to the rail. Any detection of gas, flames or heat (by the meltable pipe supplying compressed air to the jack that retains the bar) or actuation of one of the emergency stop buttons on the site, releases the hook retaining bar, thus causing the automatic and instantaneous closure of the valve or valves at the bottom of the rail tanker or wagons.

Where the hooks are motorised or attached to a bar retained in position pneumatically, it is no longer necessary to use a chain or cable to remotely operate the hook. Some of the advantages of motorised hooks are the following :

• They have been proven on a number of sites.

• These systems are integrated into the site safety scheme, since they operate automatically if gas or flame is detected or an emergency stop actuated. • They are fail safe devices, since in the event of an anomaly they take up a safe position. • These devices are easilv tested.

Tanker trucks livery nozzle (liquid or gas) on road tankers (small and large bulk carriers) is fitted with an internal safety valve usually operated hydraulically. These valves close automatically in case of tire thanks to the presence of a fuse plug. However the closure of these safety devices cannot be integrated into the automatic site safety scheme. This aspect deserves close attention.

( 'oo/ing systems on mobile tankers Faulty operation or weaknesses of cooling systems in installation are often blamed when scenarios develop catastrophically (into a BLEVE). LPG loading and unloading units are not usually fitted with fixed spray systems. Only those sites where fixed tanks have been mounded are usually fitted with such systems, the embankment of fixed tanks (on existing sites) releasing substantial amounts of firefighting water. Both rail and road tankers are very frequently fitted with a sunscreen. Small tanker trucks (that fill up at LPG sites) are provided with a rear locker containing the different components to be protected. Rail tankers are fitted with skirts at the bottom where the tanker is secured to the chassis. The effectiveness of fixed spray systems could therefore be significantly and adversely affected by these arrangements. Accordingly spray systems should combine fixed installations (headers) and judiciously located fire hydrants so as to be able to spray all the road or rail tankers involved as well as local areas not cooled by the fixed installations. In order to help the cooling of rail tankers, it is preferable not to place two trains side by side because in that case effective spraying of the arms (between the two trains) and the wagon nozzles is extremely difficult if not practically impossible. The time taken to start up fixed systems (fixed headers) should be as short as possible. Automatic spraying, initiated by the gas or flame detection systems (at the very least) would probably ensure effectiveness.

LESSONS

Except in the two cases of accidents concerning failure of the breakaway coupler, one can note that the installations blamed in the accident reports were not usually fitted with the safety systems described above. In concluding this chapter on the feedback of experience concerning LPG loading and unloading operations, it may be noted that in the absence of satisfactory safety arrangements on these installations, two main phenomena may occur :

• explosion or ignition of a gas cloud following the accidental release of LPG to the atmosphere , • a BLEVE in a mobile tanker.

CONCLUSION

This study is intended to provide the French Ministry of Environment with a reference base regarding regulatory trends in a few neighbouring countries concerning the best industrial practice. It may also provide guidance for developing French regulations for LPG.

table :

 : This table illustrates the general trends for the various industrial configurations that exist. Of course, there are exceptions, notably concerning the number and type of storage tanks.

	Type of	Type of	Type of tank	LPG entry	LPG	Remarks	Site
	site	location				despatch		workforc
									e
	Refinery	Large		Spheres (> 10)		Pipe	Despatches	>100
		industrial	horizontal	(Internal)	Ships	frequently	(firemen
		complex		tanks (>10)		Wagons	made	by	on	the
							Trucks	independent	site)
								sites
	"Buffer"	Large		Spheres	Pipe	Wagons	Entry	by	>20
	site	industrial	Refrigerated	Ship	Trucks	truck very
		complex		tanks				rare.
				Underground
				cavities
	Filling	Industrial	Spheres (< 10)	Pipe	Trucks	For	About 20
	centre	zone	or	Horizontal	Wagons		packaged
		suburban	tanks (< 10)	Trucks		LPG,	the
		zone						cylinders
								are
								despatched
								by truck.
	Interme	Industrial	Spheres (1 or	Wagons	Trucks		Of	the
	diate	zone	or	2)		Trucks			order of 2
	depot	suburban	Horizontal
		zone		tanks (<4)
	Local	Suburban	1	horizontal	Trucks	Trucks
	depot	zone		tank (volume
				< 120 m 3 )
	Overview of French LPG sites

  As an example, the following table summarises the situation as to the regulatory requirements for safety valves on liquid outlets from tanks.

		l sl valve			2 nu valve	Comments
	France	Motorised,		Motorised	Fail safe
		inside the tank
	Netherlands	Manual,			Motorised,	Fail safe
	(recommended)	as close to tank as		as close as possible
		possible, 1 st flange welded	to 1 st valve
	United Kingdom	Motorised,		Motorised,	Fire safe
	(recommended)	or	excess	flow	if 1 st valve manual
		valve,
		or non-return valve
	Belgium	Motorised				Fail safe
		non-return valve
	Italy	Liquid	outlet	:	Excess flow valve	Fire safe
		manual			Non-return valve	Valves	designed
		Liquid	outlet:		for
		manual				P > 40 bar
	<• Distances from establishment boundaries
	• Distances between tanks
	• Protection of water
	• Fire lighting measures
	• Gas detection
	• Control valves
	• Relief valves
	• Level measurements
	• Pressure measurements
	• Temperature measurements


S Vardoulakis '

N Gonzalez-Flesca

B E A Fisher

Air quality monitoring and modelling techniques for street canyons: the Paris experience

A better understanding of the dispersion and transformation of atmospheric pollutants in urban micro-environments is required to address the increasing public concern about human exposure in such areas. A joint research program has been established between INERIS (France) and University of Greenwich (UK) with the aim of developing efficient air quality monitoring and modelling methodologies to cover the needs of public health and road traffic managers in Europe.

An intensive monitoring campaign was conducted at a representative canyon street in Paris in winter 1998. This experiment was designed to establish the spatial and temporal variation of pollution within the canyon, and test readily available dispersion models. Active and passive techniques were used to sample a wide range of traffic generated pollutants (VOC and inorganic gases) at different heights and distances from the kerb. Local meteorological and traffic information was also obtained. The observed CO and NO concentrations were compared with predicted values, calculated using AEOLIUS, the street canyon model developed by the UK Meteorological Office.

The results demonstrate strong spatial pollution gradients within the canyon, large differences between roadside and background pollution levels, and pronounced temporal variability.

Introduction

In recent years, the increasing public concern about the adverse health effects of atmospheric pollution has led to the revision of air quality legislation at national and European level. Consequently, more stringent regulations have been proposed by the European Commission for several toxic gases mainly induced by road traffic (CO, NO 2 , benzene, ozone, etc.)

In most European countries, municipal authorities have an important role in ensuring that the air quality objectives are achieved. Particularly in the UK, the Local Air Quality Management legislation (Part IV of the Environment Act 1995) requires local authorities to conduct periodic reviews and assessments of air quality. In the cases where the objectives specified in the Air Quality Regulations 1997 are not likely to be met by the end of 2005, an Air Quality Management Area (AQMA) has to be declared. In such a case, the local authority has to carry out an assessment of present and future air quality in the area concerned, and prepare an action plan in order to reach the objectives [START_REF]National air quality strategy: review of the United Kingdom, Department of the Environment, Transport and the Regions[END_REF].

The compliance with regulatory standards is one of the tasks related to air quality that local administration has to undertake. In addition to that, health risk assessments, traffic management and transport planning studies need to be carried out on a regular basis. To manage these tasks, competent authorities need efficient monitoring and modelling tools and methodologies to determine pollutant concentrations in ambient air. As far as actions need to be taken at local level, these tools should produce reliable results at a low acquisition and operational cost. Furthermore, they should be user-friendly and well documented.

Within this context, particular attention should be given to those environments where population exposure to atmospheric pollutants is likely to be significantly higher than the urban average (e.g. busy streets and intersections, highways, petrol stations or industrial plants). A series of air quality monitoring campaigns is being conducted in Paris by the Institute National de l'Environnement Industriel et des Risques (INERIS -France) with the collaboration of the University of Greenwich (UK), aiming to develop a standard method for the characterisation of such environments.

The experimental approach adopted in this study comprises: (a) the use of mobile air quality and meteorological monitoring equipment for the spatial and temporal characterisation of urban micro-environments; (b) the application of simple dispersion models for assessing their potential as predictive tools.

2 Field experiment

Site description

A field campaign was carried out in December 1998 in Bd. Voltaire, a typical four lane avenue of Paris with wide pavements and car parkings on both sides of the street. The part of Bd. Voltaire which was selected for this experiment constitutes a nearly perfect canyon with uniform buildings lining up continuously on both sides, height-to-width ratio of 0.8, and no major intersections along a straight road segment of approximately 300 m. Traffic lights were operating at both ends of the canyon, and there was a pedestrian crossing at a distance of 34 m from the main sampling point. The street axis bearing from the north was 140° and therefore nearly perpendicular to the westerly winds prevailing in the region during the measurements.

Measurement techniques

Parallel techniques, both active and passive, were used during one week to sample a wide range of traffic related atmospheric pollutants (CO, NOx, O 3 , VOC). For the same period of time, local meteorological and traffic data were also collected.

Continuous CO, NOx, and O 3 analysers based on radiation absorption principles were used for the description of the temporal variation of pollution levels in the street. These analytical instruments were sheltered in a trailer, which was parked on the east side of the road.

Diffusive VOC samplers were located at different heights on both sides of the canyon in order to reveal the spatial variability of the compounds. For the estimation of the urban background contribution to the concentrations measured in the street, passive samplers were also placed in an adjacent park locations.

Active sampling for VOC was carried out during one day of the campaign. Ambient air was pumped for one hour periods at a constant flow rate through a tube filled with the appropriate adsorbent. The hourly VOC concentrations obtained using pumped tubes were directly comparable with the observed CO levels, since both measurements were carried out through the same sampling line.

Carbotrap-B Supelco [START_REF] Bates | Ambient volatile organic compound monitoring by diffusive sampling. Compatibility of high uptake rate samplers with thermal desorption[END_REF] was used as adsorbent for passive and active VOC sampling. After removal from the tubes with thermal desorption, the VOC samples were analysed in the laboratory using Gas Chromatography (column type: CP-SIL 5CB, 50 m X 0.32 mm, 1.2 um). A quality assurance programme, including sampling duplicates, blanks and instrument calibration with standard gases was followed during the sampling and analytical work.

A 3-D ultrasonic anemometer and a weather mini-station were used for meteorological monitoring. These instruments were situated on the top of a mast (of 3.7 m height) next to the trailer, at a distance of 8.5 m from the wall of the nearest building. The location of the sampling and monitoring equipment is shown in Figure 1. Traffic data were continuously recorded by an automated counter located at the end of the canyon.

Results

Correlation between CO and benzene

Most of the atmospheric pollutants generated by traffic in urban environments (e.g. VOC, CO) can be considered as inert compounds due to the very short distances between sources and receptors. For this reason, the proportionality between them is expected to be nearly constant in a specific area and for a period of time with no significant changes in vehicle fleet composition and traffic pattern. If a simple mathematical relationship expressing such a proportionality between CO and benzene is established, then it will be possible to estimate CO concentrations using benzene measurements and vice-versa on the basis of this relationship [START_REF] Pfeffer | Air pollution monitoring in street canyons in North Rhine-Westphalia, Germany[END_REF].

In order to establish such a relationship, active VOC sampling was performed in Bd. Voltaire during one day of the campaign, simultaneously with CO monitoring and through the same sampling line. Figure 1 shows the hourly variation of the detected benzene, toluene, m,p-xylenes, and CO concentrations. Figure 2 illustrates the linearity between CO and benzene measurements (correlation coefficient = 0.93, slope = 3.97 x 10" 3 , and intercept -0.15 x 10" 3 ). The empirical formula obtained from this regression, benzene (ppb) = 4 x CO (ppm), can be consequently used for the calculation of CO levels at all locations where benzene measurements are available, or for the estimation of benzene variation with time. This simple methodology makes use of the practical advantages of passive-active VOC sampling (low cost and autonomy-portability of samplers) and continuous CO monitoring (accuracy and high time resolution) to provide a detailed temporal and spatial description of the pollution levels in an urban canyon.

Spatial and temporal variability

Using benzene as an indicator, strong pollution gradients were identified in the horizontal and vertical sense within the canyon. Differences of more than 2 ppb of benzene were observed at street level between the two opposite sides of the canyon, and of more than 1 ppb between roadside and urban background (Figure 3). A hot-spot of benzene (weekly average: 4.5 ppb) was detected on the leeward (up-wind) side of the street at 4.2 m height. In addition to the horizontal pollution gradients, a significant reduction in benzene concentrations along with the height was also observed. Very similar trends were identified for the rest of the VOC compounds sampled with passive tubes during the campaign.

While benzene measurements described the spatial variability of pollution in the street, CO continuous monitoring provided detailed information on the temporal variability of inert pollutants. Two peaks of CO were observed during the campaign. The first one (16th December) can be explained by the presence of low wind conditions (wind speed < 2.5 m/s) in the region, and the second one (17 December) by the presence of relative low winds (2.5 -3.0 m/s) blowing from directions parallel to the street axis (Figure 4).

Model simulations

The observed CO and NO concentrations were compared with predicted values, calculated using AEOLIUS, the street canyon model developed by the UK Meteorological Office [START_REF] Buckland | Validation of a street canyon model in two cities[END_REF]. This model is designed to calculate a series of hourly concentrations of a pollutant at a single receptor location on either side of the street. It requires synoptic meteorological data, traffic information, emission factors, and description of the topography [START_REF] Buckland | Nomograms for calculating pollution within street canyons[END_REF].

AEOLIUS is based on the OSP Model [START_REF] Berkowicz | Modelling traffic pollution in streets[END_REF], which calculates the concentration of pollutants in the street as the sum of three components: the contribution from the direct flow of pollutants from the source to the receptor, the recirculation component due to the flow of pollutants around the horizontal wind vortex generated within the canyon, and the urban background contribution. The direct component is calculated by the model using a simple plume dispersion algorithm, while the recirculation component is calculated using a box model formulation. Finally, the background contribution is an additive term introduced by the user.

In this application, the diurnal variation of measured CO and NO concentrations was clearly reproduced by the model (Figures 5 and6). Nevertheless, the model predictions were quantitatively satisfactory only after introducing a constant fitting parameter. Given the strong pollution gradients in the street, this adjustment may be justified by the fact that the model was not configured to calculate the concentration of pollutants at the exact location where the measurements were taken. In addition to that, it is expected that the predicted concentrations would be closer to the observed values if locally measured (above-roof) wind data had been used for running the model. Finally, AEOLIUS appears not to be able to reproduce the measured peaks of pollution on an hourly basis, which is expected as models are rarely able to capture extreme pollution events [START_REF] Manning | Field study of wind and traffic to test a street canyon pollution model[END_REF].

Conclusions

A combination of air quality monitoring and modelling techniques has been proposed for assessing air quality in urban canyons. During the presented campaign, the simultaneous use of passive and active sampling systems provided a detailed description of the temporal and spatial variation of atmospheric pollution in the street and its vicinity. The strong horizontal and vertical concentration gradients may raise questions about the representativeness of routinely obtained air quality data from fixed monitoring stations.

The empirical CO-benzene relationship established for the specific environment can be used for achieving a better time and space resolution of roadside concentrations for both compounds. AEOLIUS can give reliable CO and NO predictions when it is carefully calibrated by measurements.

Following these air quality monitoring-modelling techniques, an optimum use of resources can be achieved. The relatively low cost of monitoring devices (e.g. passive and active tubes), the public domain software (AEOLIUS), and the limited amount of computational time and user expertise involved, make this method a cost-effective tool for the determination of air quality levels in urban canyons.

Figure 5 :

 5 Figure 5: Time series of measured and predicted CO

Figure 6 :

 6 Figure 6: Time series of measured and predicted NO

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							benzene
					toluene x~-m,p xylenes Benzene (ppb)
	h: 20.2m	3.1 passive tubes	......CO	2.0	h: 17.2m
											25 m
		h: 4.2m	4.5	Anemometer & weather station		h: 4.9m Analysers & active samplers	1.3 • h: 2.8m
	S	16	9	16	9	16
	10 14/12Date & Time 11 12 13 14 15 30 m	16	17	18	19
			Figure 3: Spatial variability of benzene in Bd. Voltaire (Paris)
		Figure 1: Daily variation of benzene, toluene, m,p-xylenes, and CO
											360
											. 330
		7 6								300
											270
				y=3.9689x-0.1493
	(qdd) Benzene	5 -	.	R 2 = 0.8634						240 210 180 .90 -150 120	rection (deg) Wind di
											60
		4 -									30
											0
	9		16	9	16	9	16	9	16	9	16
	14/12/98	15/12/98	15/12/98	16/12/98	16/12/98	17/12/98	17/12/98	18/12/98	18/12/98	18/12/98
		3-,			Date & Time
		0.80	1.00		1.20		1.40		1.60	1.80
		CO (ppm) Figure 4: Time series of CO, with above-roof wind and direction
					Figure 2: Benzene against CO

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	9	16	9	16	9	16	9	16	9	16
	14/12Date & Time

Acknowledgements

The authors would like to thank Jean-Claude Pinard (INERIS) for his technical support, Armelle Frezier (INERIS) for the chemical analysis of the samples, and Mairie de Paris (Direction de la Voire) for the traffic data furnished.


J Chaineaux

C Devillers

P Serre-Combe

BEHAVIOUR OF A HIGHLY PRESSURISED TANK OF GH z , SUBMITTED TO A THERMAL OR MECHANICAL IMPACT

INTRODUCTION

Safety is one of the concems which may limit a fast and large increase in the use of GH z äs a füel for engines in the füture.

Furthermore, for a given autonomy of a vehicie, the choice of a storage pressure of several hundreds of bars will significantly reduce the volume of the necessary tank(s). Whatever this pressure and whatever the volume of the tank(s), the storage System must be designed in such a way that the consequences of an accident, in which this System would be submitted to a thermal or mechanical ünpact, would be äs low äs possible.

Experimental work, co-funded by the EU and monitored by the Joint Research Center at Ispra site (I), was carried out in collaboration with INERIS, AIR LIQUIDE and CEA, in order to :

• define a GH a storage System likely to equip a H 2 -füeled road vehicie, • have it built, • study its behaviour, when it is highiy pressurised (700 bar) and submitted to a thermal or mechanical impact likely to occur in a road accident.

DESCRIPTION OF THE HIGHLY PRESSURISED GH, STORAGE SYSTEM

A real storage System may be composed of a set of several identical tanks, each one being equipped with the same safety devices. The components of the storage System which were built for the need of this work, were the following :

• one cylindrical composite 9 dm 3 cylinder, made of an aluminium liner, wired with carbon fibre impregnated by an epoxy resin and having a service pressure PS = 700 bar (photo l) ; this cylinder was manufactured by COMPOSITE AQUITAINES 4 , • one flow limiter (0,35 mm diameter hole), one thermal füse and one isolating valve äs safety devices.

The diameter of the flow linüter was defined in such a way that, for a minimum storage pressure of 40 bar, the hydrogen mass flow would be 0,23 g/s, which is the minimum flow needed by the engine. The thermal füse opens at 80°C. These safety devices have been fitted to the pipe supplying hydrogen from the gas cylinder to the engine, according to the diagram in Figure l.

MEASUREMENT OF THE CONCENTRATION FIELD RESULTING FROM A LEAK

In case of the rupture of this pipe, there would be a leak of hydrogen, through the flow limiter. Such a rupture has been simulated for a storage pressure of 700 bar and the concentration field, generated by the discharge of hydrogen into air, äs a free jet (without obstacles), has been measured.

The theory of high speed jets discharged into free air indicates that :

• because of the turbulence of the jet, hydrogen rapidly mixes with ambient air, generating a concentration field,

• this concentration field is such that 3 zones can be distinguished : zone l which includes the outlet, where the hydrogen concentration is higher than the upper explosivity lünit (UEL= 75 % vol.), zone 2 where the hydrogen concentration is lower than the lower explosivity lünit (LEL = 4 % vol) and zone 3 in which the hydrogen concentration is between LEL and UEL. In zone 3, the mixture is explosive (cf. scheme on Figure 2), • the volume of zone 3 depends only on the diameter of the outlet and on the instantaneous hydrogen pressure in the bottle, • this volume continously decreases äs the hydrogen pressure decreases ; it is maximum when the hydrogen pressure is maximum, i.e. 700 bar.

Six hydrogen sensors have been placed on the jet axis, at different distances x fi-om the outlet of the flow limiter, in order to measure, at the beginning of the discharge, the maximum hydrogen concentration cmax. These sensors, in house designed and fabrication, have a short response time, lower than one second.

The Variation of the hydrogen concentration measured by each sensor at the beginning of the discharge, has been given previously (l). More detaüed results about the characterisation of the concentration field resulting fi-om jet discharges have been given in (2).

Figure 3 shows that the Variation of (l/cmax) äs a fünction of x is linear. This result corresponds to an hyperbolic decrease of cmax along the jet axis. Moreover, it can be seen that cmax is equal to LEL for x =1,9 m. So, at the beginning of the discharge, the volume of the explosive zone ( 3) is maximum and can be evaluated to be 20 dm 3 .

THERMAL AND MECHANICAL IMPACT TESTS

Definition

Different information has been drawn fi-om :

• accidental data sets,

• French or foreign Standards and regulations, concemmg the storage Systems for other gaseous füels, such äs natural gas, • proceedings of hydrogen symposia. This information has been used in order to define thermal or mechanical impact tests to simulate the real impacts which the GH z storage System of a vehicie is likely to sustain in a road accident.

TABLE I : Definition of the impact tests carried out

For the tests l to 4, the gas cylinder was put inside a wire fenced cubical enclosure (side length : 4 m), the walls of which have been designed to stop the missiles resulting from the bursting of the gas cylinder (photo 2).

Description and results of the tests

Testn0!

The behaviour of a gas cylinder (target gas cylinder) was tested when its wall is impinged by a jet fire, discharged from the outlet of the open thermal füse of a nearby bottle (source gas cylinder).

The pressure inside the target gas cylinder increased gradually for a little less than 3 minutes, until the gas cylinder bursted, producing about 15 variously sized fragments.

The buming jet impinged the gas cylinder dose to its bottom and far from its thermal füse ; thus, because it stayed closed, the füse was not able to prevent gas cylinder from bursting.

During the burst, a large fraction of the hydrogen nüxed with air and bumed.

Testn°2

The behaviour of a gas cylinder was tested by subnütted it to the flames of an hydrocarbon pool fire. Unlike test n°l, the thermal füse opened within less than 2 minutes and the gas cylinder totally emptied äs a buming jet, within less than 8 minutes and without bursting.

Testn°3

A detonating cord was placed around a gas cylinder which was then pressurised with hydrogen up to 700 bar. When the cord was ignited, the gas cylinder burst in two fragments and the consecutive phenomena were :

• the projection of the fragments (initial speed dose to 100 m/s),

• the production of an aerial pressure wave, • the mixing of hydrogen with air and the ignition of the hydrogen-air mixture, äs a fireball (photo n°3).

From the maximum aerial overpressure, the effects can be considered äs equivalent to those produced by the detonation of 450 g of TNT.

The main part of the released energy comes from the expansion of the initially pressurised hydrogen and represents a TNT equivalent of 300 g. A secondary part of the released energy comes from the explosive contained in the detonating cord and it represents a TNT equivalent of 110 g.

It appears that the TNT equivalent of the released energy is a little smaller than the one deduced from the pressure effects. So, it can be considered that the energy released by the combustion of hydrogen has only a weak TNT equivalent (some tens of g). This result is confirmed by the fact that on the video-film, the fireball has a weak expansion. Moreover, a TNT equivalent of some tens of g signifies that the ratio of the mass of hydrogen which has exploded to the total mass of hydrogen stored in the bottle is lower than l %.

Conceming the thermal effects, the combustion of hydrogen has been so rapid (duration < l second) that with a heat flux sensor having a Standard response time, no heat flux was measured.

The contribution of hydrogen to the mechanical and thermal effects produced during test n°3 was weak but, without any exhaustive study of the influence of each relevant parameter upon this result, it should not be considered äs a general ruie.

Testn°4

A hydrogen-pressurised cylinder was subnütted to the impact of a gun bullet, shot at point-blank ränge and having an initial speed of about 850 m/s. The angle between the shooting axis and the cylinder axis was 45°a nd the impact zone was at the bottom of the bottle.

The bullet has passed trough the cylinder, which did not burst (photo n°4). Hydrogen discharged through both holes äs two jets, but did not ignite.

Testn°5

A gas cylinder was half-filled with water and dropped from a height of 14 m, over a concrete slab (from such a height, the speed of the bottle when it touches the ground is dose to 60 km/h). Then, a hydraulic rupture test was done : the cylinder rupture started at its bottom, which was the impact zone, for a pressure equal to 1000 bar. This figure is much lower than the normal rupture pressure, 1750 bar, and it can be concluded that the fall test strongly modified the mechanical characteristics of the cylinder bottom (photo 5).

Testn°6

Test n°6 was a crash car Simulation : the cylinder was fixed horizontally on to a heavy concrete block, at such a height that it could be impacted upon by the bumper of a car crashing into the block. It was then pressurised by nitrogen under 700 bar. The car was launched by an air-gun and, at the crash time whose speed was 65 km/h and its kinetic energy was 144 kJ. The crash damaged the cylinder wall (photo 6), but the cylinder did not burst.

A hydraulic rupture test was done after the crash : the cylinder rupture started at its cylindrical part, where the impact had damaged it, but the rupture occurred for a pressure of 1700 bar, which is dose to the normal rupture pressure : the crash test did not significantly modify the mechanical strength of the cylinder.

CONCLUSION

The behaviour of a highiy pressurised (700 bar) GH z composite gas cylinder was experimentally studied, by submitting it to different thermal or mechanical impacts simulating those of a car crash. The cylinder was equipped with a thermal füse (80°C opening temperature) and a flow limiter (0,35 mm in diameter).

The main results of the 6 tests performed are the following :

• the maximum length and volume of the explosive hydrogen-air mixture generated in the case of a leak discharged in free air through the flow limiter are respectively 1,9 m and 20 dm 3 . • the thermal füse cannot prevent the gas cylinder from bursting, if the impinging jet flame coming fi-om a nearby cylinder is too far from the füse, • when a cylinder bursts, the main part of the released energy comes from the expansion of hydrogen ; moreover, hydrogen mixes very rapidly with air and bums in a fireball. However, compared to the mechanical effects of the expansion, it has been shown that the contribution of hydrogen combustion was small. Finally, the thermal effects were negligible because the duration of the fireball was very short, less than l second.

BIBLIOGRAPHY

(1) Chaineaux (J.) : Leak of hydrogen from a pressurised vessel. Measurement of the resulting concentration field. Workshop on dissemination of goals, preliminary results and validation of methodology, Bruxelles, 11 mars 1999, p. 156-161. ( 2)

Ruffin (E.), Mouilleau (Y), Chaineaux (J) : Large scale characterisation of the concentration field to supercritical jets of hydrogen and methane. J. Loss Prev. Process Industr., 1996, vol. 9, n° 4, p. 279-284.

Isolation valve

Figure l :Figure 2 :Figure 3 :

 l23 Figure l : Diagram of the gas cylinder, equipped with a thermal ßise, a ßow limiter and an Isolation valve

Table l

 l gathers the main features of the 2 thermal impact tests and the 4 mechanical impact tests which have been carried out.

	Test number
	1
	2
	3
	4
	5
	6

Nature and initial pressure of the gas inside the gas cylinder (bar)

		Impact type	Main features of the
			impact
	Hydrogen -700	Thermal	Behaviour when submitted
			to a buming jet
	Hydrogen -700		Behaviour when submitted
			to an hydrocarbon pool fire
	Hydrogen -700		Rupture by detonating
			cord
	Hydrogen -600	Mechanical	Behaviour when submitted
			to a gun bullet
	Without any gas, half-filled with		Fall test
	water		(+ hydraulic rupture)
	Nitrogen -700		Crash test
			(+hydraulic rupture)

INERIS, B.P. n°

2, 60550 Vemeuil-en-Halatte 2 AIR LIQUIDE, DTA, BP n° 15, 38360 Sassenage 3 CEA/CEREM, 17 nie des Martyrs, 38054 Grenoble Cedex 4 COMPOSITES AQUITAINE, 19 route de Lacanau, 33160 Salaunes Cedex