B Veyssiere

R Bouriannes

U Ditonique

Ra

C Proust

ESTIMATION OF THE TEMPERATURE OF STARCH PARTICLES-AIR FLAMES

Introduction

If the ability of reactive solid particles to give rise to combustible mixtures when they are finely dispersed in an oxidizing gas is well known since a long time, the actual mechanisms governing the propagation of combustion in this kind of reactive mixtures is far from being well understood. The reason for this is an insufficient knowledge of the fundamental properties of characteristic parameters of dust flames. To progress in the prediction of dust explosion hazards and of their effects, substantial fundamental results concerning the structure and properties of dust flames are needed.

Many works have been devoted to the measurement of the explosion pressure of dust air mixtures inside closed vessels and to try to derive the combustion rate from pressure evolution as function of time. In spite of the interest of this method of investigation, due to the simplicity of carrying out experiments, it does not permit to have a direct access to the measurement of the characteristic parameters of the reaction zone and to investigate its structure. As a result, several researchers 1 ' 2 '-5 ' [START_REF] Jarosinski | Quenching of dust-air flames. 21 st Symposium (international) on combustion[END_REF] have undertaken the study of flame propagation in tubes. In previous papers, we have described an experimental method to study the propagation of a flame at constant pressure^, displayed original results in the case of laminar starch particles-air flames [START_REF] Proust | Fundamental properties of flame propagating in starch dust-air mixtures[END_REF] , and discussed the possibility to derive the laminar burning velocity from the registration of the parameters of a freely propagating laminar flame**. However, despite the interest of these new results concerning the flame shape or fundamental parameters, such as the laminar burning velocity, the quenching distance,...the information to our disposal is yet insufficient to permit a correct description of a dust flame. Indeed, progression in this domain is dependent on the knowledge of another fundamental parameter of the flame which is the temperature. But, until now, we have only rough and contradictory results about the temperature of dust-air flames, as a result of the great difficulties to perform experiments of direct measurements of the temperature in this kind of reactive systems. We expose, hereafter, the first effort made to acquire new and original experimental results on this problem.

Experimental Method

Experimental setup

The method used to study the propagation of laminar dust flame at atmospheric pressure has been described in detail elsewhere [START_REF] Proust | A new experimental apparatus for studying the propagation of dust-air flames[END_REF] . Experiments are performed in vertical tubes. The suspension is produced at the bottom in a generator (see Fig. To get reliable results from thermocouple measurements, they have to be chosen so as to fulfill different requirements which may be difficult to satisfy in the same time: to be sensitive at low temperatures, support high temperatures (greater than 1000 K), have the shorter risetime possible, resist mechanically to the passing of the flame and the panicles. For performing our experiments, we have used thermocouples specially designed at LED. They are made of 25p.m-diam. chromel-alumel wires with a junction welding having a 25}im diameter, which gives them a 10ms risetime. The junction wires are coated inside thin refractory rods. These thermocouples can be mounted at different places along the tube; the junction is generally located in the centre of the cross section, but also near the walls. In some experiments, we have also used classical 200-)i.m chromel-alumel themiocouples. They have a better mechanical behavior, but their risetime is 200 ms.

Optical Pyrometer

We have used a pyrometric device based on the method of emission-absorption by the flame, which has been specially designed at LED for measuring the temperature of the solid phase in solid particles-gas mixtures. This apparatus has been described in detail elsewhere [START_REF] Bouriannes | Measurement of dust-air flame temperature[END_REF] . Its principle consists in processing three signals obtained by recording: (i) the emission of a reference source in the absence of the experimental medium, (ii) the self-emission of the medium, and (iii) the emission of the reference source through the experimental medium. The reference source is an infrared emitting diode. The originality of the apparatus consists in recording all signals by the same photomuitiplier, that is along the same optical path (see Fig. l), and separating the different signals by modulating the emission of the source to distinguish the continuous part from the modulated one. The working wavelength of the device is 850 nm, the frequency of source modulation is 2 kHz, and the diameter of the zone explored in the flame is 3mm.

Flame characteristics

Our experiments have been performed in starch particles-air mixtures. The particles had a 20-jim mean diameter and their concentration in the mixture varied in the range 0-250 g/m^, that is, for lean or siQichiometric mixtures. An example of a typical laminar starch-air flame propagating in the tube A is shown in Fig. 2. In our previous works 5 - [START_REF] Veyssiere | Estimation of the laminar burning velocity of starch particles-air mixtures[END_REF] , we have displayed the dependence of the laminar burning velocity S u on the mass concentration a of particles and shown that the value of S u was maximum around the stoichiometry. But it appeared that the value of S u was slightly influenced by the size of the cross section of the tube: in the tube A, the maximum value of S u is 0.27 ± 0.05 m/s, whereas it is only 0.22 ± 0.05 m/s in the tube B. With the same starch particles and with an experimental device close to ours, but with a cross section of only 0.05 m x 0.05 m, Mazurkiewicz and Jarozinski 8 derived a value of S u of only 0.12-0.15 m/s. This indicates that flame propagation is influenced by the presence of tube walls and leto suppose that the dimensions of the larger tube (A) may be hardly sufficient to minimize the effects of lateral losses to the walls. The dependence of quenching distance on the concentration of particles has been also studied in tube A. It has been shown that the quenching distance was minimum around the stoichiometry and equal to 7 mm. Those measurements have permitted us to estimate that the lower flammability limit is obtained for a particle concentration o*=70g/m 3 and that the flame thickness could be of the order or magnituae of 3-4mm.

Results of temperature measurements

A typical example of the signal recorded with a 25-}im thermocouple in the tube A is shown in Fig. 3. After a sharp increase of the signal at the passing of the flame front, the maximum value is reached within i?ne hundred microsecond^ Then, the signal decreases slowly and presents a lot of fluctuations. It is interesting to compare the signal delivered by a 25-jim thermocouple with a that delivered bv a 200-um one as shown by Fig. 4: There exists an important difference in tne nrst part or me signal as a result of the difference in risetimes. But later, the two signals display the same evolution as function of time: particularly, it can be observed that temperature maintains with large fluctuations at a high level during an important time interval (several hundred of microseconds). We have plotted in Fig. 5 the value of the maximum temperature as function of mass particle concentration measured in the tube A. One can observe that the maximum is reached around the stoichiometric concentration. The results of temperature measurements made with 25-jim thermocouples in tube B reveal (see Fig. 6) that, for lean mixtures, there are no significant differences in the values of the maximum temperature recorded in the middle of the cross section of the tube B in comparison with the results of tube A.

Moreover, measurements made with the thermocouple located at 3 cm from the wall, thus recording the temperature evolution along the side of the flame, leads to maximum values of the temperature very close to that recorded at the flame tip (see Fig. 7).

With the optical pyrometer, a first series of experiments has been done for lean

Discussion

Comparison of the values of maximum temperature measured by means of thermocouples, with the thermodynamic values of the temperature of the adiabatic flame displays a deficit of several hundred degrees of the measured values, up to 500 K for stoichiometric concentrations (see Fig. 6). A temperature deficit of the same order of magnitude had already been observed by Smoot and Horton 9 in the study of laminar flames propagating in pulverized coal dust-air mixtures. We have verified that the correction due to radiative heat losses by thermocouples is inadequate to explain this discrepancy. With the pyrometer, the gap between experimental and theoretical values is reduced, but remains however significant (about 200 K). The difference between the values indicated by the two methods for measuring the temperature may come from the working principle different for the two apparatuses: the thermocouple indicates the temperature of gases, whereas the pyrometer indicates that of particles. Anyway, it is legitimate to suppose that this temperature deficit should not be attributed to the method of temperature measuring, but to the phenomenon itself.

The 25-\itn thermocouple records show also that the maximum temperature is reached about 100 ms behind the flame front. As a result of their too long risetime, the 200-jim thermocouple are inappropriate for determining the maximum temperature. The time (300-400 ms) during which temperature maintains at a high level with, however, important fluctuations, is consistent with the existence of packets of dust burning with a delay behind the main flame front, as attested by photographs. The fact that the temperature measured at the rim of the flame is quite the same as that measured at its tip indicates that the lateral losses should be unimportant at the scale of the flame. As regarding the maximum temperatures recorded in the larger and the smaller tube, it appears that the differences in the values of S u noticed previously between the two apparatuses, should not be attributed to problem of adiabaticity, but rather to mechanical effects of boundary layer.

In pyrometric records, the maximum of temperature is reached later than in thermocouple measurements. This is probably due to the fact that the temperature delivered by the pyrometer is a value integrated over the cross section of the tube. As shown by photographs, the shape of the flame is elongated with important curvature of the front: thus the maximum temperature is obtained when the cross section surface of the flame has reached its maximum, which is achieved about 200ms behind the flame tip.

The substantial decrease of the absorption coefficient at the rear of the flame front indicates that, at the considered concentrations, the medium becomes nearly transparent during combustion, which is an additional confirmation that, for starch particles-air mixtures, combustion occurs in gaseous phase. The duration of the zone with low value of absorption coefficient is consistent with the length of the flame plume observed on the photographic records (Fig. 2). The re-increase of the absorption coefficient behind this zone is likely to be due to the turbulent mixing of the unburnt particles with gases, which generates again a suspension having optical properties of a semi-transparent medium.

Finally, the more plausible explanation of temperature deficit seems to be the heat loss due to flame radiation toward the burnt products at the rear of the front.

Nevertheless, this hypothesis requires further examination.

Conclusions

The temperature of a starch Darticles-air flame freely propagating in tubes has been measured by means of short risetime tnermocouples in two different setup and with an optical pyrometer in the larger tube. It seems to be confirmed that there exist a deficit of the measured temperature values in comparison to the theoretical value of the adiabatic flame temperature, despite this deficit is less important in pyrometric measurements than in those obtained with thermocouples. Our results diverge from those of Mazurkiewicz and Jarozinski** who have obtained in the same mixture values greater than ours. However, their results are questionable since in the same time, those authors display a dependence of the laminar burning velocity on the particle concentration which presents around the stoichiometry a behavior opposite to that expected. Finally, it appears of great interest to go on in improving experimental methods for measuring the temperature of heterogeneous solid particles-gas mixtures. There exists vet a great uncertainty in the knowledge of the temperature of flames of this kind, and further information is needed about the heat transfer processes inside and outside of the flame.

Additional experimental results will be shown at the moment of presentation.

  l) and flows in a laminar regime within the tube up to the top, which permits to fill the tube with a homogeneous suspension. At the time of ignition, the tube is open at the bottom end and closed at the upper one. Ignition is achieved near the open bottom end by means of an electrically heated wire. As a result, a laminar flame propagates up to the closed end of the tube. Two different setups built on the same principle have been used, the first one (A, located at ENSMA) is 3-m long with a square cross section 0.20 x 0.2 m and the second one (B, located at INERIS) is 1-m long with a square cross section 0.1 x 0.1 m. Both are glass made, allowing visualization of flame propagation with cinematographic or video camera, and measurements by optical methods. Temperature measurements Two different methods have been used to measure the flame temperature: thermocouples and optical pyrometer. Thermocouples

  mixtures, at particle concentration around G=150g/m 3 . Typical signals delivered by the pyrometer are shown in Fig.8: signals (a) and (b) represent solid particles temperature and absorption coefficient evolution, respectively. Before the arrival of the flame, the temperature signal has a constant value corresponding to the threshold of the sensitivity of the apparatus. On the passing of the flame, it increases whereas in the same time the absorption coefficient sharply decreases. Maximum of temperature is reached simultaneously with minimum of absorption coefficient, within about 200 ms. The value of this maximum temperature is around BOOK. Then, the temperature decreases and returns to its initial value after about 2s. The absorption coefficient ensues the opposite behavior, re-increasing to reach a constant value.

Figures •Fig. 1 Fig. 3

 13 Figures •

Fig. 5

 5 Fig.5 Variation of the maximum temperature behind the flame front recorded by the thermocouple, as function of the mass particle concentration in the tube A.

Fig. 6

 6 Fig.6 Comparison of the temperatures recorded by thermocouples • in tube A and o in tube B, with the theoretical values of the adiabatic flame temperature

Fig. 8

 8 Fig.8 Typical signals delivered by the optical pyrometer in a starch particles-air flame (a) temperature, (b) absorption coefficient.


G Mavrothalassitis

- R Bouet -B

P Chhuon -J

Pineau

USE OF PERTINENT SOFTWARES IN RISK ANALYSIS

ABSTRACT

The first need of the risk analyst is the availability of pertinent softwares to assess, in a realistic way, the maximum effects of possible accidents such as pressure pulses, thermal fluxes, accidental missiles formation and projection and toxic releases of gases, vapours, mists, soots or dusts.

To be useful to risk management, this approach has to be quite simple but also as realistic as possible. An underestimation as well as a crude overestimation of the effects may prove dangerous.

A lot of softwares aim at this purpose. The analyst has to make sure he is using a suitable tool. This involves : •

The knowledge of how to use it (it is usually time consuming and depends on the aptness of the theory and the user's manuals) The analysis of the tool according to its internal consistency • Comparisons of the results with calculations that might be otherwise assessed • Comparisons of the calculations with existing data when possible (experiments and/or investigations of past accidents).

The paper aims at the first three above mentioned points, dealing with the comparisons of individual critical analyses of the following commercial softwares : CAMEO, CHARM 6.1, PAMPA 2.1, PHAST 3.0, TRACE 2.5.4.

When considering for example the physical consistency of models and submodels, the user-friendliness, the qualities of the data base and the explanations given in the documentation, it is possible to define an evaluation protocol for further studies.

To summarise, the use of pertinent softwares is an absolute prerequisite before determining criteria for acceptability of risks.

CONTEXT OF RISK ANALYSIS

For a long time, INERIS has been interested in prevention and protection against the effects of fires and explosions in industrial facilities in various sectors : chemicals, oil, agri-foodstuffs, metals industry, energy, coal mines and more recently, the carriage by rail of dangerous goods. Studies have also concentrated on physical modelling and experimentation on the involved phenomena as well as on the definition and testing of detection, prevention and protective devices in order to suggest safer operational conditions.

Another aspect of the work performed by INERIS's experts is to deal with accident investigations such as fire in fertilizer storage plants, hydrocarbon fires, unconfined explosions following leaks of flammable gases, explosions of grain silos and in metal processing plants.

When carrying out such an accident analysis, it is essential to use different types of computation software to calculate effects. The authors were also involved in safety cases, for which the use of these softwares was very important.

One of the purposes of risk analysis is to define the maximum effects of accident scenarios (eventually reduced by taking into account the technical measures of protection implemented by the manufacturer).

For all these tasks, the effects to be considered may be pressure pulses, thermal fluxes, accidental missile formation and projections and toxic releases of gases, vapours, mists, soots or dusts.

To perform such calculations of effects, INERIS developed and used its own tools (BIGEXP on explosion effects, MISSILE about projection of debris, JET on unconfined explosions from gaseous jets in atmospheric air, FNAP on radiative effects of poolfires...) or considered commercially available softwares.

But for plant managers, for insurance or control organizations and for competent authorities dealing with control of high-risk industrial sites, this approach has to be quite simple but as realistic as possible. An underestimation as well as a crude over estimation of the effects may be dangerous.

Thus, one of the first cares of the analyst is to make sure he is using a suitable validated tool. The point of view taken into consideration is that of the user to make him sure he is using a suitable tool, when considering the following questions :

Is it easy to use the software ? (It is usually time consuming and depends on the aptness of the theory and the user's manuals) Is the tool internally consistent ? (for instance may I calculate the same flow rate while considering a hole on the wall of a reservoir or considering a same size null length pipe ?) May I obtain the same results as those of calculations which might be otherwise assessed ?

European Technology & Experience in Safety Analysis and Risk Management-SRA-Europe, Rome, 18-20 octobre 1993

Are comparisons of the calculations of existing data available ? (These data may be drawn from experiments and/or investigations of past accidents). This paper will deal successively with the following points related to: User friendliness of the software Quality of the data bases • Internal consistency of the software • Comparisons of the results against calculations.

The following versions of CAMEO, CHARM 6.1, PAMPA 2.1, PHAST 3.0 and TRACE 2.5.4 softwares were considered. These softwares are integral ones.

USER FRIENDLINESS OF THE SOFTWARE

Conditions of use of the software

This point first includes questions related to the conditions of use, such as: cost equipment needed (PC or workstation, graphical tools, size of RAM, ROM...) ease to install the software in the computer (are the steps of installation clearly defined in the Manual ? Is it possible to have an efficient help from the retailer or from the developer of the software ?) relevancy of answers (may the user ask questions directly to the developer or is there a retailer's interface ? Does the developer remain working on the same -or related -topics ?)

Use of the software

This point includes a lot of questions germane to the use itself :

1) The product, we feel, is not only a software. It's a package which includes both the software and the Manuals (Theory and User's Manual).

The quality of the manuals is a main feature of this package.

1.1 Is the user, after reading the so called "user's Manual", able to run the case he intends to assess ? 1.2

Are the results clearly explained ? Are relevant examples given, explaining the definition of messages, the significance of values... ? * To give an example, we had to study a software dealing with atmospheric dispersion, the snapshots of which were not clearly defined. Thus, a crude reading of the results could bring the analyst to think the severity of a permanent emission increases with time. This is obviously not true after the regime is established at the point under consideration. The lack of information in this case was related to the algorithm used to represent the permanent emission as a succession of equal puffs. * Another example is related to the interpretation of results. Another software reports the results as if it was only possible to consider permanent emissions. Thus the information given as "cloud radius", "cloud height", "mean concentration"... have different meanings : When the emission is instantaneous the meaning of the words is correct: the software describes the evolution of the cloud while it is advected and it vanishes. When the emission is permanent, the cloud is represented by means of windows, the height of which is reported as "cloud height", and the semi-width as "cloud radius". 1. [START_REF]Control of urban development around high-risk industrial sites -guide[END_REF] Are the hypothesis and ways of modelling accurately described in the Theory Manual ? For instance, the Theory Manual has to describe the way chosen to assess aerosol formation. Is it by way of Weber's number ? Is it possible to take account of mechanical tearing ? Is it only assuming empirical approaches ? To be efficient, the Theory Manual has to be clear, complete and to show completely the limitation to modelling.

2) Do the results include reference marks to allow the analyst to be able to recognize the case he is dealing with ? If the case is not referenced on the listings and on the graphs, the use of the software may be tedious for it is not possible to run a succession of cases without having to stand around the machine. This practical point is very important when the user wishes to analyse the consequence of the variation of a given parameter.

Among the softwares we examined, only a few reference the cases studied.

3) Is it possible to store in memory the cases studied ? This is useful when studying a given plant and analysing different cases around the same topic. Such a study, if no storage is possible, is tedious and time consuming.

Quality of tools to assess phenomenon evolution

Another point of concern in user-friendliness of the examined version of the software is related to the quality of tools available to assess phenomenon evolution. For instance on dispersion :

• Are vertical and horizontal cross-sections of the cloud available as a function of time ? Is it possible to have the history of concentration at each point ? Is it possible to choose only points on the downwind axis ? Is it possible to calculate directly the dose (|C n dt, in which C is the calculated concentration at the point under consideration. C is a function of time t. n is related to a toxical effect according to the relation C n t=cte, t being the time of exposure) received at these points ? We had to examine a version of a software which could only give calculated concentrations at the points of a universaly settled logarithmic grid. Such a version does not fit closely the requirements of the analyst.

Are the listings complete with size, position of the cloud, concentration, temperature, time, description of pools formed by rain-out ?...

Error messages and guard-rails

Another point with regard to the user-friendliness of the version examined is related to the error messages and the presence of guard-rails testing the physical consistency of the data introduced to calculate a case.

Our work underlined versions of softwares in which it was possible to calculate gaseous explosions of solids, or to consider a hole diameter greater than the diameter of the tank, or a reservoir containing liquid at atmospheric temperature in the ceiling of which pressure may be different from the saturated one!

Limitations of the model

The last point with regard to user-friendliness of the version examined is related to a clear description in the Theory Manual of limitations of the software. This has never been encountered in the Manuals of the examined softwares versions. However, it is very important. To give an example : assuming 1 kg of chlorine is dispersed downwind, what is the reliability of a result giving 30 ppm of this gas at more than 1850 m downwind when you do know that the mechanisms of dispersion have been calibrated from experiments where tons of chlorine were released?

It is important for the analyst to know the minimum order of magnitude he can consider to carry out significant calculations.

QUALITY OF DATA BASE

One function of the softwares used is to give the physical properties of species involved in the study, in order to allow calculations.

Usually, these properties are stored in one or several files. For the analyst, the main features of the data base are:

The number of species involved, and their nature. The best is obviously to have as many species as possible. Practically, we noted that softwares designed by chemists do not usually include a lot of species used in oil plants. For instance, consideration of hexane is not sufficient when studying an oil storage. On the other hand, a data base that includes a lot of aromatic and aliphatic species does not necessarily include other products, such as T.F.M. A (Metatrifluoromethylaniline) • The ease with which to create a mix of the species of the base, to add new species or to modify a property.

We noted it was sometimes possible to add a new species without difficulty but without analysis of the consistency of the properties introduced. » The capacity of the data base for constituting a library of physical properties. One may quote that the PHAST data base gives an analysis of all the properties as a function of temperature and pressure. This aspect is very useful for thermodynamic calculations and constitutes, in itself, a useful tool. • The completeness of the base concerning toxicity. Are there values given about n ? (n being related to an effect according to the relation C n .t= cte where t is the time of exposure).

INTERNAL CONSISTENCY OF SOFTWARE

The purpose of this part of the examination is to make sure the tool the analyst uses is consistent. Problems of consistency may rise about several topics.

Consistency in the software architecture

These questions are linked to the architecture of the software and can be summarized in the following one : "If several ways exist to deal with the same case, are the results in every way the same ?" For instance, when studying the outflow from a definite reservoir containing liquid, are the initial gaseous outflow the same : -when calculated through a hole in the top of the gaseous part, -when calculated from an equivalent reservoir which contains only gas ?

These problems of consistency are mainly relevant when, for instance, flammable properties and modelling have been added on a software built initially to deal with dispersion.

Boundary problems

The main points of consistency arise at the boundary of domains where continuity must be fulfilled, according to the question "when physical conditions are very close, are the results close ?" The problems may arise according to several boundaries and the results pertain mainly to calculation of source term and of dispersion.

1) In a phenomenon itself

To give an example, one may quote a monophasic gaseous flow from a hole in a reservoir. According to the pressure inside it, the flow may be hyper or sub critical; the critical pressure is a function of y (rates of the heat contents Cp/Cv). Physically, flow rates are to be very close when the pressures inside the tank are very close on both sides of the critical pressure. This may not be true in the calculation, owing to the mechanism chosen to calculate the value of C(j (constriction coefficient).

2) When the conditions given are close to those of a change of state For instance, around the saturation curve, there may be a domain of (P, T) for which calculations can't be done. This may be related to the equation chosen (virial coefficients,...).

3) When the different conditions vary continuously

For instance, when everything about the reservoir and temperature (of reservoir, atmosphere and ground) is set as well as a given wind velocity, one has to obtain a continuous trend when passing from stability class C to F.

4) When conditions are close to the boundary of different modelling domains

For instance, two gaseous leaks, the first of CO, the second of ethane, from the same reservoir at atmospheric temperatures have to lead to very close dispersion calculations. In certain softwares, this may not be true for the continuity at the boundary of domains heavy gas -passive dispersion is not fulfilled. Related to the same topic is the distinction between an instantaneous and a quick continuous emission. Are the results slightly different when the release is instantaneous or when the same amount of species is released over a few seconds ? 5) Lastly, when conditions are close to an internal boundary of modelling which is unknown to the user. This happens for instance in some softwares where the extension of the pool may be not limited. This happens also when a software does distinguish between different physical cases : for instance, when pouring CS2 on water, it is possible to calculate an important extension of the pool though CS2, heavier than water, sinks to the bottom of the dyke.

COMPARISONS OF RESULTS WITH CALCULATIONS THAT MIGHT BE OTHERWISE ASSESSED

After examining user-friendliness, quality of the data base and internal consistency of software, the next step consists in comparing the results with calculations that might be otherwise assessed using physical modelling of the phenomena.

For each software, comparisons are systematically made about a lot of calculations. Some examples are given related to source term, dispersion and flammable properties.

Source term

Calculation of flow rate in a monophasic gaseous flow through an orifice as a function of pressure and temperature inside the reservoir (Cf table 1). Pressure drop for the same flow through a pipe, as a function of the length of this pipe. Does the software take into account viscosity ? Calculation of a liquid flow rate through an orifice. Some flow through a pipe. Are pressure drops function of viscosity ? Discharge velocity related to phase. Flashing fraction and temperature of release.

• Formation of aerosols. Is potential condensation considered ?

Are there calculations of diphasic flow ? When ? Empirical formulas ? Rain out and mass balance between flash, rain out and aerosols.

Emptying the reservoir as a function of time. Do the results lie between results obtained for an isothermal or a adiabatic discharge ? • Pool formation, extension and evaporation, (table 2 and3).

Dispersion

Influence of wind speed, Influence of density (Cf able 4 and 5), Influence of air moisture, • Influence of roughness, Jets, • Transition from dense gas to passive dispersion.

Flammable properties

One has to note that the importance given to flammable properties depends on the main features of the software. The investigated softwares are very poor on flammable phenomena for their main purpose is source term and dispersion. When the software includes flammable effects, comparisons are made considering: • a given pool fire, various sizes and products involved (hydrocarbons, alcohol,...) » BLEVEs of propane, butane, ethylene oxide » UVCE related to a given flammable mass of product, the concentration of which is between LIE and LSE(Cftable6).

CONCLUSION

In the analysis of the various softwares we investigated, user friendliness was examined by reference to conditions of use, the use itself, the quality of tools to assess the evolution of the phenomenon, error messages and the presence of guard-rails and limitations. With the exception of one software, user friendliness was rather poor.

With regard to the quality of data base, only one of the investigated softwares showed an ability to constitute a complete library.

The internal consistency of a software is related to its architecture and to the boundary problems. It would be desirable to improve this aspect, even if one of the investigated softwares was rather consistent.

The calculations we performed emphasized great discrepancies when comparisons were possible. Flammable properties were very poor as regard explosion effects and accidental missiles.

Further developements of such a work on software evaluation requires the definition of an accurate protocol. Nevertheless it is very important not to use only integral models in order to assess the phenomena more accurately with methods such as 2D or 3D finite differences or finite elements hydrodynamic models.

Naturally, the physical aspects have to be integrated in the purely computerized requirements such as graphical outputs of results in connexion with intermediate results.

Further developments will deal with other commercially available softwares, using funding from the French Ministry of Environment.

  INITIAL CONDITIONS Mass of release 10000 kg of liquid CS2 Pres = Patm Tres = 293 K = Tamb = Tground Mean rugosity of ground Meteo D3 Calculated mass flow rate kg/m^.

TABLE 1 GASEOUS LEAK : CALCULATION OF INITIAL MASS RATE

 1 A dash means it is not possible to deal with the proposed case, using the given software.

	INITIAL CONDITIONS : Subritical flow
	Release of CO (yco = 1.404)
	Pres = 1.5bar Vres=100m3 Tamb = 293K 0 hole = 50 mm
		Velocity of release	Release Mass rate	Constriction
		v eject m/s	kg/s	coefficient (Cd)
	Reference calculation	258.1	0.663	1
	Software 1	256.6	0.447	0.67
	Software 2	_ *	0.455	0.69
	Software 3	7129.7	0.650	1
	Software 4	*	0.71	. *

*

TABLE 2 POOL EVAPORATION : INFLUENCE OF

 2

					AMBIENT TEMPERATURE
	INITIAL CONDITIONS :
	Instantaneous release of 10 tons of vinyl chloride
	Pres = Patm Tres = 230K MeteoD3 Ground	: concrete Tamb = Tground
		Calculated mass flow rate	kg/m 2 s
	Softwares 1	T ground 283 2.67 10" 2	K	293 K 3.59 10-2	303 K 4.39 10-2	313 K 5.08 10-2
	2	0.15		0.22	0.28	0.34
	3	2.6 10-2		3.6 10-2	4.6 10-2	5.6 10-2
	4	1.38 10-2		1.42 10-2	1.48 10-2	1.54 10-2

TABLE 3 POOL EVAPORATION : INFLUENCE OF GROUND NATURE

 3


C M Groupe Charlionnagesde

Didier Driancourt

Jean-Pierre Donnadieu

Michel Oberlinkels

INERIS Yves Paquette

METHOD FOR RECLAIMING OPENCAST SITES fN THE CENTRAL AND SOUTHERN COALFIELDS (

Groupe Charbonnages de France (CdF) has started a vast and exemplary programme for the reclamation of opencast mining sites at the Herault Operations Unit of the Central and Southern Coal Basin.

The motivations for reclamation, based mainly on restitution of the natural and life environment, as well as on respect for the Mining Legislation, have resulted in the conception and implementation of methods for the preparation and execution of reclamation procedures on worked-out mining sites. This is a continuing obligation when responsibility is accepted for the human problems posed when mining comes to an end.

The method involves a number of phases represented in a coherent series of cartographic documents and specialised studies, ranging from the planning of the approach, to the longterm follow-up of the reclamation procedures. It calls for a wide range of skills managed through a true engineering concept.

The developments in progress at the opencast coal mining sites at Herault are presented in the second part. The principles and the examples of actions taken illustrate the reclamation work in the opencast mines, the stabilisation of the waste dumps, control of erosion, protection of drainage structures, preservation of water quality, landscaping studies and replanting methods.

CdF

:

I -INTRODUCTION

The activities presented are the result of collaboration between HBCM, INERIS, responsible for the coordination of the studies of the sites within the context of an ECSC research project, "Rehabilitation of old mine workings", and SIR AS, a branch of CNR, responsible for managing the restoration project in the mining sites belonging to the Herault Operations Unit.

The mining deposit of Graissessac basin extends over 20km and is in the form of a syncline, 2km wide in the area being mined.

The underground workings were shut down in 1962 after a total coal production of 30 million tonnes. The mining was developed mainly along the north flank of the syncline, in 7 to 8 seams of between 30° and 50° dip.

Since 1956, 4.6 million tonnes of coal with 29 million m 3 of overburden were extracted by open-pit on 5 mountain massives (Plaisance, Rive Gauche, Rive Droite, Cap Negre, and Orb). The mining ended in 1993. The pits situated at mountains tops, were worked in benches, frequently leaving as such, with no backfilling, while the overburden materials were dumped on hillsides, at limit of equilibrium at heights of 40 to 250 metres.

Altogether, the sites to be reclaimed represent an extend of 400 hectares. The provisional duration of the work is 4 years. CdF has decided to carry out a particularly exemplary restoration on the Herault sites and has procured the necessary financial and technical means.

II -THE MOTIVATIONS

With the stoppage of production, the cessation of all coal mining activity demands the complete and definitive reclamation of the mining and production sites, in order to be able to proceed to the renunciation of the mining concessions.

The motivations for the reclamation are as follows:

• respect for mining legislation so that the final state of the sites will be approved by the Administration and renunciation to the mining concessions can be obtained,

• reintegration of the sites into the environment in order to maintain the biological richness and variety within the landscapes,

• restitution to the local population of a pleasant living environment that can constitute one of the factors in the local socio-economic development,

• design and implementation of a strategy in the matter of reclamation (carrying out the work in accordance with the projects, planning the work with the estimation of costs and time scales, optimising the operational process.),

• making it possible a longer phasing out of all activities so as to provide better conditions for finding new jobs for all personnel, while carrying out the restoration process with the available mining workforce.

All these motivations depend on allowance for any existing constraints and respect for any commitments concerning:

-notice or environmental study for the most recent operations, -constraints pertaining to the land and agreements with the land owners, -agreements and discussions with the municipalities, the departements, the local associations and business concerns, for the future use of the sites.

Ill -A GENERAL METHOD FOR RECLAMATION OF THE SITES.

Awareness of the stake represented by the reclamation of the sites has led to the preparation and implementation of modalities of organisation and management, in order to achieve this restoration and while so doing, to ensure best performance.

The method comprises a group of sequential phases represented in cartographic documents and individual studies. In the course of their development these documents fit together in a logical succession.

III.l -Preparation of the rehabilitation project.

The different stages of action are the following :

•

Definition of the context of the action;

by allowance for any constraints (legislation and regulations, Environmental Impact Statements commitments, land ownership, ecological and environmental pressure, available financial means),

-by defining the final reclamation as a function of the future valorisation of the site, -by determining the actions and the methods to be initiated by arrangement with the Administration and the communities.

• Evaluation, as far as possible, of the initial condition of the site by a historical study of the archives.

This phase is put into concrete form by the development of basic plans on a standard scale, integrating:

-topography:

-initial, previous to the mineworking, -current, by photogrammetric restitution;

-geology:

-nature of the strata, presence of coal seams, -faults and fissures, dips, folds;

-hydrography:

-list of streams, springs, water captures, -study of versants;

-records of operations:

-overall plan of underground mining operations, -extensions and maximum excavation of opencast mines, -piezometric and recorded conditions of water circulation in the mine workings;

-mapping of land ownership:

-properties, renting/tenancy, covenants, sales agreements, etc.;

-analysis of the present condition of the site with the help of cartographic records.

This means the preparation of a plan in which are presented the elements of the following inventory:

-fill areas: dumps tops and slopes, berms, rock falls, dirt roads, -outcropping rocky zones: dips of stratas, -zones in a natural state not affected by the mining, -visually unstable zones (fissures, gullied hollows, unstable blocks),

-state of the vegetation, -flow circuits of surface water, -location of orifices and galleries emerging on the surface.

The production of all these documents requires the tools necessary for their preparation.

Adequate human and material resources on this level must be made available for the launching of the project, i.e.:

-the creation of an internal team assigned to the rehabilitation, -organisation of the management of the plans and documents, -definition of computerized tools (software for mining infography),

-establishment of a plan of in-house and external communication on the subject of environment,

-the storage of all data arising from the reclamation procedure (aerial and ground photography, video, archives).

III.2 -Validation of the principles selected for the reclamation.

The principles for the running of a reclamation plan are dictated by the following requirements:

a) Guarantee of the long-term stability of the terrain.

In order to ensure perpetuity of the work carried out, a safety factor for long-term stability, greater to or equal to 1.3, is the one most frequently selected for the bank and fill slopes and remaining footwall faces.

b) Control of water circulation and preservation of water quality.

In order to prevent gullying of the ground by running water and ensure the stability of the structures, a drainage system for surface water is built, in order to collect the water and evacuate it into the natural medium.

The impact of underground waters in relation to underground mine workings is controlled by knowledge of the circuit and by monitoring the quality of these waters.

c) Public safety.

The operations are carried out with the aim of eliminating to the maximum, the dangers occurring over the site as a whole, such as the fall of stones and rocks. The zones at risk are protected by earthworks or natural barriers (copses of spiny bushes) or even by fences.

d) Landscaping aspect: to speed up return to a natural balance.

To integrate the sites within their ecological and scenic environment, a certain number of measures are adopted to take account of the severe restraint related to the local climate, the very rocky substratum and the topography.

e) Valorisation of the sites: taking the human aspect into account.

All future uses of the land, compatible with the principles listed above, and which do not call in question again the integrity of the reclamation of the sites, must, as far as possible, be allowed for in the reclamation projects. -definition of replanting principles, -studies of the terrain in order to determine the landscaping units and the visual impact of the restored site, -visualisation of the final state on different media.

This phase of study makes it possible to define a group of recommendations concerning the management of water, air, ground and substratum, fauna and flora, landscape and human aspect.

III.3 -Realisation of the project and of the work of reclamation.

At the stage of realisation, the successive phases are as follows:

• Choice of a type of project (e.g.: filling of pit, creation of a plan for water for agricultural or forestry purposes, facilities for leisure, remodelling),

• Preparation of the work by a breakdown of the group of actions into a series of elementary operations pertaining to each working and each site, in order to control:

-the human and material means, -the actions in terms of earth and rock volumes moved, -the budget per type of economic function:

-studies for the project, -conduct and monitoring of the operation, -dismantling, -making the mine workings safe, -banking and digging = earth movement, -construction work = special surface operations, -finishing, -the planning of successive operations in each working.

•

Realisation of thematic plans:

-plan of final state, -plan and table of fill and excavation phases, -plan of earthworks, -phasing of operations, -drainage of surface water.

• Visualisation of the phasing of the operations and of the final state by data processing on block diagrams, on photomontages or on models.

• Realisation of the work by:

-formation of a team responsible for the reclamation, provided with specific mining equipment and trained in its use, -preparation for the operations by a precise topographical layout on the worksite, -control of the operations by monitoring the performances and the costs in order to optimise the operations for which provisions have been made as a function of actual conditions on the worksite, -monitoring of the efficiency of the reclamation work, while in progress and also a posteriori, i.e.:

-the topography, -the conformity of how what has actually been done with the project, -the outputs and costs of each operation, -the adherence to the planning, -the environmental measures (for example, the quantity and quality of the water).

In rehabilitation work, the purpose of preparation and follow-up is to be able to:

-control all the operations concerned so as to reduce the costs and increase the outputs, which will benefit the operations or the following projects, -develop a quality objective in carrying out the work while training and making the personnel aware of the objectives to be achieved, -rapidly master any problem relative to the technical aspect and to the environment.

III.4 -Follow-up of actions and long-term measures for a return to the natural environment

It is important to verify that the objectives and environmental targets have been reached, so that, if necessary, corrections can be made:

-after reclamation of the surface and underground water the drainage must be inspected, especially after periods of heavy rain, -the ground stability can be monitored, if necessary, by maintaining a system of auscultation and by the maintenance of structures, -the ecological and landscape integration by sowing herbaceous plants and shrub plantations must be part of a natural rhythm allowing the reconstitution of the surrounding herbaceous and woodland groupings. It is important, by periodic assessment, to keep track of the state of the vegetation, making sure, if necessary, that actions are taken for its maintenance (Seravert Procedure).

IV -ECOLOGICAL AND LANDSCAPE PLANNING

The essential objective of the reclamation is to integrate the sites of the old opencast workings within their scenic and ecological environment and to do so by conserving the biodiversity of the region.

There is the possibility of adapting the concept of landscaping by taking into consideration the wishes of the new users of the site.

The study of landscape defines the structural elements of the environment of the site, itself resulting from the conjunction of the ecological context (substratum, climate, vegetation) and the anthropic action (impact of mining, new layouts...). The important points in the local landscape (biological richness, socio-cultural heritage, aesthetics...) then define the framework of the replanting project.

The project must take into account the site specific conditions which are not favourable to the planting of vegetation:

-poor biogenic capacity of the substrata, -a mediterranean-type mountain climate: severe and dry for long periods, -access sometimes difficult and thus limited maintenance.

These restrictive factors make it necessary to use hardy plants, vigorous, adapted to the local ecological conditions and not requiring a lot of attention. The most suitable plants are those that develop spontaneously near the site; the list of species to be planted is thus drawn up after a detailed census of the local vegetable groups.

The principle of the distribution of the vegetable masses is laid down taking care not to overemphasise the "staircase-type" horizontal lines of the benches or tracks. The plantations are laid out in a discontinuous way, by thickets alternating with meadow surfaces or extending the pre-existing wooded areas.

The plantations consist mainly of young trees, forestry type transplants, which have a very satisfactory rooring rate and a low planting cost. Some more mature subjects can be implanted locally to act as a screen or for immediate effects as signals.

Most of the surfaces are planted with grass using hydraulic sowing by the SERA VERT method in which herbaceous mixtures are used, consisting of a large number of wild, flowering species.

At an early stage, these species are gathered into natural plant groups, then selected and cultivated in ecological conditions close to those of the sites where they will then be reinstalled.

SIRAS thus obtains exclusive native species that can be sown on sites where it is difficult to restore the plant life. The SERA VERT mixtures, by their great specific diversity (15 to 20 species sown), make it possible to obtain a resistant, perennial vegetation, totally adapted to the sites to be restored and fitting in perfectly with the local plant life. Furthermore, the hydraulic sowing operations extend over 2 years so that the progressive installation of young plants can be observed and so that the complementary fertilisation guaranteeing the success of the landscaping can be carried out.

V WHAT IS BEING DONE AT PRESENT ON THE HBCM SITES IN THE GRAISSESSAC COALFIELD

The reclamation of the sites on the Cap Negre massif started in 1992, over an area of 60 hectares.

•

The reclamation of the pits

The old open pits from which 10 million cubic metres of material were extracted, are being partly backfilled with materials from the overburden dumps deposited on hillsides around the pit during exploitation work. These operations make it possible to stabilise the benched open pit faces and the coal seams footwalls, dipping at 35°, and very much fractured and dislocated.

Materials containing the most sandstones are tipped into the bottom of the pits and on the benches, so as to provide a draining subfoundation and to increase contact with the strata in place. The finest products of the shale then serve to form slopes and benches, suitable for planting.

The lowering of the pits crests provides sandstone blocks for rocky filling. The upper parts of the slopes thus become flatter. Such a rounded contouring limit the distant visual effect of the excavation on the landscape. The gritty scree at the top of the overburdens and left in its present state will be the subject of subsequent coloration treatment by the Naturoc process.

» The construction work

Taking into account the run off waters and the underground infiltration makes it necessary to construct a very dense system (140 linear metres to the hectare, on average) of water collectors, the cross-sections of which are calibrated for absorbing the heavy rain of thunderstorms.

This network consists mainly of draining benches angled to the slope and with a longitudinal dip of 2%. They are compacted in order to make them last longer and in order to encourage a free flow of water.

It also means:

-trenches dug out in the natural terrain, -settlement ponds for fine material during the whole of the reclamation procedures, -downslope drainage trenches across dumps sides, protected from regressive erosion by massive rockfill packings. The aim is to obtain, as often as possible, this type of collector in the natural medium, in order to ensure the permanence of the structure.

The torrential gullying, which has had a massive impact on the streams situated downhill of the waste dumps make it necessary to recalibrate the water courses, eliminating all artificial objects (pipes, channels, concreted zones) related to former mining activities.

VI -CONCLUSION

After remodelling and replanting, the effect of the old mine working will be greatly reduced, or even eliminated, and the sites, thus restored to their former state, will be part of the new landscape identity of the region. These vast spaces will constitute the site for numerous activities, such as hunting, or more modern activities -walking and cycling excursions, paths for exploring and getting to know the medium (ecology, geology...). This will be the successful conclusion of an operation for the valorisation of a region steeped in history, reconciling respect for the regional heritage and socio-economic interests.

f)

  Orientation of specialist studies to aspects indispensable to the concept of the project and, of the stability of waste dumps and pit faces, -analyses of the risks of residual subsidences or even collapses of underground mine workings.• Hvdrogeological study (INERIS, SIRAS):-study of the effect of mine workings and rehabilitation operations on the surrounding hydrology,-analysis and synthesis of the water flows in the old underground workings, -location of the resurgences and dewatering galleries from the old underground workings (analysis of the quality and quantity of the water),-study of the influence of the reclamation work on the hydrology: modelling of the versants, filling up of opencast mines, closing of openings to underground workings.• Landscaping study (SIRAS):

  Charbonnages de France HBCM : Houilleres de Bassin du Centre et du Midi (Groupe Charbonnages de France)

	INERIS : Institut National de l'Environnement Industriel et des Risques
	ECSC	: European Steel and Coal Community
	SIRAS	: Societe Internationale de Rehabilitation et d'Amenagement des Sites
	CNR	: Compagnie Nationale du Rhone

The sandstone structural slabs, which correspond to the coal seams footwalls, are kept as they are, when the fracturation allows this. The important thing is to reduce the volume of the backfill and to conserve, in the landscape, elements of geological structuration. These slabs are slightly notched (tops knocked off) and earthed up at the bottom by deposits of waste material, in order to improve their stability and prevent the fall of blocks. Protective structures (berms, trenches) shall form a barrier to prevent the approach of these walls and a natural protective medium will also be set up (a thick copse of spiny bushes).

This earthwork as a whole is being done with bulldozers of the Caterpillar D9H type and with Liebherr 962 hydraulic excavators coupled with 35 tons Caterpillar 969 dumpers. The average transport distance is 270 metres. The earthwork for the reclamation of the sites represents 11% of the total volume that has been dealt with during the working of the open pits.

•

The waste dumps A large number of dumps of shales and sandstones were created on the hill side by tipping, sometimes at great heights (200m), causing segregation of the coarse materials at the base.

They are all at their limit of equilibrium without draining bench and have unstable features such as gullying, plane surface slips and settling cracks. They were subjected to replanting but this rapidly deteriorated because of the occurrence of furrows and the inroads of erosion.

The remodelling of a large number of these dumps is therefore necessary, so that their longterm stability can be assured and to protect the ground from gullying and allow correct taking roots of a perenial vegetation which will reduce their visual impact.

Part of the material on the top of the dumps has been removed and this material is used for reclamation of the open pits. The average slopes of the dumps are generally reduced from 37°t o 26°, ensuring a safety coefficient greater than or equal to 1.3.

Drainage benches, 5 metres wide, are placed every 20 metres dowslope, in order to reduce the elementary versant basin with intermediate slopes angled at 31°. The outline of the slopes is flat, very regular and with no apparent blocks. This surface contouring is done by bulldozing.

The berms ensure a lateral flow of the running water and eliminate any risk of gullying. The judicious choice of the system of benches makes it possible to optimise earthmoving.


S Honnons

D Oberson

A Wastiaux

S Dzwigaj

H Pezerat

M Volante

B Fubini

J M Porcher

PULMONARY RESPONSES TO SILICA DUST: THE INFLUENCE OF CRYSTALLINE STRUCTURES AND PHYSICO-CHEMICAL / PROPERTIES

The inhalation of silica crystalline polymorphs leads to the development of pulmonary nodules that vary in extent and in fibrotic content.

In this study, a single protocol was used to test different silica samples (i.e., 2 non-crystalline samples: one vitreous silica, one diatomaceous earth , 4 crystalline samples: one pure a-quartz ground in a wet atmosphere, one of the same quartz heated until it becomes oc-cristobalite and 2 cristobalites obtained by heating diatomaceous earth).

Wistar rats received a single intra-tracheal injection of alveolar dust and were followed over a period of 3 months.

The results were exploited using macroscopic examination (wet lung weight), histological examination and biochemical dosing (hydroxyproline, lipid, and silica content).

The results showed that vitreous silica, diatomaceous earth, wet-ground quartz and both types of cristobalites are responsible to a greater or lesser extent for the pulmonary reaction typical of exposure to silica (i.e., nodules ); with different cellular and fibrotic surface areas for each sample.

a-cristobalite (obtained from the wet-ground quartz heated to a very high temperature; 1,300 °C) leads to the formation of only small foreign-body granulomas.

All crystalline minerals tested caused alveolar lipoproteinosis. It was thus concluded that the crystalline structure plays a less important role than the surface state in the formation of silicotic nodules.

INTRODUCTION

The inhalation of dust containing crystalline silica has long been known to be a direct cause of a serious lung disease, silicosis [START_REF] Seaton | Toxic Effects of Silica Aug 1987, Institute ofOccup[END_REF]. The reactivity of a-quartz dust in in-vivo experimental studies was rapidly found to present considerable variations. The numerous studies aimed at individualizing the physico-chemical characteristics of different types of a-quartz have not been able to explain the observed variations in biological reactivity [START_REF] Adamson | Instillation of Chemotactic Factor to Silica-Injected Lungs Lowers Interstitial Particle Content and Reduces Pulmonary Fibrosis 1992[END_REF][START_REF] Begin R | L Sustained Efficacy of Aluminum to Reduce Quartz Toxicity in the Lung[END_REF][START_REF] Fubini | A Novel Type of Active Site at the Surface of Crystalline SiO2 (d quartz) and its Possible Impact on Pathogenicity 1991[END_REF][START_REF] Fubini | The Possible Role of Surface Oxygen Species in Quartz Pathogenicity 1989[END_REF][START_REF] Fubini | BOLIS V Chemical Functionalities at the Silica Surface Determining its Reactivity when Inhaled Formation and Reactivity of Surface Radicals[END_REF][START_REF] Pezerat | activite" de Surface des Particules en Relation avec leurs Proprietes en Milieu Biologique[END_REF][START_REF] Wastiaux | Quartz Surface and Fibrogenicity Sept 1991, 7th Intern. Symposium on Inhaled Particles[END_REF][START_REF] Wiessner | The Effect of Crystal Structure on Mouse Lung Inflammation and Fibrosis[END_REF]. What is more, the idea that the crystalline structure could condition the nocivity of inhaled silica dusts has been called into question [START_REF] Hemenway D | Differential Lung Response Following Aerosol Exposure to Polymorphs of Silicon Dioxide[END_REF][START_REF] Beskowr | Silicosis in Diatomaceous Earth Factory Workers in Sweden 1978[END_REF][START_REF] Bye | In-vitro Cytotoxicity and Quantitative Silica Analysis of Diatomaceous Earth Products[END_REF][START_REF] Jacobson G | A 21-Year Old Radiographic Follow-up of Workers in the Diatomite Industry 1977[END_REF][START_REF] Gross | Functional and Morphological Changes in the Lungs after a Single Intratracheal Instillation of Silica 1984[END_REF][START_REF] Hemenway | Surface Functionalities are Related to Biological Response and Transport of Crystalline Silica Sept 1991, Inhaled Particles[END_REF][START_REF] Hemenway | What is the Relationship between Hemolytic Potential and Fibrogenicity of Mineral Dusts? (in preparation)[END_REF]20].

In this study, a single protocol was used to test different silica samples: 1 diatomaceous earth sample, 2 cristobalite samples obtained by heating diatomaceous earth, 1 pure a-quartz ground in a wet atmosphere and the same quartz heated to l,300°C. Another sample of amorphous vitreous silica had been tested following the same protocol in a previous study.

MATERIALS AND METHODS

Groups of 6 female EOPS Wistar rats supplied by If fa-Credo (France) received a single intratracheal instillation of 30 mg of alveolar dust suspended in saline. Three control animals received saline alone. All animals were housed in a controlled area for a period of three months.

Silica samples provided by H. Pezerat (CNRS, France) :

-1 diatomaceous earth sample (Diat), -1 "cristobalite" (CR 1210) obtained by heating the same diatomaceous earth , -1 other "cristobalite" (CR 1212) obtained by heating different diatomaceous earth.

These three dust types were not subjected to grinding in our laboratories, and the alveolar fraction of less than 6|i was obtained using an elutriator. The granulometry was carried out by MEB, as these dust particles partially retain the shape of fossilized diatoms, making it difficult to measure their aerodynamic diameter with precision.

Silica samples provided by B. Fubini (Univ. Torino, Italy):

-a very pure quartz sample ground in a wet atmosphere (Qtz). The alveolar fraction of less than 3| X was obtained after grinding by centrifugation, -the same quartz was heated for four hours to l,300°C in an inert atmosphere (Qtz 1300). The heat changed the crystalline structure, transforming this sample into a cristobalite with different granulometric properties. The obtained granulometry remained within the limits of the alveolar fraction but decreased the number of instilled dust particles (i.e., some of the final particles presented greater volume that the original quartz). Silica samples provided by CHERCHAR (France):

-a vitreous silica (VS) was obtained by grinding melted quartz. The alveolar fraction of less than 3ju was obtained using a cyclone.

Histological method

The animals are sacrificed following standard operational laboratory procedures three month after exposure. The lungs are then removed and weighed. The left lung is preserved after insufflation. For the histological examination, the samples are dyed using Hematein-Eosin -Saffron.

Biochemical method

After removing a sample from the left lobe for the histological examination, the right lung is again weighed and, in some cases, stored at -20°C until biochemical quantification is carried out. The samples are dried at 137°C (overnight). Individual quantification of lipids is obtained by three successive ethyl alcohol extractions; they are then weighed after evaporation. The hydroxyproline content of each lung is determined according to the method developed by Stegemann [START_REF] Stegemann | [END_REF] by oxidation with chloramine T at pH 6, followed by a reaction with paradimethylaminobenzaldehyde in the presence of perchloric acid. The absorbency of the obtained pyrrole derivative is measured at 560 nm.

The silica is quantified using the method developed by King [13].

Statistical analysis

Results were expressed as the mean ± standard deviation (sd), used as an index of variation. Experimental results were subjected to variance analysis (i.e., ANOVA test). When there was a significant F value for the effect of dust, the individual means were compared for significance using the t test.

RESULTS

The weight of wet lungs and the results for the different biochemical parameters (e.g., hydroxyproline, lipid and silica content) are presented in Figures 1, 2, 3 and4.

The histological examinations gave the following results: Diatomaceous earth: the alveolar lipoproteinosis is barely visible, in some cases nearly invisible. Granulomatous-like areas are scattered around the pulmonary parenchyma, located mainly around the small airways and alveolar walls. These cannot be considered true silicotic nodules, but rather coniotic collections, as the contour of such collections was angular, the cellularity intense and the collagenization weak.

Cristobalite (12101 cristobalite (1212) and a-quartz (Qtz): for these samples, the alveolar lipoproteinosis is intense, and is associated with foam cells. The silicotic nodules are characteristic, numerous and often located near the terminal bronchioles.

The histological analysis does however indicate structural differences: the nodules caused by the two cristobalites show weakly cellular cores, revealed by their yellow color under the saffron dye, and a peripheral crown that is highly cellular. What is more, for CR 1210, the centers are proportionally greater in volume than those for CR 1212. The nodules caused by the a-quartz did not however show this delimitation, the collagen bundles (dyed yellow) were mixed together with the cellular elements.

a-quartz heated to 1.300°C (Qtz 1300): the alveolar lipotroteinosis is intense and is associated with foam cells. No silicotic nodules are observed and the few cellular collection that are observed are foreign-body granulomas surrounding the particles of greatest volume.

Vitreous silica (VS): the alveolar lipotroteinosis is discreet or nearly invisible. No silicotic nodules are observed, but there are some coniotic collections with angular contours formed essentially of cells with a small number of collagen bundles.

Biological grading: if the quantification used is that was previously proposed [START_REF] Begin R | L Sustained Efficacy of Aluminum to Reduce Quartz Toxicity in the Lung[END_REF] with Intensity x Profusion, obtaining:

• Diat 4 -CR 1210 -CR 1212 -Qtz: 9 -Qtz 1300 1 -VS: 4

For the different samples that were tested, the injuries described as successive to overloading [START_REF] Morrow | Dust Overloading in the Lungs Update and Appraisal 1992[END_REF] (e.g., thickening of the alveolar walls, cubic metaplasia...) were rarely observed.

DISCUSSION

In-vivo experimental studies of the comparative nocivity of silica particles pose the problem of which biological parameters should be taken into account. What is more, certain parameters such as the histological method cannot be easily quantified.

The most readily accessible measurement is certainly that of wet lung weight. This measurement may however encompass some rather diverse modification, since the increase linked to the formation of silicotic nodules and that linked to alveolar lipoproteinosis are indistinguishable. The silicotic nodules include numerous collagen bundles which can be quantified using the hydroxyproline method. These nodules are also formed of variable cell quantities. The quantity of lipids increases if there is a large number of cells since the cellular membranes are rich in lipids. Alveolar lipoproteinosis is also rich in lipid structures; it is thus impossible using biochemical quantification to distinguish between the lipid increase linked to cell quantity from that linked to lipoproteinosis. In this case, a histological examination must be carried out.

We can also take the example of samples CR 1212 and Qtz 1300; if we examine the wet lung weight, CR 1212 is the most reactive and Qtz 1300 is weakly reactive. If we examine the hydroxyproline quantification, the CR 1212 is found to be significantly less reactive than CR 1210 or Qtz. As for Qtz 1300, it presents nearly the same level as the control group. It we turn to the results for lipid quantification, CR 1212 once again appears to be the most reactive and Qtz 1300 is found to be more reactive than diatomaceous earth. The histological examination shows notable eellularity on the silicotic nodules for CR 1212, whereas Qtz 1300 shows significant alveolar lipoproteinosis.

If only the histological examination is used, the quantification of injuries becomes quite difficult. It must be noted that the proposed scores [START_REF] Begin R | L Sustained Efficacy of Aluminum to Reduce Quartz Toxicity in the Lung[END_REF] do not take into account the influence of lipoproteinosis (hence the very low score for Qtz 1300). Nor do they quantify the percentage of cellular elements relative to the collagen bundles in the silicotic nodules. This will lead to discrepancies between biochemical and histological results for certain samples [18: previous study conducted in this laboratory]. Only an image analysis quantification technique based on selected cross-sections of lung tissue will be likely to offer reliable histological grading.

It thus seems that a combination of different biochemical and histological parameters is needed to provide an accurate evaluation of in-vivo nocivity of silica dust.

Using a combination of these biochemical and histological elements would thus allow us to determine what is actually modified, either by evaluating changes in the crystalline structure or by changes in the surface properties of the particles under study.

The two of the silica types considered as non-crystalline (i.e., diatomaceous earth and vitreous silica), therefore present relatively weak nocivity (perhaps linked to overloading). Such silica types provoke virtually no reaction that can be considered characteristic of silicosis (e.g., silicotic nodules or alveolar lipoproteinosis).

Both crystalline silica types (CR 1210 and CR 1212) obtained by heating diatomaceous earth, as well as the wet ground a-quartz (Qtz), gave rise to silicotic nodules and to alveolar lipoproteinosis. CR 1210 and CR 1210 did however present nodules with histological structures different from those found with Qtz. What is more, a larger quantity of collagen is found to form with CR 1210 than with CR 1212.

Lastly, Qtz 1300 (which presents the crystalline structure of a cristobalite) gives rise to alveolar lipoproteinosis of equal intensity to that found for CR 1210 and CR 1212 and Qtz samples, but no silicotic nodules are observed.

Quantifying the silica in the lungs after sacrifice may provide a representation of lung clearance. No clear correlation with the crystalline structure or with induced pathologies is observed since Qtz 1300 and CR 1210 seem to present better clearance than CR 1212 and Qtz.

The results for such biological parameters will require a more in-depth comparison with the physico-chemical properties of the samples used in this study (e.g., surface state...). The reactivity of the Qtz 1300 [START_REF] Bye | In-vitro Cytotoxicity and Quantitative Silica Analysis of Diatomaceous Earth Products[END_REF][START_REF] Hemenway | Surface Functionalities are Related to Biological Response and Transport of Crystalline Silica Sept 1991, Inhaled Particles[END_REF] confirms the relatively limited influence of the crystalline structure on the formation of silicotic nodules (the characteristic of chronic silicosis).

  • significantly different compared to control group and to Diatom and Qtz 1300 groups.

Fig. 1 :Fig. 2 :Fig. 3 :Fig. 4 :

 1234 Fig. 1 : Lung weight (g)

ACKNOWLEDGMENTS

J.P. Lefevre and A. Gaudillot for the in-vivo study, M. Fray, A. Lebrun, A.M. Oisel for the histological and biological data, B. Graham for the translation.

Financial support was gratefully received from CECA, Convention No 7280/03/006.


Sprague Dawley

Wistar Rat

Strains S Honnons

D Oberson

J M Porcher

IN-VIVO EXPERIMENTAL MODEL FOR SILICOSIS: FISHER 344

The selection of an experimental model for silicosis requires a thorough understanding of a number of different pulmonary parameters specific to the animal that is to be used (e.g., clearance time, penetration curves, anatomical differences...), and of the sensitivity of the strains that are to be used.

The pulmonary response of three rat strains (i.e., Fisher 344, Sprague Dawley, Wistar) to silica dust were compared using two different exposure methods: intra-tracheal injections and inhalation. The test periods lasted 3 months for injection and 6 and 12 months for inhalation.

The histological study of the lung revealed a distinct nodular reaction among Sprague Dawley and Wistar strains. Intra-tracheal injections led to the development of fibrotic nodules among Wistar rats, whereas such silicotic nodules were infrequent among injected Fisher 344 rats, and almost absent when exposure was by inhalation.

Sprague Dawley and Fisher 344 rats showed frequent thickening and metaplasia of the alveolar walls near the terminal bronchioles. This tendency was particularly pronounced among rats exposed by inhalation (especially among Fisher 344 rats).

Evaluation of wet lung weight (i.e., hydroxyproline, lipid and silica lung contents) reveals an increase in the different parameters for Sprague Dawley rats relative to the other two strains, regardless of the type of exposure. It has thus been concluded that Wistar rats are the best experimental model for silicosis, as their pulmonary reaction is more characteristic than that of the other two strains.

INTRODUCTION

The inhalation of dust containing crystalline silica is known to cause silicosis, a serious lung disease. This disease has been studied extensively over the years [START_REF] Seaton | Toxic Effects of Silica Aug 1987[END_REF]; many of these were in-vivo experimental studies on the rat. A major question for in-vivo toxicology studies has, however, never been dealt with: the selection of an experimental model. This selection requires a thorough understanding of a number of different pulmonary parameters specific to the animal that is to be used (e.g., clearance time, penetration curves, anatomical differences... [START_REF] Hickey | Lung Deposition and Clearance of Pharmaceutical Aerosols: What can be learned from inhalation toxicology and industrial hygiene?[END_REF][START_REF] Miller Fj | Lower Respiratory Tract Structure of Laboratory Animals and Humans: Dosimetry Implications[END_REF][START_REF] Oberdorster | Lung Dosimetry: Pulmonary Clearance of Inhaled Particles[END_REF]) and of the sensitivity of the strains that are to be used. As with different human populations presenting different levels of sensitivity to pathogenic or toxic substances [START_REF] Honda | Immunogenetic Analysis of Silicosis in Japan[END_REF][START_REF] Nagaoka | Studies on Production of Anticollagen Antibodies in Silicosis[END_REF], it is known that different rat strains will vary in their sensitivity to an identical aggression [START_REF] Phan | Lung Cytokine Production in Bleomycin-Induced Pulmonary Fibrosis[END_REF]. Numerous studies are to be found in the literature, sometimes using mice, but most often rats of different strains, usually Fisher 344 [START_REF] Hemenway D | Differential Lung Response Following Aerosol Exposure to Polymorphs of Silicon Dioxide 1984[END_REF][START_REF] Absher | Biphasic Cellular and Tissue Response of Rat Lungs after Eight-Day Aerosol Exposure to the Silicon Dioxide Cristobalite 1989[END_REF][START_REF] Gross | Functional and Morphological Changes in the Lungs after a Single Intratracheal Instillation of Silica 1984[END_REF][START_REF] Hemenway | What is the Relationship between Hemolytic Potential and Fibrogenicity of Mineral Dusts? (in preparation)[END_REF], Wistar and CD (SD) BR [START_REF] Osornio-Vargas A | Lung Cell Toxicity Experimentally Induced by a Mixed Dust from Mexicali, Baja California[END_REF]. This perhaps explains some of the discrepancies between the different results obtained [START_REF] Absher | Biphasic Cellular and Tissue Response of Rat Lungs after Eight-Day Aerosol Exposure to the Silicon Dioxide Cristobalite 1989[END_REF][START_REF] Gross | Functional and Morphological Changes in the Lungs after a Single Intratracheal Instillation of Silica 1984[END_REF]. In our laboratory, the experiments were carried out with Wistar rats supplied by Iffa Credo (France). A study was started to compare the pulmonary response of three rat strains (i.e., Fisher 344, Sprague Dawley and Wistar) to silica dust using two different exposure methods: intra-tracheal instillation and inhalation.

MATERIALS AND METHODS

Three different strains of EOPS rats were exposed to a-quartz. The Sprague Dawley (SD) and Wistar (W) strains were supplied by Iffa Credo (France), and the Fisher 344 (F) were supplied by Charles River (France).

Two methods of exposure were used: intra-tracheal instillation and inhalation.

Intratracheal Instillation

The silica (a-quartz) used was 227 Quartex. Cyclone treatment was used to obtain granulometry corresponding to the alveolar fraction.

Numerical distribution

94.29% j 5.27%

1 -2n 0.44% 2 -7^1. Prior to instillation, the particles were suspended in saline and then ultrasonically agitated. 10 males and 10 females from each strain received an instillation of 30mg of silica; the control group consisted of 5 males and 5 females from each strains and received saline alone . The animals were housed in a monitored area for a period of 3 months.

Inhalation

The silica used was Ni-silica supplied by Moulin des Pres (Offronville, France); this is a mixture of sand and stone ground in a humid environment. Granulometry was carried out using an optical microscope.

Numerical distribution 89.12% <l|i 9.41% 1 -2\i 1.32% 1 -3.5(1 0.15% 3.5 -5n The exposure was of the "Full body" type. 14 males and 14 females from each strain were exposed to a concentration of 100 mg/m^, 6 hours per day, 5 days per week and over 4 weeks. The control group consisted of 6 males and 6 females from each strain. They were not exposed and were housed in identical conditions for the duration of the study. For each strain, 7 exposed males and 7 exposed females, as well as 3 control males and 3 control females, were sacrificed at 6 months, the other animals will be sacrificed at 1 year.

Histological method

The animals are sacrificed following standard laboratory procedures at 3 month for the rats from the intra-tracheal instillation group and at 6 and 12 months for the rats exposed by inhalation. The lungs are then removed and weighed. The left lung is preserved after insufflation. Following the histological evaluation, the lung samples are dyed using Hematein-Eosin-Saffron, Sirius red and reticulin.

Biochemical method

After having taken the sample of the left lung for histological evaluation, the right lung is once again weighed and, in some cases stored at -20°C until biochemical evaluation. The samples are dried at 137°C overnight. The lipids are extracted in 3 successive stages using ethyl alcohol; they are then quantified after evaporation by weighing. The hydroxyproline is evaluated using Stegemann's method [16], oxidation by chloramine T at pH 6 followed by reaction with paradimethylaminobenzaldehyde in the presence of chloric acid. The absorbance of the obtained pyrrole derivative is measured at 560 nm. The silica was quantified using the method developed by King [7].

RESULTS

Histological results

At 3 months after intra-tracheal instillation, silicotic nodules are clearly visible among W rats the nodules are numerous, with a slightly greater number among the females. Both males and females often present collagen cores surrounded by a cellular crown. Among SD rats, the nodules are smaller and fewer in number, consisting of cells interspersed with collagen bundles, but quasi acellular collagen core is not observed as it is with W rats.

Among F rats, numerous coniotic collections (i.e., areas with angular contours and irregular shapes consisting primarily of a cell and dust mixture) and very few silicotic nodules are observed; the nodules can actually be of greater volume than those observed among SD rats but they never present "collagenized" cores such as those seen with W rats.

All three strains present alveolar lipoproteinosis with foam cells. Thickening of the alveolar wall with inflammatory cells and cubic metaplasia of the alveolar cells are also observed for all strains (usually near the terminal bronchioles). These injuries are less pronounced and of more limited extent among W rats than among the other two species.

Six months after exposure by inhalation, the silicotic nodules are numerous and clearly distinguishable for W rats. They do, however, remain cellular and "collagenized" cores, such as those found after intratracheal instillation, are not observed. SD rats also react by forming silicotic nodules smaller than those observed on W rats. F rats, however, present only angular areas of cells resembling coniotic collections.

The difference is even more pronounced at 12 months after exposure; W rats then present largevolume nodules whereas the round silicotic nodules are not always visible among F rats. Other pulmonary modifications (e.g., alveolar lipoproteinosis with foam cells, thickening of alveolar wall (with cells and collagen), cubic metaplasia of the alveolar cells or "bronchiolization") are observed for all three species. At 12 months, however, these frequency of such modifications is greatest among F rats, followed by SD rats.

Biochemistry

The

DISCUSSION

The results of biological quantification for each strain should be interpreted according to the values found among control animals. Little difference is observed between the three strains: After intratracheal instillation, the increase in wet lung weight and in hydroxyproline content can be considered roughly equivalent for the three strains. For exposure by inhalation, F rats seem least reactive and SD the most reactive if only biochemical parameters are taken into account.

Quantifying the silica in the lungs after sacrifice may provide a representation of lung clearance. SD rats seem to present the best clearance after intratracheal instillation. When exposure is by inhalation, F rats present the best clearance, followed by SD and W rats.

The histological examination of the lungs reveals two types of injury. Considering the doses at which the animals were exposed, certain overloading probably occurs [START_REF] Morrow | The Setting of Particulate Exposure Levels for Chronic Inhalation Toxicity Studies 1986[END_REF], Recently described injury due to overloading [START_REF] Morrow | Dust Overloading in the Lungs: Update and Appraisal 1992[END_REF] have been identified: cellular and collagenous thickening of the proximal alveolar walls, coniotic collections, cubic metaplasia of the proximal alveolar cells. These injuries have been described primarily for F rats. In this study, they were found for all strains; they are more pronounced among SD and F rats, and are especially pronounced among F rats exposed by inhalation.

The other type of injury that was observed is considered characteristic of silicosis (i.e., silicotic nodules and alveolar proteinosis with foam cells). The silicotic nodules are not very pronounced or are completely absent among F rats; they are not pronounced among SD rats, whereas the nodules are always clearly visible among W rats, which in this study was the only strain that presented "collagenized" cores after interstitial intra-tracheal instillation.

If only biochemical parameters were to be taken into account, it would seem that SD is the most sensitive strain, and thus the best experimental model.

But when these biochemical results are compared with histological examination, it becomes apparent that W rats present the pathology most characteristic of silicosis, SD rats present a mixture of pathologies, some due to overloading and others to silicosis, which explains the higher biochemical quantification values. As for F rats, most of the observed injuries can be attributed to overloading, and they develop few "silicotic" injuries, which is not apparent from biochemical data alone.

It has thus been concluded that, of the three strains studied (Sprague Dawley, Wistar and Fisher) the best model for the experimental study of silicosis is currently the Wistar strain. It should be noted that the data for a strain can "drift" over the years, and the sensitivity of the animals may thus be altered.

  results of biochemical quantification are shown in Figures I & II.

ACKNOWLEDGMENTS

We would like to thank J.P. Lefevre and L. Cornu for their assistance in exploiting the data and B. Graham for the translation.