l. INTRODUCTION

A first Step of Accident Analysis (AA) working group ended last Autumn 1994 at the ESReDA Autumn Seminar on Accident Analysis, by presenting a report on the Initial Assessment of Strengths and Weaknesses of Current Accident Databases. This report was part of an on-going collaborative exercise and dealt with an overall "broad brush" assessment of the Status and perception of current accident databases in Europe, äs seen by users.

For this exercise, a questionnaire was distributed by AA group members in 13 different countries. 93 questionnaires, valid for analysis, were returned and analysed at DPLU which issued the report.

From this investigation, about 85, either dedicated in house or generic, databases were identified.

As a conclusion of this report, it was emphasized in a recommendation : "Consideration be given to the future convergence of current accident databases and the development of a future European or international network accident database. Immediate consideration be given to producing an ESReDA Directory of Accident Databases".

The ESReDA Executive Committee accepted and supported by funding the preparation of the above mentioned Directory which later will be described in details.

For defining the goals of this Directory, a AA meeting was held in December 1994 and defined a database description form.

We will first explain briefly the purposes of such a Directory. Then, some comments and main peculiarities on databases involved will be given.

As a conclusion, the needs for efficient networking of database operators will be emphasized.

II. DEFINITION OF A DATABASE DESCRIPTION FORM, INQUIRY AND PURPOSES OF A DIRECTORY THEREOF

In the database description form (Annex 1) four sections were identified : identification, technical aspects, access conditions and use, and database details.

The inquiry phase was launched in 1995 and the form addressed to the previously known database operators. An extension of contacts with other database managers was carried out.

Answers were received for 47 database operators. Very surprinsingly, only 13 previously identified databases are included in this Directory.

In order to promote äs many answers äs possible, an announcement of this work has been done to different technical Journals, mainly in France, Norway and United Kingdom.

The goal of such a Directory äs a tool for engineering companies, competent authorities, consultants, universities, research organisations, insurers, would be to get information on accidents in various industries and transportation Systems. It is to be considered äs a first step for getting a future convergence of current accident databases, each database becoming part of a larger network in the future. Every operator has to be an expert of the area in which he is collecting data for insuring a high level of data dependability : further a specification of minimal requirements has to be drawn in considering mainly data input.

With such a goal, it must be realized that the end-users of the data may have various objectives :

. identify accident scenarios . identify deficiencies of potentially hazardous plants, buildings and transportation Systems (in design and Operation)

. help to identify whether current emergency procedures are appropriate . assist national and international competent authorities, financial and insurance companies to formulate proactive policies . assist consultants in their tasks dealing with safety cases and experts in accident investigations . develop quality aspects for data and sortware . improve total quality management of safety and training of operators and managers . collect reliability data and failure rates . look at compliance with regulations, codes of practice and Standards . develop research project for understanding involved hazardous phenomena, hazardous situations and initiating events . encourage the incorporation and use of databases in the curricula of universities and other academic courses . improve the right to know attitude of large public.

III. COMMENTS ON THE ACCIDENT DATABASES DIRECTORY

These comments will be given successively for the four sections : identification, technical, access and use, database details. They are very broad comments to be revised when the work on the Directory is finished and then given äs an introduction of the Directory.

Section 1 : Identification

A classification scheme can induce a single answer on the following items : Government/Authority (26), Industry (8), Insurance (1), Consultant (5), University (1), International Organization (3). Between brackets, after each class, the number of collected forms is given. It must be pointed out the vast majority of answers from "Government/Authority" class. As a consequence, the regulations and their violations are certainly more dealt with in this type of database.

The fact that e.mail was only mentioned by four organizations is to be considered later if more efficient networking of databases is to be seeked for. 30 of the 47 databases are operated in DK, 4 in France and 5 in Norway and 4 international organizations. The other involved countries are Canada, Finland, Romania, Sweden, Holland, The working language is predominantly English.

The search and analysis capabilities is mentioned by a "yes" in 27 answers, the operating Systems being predominantly distributed mainly between Windows (50 %) and DOS/OS2/UNIX (w 25 %).

Section 2 : Technical

As regards the data storage, only one answer reported a totally paper based database. Three additional answers mentioned part use of a paper support (generally for old data).

Apparently, 20 different database programs are used and only 3 are mentioned 5 times ; Dbase, Oracle and Dataease. Such a remark may be considered at a later stage of networking äs a rather important difficulty preventing the rapid exchange of information between databases operators.

The data could be retrieved under searchable fields, texts and records with 2 exceptions for which only free texts were searchable.

Section 3 : Access and use

Among the 47 databases collected, only 8 are available without restriction. Although, about half the 39 others can be bought by the end-users, in some instances under CD-ROM versions.

Regarding the intended use (multiple answers possible), äs mentioned by the operators, the number of quotations are : 4 for multipurpose 29 for Government/Authority 21 for industry 10 for insurance 15 for consultants 11 for university 12 for research organization 8 for international organization 4 for general public 1 for training. As mentioned above, the Government/Authority databases collected are 26. If they can be used predominantly to check the policy against accidents, it does not mean that they are exclusively dealing with such an aspect : only 7 are 100 % dedicated to the Government/Authorities purposes.

However, the interest from other parties is very large and would imply for the future a better definition of final goals when learning from experience is to be considered.

When looking at the type of access and at the availibility of the database to be bought, äs a whole or in part, 16 operators give this possibility to customers. A significant number of database being on CD-ROM and regularly updated. The selling price could be in the order of magnitude from 3 000 to 12 000 US dollars. When the database is accessible on line (10 cases), the access fee for one research, between 50 and 300 US dollars, is strongly dependent upon the extent of the research.

In many occasions, a documentation (multiple answers possible) is available to users :

. user's manuals for 22 databases . thesaurus or code manual for 9 databases.

Regarding the source Information (e.g. accident reports) their availability to users is mentioned for 20 cases. Such an attitude must be looked at in details because dependable data need the checking of the source information in many instances.

Section 4 : Database details

The following types of data (multiple answers possible) can be found in the databases (with number of quotations) : coded data : 31 free text searchable : 28 free text non-searchable : 6 keyword : 29 numeric : 29

The industrial areas and activities (multiple answers possible) are the following (with numbers of quotations) : offshore : 1 2 nuclear: 4 refining : 16 chemical : 18 transport : 31 pesticides agriculture : 1 water pollution : 5 explosives : 2 fires : 3 mines : 1.

The 40 databases for which the number of records are reported include 488 753 reports, with a minimum number of 150 and a maximum of 79 000.

From the 39 databases giving the time period covered, 6 were initiated before 1969, 14 in the seventies, 10 in the eighties and 9 in the nineties. The criteria for including accidents and incidents are given thereafter with the number of quotations (multiple answers possible) : all below mentioned criteria used : 4 chemicals involved : 21 type of hazardous events : 30 near miss : 7 number of fatalities : 14 number of injuries : 9 material losses : 8 environmental losses : 11 according to gravity scale : 7.

Among the other criteria for inclusion, fires were mentioned four times. The other following criteria were only reported once : helicopter accident, chemical poisoning, accidents sent by authorities, railway accidents, offshore oil gas drilling mining units, complaints from inhabitants and "required by law to report accidents or failures".

IV. CONCLUSION

One of the most interesting conclusion drawn from the forms is the very large number of accident reports mentioned in each database (about 12 000). Certainly, it implies a lot of redundancies äs regards the criteria chemicals. An important task should be for example the avoidance of multiple entry of the same incident or accident in various databases. At last Autumn ESReDA seminar, it was proved that the input of the same accident in various databases lead to uncertainties in the data included and induce loss of confidence from the users. Such a drawback should only be avoided by networking of databases dealing with the same field.

Generally speaking, the dependability of data must be improved by using a process in which both the chemicals and process or Systems involved should be checked. Regarding the effects of accidents, a gravity classification is only reported in very few cases. Efforts should be devoted to develop a well accepted incident report form using some types of gravity (and probability) scale.

The working group "Accident Analysis" could direct its efforts into these objectives for which harmonization of methodology of data collection, analysis and checking, networking and standardization of tools are important. At a European Union level, a project could be developed between interested database operators. This Directory should be considered äs a first step to improve the dissemination of dependable data to Potential end-users.

Accidents in Industry and Transport of dangerous Goods

  of aecident/incident records 6. Approx. number of aecident/incident records added per year 7. Does the database contain equipment population data and/or operational data which allows aecident frequencies/rates to be estimated?for including incidents in the database: D Chemicals involved Specify:.......... LJ Type of hazardous event Specify:..........

ESReDA Working Group 11 24. January 1995 Accidents in Industry and Transport of dangerous Goods

  .......................................... 1-3 Other, specify: ...................................... U Consultant ...................................... English,...) : ........................................................................

	2.8 Organization/company classification
	JL Database U Govemment/Authority	LJ University
	U Industry 1.1 Acronym/common short name Area: ...,	U Research organization
	1.2 Füll name	D International organization (e.g. OECD, UN,...)
	LJ Insurance
	2_ Operator 2.1 Organization name 2.2 Owner's organization/company name : ........ (ifdifferentfrom2.1) 2.3 Contact person Area: . Database storage: 2.4 Contact person's address LJ Paper-based (non-electronic) only
	LJ Electronic
	2.5 Contact person's telephone no. 2. Database
	2.6 Contact person's telefax no. 2.7 Contact person's e-mail no. (e.3. Working language
	(e.g. French, 4. Retrieval of data:	(continued...)
	LJ Searchable fields, text, and records
	L] Searchable free text only
	LJ Non-searchable free text only

Area: .......................................... ll.:;::...::::,....:::::..,::,.::,:,.:..:.1 g. Access, dBase, FoxPro,....) : ........................................................................

ESReDA Working Group 11 24. January 1995 Accidents in Industry and Transport of dangerous Goods

  ...............................................

	5. Does the database, äs supplied to users, provide search and
	analysis capabilities (e.g. statistical analysis, cross analysis,...)?
	D Yes	D No
	If Yes, does it run under:	If No, what Software is needed?:
	D Windows ...D DOS/OS-2/UNIX,....
	(please tick all boxes that apply)
	1. Status of database:
		LJ In Operation, regularly updated
		U In Operation, no longer updated
		D Under development, avaüable(date):
	2. Availability:
		U Restricted to own organization
		U Open (no restrictions)
		I-l Restricted, specify:	................

ESReDA Working

Group II 24. January 1995 Accidents in Industry and Transport of dangerous Goods

  Area : ................................... D Insurance. Area : ................................... LJ Consultant. Area : ................................... Other, specify: ..........................................

	3. Main existing/intended users of database:
	Percentage:
	U Government/Authority
	1_J Industry. L-] University
	U Research organization
	D International organization (e.g. OECD, UN,...)
	U (please tick all boxes that apply)
	4. Type of access:
	U Database may be bought (whole or in part)
	Format:
	D Diskettes
	D CD-ROM
	D Tape
	U Hard copy paper
	LJ Hard copy microfilm
	(continued...)

ESReDA Working Group 11 24. January 1995 Accidents m Industry and Transport of dangerous Goods

  Other, specify: ........................................ ...................................................... Typical data search : ........................................................

		U User specified Output (e.g. data compilations, statistical
		analyses,....). Specify:
		Format:
		LJ Hardcopy
		D Diskettes
		U LJ Online access, direct from operator
		D Online access, via host (e.g. DIALOG, QUESTEL,..)
		(please tick all boxes that apply)
	5. Cost of access (US Dollars); if free of Charge, please state
	Database purchase/subscription	: ..

Specify: .......................................................... U Other, specify: ................................................. Online access : ........................................................ (continued...) ESReDA Working

Group II 24. January 1995 Accidents in Industry and Transport of dangerous Goods

  .................................... Other, specify (type, cost) : ...................................... 6. Demonstration version available?: U Yes. Medium: ...................

	Published reports (e.g. periodic
	statistical reports)	: ..D No
	7. Available user documentation:
	LJ User's manual	Language (e.g. French, English,...):
	L-J Thesaurus or Code manual
	(with code explanations)	Language (e.g. French, English,...):
		Language (e.g. French, English,...):
	(please tick all boxes that apply)
	8. Source information (e.g. accident reports) available for users?
		D Yes
		D NO

D Other. Specify: ........................................................ ESReDA Working Group H 24.

January 1995 Accidents in Industry and Transport of dangerous Goods

	l. Typeofdata:
	U Coded data (e.g. CAS number, code for installation
	type,...)
	U Free text, searchable
	U Free text, non-searchable

U Keyword, descriptor or controlled text fields U Numerical values (e.g. quantities, no. offatalities, financial losses,.....)

(please tick all boxes that apply) 2. Industrial area(s) and activities covered:

Accidents in Industry and Transport of dangerous Goods

U Environmental losses

Specify:. U According to gravity scale. Specify:. D Other. Specify:.

(please tick all boxes that apply)

9. Do you have data exchange arrangements with other database operators? (This Information will not be induded in the directory) D Yes. Specify:

D No

Other information which may not necessarily be induded in the directory (e.g. present/planned developments, etc.):

ESReDA Working Group II 24. January 1995


A COMPARISON OF METHODS FOR THE MEASUREMENT OF METHANE EMISSIONS FROM MUNICIPAL SOLID WASTE LANDFILLS FOR THE PURPOSE OF EVALUATING THEIR CONTRIBUTION TO THE GREENHOUSE EFFECT

HAL is a multi-disciplinary

INTRODUCTION

This study was funded and co-ordinated by the French Agence de I'Environnement et de la Maitrise de 1'Energie (Ademe) in the framework of the French research programme on the evolution of the climate and the atmosphere, with the specific aim of estimating the contribution to the greenhouse effect due to methane emitted by municipal solid waste landfills. The objective of the study was to assess and compare different methods for evaluating methane flux densities, with respect to the qualification of the methods in metrological terms, as well as their potential for practical implementation at landfill sites. This preliminary step, preceding the execution of direct measurements at selected sites, will enable researchers later on to validate existing emission models and establish by extrapolation an inventory of methane emissions covering all municipal solid waste landfills in France.

EQUIPMENT AND METHODS

Five methods were tested, in two sets of comparisons. Two localised methods were tested: accumulation chambers developed by the Institut National de I'Environnement et des Risques (INERIS) and by the Institut de Protection et de Surete Nucleaire (IPSN). Three atmospheric methods were tested: a mass balance technique and eddy correlation developed by the Institut National de la Recherche Agronomique (INRA) and a tracer-gas technique developed by IPSN. These methods were tested using two regulated-emissions devices installed by INERIS: a laboratory test-bed for the accumulation chamber methods, and an outdoors regulatedemissions site for the atmospheric methods.

Accumulation Chamber Methods

The INERIS method uses an external-recirculation chamber covering an area of 0.25 m 2 and with an enclosed volume of 30 litres (1). The internal atmosphere is renewed using an external pump with a flow rate on the order of 10 1/minute. The rate of methane enrichment of the recirculated mixture is monitored, and used to deduce the local methane flux of the covered surface. The methane flux derived outside the chamber is analysed using classical laboratory flame-ionisation chromatography. The chamber was validated beforehand in laboratory tests to ascertain the corrective factors to be applied to adjust for the influence of the measurement on the measured flux.

The IPSN method uses a cylindrical accumulation chamber which also serves as the measurement chamber (2). It covers an area of 0.06 m 2 and has a usable volume of 19 litres. A fan placed inside the chamber ensures evenly-distributed filling throughout the accumulation phase The chamber is equipped with instrumentation ensuring continual measurement of methane concentration, differential pressure between the interior and the exterior of the chamber, and temperature inside the chamber. The sensor is a semiconductor (TGS doped SnO 2 , Figaro Engineering Inc., in an atmosphere desiccated by silica gel). These two chambers were compared using a test-bed allowing regulated biogas emissions, built by INERIS. The bench consists of a lm x 2m parallelogram-shaped bed of wet sand, roughly 30cm deep; a mixture of methane, carbon dioxide and water vapour is injected into the bottom of the bed under controlled conditions. The methane and carbon dioxide fluxes are regulated by mass flowmeters and distributed in the lower part of the bed by numerous pinhole-perforated tubes. The sand used in the bed and the emitted gas are heated to a temperature between 15 and 50°C by a heating pad placed in the lower part. On one side a fan is used to create air movements above the sand bed that simulate a wind of steady speed and direction. The CH4/(CO 2 + CH4) mole ratio is maintained at a constant value equal to 60%. Methane flux densities ranging from 0.1 to 200 N ml / m 2 / minute can be obtained with this set-up Six tests with different flux densities between 0.1 to 200 N ml / m 2 / minute. For two of the tests, d2w and d7w, a steady wind blowing at 4M/s was simulated.

Estimation of global flux on the basis of local measurements was not addressed in the framework of this comparison using these two non-integrating methods.

Atmospheric Methods

The eddy correlation method (INRA) relies on the principle that the flux density of a compound passing over a horizontal surface at a given time and place can be calculated as the product of the vertical wind speed and the concentration of the compound in question (3). This method requires measurement of the vertical wind speed, and of the compound concentration at the same place and moment in time with a frequency of at least 10 Hz. The experimental system is essentially composed of a three-dimensional sonic anemometer (Solent model, Gill) that measures wind components in an orthogonal system and air temperature at 20 Hz, and an adjustable laser diode spectrometer (Aerodyne Research Ltd.)

The mass balance method (INRA) relies on the principle that for a finite surface area, no matter what its characteristics, the flux emitted between the surface edge and the point of measurement is equal to the horizontal flow of the compound in question, integrated over the entire height of the boundary layer extending above the surface in question (3). The methane flux is estimated using measurement of wind speeds and methane concentrations at five heights in the lower atmosphere. Wind speed is measured using cupel anemometers (Cimel, Paris) Average methane concentrations are measured afterwards from air samples pumped into Teflon bags placed in rigid containers. All measurements and air sampling controls were carried out using a central data recording station (model CR10, Campbell Scientific Ltd.)

The tracer gas method (IPSN) consists in calculating the methane flux by measuring an atmospheric transfer coefficient (K) obtained using a tracer gas. Between an effluent source and a given point, K is the ratio between the integrated concentration of effluent at this point and the mass of effluent released (4). The method used consists in determining K by emission of a tracer gas under conditions that are as close as possible to those of methane emission, and in measuring simultaneously at the same point the concentrations of the tracer gas and of The eddy correlation method systematically underestimated methane flux density by a factor of 1.5 to 3. This disappointing result has been attributed to a too-small test field and to the discrete level of methane emissions. The mass balance method correctly measured intermediate flux densities with a margin of error of less than 30%, but gave unsatisfactory results for very low values, that were overestimated by a factor of 10 to 20, and for very high values, that were underestimated by a factor of 2. Problems with the operation of the sampling system would appear to be at least partly responsible for the poor functioning of this method. The tracer gas method yielded good results for mid-range and high flux densities, with a margin of error of less than 20%. This method worked less well for low flow densities, that were overestimated by a factor of 2.5 to 3.5, even though the actual values were always within the uncertainty margin. This problem does not seem to be linked to the method itself, but to the difficulties encountered in measuring low methane concentrations.

DISCUSSION

This series of tests appears to establish the superiority of the INERIS method in the accumulation chamber method category, and that of the IPSN tracer gas method among the atmospheric methods. This conclusion must be nuanced, however. The final goal is to measure methane fluxes at actual municipal solid waste landfills, hence under conditions very different from the highly favourable conditions of the INERIS test-bed or the Etouy site. For instance, in the case of the INERIS accumulation chamber method, the test-bed measurements were made using a gas-phase chromatography column that would be replaced by a portable detector in the field. It is known that the biogas emitted at landfill sites has a complex composition. Care must therefore be taken to avoid interference problems when detecting methane with this type of detector. Regarding the IPSN tracer gas method, this method works well in principle if the methane and the tracer gas are emitted in identical fashion. This condition was fulfilled in Etouy, because the two gases were emitted through the same network of injectors. But how can these conditions be respected at a real-life landfill, where methane fluxes will be unevenly distributed and not known prior to measurement? Inversely, the least effective methods in the comparison are not without relevance for real-life situations. The sensor mounted in the IPSN accumulation chamber is noteworthy for its low cost, light weight and low energy needs. Experimental conditions at the test site were probably not very favourable to the application of the INRA methods, particularly the eddy correlation method.

The detector used for this latter technique performed remarkably well.

In conclusion, on-site experimentation now appears indispensable. Plans are to retain one accumulation chamber method and one atmospheric method for this further work, as the two types of method have not yet been compared directly. In light of the above results it seems natural to retain the INERIS chamber method and the IPSN tracer gas method. It would be interesting, however, to include the IPSN TGS sensor in the loop that INERIS will install on its accumulation chamber.

A

  comparison of methods for the measurement of methane emissions from municipal solid waste landfills for the purpose of evaluating their contribution of the greenhouse effect D. Savanne, Philippe Cassini, Zbigniew Pokryszka, Christian Tauziède, A. Tregoures, P. Berne, J.C. Sabroux, P. Cellier, P. Laville To cite this version: D. Savanne, Philippe Cassini, Zbigniew Pokryszka, Christian Tauziède, A. Tregoures, et al.. A comparison of methods for the measurement of methane emissions from municipal solid waste landfills for the purpose of evaluating their contribution of the greenhouse effect. 10. Congrès Mondial pour l'air pur, May 1995, Helsinki, Finland. ineris-00971957

Table 2 .

 2 Comparison of measurement results using atmospheric methods with actually emitted flux densities

  Likewise, it would be interesting to ascertain if the adjustable laser diode detector used by INRA can improve measurement of low methane concentrations. If so, the effectiveness of the tracer gas method for low flux densities could be markedly improved by using the laser diode detector as a supplementary device. NOTES 1. POKRYSZKA Z., TAUZIEDE C,JODART A., (1994). Compte rendu de l'intercomparaison des methodes de mesure du flux surfacique de gaz par chambre du 16 au 20 mai 1994, resultats des mesures effectuees par 1'INERIS. Rapport INERIS, contrat Ademe n° 3930021, quatrieme partie, decembre, 12 pp.2. SABROUX J.C., DAJLEVIC D., ESPIET F., MAUREL J.M.,RICHON P., (1994). Intercomparaison des methodes de mesure des densites de flux surfaciques du methane par chambres d'accumulation, resultats et evaluation des mesures effectuees sur le bane d'etalonnage de 1'INERIS du 16 au 20 mai 1994. Rapport d'etudes SERAC/LEIRPA/94-19, contrat Ademe n° 3930020,28 pp.3. CELLIER P., LAVILLE P., FLURA D.,TAUPIN F., (1994). Intercomparaison des methodes de determination des flux de methane emis par les decharges d'ordures menageres : correlations turbulentes et bilan de masse, Rapport INRA-Grignon, Unite de Bioclimatologie, contrat Ademe n°3930022, decembre, 11 pp. 4. TREGOURES A., BERNE P., GUELFF C, RAVENTOS C, SESTIER-CARLIN R.,(1994). Mesure de flux de methane par tracage gazeux sur le site d'emission controlee d'Etouy du 13 au 16 juin 1994. Rapport IPSN, contrat Ademe n° 3930020, Premiere partie, novembre, 30 pp.

10th World Clean Air Congress, Helsinki,


BLASTING VIBRATIONS CONTROL: THE SHORTCOMINGS OF TRADITIONAL METHODS.

Pierre M. VUILLAUME (l), Thierry BERNARD (2), Michel KKZLO (l).

SÜMMARY.

In the context of its studies for the french nünistry of the environment and for the French national coal board, INERIS (the French Institute for the industrial environment and hazards, formerly CERCHAR) has made a complete critical survey of the methods generally used to reduce the levels of blasting vibrations.

It is generally acknowledged that the main parameter to control vibrations is the so-called "instantaneous charge", or charge per delay. This should be reduced äs much äs possible in order to diminish Vibration levels.

On account of this, the use of a new generation of blasting devices, such äs non-electric detonators or electronic sequential timers has been developped since the seventies.

INERIS has collected data from about 900 blasts in 2 quarries and 3 open pit mines. These data include "input" parameters such äs borehole diameter, bürden, spacing, charge per hole, charge per delay, total fired charge, etc ... They also include "Output" measurements, such äs Vibration peak particie velocities, and main frequencies. These data have been analysed with the help ofmulti variable statistical tools.

Decreasing the charge per delay with the help of priming devices such äs non electric detonators or electronic sequential timers improves the levels of vibrations, but only to a certain point. After this point, the phenomena are far less well controlled than in traditional pyrotechnic timing and the perturbations seems more erratic. The total fired charge, the accuracy of pyrotechnic delays and the adjustment ofthe timer also have a strong influence on Vibration levels.

Blasting tests were undertaken to evaluate new methods of vibrations control, such äs the superposition of Vibration signals. These methods appear to be accurate in many critical cases, but certainly would be highiy improved with a better accuracy offiring delays. The development of electronic detonators seems to be the way ofthe füture for a better blasting control.

The numbers between square brackets refer to the bibliography list.

INTRODUCTION.

In the context ofits studies for the french mirüstry ofthe environment and for the French National Coal Board, INERIS (French institute for the industrial environment and hazards, formeriy CERCHAR) has made a complete survey ofusual methods to reduce the levels ofblasting vibrations, in order to advise field managers and environment inspectors.

Data from about 900 open pit blasts in 2 quarries and 3 mines have been collected and analysed with the help of multi variable statistical tools, in order to understand the mechanisms of developping or controlling vibrations, according to the blasting technique used.

Blasting tests were undertaken to evaluate new methods of vibrations limitation, such äs Vibration signals superposition.

CONTEXT OF THE STUDY.

Within the last two decades, blasting has evolved in Europe, with the increase of drilling diameters and the more frequent use of large blasts, in order to supply material to larger loading and hauling equipments. The research for better quality control ofblasting results was also a factor ofdevelopment.

In the meantime, regulations conceming blasting vibrations limitation have been drawn up and published, on account ofthe increase in general concem about environment. These regulations are generally more severe than those ofcountries like the USA or Canada, since the density ofurbanization is higher on the old continent. In addition, in Europe, masonry is the most frequent structure of buildings, including numerous historical monuments. But this masonry is much more sensitive to vibrations than the concrete of industrial buildings or the wooden housing structure, that is very frequent in Northem America or Scandinavia.

For all these reasons, electric or non electric sequential firing techniques are nowadays very successfül, in order to diminish the so-called "instantaneous Charge", that is considered äs the main parameter for controlling Vibration levels.

The practice ofsuch techniques must be controlled with the help ofa certain number ofrules, in order to avoid misfrres, äs well äs Vibration superposition. For instance, one ruie is that all the electric firing circuit or non electric shock tube network must be initiated before the detonation ofthe first charge. The second ruie is that the difference in time between any two detonations of all the charges must be greater than 8 ms, in order to avoid Vibration superposition due to the scattering ofpyrotechnic delays [l].

Nevertheless, since millisecond detonators starting at long delay times are not common in Europe, some new ruies have been adopted in order to keep these firing techniques possible with only a few number of pyrotechnic delays. For instance, the first ruie previously mentioned has become that all the electric firing circuit or non electric shock tube network must be initiated in a certain radius around the current detonating charge.

The experience shows that, thanks to the use ofsequential blasting, vibrations levels have been generally reduced, but remain unsuitable for the neiborhoood and are erratically above the authorized limitations.

As it is rather difficult to directfy analyse these phenomena, for instance with the help of in-situ measurements, a large scale data collection has been undertaken and a multi variable statistical analysis has been set up.

For the most critical cases, the technique of superposition of vibrations signals has been more recently developped. This technique has also been analysed.

MÜLTI VARIABLE STATISTICAL ANALYSIS.

Description of the data base.

As a general principle ofstudy, it is admitted that blasting is a tool for transforming the energy release of the explosive into mechanical energy. This may be positively used, for instance in the fragmentation or the adaptation of the muckpile shape. But it may also have negative effects, like noise, flyrocks and vibrations.

FIGURE l: THE "BLACK BOX" OF BLASTING.

Drilling pattern

Typeof explosive

Hydrology

Y V "INPUT" PARAMETERS "OUTPUT" PARAMETERS

So, let's consider the blast äs a "black box" that controls the distribution between positive and negative effects of mechanical energy (figure l). The effect ofthis "black box" depends on "input" parameters, that may be classified äs "natural" parameters (existing geological and geographical conditions, hydrology, etc ...) and "exploitation" parameters (drilling pattem, explosive energy, charge per hole, charge per delay, charge per period offiring time, total fired Charge, etc ...).

"Output" parameters are fragmentation, shape of the muckpile, environment injuries, etc ... In this particular study, the work was focused on vibrations : longitudinal, transversal and vertical maximum peak partide velocities, äs well äs corresponding main frequencies.

The aim ofthis study is to bring to the fore the influence ofinput parameters (natural and exploitation Parameters) on Output parameters (vibrations) in open pitjobsites.

Finally, data were recorded for several hundreds ofblasts, each ofthem being a recording, äs shown m table l. Table 2 shows the origin of data (3 mines and 2 quarries), the period of collection, the type of blasting technique used, the number of recorded parameters and the number ofrecordings for each site. All in all, 865 recordings have been collected.

What is multi variable statistical analysis ?

Each site's data constitute a huge matrix of 19 to 31 columns and 96 to 206 lines. Of course it is an impossible task to inunediately deduce the correlations between the parameters. Therefore, multi variable statistical analysis means were used, such äs principal component analysis CPCA), factorial discriminant analysis (FDA) or multiple regression.

As many readers are certainly not specialists in multi variable statistical analysis, we will try to give a simplified example in order to explain the global methodology.

If we want to examine the correlation between 20 or 30 parameter, we would have to imagine data points within a space of "n" dimensions. But it is virtually impossible to visualize "n" dünensions if n is greater than 3. It is easily understood that, even in a "n" dimension space, the scattered group of points is approximately ovoid-shaped. This ovoid has a length, a width and a thickness, that is to say so-called principal axes. In an "n" dimension space, there are "n" principal axes. For instance, the principle of principal component analysis (PCA) is to caiculate the direction ofthese axes with the help ofthe least square method. The principal components are more or less correlated with the original parameters, so that only a few of them are significant. The points are projected onto the most significant planes (2 components). The correlations between parameters become more perceptible immediately.

Results.

Some strong specific correlations have been detected for one site and may be the opposite on another. For instance, the presence of water in the boreholes may provoke an increase or a decrease in the levels ofpeak particie velocities. Ifthey diminish, it may be that the matter is infiltrated rain water. In this case, it is obvious that infiltrations mainly occur in naturally fragmented rock masses, that will tend to attenuate the shock wave. Ifthe peak particie velocities increase with the presence of water, the matter is more probably the presence ofa water layer, which, on the contrary, may ensure a better transmission of shock waves.

It must be remembered that the aim ofthe study is to bring to the fore the most general correlations that may be usefül for the entire blasters community. Therföre, we do not want to publish spedfic quantitative relationships between parameters, which would be appropriate for a unique jobsite, nor general quantitative relationships, which would not be appropriate for any particular site.

We prefer to show the general trends that were oberved at alljobsites. These are shown in table 3. In this table, the arrows show the direction of the effect and their size shows the quality of the correlation. Some well known former results are successfülly confirmed :

-the peak particie velocities are logically decreasing fünctions ofthe distance from the blast; -the peak particie velocities are increasing fünctions ofthe so-called "instantaneous Charge"; -the frequencies are decreasing fünctions ofthe distance from the blast.

In the same way, less known results are also confirmed and generalized [START_REF] Boinier | Analyse des vibrations liees aux tirs de la nüne ä ciel ouvert de Decazeville[END_REF] : the peak particie velocities are increasing fünctions ofthe total fired charge.

It is shown that most of the correlations with frequencies are poorer than those obtained with peak particie velocities. Hence, the frequencies seem more difficult to control.

Conceming the peak particie velocities, some few significant correlations are obtained with input Parameters like the borehole diameter and drilling pattem surface. Some other input parameters are well correlated with the velocities, such äs the number of fired boreholes or the number of rows, but they have a direct or indirect link with the total fired charge.

The correlations observed between the velocities and the charges fired per period of 8 or 16 ms are of more interest; the higher the charge fired within a short period, the worse the vibrations control. So, it seems that peak particie velocities are less well controlled when the timing technique is electronic.

Of course, this must be due to the scattering of pyrotechnic delays, since it is clearly demonstrated that the velocities decrease when the delay between charges increases. That is the reason why we deliberately maintain "instantaneous charge" beween quotation marks.

What is the meaning of "instantaneous Charge" ?

The "instantaneous Charge" is well defined when the delay between charges is constant and relatively great (usually 25 ms in non electric timing and greater than 30 ms in electronic tinüng).

It is well known that the delays of detonators are normal-distributed and that their scattering increases when the detonation time increases. For instance, in the case of 25 ms delays detonators, the most common in France, the Standard deviation of detonation times may go up to 7 ms, within a total ränge of 500 ms (20 available delays).

If we consider an average Standard deviation of 4 ms, it is easily shown that the overlap probability, which must be less than l %o in France with the normal pyrotechnic delay difference of 25 ms, may increase up to approximately 20 "/o if an electronic timer reduces to 8 ms the actual detonation times difference (figure 2).

FIGURE 2 : OVERLAP PROBABILITY WITH ELECTRONIC SEQUENTIAL TIMERS.

8 ms electronic delay difference

K----»

This figure is given äs an example in the case of two single detonators. For a large number of charges, the overlap probabilities of all detonators may be cumulative and it is not surprising to observe some erratic surpassings of the authorized peak particie velocities values for blasts that are usually well controlled.

For these reasons, we think that "instantaneous Charge" should preferably be defined äs "near instantaneous Charge", that is to say : the maximum Charge fired within a short period of time. Apart from changing the sequential firing technique, the prediction ofblasting vibrations could be made on the basis ofthis new concept.

Thus, the "8 ms ruie" should be reconsidered. However, in this case, all ofthe advantages ofsequential firing are to be reconsidered.

SÜPERPOSITION OF THE VIBRATIONS SIGNALS.

Principle.

The aim ofthis technique is to fire the charges at adequate detonation times, so that the emitted Vibration signals reach a place needing protection in phase Opposition. So one may hope that particie velocities cancel each other out.

There are several methods to obtain this result in practice. The one we choose for testing seems to be most pragmatic [START_REF] Bernard | Les vibrations dues aux tirs de nünes : methode generale pour prevoir les niveaux et caiculer les plans de tir (Blasting Vibration : a general methodfor prediction and designing blasfing patterns)[END_REF]. Several series oftests have been undertaken in two quarries and one mine.

The basic hypothesis ofthe method is that a Charge that is fired in a certain area ofthe jobsite produces a reproductible signal at the monitoring point.

As blasting vibrations are not perfect sine waves, and äs the behaviour of the rock mass is heterogeneous, it is practically impossible that particie velocities perfectiy cancel each other out. One or several single charges are fired in the area and the corresponding Signals are monitored at different places, including the one to be protected (notice that it is also possible, but more complicated, to deduce the elementary signals fi-om a complete production blast). Then, a füll scale blast is sünulated, involving äs many charges äs the normal blast of the quarry, with different detonation times. The geometry ofthe whole blast and the velocity oftransmission ofthe shock waves on the site are taken into account. For instance, figure 3 shows the way of caiculating the superposition of two charges with a detonation times difference ofAt.

Results.

One representative test was undertaken with a shot of 10 single column boreholes fired with the same pyrotechnic delay at the bottom, while a constant detonation times difference At between boreholes was given with the help of a sequential timer.

Figure 3 also shows the computerized peak particie velocity in one of these test, versus the detonation times difference At. The graph gives the expected peak particie velocity for Optimum detonation times differences : optimization is possible for values ofAt of 14 or 44 ms.

We observed a constant reduction by about 40 % of peak particie velocity, when comparing it with the normal pyrotechnically delayed blast, involving the same drilling pattem and the same charges per borehole. This result was quite reproductible with a 44 ms detonation times difference.

We decided that a test with a 14 ms detonation times difference was not suitable, since the overlap probability of charges detonations, due to pyrotechnic delays scattering, would have reached the value of 5 "/o. Looking at the shape of the graph in figure 3, it is easily understood that a shift of 2 or 3 ms on both sides of the Optimum of 14 ms would largely change the results. The risk of surpassing the legal limitation of peak particie velocities would have been unacceptable at this particular site.

More generally, the superposition method of blasting Signals is effective. But, when the Optimum ränge of delay differences between the charges is too narrow, the benefits of the method may be outweighed by the scattering of pyrotechnic delays.

Moreover, some tests undertaken show that the method is less beneficial when there is a great number of boreholes. Again, this is due to the scattering of pyrotechnic delays, which can accumulate if the number of detonators is greater. But it is also due to the enlargement of the total blasting surface, which introduces scattering in rock mass behaviour.

The development of electronic detonators should improve the accuracy of the method [START_REF] Bernard | Radio-controlled detonators and sequential real time blasting applications[END_REF].

CONCLUSIONS.

It is obvious that non electric or electronic technologies of sequential äming have largely improved blasting results from the point of view of the production, while they also have made it possible to reduce the levels of blasting vibraäons (figure 4).

In France, the most severe limitaüon of peak partiele velocities is 2 mm/s for the lowest frequency taken into account (l Hz). Thanks to these technologies, this limitaäon is seldomly surpassed in the most cridcal cases. But this study shows that these technologies make it impossible to prevent erratic phenomena, that may be unacceptable for surrounding residents. The limits of the methods are particularly reached in the case of large blasts, since sequential blasting still requires the use of pyrotechnic delay detonators. The scattering of their delays provokes a loss in the control of undesirable blasting effects. Some common ruies of sequential blasting -such äs the famous "8 ms ruie" -should be reconsidered. However, in this case, all ofthe advantages of sequential firing are to be reconsidered.

The superposition method of blasting Signals is effective, but it is also limited by the actual accuracy of pyrotechnic detonators.

The development of electronic detonators, having an improved accuracy, will consitute a new step in the control of vibrations.

1 :

 1 Institut national de l'environnement industriel et des risques (INERIS), Vemeuil en Halatte, France. 2 : Compagnie Nouvelle de Scientifiques (CNS), Nice, France. 22eme Conference annuelle « Explosives and Blasting Technique, Orlando, 4-8 fevrier 1996, p. 210-22.

FIGÜRE 3 :

 3 FIGÜRE 3 : PRINCIPLE OF SÜPERPOSITION OF THE VIBRATIONS SIGNALS.

FIGURE 4 :

 4 FIGURE 4 : SCHEMATIC HISTORY OF BLASTING VffiRATIONS (IN FTIANCE).

TABLE l : STRÜCTURE OF DATA BASE.

 l

	"INPUT" PARAMETERS	"OUTPUT" PARAMETERS
	Natural parameters	Exploitation parameters	3 peak partide velocities	3 frequencies
	Recordings
	0-
	fl.
	Q-
	• O.
	• O-
	• O.

TABLE 2 : DESCRIPTTON OF THE DATA BASE.

 2

				Mines		Quarries
	Jobsite	A		B	C	D	E
	Number of recorded	25	31	19	29	20	21
	parameters
	Date of beginning	05.93	01.95	01.93	04.91	01.91	01.91
	Date of end	02.94	03.95	11.93	08.94	04.91	06.94
	Type of sequential timing	Electric	Electric	Non electric	Electric	Electric	Electric
	Number of recordings	132	187	206	113	96	131


Guy Mariair Claude Cwiklinski

Fabrice Marliere

A REVIEW OF LARGE-SCALE FIRE TESTING FOCUSING ON THE FIRE BEHAVIOUR OF CHEMICALS

A review is presented of the main features of the fire behaviour of chemicals, äs assessed by largescale experiments in a senü-confined environment. The paper focuses on those chemicals whieh contain at least one hetero-atom fixed to their hydrocarbon basic stmcture, rather than on classical hydrocarbons for which much work has already been published. It emphazises results dealing more especially with the generation of heat and toxic combustion products in well ventilated conditions. Some aspects of the implication of lab-scale tests in the related area are also proposed, for comparison purposes. Finally, comments in tenns of progress in the risk assessment of thermal and chemical ünpacts of fires of chemicals are finally made in matter of a conclusion.

INTRODUCTSON

An extensive and urgent need ofusefui engineering data dealing with the fire hazard of chemicals was recognised in Europe in the mid 70's. This concem has increased even more in the 80's with the implementation of reinforced legislation in the field of industrial risks -enhanced by the so-called "Seveso Directive" 82/501/EEC and its amendments 8 and because some real case accidents have affected the Environment dramatically 2 -3 .

INERIS and few other European centres contributed to the subsequent applied research by the use of large-scale fire testing techniques, which were thought able to bring macroscopic, signifieant and meaningfül results ofdirect practical use for the industry.

Within this overall context, the present paper is reporting mainly on fire knowledge achieved experimentally, at a large scale, on a variety of chemicals, mostly at the INERIS large scale fire testing facility located in Vemeuil-en-Halatte, France. In the field, INERIS has gained considerable experience on a variety of products acquired over a long term period of time (nearly ten years). Most tests were carried out in ventilated conditions in accordance with ISO TR 9122 fire classification 4 , since such conditions were typical of French industrial premises.

Chemicals investigated thus far have been most of the time commercially-important materials such äs pesticides (diuron, dimethoate, high sulfur content füngicides, other insecticides and herbicides...), fertilizers (temary type), pharmaceuticals, nitrogenated solvents and other liquid basic chemicals (acetonitrile, adiponitrile, ethylene diamine, aromatic isocyanates TDI and PMDI). C-H or C-H-0 solvents (n-Heptane, isooctane, toluene, methanoi) have also been tested äs reference materials.

TOOLS FOR LARGE SCALE TESTING OF CHEMICALS AND INDUSTRIAL PRODUCTS

Early testing facilities consisted of free open sites where very simple but usefui series of large scale bum tests were carried out in freely ventilated conditions on classical hydrocarbons, only requiring pans of various sizes in terms of special equipments. Major results achieved from such types of experiments (largely discontinued today by scientists for environmental reasons with few exceptions [START_REF] Wackeriig | The aftermath ofthe Sandoz fire[END_REF] ) were a first and still partially valid evaluation of scale effects of fires on flame height and regression rate of liquid pools for numerous products. A well known example of experimental work achieved that way was the pioneering experimental study of Blinov and Khudyakov [START_REF] Blinov | Certain Laws Goveming the Diffusive Buming of Liquids[END_REF] . Review papers on pool buming with hydrocarbon fuels were made available in the early 70's [START_REF] Hall | Pool Buming[END_REF] and updated in the 80's 8 ' [START_REF] Babrauskas | Estimating Large Pool Fire Buming Rates[END_REF] A further step was accomplished with the appearance of experimental test rigs which allowed largescale testing of rooms fully equipped with fumiture äs in private dwellings. For the industrial needs, two types of large scale versatile units were then developed, more or less in a parallel way, and both are still in use. The first design consists of a large hall fitted with a hood System suitable for collecting and characterising all the fire gases resulting from in-door storage commodity bum tests, rating up to about 10 MW of effective heat release. This concept was first developed by Factory Mutual (USA), the Swedish laboratory SP recently commissioned the same kind ofequipment in Boras [START_REF] Dahlberg | The SP Industry Calorimeter, for rate of heat release measurements up to 10 MW[END_REF] . Those equipments and related procedures are adequatly designed for the measurements of the actual heat release rates of fires.

The other type of equipment developed for large scale fire testing is the wind tunnel design to which the INERIS main fire testing facility belongs. Formerly designed for studying the fire risk in coal mines, some of the existing equipment has extended its scope to fires in road and rail traffic tunnels and inside warehouses and other industrial storage premises. Basic information was reported"' [START_REF] Mariair | Large-scale testing in the INERIS fire gallery : a Major Tool for both Assessment and Scaling-up of Industrial Fires[END_REF] together with some example results on fire tests involving solid and liquid chemicals. Prom the air admittance (controlled by a sliding door) to the Stack diluting the fire gases, the unit is composed of: -a horizontal section (the wind tunnel part) which is nearly 50 m long and presents an open section of about 10m2, -a vertical "tower", about 12m high, with a rectangular cross section (6 m2), at the top of which the main sampling ports are positioned for the analysis of the fire gases and the heat release rate measurements (at a place so-called the "mixing point"), -a vertical column guiding the fluids (the fire gases mixed with entrained air) to the gas cleaning unit which may also serve äs a cooling unit (use of inner water curtains), -a gas cleaning unit comprising a dry dust filter and a wet scrubber, -the final attachments (exhaust fan and Stack).

The overall volume of the unit is about 600 na [START_REF] Wackeriig | The aftermath ofthe Sandoz fire[END_REF] , to which an 18 m 3 enclosure must be added which may be used with or without connexion with the main unit, depending on the aims of experiments. The walls comprise an extemal metal sheet of 5 mm and inner linings made of both insulation and refractory materials.

Testing procedures generally applied in the fire gallery are designed to keep environmental Parameters äs far äs possible representative of the real fire scenario studied. They must be able to meet many goals in a single run, due to their costs. Therefore, related fire tests are systematically and heavily instrumented with local and distant measurements allowing thermal and mass balance assessments to analyse efficiently the chemical äs well äs the thermal responses of the fires, following some of Peacock's suggestions 13 . A video recording of the fires is also considered of the greatest importance, äs visual observation may play a major role in the understanding of important phenomena related to the experimental fires, äs recently outlined by Hirano and Saito 131 " [START_REF] Notarianni | Smoke Production from large oil pool fires[END_REF] . More specific aims depending on each work undertaken may apply for specific set-up and testing protocols (testing liquified gases in a pool configuration for instance).

From a general point of view, an adequate test procedure for characterising the fire behaviour of solid materials on a large-scale is a rather complex goal äs it must take into account that the combustion rate äs well äs main properties of the fire plume resulting from a fire scenario closely depend on :

-the chemical nature and formulation of the product, -the state of division of the commercial product (basically due to the actual chemical physical state and at a macroscale, consequent upon the packaging, conditionning, and storage conditions äs well), -the confinement of the storage premises -a three dimensional character.

For testing the fire hazard of generic liquids to assess the fire behaviour of bulk storage capacities , the pool fire configuration chosen and continuously improved by INERIS is based upon the technical approach of Emori and Saito 14 According to this experimental arrangement, the pan determining the size of the buming pool of the tested product is installed in a wind tunnel (see figure 2) and is lying on a weighing platfonn. Optional features deal with the possibility of providing a buming phase with the level of product being maintained constant in order to observe a steady state. More simply the product may be bumt in a batch procedure where a detemüned amount of product is totally poured in the pan prior to the ignition. The constant level facility is fairiy easily obtained for most fuels by providing a simple regulation loop which includes a thermocouple sensor measuring the temperature at the desired Position of the interface between the liquid and vapour phase. Both techniques are usefül depending on the fire scenario which is to be addressed. A constant level test, for example, is related to a pool fire being fed in fuel continuously from a leakage in a damaged storage capacity, whilst the altemata» procedure represents a pool fire scenario inside a capacity containing a combustible liquid, is The experience of INERIS in the field considerably increased and was validated rurther through the EUREKA499 "Firetun" project, where pool fires of heptane from Im 2 to 3 m 2 with a constant level mode were monitored from a distance ofmore than 350 m from the pan [START_REF] Casale | Heptane Fire tests with Forced Ventilation[END_REF] .

SOME RESULTS DEAUNG WITH THE THERMAL AND CHEMICAL ASPECTS OF FIRES INVOLVING PESTICIDES AND OTHER ATYPIC CHEMICALS

Dealing with the fire problem with pesticides, we comment hereafter on the chemical issue of such types of fires, based on a series of 5 different large scale (150 kg to 400 kg) experiments carried out in our fire gallery. Detailed information on procedures and overall results may be found in another paper regarding diuron and dimethoate [START_REF] Cwiklinski | Incendie dans les stockages de produits phytosanitaires. Les apports de l'essai en grand[END_REF] . All products were tested äs commercial formulations including the active chemical, the additives (inert or combustible) and the packaging materials äs well. Three of the products are named with a code due to commercial agreements. "Product A" refers to a test involving a single product, "pallet B" refers to a "cocktail" commodity of 5 different commercial grade herbicides, "pallet C" refers to a test involving 5 different herbicids in a procedure very similar to "pallet B". Additional information refers to the hetero-atoms existing in the formulations involved. From table l, we may point out the great Variation in the conversion ratio of the hetero-atoms in the toxic gaseous components.

Large-scale testing is clearly sometimes the only way to qualify very specific fires such äs those involving nuneral products e.g. fertilizers, sulfür... which are commercially important chemicals containing no combustible carbon in their chemical structure. Temary fertilizer represents a specific hazard related to behaviour in fire conditions. Although it is excessive to speak of the fire hazard with such an essentially mineral material, a highiy exothermic thermal decomposition may be feared. In bulk storages, this can give rise to thermal threats äs with more classical fires.

The thermal and chemical aspects of such a fire have been examined experimentally at INERIS, äs a consequence of an actual French accident involving 850 tons of 15-8-22 NPK fertilizer in bulk storage near the town of Nantes. The procedure adopted was a simulated bulk storage of l ton capacity containing a similar fertilizer inside the fire gallery. Decomposition was very successfully initiated by a electrical plate raised to only 220°C. Important results regarding the thermal aspect were (I) a much higher thermal decomposition propagation rate than expected (From the classical medium scale test carried out by the manufacturers to qualify the reactivity of such products), (II) a rather small thermal heat release and (DT) the refractory property of the solid residues. Relevant fire-fighting techniques must take care of solid phase transformations occurring in the residues to cool the buming storage with some efficiency. The major chemical findings of the large scale test carried out were that half of the product is to be expected to be released äs a mixture of toxic chlorinated and nitrogenated compounds in significant amounts (HC1, Clz, NzO, NOz, HNOs,) diluted in water vapour, ammonium chloride and molecular nitrogen. More exhaustive information related to this test was reported previously by Cwiklinski [START_REF] Cwiklinski | L'essai en grand -Une approche preventive et previsionnelle pour l'incendie en milieu industriel[END_REF] . Sulfür fires were also briefly investigated in the form of high sulfür content (80% to 99%) in füngicide trade products. Tests were carried out on two quality product (a technically pure grade of micronised sulfür powder and an 80% S containing grade diluted with 20% of inert material). They revealed, surprisingly, completely different fire behaviours. The pure grade type of sulfür tumed rapidly into a moderately active blue flaming pool fire, with a small buming velocity (some 4 to 8 g m-2 s-1) which was expected since the melting point of sulfür is about 112°C. The 80% grade on the other hand was looking like a non flaming coal dust fire leaving a great part of solid residue, but released äs well massive amounts of SOz, with practically no visible fire activity.m the latter case, a non glowing solid layer forms at the pool surface and may induce a false Impression of natural extinction.

FIRES INVOLVING NITROGENATED SOLVENTS AND AROMATIC ISOCYANATES

Very few experiments have been reported previously on the fire behaviour of liquid nitrogenated solvents, even on the lab scale. We have just noticed the earlier work of Burgess [START_REF] Burgess | Diffusive Buming of Liquid Fuels in Open Trays[END_REF] who included in their list of investigated products UDMH (unsymetrical dimethyl hydrazine) and DETA (diethylene triamme) in terms of buming rates, and more recently, the contribution of Barteids and coworkers [START_REF] Barteids | Emissions from medium scale fires of chenücals[END_REF] who have also carried out experiments at a medium scale including EDA (ethylene diamine) and TDI (toluene diisocyanate) alone or in a mixture with xylene [START_REF] Barteids | Emissions from medium scale fires of chenücals[END_REF] with the aim of evaluating emissions.

INERIS has been studying the fire behaviour of liquid nitrogenated products within several long term applied research programmes including products like TDI, "ACN"(acetonitrile) or ADN [START_REF] Weiss | Hazardous Chemicals Data Book[END_REF] and NFPA325 M).

The overall phenomenology of diffusive buming features of some of the N-containing fuels tested are graphically illustrated through figures 3 to 6 where examples of directiy measured or caiculated Parameters related to those fires are plotted versus time. Figures 3 and4 point out how much the heat release rates may be affected by the operational procedure, since a significant increase is systematically observed once the level of liquid is no longer kept constant (tenninal phase of most of the runs), due to a modification in the thermal balance at the liquid surface level [START_REF] Hanüns | Heat Feedback to the Fuel Surface in Pool Fires[END_REF] . The peak value may be about 125 % to 130 % the value reached during the steady state obtained betöre that procedure change. The first sharp peak in the HRR curve plotted in figure 4 refers to the eombustion of the flammable solvent (l liter of n-heptane) used to make the ignition easier (high flash point of adiponitrile). Figure 5 referring to an acetonitrile pool fire shows the highest COi/CO compared to other products. This parameter has decreased down to 20/50 with aromatic isocyanates pool fires, and was at a mid-range level with adiponitrile (200 to 300). Finally, figure 6 illustrates the high levels of NO, (in terms of volumic concentrations) characterising all products tested. Such a result was naturally expected owing to the relatively high nitrogen content in the molecules (see table l).

For TDI and ADN, addition of l to 2 liters of flammable liquid (heptane) was used before ignition either with a spark alone or through the assistance of a start-up bumer to get quick seif sustained diffusive and complete buming of the fuels. ACN and EDA, on the other hand, were directiy ignited äs for flammable liquid hydrocarbons with a simple electrical spark.

PMDI was the only -product buming in a quite different manner leaving a large amount of carbonaceous char due to polymerization processes activated by the combustion [START_REF] Mariair | The Commercially Important Di-isocyanates in Fire Conditions. Part 2 : Polymeric 4,4" di-isocyanate diphenyl methane (PMDI)[END_REF] . No further comment will thus be produced here regarding this product. Detailed procedures and results regarding 0.25 m 2 and l m 2 pool fires of TDI have been also extensively reported by Mariair, Sand and Prager, together with other related work carried out by Bayer and Rhone-Poulenc 23 -24 pool area (m 2 ) buming rate (g-m-V): Tnax above pool (°C) T^underrooffC)

T"" at tower (°C) eff. HRR (kW) "conv". HRR (kW) toluene diisocyanate TDI(c) 0.25 buming rates refer to buming phase without a constant level of füel in the pan. "conv" HRR refers to the gas stream enthalpy äs determined at the mixing point in the tower 3 shows a comparison of all nitrogen containing fuels tested in terms of buming rates and thermal response. With the exception of acetonitrile (the lowest molecular weight), all fuels showed a relatively moderate buming rate compared to those of typical flammable liquid hydrocarbons äs compiled previously by Babrauskas [START_REF] Babrauskas | Estimating Large Pool Fire Buming Rates[END_REF] and in other findings of INERIS related to more classical fuels (n-Heptane : 70 to 90 g m'V,...). Those values are also consistent with data quoted by Weiss [START_REF] Weiss | Hazardous Chemicals Data Book[END_REF] for other N-fuel compounds like UDMH (asymptotic buming rate equals 51 g.m'V) or DETA (asymptotic value equals 22 g.m'V). Consequently, the effective heat release rates reveal levels far below the conservative value of 3300 kW /m 2 suggested by Alpert [START_REF] Alpert | Evaluation of Unsprinklered Fire Hazards[END_REF] to quickly evaluate the thermal impact of flammable liquid pool fires. These results were indeed more or less expected owing to the relatively high content of N in all the molecules tested (see table l). Chemical fate of carbon and füel-N in the gaseous releases is detailed for some experiments in table 5.

Aromatic structures revealed by far the highest levels of CO and soot emissions. With EDA, CO was hardly measurable in some cases. Major yields of N-containing fire gases were N0^ (85 to 90% of NO) and HCN, whilst other N-containing gases sometimes detected were found in very small amounts in the conditions of the experiments (fuel controlled buming). Global conversion rates of N in total Ncontaining combustion products were systematically low (in the order of 5% or less) compared to solid fires (see table l) which supports the assumption that in this case molecular nitrogen is fortunately (regarding the high potential yields, see table 3) the major N-containing gaseous release.

CO

ADVANCEMENT IN USE OF LAB-SCALE TESTS TO PREDIGT REAL F1RE SCENARIOS FOR CHEMICALS

It is generally admitted that lab-scale fire tests suffer from apparatus dependancy, more than large scale tests, even for versatile tools like the Cone calorimeter (ISO 5660), or the 50kW flanuoability apparatus developed by Tewarson [START_REF] Tewarson | Heat release rate in fires[END_REF] and co-workers. However, they are woridwide recognised tools for ranking materials and more generally for assessing thennal äs well äs non thermal fire damage [START_REF] Tewarson | Nonthermal Fire Damage[END_REF] regarding building products and polymers, äs a result of tremendous efforts undertaken over the two last decades. Addressing the fire behaviour of chemicals is a relatively recent challenge for those equipments which are promoted for instance in Europe by laboratories such äs VTT, ISSeP 29 (use of a cone calorimeter), and Rhone-Poulenc (use of a special Version of the Tewarson apparatus [START_REF] Costa | Mistral l project[END_REF] ) in the framework of EU sponsored R&D like Mistral (MM-STEP 92), Warehouse Fires (MIH-STEP96), or Combustion (STEP109) [START_REF] Cole | Proceedings of the Industrial Fires Workshop held in Apeldoom[END_REF] 6 summarises experimental data on two pesticides (diuron and dimethoate) for which some comparisons are possible, and seems to justify some optimism. It must be outlined, however, that accurate comparisons are difficult since fully commercial grades were used in largescale tests, while pure active chemicals were bumt on the small scale (This background justifies in particular the absense of data regarding CO and C02 yields in the dimethoate large-scale test). Data regarding lab-scale fronT VTT [START_REF] Kakko | Toxic combustion products of three pesticides[END_REF] dealing with dimethoate and results reported by Rhone-Poulenc on diuron are relevant for basic comparisons with large-scale tests in well ventilated situations (21% of Oz in fresh air stream in all combustion Systems).

Similar comparisons dealing with other N-containing füels mentioned previously would have led in the same way to more pessimism to date, especially with TDI [START_REF] Mariair | The Commercially Important Di-isocyanates in Fire Conditions. Part l : Toluene Di-isocyanate (TDI)[END_REF] . When testing liquids is concemed, lab-scale procedures require special care and may still need improvements, äs suggested by work in progress 33 .

CONCLUSIONS

The large-scale experiments on chemicals carried out by INERIS which have been briefly overviewed in this paper have revealed how variable the fire behaviour of chemicals may be, depending notably on their chemical structures and physico-chemical properties. In terms of chemical fate in particular, we have shown how different the issue may be, depending on the product, the type of potentially hazardous chemical element involved and the size of the experiment. An extended appropriate use of füll-scale tests together with parametric studies on adequate lab-scale tests will still be needed in the future to improve understanding of scale effects and to provide via simple routes adequate knowledge of the behaviour on chemicals which are so numerous and often much more complex in their formulation than classical hydrocarbons. hi the light of experience achieved to date, we consider in most cases the following data äs conservative values for risk assessment purposes related to fire behaviour of large storages of various industrial chemicals in well ventilated conditions :

*average buming rate : 20 to 60 g m-2 s-1 (sulfur storages would justify an exceptional lower buming rate assumption), *N conversion rate into nitrogenated toxic compounds 40 % max (N0" and HCN, isocyanates if relevant), *S conversion rate into sulfur gaseous compounds : 100%, *C1 conversion rate into chlorinated gases 100 % (most ofthe time 100 % into HC1) *other halogens conversion rates into related halogenated acid : 100 %, *survival fraction (in case of very toxic compound): l to 2 %.

  Figure l : view ofthe INERIS fire test gallery

Figure 2 :

 2 Figure 2 : experimental principle for ventilated pool fires

  (a)at 20°C.(b) polymeric 4,4' diphenyl methane diisocyanate, see paper[START_REF] Mariair | The Commercially Important Di-isocyanates in Fire Conditions. Part 2 : Polymeric 4,4" di-isocyanate diphenyl methane (PMDI)[END_REF] for complete infonnation on the structure.(c) nitrogenated fuels in the work of Burgess^only, not tested by INERIS (d) reference hydrocarbon füel (e) refers to pure monomeric MDI (C^HioO^N;)[START_REF] Mariair | The Commercially Important Di-isocyanates in Fire Conditions. Part 2 : Polymeric 4,4" di-isocyanate diphenyl methane (PMDI)[END_REF]

  not yet available ; (b) not determined ; (c) 1,66 m 2 fest: 2 pans of l m 2 and 0.66 m2 (c) mixture 80/20 of2,4-and 2,6-isomers. Figures in parentheses for

  the

Table l

 l Table l gives the fate of those chemicals in fire conditions in terms of emissions of toxic combustion products.In all cases, the tested commodity comprised a wood pallet with packaging materials made of cardboard and polyethylene. In all experiments, solid residues were observed. Survival fractions of active chemicals from the pesticide formulations were sometimes noticed äs reported by Atkinson et al with organophosphorous compounds'[START_REF] Hall | Pool Buming[END_REF] in those experiments where very turbulent flaming buming phases were reached.

		diuron (a)	dimethoate (b)	product A	pallet B	pallet C
		CgHioNzOCIz	C5Hi2N03PSz	C, H, 0, N	C, H, N, 0, S, Cl	C, H, N, 0, S, Cl
	NO,	6.4	1.0	8.2	23	1.7
	HCN	5.5	7.1	0.4	3.6	1.2
	MIC	(c)	traces	0.2	(c)	(c) »-
	anunes	traces	(d)	4.9	0.1	traces :s
	SOz	-	31.3	-	81	74
	CH3SH	-	20.9	-	(d)	(d)
	HC1	50.8		-	23	31
	survival
	fractions of	no	yes	no	yes	no
	pesticides
	(a) product used for the test was 80% of diuron diluted in inert materials
	(b) tested äs a mixture of 400 g/l in organic solvents (mainly xylene)
	(c) not detected ; (d) not available

: yields of gaseous toxic emissions (in % of theoretical maximum) from large-scale fire tests involving various pesticides

  Quantities of products involved ränge between 20 to more than 300 liters depending on scale and expected test duration (at least 40 min) Table2summarizes the physico-chemical properties of the whole set of products containing nitrogen which were involved in the experiments plus some additional basic thermochemical data. As shown, nitrogen-fuel is present in various types of functional groups in the chemical structures involved. Nitrogen appears m nitrile groups in ACN and ADN, or in isocyanate groups in TDI and PMDI, or linked in the form of amine groups in EDA.

					Q < <*-o
					2 <a
	name of products	formulae	mol. weight (g)	N content (%)	l Boil. Point (°C)	Freez. Point (°C)	Flash Point (°C)	density (a) (g/cm 3 )	AH^". (kJ/g)	Ahy, .(ü/g)
	ACN ADN	CzH3N CÄN,	41 108	34.1 25.9	OS. »	82 295	-45 +2.4	+6 +163	0.79 0.96	30.1 33.1	0.73 0.56
	TDI PMDI (b) EDA DETA (c)	QHAN, Ci5Hio02N2(e) cw, C4H"N3	174 320/400 60 103	• <» S § 11/11.2 16.1 46.6 E 40.8	251 -116 207	<15 <10 +8.5 -39	130 230 (e) +40 +98	1.22 (1.20) 0.909 0.95	23.6 n.a. 28.6 30.9	-n.a. 0.67 n.a.
	UDMH (c)	CÄNĈ	60	46.6			249	-58	-15	0.79	32.9	0.61
	Heptane	7Hi6	100	0			98	-90	-4	0.68	44.6	0.32
	(d)

0/}PJ JP/OIU 03/503 (adiponitrile).

Table 2 :

 2 physico-chemical properties and thermochemical data of nitrogenated liquid fuels tested on large (or medium) scale. (Most data from

Table 3 :

 3 buming rates and thermal parameters of experimental pool fires

		acetonitrile	adiponitrile	ethylene diamine	TDI
			^a (all values in g/g)
	COz	2.15	2.44	1.47	2.28
	CO	1.36	1.56	0.93	1.45
	NO, (äs NOz)	1.12	0.85	1.53	0.53
	HCN	0.66	0.50	0.90	0.31

Table 4 :

 4 maximum theoretical yields y^ of main combustion products Table

Table 5

 5 comparison of gas vields from various l m 2 pool fires

		EDA	TDI	ACN	ADN
			(all values in mg/g)
		<1	36	2.4	6
	COz	unreliable	1620	2370	2300
	No, (äs N02)	18	1.7/2	14	22
	HCN	about 0.2	4	0.05 (a)	2.5
	TDI	-	0.7/0.9	-	-
	NHs	about 0,2	(b)	traces
	ainines	traces		(c)	n.a.
	nitriles			traces
	NaO	-		traces	-
	(a) locally much higher value (b) not available (c) not detected

table 6 :

 6 . comparison between large-scale and lab-scale tests on chemicals All authors of this paper are involved in fürther work regarding how far so-called lab-scale tests may help large-scale techniques and modeling tools to give a better appraisal of the real fire behaviour of chemicals. Table

		fire tests on diuron		fire tests on dimethoate
		INERIS	Rhone-Poulenc	INERIS	VTT	VTT
		(large-scale)	(Tewarson)	(large-scale) CC(50kW/m2) CC (25 kW/m2)
		mg/g (b)	mg/g	mg/g (b)	mg/g	mg/g
	C02	1136	843	(a)	(a)	(a)
	CO	68	78	(a)	(a)	(a)
	NOx	25	5	2	14	4.5
	HCN	13	13	8	6.7	5.2
	HC1	160	144
	S02	-		175	560	510
	CH3SH	-		88	not determined	not determined
	soot	yes	yes	yes
	residue	yes	yes	yes	not reported	not reported
	(a) not relevant, since lab-scale tests were performed with pure active chemicals, contrary to large-
	scale tests in the INERIS gallery. (b) refen-ing to the pure active chemical

ACKNOWLEDGEMENTS

The authors wish to thank public or private bodies which make the work possible by their financial support or their technical assistance, namely : -the Commission of the European Community (supporting and promoting the Mistral I and II European projects) -the International Isocyanate Institute Ine (fire behaviour of aromatic isocyanates) -the French Ministry ofthe Environment (Industrial Environment Service).


G Senfaute

C Chambon

P Bigarré

Y Guise

J P Josienl

MICROSEISMIC CRITERIA FOR ROCKBURSTS HAZARD ASSESSMENT

Within the Provence opération Unit (France), microseismic remote monitoring is integrated within a research strategy bearing on areas submitted to dynamic phenomena risks. The purpose of this study is to characterise and analyse the induced microseismic activity during the opération of deep sites, in order to obtain identification criteria for the zones likely to generate such phenomena. The detailed study of the space distribution of microseismic focuses enables consistent corrélations to be demonstrated between the localization of the focuses, the changes in the state of stresses in the massif during the mining opération and the configuration of exploitation. The results hâve opened interesting perspectives into the analysis of pressure rockburst risks, by microseismic listening.

Introduction

The Gardanne (France) lignite deposit is located in the Centre and South of France Basin Coal mines. It is a sub-horizontal deposit, corresponding to a basin defined by the Mastrichian phase. The exploited coal layer offers a thickness of 2 to 3 mètres depending on the sectors. The wall and hanging wall, over a thickness of 250 meters, are of limestone nature. The rest of the underlaying séries is formed with clay maris and North American Rock Mechanics Symposium, Montréal 19-21 juin 1996 limestones. The opération is carried out according to the longwall caving method, currently at a depth of approximately 1,200 mètres. In the last few years, with the increasing depth of the site, various rockbursts occurred in the opération.

The particular susceptibility of the deposit to dynamic instability phenomena dictated the development of a number of studies in order to better comprehend the occurrence mechanism of thèse phenomena and therefore limit their effects, whilst forecasting the phenomena whenever possible. In this scope of work, a seismic listening network was implemented at the Provence Opération Unit. Since then, significant improvements were achieved thanks to this seismic network. They enable the microseismic activity recorded in the daily reports to be integrated and associated with data drawn from site opération feedback, therefore facilitating safety-related decision-making by the operators.

Description of the seismic chain

Data acquisition channel

The seismic network is comprised of eight vertical stations of uniaxial geophone type as well as two tridirectional stations (natural frequency = 1 Hz). Three vertical stations and two tridirectional stations are laid out on the surface. Data transmission from this surface network to the central site's mainframe is by RF, whereas four stations installed at the working stall are wired to the central site's mainframe (figure 1).

G

Ethernet network

G>

• V - s»

JUL

Triggering everj

On-line monitoring System

Figure 2: Seismic data acquisition and processing System. 1) event détection; 2) data acquisition on the master PC, switching of the PC to slave mode and pre-processing of the signal; 3) data transmission on multitask machine; 4) complète signal processing; 5) data stqrage and database type file System update; 6) interactive processing of the events in order to validate the calculated parameters.

Data processing

The automated processing run by a multitask machine in the network enables an automated bulletin to be edited for each event. The automated calculation of the wave arrivai time is firstly based upon the neuromimetric network technology (SCOP : : automated pointing connection System) which détermines a probable wave beginning présence range (Bigarré et al. 1995) and the upon the STA/LTA method (Allen, 1978) which involves a précise pointing of the wave arrivai time. An interactive treatment can be chained a few moments after the automated processing of the event, in order to validate the calculated parameters. Finally, a database type file System is updated permanently in order to allow a further statistic study of the fondamental parameters which characterise the microseismic activity generated by the various operated sites.

Focus location accuracy

The location of tremors is an essential parameter in the analysis of the microseismic activity. The absolute accuracy of the hypocentre calculation dépends on various criteria: the géométrie configuration of the network, the knowledge of the wave propagation rates and paths, the sampling frequency of the acquisition System as well as the pointing operation's reliability. Expérience demonstrates that the knowledge of a wave propagation rate model as close as possible to the real geological world is essential in order to obtain a proper accuracy of the coordinates (X, Y, Z, T) for each event. [START_REF] Senfaute | La surveillance microsismique de l'exploitation souterraine du charbon aux Houillères de Provence[END_REF] hâve developed a suitable wave propagation rate model for locating the focuses derived from the Gardanne area. It is a slanted multilayer model, which delivers locations with an accuracy of approximately ±50 mètres.

Space distribution study of microseismic events

Although ail rockbursts make up seismic events, ail seismic events do not degenerate into rockbursts. The intrinsic causes, if any, for such particular seismic events, are not well known and their shorten forecasts raise intricate problems. Therefore, the abrupt energy release may occur at various points with respect to the opération face front, for example:

-in the operated layer, ahead of the working face, -backward of the operated working face, -in the pillars located next to the opération, -in two or more of the above places, simultaneously or almost simultaneously.

Therefore, the study on the space distribution of the seismic focuses is particularly significant in the analysis of the microseismic criteria for evaluating a hazard. A detailed study on the localization of the microseismic focuses induced by the opération of working face 07 of the Estaque district at the Provence mined is carried out in this framework.

Working face 07 at the Estaque district is located to the South of the deposit. It is northeast oriented, with an inclination of approximately 10° westwards. The study period is between October 1992 and July 1993; it concerns 720 mètres of operated working face, for which a total of 2,223 microseismic events were recorded. The décision to study the space distribution of events associated with this working face was made according to the following criteria:

-this working face was operated following two différent configurations, which allows the behaviour of the microseismic activity to be studied in two separate situations (figure .3);

-the opération of this working face was affected by various dynamic phenomena;

-4--its central position with respect to the geometry of the seismic network allows a good accuracy in the location of the focuses to be expected. for working face 07 in the North Estaque district.

A high standard of accuracy in the wave arrivai time is a prerequisite for the proper location of the focuses. For this purpose, it was necessary to process manually 2,114 seismic events, that is to say, to carry out a manual pointing of the beginning and end of the wave on 19,026 seismic signais. This processing ensures a large part of the sought accuracy in locating the focuses.

Location of the microseismic focuses with respect to the operated working face

For each event, the distance between the working face and the seismic focus was determined, as well as the location with respect to the working face, that is to say, to the rear or to the ahead of the working face. The results demonstrate that microseismic focus distribution strongly dépends upon the opération geometry, namely:

-in geometry 1 (the working face runs along the old mined areas), the events are localised through the complète range of magnitudes ahead the front and behind the face, but they are more numerous to the ahead of the face, between 0 and 50 mètres from the working face;

-in geometry 2 (the working face runs along a pillar) the seismic events are also localised to the rear and to the ahead of the working face, but contrarily to geometry 1, they are more numerous to the rear, between 0 and 80 mètres from the working face.

-5-

Thèse results provide a first classification of the seismic events:

-Class A events : a population of events located ahead of the working face. The ahead of the working face which follows the progress of the work is an area of high dynamic stresses. The load application and the fracturing of the ahead of the working face would be the generating cause for thèse events.

-Class B events: a population of events located between 0 and 80 mètres to the rear of the working face. Several events, amongst which the caving-in of the back face as well as the particular opération configuration would account for the occurrence of thèse events.

Thèse results outline a correct consistency between the location of the microseismic focuses and the changes which occur in the sites in the course of opération. A quantitative study of the event distribution will enable concrète criteria to be drawn up, as regards the preferential location of the focuses.

Quantifying the microseismic focus distribution

In order to quantify the event distribution, the mined face is broken down into areas. In this break-down analysis, the working face is divided into 16 différent areas (figure 4).

Each area will contain the corresponding events (both in numbers and in percentages), classified by magnitude classes and geometry of exploitations. The event locations in thèse 16 areas will enable the preferential distribution of 2,114 microseismic events recorded during working face 07 opération to be analysed. -6-S mail microseismic events: magnitude < 2.0

In geometry 1 (the working face runs along the old works of an adjacent face), the microseismic events of a magnitude of less than 2.0 are localised within the operated working face and preferably to the front of the face at about 25 mètres from the working face (figure 5a), whereas in geometry 2 (the working face runs along a pillar), the events are preferably localised to the rear of the working face at about 25 mètres to the rear and to the outside of the operated face, that is, in the pillar area (figure 5b). The preferential distribution of this category of events highlights the bearing faces of the voids created to behind the working face. There, in geometry 2, the pillar adjacent to the opération would make up a signifïcant bearing area due to the void in the back face. The pillars which bound the old opérations make up overloaded areas. The opération working faces reaching this type of configuration area would create an overload in the areas already overloaded, which would resuit in microfractures which account for the occurrence of thèse small seismic events. In an opération adjacent to old works (geometry 1), the small events are preferably localised ahead of the working face (this would characterise the main bearing area of the voids created at the back of the face).

Strong microseismic events: magnitude >. 2.5

In geometry 1 (the working face runs along the old works of an adjacent face), the microseismic events are localised within the operated working face and preferably ahead of the face, between 25 and 100 mètres to the front (figure 6a), whereas in geometry 2

(the working face runs along a pillar), the events are also grouped within the operated panel and preferably to the front of the working face, between 20 and 50 mètres from the face (figure 6b). Thèse strong tremors (magnitude > 2.5) would be représentative of the dynamic loading and fracturing at the front of the working face. Part of this category of events is also localised in the area of the old works in the adjacent face. They would be associated with the opening or slipping of former fractures revived during the opération of the new adjacent panel. Syrek et Kijko (1988) obtained similar results in the Polish coal mines. Thèse authors demonstrated that the most energetic events are preferably localised ahead of the mined face.

Microseismic focus location and rockbursts

The opération of working face 07 at the Estaque district was affected by rockburst events.

Thèse phenomena are localised in an opération configuration where the operated panel runs along the old works of an adjacent face (geometry 1, figure 6a). AU thèse seismic events associated with damage (rockbursts) are localised next to the working face front, between 0 and 50 mètres to the front and on the side of the old works in an adjacent face.

Thèse results demonstrate that strong events (magnitude > 2.5) localised next and ahead of the working face, on the side of the old works and essentially between 0 and 50 mètres to the front of the working face, would be microseismic events creating a potential risk of rockbursts.

-8-4.

Conclusion

The study of the space distribution of 2,114 microseismic events highlights consistent corrélations between the location of the focuses and the load application areas, in the course of opération. The results show that the opération configuration appreciably influences the preferential location of microseismic events.

In terms of the évaluation of a hazard based upon the location of the focuses, the results seem to indicate that when the focuses of strong tremors are very close to the operated working face front (essentially ahead of the face and on the side of old works in an adjacent face), a potential risk of pressure rockburst would exist. This could make up a microseismic criterion of dynamic instability hazard. The identification of this "criterion" is a major milestone and is used as guideline in the research for far more detailed criteria.

Bibliography

Allen V., 1978. Automatic earthquake récognition and timing from single traces. Bull Seism. Soc. Am. 68, No. 5, pp 1521 -1532.

Figure 1 :

 1 Figure 1: Geometry of the local Provence U.E. seismic network

Figure 3 :

 3 Figure 3: Schematic view of the opération configurations (geometry 1 and geometry 2)

Figure 4 :

 4 Figure 4: Graphie illustration of working face 07 break-down into areas, in order to quantify the seismic focus distribution. The X axis, at the centre of the square, corresponds to the mined face, whereas the Y axis, at the centre, corresponds to the central axis of the working face.

Figure 5 :

 5 Figure 5: Preferential location of small seismic events (magnitude < 2.0) induced in the course of opération of working face 07 at the North Estaque district, according to two separate opération configurations: a. geometry 1; b. geometry 2.

Figure 6 :

 6 Figure 6: Preferential location of small seismic events (magnitude > 2.0) induced in the course of opération of working face 07 at the North Estaque district, according to two separate opération configurations: a. geometry 1; b. geometry 2.

  Ben Sliman K., Besson J.C.,Mandereau G., Chambon C, 1990. "La surveillance sismique : un outil d'aide à la planification des chantiers miniers sujets aux phénomènes dynamiques" (Seismic monitoring: a tool for planning mining sites submitted to dynamic phenomena). 3 r£ ^ Franco-Polish Symposium, Wroclaw. Studio Geotechnica et Mechanique. Vol XI No. 1 and 2, pp 55-68 Bigarré P., Labiée S., Dodo Amadou A., Piguet J.P., Josien J.P., 1995. "Utilisation de réseaux neuromimétriques pour la localisation automatique d'événements microsismiques" (The use of neuromimetric networks in the automatic location of microseismic events). International Congress on Rock Mechanics, Tokyo. Gibowiez S., 1990. Keynote lecture: the mechanism of seismic events induced by mining, 2°d. Int. Symp. Rockbursts and Seismicity in Mines, éd. Fairhurst, C. Balkema, pp 3-27. Senfaute G., Bigarré P., Josien J.P., Mathieu E., 1994. Real-time microseismic monitoring; Automatic wave processing and multilayered velocity model for accurate