INTRODUCTION

Sensors used in explosimeters for the detection of explosive gases are generally catalytic. The most widespread are catalytic pellets.

A metallic oxidation catalyst is heated to a sufficiently high temperature to oxidize the gas. The oxidation reaction increases the temperature of the catalyst which increases its electrical resistance, whose amplitude is proportional to the gas concentration.

In the 1950s we developed a sensor of this type for the mining industry. It was based on a platinum filament and destined to detect methane, responsible for mine explosions.

The filament is distinguished from the catalytic pellets by its operating temperature: 1000°C instead of 600°C, which confers on it the advantage of being relatively insensitive to fouling and catalyst poisoning. The disadvantage, however, is rapid wear, preventing it from operating permanently.

The measurement technique thus involves energizing the sensor just long enough to make the measurement and then turning it off for as long as the application permits.

The first instruments of this time could run for 100,000 measurements, or about 9 months at the rhythm of one measurement every 4 minutes.

By improving the filament heating technique, the measurement capacity has been increased considerably: 10,000,000 measurements with the last methanemeter recently marketed, or a lifetime of 1.5 years at the practically continuous measurement rhythm of once every 5 seconds.

Endowed with these performance characteristics, the platinum filament sensor is today a reliable solution for explosimetry, in particular in environments polluted with certain catalyst poisons such as sulfur-containing products, which other catalytic sensors resist poorly.

In addition, the technique involving brief heating pulses, applicable only to filament sensors since it requires a very low thermal inertia of the sensor, has enabled new procedures to be developed for the identification of certain combustible gases or vapors and for the measurement of methane concentrations up to 100% v/v.

DESCRIPTION OF THE SENSOR (figure 1)

It is composed of two spiral filaments made of pure platinum : a detector filament and a compensating filament, both 80 fxm in diameter but of unequal lengths.

The filaments are enclosed inside a hemispherical chamber made of sintered metal, enabling the natural diffusion of gases. They are welded to massive high thermal inertia antennas, that emerge from the chamber through isolated ports.

An activated charcoal filter inside the chamber surrounds the filaments and protects them from catalyst poisons, in particular silicones.

OPERATION

Detector filament

During the measurement period, a current I passes through the filament, raising its temperature in the center to 1000°C by the Joule effect.

Its electrical resistance Rd is a function of temperature T, which depends on I and on the quantities of oxidized gases.

The temperature of the filament is not the same along its entire length because of the cooling caused by the metallic supports.

Catalytic activity occurs on the central spires, whose temperature is higher than 800°C (figure 2).

The detector filament is appropriately treated to eliminate impurities in platinum.

Its temperature is determined in order for catalytic activity to be maximal at low methane concentrations, lower than the L.I.E., and to burn off products that could foul its surface, thereby reducing the active sites on which the oxidation occurs.

Compensating filament

This filament does not undergo a purifying treatment and is heated at a lower temperature, about 600°C on the central spires. At this temperature, catalytic activity starts at the stoichiometric concentration of 10% v/v for methane.

The compensator has a dual role: it compensates the thermal effects that interfere with detector measurement (temperature and thermal conductivity of the ambient medium), and detects high levels to remove any doubts concerning detector measurement (figure 3).

Re (600°C) = 0.73 Q, Rc(0°C) = 0.29 Q 3. CHARACTERISTICS 3.1. Lifetime
Sensor lifetime is that of the detector filament. Platinum wear begins at 600°C and is particularly high around the operating temperature of the filament (at temperatures close to 1000°C, the rate of wear of the platinum filament is proportional to the cube of temperature). It is thus desirable to control this temperature throughout filament life, in particular when there is a supply of additional heat resulting from the oxidation of a gas.

Filament wear, greater in the central zone, results in a reduction in the cross-section of the wire, increasing resistance when cold Rd(0°C) and when hot Rd(T). This increases the explosimeter readings by a constant quantity and thus requires frequent recalibration of apparatus zero (reading in pure air).

Sensor lifetime thus depends on the duration of the measurement and on filament temperature during the measurement.

The various heating techniques used in several generations of methane detectors in order to increase lifetime have attempted to reduce the duration of the measurement and to control temperature.

Response time of the methane deteefor (figure 4)

The response time of a methane detector or an explosimeter is the time it takes to indicate 90% of the value of a concentration of gas G.

The response time of the instrument depends on :

-the response time of the sensor (Tsens), which is the time the gas takes to fill in the combustion chamber,

GTM mine gas detector

Since the sensor can be placed at a distance from the measurement device, this heating mode was chosen to overcome voltage drops in the cable and in the contacts.

It has a classical bridge structure. A constant intensity 0.74 A current passes through the filaments and raises them to operating temperature in about 1.5 seconds. The zero potentiometer is used to adjust Ub to offset the shift caused by sensor wear.

When a gas is oxidized on the detector, Rd increases, Ua increases more than Ub, and the measurement signal (Ua -Ub) increases : about 50 mV per % volume CH4.

Measurement time is defined as the time the operator requires to read the galvanometer display.

Constant current heating offers a very low measurement capacity, with an excessively long response time. The measurement rhythm of methane detectors operating according to this principle was set at 4 minutes in order to obtain an acceptable compromise between response time, sensor lifetime (9 months) and the frequency of recalibration (weekly).

Filament temperature, proportional to Rd(T) x 1^, increases with increasing filament wear. Wear is also considerably accelerated by gas oxidation: the heat supplied by the current is supplemented by those arising from the oxidation reaction: these instruments have a life time of only 30,000 measurements in 2% v/v CH4.

On the other hand, this technique provides considerable sensitivity, about 50 mV per % v/v. 4.2 Constant bridge voltage heating (figure 6): remote mine gas detector CTT63/40 T multifunction mine gas detector GTM67A During a measurement, voltage at the terminals is adjusted to 1300 V.

If gas is oxidized on the detector, Rd increases, thus I decreases and Ua increases.

The temperature increase of the filament in the gas is less than in the constant current technique, since the heat added by the oxidation reaction lead to a decrease in those supplied by the current which decreases.

Similarly, when the filament wears, Rd increases but I decreases. Detector temperature increases as the filament wears, but less than in the constant current technique. 7) : remote mine gas detector MT85 f multifunction mine gas detector GTM741

Constant partial voltage heating (figure

The potential differences at the terminals of the compensator and detector filaments are held constant. The potential difference at the terminals of the two filaments mounted in series is adjusted to 1.300 V.

A potential limiting circuit prevents Ua from exceeding 0.760 V by shunting a current (Imeas) when Rd increases The decreased current in the detector attenuates the temperature increase caused by gas oxidation or filament wear. The effect is more pronounced than in the case of the constant bridge voltage set-up.

Increased measurement capacity is partially due to the reduced heating time, brought down to 1.3 seconds (in order to enable the measurement to be read, a circuit keeps the measurement in memory during filament extinction).

The intensity of the heating current, high at the beginning since the filaments are cold, enables operating temperature to be reached in about 1 second (figure 8).

The measurement signal is memorized during the last 300 ms.

Characteristics of the GTM741 mine gas detector using this technique :

-Measurement rhythm :15 s, -Sensor lifetime : 1 year, -Response time : between 15 and 30 s, -Calibration frequency : weekly. The increase to operating temperature occurs very rapidly by a constant high intensity current. When this temperature is reached, a circuit maintains the resistance at Rd (1000°C) regardless of gas concentration, by acting on current intensity : if additional heat are supplied by the oxidation of a gas, the circuit decreases the Joule effect heat by reducing the current.

Rd(T) = RlxR3/R2

Temperature rise of the filament lasts 0.2 s; I = 1.4 A (figure 10).

When Rd(T) = 1.03 Q, the controller reduces intensity in order to maintain Rd at this value.

Variations of the plateau potentiel Ud is the measurement signal. The measurement is memorized before the current is cut. This heating technique confers a very long lifetime on the sensor: 10,000,000 measurements and independent of the quantities of gas oxidized by the filament. This is due to 3 factors :

-reduced heating time, -temperature control during measurements, -slight decrease in filament temperature as it wears: with increasing wear, Rd(0°C) increases. Since Rd(T) remains constant (1.03 Q) filament temperature decreases.

Wear is independent of the gas history of the filament. In this case, it depends only on the number of measurements, which enables zero drift to be simulated in order to carryout an automatic correction and thus considerably reduce maintenance operations.

Consumption is very low as a result of the short heating time and the suppression of the compensating filament.

Comment: the compensating filament can be replaced by a low consumption temperature sensor (thermistor, semiconductors, etc.). Although changes in relative humidity are not compensated, their influence on measurements remains negligible, since they are lower than 0.1% v/v CH4 at 80% R.H.

The "removal of doubt" at high methane concentrations, which was assured by the compensator and made indispensable by the low measurement rhythms in the initial methane detectors, can be replaced by a "locking" alarm circuit, as in continuous measurement explosimeters.

A practically continuous measurement rythm of 5 seconds leads to a consumption of 0.024 Joule, i.e. a mean current of 0.07 A.

The device requires a power supply higher than 1.2 V. A 2-element 2.5 V nickelcadmium battery is sufficient.

Characteristics of the GTM90C mine gas detector using this technique :

-Measurement rhythm: 5 s, automatically increases to 2.5 s if the concentration increases, -Sensor lifetime : 19 months, -Response time : 15 to 18 s, -Response time for the alarm to an explosive concentration : < 5 s, -Consumption : 0.09 A (0.02 A for the electronic circuits), -Automatic zero correction : every month.

Summary table

Table 1 (see appendix) summarizes progress in the characteristics and performance of the different techniques.

Conclusion anrj

The properties of the platinum filament sensor, designed 30 years ago for mining applications, are today optimally used as a result of the perfected conditioning of its power supply. At a similar response time, its electrical consumption is lower than that of low consumption catalytic pellets.

Its high operating temperature effectively protects it against certain catalyst poisons.

Its field of application now extends to industrial and domestic gas detection. The technique of heating by short pulses, specific to the filament with low thermal inertia, enables the principle faults of catalytic oxidation to be overcome, with several improvements: measurement range limited to the stoichiometric value of the air-gas mixture, and absence of selectivity.

Examples :

-0-100% v/v methane detector (figure 1

la)

The heating pulse is decomposed into two temperature plateaus :

-1 st plateau at T < 400°C : the filament operates as a hot wire detector and furnishes measurements of concentrations higher than stoichiometry, -2nd plateau at 1000°C : the filament gives the measurement of concentrations lower than stoichiometry.

The zero of the hot wire detector is done automatically each time the measurement is lower than the L.I.E.

-Identification of the gas (figure 1 lb)

The catalytic activity of a combustible gas or vapor as a function of oxidation temperature follows a law specific to each species. The combustible product can be identified by measurements made at different temperature plateaus. Zeros at the 3 temperatures are done automatically when the air is pure.

these new techniques involving signal processing and algorithm execution, and is continuing work on the platinum filament sensor in order to improve its performance characteristics ; thus, a new smaller one, to reduce response time, is being developed.

-

  the extinction time (Text) separating two consecutive measurements, -the occurrence of the measurement in relation to the gas concentration. If Text > Tsens then : Tsens < response time < Tsens + Text 3.3 Electric consumption Wmeas = energy consumed during the measurement = (Rd x Id 2 + Re x Ic 2 ) x Theat Pmeas = power dissipated during the measurement = Rd x I 2 Pmean = mean power = Pmeas x Theat/(Theat + Text) Mean power takes into account the extinction time of the filament. It determines battery autonomy for portable apparatus. Theat = filament heating time = duration of measurement Text = duration of filament extinction4. HEATING TECHNIQUES AND PERFORMANCESA number of different techniques have been used since the creation of the sensor, as developments in electronic components made them possible. We will describe them in the chronological order of development of the methane detectors that used them.

4. 1

 1 Constant intensity heating (figure 5^ : remote mine gas detector CTT63/40.

4, 4

 4 Heating hv rapid ffpineratiire H^ and constant detector filament resistance (figure9) : GTM90C ming gas detector

Fig. 1 .Fig. 2 .

 12 Fig. 1. Platinum filament sensor

Table 1

 1

			d.d.p. at terminals detector filament (Volt)	intensity through the filament (Ampere)	filament resistance (Ohm)	consumption during the measurement (Joule)	life time or capacity of measurements
	constant	air	0.76	0.74	L03	2.9	100,000
	intensity cm 2%	0.86	0.74	1.15		30,000
	constant	air	0.76	0.74	1.03	2.9	250,000
	Dnage voltage CH4	0.80	0.72	1.12		100,000
		2%
	constant air	0.76	0.74	1.03	1.25	2,000,000
	poTlldi
	voltage CH4 2%	0.76	0.71	1.08		1,000,000
	constant	air	0.76	0.74	1.03	0.36	10,000,000
	resistance	CH4 2%	0.72	0.70	1.03		10,000,000


Francis Wojtkowiak

D Thibodeau

Comportement de la couronne soutenue par cäbles d'ancrage d'un chantier d

published or not. The documents may come

Comportement de la couronne soutenue par câbles d'ancrage d'un chantier d'exploitation de la mine souterraine de sotiel (Andalousie-Espagne)

l INTRODUCTION

Le renforcement des structures minleres par boulonnage ä l'aide de cäbles ä ancrage reparti a connu ces dix demieres annees un grand developpement dans les exploitations minieres souterraines d'amas polymetalliques d'Amerique du Nord, et plus particulierement du Canada, des pays nordiques tels que Süede et Norvege, et d'Austratie. Alors que la pose de ces cäbles se mecanise de plus en plus, on est force de constater que le dimensionnement de ce renforcement est encore aborde de manlere tres empirique et gagnerait sans aucun doute ä etre rationalise.

En vue d'elucider le comportement mecanique de tels cäbles et leur role exact dans le soutenement des excavations dans les massifs de röche dure fracturee, l'Universite Laval de Quebec a mis au point un dispositif original de mesure des efforts qui s'exercent localement sur ces cäbles, la jauge TENSMEG 70 [START_REF] Choquet | Development and field testing of a tension measuring gauge for cables bolts used äs ground support[END_REF], fabriquee et commerclalisee maintenant par la societe Supportek. Nous avons utilise ces dispositifs pour etudler le comportement de cäbles d'ancrage soutenant la couronne d'un chantier d'exploitation de la mine souterraine de Sotiel (Andalousie, Espagne).

L'ensemble des mesures d'effort effectuees sur une dizaine de cäbles d'ancrage indique clairement que la couronne renforcee se comporte typiquement comme un assemblage de blocs delimites par les plans de

-AE (1-V) tir \ 1 / 2 E (1-f) (l+i/) (l-2r) (l+l/) (l-2f)pgj
dans laquelle E est le module de Young, V le coefficient de Polsson et ft la densite du massif rocheux. Le caicul des contraintes induites par les tirs n'a ete effectue que pour les trols dernieres phases d'acquisition, comprises entre le 19 fevrier et le 17 octobre 1990, car, ce sont les seules qui presentent suffisamment de donnees pour un traitement statistique.

L'analyse en composantes principales confirme bien l'existence d'une relation entre les contraintes induites par les tirs d'abattage et les efforts s'exercant sur les cäbles, puisque le pourcentage explique par le premier axe principal est respectivement de 50,6 %, 43,2 % et 46,2 X pour les phases 3,4 et 5. Pour une meme phase d'abattage, cette analyse a pennis egalement de correler le comportement de certains cäbles et de comparer les perlodes de mise en tension des uns aux periodes de relächement des autres. Enfln, plusieurs analyses en composantes principales ont ete effectuees sur les donnees de la phase 5 en decalant les tirs d'un certain nombre d'intervalles de temps de maniere ä quantifier le delai de reaction des jauges ä un tir donne. La correlation entre les efforts mesures et la contrainte induite par le tir est maximale pour un Intervalle de temps de 7 j ours.

Les resultats de mesures sur les cäbles et de l'etude statistique nous permettent d'assimiler le comportement de la couronne

Effort en kN

Cäble n* 22 Ce logiciel est constitue de deux codes distincts derives de l'algorithme de base de [START_REF] Warburton | Implication of keystone action for rock holt support and block theory[END_REF] qui decrit la defonnation d'un massif rocheux fracture comme etant un processus qui se passe exclusivement le long des discontinuites, les blocs proprement dits etant rigides et indeformables. Le prämier code permet de reconstituer par Simulation un reseau de discontinuites suivant l'algorithme defini par [START_REF] Heliot | Generating a blocky rock mass[END_REF]. Le deuxieme code analyse la stabilite de chacun des blocs suivant la theorie de blocs-des proposee par [START_REF] Warburton | Implication of keystone action for rock holt support and block theory[END_REF]. Pour les blocs qui peuvent se deplacer, le type de mouvement est determine (chute libre, plan, diedre...) et un coefficient de securlte vis ä vis des risques de chute lui est assigne en fonction des caracteristiques mecaniques des discontinuites et des forces de confinement (Asof 1990). L'analyse des resultats de Resoblok se fait ä partir des statistiques de base (moyenne, ecart-type...) et de la distribution du nombre et du volume total de blocs instables obtenue pour un ensemble donne de simulations.

f a Cäble n°23 v , 0 '? " 3 • »«(!• • • , * ^ ,-•. ^.S^' V 4-^tfr 10 • ^ ^^y yä«.,^ a* • »' " »• ^D IMIllllfl^l i'™llll ^-M^ftMtt
De maniere ä juger de l'efficacite du soutenement par cäbles d'ancrage, la stabilite du chantier minier a ete etudiee en premier lieu sans soutenement, puis en tenant compte du schema de boulonnage au cäble pratique ä Sotiel. En tenae de cohesion, nous avons caicule la contribution d'un cäble d'ancrage ä la resistance au cisaillement d'un joint ä partir de i'equation proposee par [START_REF] Rosengren | Preplaced cable bolts for slope reinforcement in open cut mines -Seme congres international de mecanique des roches[END_REF], en supposant un angle d'Installation du cäble de 30° avec la normale au joint, un angle de dilatance de 0° et un angle de frottement de 30° pour les joints. Une cohesion de 3 MPa a ainsi ete caiculee pour les joints renforces.

79 simulations ont ete effectuees pour chaque cas ä savoir : excavatlon d'un chantier minier sans soutenement (cohesion nulle) puis avec soutenement (cohesion de 3 MPa pour les joints). Les principaux resultats de ces simulations sont recapitules dans le tableau n" l ci-apres. Avant de commenter ces resultats, signalons que, sans soutenement, 32 X seulement des simulations effectuees donnent plus d'un bloc instable avec une preponderance (25 2) pour l'Intervalle compris entre l et 10 blocs instables. 51 t de ces simulations ne donnent aucun bloc Instable. Du point de vue du volume total des blocs instables, 50 1 des simulations conduisent a un volume total inferieur ä 0,001 m mais pres de 20 T. correspqndent ä un volume total superieur ä 10 m .

Avec un soutenement, 85 2 des simulatlons n'indlquent aucun bloc instable. L'Intervalle compris entre l et 10 blocs instables ne represente plus que quelques pourcents de l'effectif. En volume, pres de 95 % des simulations obtiennent un volume total de blocs instables inferieur au m . Ces premiers resultats demontrent, si besoin en etait, l'effet benefique du renforcement par cäbles d'ancrage sur la stabilite des couronnes.

Ceci dit, ce traitement prellminaire des resultats des simulations aet essentielle ment l'accent sur l'lmportance en effectif des blocs,de tres faible volume, inferieur ä 0,001 B . Lors des operations de purge, la plupart de ces blocs sont elimines et presentent, dans tous las cas de figure, un facteur de risque beaucoup noins important que les blocs plus volumineux qui ne peuvent pas etre elimines par simple purge. II faut donc mettre l'accent dans l'Interpretation des resultats des simulations sur les blocs de plus grande taille, qui mettent veritablement en cause la securite du personnel et du materiel d'extraction, en les ponderant. La technique de ponderation choisie a ete decrite par [START_REF] Xu | Simulation statistique de discontinuites et evaluation de la blocometrie de massifs rocheux. Application ä l'analyse de l'ecoulement et de la stabilite[END_REF]

  II s'agit des jauges n° 2 des cäbles n° 19, 20 et 27 et des jauges n° 3 des cäbles n° 9, 20 et 22. Les efforts mesures par ces jauges sont faibles et sont compris entre 0 et 30 kN. Toutes les autres jauges indiquent par contre des forces dont l'intensite varie dans le temps. Les cäbles subissent en effet des cycles de chargement et de dechargement d'amplitude et de duree variables. Les efforts qui s'exercent sur les cäbles peuvent etre localement tres importants, superieurs ä 100 kN, voire atteindre la Charge maximale admissible par le cäble d'ancrage (250 ä 270 kN) provoquant ainsi sä rupture et/ou celle de la jauge. Lorsque le cäble est sollicite en decä de sä llmite de rupture, il est frequent d'observer apres un pic de Charge une phase de dechargement du cäble plus ou moins rapide (quelques jours) suivie d'une stabilisation des efforts s'exercant sur le cäble ä une intensite comparable voire Interieure ä celle precedent la phase de chargement. L'examen detaille des courbes de reponse des cäbles d'ancrage fait apparaitre une relation de cause ä effet entre les tirs d'abattage dans les chantiers voisins et les efforts dans les cäbles peu de temps apres le tir. Pour conf Inner cette

	raccourcissement de la base de mesure du par exemple ä des efforts de compression : l'axe des ordonnees des diagrammes de la figure n° 5 ne comporte donc pas d'echelle pour les valeurs d'effort negatives. De l'ensemble des mesures effectuees en conditions reelles d'exploitation sur les	jours en fevrier 1989 ; 64 jours, de cäbles lors des differents tirs, la fevrier ä avril 1990 ; 47 jours de juin ä distance du tir par rapport au chantier aoüt 1990, et enfin 26 jours de aoüt ä experimental ainsi que la quantite octobre 1990. Les trols tranches de mine-d'explosif utilisee doivent etre prises rai ont ete respectivement abattues en en compte. Jaeger et Cook (1979) fevrier 1989, fevrier 1990 et en octobre mentionnent que Duvall et al. proposent de 1990. caiculer la vitesse particulalre maximun A
	neuf cäbles d'ancrage, 11 ressort que le	ä partir de l'equation suivante :
	Fig.3 Implantation des cäbles Instrumentes comportement de chaque cäble depend d'un certain nombre de facteurs geometriques (tels que la position du cäble dans le chantier d'exploitation : milieu de la couronne, entre piliers residueis,etc), structuraux (tels que la fracturation dans laquelle H et n sont des constantes 3 INTERPRETATION DES MESURES EFFECTUEES :,V2 \n SUR LES CÄBLES D'ANCRAGE A -H La figure n° 5 represente, en fonction du temps et des principales phases de tirs d'"abattage, l'evolution des efforts naturelle et induite par les tirs empiriques, W la masse en kg d'explosif mesures en trois points differents de d'abattage de la couronne), et de la utilisee et r la distance en m entre la chaun des cäbles d'ancrage n° 22, 23 et presence d'importantes heterogeneites Position du tir et le centre du chantier 27. Notons que sur ces diagrammes, les lithologiques (ecailles schisteuses) au Instrumente. A partir de cette vitesse ordonnees positives correspondent a une sein du minerai. particulaire, la contrainte induite par le elongation de la jauge, donc du cäble, La repartition des efforts le long d'un tir ff . (MPa) peut etre caiculee ä l'aide soumis ä des efforts de traction. Les jauges utilisees, de par leur conception, ne sont pas adaptees ä la mesure du meine cäble est rarement homogene et de l'equation proposee par Jaeger et Cook surtout eile evolue d'une phase d'abattage ä l'autre. Rares sont les jauges qui indl-(1979) :
	quent, pendant pratiquement toute la duree
	de l'experimentation, la meine intensite
	discontinuite najeurs. Une analyse en composantes principales a permis d'etablir une relation certaine entre les contraintes induites en couronne par les tirs d'abattage ä l'explosif et les variations d'intensite des efforts s'exercant sur les cäbles. Pour completer cette premiere analyse des resultats et ameliorer notre comprehension des Interactions du massif rocheux fracture et du soutenement par cäbles d'ancrage, une etude de • stabilite de la couronne a ete entreprise en mettant en oeuvre le logiciel Resoblok, developpe ä l'Ecole des Mines de Nancy. Dans sä forme actuelle, ce logiciel est un ensemble de deux Codes. II s'agit, en premier lieu, d'un generateur de blocs definis ä partir de champs de fractures simules prenant en compte les caracteristiques statistiqües de la fracturatlon naturelle. La stabilite de chaque bloc alnsi defini est ensuite analysee independamment des autres blocs, selon la theorle du bloc-cle de Warburtpn (1987). Une premiere aodelisation OUEST geometrique de la fracturatlon du gisement de Sotiel ä l'aide de Resoblok a ainsi permis de demontrer la necessite et Fig.4 Coupes schematiques de la couronne du chantier minier experimental d'effort. observation purement qualitative, une analyse statistique en composantes principales a ete realisee sur les deux variables suivantes : les efforts mesures par les jauges et les contraintes induites par les tirs en couronne du chantier minier experimental. Pour tenter de correler les efforts s'exercant sur les
		surtout l'efficacite du renforcement des

  un chantier d'extraction. La repartition et l'evolution des efforts alnsi mesures dependent bien sur d'un certaln nombre de facteurs geologiques et de la methode d'exploitatlon, mais le comportement des cäbles est sans aucun doute correle aux tirs d'abattage contigus. Ces tirs ont pour effet de perturber l'etat d'equilibre du massif rocheux fracture qui se comporte comme un assemblage de blocs renforce par des armatures qui en assurent egalement l'integrite. Le dimensionnement du soutenement par cäbles d'ancrage suppose donc, dans le cas de la mine de Sotiel, une meilleure comprehension des interactions du massif rocheux et du soutenement. Pour ce faire, de telles experlmentations doivent se poursuivre dans d'autres contextes geologiques et miniers. Elles doivent aussi etre menees parallelement au developpement de nouvelles approches pour la modelisation geometrique de la fracturation naturelle et du comportement mecanique des massifs rocheux, telles que les modeies de blocs qui fournissent dejä des resultats interessants et directement exploitables par l'Ingenieur. REMERCIEMENTS Les auteurs remercient Mrs C. Alvarez et J.A. Ros de la societe miniere Almagrera pour leur collaboration active et efficace dans l'experlmentation realisee ä Sotiel, et la Direction Generale "Science, Recherche et Developpement" de la Commission des Communautes Europeennes pour son soutien financier au projet.

						geometrique de la fracturatlon du giseoent
						de Sotlel.
						5 CONCLUSIONS
						L'experimentation menee dans la mine
						souterraine de Sotiel, en conditions
						reelles d'exploltation, a permis, en
						premier lieu, de valider un dispositif de
						Besure des efforts qui s'exercent sur des
			. Elle consiste ä	cäbles ä ancrage reparti soutenant la
	diviser la sonme des volumes compris dans	couronne d'
	un Intervalle de volume prealablement
	choisi (par exemole, classe des blocs -
	superieurs ä l m et Interieurs ä 10 m ),
	par la somme de tous les volumes obtenus
	pour un ensemble donne de simulations, et
	de reporter la valeur cumulee en fonction
	de la racine cubique de la bome supe-
	rieure de la classe concerr-e.". ta courbe
	ainsi obtenue permet, au meine titre qu'una
	courbe d'analyse granulometrique, de
	determlner le volume cumule des blocs
	representant le passant ä une certaine
	fraction du volume total des blocs
	instables. A titre d'exemple, dans le
	tableau l, nous avons reporte le volume
	cumule du ou des blocs representant le
	passant ä 35 X, 50 t et 65 2 du volume
	total des blocs instables.
	Tableau n° l : Resultats des analyses de
	stabilite de blocs
	Blocs	Nombre	Volume total en m
	insta-sans	avec	sans	avec
	bles	cäbles cäbles	cäbles	cäbles
	Minimum	0,0	0,0	0,0	0,0
	Maximum	23,0	7,0	720,0	50,2
	Moyenne	2,2	0,2	33,0	0,7
	Ecart-	4,1	0,9	120,0	5,7
	type
	V 35X			233,0	19,8
	V 50%			343,0	31,3
	V 65X			512,0	46,6
	Avec le soutenement, on observe une augmen-
	tation considerable de la securite du
	chantier puisque le passant ä 35 2 du volu-
	me total des blocs correspond ä un volume
	cumule des blocs instables de l'ordre de
	20 B au lieu de 230 m en l'absence de
	cäbles d'ancrage. Notons qu'en avril
	demier, un bloc de 177 m s'est detache
	de la couronne non soutenue d'un chantier
	minier a la sulte d'un tir d'abattage
	contigu au chantier. Ce volume est du meme
	ordre de grandeur que les voluaes de blocs
	instables determlnes par la modelisation


Large scale testing in the INERIS fire gallery:

A major tool for both assessment and scaling up of industrial fires involving chemicals The INERIS Fire Gallery is one of the large scale test-rigs being at disposal of INERIS' researchers (and their financial Sponsors) to carry out experimental studies in the field of industrial risks and Environmental concems.

Devoted especially to the fire problem, the Fire Test Gallery (fig. l) comprises a 50 m long horizontal wind tunnel of about 10 m 2 cross section, ending in a 11 m high 'tower'. This vertical segment is divided into two operating zones : the upward rectangular cross section ( 6 m2) element, recently refitted with extended measuring facilities, is housing main of the gas sampling equipments connected to the 'mixing point'.

The downward (circular cross section) is equipped with a water curtain device acting äs a first stage washing unit and air-cooler. Beyond the tower the gas stream is crossing a gas cleaning unit (IQ g series a dust dry filtrer connected to an adjustable water scrubber) which removes gaseous and solid polluants or noxious compounds. Thig equipment can remove tens of kilogrammes of non desirable compounds such äs HCN or HC1 potentially emitted m a single fire trial and thus allows experimental scenarios involving products with high toxic Potential (äs regards their decomposition products).

An adjustable exhaust fan placed between the gas cleaning unit and the stack allows controlled Ventilation of the fire zone at flowrates comparable to those observed in industrial premises Of course, both the horizontal and upward vertical sections walla comprises refractory linings and insulation material layers authorisine the users to carry out experiments with hight heat release rates and temperatures (peak thermal power up to 10 MW, temperatures up to 1200 °C) 2 The füll scale fire fest main features Among the advantages claimed of the full-scale approach, let us point out the following : * it is a realistic fire scenario äs regards the industrial fire disaster event:

* quantities of products submitted to a fire scenario may typically ränge between 100 kg and 1000 kg for bulk material or commercially packaged in bags,or liquid products stored in plastic drums * l : l scale may be used for fire scenarios related to manufactured industrial apparatus or building materials (electric transformers, other electric devices, rolling stock, insulation panels...), * significant information are reasonably expected at each stage of a classical fire development [ease of ignition, fire growth mode, eventual seif extinguishment tendency, datas related to the flash-over and postflash-over periods,... (see fig. 2). * Mass effects generally masked at the laboratory scale (DIN fumace, Tewarson apparatus, cone calorimeter...) may very often be revealed through this large-scale approach * Extensive qualitative and quantitative information are collected and recorded in real time and may be re-used further for modelling or extrapolation studies purposes thanks to the availability of a wide set of measuring or monitoring instruments i.e. :

-continuous or quasi-continuous control of gaseous effluents performed by gas analysors for numerous species such äs CO, COg, Oa, SOa, total HC, NO, NOg, NHa, HC1, HCN.NgO, COCIz, some amines...), -thermal impact assessed by thermocouples and heat fluxmeters or eventually by means of infra-red thermography, -video camera recorders, allowing füll witnessing the fire evolution which may be performed m a play-back mode , -additional analytical means (use of impingers or suit collectors for instance) to quantify other chemical impact of the fire (vapors or aerosols, suits, solid residues...). * Heat Release Rates measurements based on oxygen consumption 2 may now be applied with a good accuracy in the same way it is systematically operated on the cone calorimeters or Tewarson apparatus. Correlations studies are thus expected to get the best chances of succes, since this parameter is now believed to be of prime importance in the laws governing the fire conditions t prope/'/i ture pras-ü J bl l i t i es of 'spun tannouf; ext ine t j nn FSg. 2: tvpical curve offire devfiooment * moreover, äs concerns the chemical point of view, where the scientific community is still largely lacking of crucial information, there is no actual äquivalent for the assessment of the plume fire source term generally required in the framework of the safety studies demanded now by national äs well äs international regulations (Seveso Directive, EPA new regulation on the storage of chemicals) 2 M. JANSSENS, " Measuring Rate of Heat Release by Oxygen Consumption", Fire Technology, August 1991 We do not deny that the method suffers from some drawbacks : such experimentations are known to be rather costly and besides they only reveal quantitative information on aimed physical or chemical Parameters. To cope with the fact, one must carefully prepare the testing Programme, and eventually use complementory tools prior to the fullscale experimentation in order to enlarge the expected benefit.

Qualification and experience achieved

Since the commissioning of the unit, over 10 years of fruitfui experience has been gathered, leading to several fully controlled largescale procedures suitable for various purposes :

-home-standard procedure for palletised solid products (powders, granulös...) with various ignition Systems (gas bumers, radiant panels, solvant pool-fire) -pool-fire test procedures (with management of a constant liquid layer in trays) for more or less flammable liquids (size ranges easily between 0,25 m2 and 2 m2 in fully controlled Ventilation conditions) -use of a calibrated wood-crib äs ignition procedure (mining equipment or tunnel linings)

The following tests results could be made partially available to our future 'MISTRAL' partners (especially for the modelling validation steps of FLAMME 2 or 3) äs a manner to join scientific efforts on related topics even if at the moment no European partnership with CEA has yet been contracted :

-thermal and chemical datas on various pesticides (Diuron, Dimethoate, other commercially important agro-chemicals of various types (organo-phosphorous, carbamates, ...) and fertilisers (NPK type) 3 -equivalent information on basic chemicals of PUR manufactoring (di-isocyanates) 4-detailed quantitative information (mostly thermal) on the impact ofa calibrated wood crib (300 kg and 450 kg), obtained in the framefork of European Research contracts 5 -sets of chemical datas on nitrogen containing gaseous compounds issuing from chemicals involved in industrial fires.

" C. CWIKLINSKI, " Incendie dans les entrepöts de produits phytosanitaires. Les apports de l'essai en grand", R.G.S Journal, n 0 110, febr. 1992 (M French).

Besides, qualification work on both the Fire test Gallery and the applied test methodologies have been fairly largely undertaken at both national and international levels :

-The INERIS pool-fire testing procedure has been chosen by the I.I.I 6 . (a trade society grouping main isocyanates worid producers) for the assessment of the fire behaviour of two of the main di-isocyanates available on the market The procedure was also successfully applied in the framework of the European EUREKA 499 "Firetun" project. related to fire safety into traffic tumiels, -Several studies were carried out with an important experimental phase taking place in the fire test gallery in the recent past äs experimental supports of ECSC research projects, -besides, äs often äs needed, INERIS applies to home-made softwares under constant development named Bigexp or Jehinc (which could be at last a usefui link with MISTRAL modelling tasks) or conventional 3D fluid dynamic modelling packages (see fig. 3).

Draft view of some recent INERIS results issuing füll scale experimentations

Work has been performed with both following purposes :

-focused on accurate targets in the framework of commerdal Services -more general aims leading to better scientific knowledge of behaviour of materials submitted to fire conditions ^International Isocyanate Institute Inc.

* Following the Nantes NPK fertilisers warehouse fire which in France induced the Authorities' decision to evacuate 30,000 people out of the town, duplicating the accident at a realistic scale inside the Fire test gallery was decided. We reproduced a bulk storage capacity inside the gallery ; the ignition procedure was arranged in relation with the presumed cause of the accident ("hot point" induced by electrical failure) Fig. 4 gives an overview of the chemical characterisation of the plume fire obtained through the experimentation (1000 kg submitted to thermal decomposition leaving 512 kg of solid residue

  at Ineris Fire Department ** Chemist Engineer, Head of Ineris Fire Department l The INERIS 1 Fire test facüity

fig. 3 :

 3 fig.3:3D modelling offlowlinps inside the INERIS Gallerv at ionction of horizontal and vertical sections (inducgd bv a wood crib) computed yith the Phopnics code.

  ).On behalf of the International Isocyanate Institute, we carried out a series of experiments on TDI pools with the aim of evaluating the fire hazard. Fig.6presents some of the results.

	identified compound		mass (kg)	volume (m3 at Ö°C)'
	C co HCN	O	a	| ln^l 220 0,4	112 9,3 . .-..^..0,3,,," "
	NOx (äs NOg)				0,1		0,05
	S (isocyanates)				<ö,öi		-
	SOa					8,4		2,9
	S (mercaptans) S (aldhehydes)		S	i	E <0,02	-	.	12,96 -
	soots					0		-
	condensables		40, water, dimethoate	-
	identified compound CO phosphorated products	mass (kg) 7,2 (traces)... not determined	volume (m3 at 0°C) 5,7 -
	COa HC1 Fig. 5: chemical characterisation of the fire pl^ime from the dimethoate fire 7,35 8,0 9,0 3,7 4,9 (120 Sät 400 g/l) 2,8 Clg NH4C1 87,7 36,7 43 Buming pools of TDI 7
	NaO					39	19,9
	NOs					2,15	1,0
	HN03					36	12,8
	N2				57,6/76,5	46,1/61,2
	HaO total test ID # Quantity ofTDI 8 (kg)			l 25	238/215 488	2 75	291/268 420
	Fig. 4 : global composition offumes issuing H NPK ternarv fertiliser "fire" pool area (m") 0,25 1,00
	air flow rate (m3)			"10000		»10000
	burning rate (kgin^min" 1 )			1,38		2,0
	42Pestiddes effective HRR (kW)		122		560
	gas concentrations : * The fire behaviour of dimethoate, CgHi^N^PSg (concentrated solution), C02 (%) 0,25 1,05 belonging to the organo-phosphorous pesticides family was analysed in CO (%) 70-80 350 various fire scenarios (impact of the solvant alone, use of full-commercial NOx (ppm) 10-12 10-12 packaged product...). HCN (ppm) (2) 40
	TDI (mg/m3) Fig. 5 presents main chemical figures obtained from a fire scenario 10-15 8-10 gasyields (mg/g) : involving 120 l of dimethoate (60 bottles of l liter and 60 liters buming initially äs a pool), disposed on a pallet. -COg 2090 1620
	-CO					41,1		36
	-HCN				(1,2)		4
	-NOx (äs NOg)			10,4 -12,5	1,7-2
	-TDI				5-7,5		0,7 -0,9
	molar ratio C02/CO			32		29
			Fig. 6: characterisation of burning pools ofTDI
	7 G. MARLAIR, P.H. PRAGER, H. SAND ; "The hehaviour of commercially important
	di-isocyartates in fire conditions" -Part I ; toluene di-isocyanate (TDI) ; submitted to
	Fire and Materials
	8 commercial mixture 80/20 ofthe two isomers

INERIS : Institut National de l'Environnement Industriel et des Risgues,, Parc technologÜJtie ALATA -F60550 VERNEUIL-en-HALATTE, France

G. MARLA1R, H. SAND, "Assessment of the fire ha.za.ra. of a burning pool of Toluene di-isocyanate (TDI)", Journal of CellularPolymers, vol 11 n'' l, 1992 °ECSC Research contracts n ° 7262 31223 03 & 7262 01 31225


The present comprehensive report draws from two of the three sections of the safety documentation :

the safety arrangements which are the foundation for the Fixed Link Operation the operating procedures describing the sequencing of activities.

The third part deals with : the operating ruies which detail the required actions.

In view of the control of safety responsibility exercised by the govemmental authorities (1), who assess the hazards and risks to which both users and statt present during operations are exposed, the Safety Authority have called on English (2) and French consultants to help them in their task ot analyzing the Safety Case.

The subject ot this report is limited to the assessment by the French consortium created on this occasion around EDF-CLI and INERIS. Noteworthy is that the EDF-CLI consultants have references in the tields of industrial satety and in particuiar nuclear safety, and the INERIS consultants in classitied industrial plants. (7) For the time being, the scope of this present analysis is limited to the preliminary safety case report ; all associated remarks are therefore to be taken äs provisional. Two more elaborate reports, the Interim and the Final, are being drafted and shall integrale comments by the Safety Authority.

It is important to specify that the consortium's remit does not include the examination ot security matters which are studied within olher torums. Also, since certain studies are not yet completed, in particuiar on operational safety management. signalting and on board or centralized control and command, the tollowing comments are incomplete and likely to be amended.

A first section ot this document shall briefly describe the Channel Tunnel Fixed Link.

A second section shall look at the respective roles ot the deterministic and probabilistic approaches which have both been retained for the Satety Case Report.

Finally, a third section shall contain provisiona! comments ot the consultants tollowing the Preliminary Satety Case Report.

l. SYSTEM DESCR1PTION

The Concession Agreement given to Eurotunnel applies to the Channel Tunnel Fixed Link (total length approx. 50 km, with 37 under sea). This transport System provides a permanent fixed link beiween the road and rail networks ot France and the United Kingdom. It comprises a rail System and a road System inside the terminais on either side of the Channel. These terminais are linked by two single track rail tunnels and one central Service tunnel dug under the Channel.

1.1.

Modes of Operation

Two modes of Operation apply to the Channel Tunnel.

The rapid transfer of road vehides (tourist vehicies, coaches, lorries ... and their passengers) by way of shuttle trains.

The passage of through-trains (passengers, freight) thus linking via the tunnet, the national rail networks for all types of trains, including the high speed trains of the French "TGV" type.

Both diesel and electric tocomotives can be used to pull rolling stock.

In normal operating conditions, both running tunnels are used in one single direction each. However, at several places along the Channel Tunnel, trains can pass from one track to the other using crossovers. This allows for operations inside the tunnel to continue when a section of track iocated between two successive crossovers is out of Service-This could arise for example : during tunnel maintenance (railway equipment, civil engineering general equipment) following a rail incident preventing traffic on a section of track (breakdown of a train, faifure of a catenary, ...).

The main functional characteristics of the Link are the following :

The Channel Tunnel shall operate for rail and road traffic round the dock and year round.

The signalling System will allow for the passage of 20 trains per hour in each direction at the beginning of operations. Once the supplementary equipment has been installed, the allowance shall be for 30 trains per hour in each direction. 160 kitometers per hour shall be the maximum authorized speed along normal sections, except for freight trains.

For shuttle trains, total journey time shall be approximately 35 minutes inside the tunnef, plus 15 minutes for departure and boarding formalities, namely a total of 50 minutes.

Terminals

Traffic is controlled from the terminais which comprise all the facilities required for rail traffic manag ement äs well äs infrastructure for receiving passengers, for customs controls and for the transfer of road traffic on to the shuttle System.

On each terminal, a rail network is comprised of: a rail loop (on the British side, the loop is in a cut-and-cover), platforms ensuring access to the shuttle trains, junctions with the national rail networks, stabling and maintenance areas for rolling stock (depots, workshops, yard).

I.3.

Other equipment

Concerning tunnel and track civil engineering : rail tunnels are connected through crossovers and piston relief ducts, rail tunnels are connected through communication cross-passages to the Service tunnel.

tunnel low points are equipped with sumps for the collection of seepage waters.

Among other fixed equipment:

a Ventilation System used for the renewal of air within the tunnel, for the swift extraction of smoke in the event of a fire, for pressurising the Service tunnel to keep it smoke free to shelter passengers in the event of a fire, for the supply of fresh air to technical rooms. It is comprised of two separate networks -the Normal Ventilation System and the Supplementary Ventilation System only used during abnormal or degraded operating conditions ^;

an in-tunnel cooling System using a water cooling network to absorb the heat generated by the trains ; the technical rooms are equipped with forced Ventilation sucked in from the Service lunnel ; a fire-fighting System comprised of an in-tunnel detection System and fire mains and in the technical rooms, automatic extinguishing Systems ; electricity supplied from the sub-stations for traction power supply and all auxiliary networks ; a catenary and earthing circuit ; rail signalling ; a main traffic control center on the U.K. side and a stand-by one on the French side ; control and communication Systems including : an in-tunnel emergency telephone network a network for communication between terminais an in-tunnel radio communication System.

II. OBJECTIVES OF THE "PROBABILISTIC AND DETERMINISTIC" APPROACHES

"Deterministic" approaches serve mostly to demonstrate the strength of the concept by applying Codes of Practice and well established design regulations and Standards. "Probabilistic" studies, on the other hand, are used to demonstrate the acceptability / tolerability of residual risks resulting from beyond design failures.

The approach selected, both probabilistic and deterministic, will lead to determine reasonably acceptable measures for reducing the risk.

Probabilistlc approach.

A probabilistic analysis uses a quantitative risk assessment (QRA) in order to determine the acceptability of these said risks on the basis of the defined criteria. A QRA is based on the following : risks identification, predicted accident rate, modeling of accident consequences, caiculations of the risk exposure of a person. assessment of the main factors contributing to the overall risk.

In the case of a System of such original design äs the Channel Tunnel Fixed Unk, any application of a quantitative risk assessment must be done with great care äs it is difficult to refer to any statistics on equipment failure since this equipment is of an innovative design. However it appears fully justifiable to work from the consequences of accident scenarios which have happened in Underground transport Systems. To that effect, a detailed analysis of all of the accidents which have already happened, is enlightening.

No accident scenario must be waived aside however low its occurrence frequency may seem ; also, the decision to carry a given class of dangerous goods needs to be made in the light of all its consequences, in particular concerning whether the release of toxic products or a fire are possible (6). Besides the goods classed under dangerous goods, other combustible products may present a risk which is far from negligible when in a confined environment. The history of lorry fires in the Mont Blanc and Frejus Tunnels demonstrate that reels of cotton thread or plastic objeds have produced very touchy situations due to the thick smoke which was generated.

Risk criteria and acceptability.

One basic aspect is, of course, the risk acceptability criterion. A difference must be made between individual risk and societal risk (2). And it is important to point out that the French regulatory approach on transport is undergoing quite an evolution (4), contrarily to the British approach which, for instance, sets a tolerability threshold for individuai risks at 1 x 10'3 per year for workers. However this figure is based on accident statistics data and only takes into account existing facilities.

As a reference, it was also accepted that a passenger travelling by train from London to Paris should be in the pari of the journey through the Tunnel, äs safe äs in the equivalent journey (i.e. 50 km) from either Waterloo and Folkestone, or from Sangatte and Paris.

Concerning the societal risk, practically speaking, curves plotting accident frequencies against the number of fatalities will be used. These curves were obtained from rail accidents statistics.

In the risk criteria approach, it is mostly the risk of fatality which has been taken into account.

The method shall essentially compare the quantified risks of undesirable events with the selected risk criteria . taking into account the functional analysis and the development of fault and event trees.

The British approach has chosen the ALARP principle (As Low As Reasonably Practicable). Within the whole ALARP probability region which limits are in a 1/1000 ratio, any risk is tolerable only if its reduction is impracticable or if its cost is grossly disproportionate with the improvement gained.

This region shows an upper level above which risk is intolerable (for high probability of occurrence of an undesirable event) and a lower level below which risk is considered äs negligible (for low probability of occurrence of this event) and therefore tolerable.

In the case of the Channel Tunnel Fixed Link, the Safety Authority has accepted this latter approach.

11.1.2.

Undesirable events

The main initiating events studied under the QRA are fires, collisions and derailments.

Evaluating their frequency is done through a fault tree.

The consequences of these events are modeled using an event tree, a tree which brings out the undesirable events in fine.

Deterministic approach

The main purpose of the deterministic approach, both on design and operational management aspects. is to prove, for different situations, that the severity of consequences is äs limited äs possible.

For this case study, a definition of safety parameters with associated criticality is to be dealt with for every Situation.

In order to consider human and technical failures, measures are to be taken and graded in different levels :

Prevention which consists in designing, constructing and operating the Installation so äs to give it protection to avoid failures and to limit their consequences throughout a ränge of selected normal and abnormal situations. Often important safety factors are included mainly at the design stage.

Monitoring and protection of the installation during operations which is assured by operating arrangements, procedures and rapid shutdown / interlock Systems, while the functionality of equipment is verified by means of periodic tests and non-destructive inspections. Operating ruies are additional to safety devices.

Protection against occurring incidents or accidents äs a result of technical or human failures, despite these safety and operating arrangement. The installation is then equipped with very reliable safeguard Systems whose sole function will be to limit the serious consequences of these incidents and accidents to acceptable levels, taking account of their estimated probability.

Finally, preparation for the management of serious by highiy untikely accidents would assist in controlling serious or complex situations which have not been predicted.

The safety parameters which encompass all aspects of the System (technology, human and organizational), relate to each of the levels listed above. All arrangements confining them within a given region are äs many barriers limiting the severity of an incident or an accident.

6-

The safety parameters refer to various situations which were selected for the envelope character of the operating situations under study, hence, it is far more sensible to establish envelope operating situations in order to identify the most relevant safety parameters. Nevertheless furtner Steps of the analysis will deal with the exhaustiveness of the approach.

To carry out such an analysis of a Situation, a functional breakdown is necessary in order to bring out the failure conditions by following a procedure which is quite similar to a failure modes and effects analysis (FMEA).

ooOoo

The final advantage of tnese two approaches is that the obtained results can be compared through a cross analysis. Thus, both are based on possible failures whose knowledge is the keystone for operating safety organization. For Operation, the deterministic approach results in catalogue of safety parameters for which the probabilistic approach allows to adapt the convenient Operation monitoring according to the severity and gravity of undesirable events.

III. PROV1SIONAL COMMENTS OF THE CONSULTANTS ON THE PRELIMINARY SAFETY CASE REPORT.

Organization

The consultants started by defining Iheir working method and the work procedures which would allow for the best relationships between the consultants and the Safety Authority (fig. 1).

A major objective was to try and obtain a common position from the French and British consultants. This proved possible : reports were drafted in common and submitted to the Safety Authority.

Concerning work procedures, the organization was based on a grid showing the EDF-CLI and INERIS consultants 1 specialties (see fig. 2). This grid is identical to the one considered by Electrowatt, the English consultant.

Since various situations to be analyzed called for specialized consultants, lead roles were defined äs well äs processing methods (see fig. 3).

2. Analysis of the Preliminary Safety Case Report

The following main provisional remarks concern the Preliminary Safety Case Report.

The scope of these comments is limited to : 111.2.1. The quantitative risk assessmenl and the risk criteria (probabilistic section).

111.2.2.

Safety management linked to the definition of safety parameters (deterministic section).

The authors draw the attention to the fact that the following comments are provisional since only a limited number of scenarios have been studied so far and it is therefore impossible at this time to judge the exhaustiveness of the analysis.

A reminder also to point to the fact that operational characteristics can be normal, reflect a degraded mode or an emergency Situation. This implies that the safe operational envelope must be defined in order to predict any passing from one operational mode to another.

lli.2.1. Quantitative risk assessment and risk criteria

A preliminary analysis was carried out taking into account a sample of plausible events : Eight events were considered :

Fire in a vehide in a tourist shuttle Fire in a vehide in a heavy goods vehide (HGV) shuttle Fire in a passenger through-train coacn Derailment of a freight train Derailment of a tourist shuttle Derailment of a passenger through-train Derailment of an HGV shuttle Collision between two trains (general).

Noteworthy are the three initiating events which have been selected : fire, derailment and collision.

At this stage of the study, it is worin reminding that the circumstances in which these various events occur snall most likely need to be studied in greater depth, taking into account in particular the types of dangerous goods, substances and materials carried, the consequences of incidents inside the Service tunnel, the operating circumstances and the exact nature of the trains accepted through the tunnel. Others events could also be studied : for instance the release of toxic products and failures of utilities.

The analyses by event trees were quantified mostly on the basis of British Rail operating statistics. The analysis will need to be extended to include the statistic results of other rail companies.

-

In view of the various types of trains, a more detailed analysis is still to be made, which would include other events and all of the operating conditions.

The consultants have insisted on the need to also include statistics from the Operation of Underground railways and reliability data determined by equipment firms.

Finally, uncertainty äs to the statistical data used needs to be specified.

8-

111.2.2.

Safety management linked to the definition of safety parameters.

Safety operating management organizes all activities of Operation, maintenance and relationship with the environment outside the Fixed Link System.

This organization is based on the definition of a sei of safety parameters. These parameters must in turn be maintained within regions or in states ailowing for a safe Operation.

It must provide for experimental operational feed-back from the System through the recording and analysis of incidents and accidents, and collect reliability data. In that way. the design and related safety studies (hazard analysis, FMEA, fault trees and event trees) can be verified or corrected on the basis of lessons drawn from accidents or foretelling incidents, and from the obtained reliability data. The organization of this feedback is to be defined, when the operating management is finalized.

It must also control the modifications. in order to ensure that their impacl on the design will indeed be taken into account, in particular for the catalogue of safety parameters and for a correct commissioning of the latter.

Working in conjunction with the system's designers, maintaining the evolutive nature of the safety studies ought to be an objective of the operational safety management System.

The present development of the Safety Gase has not yet allowed for designing the operational safety management System. So far, a list of safety parameters corresponding to a few given situations has been established. This list must be äs comprehensive äs possible and provide a classification following the definition of a criticality rating. Thus far, it applies to the following situations : normal Operation of a tourist shuttle normal Operation of an HGV shuttle operating a Channel Tunnel train on a single track in a section dose to a portal operating a freight train on a singte track in a central section of the tunnel evacuation outside and along the shuttle in the event of a fire on board a tourist shuttle evacuation to the Service tunnel in the event of a derailment of a tourist shuttle evacuation to the service tunnel in the event of a fire on board an HGV shuttle uncoupling a Channel Tunnel train operating on a single track near a portal.

At this stage, the analysis of the "normal Operation of a tourist shuttle" Situation is the only one which has been given to the consultants. It provides a first series of safety parameters with their criticality rating.

-In this Situation n° 1, the present analysis emphasizes signalling failures äs the most critical, which was predictable. This first remark highiights the amount of attention which must be given to the reliability and the maintenance of the signalling System.

The anafysis of the Channel Tunnel Safety Case Report remains pending . So far, the consultants make provisional conclusions on the Preliminary Safety Case and other documents such äs safety arrangements (volume B : System description and volume F : transport of dangerous goods) and risk criteria. These conclusions were given to Eurotunnel through the meetings of Safety Authority for the Safety Case, meetings at whicn the consultants were invited. Many aspects are still quite incomplete (safety parameters, description of accident scenarios). This task alfows for the integration of both the French and British approaches to risk analysis.

The objectives are : a presentation of design coherence testing out this coherence by comparing the risk with a predetermined criten'on and applying the ALARP principle using the most extensive catalogue of safety parameters, to identify a coherence between design and safety studies on the one hand, design and the operational safety management system on the other.

One of the expected advantages of this work between authorities, operators and consultants, is to determine äs best äs possible what the safe operating conditions for such a System are. Experimental feed-back into safety management including incidents and accidents is a major asset to improve the levet of safety.

Finally, cross-comparing the results of the quantitative risk analysis with the list of safety parameters is essential and will have to be done in order to ensure the coherence and exhaustiveness of the Pixed Link Safety Case.

  FIGURE l

ANALYSIS OF SITUATIONS

Breakdown of the leader roie:


Christophe Proust

BXPBRIMBNTAL DBTBRMINATION OF THB MAXIMOM FLAMB TXMPBRATURBS AND 07 THB LAMINAR BOTNING VBLOCITIBS FOR SOMB COMBUSTIBLB DUST-AIR MIXTÜRBS

come

Experimental determination of the maximum flame temperatures and of the laminar burning velocities for some combustible dust-air mixtures

The "tube method" and a "direct method" have been used in order to detemine laminar buming velocities. Values of some tens of cm/s have been obtained. The agreement between both methods is satisfactory indicating that the "tube method" seems adequate for measuring laminar buming velocities of two phase mixtures. With this Information the previously observed (Veyssiere and Proust, 1990) dependency of Sl with respect to the geometry of the experimental setup is discussed.

Thin (25 pm and 50 pm) thermocouples have been used to measure *>axinium flame temperatures. Caiculation of the theorical values of this parameter have also been performed and a significant diacrepancy between theoretical and experimental values appears. The physical meaning of this discrepancy is addressed.

Standard explosion parameters (KST, Pmax,-) have also been ^etermined with a "20 litre-sphere" for the mixtures investigated. The existence of links between these parameters ^d the buming properties of the mixtures like the laminar buming velocities and the maximum flame temperatures is discussed briefly.

Fifth International Colloquium on Dust Explosions, Varsovie, 19-22 avril 1993, pp. 161-175

l-Introduction

In view o£ • -h e psssifc.le consequences of a dust explosion, it is acknowledged ^hd-, there ^.s a need for assessing ehe reliabilicy ':f the tools • _;3ed to assess the explosion hazard anü of the protection ".eir.-c'is. Surely fcr this, a better understandinc of ehe mechanisms c£ ^st expiosion development is compulsary. In particular a better knowledge of the different flame propagation regimes i s necessar^'. In this area, some progresses have been performed in the recent years (Proust and Veyssiere, 1988;Rzal et al., 1991;-Kauffman et al., 1987;Wolanski et al., 1990;Mazukiewicz et al., 1990;Pu et al., 1988)

j. -Bxperimental defcaila

Among the various techni-TJes available (Tai et al., 1988;[START_REF] Bradley | Buming rates in turbulent fine dust-air explosions 22nd[END_REF]Proust and Veyssiere, 1988;Smoot and Horton, 1977;[START_REF] Marshall | Partide size effect and flame propagation control in l^[END_REF]Mazurkiewicz and Jarosinski, 1990), it appears t..^at using a "flame propagation tube" (Proust and Veyssiere, 1-5S) seems to be well fitted with respect to the determinaticn c; Sl and of several other flame characteristics. We thus selected this latter technigue. Three kinds of corribustible particie-air mixtures were tested.

The particies were: starch dust, lycopodium, sulfur flower. Some characteristics of the particies and of the suspensions are presented in table l. The (mass) average partide diameter is in the ränge of a few tens of micrometers.

2-Maxiaufli flame fcemperatures

2.l-Results

The results obtained with the 50 »im thennocouples are presented in figure 2, 3, 4 respectively for starch dust-air mixtures, sulfur flower-air mixtures and lycopodium-air mixtures. The junction of the thennocouples were installed on the axis of the tübe.

Caiculations of the theoretical maxilnum flame temperatures were also perfomed, assuming no heat losses, taking into account the production of a great ränge of species äs well äs dissociation at high temperatures. The results are presented on the same figures äs the experimental values.

The scattering of the results might be partly due to the experimental error on the composition of the mixture but other phenomena might also be important such äs the thennal inertia of the sensor and the perturbations induced in the flame front by the holder of the thermocouple.

If mean curves are plotted through the experimental points and compared to the theoretical curves, it appears that the measured values are globally lower than the theoretical ones. For instance, for nearly stoechiometric conditions, the difference is of the order of 750 °C for starch dust-air Suspension and 500 °C for the other mixtures.

In order to analyse this temperature difference, the influence of the transducer need to be considered.

2.2-Influence of the tranducer

The influence of the thennal inertia has to be considered. Simiiar resuits were found previously (Proust, 1988;Proust;and Veyssiere, 19385 and, since

2.3-Heat losses of ehe flame by radiation

This investigation has been limited to fiames propagating in starch dust-air suspensions.

The light emitted by the flame front in the direction of the walls and not absorbed or reflected (toward the flame) by the particies of the Suspension is lost. The characteristic length for the attenuation of the intensity of the light by the Suspension is of the Order of a few cm (Proust, 1988) so that the amount of energy lost by flame radiation is likely to depend on the geometry of the experimental setup äs suggested by Veyssiere and Proust (Veyssiere and Proust, 1990).

On figure 6 are plotted the measured values of Tfmax obtained previously (Proust and Veyssiere, 1988) in similar conditions (similar thennocouples, same mixtures) except that the experimental setup is two times larger than the present one. Corresponding data from the present work are also shown on this graph. It can be shown that the measured value of Tfmax are simiiar in both Setups indicating that heat losses by flame radiation do not seem to have a great influence. But further work is needed to confinn this.

3-Laminar burninff velocitiea

Several methods can be used to determine the laminar burning velocity (Lewis and Von Elbe, 1987;[START_REF] Andrews | The burning velocity of methane-air mixtures Comb[END_REF] but with the experimental setup used in the present work , two of them are particularly suited: the "direct" method and the "tube" method (Proust, 1988;Proust and Veyssiere, 1988; Veyssiere et Proust, 1990;.

3.l-"Tube" method

With the experimental conditions considered, Sl can be derived from the flame speed and shape according to the following expression:

Sl = S . Ap / Af [i]
where S is the flame speed, Af the flame front area and Ap the projected flame area on a plane perpendicular to the direction of flame propagation. Provided the flame geometry is simple enough, the deierrr.ination of Sl by this method is simple and only requires a video equipment. for lycopodium-air suspensions (47 cm/s) . For sulfur flower-air and starch dust-air mixtures, Sl is of the order of 20 cm/s.

3.2-"Direct" rngi-hnF

or the "tube" method to give reiiable results some requirements have to be fulfilled. Por instance the laminar buming velocity has to be constant over the flame front. The "direct" method allows the detennination of the local buming velocity. In this latter method Sl is directiy derived from its definition:

Sl = s . n -U . n [2]
where n i s the unit vector normal to the flame front at the point under consideration and U the flow velocity (vector).

The experimental detennination of Sl with this method is difficult since S and U have to be sufficiently accurate and U has to be detennine very dose to the flame front. Por this, the tomographic technique was used (for further details see: Proust and Veyssiere, 1988) . The particie velocity is derived from the luminous traces left by the particies on the video pictures (figure 12) . The flame speed is derived from the flame movement on several successive frames . The applicability of this method seems limited to lean mixtures for which the movement of a single particie can be isolated. Purthennore, the precision on "î s not very good (perhaps ±25%).

Some experimental detenninations of Sl with this method have been performed with the mixtures considered in this paper and are presented in figures 9. 10 and 11. Given the accuracy of the "direct" method, the results are in good agreement with those obtained with the "tube» method, indicating that the latter seems reiiable with the experimental conditions used.

3.3-lnfluence of the tube diameter

The laminar buming velocities of flames propagating in starch dust-air suspensions have been obtained (Proust and Veyssiere, 1998) with experimental conditions very similar to those described previously (cf 5 1.1) except that the experimental setup was two times larger (tube diameter 0.2 m). These results are presented in figure 9.

it appears that the results obtained in the present work are approximately 20 % sinailer indicating a significant influeace of the geometry of the experimental setup (Veyssiere and Proust, 1990) . The origin was firstly attributed to heat losses of the flame by radiation. However. äs shown before (cf 5 2), the maximum flame tanperatures are very similar in both Setups indicating that heat losses (by radiation), all other phenomena excluded, are not likely to justify such a Variation.

However, ahead of the flame front is generated a flowfield which can .be seen on the pictures obtained with the tocnographic technique. It can be shown (Proust, 1988;Lewis and Von Elbe, 1987) that the existence of this flow is closely linked to the flame front geometry through expression [2] . This flow might be partly induced by the gravity forces acting on burnt products. pushing the flame upward (elongating it) and "forcing-the Suspension to flow around the flame front but other phenomena such äs flow velocity profile in the bumt products (Guenoche and Jouy, 1952;Marskstein. 1964;Lewis and Von Elbe, 1987) might also be considered.

Aerodynamically, the flame tip might be regarded äs a Stagnation point. Near the walls. the flow is submitted to friction and a boundary layer appears. In these regions, velocity gradients are produced and the flame is "stretched" (Lewis and von Elbe. 1987). Since Sl is dependent on the magnitude of this Stretch (Matalon, 1983), it appears that flame Stretch might be taken into consideration in order to understand the influence of the geometry of the experimental setup on Sl possibly in connection with other factors äs for instance heat losses of the flame [START_REF] Libby | Strained premixed flames under nonadiabatic conditions Comb[END_REF] .

4-Standard explotivity paraaeter«

Standard explosivity Parameters for starch dust, lycopodium and sulfur flower in Suspension in air have been detennined with the classical "20 litre sphere". The maximum explosion overpresure pmax and the well-known KST coefficient obtained are presented in table 2. pmax represents the total (thermal) energy released during the cciribustion and can thus be compared to Tfmax. In table 2

5-Conclusion»

In this paper are presented some results of measurements of the laminar buming velocities, Sl. and of the maximum flame temperatures. Tfniax, for starch dust-air mixtures, lycopodiumair mixtures and sulfur flower-air mixtures (mean partide diameter between 25 and 45 faa} .

The classical "tube method" has been used in order to determine laminar burning velocities. Values of some tens of cm/s have been obtained. In order to assess he validity of this method, it has first been used for premixed gaseous mixtures (CH4-air) in the experimental setup described. The results are compared with the best available data for these mixtures and the agreement is satisfactory. in addition, some direct measurements of Sl for the studied particie-air mixtures have been performed by using a tomographic technique allowing the simultaneous determination of the flame speed and mixture velocity ahead of the flame front. The results are compared with those obtained with the tube mechod and the agreement is again satisfactory indicating that this method seems adequate for measuring laminar buming velocities of two phase mixtures.

Thin (25 pm and 50 pm) thermocouples have^been used to measure maximum flame temperatures. Caiculation of the theorical values of this parameter have also been perfonned and a significant discrepancy between theoretical and experimental values appears. This discrepancy is partly due to the thennal inertia of the transducers.

Standard explosion Parameters (KST, Pmax,-.) have also been determined with a "20 litre-sphere" for the same mixtures. The physical meaning of these Parameters is briefly discussed in relation with laminar burning velocities and maximum flame temperatures. Prom the few data available, it appears that Pmax varies in the same way äs Tfmax indicating that Pmax seem to represent conveniently the total amount of energy released during the explosion. It also appears that KST is not directiy linked to the combustion and flame propagation charactistics of dust-air mixtures and it is suggested that classifications of dust according to KST values might be different from those derived from the buming properties.

  conceming laminar, cellular, turbulent and detonation propagation regimes. The laminar flame propagation regime seems particularly interesting since, provided the experimental conditions are convenientflame temperature) should depend oniy on the mixture and seem good candidates for ehe definition of explosion Parameters which depend only on the nature of the mixture. Moreover, refering to the information availaüle (Proust and Veyssiere, 1988; conceming the similarities and differences between gas and dust explosions, it might appear that the other flame propagation regimes {except detonation) could be linked to ehe laminar one. Frorn this point of view, the knowledge of the interesting. In the following are presented and äiscussed experimental methods and results of the measurement of the laminar buming velocities, Sl,

  Temperature measurements of laminar flames propagating in starch dust-air mixtures have been perfonned with finer thennocouples (bead diameter= 25ttm) installed on the axis of the tube. The results are presented on figure 5 together with the measurements made with the 50 pm thennocouples and the theoretical values of Tfmax. Mean curves are also plotted. It appears that the rtenqperature determined with the 25 (im thermocouples are about 250/300 °C larger than those obtained with 50 pm thennocouples indicating a significant influence of the thermal inertia of the tranducer at least for the case of flames propagating in starch dust-air mixtures. Although, the time constant of the 25 pm thennocouples is about ten times smallertemperatures and the experimental data: for a nearly stoechiometric mixture the experimental data are about 500 °C lower than theoretical values.

  kind of dust is shown in figure 8. The values of the laminar buming velocities versus the nature of the dust and the concentration of particies in the Suspension are presented in figures 9, 10 and li. The results are scattered. One cause of

	front for one this dispersion is the difficulty for estimating with precision
	the flame front area. For	stoechiometric conditions, the
	laminar buming velocities are given in table l. These values
	are of the same order of magnitude than for some gaseous
	mixtures such äs CH4-air. The largest values have been obtained
	Th&refcre, this methcd has been ex-censively applied to determine
	tr.v. lair.inar	bu:~n_-';g • --e-^cit ; • ;?s	for	the dust-air mixtures

This metnod has been used for the determination of the laminar burning velocities of premixed gaseous flames propagating in the experimental setup c; figure l. Homogeneous methane-air mixtures were used since reliable data are available for these mixtures

(Ar.drews and Bradley, 1972'

. Obtained values of Sl are displayed in figure

7

with a curve representing the best available data in ehe litterature. 11 appears that the present results are very cloets to the published values indicating that the "tube" method i-s applicable in the preser-t experimer-tal conditions.

  have been reported the theoretical values of Tfmax for the stoechiometric mixtures considered (taking the experimental data instead of theoretical values does not change the following development). It can be observed that the lowest value of Pmax is obtained for sulfur flower-air mixtures which also exhibit the lowest value of Tfmax. KST should be liriked to the rate of energy release. It seems that KST could be related to Sb = Sl . Tfmax / To where To is the initial temperature of the mixture. Sb represents the volumetric production rate of bumt products by unit flame area. in a closed vessel, it can be easily shown that this rate is related to the rate of pressure rise. Sb has been caiculated for the mixtures under study (table 2) . Considering KST values, it appears that the rate of energy release of starch dust in air i s lower than for sulfur flower-air suspensions. Comparison between Sb values indicate that within the experimental accuracy, the combustion should give the same rate of pressure rise. This indicate that the rate of pressure rise in the Standard

	apparatus depends on additional factors	(such äs initial
	turbulence) and that KST might not be directiy linked with the
	flame properties. In these circumstances, a classification of
	the dusts established on the basis of flame propagation and
	combustion properties might be different froro another based on
	KST values. Consequently, it might be preferable to consider KST
	äs a scaling parameter for explosions developping in a "similar"
	way äs in the 20 litre sphere. Same care is required when it is
	intended to use this Parameters for explosions occuring in very
	different conditions like in pipes.

  On flame Stretch Comb.Sei. andTechn., vol. 50, pp. 219-229 MAZURKIEWICZ J., JAROSINSKI J. (1990) Temperature and laminar burning velocity of comstarch dust-air flames 4th Int. Coll. on Dust Explosions, Porabka-Kozubnik, PolandPROUST Ch. (1988) Contribution ä l'etude des mecanismes de propagation des flammes dans les melanges heterogenes gaz-particules solides PhDThesis, submitted 19th April 1988, üniversity of Poitiers, France, ref 129 PROUST Ch., VEYSSIERE B. (1988) Fundamental properties of fimes propagating in starch dust-air mixtures Comb.Sei. andTechn., vol. 62, pp. 149-172 PU Y., JAROSINSKI J.. TAI C. S., KÄUFFMAN C.W., SICHEL M. (1988) The investigation of the feature of dispersion induced turbulence and its effects on dust explosions in closed vessels 22nd Int. Symp. on Comb., pp. 1777-1787 RZAL F., VEYSSIERE B., MOÜILLEAU Y.. PROUST Ch. (1991) Experiments on turbulent flame propagation in dust-air mixtures 13th ICDERS, Nagoya, Japan published in Progress in Astronautics and Aeronautics Series SMOOTL.D., HORTON M.D. (1977) Propagation of laminar pulverized coal-air mixtures Prog. Energy Comb. Sei.. vol. 3. pp. 235-258 TAI C. S., KÄUFFMAN C.W.. SICHEL M.. NICHOLLS J.A. (1988) Turbulent dust combustion in a jet-stirred reactor Progress in Astronautics and Aeronautics, vol. 113, pp. 62-86 VEYSSIERE B.. PROUST Ch. (1990) Estimation of the laminar burning velocity of starch particiesair mixtures 4th Int. Coll. on Dust Explosions, Porabka-Kozubnik, Poland

Effect of dust concentration on detonation parameters in grain dust-air mixtures 4th Int. Coll. on Dust Explosions, Porabka-Kozubnik, Poland

Acknowledgerneut•

The author is grrafcefui to mr J.M. Charpentier for Ais act-ive partic-ipation In the achievement of the experlmeatal work and to the frencA Minis try of Environment for its finsacial suffport.


F Deschamps

L E Calvez

USE OF ECOTOXICOLOGICAL METHODS FOR EVALUATING RISKS CAUSED BY CONTAMINATED SOILS

Industrial practices in the past have left a fairly large number of sites where the soil may be higly contaminated by chemicals dangerous for men or for ecosystems, either directiy, or through their transport to ground waters.

The evaluation of the initial contamination level and of the relevant risk, äs well äs the evaluation of the residual risk after rehabilitation ("how clean is clean") are most offen based on a complex and erstly analytical approach whose results cannot be easily interpreted in terms of impact on the ecosystem.

The aim of the present paper is to discuss the potential contribution of ecological methods for the global assessment of the risk. General characteristics of soil contamination and of rehabilitation methods are presented äs well äs the impact on ecosystems and investigation methods based on ecotoxicology. A methodology is proposed and the first results are discussed.

l. INTRODUCTION

The understanding of risks for mankind and for ecosystems created by contaminated soils is a relatively old concept. Regulations concerning the protection and restoration of this milieu, on the other hand, have not been developed to any significant extent.

Considerable research is under way to define methodologies for approaching the problem : evaluation of the extent of contamination and the corresponding risks, definition of criteria for starting rehabilitation operations, definition of quality aims of rehabilitated soil äs a function of the projected future use, in response to the question "How clean is clean ?" "i.e." up to what point should we decontaminate ?

The present communication first reviews the main characteristics of soil pollution and its associated risks, and then presents the first results of an approach based on applying ecotoxicological methods for an overall evaluation of toxicity towards ecosystems.

Fourth International KfK/TNO Conference on Contaminated Soil, Berlin, 3-7 mai 1993, p. 403-408

SOIL POLLUTION

Current criteria for declaring a given soil polluted are primarily analytical : a polluted soil is one containing well defined substances at concentrations higher than a level that is currently sei in a rather arbitrary manner, for example :

-heavy metais, -various inorganic pollutants, -polycyclic aromatic hydrocarbons, -halogenated hydrocarbons, -pesticides

The magnitude of the difference between the measured concentrations and the specified levels triggers the intervention, which may be a simple monitoring Operation or may go all the way to decontamination. Since the cost of the latter Operation can be excessive, we measure to what point it would be usefui to reserve decontamination to cases where toxicity is unambiguously demontrated. From this point of view, the analytical approach is insufficient. Knowledge on the toxicity and ecotoxicity of individual substances remains partial and their synergistic possibilities are even lese well known. In addition, in a complex medium such äs soil, a heterogeneous 3-phase System where a number of physicochemical reactions may occur and, at least down to a certain depth, biological reactions äs well, the real toxicity of transformation products is difficult to assess.

Overall tests based on ecotoxicology type bioassays should thus be added to the methods used to evaluate the initial contamination of a soil and the effectiveness of any decontamination efforts made.

ECOTOXICOLOGY

Ecotoxicology is the science that studies the toxic effects of chemical or physical agents on living organisms, especially on populations and communities within ecosystems. Ecotoxicology also studies the interactions of these agents with the physical environment in which these organisms live, äs well äs the transfer pathways of the agents (Butler 1978).

The discipline has a dual aim : to predict the future consequences that can be expected from the release of a given contaminant into the environment, and to evaluate the magnitude of damage to ecosytems following their contamination.

Various methodologies have been developed to attain these aims :

-In the laboratory, fest conditions are simplified to their extreme and are strictiy standardized to ensure the reproducibility of the results. Each pollutant or each pollutant/species pair is studied alone and the experimental milieu is chosen to be äs neutral äs possible, except if it is the actual object of the fest. Many of these tests are currently Standards or are internationally recognized and have been developed primarily to predict the risks related to various steps in the täte of chemicals in the environment.

-Direct effect : acute, subacute, chronic toxicity.

-2--Biodegradation in aqueous milieus.

-Propensity to bioconcentration (milieu-species relationship) and to bioaccumulation (relationships between species and the food chain).

-Inhibitory effects on reproduction, growth, predation, etc and more generally, behavioral modifications.

The tests involve species belonging to different trophic levels : bacteria, micro-crustacea, fish, worms, mammals, insects, birds ... algae, lichens, higher plants, .... The extralaboratory aim of ecotoxicology (in the field) is to evaluate the true impact of a local contamination on the animal and plant species dwelling there, in comparison to the state preceding the contamination if it is known, or in comparison to the state of the same type of ecosystem reputed undisturbed. The corresponding approach remains highiy empirical and is most offen based on criteria of presence/ absence of given species. It may be extended, but in this case costs increase considerably, because of the need for assays of chemical or biochemical markers destined to show exposure to certain toxic agents or their effects.

Between these two extremes of laboratory and field studies exists work whose aim is to improve the representative nature of bioassays, at the cost of increasing complexity in the control of parameters (microcosms, mesocosms, etc).

STUDIES CONDUCTED AT INERIS

INERIS has available the means and qualifications for carrying out a number of ecotoxicology tests with respect of Good Laboratory Practices. It is currently working on the valida"bion of an evaluation protocol for soll pollution and the risk of long-distance pollution resulting from it (fig. l).

The tests carried out are based on Standard methods, adapted if necessary to the special cases studied. They involve the soil itself (worm life, germination capacities) and the aqueous extracts obtained by leaching it (bacteria, daphnia, fish, algae, etc).

The soil samples chosen were subjected to detailed physicochemical characterization. It thus becomes possible to determine any potential correlation between overall toxicity äs shown by bioassays and chemical composition. The soils tested were sampled from :

-the immediate surroundings of a mixed domestic and industrial waste site, -a site used to treat wood by impregnation with carbochemistry products, -soil samples from abandoned coking plants, -the inert residue of an inorganic material manufacturing process.

The initial results are summarized in fable l. The "Daphnia magna" and "Photobacterium" fests were done on leachafes according fo Standard NF X 31-210 and the "Eisenia fetida" fest was done on the soil itself.

The numbers in the different columns represent the percentage of soil or of leachate leading to 50 % Inhibition of mobility or of light emission, or 50 % mortality in the population tests.

The observed toxicity is higher äs the number is lower. "Tests of Inhibition of "Daphnia magna" mobility and of the inhibition of light emission by "Photobacterium phosphoreum" are bioassays that can be used to show phenomena of sublethal toxicity, while the fest with "Eisenia fetida" can be used to show a lethal effect directed against this organism".

CONCLUSIONS

The initial results are encouraging for the continuation of our efforts, enlarging the battery of ecotoxicology tests to use and the ränge of soil types to examine. Ultimately, this work should enable us to propose the most relevant and least costly fest(s) for screening the toxic properties of soils before starting a series of detailed analyses. The latter, however, will evidently remain necessary if screening brings to light a toxicity justifying decontamination. Only the precise knowledge of the chemical species to be eliminated will enable us to choose the most effective rehabilitation method af the lowest cost. "In addition, these tests sould enable us to evaluate the effectiveness of a soil rehabilitation method and to respond to the question "How clean is clean ?".

CN, metais

At this stage of the research, the results are still too few in number to be able to establish unambiguous correlations. It is to be noted, however, that ecotoxicology tests have a good degree of discrimination.

Fig. l -

 l Fig. l -Draft for Protocol to evaluate the level of soll pollution