C Didier

P Bonneviale

Y Guise

CLOSING DOWN AND SECURING UNDERGROUND MINING WORKS IN FRANCE. LEGAL AND TECHNICAL ASPECTS

For many years the French economy was based on a quite developed mining indu stry (jron, coal, salt, potash...].

leqal person or corporate body, authorisinq the exploitation of the substance subject to the contract a q a i n st a fee. I he word concession is also used to define the area qranted to this person or body to perform his or its activity. I herefore, the concession is the ad mini strati ve entity of reference in IVI i n i n q Law. I he present reference of the Fren ch I i n i n q Kegulations is the French IVI i n i n q Lode drafted in I oOO ]_£-}• t contains all current requlations and la ws pertaininq to the openinq, operation and closure of mine works.

It notably mentions that

when the mining activity ceases (concession revocation or waiverj, the exploited area returns to the concessible domain.

If the former opera to r disappeared or is failing, the Jtate guarantees possible problems which could result from old

Closing Down Mine Works

Over the last few years, the growing awareness of safety and environmental issues, as well as the knowledge acquired with the first closures, led the French Oovernment to stre nqthen the leqal procedures p erta ininq to the closure of mine works. I he French Oovernment notably decided to inteqrate the notion of mine works rehabilitation to the mining la ws and regulations in order to secure these si te s and limit their impact on the environment. In the following, we will mainly present the procedure to implement f o r a definitive closure of mine works application, as the concession waiver procedure is mainly ad mini strati ve. r\\ I sectors liable to affect the surroundings must be included in these steps. I herefore, the application completed by the Loncession'Holder must deal with the following topics.

Mine Works Definitive

• impact on water resources [hydrology, h y d ro g eo I o g y, underground water regime modification, quality, etc.J,

• land stability [embankment stability, subsidence, collapse, etc.J,

• hazards associated to mine gas [hazardous gas emission or a ce u m u I ati o n J )

• treatment of mine works openings [sh afts, tunnels, adits, etc.J j

• problem with the dumps, dams and waste tips,

• rehabilitation ofthe sites and management ofthe surface facilities [buildings, head frames, etc.J

• possible measures that have to be ta ken in order to protect the rare animal species living in the old works

[especially chiropteraj and those intended to preserve the archaeological interests. It is essential to know the quality of the water before the works started (zero status] in order to assess the actual impact of the si te operation in terms of quality. Water in some regions naturally had a very high mineral content even before the mining activity starts.

Jeveral additional procedures can be envisioned to assess the foreseeable impact!

• comparison with neighbouring mines or areas which are already submerged,

• laboratory analysis and tests to define the type of receiving land [content of pyrite, etc.]j

• analytical or empirical approaches (sometimes one considers that the concentrations in minerals are reduced by half each time the water ofthe underground mine reservoirs is renewed],

• hydrogeochemical modelling taking in to account the oxygen content of water. IVI ore oxidizing meteoric water generate a scrubbing ofthe grounds more unfavourablethan deep water more reducing.

I he mining re~emergence points are analysed in terms of impact on the surroundings rather than in terms of run~off water quality. I herefore, an analysis of the type of receiving environment and of its use must be integrated.

Hazards Linked To Gas Within the Former Works

VV performance of venting wells located adequately to discharge gas from the underground « traps ». I hese works make possible to check the evolution of the gas reservoir parameters (composition and pressure] as well as to provide a controlled and consequently safe outlet for the gasj drainage of gas which consi sts in using an exploitable gas mixture found in the f o rimer works (e.

Hazards Linked to Former Mine Works with Surface Openings

It is of prime importance to secure f o rimer mine openings (sh afts, adits, tunnels which are close to the surface] as thousands of them are scattered over the French territory in very different environments [sometimes on urbanised sites] and their location is often not well known. I hese works were generally partially or integrally backfilled at closure.

However, although they have been backfilled, these former works represent a hazard for the surface land, under certain conditions, and th eref o re for persons and properties. Indeed, some accidents occurred in France or in neighbouring countries over the past decades. Un f o rtunately, in certain cases, they even turned out to be lethal. I he main problems resulting from f o rimer mining openings are the risk of entry in old works, collapse, asphyxia, explosion, etc.

I o secure the land above these works in a satisfactory way, it is essential to locate and treat the repo rted or suspected openings in an efficient and sustainable manner. Furthermore, for a given opening, a more str ingent treatment will be required if it is located in an urbanised area than in a remote area to guarantee the same safety level.

wne of the major stages of the analysis is the selection of the most adapted technique to secure the opening. When the combustion of a tip has already started and the extension ofthe fire is hazardous, measures such as the performance of fire barrier trenches, the removal of material in combustion and its spreading on non" sensitive areas, the implementation of a regular site monitoring, the prohibition of public access to the site, and/or control of the sur fa ce development and planning neighbouring the area. In the case of spoil heaps in combustion it is advisable in particular to analyse the risks of f o rmation of gas as a result of water presence r\ precise knowledge of the si te must be acquired in order to assess the quality downgrading risk for the surrounding ground water tables and rivers. I o locate the various rivers or ground water tables surrounding the site and assess their vulnerability, a hydrogeolocial study must be p erf o rimed, furthermore, this study also charac te rises the tip permeability and that of its f o undation. f required, the pétrographie and mineralogical material study characterises the sensitivity to downgrading water quality. Finally, the examination of events which took place in the past and which affected the site or other neighbouring sites provides interesting information.

VV ith the results of the various studies, it is possible to assess if the f o reseeable long term consequences are in compliance with the si te s sensitivity or if the implementation of possible counter~measures must be envisioned.

-i> I ip covering up and flank replanting to limit water infiltration and emission of harmful particles, reduce the impact on the landscape and reinforce the stability of its flanks.

^•* Our fa ce water management to limit the run off and percolation of surface water as well as the risk of water pollution and flank erosion.

-1> Uther techniques, although much more exceptional, can be envisioned! displacement of the tips, addition of alkaline material, bioremediation, creation of sealed barriers, etc.

Environmental Impact associated with Surface Facilities

  If required, the Loncession'Holder must define and implement the counter measures most adapted to the si te. I ypically, three types of water treatment processes are distinguished! --. D -? Preventive measures I he possible modification of the underground water flowsheet can be mentioned among the preventive measures (to help the short circulation networks which are close to the surface in order to limit land leaching]. /An oth er preventive measure which can be mentioned is the implementation of alkaline backfilling to neutralise the p H of the water discharged at the sur fa ce. P h ysico'chemi str y IVIany p h ys i co ~c h e m i stry treatments allow processing of low quality water. I he selection of one technique rather than another mainly depends on the type of released water. /\m ong the most commonly used techniques are evaporation, oxygénation, neutralisation, décantation, flocculation, filtration, bioremediation, etc.

  g.! OH 4]. I his technique implies a depressurisation of the reservoir which prevent non~controiled gas discharge at surface. I he exploited gas can then be utilised (boilers, etc.] or simply rented, ^•* I a n d ~ use management to prevent an increase in the hazard zones (prevent the building of any underground non" ventilated empty volumes for example],

  [particularly during rainy period of timej. It is also advisable to prohibit the access by the in sta I I ati o n of effective fences able to forbid the penetration of people 2.5.3 Impact of the Waste Tips on the Environment a / Impact on the landscape I he bigger the waste tip and the fl atter the land, the stronger the visual impact on the landscape. I he replanting of the tip generally I i m its t h is impact. b / Impact on the air Generally, the consequences of dust emissions are limited. However, they must be precisely assessed if the tips concern exploitation of su bsta nces particularly harmful to the environment and human health [uranium], I he coal spoil heaps in combustion, most of the time old, reject in to the atmosphere harmful gases [LU, H 2 O, etc .J which, however, that downgrade the quality of underground waters in contact with former mine works.

  Problems Persist Although Mining Activity Ceases International competition, slumps in prices and the exhaustion of mineral supplies affected the French mining activity and caused its progressive decline. I his decline started in the I yOUs and became sharper at the beginning of the I yyUs. I he last iron mine in France closed down in I C/C// . I he exploitation of coal mines is planned to come to an end in ZUUO

	and	this	of potash		mines		in ZUUo.	loday,	most	metal	mines	have	disappeared	and the exploitation	of uranium	is
	i ns i g n i f i ca nt.
	IVI a ny	lethal		accidents	have	marked	the French	mining	indu str y	(Loire	loyy	! LXJ I people	died	after	a	firedamp
	explosion,	Lourrières	I yUu .	l,Uyy	people	died	after	a coal	dust explosion].	I he hazards	of mine	operation	were
	stro ngly reduced thanks to scientific progress, the development of preventive	measures and the gradual reduction of the
	mining activity. However,		mining works remain one of the indu str ial activities most liable to have a long term impact on
	the environment and human activity.	I h eref o re, although the mining activity is bound to cease, hazards remain.	Indeed,
	it would	be senseless to believe that it is possible to fully rehabilitate the land and return to the pre~mining	state
	long term the environment will inevitably bear the scares of this activity [ I J .
	1.2 Legal Scope
	1.2.1 French Mining Regulations
	At the beginning ofthe / \ l / \	century, Napoleon	I	ordered a full ref o rm ofthe French La ws pertaining to mining.	I he
	French current French Oovernment IVI i n i n g Keg ulations are based on this ref o rm. priorities were largely modified since the progressive I herefore, in French closure	of Law, the d if f eren ce between iron and potash mines in the mines last
	few and	years quarries and the directly planned results from ending	of the coal a fundamental exploitation Act da ted in ZUUO. lolU,	I he which main has underqone goal consi sts now few chanqes of managing since then. the	post In
	mining France, the difference period by ensuring b etwee n mines and quarries the closing and the securing is made accordinq to the type of extra cted of old mining works in best conditions.	material as opposed	to
	many other countries, which define the d if f eren ce accordinq to the implemented	technique	(str ip mining,	underground
	I he	French		mining		regulations	changed	a	lot	in the	last	I U years.	I he	definitive	closing	of	old	exploitations	is	now
	miningj. Under French Law, the exploitation of materials defined as eligible for concession	is ruled by the regulations
	subjected	to strongly	demanding	procedures.	I he authorities	decided	to apply	a policy	based	on a syste matic	prevention
	on	mines,	and the exploitation	of materials	defined	as	norrel ig ible f o r concession	is ruled	by the regulations	on
	of	risks	and annoyance	by	imposing	the owner	to take	any	measures	that	could	ensure	a long	term	safety	of goods	and
	quarries.	I he materials	eliqible f o r concession	include	mineral substances which	were considered	as str a te q i c and of
	people	as well	as limit annoyance that	may affect the	environment.
	prime	impo rta nee for national sovereiqnty.
	r\	brief		overview		of	the		historical	and	technical	background	of	the	French	mining	exploitation	as	well	as the	main
	disasters	that		cast	a tragic	shadow	over	its hi sto ry	are firstly	exposed.	I he typical	content	of	a	mine	works	definitive
	closure	application	is then		presented.	I he main	goals ofthis	kind	of procedure	consist of defining	residual	risks ndeed, resulting mines
	from are subject to the the exploitation concession and determining rule.	the counter Concession	measures that are best appropria te to limit refers to the contract, entered in to between the French them.	Ota te and a
	I N F_ r\l O	is a French	National	Institute	dealing	with	risks	and	indu str ial safety	issues.	t achieves this kind of defir
	closure	applications	in close cooperation	with the owner	and the authority	in charge	of the	instruction.
		y WOrQS*	Underground		IVI ines, Llosure,	French	Kegulations, Jecuring,	Kisk,	I impact, Ota b i I ity, VV ater,
	1. General Context and objectives
	1.1 Historical context
	1.1.1 An Ancient Mining Tradition
	Like most other Western	European countries, France has an ancient mining tradition. In uaul, gold, silver, lead,	copper,
	tin, iron and possibly zinc and antimony were mined as early as the uallo'Koman	era. However, due to the decline	ofthe
	r\o man Lmpire and numerous barbaric invasions, mining activity development came almost to a halt. It is only atthe end
	of the first millennium	that mining	activity started growing	again, notably	in taster n France (^/x I ~/\ I I I	centuries].	Loal
	exploitation in Oouthern and Lastern France also started during this	period.
	Ubviously, the ndu st rial Kevolution	^/X V I I ~/\ V I I I	centuries] played a major role in mining activity development.	I his
	activity, which was mainly a craft indu stry, progressively	grew into a large scale indu stry thanks to the great	inventions
	(^stea m engine, use of blasting powder] and the technological	leaps ofthis period.	I he prospected and exploited	minerals
	were	broadly		diversified		at the beginning	of the / \ l / \ century	(^petrol,	oil shale, tung ste n, manganese,	aluminium,
	fluorite, zinc, talc, phosphate,	etc.].
	wver	a century,	large	mineral	fields were	built to cope	with the gro wth	of the heavy	indu stry essential to the Nation
	development.		Loal		(_f o r energy],	salt	\f o r chemistry],	iron	\f o r th e stee I indu stry]	and potash	\f o r fertilisers]	were
	intensively	exploited	throughout	France.	I he mining	activity	provided	sufficient	income	to entire	regions.

/After th e Jecond VV o r I d VVa r, the French mining indu stry was at its peak due to the national effort in rebuilding the country and reducing France energy dependency.

1.1.2 I hese su bsta nces are mainly hydrocarbons (oil, qas, coal], salt, potash and metals, wn the contrary, quarries are mainly used to extract buildinq material (limestone, chalk, gypsum, slate, etc.J.

In France, land owners have no riqht over the underqround minerals or su bsta nces eliqible f o r concession,

  and perennial closure of the former works entries, and at guaranteeing that the surface works and facilities do not jeopardise public safety and health or the main characteristics of the natural surroundings, furthermore, the procedures to secure a site must be in accordance with stringent requirements concerning environmental pro te et ion.I o this end, the current, past and future consequences of the closure on the underground and surface water source, flow and quality, as well as mine gas migration, must be studied.

	In accordance administration ofthe steps it plans to implement in observance of the fundamental re str ictions and obligations with the French IVI ining Lode, modified by an /Act in I c/C/4, the Loncession'Holder must noti f y the pertaining • public safety and health, • main characteristics ofthe environment whether on land oratsea, • integrity ofthe public or private buildingsj • public road p reserv ati o n ] • archaeological i n te rests, agricultural i n te rests, • National Heritage Preservation and protection of o utsta nding natural sites, • protection of water resources (ecosystem preservation, protection again st pollution, valorisation of water as an economic resource, etc.J. I he envisioned measures must mostly be aimed at preventing hazards associated with subsidence or collapse, at a / from a technical standpoint, the definitive closure of mine works procedure constitutes the major step. I he Loncession'rio Ider, f o r the definitive works closure to be awarded by the «Préfet» [french regional administrative authority], must assess the f o reseeable consequences of the f o rimer works on the environment to define and implement counter measures. I he Préfet can impose to the operator complementary measures to those that have been proposed. b / wn ce the definitive closure is awarded, the Loncession'Holder must transmit to the IVI i n i ster in charge of mines a concession waiver application. If this waiver is accepted, the Ooncession~Holder is released from its responsibilities, the mining right is cancelled and the concession goes back to the Ota te and is th eref o re p art of ensuring an efficient I he legal procedure which must be implemented to close down a mining site is twof o I d . the domain eligible f o r concession once again.

Closure Procedure

	1.3.1 Goals of the Procedure
	I he Loncession'riolder	must transmit a mine works definitive closure application to the Préfet at lea st six months b ef o re
	the definitive closure of all or part of the works. r\n act d rafted in laaC) precisely defines the content of this application.
	I his application must be as complete as possible and I ists any pollution liable to affect the surroundings after the closure
	of the underground	mine works.	I he Loncession'Holder,	after a general presentation of the sites concerned by the final
	closure application from the geological, hydrogeological	and operational standpoints,	must establish a list [in terms	of
	quality and quantity]	of the consequences that the underground	works	have already	induced	on the environment.	I he
	LoncessioiTfiolder	must then endeavour to assess the long~term	consequences	of the definitive closure of the works.
	Finally, he must define the possible co u nter~ m easu res which he considers most appropriate and which could guarantee a
								T	rĥ
	azard level in compliance with the use which	is made of the land above.	I hese measures, based on the	Concession"
	Holders study, are subject to verification by the French /~\d ministration which can either validate or complete them	if
	considered	necessary.

Technical Content of a Definitive Works Closure Application 2.1 Environmental Impact on Underground and Surface Water

  drafting for the underground works]. r\s these documents are essential to all studies which will be performed consequently, they must be launched as soon as possible. of the sur fa ce land use in the direct surroundings of the future re~emergence points, or at the lower points ofthe topography liable to be flooded by the rise ofthe water level over time.2.1.2 Impact of the Underground Works on the Surrounding Networks in Terms of Quality

	application or the additional	provisions.
	1.3.3 Studies Performance
	I he performance of a definitive closure application	is generally a difficult and str ingent task.	I he examined topics are
	I he closure of mining works can affect the quality of underground and surface water.	I he acid drainage	phenomenon
	both	numerous		and varied.	Furthermore,	they	of te n influence	one another.	For example,	a rise	in the water	level,
	(p H reduction, dilution of the metals contained in the ground] is a major cause for water quality downgrading, in	many
	f o Mowing the mine draining	pumps shutdown, can influence the land stability.	In the same sense, the selection of the
	metal mines and in coal mines which have a high level of pyrite. Large concentrations at re~emergence level can also be
	procedure to secure former shafts or adits depends on whether mine gas is reported or not.
	caused by the dilution of sulphate ions.
	It is important to rationalise the work schedule	in order to cut back the delays and costs for the various studies.	I he
	typical schedule of studies to be p erf o rimed is the following [' \-
	a / ueneral synthesis ofthe mining	activity
				Generally,	the analysis	s ta rts with	the basin	geological	synthesis	and with	the mining	works	synthesis
	[summary plan I he impact of a mining activity	on	underground	and surface	water	is twofold,	impact	in terms	of quantity	[modification
	of the run'off	water	routes,	rise of the ground	water	sheets,	re~emergence	of water,	etc.] and	impact	in terms	of	quality
	[modification	of underground	and surface	water	quality].
	For the Ooncession~Holder,	the main	goal	is to limit the impact of the final	closure	on the surrounding	water	basin
	regime.		I ypically, the procedure implemented to assess the mining works impact or possible impact in terms of quantity
	consists of five major	steps!
			I.	assessment ofthe residual unfilled mining voids resulting from the activity9
																					(	\-
		L,	identification	of underground	reservoirs	^location	and	connection^,
		G.	assessment ofthe	underground	reservoirs fill up speed	[hydraulic	assessmentjj
		4.	location	ofthe	re~emergence	points,
		0.	assessment ofthe	impact on the surrounding	hydrogeological	and	hydrological	networks.
	I he	impact	evaluation	on	the	surrounding	hydrogeological	n et wo rks	generally	requires	an	advanced	hydrogeological
	study	in		order		to	determine	the	water	level	after	sta bilisation.	t	is necessary	to	take	into	account	the	OU	years	return
	1.3.2 Investigation of the Application period precipitations on the short term [the month]	and	the	longest	term	[the	year].	It	is also	necessary	to	take	into
	I he final account the closure capacities application of evacuation must be examined of the discharge by the various concerned system, the water level	administrative being able to	services and local be temporary located	councils higher
	during than the	its investigation levels of emergence in accordance points and	with thus to flood the French particular Laws	and Kegulations, sectors or cellars	I herefore, located even a sufficiently higher than the detailed discharge and
	precise document must be esta blished so that exp erts can give their opinion on the quality ofthe performed studies and syste m .
	relevance of the suggested If applicable, the most appropria te counter~measures. counter measures However, this document can be defined by	must also be under standable by non~special ists the Loncession"Holder once the impact of the
	[mayors, members of non~profit corporations, former works has been assessed. I ypically, the following etc.J.	measures can	be	mentioned!
	It is advised to draft a synthetic memo, within the reach of a n o n "tec h n i c i a n, but which nevertheless contains the major ^•* water flow modification [perf o rmance of plugs and sto ppings in the f o rimer works, creation of artificial re"
	elements emergence of the application points],		\_L-\.	It is also	advised	to enclose	a glossary	of technical	terms	essential	f o r a	good
	u n d ersta nding		of the document.
	-1> possible	uphold	of the	pumping	system	[to	prevent submerging	the	bordering	underground	works	still	in	activity
		or	flooding	the	lower	points	of	the	sur fa ce	topography].	I his	solution	must	only	be	selected	in	very	specific
		cases,	when	no	other	solution	can	be	envisioned	[such	as the	achievement	of	stoppings	in	order	to	protect	the
		works	still	in	activity	or	the	creation	of	artificial	emergence	points]	.	For	obvious	reasons,	in	a	long	term
		prospective, the	use oftechniques	which	require	regular	maintenance	must	be	limited	as much	as possible.	VV hen

I he definitive file must obviously con ta in the essential documents and plans [mining method descriptions, limits of the several exploited panels, thickness of layers, height and characteristics of recovery, major geological accidents, etc.J. Once he has acknowledged the content of the application, the Préfet can either valida te the technical proposals or prescribe further measures which were not planned by the Loncession'Holder but which could prove to be necessary, f the Loncessioirriolder fails to complete the prescribed works, the Prefect designates somebody to perform the plans and works required to secure the site at the Loncession"Holder s expenses. I he Préfet notifies the final works closure by decree f o Mowing report confirming that the measures implemented by the Loncession'Holder are in compliance with the b / /An alysis ofthe mining activity consequences I ypically, the hydrological and h y d ro g eo I o g i ca I specific studies are often performed first [indeed, the results of these studies influence most of the other studies to be p erf o rmedj. I he sur fa ce sta bility study and the analysis of the hazards associated to the presence of gas can start as soon as the h y d ro g eo I o g i ca I study is well underway. I he conclusion of the sur fa ce stability and hazardous gas studies are useful to secure f o r m er s h afts and adits.

I he other specific studies [waste tips, surface facilities, etc.J are generally independent from the previous studies. I h eref o re, it is not essential to integrate them to a specific sta ge ofthe schedule.

2.

2.1.1 Impact of Underground Works on the Surrounding Networks in Terms of Quantity they must nevertheless be implemented, it must be defined in which it belongs to control the good state of th e works and to ensure the finance charges (operator, services of the Ota te, etc. ], ^•* limitation

2 Environmental Impact and Hazards Associated with Land Stability

  Limestone drains or lakes and artificial wetlands are among the major passive treatments.

						(pillar		sta b i I ity, behaviour	of the	roof]	and, possibly,	on	the	implementation	of the exploration	works	(we I I
						boring,	geophysical		methods]	to define the land	and detail the calculation	assumptions.
	For	sectors		solely		subject to	a sur fa ce subsidence	risk, the	main	purpose	of a stability	study	is to	establish	the zone	of
	influence 2.2.3 Counter Measures Definition of the former mining works on the overlying	strata.	I ypically,	the zone	of	influence	includes	all plots	of	land
	directly	undermined,		as well	as a non~undermined	strip	of	land	which	corresponds	to the external	border	of the	works
	I he filling	(by	backfilling	or cavingj	or rein f o rcement	of the	cavities	are solutions	which	can	only	be envisioned	in	few
	[lateral	influence	of the	worksj.
	very	specific	cases		for	obvious	financial	and	technical	reasons.	I herefore,	generally,	only	the	works	which	are	very
	wn ce the location close to the surface of all underground are secured in such works a way. is known n other with	a satisfactory cases, the trend	precision, the main consi sts in defining difficulty risk perimeters of the analysis in which is
	to determine preventive principles the value	of y, the works are defined in terms angle	of influence of development on the covering and urbanisation [ i .e. the width of the sur fa ce of lateral area.	influence]. I hese provisions I his	angle can
	notably range from depends a simple on the type control	and thickness of the urbanisation of the overlying to a strict	strata, the slope building prohibition of the rockbeds, in this area,	the width which can	of the even	exploited be closed
	strip, down	the presence and fenced	of faults, in certain	the existence very specific cases. of several	exploited	seams,	etc.	I he value	of this	angle	can	be defined	with
	sur fa ce	subsidence		measurements	if they	exi st,	or	based	on	a	similar	study	p erf o rimed	for	neighbouring	works	and
	Uf	course,	the	problem	becomes	trickier	f o r the	management	of	the	existing	buildings,	notably	if they	are	located	in
	presenting	similar	geological	and operational	contexts.
	areas	of	high	risk		for	the	safety	of	people	and	properties.	If	no	rein f o rcement	of	the	land	or	buildings	can	be
	In the case of methods implemented and the surface facilities ensuring the integral cannot disappearance be displaced, the of empty implementation mining spaces after operation, subsidence of monitoring devices can be	can envisioned occur
	f o r a period (traditional	which geotechnical is generally devices, qui te micro~seismic limited and well monitoringj, known	after VV hatever extraction. the type I h eref o re, the long of selected measurement term behaviour devices, study the
	of land monitoring atthe does surface not	must f o eus on the assessment of the site sensitivity to the two following cancel the risk, it simply allo ws to manage it and inform the population	parameters! and authorities	in case	of
	abnormal	evolution	of the underlying		cavities.
		a /	Kesidual	subsidence	risk
						I he	residual	subsidence	corresponds	to	the	subsidence	phase	which	extends	after	extraction	and	which	is
					generally very reduced. If the duration of this phase and of the sector's operation is known, it is possible to
	I he	identification		of the collapse	risk	is a very tricky	appraisal	which	requires	a perfect	knowledge	of the context of	the
	works	and	of the		breaking	mechanisms	liable to	affect the	underground	works	stability	[pillar	breakage,	breaking	down
	of the roof,		etc.J.		I he analysis	consists	in	locating the	potentially	unstable	areas and	identifying	the types	of	phenomena
	which	could	affect the	land at the	surface.
		a /	I ype of foreseeable	disorders
	I he	identification		of	the	type	of	disorder	liable	to	affect	the	sur fa ce	sta bility	is	based	on	a	visual	inspection	of	the
						underground	works		[when	possible]	and	on the thorough	analysis ofthe	site conditions	and	mining	plans.	I he
						appraiser	must	then	identi f y	the	various	breakage	scenarios	liable	to	affect	the	area.	Uepending	on	the
				P. assive treatments covering s nature and thickness,	he	must determine	whether the	land	at the surface	is liable to collapse	or	not.
						Generally,		a rock	covering		made	of poorly	competent	rockbeds	favours	gradual	breakage	which	gives	rise	to
				I he purpose	of	passive treatments	is to	improve the quality	of the released	water with	natural	chemical	or
						a gradual	and	smooth	collapse	of the surface. On	the	contrary, the	breakage	of rigid	and	competent	rockbeds
				biological		processes		which		require	neither	permanent	maintenance	nor	the	sustained	addition	of	chemical
						in the roof can favour	a sudden	movement	ofthe	land atthe surface	[spontaneous	collapse].
	b / Oensitivity benerally, of a site to the collapse breakage da te products. I he long term behaviour of the land even approximately. I o overcome of former undermined works by this difficulty, with mining the abandoned works stro ngly rooms sites are studied	and depends pillars on in terms of	can the predisposition in no way mining methods be assessed, used. to a type of
	C~ benerally,	the i nsta b i I ity . methods	which	fully	fill	up	underground	mining	voids	after	closure	( ^caving,	backfilling,	\ etc. J only	give
	rise		to	surface	subsidence		phenomena.	lo	the	contrary,	works	which	allow	residual	empty	voids	to	persist	(notably
						I o determine	if a sector	is sensitive to the	collapse	risk	of its surface, the three following	parameters	must	be
	rooms	and	pillars technique]	are liable to give rise to surface	land	collapse	phenomena.
						checked	simultaneously.
	In	this	last		case	two		types	of	phenomena	are	likely	to	occur!	generalized	collapses	or	sinkholes.	I he	less	the	ratio
										•			sectors ofthe	underground	works	have	not yet caved	in when	the study	is	performed•
	between	the	height	of	the	recovery	over	the	thickness	of	the	extracted	ore, the	greater	the	amplitude	of	depressions	or
													certa in ofthese	sectors are liable to cave	in with	time,
	co I I a pses.
										•			the f a I I ~ i n ofthe	sectors	is liable to cause a collapse ofthe	land	at the sur fa ce.
	I he	assessment	of	the	long		term	stability	of	land	at the	surface	is	qui te	often	a tricky	procedure	requiring	thorough
						I he selection	of an	adapted	appraisal	procedure	to	characterise the sensitivity	of a site to the risk	of	collapse
	knowledge	of the	mining	works	con text.	Notably,	it is essential	to	research	any	available	in f o rmation	pertaining	to	the
						of	the		surface	notably	depends	on	the	type,	extension	and	context	of	the	mining	works	as	well	as	on	the
	type	and	thickness	of	the	covering,	the	hydrogeology	of	the	area	(location	of	submerged	sectors	or those	that	will	be
						accuracy	and	quantity	of information	available on these former	works.
	submerged	in	time,	and	those	that	will	never	be	submerged],	the	operation	parameters	(mining	technique,	size	of	the
	p i I I ars,	e x i ste nee I ypically, of	works the analysis with several is based levels, on	etc.], a close	and study the	geotechnic of the si te	characteristics [signs of disorder of	the at the ore sur fa ce, and the	recovery, back~analyses in
	particularthe carried water	effect on the rocks out on old collapses if the works which have have to occurred be	flooded. in the	same	exploitation	or	in	bordering	exploitations
						presenting		similar	characteristics,	etc.],	an assessment by	modelling	and	a calculation	ofthe	works	behaviour

2.2.2.1 Method for General Assessment of Subsidence Risks determine if a sect or is sensitive to a residual subsidence, and if so, f o r how long. b / Jubsidence resurgence risk I he two main exogenous facto rs liable to trigger a subsidence resurgence are a rise in the water level within the f o rimer works, and the application of an excessive burden on the surface [n ota bIy as a consequence of sur fa ce urbanisation]. I he sectors which are the more sensitive to a subsidence resurgence are generally the sectors close to the surface and not yet submerged but liable to become submerged in time, as well as the sectors intended to be used atthe surface. 2.2.2 Method for General Assessment of Collapse Risks

5 Environmental Impact and Hazards Linked to Waste Dumps and Tailing Dams

  various possible breakage scenarios. /\m ong these parameters we can mention the size and statu s of th e works, the geology, the hydrogeology, the presence of gas, the type of use which is made of the land above and around.I he selected techniquemust allow the works to be in compliance with the various requirements as regards the risks liable to affect persons and properties within the area influenced by the mining works, i.e.! definitively preventing any entry to the f o rimer works and guaranty that the opening cannot be violated by acts Jtu d y of sta bility conditions with methods of calculations typically implemented to slope stability [t)J.If the stability study highlights a breakage risk of the str u cture, specific provisions guaranteeing its long term sta b i I ity must be implemented. I hese provisions depend on the site configuration and characteristics, and or the type of breakage which is liable to occur. r\ mongst the most frequently implemented counter measures, one can notice.^•* waste tip rehabilitation, flank reshaping, building of banks and benches, p erf o rmance of rip~rap at the f o ot of th e embankments, management ofthe surface water, replanting ofthe slopes. It is necessary to eliminate or at leastto bring back to an altitude compatible with the stability of the deposit the water tables located inside the deposits

		[th is measure is particularly essential for tailing	damsjj
	-i> definition of measures pertaining to the use of the surface to prevent building above unstable areas if the stability
		can	not be guaranteed,	in spite of dispositions	carried	out.	I his case	must	however	remain	exceptional, the
		general rule being to ensure the stability ofthe	deposits,
	^•* mon ito ring, visual or with appropriate devices including when it is necessary the presence of piezometers in order
		to characterise the h y d ro g eo I o g i c conditions in the deposits.
	r\ method aimed at selecting a technique f o r a given environment and opening was developed by I I \l F_ Kl O [Oj. It d et ails the general 2.5.2 Coal Waste Tip Combustion
	major I he waste tips from coal mining sites sometimes contain a large amount of carbonateous matter liable to ignite characteristics which must be collected to make sure that no fundamental parameter was forg otte n during under the
	vandalism• certain conditions. In France, about / UU coal waste tips are reported, almost half of them have already partially or totally burnt down [/J. I he coal waste tips can be ignited in two ways, ignition by external causes which is of te n accidental [f o rest fire or bush fire] and spontaneous combustion. Jpontaneous combustion is a physical phenomenon liable to take place if various parameters pertaining to the type of material [volumes of carbonated matter, granulometry, presence of pyrite, etc.], to the structure of the tip [type of implemented dumping syste mj as well as to the outside environmental study of the ôf conditions [climatic conditions, water] are combined.
	I he appraisal procedure to characterise the sensitivity of a waste tip in terms of spontaneous combustion breaks	down
	* securing into 4 fundamental stages. the land	above	and around	the works	in the long	term.	I he treatment	must	be perennial	and
				dimensioned	to reinforce the surrounding	rocks	in order to prevent disorders which	are not in	compliance
		I.		Jtudy ofthe geological, h y d ro g eo I o g i ca I, climatic and dumping	contextsÔ
				with the type of land use and which are due to the structures C /	ageingj	\ .
		-i> controlling the problems associated with gas, if required, notably by preventing any non~diffuse gas emission
		G.		fhysico'chemical characterisation ofthe waste tip material [sensitivity to spontaneous combustionjj
				and	syste matically	shutting	down	dead~ends	or cavities	located	close	to the opening,	where	gas	could
		4.		Jtu dy ofthe data and determination ofthe waste tip sensitivity in terms ofspontaneous combustion.
				a ce u m u I ates,
	I he sel ect	of counter measures is associated with the preventive or curative asp ects ofthe	intervention.
		^•* manage the problems associated with drain water	in the mines, notably	by preventing	possible future	water
		Préventive	measures.
				releases within urbanised areas which were not designed for this	purpose.
		I he ignition can be prevented	by limiting air penetration	into the dump, by implementing	a covering	layer	of
	protected	animal inert material, by controlling and clearing the flanks, displacing the sensitive str u ctures located near to the species elected residence in old mining works [chiroptera in particular], these principles must be
	adapted to allow the passage ofthese animals, while preventing the penetration of the people. si te, and by controlling the development and planning ofthe sur fa ce next to the area.
		Uurative	measures.
	I he exploitation of underground mines generates the constitution of large barren waste heaps next to the extraction sites,
	known as waste tips.	I he materials can consist of excavated	matter or waste from a processing or transformation	line.
	I he waste is transported with lorries, carriages, etc.	I he main hazards associated to the presence of such works at the
	sur fa ce once the underground	mining	works	are closed	down	are threefold! local and general	long term	instability,
	combustion of certain coal waste tips and nuisances they are liable to cause to their surroundings (air, water].
	2.5.1 Long Term Stability of the Works
	I he waste tip and tailing dam long term stability is not always guaranteed. Large scale incidents associated to	instability
	can jeopardise	sensitive	str u ctures	neighbouring	these tips	(/~\b erf a n	I a DO, buffalo	Lreek	I c/ / Z]. I he breakage	of a
	dump	or of its f o undation	generally	results	in an unfavourable	evolution	of one or several	fundamental	parameters
	controlling	its stability	[geometrical	configuration, building	mode, type of land on which	it is si ted, the hydraulic and
	climatic	conditions,	excessive	burden,	modification	of the embankment	geometry),	IVI any instability	phenomena	can
	affect the waste tips.	I hese phenomena are generally M sted within the major slope instability categories (gradual	slumps,

2.

slumps which turn into land slides, surface erosion, etc.]. I ypically, the appraisal procedure which is implemented to assess the sta bility conditions of the tips or dumps comprises four fundamental steps .

I . Jtu dy of the geological, hydrogeological and operational contexts (in particular presence or risk of f o rmation of a water table in one or both ofthe deposit or the supporting soils],

Z.

Ueotechnical study ofthe work (detection of breakage figures]j G.

Ueotechnical characterisation ofthe materials in the waste ti ps ] 4.

L. . Jtu dy of the tip ^presence of cracks, emission offumaroles or gases, suspicious smells, etc .^ ,

  , washing, etc. I he major environmental impa cts of the sur fa ce facilities are associated with hazards due to the f o rimer facilities in sta bility [headframes, buildings, etc.J, to the possible scattering of toxic compounds, and to landscape downgrading.I o évalua te such impa cts and define adapted counter measures, a specific analysis exi sts in French regulations [oj. It is notthe aim of this paper to develop this so'called «Oimplified Hazard /Assess ment Procedure ».

	Under	French	Law, the only	facilities	considered	as mining	facilities	are the infrastructures	essential	to the	mine
	operation.	I h eref o re, the material	processing facilities (^chemical	treatments	in particular]	are not considered	as such
	except f o r the purely physical processing	like crushing,	si ft ing


Olivier Salvi
email: 01ivier.salvi@ineris.fr

Didier Gaston

WHY CHANGING THE WAY TO MEASURE THE RISK ?

The SEVESO II Directive gives the ruies to identify high risk potential establishments with the amount of hazardous substances handled and their operators have to produce safety reports. Although ruies are well established to identify potential risk, there is no method to measure the risk level which takes into account safety devices and safety management Systems implemented by operators. In fact, the lack of ruies to ürtegrate the prevention made by operators has negative effects : • Operators are not encouraged to increase the risk prevention, • Risk decision-makers have no clear opüüon of the real risk level, • The risk expert's job is tricky because of the lack of method to identify reference scenarios. Furthermore, the risk level is appreciated in fact throughout an effect distance. This way is too simple to give a pertinent enough risk assessment. In fact, risk evaluation should include other Parameters to be more representative : the area concemed by the phenomenon, its kinetic, the abüity to generate domino effects. Because of all above reasons there is a need to define ruies to identify scenarios integrating the prevention made by the operators and then to evaluate them by taking into account the characteristics of the phenomenon involved.

CONTEXT AND REQUIREMENTS OF THE COUNCIL DIRECTIVE 96/82/EC

The Councii Directive 96/82/EC of 9 December 1996 on the control of major-accident hazards involving dangerous substances, known äs SEVESO 11 Directive, aims at the prevention of major accidents and the limitation of their consequences for man and environment, with a view to ensure high levels of protection throughout the European Union in a consistent and effective way. It applies to industries that use a significant amount of materials that are hazardous to people and the environment Operators of such industries must demonstrate that they have assessed the risks and are managing it, that they have a policy for the prevention of major accidents and a safety management System, and that finally they have adequate response plans in case of emergency. Accordingly, a better management of hazards is necessary. Also tools have to be used to help the operators to carry out the risk analysis and to build a safety management System. Such tools have to be recognised by the Public Authorities and the decision-makers in charge of risk control. After reading the Directive, the objectives in terms of risk management are clearly laid down but the remaining question is : how to reach them ? As the documents produced by the operators have to be demonstrative, it would be usefui that the analysis led by the operators follows a recognised methodology. The multiplicity of methods for the evaluation of major accident hazards äs a result of difference of cultures, makes it difficult to propose a hannonised procedure. However, some aspects of the different approaches can be put in common such äs scenario identification and gravity evaluation.

PERVERSE EFFECTS OF THE LACK OF ADEQUATE METHOD TO MEASÜRE

THE RISK

Although mies are well established to identify risk potential on the base of the quantity of dangerous substances (Airnexe I of the Councii Directive 96/82/EC), there is no conimonly recognised method to measure the risk level of units, which takes into account safety devices and safety management system implemented by operators. In fact, the lack of rules to integrale the prevention made by operators has negative effects : 1. Risk prevention not encouraged Often, after identification of the establishments covered by the Directive, its risk is perceived by the Authorities and the decision maker mostly throughout the use of safety distances taken from the safety report. For example, articies 11, 12 and 13 may all give rise to a concept of 'zones' around a SEVESO establishment linked to, respectively [START_REF] Christou | Guidance on Land Use Planning äs required by Councii Directive 96/82/EC (SEVESOII)[END_REF]: • Emergency planning ; • Land-use planning ;

• Information to the public on safety measures and behaviour in the event of an accident. It follows that for the population and for some actors involved in risk management at a geographical scale, the risk level of an establishment is directiy proportional to the safety distances or safety areas allocated for the above mentioned uses. Finally, the most commonly used risk level index is scaled in meters. The perverse implication of such an ünplicit index is that operators are urged on restricting the consequence of the scenario by implementing protective devices like water curtains, detection Systems connected with quick closing valves... On the other hand, prevention has no benefit on the effect of major accident scenarios because it does not reduce its consequences. That is why operators are not encouraged to improve the prevention. This Statement must be also linked to the fact that the majority of the major accidents reported in the Community are the result of managerial and / or organisational shortcomings. Besides, it also must be noticed the new occurrence of so called 'post SEVESO accidents' which involved failure of safety devices [START_REF] Lechaudel J-F | Assessment of two accidents involving safety devices[END_REF], that sufiered from non appropriate maintenance and testing. To sum up, on the one hand, the Councii Directive 96/82/CE asks efforts from the operators to demonstrate that they implemented a major-accident prevention policy and a safety management system, on the other hand, the uses and in particular the zoning established from these documents (safety report), do not urge an efiicient prevention policy. The SEVESO Directive, viewed äs a good example of 'goal-setting' legislation needs, in addition, the development of a methodology, first, in order to guide the choice of reference scenarios that have to be selected in fünction of their use (emergency plans, land-use planning, acceptance of siting new establishments). Second, a risk level evaluation that would take into account the prevention made by the operators would encourage them to invest in actions to improve the efficiency of the safety management.

No clear opinion of the real risk level

In the first part, it was demonstrated that the risk level of an establishment is perceived through the safety distance reserved around the plant for land-use planning or for emergency plans. But the quick analyse of major accidents, in comparison with the safety distances around industrial sites shows a great gap. Safety distances in case of toxic releases are widely beyond the limits of the establishment (often more than l or 2 km). However, except the accident at Bhopal in 1984, the accident reports only mention some injuries, sometime serious and within these limits [START_REF]Secretariat d'Etat aupres du Premier Ministre Charge de l'Environnement et de la Prevention des Technologiques et Natureis Majeurs -DEPPR -Service de l'Environnement Industriel[END_REF][START_REF] Christou | The control of major accident hazards : The land-use plamiing issue[END_REF]. On the contrary, safety distances in case of flammable releases are often inside or in the dose neighbourhood of the establishment (300 to 500 m). However, the accidents reports often mention fatalities and serious injuries, füther away [START_REF]Secretariat d'Etat aupres du Premier Ministre Charge de l'Environnement et de la Prevention des Technologiques et Natureis Majeurs -DEPPR -Service de l'Environnement Industriel[END_REF][START_REF] Christou | The control of major accident hazards : The land-use plamiing issue[END_REF].

Barnesville

Example of accidents given in document [6]

In the case of 'tables of appropriate Separation distances' use for instance in Sweden [START_REF] Christou | Guidance on Land Use Planning äs required by Councii Directive 96/82/EC (SEVESOII)[END_REF], it can be noticed that the greatest Separation distances also are for toxic products. This general trend demonstrates that the safety distances for toxic release seems to be overpredicted in comparison with the safety distances for flammable substances. This trend can be analysed both for consequence based approach and for risk based approach.

No consistent approaches

In fact, risk experts from all EU countries mostly agree with the major accident scenario. When asking different experts from European Countries about the definition of the scenario chosen and evaluated in the safety reports, the answers will not always be the same. In fact, there is no recognised definition of the major reasonable, credible or realistic scenario. Generally in France, because of the French consequence based approach, the scenario chosen are such äs BLEVE, total instantaneous loss of Containment, instantaneous rupture of the largest pipeline leading to the highest mass flow, fire in the largest tank, explosion of the largest mass of explosive... [START_REF] Christou | Guidance on Land Use Planning äs required by Councii Directive 96/82/EC (SEVESOII)[END_REF][START_REF] Pineau J-P | Application of the Seveso Dirrective in France[END_REF] However sometimes, the urban constraints of residential area development or new road constructions in the vicinity of existing establishments urge the Company to reduce the safety distances. Then it is proposed to choose a more 'realistic' scenario than the previous one, by taking into account the efficiency of mitigation devices that already existed or that will be implemented. In fact, because of the lack of ruies for identifying the scenario, the expert's Job is tricky. He can't rely on an established method to put aside the major scenario and to choose other scenario characteristics.

Because of all above reasons there is a need to establish mies to identify scenarios integrating the prevention made by the operator and to propose a method for their evaluation. This evaluation will allow to properly measure the risk of a unit depending on the phenomenon involved.

A new method for risk evaluation

First, it is proposed to define a method giving ruies for the identification of scenarios that take into account mitigation devices and risk prevention actions. Then the evaluation of the scenario should consider more representative parameters than distances, and their evaluation should be caiculated by integrating the effect area concemed with the phenomenon, its kinetic, its potential to generate domino effects...

Scenario identification

The objective is to identify major 'Reference Scenarios' regarding the analysis of accidents data bases like MARS [START_REF] Kirchsteiger | Status and fimctioning of the European Commission's major accident reporting system[END_REF] and taking into account the current practices (state of the art) contained in the lawfül requirements with regard to conception, Operation and control, and safety niitigation devices. The reference scenario allows to find more realistic scenarios and to put aside some major scenarios, considering a unit operated today. The Reference Scenario could be identified with an algorithm based on the labelling of the substances (Councii Directive 67/548/EEC of 27 June 1967 on the approximation of the laws, regulations and administrative provisions relating to the classification, packaging and labelling of dangerous substances) and the conditions of use (pressure, temperature...). This scenario is mainly generated by extemal events (mechanic aggression, thermal aggression, earthquake...) or intemal failure that can be identified by studying the process with a method like HAZOP pointing process parameter deviation (runaway reaction, overflowing...).

Scenario gravity evaluation

In the first paragraph, it has been demonstrated that the risk level is appreciated throughout effect distances. The objective of the gravity evaluation is to caiculate a gravity index depending only on physical parameters that makes it possible to compare different scenarios. Taking into account phenomena characteristics implied in scenarios would moderate the measurement of the gravity. For its evaluation, it is proposed to quantify the influence of : • the effect area A concemed with the phenomenon : a disc in case of an explosion, the projection of a plume for the pollutant gas dispersion ; • the phenomena kinetics K : rapid for explosions, slower for dispersion and fires ; • capacity of ürtervention / to master the disaster or to limit its consequences : possible for fire and gas dispersion, but possible only by conception for explosion ; • potential of donüno effect D : emission of projectiles, interlocking of delayed phenomena. The composed gravity index G could then be a fünction of parameters only associated with the physical phenomena. Then all scenarios identified could be evaluated and ranked with this gravity index. With this index, it could be discovered that toxic substances not always generate the highest risk level. CONCLÜSION This paper emphasises that there is a need to establish a method to measure the risk of an installation by integrating the prevention implemented by the operators, otberwise it will be difficult to reach the goals of the SEVESO II Directive in all European Country, that are to improve the prevention linked in particular with the management. It is proposed that the method defines ruies to identify scenarios integrating the prevention made by the operators and then evaluate them by taking into account the characteristics of the phenomenon involved. The application of this method might result in a more consistent risk evaluation and management in the whole EU. The conclusion of the benchmark exercise under the project ASSURANCE (ASSessment of Uncertainties in Risk ANalysis of Chemical Establishments) would certainly justify the development of such a harmonised method.

  Release during 25 minutes of 40-50 tons of anhydride ammonia from a storage Rupture of a 25 mm pipe during the unloading of a chlorine rail tank car to a 50 tons storage Leakage in 2 reactors caused the explosion of 40 to 50 tons ofcyclohexan Explosion of ethylene and isobutanol in a ehemical unit producing polypropylene 30 persons injured (8 seriously) some of them were drivers on a motoway nearby, who lost control of their vehicie or tried to run away on foot Inhabitants were in the vicinity of the plant : 120 persons sent to hospital and 5 persons seriously intoxicated 28 fatalities, 89 injuries All construction destroyed within a radius of 600 m Windows broken within a radius of 13 km , big fragment at 6 km 23 fatalities, 124 injuries Plant completely destroyed Windows and walls damaged within a radius of 7 km


Jean-Luc Durka

D Reinert

Design

Design of safety-related architectures based on asic and microprocessors

Introduction

The STSARCES project is divided into five research work packages. A specific work-package, joining INERIS and BIA as test-houses, SICK and JAY as manufacturers, takes into account the foreseeable evolutions in design of safety related systems owing to continuing progress in the electronic technologies. The work programme is divided in two main parts :

• BIA and SICK defined a dual channeled microprocessor controlled device which can be configured for the categories 2, 3 or 4. BIA developed a Markov-Model for the chosen architecture. Different diagnostic coverages and on-line test intervals can be simulated.

• INERIS and JAY work on ASIC's development for a single-way safety light barrier with a dual ASICs designed for a category 4. The first part deals of techniques and requirements for ASICs design. The second part is based on methods and techniques for ASICs validation.

New topics in research

Under the term ASIC (Application Specific Integrated Circuit) we can found a partial list of the following components :

• Analogue functions or mixed functions (amplifiers, analog gates, phase-locked loops, triggers, etc.). These circuits are issued from standard cells or full-custom components.

• Digital functions (PAL, FPGA, EPLD, etc.).

• Microprocessors and their peripherals («Von Neumann» or «Harvard» structures).

For ASIC components the input document is the technical specification, and software design and simulation give the layers. The usually generated schema is only a thinking aid but it is not the viewing of the exact chip result (integrity of compilers).

For microprocessor Von Neumann structure some rules are well known (as RAM and ROM testing). These rules are not applicable for Harvard structure. This component is impossible to use for safety related purposes, and other strategies for testing need to be imagined.

System configurable for category 2 to category 4

Today, the designs are always specific for the different safety categories. So manufacturers build specific type 2 to type 4 systems in accordance to the IEC 61496 (3) . The different categories are only unit cost driven. The R&D costs and times are high. Typically they use microprocessorbased technologies in their products, but also custom specific ASIC solutions are implemented.

Tomorrow, the time to market will become shorter and shorter. So it will be necessary to reduce the R&D time to a minimum and make a project mix between the unit costs and the R&D efforts.

An interesting issue consists to build a type 2 up to type 4 configurable system with an identical hardware. The only difference is the software running in the microprocessors. The safety categories shall be selected in the final test. The main questions are :

• Which quality level of testing is necessary in which safety categories ?

• What is the minimum test repeat time in the system ?

• How long could the system continue to run after a fault detection ?

The prototype is based on two microprocessors with a 8051 core. Additionally the processor has EEPROM, a SPI interface for interprocessor communications and it allows incircuit programming. The prototypes have only safety-related digital inputs and outputs for evaluation.

Sensor Modiile

TestOut In this architecture, the microprocessor B makes a periodic test to reveal a failure to danger (e.g. loss of detection capability, response time exceeding, failure of microprocessor A, failure of the output signal switching device "OSSD", etc). The test signal simulates the actuation of the sensing device. A single fault affecting normal operation is detected by the periodic test. In this architecture, a single fault in the control does not lead to the loss of the safety function. Some but not all faults will be detected and an accumulation of undetected faults can lead to the loss of the safety function. In this architecture, a single fault in the control does not lead to the loss of the safety function, and the single fault is detected at or before the next demand upon the safety function. When the faults occur, the safety function is always performed and the faults will be detected in time to prevent the loss of the safety functions.

Behaviour under failure

To avoid any unsafe behaviour the following rationale could be used, after choosing the relevant category :

• For external signals we can use the catalogue of single faults which is the annex B of EN 61496-1.

• For internal signals the followings topics need to be analysed :

-Rules of design, including fault simulation (e.g. IEC 61508 (4) , DIN V VDE 801 Appendix A2 ( '), where some failures are described : signal stucked, loss of a function, loss of time synchronism, components drift, signal unwanted oscillations, intermittent failures. Tools of design-compilers integrity, certified versions. Low or high level langage. Suggested safety strutures. Process stability and known technology.

Validation for complex electronics circuits

For complex application specific integrated circuits a new approach in validation seems to be necessary because this type of complex components cannot be completely validated through testing. The validation procedures should be included in early stages of the design to be more effective.

For complex application specific integrated circuits (ASICs), the term ,,proven in use" should be clarified and related to the different inputs for the design process :

-process technology, -design rules for cell placement, interconnect and layout, -pre-layouted or generated macro cores, -cell libraries, including layout information and simulation models, -soft macros, -design tools: layout, synthesis, simulation.

The validation plan is shared in six main phases :

• Functional Testing Functional testing is used to reveal failures during the specification and design phases. During the functional tests, reviews are carried out to see whether the specified characteristics of the system have been achieved.

• Functional testing under environmental conditions

This method provides that the safety-related system is protected against typical environmental influences. The system is put under various environmental conditions during which the safety functions are assessed.

• Fault insertion testing

Fault insertion testing is used to introduce or simulate faults in the system hardware. However, it is difficult, by influencing inputs and outputs of a complex component, to reach all relevant internal states and nodes. Therefore this method is not sufficient for validation of safety functions. The theoretical base of fault insertion testing is a Failure Mode and Effects Analysis.

• Worst case testing

The operational capacity of the system and the component dimensioning is tested under worst case conditions. The environmental conditions are changed to their highest permissible marginal values. The most essential responses of the system are inspected and compared with the specification. The equipment under test is usually damaged when the worst case test was done successfully.

• Expanded functional testing Further to normal functional testing, it is useful to check the behaviour of the safety-related system in the event of rare or unspecified inputs. This method is implemented for testing the limits of normal use and to define the system reactions in case of unknown stress and unknown fault combinations.

• Testing of Complex Components

First, the design flow is given and described in an introductory paragraph. Second, all state of the art verification and validation steps are listed, based on the presented design flow. Third, possible hazards, e.g. reasons for common cause failures or single faults resulting in erroneous results will be identified. This will help to define a set of validation tests required for safety validation and reveal the eventual needs for additional tests.

Footnotes

Figure 1 :

 1 Figure 1 : Category 2 architecture

  Figure 2 : Category 3 architecture

  Figure 3 : Category 4 architecture

  EN 954-1. Safety of machinery : Safety related parts of control systems. Part 1 : General principles for design 2 Directive Machines 89/392 CEE modifiée 91/368 CEE, 93/44 CEE et 93/68 CEE. IEC 61496-1. Safety of machinery : Electro-sensitive protective equipment. Part 1 : General requirements and tests.

  safety of electrical/electronic/programmable electronic safety-related systems. Part 1 to Part 7. DIN V VDE 801 Appendix A2. Principles for computers in safety-related systems.


Villeneuve Author

Ph De Janti

STSARCES : AN EUROPEAN RESEARCH INITIATIVE TO HARMONIZEVALIDATION METHODS ON SAFETY RELATED COMPLEX ELECTRONIC SYSTEMS

Dans le cadre de la Directive Machines, des travaux de normalisation du CEN/CENELEC sur les parties des systèmes de commandes de machines liées à la sécurité ont mis en évidence des difficultés pour définir des méthodes harmonisées d'évaluation, aussi bien d'analyse que de test, quand sont mises en oeuvre des technologies électroniques intégrées, en particulier programmables. Aussi plusieurs organismes de recherche et de certification, ainsi que des industriels, se sont regroupés pour lancer une initiative de recherches en soutien à la normalisation, STSARCES, qui a reçu l'appui financier de la Commission Européenne. Les résultats doivent permettre d'harmoniser les procédures de certification et ainsi de réduire les barrières techniques pouvant freiner le libre-échange au sein de l'Union Européenne.

Introduction

In the new approach to machinery -89/392/EEC Directive and its amendments-it is intended both to render the machinery necessary for European industry as safe as possible from the design stage onwards and to ensure that the safety features incorporated to achieve this end do not form technical barriers to the commercial exchanges between the member states of the Community.

The essential requirements regarding the safety related parts of control systems are covered by EN 954 part 1 dealing with general principles for design and accepted as European Standard in July 1996. Current work on validation proceeding for the different technologies involved, being the goal of the draft EN 954-2, has demonstrated that no harmonized validation procedures exist for safety related complex electronic systems. A lack of knowledge has proved paramount when facing faults on complex components, which are becoming of a generalized use in the field of machinery safety.

The STSARCES (STandards for Safety Related Complex Electronic Systems) project (1) aims at speeding up the harmonized putting into practice of the EN 954 part 2 by the European Test-Houses as well as by manufacturers of the European Union. Along with research programmes, it faces the problems raised by divergent approaches between the EN 954 and the IEC 61508 Standards, which are strategically valuable to the European economy, since this International Standard, likely to be wholly published during 1999, will be proposed for adoption as an European Standard. The project deals also with innovative technologies and designs, in close relationship with manufacturers, to avoid innovation obstacles.

However most of the results are foreseen to be presented by their own authors in their almost definitive form at the MONTREAL INTERNATIONAL CONFERENCE. The STSARCES Programme includes also a Seminar with manufacturers and the Standardization bodies by the last months of the project, its aim being to validate the putting-into-practice capabilities achieved by the final report under preparation by the Consortium. It is the hope of the partners in this project that the MONTREAL event, thanks to its large international attendance, might well be an excellent opportunity to hold this Seminar in the presence of the Project Officer of the European Commission.

  Brown, S.J.; Frost, S.; Health and Safety Executive, Electrical and Control Systems Unit, Technology Division. A study of the links & divergences between draft IEC 61508 and EN 954. WP4 Taskl Report (Ref: STS-WP4-1001) Issue 02, September 1998.

	5. Footnotes
	1. European Commission, contract SMT4-CT97-2191.
	2.

The Consortium

The consortium is made of 11 partners from 6 different countries :

Organization of the Work-Programme

The project comprises several steps carefully scheduled in time :

-STEP 1 : Research studies to fill gaps. Knowledge has to be developed or completed regarding assessment and validation techniques of both hardware and software safety in complex electronic components or systems (12 months).

-STEP 2 : Validation of proposed methods by applying them to different on-the-market systems of graded levels. This step allows avoidance of discrepancies between research works and practical realistic problems encountered while considering industrial safety products (6 months).

STSARCES : AN EUROPEAN RESEARCH INITIATIVE TO HARMONIZEVALIDATION METHODS ON SAFETY RELATED COMPLEX ELECTRONIC SYSTEMS

-STEP 3 : Integration by a transverse action of results and experience of the other test-houses partners in the project, and also of the participating manufacturers. It allows to reach an European agreement regarding harmonized procedures with a good acceptance by the concerned industry (5 months).

-STEP 4 : Formatting the results so that the proposed harmonized validation methods can be transfered right on time as a technical and application guide to CEN to support the EN 954-2 draft standard (4 months).

WPl In order to succeed sustaining an efficient level of communications between the partners, the tasks are organized into « clusters » of sub-tasks, and each cluster is managed by a partner being himself a member of the Steering and Management Committee of the project.

It is soundly believed by the Consortium that Software and Hardware aspects cannot be approached completely independently when facing assessment of safety related complex electronic components or systems, which are presently very often programmable ones. The "SYSTEM" approach is therefore enhanced in the course of the project, for instance in individual Work Programmes like "Validation by analysis" where an investigation is led on interconnected components and bus systems safety aspects, and also in a transverse action in STEP 3 which covers all the technical Work Programmes.

Progress status and preliminary results

The project was operationally launched in January 1998. An international Workshop was organized at 'la MAISON de l'EUROPE' in Paris on 6 March 1998.

It was a first CHECK-POINT event in the programme of the STSARCES project and attendants from all parties (twenty-three external experts from 13 countries, including CEN/CENELEC representatives) were invited to give comments on any aspects of the project, and particularly on :

• validity of the technical approach proposed by the STSARCES Consortium • points that should be reinforced or suggestions to improve the overall value of the project.

The Consortium received many requests from manufacturers and laboratories to establish working relationship in the course of the project, like IVF (Sweden), SCHNEIDER (France), SIEMENS (Germany), BFZ-Arsenal (Austria), the Central Institute for Labour Protection (Poland).The German machine tool builder's association, emphasized the importance of the STSARCES project not only for the manufacturers of safety systems but particularly for machine manufacturers which are the main users of that equipment. In order to ensure that results from the project are well accepted in the market, he asked for an efficient information flow between machine tools manufacturers and STSARCES. Therefore manufacturers will be invited to participate to an International Seminar before the end of the project.


Jean-Christophe Couillet '

Marc Prince

Application of an Artificial Neural Network to the Prediction of Firedamp Emissions in Coal Mines

Coal extraction at great depths and high Output faces lead to more and more elevated and irregulär firedamp emissions. To respect safety conditions, coal production must be programmed to limit methane emissions in airways.

In this contcxt, the prediction of firedamp emissions is an interesting tool to optimize safety and production.

Bul mathematical modelling of firedamp desorption and gas circulation physical processes involvc non-linear physical laws and a high number of hardly accessible parameters.

So artificial neural networks have been developed to model firedamp emissions : artificial neural networks äs universal approx'imators are able to learn from examples and generaiize in unknown situations.

Artificial neurat networks need a large amount of data sufficiently representative to learn the physical processes. Data relative to mining Ventilation, such äs methane concentration and air velocity in airways, are monitored and can be used to model firedamp emissions.

The model based on artificial neural networks has been calibrated and validated using data from coal faces recently exploited in Lorraine Coalfield (East of France). The model reliability has been appreciated on the results of a posteriori forecasts.

The model is used to forecast methane concentration values in airways äs a function of coal production.

l.

INTRODUCTION

Fi-ench colliery operations are now characterised by a considerable degree of mechanisation and high Output faces. Also the increasing depths at which coal is extracted is bringing about a change in the characteristics of firedamp emissions : their levels are relativeiy high, with wide variations.

In this Situation, mining operations must be conünued with great care in order to optimise safety. The presence of high levels of firedamp in the air may restrict or interfere with Output. The operator must therefore adapt production in order to ensure that the regulatory limits are not exceeded.

The ability to predict firedamp emissions can then be seen äs a particulariy attractive way of satisfying the safety requirements, äs well äs productivity goals, by making it possible to select production faces over time in the most appropriate way.

Mcthods for predicting firedamp emissions have already been developed in the past. However the early modeis used could do no more than predict average releases [JEGER, 1980], did not incorporate the effects of time and the rate of face advance, and could therefore not be used for monitoring fluctuations in emissions.

Later developments were based upon the routine statistical techniques of simple or multiple linear regression [START_REF] Pokryszka | Evolution des methodes de prevision du degagement gi-Lsouleux » -Journee technique des Charbonnages de France[END_REF]COUILLET J.-C, POKRYSZKA Z., 1996]. Although these modeis do take into account the dynamics of firedamp emissions and the local specific features of the working area äs regards firedamp, they can unfortunately provide prcdictions only on a weekly basis.

In f'act for predictions over a shorter period -a day or a shift -the problem is more complex, esscntially owing to the nonlinearity of firedamp desorption and transport. And of course it is precisely this knowledge of the emission, at least on a daily basis, that would make it possible to Programme the work more effectively.

In the same time, an higher performance modelling method has been identified äs a particulariy novel technique, that of artificial neural networks. A study was then carried out with a view to npply this technique to predict firedamp emissions at a longwall face.

This presentation of the research includes :

-a dcscription of the principles underlying the technique of artificial neural networks ; -a presentation of the major developments to optimise the prediction method ; -and a practical application to a particular case.

BACKGROUND AND MAJOR ISSUES

POTENTIAL OF THE TECHNIQUE

The artificial neural network technique is a modelling tool that has already proved its worth in a numher of fields (banking, military applications, meteorology, and so on) in dealing with prohicms äs diverse äs those concerning the prediction, classification or even the processing of ihc signal.

The advantages of this technique are its ability to reflect nonlinear relationships, to learn from examples, and also to describe the physical phenomenon to be modelled on the basis of a sample of data. Accordingly physical knowledge of the problem -usually expressed in terms of mathematical equations -is not essential for it to be modelled.

This also means that the technique shows considerable resistance to any perturbation of the basic clala (Tor example, data that are partially erroneous or biased) and an ability to adapt to possible change.s in the physical phenomenon.

On the other hand, the neural System must nonetheless satisfy certain requirements : among other things, there must be an adequate quantity of data relating to the physical phenomenon.

NEURAL NETWORKS AND FIREDAMP EMISSIONS

The mechanisms that govern firedamp desorption and gas circulation in the strata are such that it is complicated or even impossible to describe firedamp emissions in mines completely by means of a physical equation.

On the other hand, measurements relating to the coal extraction process and to the composition of the atmosphere are made frequently and regularly in existing mines. These measurements constitute a valuable database äs to the history of the extraction zones and can be used to improve undcrstanding of the phenomenon.

On (his basis the technique of artificial neural networks proves to be a suitable too! for modelling f'ireclamp emissions. Some foreign research [START_REF] Dixon | The application of neural networks to Underground methane prediction » -7" 1 US Mine Ventilation Symposium[END_REF] on this topic, and feasibility studies on a number of French coalfaces have m fact confirmed this potential.

GENERAL FUNCTIONING OF ARTIFICIAL NEURAL NETWORKS

The first developments of artificial neural networks date from 1943 when a simplified mathematical model of the biological neuron was worked out [McCULLOTH W.S., PITTS W. A., 1943]. The first artificial networks were used in the 1960s, but then it was not until 1982 that the technique saw a resurgence of interest [START_REF] Hopfield | Neural networks and physical Systems with emergent collective computational abilities[END_REF].

PROCESSING ELEMENT

The processing element reproduces the Operation of the biological neuron in a simplified manner.

Eacli neuron has a number of inputs, denoted e" from which an Output denoted S is caiculated.

In concrcte terms, each input is weighted by a synapüc weighting factor denoted pi whereupon an aclivation lunction then works out the weighted sum of these inputs :

NEURAL NETWORKS

To form a network, the neurons are connected to one another. In a conventionai structure, the neurons are arranged in a series of layers in which there is respectively : an input layer, then one or more hidden layers and then an Output layer. All the neurons in a given layer, except those in (he last layer, are then connected to each neuron in the next layer (figure l).

The input variables of the model are fed to the neurons in the input layer and the neurons in the output layer then provide certain values.

Input layer

Hidden layers O utput layer The modelling of the physical phenomenon by the neural network begins with a learning phase.

Input vcctors are presented a certain number of times to the network which then adjusts the weighting of each neuron in such a way that the caiculated Outputs are äs dose äs possible to those required.

If the network is to perform well in the learning phase, it must also respond correctiy when vectors it lias never encountered before are presented. To check this fact, new vectors are introduced to the network. A result of good quality will then validate satisfactory learning by the network.

hi this way the neural network expresses its ability to generalise population, it can deduce the ruie governing the entire population.

from a sample of the

MODELLING FIREDAMP EMISSIONS

METHODOLOGY

Dcvcloping an artificial neural network is based primarily on determining :

-the model ;

-a neural structurc adapted to the model defined and hence related to the architecture of the network. What has to be defined is the arrangement of neurons, the connections between Ihc processing elements, the transfer function and the initial weighting factors.

The mcchanism of firedamp emission involves a number of parameters such äs the geological siructure around the seam being worked, the gas concentration in the coal seams and rock strata, the CH 4 adsorption isotherm of the coal seams, the extent of degassing of the strata, the nature of the surrounding rocks, the permeability of the whole structure, and so on.

A great dcal of research has shown that in steady-state firedamp releases, the quantity of firedamp released into a particular working area depends closely on the rate of coal extraction IBRUYET, 1967 ;[START_REF] Borowski J - | Les relations entre la production et le degagement en taille » -Travaux du GIG. puhlication n°472[END_REF][START_REF] Kaffanke | Prevision ä moyen terme du degagement de grisou dans les voies de relour d'air des chantiers[END_REF].

Tbc approach using artificial neural networks also shows that it is preferable to inakc use of those variables (hat characterise the physical phenomenon being studied in the mo.st basic form possihle.

Aecordingly the model was developed so äs to relate the firedamp emissions to the face output, on the basis of the following three variables :

-d ie CHU concentration in the air return [%] and the ah-flow in the face airway [mVs], expressing the firedamp emission ;

-die distance travelled by the shearer during cutting at the face (m), refiecting the face exiraction rate.

The ncural nclwork was thcrcfore construeted using the following inpul and output variables, using :

-äs output variable :

• tlie mean methane concentration at a period located more or less far in the future -;is input variables :

• the mean methane concentrations at periods in the past ;

• the mean air flows at the past points and the predicted values at the future periods ;

• die distances travelled by the shearer in the cutting phase at the passed periods and the predicted values at the future periods.

The devclopments then involve characterising these variables with regard to the physical phenomenon of firedamp emissions. For this purpose, several configurations were prepared and lesled using data representative of the problem raised.

üllimately a synthesis of these experiments should result in the definition of the best possible prcdiction model.

EXPERIMENTS

The experiments can be illustrated using the results obtained for the "Irma Nord" face 1140/1250 at thc Reumaux mine. This face is undercut and the goaf is caved. The panel length is 1680 m for an averagc opening of 3.6 m. The Ventilation follows a U pattern with an airflow of between 38 and 50 m V .s. The face is worked on a 3 x 8-hour shift basis from Monday to Friday.

Tlie changes in the different characteristic variables (CH4 concentration, airflow and output) during working of the face is shown on figure 2 using a time interva! of 8 hours. The calculations showed first of all how important it was to have representative calibration data.

The calibration database must be sufficiently extensive so äs faithfully to represent the Output at (lie face. Similarly, the results were mostly much better when the model was calibrated over the pcriod äs dose äs possible to the prediction period.

The expcriments also demonstrated the need to construct the network carefully : a badly consiructed network will in fact never be able to provide usefui predictions, however relevant the variables.

Ullimalely, an optimal configuration was devised, capable in pariicular of learning how to model unslable liredamp emissions (changes to the volume of influence, in the Output rate, and so on).

The rcsulls given in figures 3 and 4 are from an optimal configuration of the neural network.

These arc a posteriori predictions, for which the values of CH4 concentrations caiculated by the model arc compared with those actually measured at the face. Quile apart frorn the overall shape of the above curves, the performance of the prediction can be cvaluatocl using the coefficient of con'elation between the predicted and measured values. For the caiculations done for the Irma Nord face 1140/1250, this coefficient is sufficiently dose to l for die rcsLilts (o be regarded äs satisfactory. Its value is 0,69 for the test äs a v/hole.

5.

CONCLUSION

Appiication of the technique of artificial neural networks to predicting firedamp einissions at a coalfacc has clearly demonstrated the potential of this approach.

The model was developed with the aim of predicting values of methane concentration in the air rcliii'n. These predictions are based on the past values of the methane concentration and on the p;isl and lulurc values of the othcr variables involved in the phcnomcnon considered (airfiow at I he l'ace and face Output).

The experiments clearly demonstrated the importance of the configuration of the neural network (o (he quality of the results. In fact the main difficulties arise in modelling unstable regimes of firedamp cmissions (changes in the volume of influence, face Output, and so on).

However the selected configuration learns these difficulties better than others. For modelling to he successfui, the learning data must be representative. The results also show that the performance of the prediction is conditioned by an appropriate model of the neural network.

The model devised gives entirely satisfactory results and can be used to monitor ongoing faces in sucli a way äs to pcrmit improved programming of future production.

6.

  nonlinear transfer function (p (a sigma function for example) caiculates the Output S äs a lunction of the value of the activation function, or S = (p

Figure

  Figure l : neural network

Figure 2 :

 2 Figure 2: Changes in characteristic variables for the Irma Nord face 1140/1250 at the Reumaux colliery Scveral modeis were developed and applied using data from the face studied.

Figure 4 :

 4 Figure 3 : Prediction of firedamp emissions (learning set)