INERIS 1 Accidents related to goods transportation

The transportation of goods is linked with a lot of accidents with possible consequences on man, environment and equipment.

All types of transportation systems are involved and data are worldwide collected with the purpose of learning from experience. In ARIA databases (France), every year, about 140 accidents (on a total of 1.100 reported) are mentioned concerning the transportation of dangerous goods.

On a total of 805 transportation accidents included in this database, 67 % are road accidents, 2 % involved inland waterways and coastal transportation and 23 % rail transportation.

Road transportation is a field in which a large number of accidents occurred, the consequences being worst with explosive, flammable and toxic materials. In many instances, the toxic products were the consequences of a fire (toxic fumes).

Road transportation of flammable liquids

Some typical examples are related to the transportation of flammable liquids (fuel and gasoline). A brakeless lorry containing soap and liquid alcohol involved in an accident at the bottom of a steep hill induced 10 fatalities (Les Eparres, France, January 7 th , 1993).

Road transportation of explosives

In rare occasions, explosive substances and articles are involved : a typical example is an accident on a highway on May 13 th , 1993 at Etoile-sur-Rhône, France, in which 3 tons of pyrotechnic substances were involved. A fire and an explosion were triggered by a collision and the lorry driver was killed. Fortunately, this accident occurred during the night with a very sparse traffic.

Another example is the Walden Truck accident, occurred on August 5 th , 1998 in Canada, in which a transport containing about 18 tons of explosives fired after a collision on the roadside and detonated. Fortunately, an area approximately 600 meters in both directions of this fourlane highway was vacated. Nobody was hurt by flyrocks and truck fragments (maximum thrown distance : about 2.5 km). The highway has been closed for a period of 11 days.

Accidents in road tunnels

The consequences of such types of accidents are worst when they arise in a tunnel. As regards strictly dangerous goods, only very few accidents are worldwide known. But it should be emphasized that the impact of tunnel transportation is low by relationship with the other parts of road systems.

Reported accidents involved carbon disulfide (Holland, USA, 1927), gasoline (Caldecott, USA, 1964), aerosol dispensers and paints, (Tauern, A, 1999). In the Mont-Blanc tunnel, in 2000, ordinary goods were involved such as margarine. In other accidents (Mont-Blanc in France, date unknown, Fréjus in France in 1980, Gothard in Switzerland in 1980, Billwerder Moorfleet in Germany in 1963, the plastic materials were involved in three cases and cotton balls in one case (Mont-Blanc).

Rail accident in tunnel

The only opportunity where dangerous goods were involved in rail tunnel is the accident in Summit tunnel in UK in 1984, after the derailment of a white spirit wagon. The initiated fire lasted 3 days. In the Channel tunnel, in 1984, only ordinary goods were involved at the beginning of a fire in a lorry embarked in the train (fats).

Rail accidents on plant premises and marshalling yards

On plant tracks and in marshalling yards, a lot of accidents are known. Only the following examples can be briefly explained.

At Aix-les-Bains station (France, 1992), a derailment of a train with three wagons containing dangerous goods (dimethylamine and ammonia) was at the origin of a release of the liquid dimethylamine. Buildings were evacuated within 400 m from the accident. The emergency situation lasted 4 days.

At La Voulte (France 1993) 20 wagons containing gasoline derailed. 3 tanks were ruptured and exploded. The fire propagated to houses and to a sewer system. A soil pollution on 26 ha was also induced.

Wreck of ships

The wreck of chemical or oil tankers is also frequently at the origin of sea and shore pollution. In 1999, the oil tanker Erika sank close to the South Brittany shores and, in 2000, the chemical tanker Ievoli Sun 30 kms ashore of Cotentin, France, with partial release of styrene and some local pollution of shellfish.

General background of regulations

In order to avoid or minimize the consequences «f these accidents, regulations were developed (and are still under further development), respectively on : In these regulations, requirements are given for the training of persons involved in the carriage and safety obligations of the participants. As regards safety obligations, appropriate measures shall be taken according to the nature and the extent of foreseeable hazards, so as to avoid damage or injury and, if necessary, to minimize their effects. When there is an immediate risk that public safety may be jeopardized, the participants shall immediately notify the emergency services and shall make available to them the information they require to take action.

Classes of dangerous goods

Class 1 : explosive substances and articles Class 2 : gases Class 3 : flammable liquids Class 4.1 : flammable solids, self reactive substances and solid desensitized explosives Class 4.2 : substances liable to spontaneous combustion Class 4.3 : substances which, in contact with water, emit flammable gases Class 5.1 : oxidizing substances Class 5.2 : organic peroxides Class 6.1 : toxic substances Class 6.2 : infectious substances Class 7 : radioactive materials Class 8 : corrosive substances Class 9 : miscellaneous dangerous substances and articles.

Principles of classification

For the majority of classes, the assignment is made in accordance with defined tests, procedures and criteria (see "UN Manual of tests and criteria").

Limitative classes : « classes 1, 7 and partially 4.1 (self reactive substances) and 5.2 (organic peroxides) Non limitative classes include remaining classes, and generally include tests, procedures and criteria.

More explanations about the criteria for classification can be found in table 1. The heading of Class 9 covers substances and articles which, during carriage, present a danger not covered by the heading of other classes.

The substances and articles of Class 9 are subdivided as follows :

Ml : substances which, on inhalation as fine dust, may endanger health M2 : substances and apparatus which, in the event of fire, may form dioxins M3 : substances evolving flammable vapor M4 : lithium batteries M5 : life-saving appliances M6-M8 : environmentally hazardous substances : » M6 : pollutant to the aquatic environment, liquid « M7 : pollutant to the aquatic environment, solid » M8 : genetically modified micro-organisms and organisms M9-M1 : elevated temperature substances : • M9 : liquid • M10 : solid Mi l : other substances presenting a danger during carriage, but not meeting the definitions of another class.

Packing groups

The requirements are different according to the various classes.

The packing is a maximum volume of 4501 or can contain a maximum amount of 400 kg.

There is a testing and approval procedure dealing with drop test, tightness, internal pressure, storage and specific tests.

As regards the packaging, the compatibility between material and goods shall be examined.

Issues to be dealt with

For about ten years, strong efforts were devoted to harmonization of classification and labelling of chemicals. Considerations were also paid to more relevant methods for characterization of energetic materials and still unclassified substances. Another important international work (OECD, UE DG Environment) concerned the DG transportation in road tunnel considering a QRA approach.

The Globally Harmonized System of Classification and Labelling for Chemicals

Since 1992, the work on the Globally Harmonized System of Classification and Labelling for Chemicals (GHS) has been carried out by the International Labour Office, the Organisation for Economic Co-operation and Development and the UN Committee of Experts on the Transport of Dangerous Goods and on the Globally Harmonized System of Classification and Labelling for Chemicals. Two sub-committees are involved :

• the sub-committee of experts on TDF • the sub-committee of GHS.

The sub-committee of GHS had been created to keep the GHS up-to-date and to promote its effective implementation.

A first GHS guiding document should be finalized by July 2002 : the draft document will be ready for discussion in December 2001.

The GHS will be taking into account the classification criteria for :

• physical hazards : about the physical hazards, the work is completed except for criteria for the flammability of aerosols. The criteria proposed are : definition of gases, liquids and solids test conditions flammability (solids, liquids and gases) reactivity (pyrophoric substances, self-heating substances, substances which, in contact with water, emit flammable gases, oxidizing substances, organic peroxides, self reactive substances, explosives and substances that are corrosive to metals) compressed gases

• health hazards

• hazards to the environment : the Globally Harmonized System of Classification and Labelling for Chemicals covers the nine hazard endpoints considered in existing classification systems : hazards to the aquatic environment, acute toxicity, skin irritation/corrosion, sensitisation, germ cell mutagenicity, carcinogenicity, reproductive toxicity and target organ toxicity. In addition, this system will also include the following hazards not yet covered by existing systems : neurotoxic effects, immunotoxic and effects hazardous to the terrestrial environment.

Classification of energetic materials

Energetic materials are those materials with a high or medium energy content typically greater than 800 J/g. They comprise explosives in Class 1, desensitized explosives in Classes 3 and 4.1, selfreactives in Class 4.1, organic peroxides in Class 5.2 and a lot of substances allocated to different Classes for various reasons, e.g. :

• nitromethane as a flammable liquid -Class 3

• ammonium nitrate as an oxidizer -Class 5.1 « nitrocompounds as toxic substances -Class 6.1.

So there is no unified scheme for classifying energetic materials even for transport. Moreover the GHS exercise for physical hazards demonstrated recently how important are the difficulties for merging systems dedicated to different purposes : UN for transport, EC for labelling chemicals, OSHA in US, etc.

Finally the best approach is to concentrate on properties, like detonability, deflagrability, behaviour in heating under confinement, thermal stability, sensitiveness to mechanical stimuli, for identifying properly the hazards and to adapt as far as possible the conditions of transport, storage, handling accordingly.

As an example, the transport of nitromethane authorized in tanks in the past has been forbidden after a severe rail accident in USA resulting in a mass explosion due to a cavitation process after impact.

Because of the actual situation which is not really satisfactory, the trend is to push to refound the UN classification system for energetic materials, creating a new Class for these materials beside the Class 1 for explosives. It will provide the opportunity to have unified classification procedures and methods and will allow industry to reduce the explosion hazard by dilution or by other means. Nevertheless attention is to be paid to such a process as addition of diluants may emphasize thermal effects in a case of extended fire.

Unclassified (but dangerous) substances in tunnel

Further to a recommendation following the enquiry on the Mont-Blanc tunnel accident, some liquid substances or substances to be easily liquefied, solid substances with heat of combustion similar to hydrocarbons should be studied for a possible classification in the road transportation legislation.

About one hundred products (oil, fats, polymers, animal or natural fats) having a high heat of combustion can be taken into consideration for such transportation and can burn. When a fire is induced in the vicinity, these material melt and can flow with a possibility of developing a pool fire.

It means that the following characteristics shall be determined :

• heat of combustion and burning rate • formation of thick and opaque fumes with soot and toxic substances production • interaction with the packing.

For The final objective of this QRA model is the production of quantitative data on DG transportation risk levels on various routes, some of which being tunnels.

The risk is characterized by the probability of occurrence and the severity (as a number of fatalities or injuries, damages to buildings and structures or environment). F/N curves qualifying the societal risk (annual frequency F to get an accident in which more than N people are killed) were defined ; individual risks are also determined considering the frequency for permanent populations. Damages to structures are semi-quantitatively defined and damage to environment are only qualitative.

A lot of simplifications were introduced in the model in which a limited number of relevant scenarios (ten) are included.

Two lorry fires scenarios (not considering DG) are also included because of the very severe risk (Mont-Blanc and Tauern accidents in 1999) in tunnel. Such scenarios are really more frequent than those implying dangerous goods.

Some ventilation configurations and the safety measures adopted (traffic control, flammable liquid drainage, monitoring system) have been studied to examine their influence on the F/N curves.

At the end of the work programme, the QRA model was produced as a software tool, available in a CD-ROM and includes a user guide and specialized guidance documents.

•

  road transportation ADR, last version, restructured applicable as from July 1 st , 2001 : • rail transportation RID, last version restructured applicable as from July 1 st , 2001 • sea transportation IMDG, Code, edition 2000, IMO, London, 2001 • air transportation I AT A, 42nd edition, 2001 • inland waterways ADNR, edition 1999.

Table 1 :

 1 classes of dangerous goods

	Class	Substance	Main criteria for
			classification
	1	explosive substances and articles	explosive properties
	2	gases	critical temperature
			< 50°C or vapor pres-
			sure at 50°C < 3 bar
	3	flammable liquids	boiling point
			flash point
	4.1	flammable solids, self reactive	exothermal reaction,
		substances and solid desensitized	bulk combustion
		explosives
	4.2	substances liable to spontaneous	self ignition
		combustion
	4.3	substances which, in contact with	water action
		water, emit flammable gases
	5.1	oxidizing substances	burning velocity
	5.2	organic peroxides	decomposition
			temperature
	6.1	toxic substances	inhalation, ingestion,
			action on skin or
			mucous membranes
	6.2	infectious substances	no
	7	radioactive materials
	8	corrosive substances	action on skin or
			mucous membrane
	9	miscellaneous dangerous	see below
		substances and articles

  these substances, possible regulations (in France and abroad) are still under discussion, considering either classification in class 9 or prohibition of transportation in runnel or possible transportation without classification when tunnels are adequately designed as regards the development of such fires, or grouping as proposed by OECD/AICPR.3.4. QRA and decision making for DG road transportationOECD developed a research program for defining a quantitative risk assessment for the transportation of dangerous goods in road tunnel. This program gave input data for a decision making system and helped for defining practical measures for minimizing the risks. All this work was funded both by OECD and European Union (DG VII). INERIS (France), W.S.Atkins (UK) and University of Waterloo (Canada) were involved in the QRA research.

Limitative class yes no no partially no no no partially no no yes no no


F Masson

J P Pineau

J J Tritsch

CONSEQUENCES OF IZMIT (KOCAELI) EARTHQUAKE (TURKEY, AUGUST 17,1999) ON INDUSTRIAL PLANTS AND SOME JETTIES

After investigation of the consequences of the Izmit earthquake in nine industriell plants, a report • was writlen for the French ministry of Environment. The main objective was the comparison with the Situation of earthquake prone French industries. General Information on this earthquake and its economic consequences in the Izmit area are first given. Then, typical accidents induced by the earthquake (referring to nine visited plants) involving dangerous chemicals (five cases) are described and proved the need for assessing equipment and infrastructure vulnerabilities, referring to consideration of regulatory aspects. Risk assessment and preventive and protective measures are to be introduced in specific safety cases dealing • with seismic ejfects for industrial plants and port areas. The objective of this safety case is to prove the stability of facilities (non total collapse), but also some functional and operational capability m Order to avoid adverse effect on man and environment.

ESTRODUCTION

The earthquake, arisen ON August 17, 1999 to Izmit ( Kocaeli), Turkey, of magnitude 7.4, is not exceptional in this region (7 earfhquakes of magnitude superior to 7 have occured since 1939) ; accelerations on the ground, between 0.2 g and 0.4 g in the stricken zones, are rather moderate considering the magnitude.

The affected zone, situated in the southeast of Istanbul, near the Sea of Marmara, extends on 200 Idlometres in length and 50 kilometres in width in a region with strong density of population and industrial plants. In the part of this region direcdy hit by the earthquake and depending of the Izmit Chamber of lndustry, 30 % of industrial plants have had important damages, 20 % can be repaired within one month and 10 % cannot be repaired. l % of the workforce was killed and the production loss was estimated äs 1-1.5 billion US dollars every month after the earthquake. Following the 7.4 magnitude earthquake in Turkey, current estimates of total insured loss have ranged from l bn to 2.75 bn US $ whereas the total damage is estimated at 16 billions US $. The earthquake involved a lot of industrial plants of the Izmit economic area (13% of Turkey industrial production).

The earthquake caused all possible underwater and on land phenomena such äs landslides and ground collapses, rockfalls, ground liquefacüon.

At the request of the Direction of the Prevention of Pollutions and Risks of the French Ministry of the Regional development and the Environment (MATE), the INERIS studied :

• intervenäon in emergency situadon within the framewoik of the fire of six floating roof tanks of liquid hydrocarbons arisen in Izmit's refinery, • the effects of fhe earthquake in indiistrial installations of lznii f "s region.

First phase, realized fioni 19 all 21 August 1999, in contact with the Direction of the Defence and the Civil Safety of the French Home Office, allowed to put in evidence the difBculty of implementation of means of intervenäon on such a fire of petroleum products in tanks.

Second phase was assured from 2 till 11 September 1999 in contact with the mission, led to the same dates, of the Fiench Association of Parasismic Engineering (AFPS).

Nine industrial plants were visited, for some of diem with the assistance of the Izmit Chamber of industry. Damages on equipment, infrastructure and buildings were invesdgated for defining typology. More detailed information about damages on infrastucture can be found in l) and 2).

VISITED PLANTS

These plants were generally located in the neighbourhood of the Sea of Marmara, often on alluvial grounds or embankments.

Visited installations were:

• a cement plant ; installation suffered only minor damages and was able to quickly restart,

• a refinery where damages concemed different tanks, a jetty, a Stack which collapsed on a process plant, a control room, the Underground network for water supply against fire, • a storage of liquefied petroleum gas ( LPG), for filling domestic bottles and lorries where damages were very minor and did not prevent a fast restart, • an installation manufacturing chlorinated products, where chlorine was made by electrolysis, but was not stored ; a lot of electrolytic cells underwent damages, buildings presented minor damages, a jetty collapsed in sea on 125 m, • an installation, including a jetty, where liquid organic products are stored and damages were minor, • an installation manufacturing aluminium profiles where certain buildings with concrete frame (concrete beams walled in with bricks and mortar or concrete slabs) collapsed, • an installation for manufacturing plastic pipes where buildings with concrete frame (concrete beams walled in with bricks and mortar or concrete slabs) collapsed killmg two wolkers, • an installation manufacturing acrylic polymers where three reservoirs let escape their content in the corresponding concrete retention pools. 250 m of jetty collapsed in sea and a concrete duct conveying some process water broke and had to be replaced.

TYPICAL ACCIDENTS BNDUCED BY THE EARTHQUAKE

During the occinrence of this 7.4 magnitude earthquake m (he laust arca, dose to fhe Sea of Mannara, some typical accidents (non exhaustive list) occuned in a refinery, in its vicinity (GPL pipeline), in an acrylic polymers plant and elsewhere.

• Six naphta tanks of a refinery were involved during five days in a fire, which did not fortunately propagate to other reservoirs or installations. A 120 m high Stack collapse during the earthquake with major effects on a process plant closed several months for complete repair. • In an installation manufäcturing aciylic polymers, a leak of 6500 tons of acrylonitrile led to the death of fhe fauna nearby because of the fonoing of a toxic cloud after release and evaporation of this liquid in concrete retention pools following a break of three pipes at tbe bottom of ihree tanks; a ground pollution occurred also because of cracks appeared in these retention pools during fhe earthquake making a pathway to ground pollution. • An Underground liquid petroleum gas (LPG) pipe connecting a refinery with storage spheres in a nearby installation broke during Ihe earthquake, led to the forming of a cloud which was ignited (flashfire) by a lony crossing the cloud and led to the fire of a nearby paint storage fäcility and of lorries with two fätalities : the lony drivers. • Broken pipes, breakage of equipment and storage facilities and on jetties let release chemicals on ground; from collapsed jetties a sea pollution was also possible at some locations, but no information was available.

Some accidents occulring in the aftermath of an earthquake shall be avoided partly by a proper design and maintenance of plants considering the effects of the seismic waves on plants, buildings and facilities.

Other accidents or their consequences are avoidable by proper action at the very begüming of the earthquake considering :

• fimctions to be maintained • operations to be stopped.

Such approaches should be related to risk assessment methodologies where the effects of sismic waves are to be related to soll structure

EQUIPMENT VÜLNERABILITY IN INDUSTRIAL PLANTS

4.l Consideration of regulatory aspects

The investigation was devoted to the evaluaäon of potential damages in relationship with the types of facilities and their location and possible accidental scenarios in relationship with the probabüity of " overaccident " (risk increase related to a dangerous plant) for vulnerable points in a plant äs requested in French regulation.

French regulation

Accordmg to the French law, industrial plants considered äs a special risk need parasismic construction, planning and Operation ruies explained m a specific study "etude parasismique ". Consideration is to be paid to seismic zoning (national and local), active faulte and site effecte, the important parameter being the Likely Historical Reference Earthquake -LHRE-(considering historical data). At the very end of the process the intensity to be considered is equal to the intensity of LHRE+1. The above mentioned specific study, part of the safety case, has the objective, knowing the seismic hazard, to define vulnerable equipment (and parts thereof) and possible accidents, the last phase being the verification of adapted dimensioning against the seismic effecte.

The objective of the study is to prove the stability (non total collapse), but also some fünctional and operational capability in Order to avoid adverse effect on man and environment

4.l.2 Turkish regulation

In Turkey, for dangerous plants, a sanitary protection cordon has to be established on the basis of a risk assesment but information is missing about the licensing process and the inspection, land use and emergency planning and specific consideration of earthquake effects.

4.l.3 Approach of the experts

Conclusions fiom Ihe observations in Tmkey could only be validated if detailed files for the plant (geotechnic studies, engineering documents, risk assessment) are made available. Until now, this work has not been undertaken.

Howe-ver, it was possible to define potential damages by reference to the ground stability. Then, taldng into account the overaccident, vulnerable equipment were globally analysed on the basis of reported observations either in industrial plants or in infrastructurc.

Influence of ground stability on potential damages

The cement plant was the only plant pardy located on solid rock, the others were built on natural or artificial embanlanents ; 5 from the 9 visited plants were dose to the seashore. Five plants were located in an industrial estate and surrounded by other hazardous plants where domino effects are possible.

Tabte l summarises the potential damages considering ground stability.

Equipment vulnerability in industrial plants

Considering the possible overaccident and possible hazards, the vulnerability was qualitatively analysed for the nine visited plants.

Energy and utilities

Electric energy was lost shortly after the earthquake. Generally, emergency supply was operating with apparently an exception in the acrylic polymers plant where a lack of energy lasted 39 hours.

In some cases (refinery), public water supply (especially for fire fighting) was also lacking.

Jetties and port areas

Some examples of the general findings are given in table 2.

Toxic cloud Explosion

From an industrial source it was mentioned that for a total amount of 34 industrial jetries ; 10 % sunk partly or totally in the sea.

It should also be mentioned that the Turkey Naval Base in Gölcuk, located on the fault, suffered extensive darnage with collapse of buidings Idlling several hundrcd militaiy personnel.

Pipes

Above ground polyester pipes located in a plant were broken but without major damages; some Underground concrete ducts (process water ) in another plant (avoiding plant Operation) or steel pipes (LPG release with a flash fire induced, water release impeding an efficient fire fightmg) in a third one have been broken.

A special attention is to be paid to connecting pipes and their connections to enclosures (fhree " guillotine" breaking in a chenucal plant inducing a 6.500 tonne release of a liquid toxic chemical.

Tanks and reservoirs

Liquid movement is certainly at fhe origin of the damages. The damages are the most important in atmospheric metallic tanks of a rather moderate volume (between 1000 and 10000 m3).

Process equipment

In Üie EQE Briefing (2) was rcported the collapse of a cooling tower in a pefrochemical plant, of cranes in a steel factory. The direct impact of the earthquake can also be mentioned on a lime tank in an acrylic polymers plant and for the collapse of a 230 m high heater Stack in the refinery.

Industrial buüdings

In many cases, buildings were built äs concrete fiamed (concrete beams walled in with bricks and mortar or concrete slabs) and collapsed. In one plant two people were killed. Paitial collapse was also ment»oned for a tire fectory.

Wifhout an assessment of fhe mechanical resistance of the buildings, it is not possible to draw valid conctusions : the design, the construction and the behaviour of the ground need to be considered altogether.

Prevention measures and emergency response

With the exception of fires in floatmg roof tanks, the fire in other bcations of the refinery were extinguished rapidly using the means available in the refinery.

As regards the floating roof tanks, it was decided to allow buming the content of tanks and to protect the neighbouring tanks by pouring water to avoid a temperature increase and fire propagation. This strategy was successfal but a bit risky in an area where LPG and ammonia tanks were m the vicinity, respectively 300 m and 500 m.

VULNERABILITY OF INFRASTRÜCTURE (l) (2)

Turkey lost electric power shortly after the earthquake because of damage to a 380kV Substation in Adapazari. Effects were also obtained in other substations and 172 transformers, mamly owing to buildings collapse (out of 240).

In the Izmit area, water is supplied from a 60 mülion-cubic-meter dam which experienced 2 metersloshing in the event Water treatment plants and major distribution Systems performed reasonably well, sustaining minor damages, local failures were suffered owing to the collapse of buildings and soil subsidence.

Roads suffered damages (especially collapse of a bridge on a bus on the main highway Istanbul-Ankara), in areas where the roads intersected the fault and where subsidence occuned. Otherwise the majority of bridges, motorway and local roads performed well.

It was mentioned a leak on <he main distribution pipeline of compressed gas at the location where the underwater part merges on land -The distribution System was more severely hit 30% of gasmeters (3600) were shut off and 500 connections had to be changed owing to buidings collapses mamly.

As reagards communications, 385.000 lines and 101 centres were located in the area hit by the earthquake ; in general, the buildings did not suffer large damages, but various consequences were obtained (flooding in a centre, batteries ruptures, cables cutting).

In Golcük and Izmit, the hoispitals did not suffered damages.

The main buflding of die fire brigade in Golcük collapsed with 20 fatalities.

CONCLUSIONS

In Izniit area, industry suffered heavy losses either related to buildings collapses, or to process failures or to intemal or extemal infiastructure failures. In general, not unknown phenomena were involved. The main lesson should be the need of risk assessment referring to regulatory requirements by experienced structural and process engineers joinüy with die application of conmion mies for seismic prone areas.

As regards the effects of overaccident (risk increase related to dangerous plant) the occurrence of a release of toxic liquid in acrylic polymers plant and a five-days fire in sfcrage tanks in a refineiy are of particular concem. It means for nie füture the need for more detaüeq risk assessment of seismic effects including consideration of soft ground motion, the locaäon versus the fault, the severity of the damage, the safety measures for avoiding and mitigating the effects, die domino effects from accidental scenarios and the application of die enaergency response m a specific study. Specific studies are also needed for port areas and jetties.

The business intenupdon losses are also to be taken into consideration. Last but not least die environmental effects especially related to die vast releases of chemicals in ground and water must be considered in situalions where logistic means for fighung and remediadng are missing for hours or days.

Table l :

 l Potential damages related to unstable ground

	Plant type and equipment	Location and surrounding	Potential damages
		conditions	related to unstable
			ground
	Cement plant	Built on rock, no housing m Ihe	Negligtole
	Rotating laln, coal powder	vicinity
	storage
	Manufacturing chlorinated	Seashore, alluvial ground	Possible, alluvial ground and
	products		possible landslides
	tanks		(seashore)
	Electrolysis cells
	Pipes
	Salt storage
	Refinery	Seashore, alluvial ground	Possible, alluvial groundl and
	Tanks for crude oil und	(housing in the vicinity)	possible landslides
	petrolemn products		(seashore)
	LPG spheres
	Birildings
	Process
	Jetty
	Liquid chemicals storage	Seashore, alluvial ground	Possible, alluvial ground and
	Tanks, Jetty	(housing in the vicinity)	possible landslides
			(seashore)
	Liquefied petroleum gas	1 km from seashore, alluvial	Likely but less probable than
	storage	ground, (housing in the vicinity)	in the three previous cases
	LPG spheres and cylinders de
	GPL, Füling stations for
	Containers and lorries Pipes
	Acryüc polymers	Seashore, alluvial ground, no	Very likely, alluvial and
	Process under pressure, tanks,	housing in the vicinity, land under	landslides
	pipes, jetty	cultivation and orchards
	Car factory	Seashore, alluvial ground	Possible, dose to the fault
			and ground movement

Table 2 :

 2 Possible hazards fiom jetty maliünction probability

	Plant type and equipment	Jetties	Possible hazards
		Overaccident probability
	Cement plant	Extremely low	Local fire
	Rotating kiln, coal powder
	storage
	Manufacturing chlorinated	High	Sea and ground pollution
	products
	Tanks
	Electrolysis cells
	Pipes
	Salt storage
	Refinery	Mean to high	LPG and oil Spills
	Tanks for crude oil und		Explosion
	petroleum products		Fire
	LPG spheres		Sea pollution
	Buildings		BLEVE
	Process		Toxic cloud ?
	Liquid chemicals storage	High	Fire
	Tanks,		Sea pollution
	Acrylic polyrners	High	Fire
	Process under pressure, tanks,		Sea pollution
	pipes, jetty


Jean-Philippe Pineau

Philippe Cassini

Risk assessment related to tunnels

Following the fire which occurred in March 1999 in the Mont Blanc tunnel located between France and Italy, an Appraisal Committee has been committed to assess the safety of 40 existing French road tunnels, with a length exceeding 1 km.

Later, a new regulatory document (circular) was issued (25/08/2000) about the safety of existing road tunnels. In this document, a new procedure is requested : a specific hazards study (SHS). A work is still under progress between different partners to define the methodology to be applied for these SHS. Every SHS will be submitted for acceptance to a National Evaluation Committee. New regulations are under preparation.

Such SHS are prepared only after achievements of preliminary studies (traffic studies, rules of operations, specific study for the transportation of dangerous goods if any...) from which a reference state if defined. The different steps of this SHS are : risks identification, definition of scenarios (standardised and customized) from which it is possible to describe a sequence of events, possible consequences and the validity of the system management of the system especially in emergency situations. The conclusion of the study is the evaluation of the safety level with possible use of severity/occurrence matrix. Proposals are then to be made by the contractor and operator to improve the safety level on weak points.

Among the difficult issues are : the need for preventive closure of a tunnel when a situation is incidental but without major consequences, the assessment of fire developments for different types of vehicles and the influence of the ventilation, the efficiency of fire fumes extraction, the definition and use of severity/occurrence matrix.

Introduction

Following the fire that occurred in the Mont Blanc tunnel on 24 th March 1999, an Appraisal Committee was given the task of reviewing the safety of 40 French road tunnels exceeding 1 kilometre in length. Later a new interministerial Circular (No. 2000-63), covering the safety of all tunnels in the national road network 1 , and including technical requirements (TR) was signed on 25.08.00 to replace that of 1981. This Circular was a forerunner of a law -under preparation at the time -covering the special procedures applicable to all hazardous infrastructure, due to be submitted to the French parliament by the end of 2001, together with its decree of application to all road tunnels, including those outside the national network but being the responsibility of regional authorities. The Decree will apply to a total of nearly 200 tunnels.

Exceeding 300 metres in length, including motorways operated on a concessionary basis, but excluding crossborder systems Annex 1 of the Circular establishes a new procedure that applies before tunnels are opened to traffic, including in particular the preparation of a Specific Hazards Study (SHS) for each facility in service, ways and means of monitoring their operation (enabling feedback of experience) supplemented by annual exercises. The procedure involves an appraisal by the Road Tunnel Safety Evaluation Committee (CESTR) issued from the initial appraisal committee.

Specific hazards studies

At the initiative of the French Ministry for Land-Use Planning and Environment, Annex 1 of the Circular includes the requirement that all the safety dossier for tunnels whether planned or in service should include a specific hazards study (SHS) referred to in very general terms: "... describing the accidents, of whatsoever origin, that might occur during operation as well as the nature and extent of their possible consequences; this study will specify, with proper justification, those measures likely to reduce the probability of occurrence of these accidents and their consequences."

As a guide to the preparation of such studies, the CETU 1 , with the assistance of the Defence and Civil Safety Direction (French ministry of Interior) and INERIS, drew up an information note on SHS (Note No. 12). This note was submitted to the Assessment Committee and was then circulated in December 2000 by the Director for Roads to "owners" and design offices. However this was merely a provisional document, to be revised in the light of experience once a number of SHS wouldhave been produced.

On the basis of experience gained since that date, a methodology for producing these studies was worked out as a result of work done by representatives of CETU, INERIS, the Ecole Nationale Supérieure des Mines in Paris, design offices and operators.

The study may begin only when a number of prior investigations have been carried out to generate a frame of reference on which the SHS is based. As regards the transport of hazardous goods, a Circular (No. 2000-82), replacing that dating from 1976, was published on 30.11.00 to supplement the Circular of 25.08.00. It introduces a specific procedure for the comparative review of risks due to hazardous materials between the tunnel route and alternative routes. This review must be quantitative in nature, as regards incident frequencies and severity levels (QRA approach) except for small non-urban tunnels2 .

_£

The Circular makes it clear that the review may in particular utilise a model developed under the auspices of the OECD and the World Roads Association by INERIS, the British contractor W.S. Atkins and the University of Waterloo in Canada. The CETU has arranged a presentation of this model together with training in its use for 2 nd and 3 rd October 2001.

In this way a frame of reference for the tunnel is defined; the principle of formulating the SHS is shown diagrammatically on figure 2. The frame of reference indicates, in a summarized manner, the systems and procedures, the tunnel environment, and gives a functional description of the installations, equipment and systems relating to operation and safety (including a summary of the review of incidents and accidents that have occurred in the tunnel and of the safety exercises).

We shall now give some details of the different steps shown schematically in figure 2. The chapter references given on the figure are those used in the CETU information note No. 12 (See paragraph 1). This stage generates a summary description of the tunnel geometrical and functional characteristics. It also gives the contractor in charge of the SHS an overall idea of the tunnel and enables it to highlight the points it perceives as essential for safety.

Identification of hazards and choice of scenarios

This process involves establishing: a list of hazards according to origin, by choosing a suitable method, the incidents and accidents likely to occur, the consequences, leading to a definition of scenarios and an evaluation of severity, a classification of the scenarios according to the estimated severity and frequency, -the selection of certain scenarios to be examined with more details in a further step.

Study of scenarios

In defining scenarios, only the first 30 minutes of their development will be normally considered, so as to investigate their consequences and the steps to be taken as regards operating instructions and evacuation schemes. The hazardous factors (heat, toxic gases, poor visibility, pressure waves, projectiles, and so on) should be investigated from the standpoint of both the tunnel and the environment.

It must also be emphasised that certain scenarios (notably those concerning fire) are required, while others are optional.

The standardised scenarios (see figure 3) establish a minimum comparability between tunnels. They are based upon standard incident events, including also standardisation of the parameters and modelling approaches necessary for describing the development of events, actions and serial consequences caused by the initial event. The optional scenarios make it possible in particular to investigate the consequences of incident events tha highlight the particular features of the tunnel.

"Owner's" report

When this work has been completed, an expert may be brought in (the Circular makes explicit provision for this). The expert should not have been involved in the previous phases. His/her role is to provide an external view of the entire approach and the proposed conclusions.

It is then up to the "owner" to set out in a report the chosen protective and preventive measures and the schedule for improvement works if any.

Note: an expert may also be brought in for the preliminary projects and for inspecting facilities already in service.

Expert opinion on the entire safety dossier

After this owner's report, an expert 3 has to write a global appraisal on the entire safety dossier.

Or a competent organisation as regards the safety of road tunnels It is requested in the circular : e For the project (POA or APOA), " appraisal of the safely by an expert " • before operation , " expert appraisal about the relevancy as regards safety requirements and other requirements included in the dossier • when examining the premises in operation " a diagnosis by an expert of the premises safety and of the operation safety

The Assessment Committee then makes the final appraisal after being made aware of all appropriate information by one of its members acting as rapporteur.

2 Some current problems not fully resolved.

2.1The decision on preventive closure

Since the accident in the Mont Blanc tunnel, the operating instructions have become a little more precise in this connection, but they are still fairly sketchy. Although in general there is provision for closure if some of the smoke extraction systems (used in the event of a fire) are lost, or if the atmosphere is too polluted or visibility is nil, the actions to be taken in case of other kinds of event, such as a lasting loss of electricity supplies, are still often poorly defined.

This being said it is nevertheless difficult to plan everything in advance since decisions have to be taken on a case-by-case basis, faced with the need to keep traffic flowing, bringing forth the need for alternative routes, with all that that entails. It then becomes necessary to highlight certain instructions to be applied automatically by the operator, subsequently modifiedin real time if necessary according to the emergency.

Predicting the development of a fire and adjusting the ventilation system

Since passed significant accidents have proved that the first 30 minutes have generally a crucial importance, the modelling of fire scenarios considered for the evacuation and sheltering of road users are based on total heat power evolutions within the first 30 minutes.

The 30 MW fire used in the Technical Instructions as regards the standards to be observed, is a rating basis for trucks (HGVs), excluding the transport of hazardous materials, and has been the subject of considerable research. However it is known that 100 MW fires are plausible, even excluding hazardous material transport, and that if these hazardous materials involve flammable liquids, 200 MW or even more can be reached. Even so, these circumstances are even more difficult to describe. As regards cars and vans, the power can range from a few MW to over 15 MW, if the fire spreads to several vehicles.

Note : the duration of fire scenarios can extend beyond 30 minutes and extinguishing can occur before 30 minutes. These aspects are also essential.

It is therefore of primary importance to describe the first 15 to 30 minutes, which are crucial for moving people into shelter. The subsequent bringing under control of the fire, using techniques that vary according to circumstances, does not really form part of the scenario to be developed. However the case of people in shelters, awaiting the arrival of the emergency services for evacuation, may deserve particular attention.

As far as safety is concerned the power developed in a fire is related -quite apart from obvious matters of the fire resistance of systems and temperature in the shelters4 -primarily to the smoke extraction methods adapted to the energy levels encountered, the important point being the toxicity of smoke and the extent to which it spreads.

• with semi-transverse or transverse ventilation the modelling of the performance of smoke extraction systems is still little developed,

• with longitudinal ventilation in an uncongested one-way tunnel it is possible to use 1dimensional modelling in the steady state which is fairly easy to handle and can be done using charts or EXCEL spreadsheets. However this type of modelling assumes that all the physical parameters are constant along the stretch of tunnel represented, and cannot therefore represent 2-D or even 3-D phenomena such as the stratification of smoke.

Accordingly they are valid only above the critical air speed which ensures that there is no stratification or "backlayering".

Of course the air velocity during the fire depends, amongst other things, on ventilation, the amount of traffic in the tunnel and the backpressures at the tunnel portals resulting from the weather. This type of model is unable to describe what happens for lower air speeds or -this is an important point -the transient phases at the beginning of the event. Transient 1-D simulations can be carried out to overcome this drawback but they too cannot take into account any phenomena of stratification and backlayering. The results provided must therefore be interpreted using qualitative evaluations based upon experience or various 3-D simulations.

• In the other cases considered (congested, one-way, with longitudinal ventilation; longitudinal ventilation in a 2-way tunnel, and above all where ventilation is semitransverse or transverse) safety is strongly related to the stratification of the smoke which can only be reproduced by 3-D simulations.

It is true that beside ID and 3D modes zone models exist that are capable of allowing for stratification, but these are used only by their authors and have not been completely validated.

A more pragmatic solution is to begin with a 1-D model to evaluate the overall air movements in the tunnel, and then to produce a qualitative description of the phenomena using this estimate of the air flow together with experience on how fire and smoke behave as a function of the air flow.

There is still a considerable need for research on this general topic in order to produce tools that can cope with these complex phenomena.

Using severity/probability matrices

For the purposes of comparing hazards between different tunnels, it is proposed to utilise standardised matrices covering severity and probability of occurrence. For frequencies it is suggested that 6 classes should be used, ranging from very frequent to extremely rare. Table 1 shows how a few French tunnels would rank because of reported cases during last years.

Typical tunnels -truck fires A B Fréjus, Landy, Chamoise C Fourvière, Las Planas D Terregaye, Saorge, TC St Germain E F "Occurrence interval" < 1 year "very frequent" < 10 years "frequent" 10 to 100 years "occasional" 100 to 1000 years "rare" 1000 to 10,000 years "very rare" > 10,000 years "extremely rare"

Table 1: Class distribution for potential frequency of occurrence of truck (HGVs) fires

It is possible to identify subsequent damages in the five classes normally used : table 2.

Severity

I "Minor or nil" II "Significant" III "Critical" IV "Catastrophic" V "Major disaster"

Damage

Material damage Light injuries Serious injuries or < 5 fatalities > 5 fatalities, < 50 fatalities > 50 fatalities

Table 2: Severity/damage relationship

It is also possible to utilise indicators of the potential severity of consequences relating to the one-way or two-way character of a tunnel, the number of tunnel tubes and their intersections, the frequency of congestion and the presence of hazardous materials; this then leads to a classification which may be for instance the shown hereunder in order of decreasing potential consequences.

2-way urban, -2-way non-urban.

1 -way, non-urban, single tube, 1 -way urban with two tubes, 1-way non-urban with two tubes.

Logically, in each case, a heavier traffic and a less suited ventilation system lead to more severe consequences.

The consequences, stalling from the incident event, themselves depend on factors for which probabilities could also be worked out beforehand (congestion, weather, etc.), or even the probabilities of which depend upon actions taken (failure of a system, human errors, emergency services not intervening before a certain time, etc.). Among parameters crucial when assessing consequences are unmistakably :

» premovement time for the road users • time to activate emergency ventilation • time to stop incoming traffic entering the tunnel • times needed for the different emergency services to arrive, which are highly specific to each tunnel.

The first three parameters are mainly to be dealt with by designers and operators.

The fourth parameter should in no way constitute a kind of commitment on the part of the emergency services, but should for example simply be the « best possible realistic » times.

Generating a severity-probability matrix would become particularly complex if the intention was to probabilise not only the incident event but also the entire scenario. It is therefore suggested at present that the matrices should be used only for a kind of initial "prescreening" approach, using the probability of the incident events alone and only the "potential" severity.

Figure 1 :

 1 Figure 1: Principle of review, improvement, compliance programme

Figure

  Figure 2 : Basis for producing a specific Hazards study (SHS)

Figure 3 :

 3 Figure 3 : Definition of scenarios

CETU : Centre d'Etudes des Tunnels

Less than 500 metres in length if they are one-way tunnels, and less than 800 metres in length if they are twoway.

This should remain below 40° until they are evacuated, even for a 200 MW fire in the most unfavourable circumstances.


Emmanuel Beknuchon', Oliviersalvf'

Sandrine Descourriere

Christian Delvosalle

IMPROVEMENT OF THE HAZARD IDENT1FICATION AND ASSESSMENT IN APPLICATION OF TBE SEVESO n DIRECTIVE

The Councii Directive 96/82/EC of9 December 1996 an the control ofmajor-accident hazards involving dangerous substances, known äs SEVESO II Directive, aims at the prevention ofmajor accidents and the limitation oftheir consequences for human beings and environment. Although mies are well established to identify potentiell risk, there is no method to measure the risk level which takes into account safety devices and safety management Systems implemented by operators.

This paper deals with theßrst sfage ofa global methodology that aims to better assess beneßts form safety devices and safety management Systems through accident scenario selection.

INTRODUCTION

Context

In several European countries, risk level is often deducted from effect distances, äs results of the evaluation of gravity and likelihood of major accident scenarios. Therefore, the identification of accident scenarios appears äs a critical point in the risk analysis process that should take into account measures related to "state of art" and philosophy of the SEVESO II Directive. Typically, risk experts have to answer the following questions :

Is the reliability of safety devices assured ?

-What is the influence of measures taken at conception level ?

-What are the benefits brought by safety management Systems ?

Because of a lack of methodology, it is now particularly difficult to point out the influence ofthese parameters specially when determining accident scenarios. This difficulty is specially relevant in France where a deterministic approach is adopted [l].

ESREL 2001, Turin, 17-20 septembre 2001, p. 1249-1256

As a matter of fact, effect distances are results of major accident scenarios that are considered independently l öf their likelihood which is not assessed. The underlyine philosophy is based on the idea that measures taken to protect people from worst cases accidents are able to behave similarly with any less serious ones.

However, this conservative and cautious approach may lead to an over-estimation of the risk level [START_REF] Gaston | Why changing the way to measure the risk ? Prqceedings 9th Anniial Conference Risk Analysis : Pacing the New Millennium[END_REF], that fails to : encourage operators to increase risk prevention, -define a relevant and accurate risk level. This paper presents the first developments of a method that, in a deterministic context, emphasizes :

-the risk level inherent to an industrial plant, by the definition of Maximum Physically Possible Scenarios (MPPS), -the influence of inherent or integrated safety ruies and regulations, state of art... by the definition ofthe so-called Reference Accident Scenarios (RAS) -the benefits brought by safety devices and safety management Systems by the definition of Residual Risk Assessment Scenarios (RRAS). This general method is also divided in three stages, that are illustrated by (Fig l ).

Figure l : Scenario Identification l

This method is being developed with the French Competent Authorities in Charge of the application ofthe Seveso U Directive.

The following paragraphs only deal with a method to identify Maximum Physically Possible Scenario (MPPS) in a deterministic way.

MPPS : Definitions and Hypothesis

As stated in the introduction, Maximum Physically Possible Scenarios characterize the risk level inherent to high-risk establishments. In a simpler way, it can be noticed that these scenarios determine the worst situations that could physically occur.

Generally, a scenario is assimilated äs a äiccession of events presented in (Fig 2), which inspired from the bow-tie approach presented in [START_REF] Bellamy | Van der SchaffJ Major Hazard Management: Technical-Management Links and the A VRIM2 Method[END_REF]. fy-• .J

Fault J'ree

The origin ofthe fault tree is determined by : Undesirable Events (U E), which are supposed to occur exceptionally in the usual conditions of Operation Current Events (Cu E), which occur more or less frequently and that are in a certain way, foreseeable.

The combination of Undesirable and Current Events may lead, according to the influence ofprevention bamers, to an Initiating Event (I E). An Initiating Event is defined äs the Step that| precedes the occurrence of the Critical Event (C E). The Critical Event is generally deflned äs a Loss of Containment (LOC).

Event tree

The characteristics of the Critical Event pointed out by the fault tree analysis may be determined by the Secondary Critical Events (SCE), taking into account protection barriers. (formation ofa pool, puff, gaseous release...).

The secondary Events may lead to Dangerous Phenomena (DP) such äs fire, Vapor Cloud Explosion (VCE), BLEVE, toxic gas dispersion... At last, Major Events (ME) are defmed äs the exposition of targets (human beings, structure, environment...) to a significant effect from the identified Dangerous Phenomena.

As previously shown, an accident scenario mainly depends on : the nature and the characteristics of the Initiating Events, the nature and properties of the substance handled, the characteristics ofthe equipment (vessel, process unit, pipe..;) involved, -the possible action ofprevention and protection barriers.

At this stage, the methodology will allow to quantify the potential hazards of a unit by the defmition of Maximum Physically Possible Scenarios (MPPS). For this purpose, it is important to identify the worst cases that could possibly occur, regardless ofany probabilistic matters. In consequence, the following hypothesis can be reasonably made to detennine MPPS:

-the eventual prevention and protection barriers are supposed to be inoperative, there is no need to detennine the possible causes of the accident for a MPPS must be representative of the worst cases. As a matter of fact, such scenarios are most of the time justified by extemal aggressions such äs natural catastrophes (seisms,...) or domino effects. For all above reasons, in a deterministic approach, a MPPS depends only on the nature and the properties of the dangerous substance and the characteristics of the equipment involved. Therefore, MPPS is fülly determined by the following triplet:

-the Critical Event (CE), which is determined by the physical state of the substance handled, -the Secondary Critical Events (SCE), that can be completely defmed by the type of equipment and the conditions ofuse ofthe substance, -the Dangerous Phenomena (DP), that are linked to the physical state and the hazards ofthe substance, regardless ofthe type of equipment involved.

The methodology argues that risk phrases may not always be sufficient to detennine the nature of Dangerous Phenomena. For example, a substance known "Highiy Flammable" (R 11) may behave like an "Extremely flammable" substance (R 12) in particular conditions of pressure and temperature.

After an adequate analysis, the risk assessor is invited to choose the risk phrase that fits the best the possible conditions ofuse or accidents (domino effects). ^

Chlorine is dassißed äs a toxic substance (risk phrase : R23).

The only Dangerous Phenomenon to consider is then a taxic gas dispersion.

Third step: ChecSdng the consistence between DP and SCE

Finally, it is necessary to ensure that SCE identified may actually lead to the DP considered. For this purpose, the methodology suggests the use of a matrix, called the SCE/DP matrix.

In most cases, the consistence between SCE and DP is immediate. However, if consistence problems appear, the analyst is invited to: check the physical phase of the substance considered in step l : "Identification ofSCE" and in step 2: "IdentificationofDP" -then, check whether the case requires a particular analysis that an overall approach falls to proceed. ^€ ^ the practical case of a pressurised chlorine vessel, the consistence ofSCE and DP is clear. It is now possible to complefely deßne the MPPS in order to build the following tree.

CONCLÜSIONS

The methodology presented in this paper allows risk analysts and competent authorities to identify systematically Maximum Physically Possible Scenarios (MPPS). This method applies to most frequently met cases m high risk industries and follows a deterministic approach.

It is clear that, in some cases, MPPS selection may lead to results that seem obvious to risk experts. However, the benefits ofthis approach are related to its methodical aspects. MPPS identification should not be considered äs a final goal but äs an attempt to quantity maximum risk level in industrial establishments. This method is indeed the first stage of an overall approach in Order to better assess benefits from safety devices and safety management Systems thanks to more detailed analysis.

The second step of the methodology aims to integrale current practices, legal and normative requirements and lessons leamt from experience in the definition of Reference Accident Scenarios (RAS).

The fmal stage of the methodology tend to taking mto account specific technical and organisational measures for prevention and protection of major accidents, m the definition of Residual Risk Assessment Scenarios (RRAS).

In France, there is a need ofobjective criteria to assess reliability ofpreventing and protecting measures, eilher technical or organisational, without using any probabilistic methods. These criteria should help stakeholders in their decision-making process to evaluate the control of major hazard accidents.

Figure 2 :

 2 Figure 2 : Accident Scenario Identiticaäon

Figure 3 :

 3 Figure 3 : MPPS for a pressurised vessel of chlorine

METHODOLOGY FOR MPPS IDENTIFICATION

This description of the methodology is illustrated by a practical example considering a pressurised ve ssel of liquid chlorine at ambient temperature. These elements of illustration are located in the text by the symbol ")€"•

First step : Definition of Critical Events and Secondary Critical Events

The first step of the methodology consists in determining the Critical Event. Clearly, this Critical Event is closely linked to the physical state of the substance involved. If this substance is handled in a fluid phase, the Critical Event is a Loss of Containment. If the substance handled is a solid, we would rather talk about Loss of Physical Integrity.

^

For apressure vessel of chlorine, the Critical Event is a ioss of Containment.

Once the critical event is characterised, it is possible to deduce the possible Secondary Events frorn the type of equipment.

We introduce here a classification of industrial equipments, based upon the work performed by the Major Risk Research Center (Faculte Polytechnique de Mons, Belgium) on domino effects [START_REF] Delvosalle | Development of a methodology for the identification of potential domino effects in "SEVESO" industries[END_REF][START_REF] Delvosalle | A Methodology for the Identification of Potential Domino Effects in "SEVESO" Industries and an Application Tool: "DominoXL[END_REF]. Nine general categories have thus been identified :

-Mass storage (essentially powder), Solid storage in small conditionings, Pressure storage, Atmospheric storage, Cryogenic storage (with cooling System), Liquid or gas storage in small conditionings, -Process equipment (reactor, condenser, distillation column...)

Loading and unloading equipments, Pipeline networks.

These nine categories allow to define a majority of equipments that may be found in high-risk establishments. In a deterministic and simplified approach, it is then possible to defme a finite number of Secondary Critical Events (SCE), for each category of equipment, depending on the conditions of use of the hazardous substance.

Practically, a matrix, called SCE matrix, is available for each equipment category and defines the Secondary Critical Events, according to the conditions of use of the hazardous substance.

The methodology wams risk analysts that the conditions of occurrence of the accident and more specially domino effects could possibly change the normal conditions of use of the hazardous substance (for exarrple, radiative heat impact due to pool or jet fires). In such cases, analysts are advised to consider the most appropriate category of equipment allowing to take into account these particular effects, after an adequate analysis. For example, a cryogenic storage might be then considered äs a pressure storage in case of failure ofthe cooling System. ^ For a pressure vessel, the SCE matrix is assumed to be asfollowed :

Second step: Definition of Dangerous Phenomena (DP)

To complete the definition of Maximum Physically Possible Scenarios, the Dangerous Phenomena (D P) must be identified. For example, if the SCE is a gas release, the D P for a substance that is known toxic by inhalation will be a toxic gas dispersion, whereas, if the hazardous substance is considered flammable, the D P will be a vapor cloud explosion or a flash fire.

In a similar way äs in step l, the definition of the Dangerous Phenomena is realised, regardless ofthe type ofequipment, considering only the properties ofthe substances (hazards and physical state).

To classify the hazardous substances, the methodology relies on the Councii Directive 67/548/EC on the classification, labelling and packaging of dangerous substances, and more precisely, on the definition of the risk phrases. The reasons of this choice are highiy intelligibte :

-The councii Directive 67/548/EC is the basis for all ruies and regulations linked to the classification of dangerous hazards at the European level (ex. Councii Directive 96/82/CE), -The use of risk phrases limits the confüsion between labelling and classification, Risk phrases are easily available, -Risk phrases sometimes introduce elements relative to physical properties of the dangerous substance (flash point, boiling point), that can be helpfül for the analysis. Obviously, all risk phrases defined in the Councii Directive 67/548/EC are not of major accident concem. Moreover, some risk phrases point out hazards that need an accurate analysis, and in consequence do not fit the Overall methodology presented in this paper.


C Rollin

H Baroudi

F Benslimane

Groundwater risk assessment for a Polycyclic Aromatic Hydrocarbons (PAH) contaminated site; benchmarking and validation of numerical transport modeis

The objective is to test the modelling approaches and the reliability of the codes used in water risk assessment. The final goal is to elaborate, for each group of pollutant, guidelines that could serve äs a scientific support for pollutant transport modelling in groundwater and soil. The modeis perfonned by 5 teams to simulate a contamination of soils and groundwaters by PAH at a disused coke plant site were compared. Hydrogeology is characterised by a superficial and a chalk aquifer, the latter being confined under a 2 meter thick clay layer. The source of contamination was determined by 40 soll sampling points. Total PAH concentrations in the soils ranged from 3 to 80000 mg/kg. 18 observation wells were implemented to monitor the aquifers. Total PAH concentrations in the groundwaters ranged from 0,1 to 40000 u.g/1. A first synthesis of the results obtained leads to the following: • naphthalene was chosen äs a tracer by all 5 teams; • hydrodynamic parameters vary from one model to another. More investigations are carried out to reduce uncertainties; • the partition coefficient of naphthalene in the different layers is unknown, which leads to high uncertainties. Batch tests are currently being carried out ; • the number and extension of the sources considered by the teams are different. Thus, modellers have to be involved in the diagnosis phase; • biodegradation is an important factor to consider even though few values are avaüable in the literature conceming anaerobic aquifers. A sensitivity analysis of fhe degradation constant has to be perfonned. The paper presents the available data used for modelling, a summary of the 5 team results and preliminary practical guidelines for PAH transport modelling.

Introductioa

When applying a risk assessment approach to contaminated sites, of primary importance is the evaluation of the fate of pollutants m groundwaters and soils. This knowledge is based on (a) the results of extensive investigations at a specific moment in time, (b) data available from momtormg of pollutants m time and space and (c) numerical modelling of the transport of pollutants in the environment. In practice, the techniques naay vary greatly among users, according to tfae available data and the requested aims of the risk assessment. The lack of a rehable methodology may inipair high quality expertise. In this context, INERIS has developed a research prograiB, based on comparisons of modelling approaches, in order to elaborate guidelines fhat could provide a scientific support for the modelling of each group of pollutant.

The approach we have selected goes further &om the mere validation of numerical codes, since the results of a model not only depend on (he way a code is used and results interpreted, but also on the quality of the input parameters and data. The comparison of the results and the search for the points leading to differences will allow to determine fhe minimum soil, aquifer and pollutants characteristics to take into account in the modelling. The proposed comparison relies on several teams treating identical cases according to their own approaches and modelling techniques. Each case is transposed into a report integrating available data from the site and specifying the type of expected results.

Study area

The site of interest is a former coke plant closed 40 years ago. The site, along a rfver, covers a surface of 10 hectares. Contamination of soils and groundwater has resulted from the disposal of tar residues.

Geology

The plant was built on an heterogeneous filling material composed of sand, silt and bricks to a depfh of about l to 5 m, placed over fine clayey saads. Under this superficial layer, gravels in a sandy matrix are found. Tbe width of this superficial aquifer varies between 1,6 and 5,8 m. The chalk aquifer, whose roof is 13 to 15 m deep, is separated from the deposits by a 2 m width confining layer of clay (caUed 'argile de Louvil') composed of very fine clayey sands. The following figure displays a SSW-NNE geological cross-section of the site.

Hydrogeology

Two aquifers may be distinguished : the superficial deposits and the chalk fonnation. The recharge of the chalk aquifer occurs to the north where the chalk outcrops. This aquifer is the main resource for drinking water in the area. The superficial water table flows from NW towards SE and the hydraulic gradient ranges from 5.10" 3 and lO' [START_REF] Zheng | MT3D : A Modular Three-Dimensional Model of Simulation of Advection, Dispersion and Chemical Reactions of Contaminants in Groundwater Systems[END_REF] . The chalk aquifer is confined, due to the presence of the clayey layer and the flow direction is NE towards SW. The hydraulic gradient is 2,8.10" 3 . Water-table surfaces are depicted in Figure 3.

3 Field investigations 3.1 Characterisation of the pollution 3.1.1 Soils 40 analysis of sampled soils (Fig. 3) have been carried out and lead to the following remarks : (a) soil pollution is located in the areas where extractors, tar oils reservoirs, oil distillation equipment were present. Total PAH concentrations ränge from 100 to 80 000 mg/kg, (b) contamination is prmcipally located in fine silty sands between 3 and 6 m deep. This soil pollution is in direct relation with the contamination of the superficial aquifer, (c) pollution is mainly represented by 2 to 3 cycles PAH (naphthalene, acenaphthene and phenanthrene).

Groundwater

5 observation wells were drilled to the chalk aquifer (PZ7, PZ10, PZ12, PZ13 and PZ24) and 13 to the superficial one. Locations of the wells and of the coke plant equipment are shown in Figure 2. The chalk aquifer observation wells reach a depth of 21 m. They were drilled in two steps to avoid contamination of the deep aquifer. All the monitoring wells have been sampled. The superficial aquifer is heavily contaminated ; high indices of pollution are found in the observation wells located at the fonner coke plant location (PZ8, PZ20, PZ22). Conceming the chalk aquifer, a slight contaniination is encountered in the monitoring wells : PAH concentrations ränge frorn 0,1 to 2 Hg/l but the drinking water level for the 6 WHO-PAH is not reached (Fig. 3).

__ umK or

Hydrodynamic parameters

Lefranc permeability teste were carried out to determine the penneability of the superficial aquifer. The average values are respectively 3,1.10' 5 , 1,3.10' [START_REF] Wexler | Analytical solutions for one-, two, and three-dimensional solute transport in groundwater Systems with uniform flow (Chapter B-7)[END_REF] [6]

[7]

[8] (*) MOC : method of characteristics (• * ) MMOC : modified method of characteristics Table l : Specifics of the codes selected by the teams. Data submitted to the modellers have been presented äs results frorn a site diagnosis. This procedure allows the modeller to select the hydrodynamic and transpolt parameters, the sources appearing to be the most appropriate, according to its experience, äs he would do in a proper risk assessment. However, some values and a ränge of Variation have been given äs an indication. The values proposed to the modellers resulted either from site investigation or from literature. The parameters that were fixed are relative to the substances : their solubility and their partition coefficient K oc .

Parameter

Results and discussion

Calibration of the flow model was performed by considering the water table levels and by setting constant head boundary conditions. Calibration of the transport model was performed by assuming that the pollution started 40 years ago at the dismantling of the coke plant and by comparing the caiculated values to the measured concentrations in the monitoring wells. Parameters values and hypothesis selected by the modellers are displayed in Table 3. After 200 years, in the chalk aquifer, estimated naphthalene concentrations differ by more than two Orders of magnitude in some of the observation wells : breakthrough curves in PZ10 are displayed below. 3 : Hypothesis selected by the teams for the modelling.

(*) : R = 1+ -~ d where p a is the apparent density of the soil, K d the distribution coefficient and 8 the total porosity of the soil. K = permeability ; ct L = longitudinal dispersivity All the teams have selected naphthalene äs a tracer of the groundwater pollution. This choice may be explained taking into account the mobility, solubility and representativity of this substance m the source (40 to 75 % of the total PAH mass. All the caiculations have been performed by assuming that naphthalene is present in the soluble phase.

The modellers have considered a constant naphthalene concentration equal to the solubility of naphthalene, which means mat the pollutant stock is important enough to assume fhe presence of a continuous source during 200 years. This hypothesis may be justified by the fact that naphthalene concentrations are very high in the soils and in the superficial aquifer (the solubility value of this substance is reached).

The differences encountered in the results are explained by the following points : J the numbers and extension of the sources considered by the teams are relatively different, fhough the diagnosis was the same. S flow calibration was not the same for all the teams : the lack of data conceming flow rates and aquifer pumping lead to uncertainties concerning the couple (permeability-recharge) obtained after calibration. A two-fold increase of both parameters values has no effect on the caiculated water table levels. S Table 3 brings to the fore the large dispersion of the retardation coefficient values selected for the modelling exercise. This is the parameter presenting the highest impact on the pollutant fate in groundwater. Data available in the literature does not allow a proper calibration of the concentrations values. 5 biodegradation phenomena were not taken into account in the modelling exercise. Whereas the upper aquifer exhibits aerobic to semi-aerobic conditions, the lower aquifer is anaerobic. The evaluation of the actual literature on PAH degradation has shown that extensive knowledge is available on the aerobic biodegradation of single PAH compounds by bacteria and füngi. However, the literature conceming natural anaerobic degradation of PAH under the chalk aquifer conditions is scarce. Some few results from recent literature suggest that biodegradation of PAH occurs under nitrate-and sulfate-reducing conditions.

Conclusions and further work

In order to reduce the uncertainties, a second report integrating the results from recent investigations has been sent to the teams involved in the project, in order to improve the modeis.

Pumping tests have been carried out to calibrate more precisely the flow model. The synthesis of the results has shown the relevance of the K a value selection. Therefore, batch measures for PAH adsorption are currently being carried out for the three geological formations present at the site. In addition to a sensitivity analysis for the biodegradation rate, INERIS is now performing laboratory tests Cmicrocosms, column tests) to determine whether biodegradation occurs at the site or not. The results are promising since biodegradation was observed in laboratory in the site conditions, i.e. sulfato-reducing conditions with bacteria isolated from the site. In situ tests, by the mean of stable isotope measurements will be performed to estimate the in-situ biodegradation rates.

Finally, we will focus on the tracer choice. Naphthalene may be used äs a basis to validate the modeis ; however, it does not give any indication conceming a quality criteria since it does not belong to the 6 WHO-PAH. Further work will be conducted to extrapolate the results obtained for naphthalene to the other PAH, and to develop a specific risk assessment approach.

  ESJ filling material CD fine clayey sands gravels in sandy matrix E3 day (Louvil formation) • sand (Louvif formation) C3 chalk

Figure l :

 l Figure l: Geological cross-section of the site.

Figure 2 :

 2 Figure 2: Locations of the observation welk and of the coke plant equipment.

  Me pollution zone wKh possible stagnant phase (supaifldal aquifer) -UmHoftotal PAH IsocentraSon-10 pgll (superficial) Limit of total PAH kocentration -2 (jg/l (chalk aquifer) Umlt of total PAH isocentratlon • 1 |ia/l (chalk aquifer)

Figure 3 :

 3 Figure 3 : Measured PAH concentrations in soils and groundwaters.

Figure 4 :

 4 Figure 4 : Caiculated concentrations in the chalk aquifer (obs. PZ10).

Table 2 :

 2 Proposed values for the modelling exercise.