Edward Lydie
email: lydie.edward@hds.utc.fr

Lourdeaux Domitile

Lenne Dominique

Barthès Jean-Paul

Burkhardt Jean-Marie

Camus Fabrice

Guerrand Martine

V3S: A Training and Décision Making Tool to Model Safety Interventions on SEVESO Sites

Keywords: virtual reality, safety intervention, risk management, multi-agents system, interactive physical simulation

V3S (Virtual Reality for Safe Seveso Substractors) is an ANR/RNTL project (French national agency for research). In this project, we aim to design a tool allowing to scenarise hazardous working situations on SEVESO sites for risk prévention, training and décision making. The tool interprets a high level task and a related risk model. It is meant for a manager to help him/her to make décisions. The manager plays thé scénario of an intervention and manages a team of virtual operators (associated with autonomous agents) in thé VERP (Virtual Environment for Risk Prévention) submitted to constraints. Depending on his/her décisions, thé incurred risks are displayed in thé virtual environment. Our architecture relies on a multi-agents platform (OMAS).

In this paper we présent some of thé features of thé tool through différent scénarios. We présent thé organisational rules of our System, how it self-adapts to thé technical competencies and thé characteristics of thé operators (human foctors). We also présent thé working environment hosting our agents.

Introduction

Thé new possibilities offered by virtual reality in terms of scenarisation and thé émergence of knowledge engineering tools for risk analysis give thé opportunity of developing new tools to improve thé training and décision making for risk prévention. Many industriai applications using virtual reality for risk management will appear in thé near future. However, dedicated applications can only represent a partial solution. Generic tools, doser to thé reality hâve to be considered. In thé V3S project (Virtual Reality for Safe SEVESO Substractors) supported by ANR, we aim at developing such a tool for external maintenance companies that intervene on SEVESO sites. This tool has to allow to scenarise hazardous working situations on SEVESO sites with avatars and autonomous virtual characters, using virtual reality and artifïcial intelligence.

The tool is meant for a manager to help him/her to make décisions. The manager and his/her team hâve to appear in thé VERP (Virtual Environment for Risk Prévention) and hâve to be submitted to its constraints.

Our hypothesis is that thé effectiveness of virtual reality in terms of training and décision making for safety management increase when operators and managers see thé impact of their décisions on thé technical, organisational and human system they hâve in charge. The importance of virtual reality is undoubtedly a priority in thé construction of a system dedicated to thé simulation of safety interventions [1] [2]. The trainee will be able to build an adéquate mental représentation of thé process and to learn from acting and interacting [3]. Furthermore, thé challenge of our technology is to allow building customized simulations (usual procédures, progressive dégradation of thé working situations, etc.), adapted to thé needs of our industriai partners. Indeed, taking into account thé concerted requirements of safety is a challenge for thé industrialists throughout thé chain of décision that marks out thé relations between thé hazardous sites and thé subtractors companies. The tool has three main functions: (i) training; (ii) scenarisation; and (iii) décision making.

> Training tool

The manager cornes to différent possible choices like to train for activity préparation or to train in constrained situation. Thé constraints could hâve two origins: (i) thé environment: difficult géographie morphology, cold, windy; and (ii) thé physical or mental characteristics of thé virtual operators (VO): tiredness, accumulated stress, hurry, hunger, alcohol.... As a training tool for preventing risk, thé analysis and control of thé risks on SEVESO sites hâve to be considered. Using virtual reality allows us to offer thé users (operators and managers) thé possibilités to become familiar with thé site while displaying thé plant under opération and finally to learn how to deteet thé defaults while playing thé scénario of an intervention. Thé traînées will be able to supervise and verify essential check-points. Depending on différent parameters, thé proposed pedagogical scénarios hâve to présent thé inhérent risk in this type of sites. The parameters are thé manager's décisions, thé environment évolution and thé virtual operators' cognitive characteristics. Indeed, thé virtual characters can simulate déviant behaviours in constraint situation, risky/hazardous operative modes or reach partial goals fixed by thé procédure in an intelligent way. Learning by action will be possible if thé traînées can efficiently and explicitly identify thé technical, organisational and individual factors simulated by thé VO.

> Scenarisation platform

The manager has to be able to rebuild accidentai cases and replay thé situation to understand thé problems encountered by thé operators, to conduct post-accidental risk analysis or to do critical event analysis. By immerging thé final operators, thé teams, thé safety analysts and thé directors in thé virtual environments (VE) especially modelled for thé training, it will be almost possible "to live" thé critical situations, thus amplifying thé operators expérience and enabling them to suitably exploit thé concepts of Human Factors and thé good practices of Organization.

> Help in décision making tool V3S has to offer thé possibility to model thé working environment and thé selected operative mode. The virtual reality interface will be connected to a blackboard presenting thé advantages and thé disadvantages of thé simulated solutions. With V3S, risk analysis before or after accidents (HAZOP, FMEA, tree of causes, tree of events, preliminary risk analysis, tasks analysis, etc.) could be done doser to thé field realities, by integrating problems related to thé Human and Organisational factors. The VERP resulting from V3S will improve thé communication and coordination between thé différent actors (users and sub-contractors companies) and will therefore support thé setting up and thé piloting of an enterprise strategy wéll adapted to thé context of thé interventions.

In order to support thé previous three points, we propose a generic tool. It will endow thé environment with autonomous decisional capacities. We don't aim at neither reproduce perfect cognitive mechanisms nor describe thé operator's cognition but we wish to simulate thé behaviours which could occur. We will simulate thé operative mode, thé évolution of thé operators, and thé. changes in thé environment. The operators should adapt to thé environment in an autonomous way. To give them thé necessary cognitive capacities we propose an approach based on thé concept of agents.

In a previous related work supported by ANVAR and VIRTHUALIS1 , UTC, ECI and INERIS hâve focused their works to demonstrate thé feasibility of such a tool. A first demonstrator has allowed to scenarise two virtual operators and a real manager who hâve to intervene on SEVESO site. A multiagents architecture (MASVERP) has been designed to manage thé decisional process of thé virtual agents, giving them autonomous capacities and organisational behaviours [START_REF] Edward | Multi-Agents Approach for Modelling Safety Interventions on a SEVESO Site through Virtual Reality[END_REF]. The previous architecture permits to show thé feasibility of such a System by developing some of thé necessary fimctionalities (planner, agent model and task model). MASVERP endow thé virtual characters with autonomous decisional skills. The remaining work is to enrich, complète thé model and to combine it with physicals and risks models. After this step, supported by ANR/RNTL, thé V3S project has started in 2006 and will continue until 2009. CEA-LIST, SEEMAGE and industrials of thé petrochemical area and dangerous products transport area hâve joined thé project. In this larger project, thé rôles of thé partners are 0 UTC for thé autonomous decisional capacities of thé virtual agents, 0 CEA-LIST for thé simulation of physical phenomena, thé behaviour of virtual manikins and thé deformable objects, 0 ECI for thé human activity analysis and thé ergonomie aspects, 0 INERIS for thé safety and risks management, 0 SEEMAGE for thé software intégration, 0 Petrochemical and dangerous products transport industrials for industrial needs.

In this article we présent thé functionalities of thé tool through différent examples and scénarios. We présent thé architecture of our System, thé organisational rules, how it self-adapts to thé technical specificities and thé charaaeristics of thé operators (Human Factors). We also présent an example of a related previous work from thé preliminary step.

State of thé Art

Virtual Reality and Risk Training

Applications dedicated to risk prévention using virtual reality are just emerging and for thé majority are still at thé stage of laboratory applications. The NIOSH 2 and FIOH 3 first expériences published in 97 were related to handling and high working [START_REF] Laitinen | Usability through Product Design: New Design Methods and Industrial Applications[END_REF]

Making décision and humans factors application

This research orientation relates to thé technical or methodological tools of decisionmaking in thé préparation and thé management of sub-contractors interventions in thé field of highrisk industry, highlighting thé taking into account of thé human factors. The expression "Human Factors" is an umbrella term for several areas of research that include human performance, technology, design, and human-computer interaction. The approach focuses Among thé various approaches for safety, one can distinguish between two main groups. On thé one hand, thé reactive approaches taking place after a critical event in term of health, safety and environment (industrial disease, incident, accident, major accident); on thé other hand, thé pro-active approaches to anticipate thé occurrence of potentially critieal events. Thé connection between various approaches is today a major stake of thé research in order to find ways to improve thé prévention and thé reliability of thé working system, and of thé environmental risks.

Behaviour modelling tools

> STEVE STEVE is a référence in thé domain of behaviour modelling tools [START_REF] Rickel | Virtual Humans for Team Training in Virtual Reality[END_REF] [START_REF] Rickel | Steve: A Virtual Human for Individual and Team Training[END_REF]. It is an autonomous, animated agent that lives in thé virtual world with students. Its objective is to help students learn to perforai physical procédural tasks. It can demonstrate tasks explaining his actions, as well as monitor students performing tasks, giving help when they need it. He has a cognitive mono-agent architecture based on SOAR [18] which allows him to know thé state of thé environment in real time, to décide what actions to undertake and how to reach his goal. In thé MRE project [19] STEVE architecture is used to build an application for peacekeeping, it allows virtual characters to cohabit with humans.

> IRISA IRISA has developed a large number of tools for behavioural modelling like HPTS++ or SLURGH [20] [START_REF] Donikian | Modélisation, contrôle et animation d'agents virtuels autonomes évoluant dans des environnements informés et structurés[END_REF]. HPTS++ is a behaviour modelling language for autonomous agents. The agents are organised in a hierarchy of automata. SLURGH is a scénario modelling language. It allows managing thé scénario data and also thé dialogue between thé characters (actors). It créâtes a determinist scénario in which thé actors hâve to share thé resources using HPTS.

> GRIC-GRAAL Developing a tool for training fïremen aims at keeping them out of danger. To do so, thé authors designed a virtual environment in which virtual firemen interact, driven by a human operator. The architecture of thé system is based on a multiagents system composed of emotional and reactive agents [22]. The agents hâve a goal to achieve; they use a Prolog planner to déterminé their actions. The plan is included in a file thé agents can access.

> MASCARET (ENIB) The physical environment represents a plant where thé exercise takes place and also includes physical phenomena that can take place in thé plant (fire, smoke, water spreading...). The traînées play thé rôle of thé différent group managers who intervene during an incident and thé traîner participâtes to thé simulation as a troublemaker. He can create dysfunctions, help thé traînées and, as a player, play a role in the team. The MASCARET model is proposed in order to organize thé interactions between agents and to give them reactive, cognitive and social abilities to simulate thé physical and social environment [12].

Multi-Agents System Approach

Proposed in thé 80' s, multi-agents Systems now appear frequently in research activities. A multiagents system (MAS) is composed of a number of agents that are interacting, cooperating and belonging to an organisation. We distinguish two kinds of agents: reactive and cognitive. Reactive agents only react to a stimulus (intern and extern) and do not use an internai symbolic représentation. Cognitive agents are able to build their own behaviour and hâve a full représentation of thé environment. But this distinction tends to disappear in hybrid agents, a mix of both species.

Multi-agents Systems are efficient to build Systems where thé notions of coopération, organisation and autonomy are crucial. GRIC/GRAAL and MASCARET experiment this approach using emotional, reactive and rational agents.

The Positioning of Our Work

Contrary to thé existing work, our approach is différent. Indeed, proposed approaches relies generally on an architecture based on informatics foundation (automates, Pétri network, expert system). Sortie works propose to build Systems while iaking into account cognitive behaviour model [23] [24] for virtual human animation for example [START_REF] Donikian | Modélisation, contrôle et animation d'agents virtuels autonomes évoluant dans des environnements informés et structurés[END_REF].

In V3S, our foundation relies on cognitive models in thé domain of safety and human behaviour in risky situations [START_REF] Hollnagel | The phenotype of erroneous actions[END_REF] [START_REF] Hollnagel | Cognitive Reliability and Errof Analysis Method[END_REF]. From thèse models, we propose new mechanisms to represent human decisional process and human errors fïnally simulate in a virtual environment. One of our added values is to propose tools integrating artificial intelligence to (i) analyse thé human process and (ii) generate errors.

Technical and Scientific Objectives

General Objective

The project aims at exploring and demonstrating thé impact on thé operators training of a virtual reality tool including Human Factors in planning and in decision-making, in thé context of high risk industry.

The originality of our project dwells in thé coupling of knowledge engineering models with virtual environment for modelling safety interventions on a SEVESO plant {Figure 1). Knowledge engineering allows managing thé knowledge in thé différent scénarios and provides with organisational and human generic databases.

The development of a generic tool in V3S is intended to integrate this knowledge in a risk calculator based on a computer model and to simulate thèse risks at a decisional level in a virtual environment. Another objective, at thé physical level, is to make thé scénarios as realistic as possible by animating virtual characters and giving physical behaviours to thé manipulated virtual objects. This coupling will give thé opportunity to integrate new expérience feedbacks and new plants in a realistic simulation automatically. The tool will be used by several industrials and SMEs of thé petrochemical area and dangerous products transport area.

Our Architecture

To achieve our goals, several components hâve to be considered and developed (Figure 2). 0 A framework is necessary to model and display thé scène and thé éléments needed by thé scénarios like equipments, tools and characters. The virtual scène will be built from CAD model. The complète simulation will be displayed in real-time in thé VERP, to increase thé realism for thé user. It will be possible to navigate in thé scène, for example by moving around an élément (SEEMAGE). 0 A physical layer to simulate thé physical phenomenon implicated (objects and virtual characters) in thé virtual environment. The module has to offer a broad range of elementary behaviours (CEA-LIST). 0 A scénario catalogue grouping thé riskedsituations to process; such scénarios include for example a description of thé working environment and thé supervised chemical process, a description of thé rôles, or thé task to achieve and thé procédure to follow in a face to face operating mode, and eventually in a degraded mode or during particular critical phases (start, end, etc.) (UTC). 0 A behavioural module according to thé environment of thé virtual characters and physical objects. The module aims at simulating physical phenomena such as smoke or dangerous liquid products propagation, virtual characters grasping tools, Connecting a flexible, etc. (CEA-LIST). 0 A decisional and diagnosis layer dealing with safety aspects. The decisional module has to give thé virtual characters autonomous decisional processes. We intend to propose a generic model which would enable to easily direct, in a virtual environment, thé behaviours of thé operators intervëning on a high-risk industrial site and thé variations on thé physical environment. The diagnosis module has to display thé pedagogical feedbacks. This module has to identify thé traînée behaviours, and to associate thé causes and thé appropriate feedbacks (UTC). 0 An interface module linking thé decisional and thé physical layer (CEA-LIST, UTC).

Decisional Layer

This layer relies on a multi-agents system with thé following entries: 0 A standard model of thé activity. The model is based on a model describing thé cognitive activity elaborated in thé APLG project (RIAM prqject, [25], [START_REF] El-Kechaï | A Plan Récognition Process, Based on a Task Model, for Detecting Learner's Erroneous Actions[END_REF]). This model results from ergonomie, cognitive and artifïcial intelligence work (ECI). Some partners (ECI, UTC) of V3S are participating to PERF-RV2 6 and some connexions exist on thèse aspects and about its uses for virtual human scenarisation.. 0 A risk model. The mode! will take into account ail thé risk factors defmed with thé INERIS databases which will permit to generate data link to thé technical, organisational and human factors. The main work of UTC is to rely upon thé capacity of thé agents to take their own décisions in an autonomous way. They should be able to: 0 Generate a plan and assume différent tasks 0 Adapt and react according to thé changes in thé environment 0 Move in a realistic way We assume that a Multi-Agents System (MAS) is a solution to reach thèse three points in terms of organisation, coopération and planning [START_REF] Edward | Multi-Agents Approach for Modelling Safety Interventions on a SEVESO Site through Virtual Reality[END_REF], We consider three types of entities in thé environment: reactive, cognitive and human. Thé reactive entities correspond to thé objeçts in thé environment, thé cognitive entities are our workers, and thé human is thé manager who interacts with thé VERP. The objects hâve différent behaviours but they only hâve to react to a spécifie action, a stimulus. For example: if thé scaffolding is knocked down, then it should fall. They do not need to hâve a full représentation of thé environment and therefore they are considered reactive. The operators are more complex as we can see on Figure 3 that shows thé architecture of our System. We should consider their physical and mental charàcteristics according to thé COCOM model of Hollnagel [START_REF] Hollnagel | The phenotype of erroneous actions[END_REF] [START_REF] Hollnagel | Cognitive Reliability and Errof Analysis Method[END_REF] . Charàcteristics could be permanent (pm) or progressive (pg): safety (pm), prudence (pm), tiredness (pg) or stress (pg), etc. Thèse charàcteristics are placed in thé memory of thé agent and are used to determinate in real time me behaviour (control mode) adopted by thé agent [29] [30]. Such charàcteristics are taken into account to construct a cognitive activity model.

Hère is thé originality of our project; actually, depending on their personal characteristics they will hâve différent ways to do thé same task without or with risk.) The way is determinate by their decisional motor (planner) according to several parameters. The planner will take into account thé task model, thé risk model to provide a plan to die operators. It will be use also in thé diagnosis module (Figure 4).

Behavioural Layers and Physical

In thé scope of thé V3S project, CEA-LIST partner aims at developing interactive simulation components. Thèse modules will help to simulate in a simplified way some of thé physics involved in thé scénario: 0 The motions of thé objects in thé scène 0 The manipulation of pipes 0 The propagation of fluids (smokes, dangerous liquid products 0 The behaviour of virtual manikins (avatars of thé real operators involved in thé tasks) when physically interacting with thé scène along the scenario Some interactive simulation components are developed in PERF-RV2 6 and SYSTEM@TIC 7 project and will be integrated in this module.

Simplified propagation of fluids will be developed according to international récent work [START_REF] De La Garza | D'une approche réactive à une approche proactive en ergonomie : apports à une conception sûre d'équipements industriels et de systèmes de travail[END_REF][32][33J [START_REF] Irving | Invertible Finite Eléments for Robust Simulation of Large Déformation[END_REF] 6).

Figure 6 Sructural Organisation

The virtual environment can be viewed as an organisation to which will be connected" thé muitiagent system. A trace of thé environment is needed.

It is an open environment. The environment should be accessible, dynamic, non-deterministic and continuous. Obviously, it is a complex system.

5. An example of a related previous work The agents evolve in a virtual environment representing a SEVESO site modelled with 3D Tools, depending on thé scénario. It consists in a pure animation of succeeding scénario steps {figure 9). We can represent a very realistic environment and obtain an excellent visual rendering. Wim thé différent virtual interfaces, our system takes another dimension. The user is merged into thé environment, in a subjective way. This highlights thé utility of virtual reality in such a project and at a higher level thé utility of an advanced tool for developing 3D environments.

Description of thé scénario

The task model is thé heart of our system {Figure 8, a, b). It détermines which actions can be done, whjch interactions and simulations are needed. It describes thé activity of an operator in idéal conditions and also in degraded conditions (missing time, imprudent behaviours, safety behaviours, tiredness, etc.).

An example : scénario progress

We hâve two agents, a cautious (AÏ) and an imprudent one (A2). The manager orders Al to secure thé area by installing markers and A2 to uninstall thé pipe. AÏ and A2 générale a plan (tasks séquence) to achieve their goal. As A2 is imprudent he wiil not wait for AÏ beaconing to go on thé scaffolding. He does not fasten himself and start to unscrew thé pipe. He does not succeed, so he décides to go and look for a grinding machine. Due to his imprudence and his lack of knowledge, he does not verify if there is still residue in thé pipe and therefore a possible risk is a liquid flow on thé floor. If a forklift truck driver passes by, he can slide. To prevent this danger, thé safety barrier is thé way AÏ will beacon thé area. If thé manager orders a spécifie configuration, he has to follow it otherwise, as he is cautious he will beacon thé area in thé safest configuration.

Conclusion and Perspectives

In this paper we detailed thé goais and ( jnterests of thé V3S project We are developing" a system to simulate thé operative mode of operators working on a SEVESO site based on a multi-agents architecture: MASVERP (Multi-Agent System for Virtual Environment for Risk Prévention). An interesting part of thé project is to work along a new axis: taking a model of risk, a high level model of tasks and a cognitive activity model into account. The goal is to allow managers to visualize thé scénario and to view thé effects of their décisions in thé environment. To achieve this goal we will use a virtual support helping us to give a realistic vision of thé process.

Figure 1

 1 Figure 1 Coupling Knowledge Engineering andVirtual Reality

Figure 2

 2 Figure 2 V3S Architecture

  Figure 3 Agent Architecture

Figure 4

 4 Figure 4 Planner Working

5. 1 .

 1 Context of study Previous work in die same field had been led in UTC with INERIS, ECI (University of Paris V) and die Polytechnic University of Milan. Partners developed a first scénario representing an opération of pipe substitution in VTRTOOLS environment.

Figure 7

 7 Figure 7 (a) fB) Cognitive Task Model Saraple

  [START_REF] Dotson | Occupational Traumatic Injury Prévention Using Virtual Reality[END_REF]. More recently, VTT4 worked on a prévention measure application on industrial equipment [7]. In thé domain of ergonomics, différent researches stjidy thé sensorimotor and cognitive human behaviour and thé analysis of thé working situations and tool design [8][9]. Let us mention finally thé domain of professional training where many studies and/or applications cases are done about safety [10] [1I][12]. Thèse différent examples highlight thé existence of an émergent need for VERP for thé professionals. In this context, INRS started a multidisciplinary project in 2002, called EVICS 5 , in order to evaluate thé contribution of virtual reality in thé domain of

training addressing professional risks

[13]

and the conception of safe system

[START_REF] Marsot | Virtual environment for Safe Design[END_REF]

. In term of applications for safety we can also quote SécuRéVi (Security and Virtual Reality) developed by ENIB

[12]

. The project helps training firemen to the operational management and command. VIRTHUALIS is an Integrated Project, in the 6th PCRD (R&D Research Program). The main feature of the VIRTHUALIS proposal is to produce new knowledge and, as such, it is responding to the undeniable need of transforming industry towards high-added value organisations, i.e., more knowledge-based ones. VIRTHUALIS proposes the development of a new user-centred technology coupled with advanced safety methods and aspects that can effectively be applied in industrial applications handling hazardous materials. The VIRTHUALIS technology will make it possible: Some partners of the V3S project are participating to the VIRTHUALIS project (INERIS, ECI) and some links exists on safety and human factors aspects.

  [START_REF] Feldman | Animating gases with Hybrid meshes[END_REF][36][37][38][39][40].

			In this project, we want to describe and simulate thé
			cognitive mechanisms of human operators. We will
			therefore implement thé physical behaviours
			realistically and in particular thé cognitive décision.
			The operators represented by thé agents evolve in
			an organisation, cooperate and aim at reaching a
			common goal. They are directed by a manager and
			therefore submitted to his orders. We describe thé
			structural organisation as follows: in thé
			organisation, an agent can play one or more rôles,
			to déterminé which agents typicaUy need to ittferact
			with others to exchange knowledge and coordinate
			their activities. Thèse interactions occur according
			to patterns and protocols dictated by thé nature of
			thé rôle itself. The cognitive mechanisms are
			reflected by thé décisions taken by thé agent
			according to thé manager orders and thé
			environment (other agents and resources) state
	Uatmdiy	I	| MxUa
	Figure 5 Behavioural and Physical Layers
		Architecture
	4. Organisational Rules and Rôles
	Usine numérique : competitiveness cluster
	SYSTEM@TIC PARIS-REGION

(Figure

  l] Burkhardt J.M., Gounelle C, Cabon P., Virtual reality, Human factors and sqfety-related issues: thé HRTHUALIS project". Proceedings of Virtual Concept 2005, Biaritz, France, 8-10 Novembre {2] Meilet-D'huart D. Michel G., Steib D., Dutilleul B., Paugam B., Dasse & Courtois R. Usages de la réalité virtuelle en formation professionnelle d'adultes : Entre tradition et innovation. In Proceedings of First International VR-Learning Seminar, Laval, France, April 2005. [3] Crison, F., Lecuyer, A., Savary, A., Melletd'Huart, D., Burkhardt, J.-M. & Dautin, J.-L. (2004). The use of haptic and pseudo-haptic feedback for thé technical training of milling in virtual reality. In proceeding of EuroHaptics ().

					>• Develop thé training module
					7. Références
	Besides, in V3S, this approach will allow to interest
	better more into human factors:
	0 Individual (technical, organisational, human
	and prescribed aspects) compétences
	0 Collective compétences: understand thé
	procédures, thé tasks, thé working rules, thé
	rôle of a working group, thé technical or
	procédural	safety	barriers,	work	thé
	communication, thé management of an action,
	thé building of a self reliance and a permanent
	coopération.
	For thé trainers, V3S will allow:
	0 Quickly conceiving training programs focusing
	on spécifies industrial need (based on feed-
	backs, accidents analysis, potential risks
	analysis, tasks analysis audit results),
	0 Measuring	thé	effectiveness	of	thé
	apprenticeship.
	Our environment is not only a training environment
	(VET), it is a VERP, standing for Virtual
	Environment for Risk Prévention including training
	and décision making. At présent, thé System offers
	thé possibility to simulate thé operative mode and
	some risk cases. According to thé operators
	characteristics	(safety,	imprudent,	expert,
	inexperienced) thé System simulate thé différent
	associated behaviours.
	The results of this work are encouraging. Several
	issues are left for further work, more precisely we
	will:
	> Exploit thé industrial data to build
	différent scénarios and risk cases
	> Develop thé physical module for fluids
	and cables objects and virtual manikins
	> Coordinate thé différent basis modules of
	our architecture
	> Interface thé MAS with thé virtual
	environment
	> Build a catalogue of scénarios according to
	thé industrial need (multiple scénarios
	engine)
	> Cons&uct and coordinate thé différent
	basic bricks pf ouf architecture
	> Exploit thé industriaï data to build
	différent scénarios and risk cases

f

VIRTHUALIS : Integrated Project, in thé 6th PCRD (R&D Research Program)

PlatEfoRme Française de Réalité Virtuelle, french Virtual Reality Platform


B Piwakowski

Detection of Underground Marlpit Quarries Using High Resolution Seismic

This paper presents examples of application of high resolution reflection seismic for the detection and location of underground marlpit quarries in the region of haute-Normandie (north-west France) . Since some of these voids are unknown they represent a real danger both for population and building activities. The experiments are carried out at three sites with similar geological setting but differing in depth of voids (30-45 m), and in ground absorption (inelastic attenuation). For each site an explosive source is used. An additional survey is performed using new portable high resolution P wave vibrator, over one of the profiles. This provides an interesting comparison concerning the choice of the source type. In spite of high ground absorption and natural irregularities of the geological structure, the results show that the detection of marlpit underground quarries, often considered as unresolved, is possible.

Introduction

The achievement of good depth and lateral resolution of seismic image requires the use of short wavelengths i.e. high frequencies (the lateral resolution which express the ability to resolve two point targets spaced by is assumed to be equal to the Fresnel radius: 8 X =R f =(Ad/2) 05 ), A=V rms /f e , V rms is the stacking velocity anàf e is the exploitable signal frequency). Since ground absorption increases with frequency, f e is always limited. According to the general principle, the increase oif e requires powerful and wide band sources (i.e. emitting very short pulses. However, the latter condition limits radiated energy and the above requirements are contradictory. Finally, the obtained resolution is generally "imposed" by the ground absorption and is always a function of the propagation velocity. The detection of shallow tunnels and voids using High Resolution Seismic (HRS) involves the same type of considerations but additionally; the limited size of researched targets induces other problems: 1. If the size T of detected target is close or smaller than wavelength A, the geometrical reflection practically does not exist and is replaced by a "diffraction", 2. If T/A. ratio decreases, the diffractions originating from target limits (i.e. edge waves) can even cancel each other. Finally, the diffraction signal tends towards zero when T/A. tends towards zero. 3. In order to increase the reflected signal level for a given target size T, the only mean is to decrease A. But, as it was mentioned previously, decreasing of A is limited by the soil absorption and it should be admitted that under given particular field conditions a void may be not detectable at all. The above reasons explain why the detection of underground cavities remains fundamentally difficult and why several cases are not solvable. Except some general principles, each case requires a particular study. Indeed, the cases presented in this paper relate such situation where the extremely high absorption limits f e , even for the relatively small depths. The presence of voids perturbs the waves propagating downwards and upwards from the markers located beneath. This results i a so called masking of the deeper seismic markers. Our experience shows that between different void induced perturbations, masking effect is always dominating [START_REF] Piwakowski | From high resolution land seismic imaging to very high resolution: state of the art, limits and fild examples[END_REF]. This symptom is often followed by the perturbation of the closest upper marker. In order to express the detectability of a void, we have introduced the anomaly coefficient AN [START_REF] Piwakowski | From high resolution land seismic imaging to very high resolution: state of the art, limits and fild examples[END_REF] defined as AN = S c IS f forS c ^Sf , where S c is the surface of void and S f is the Fresnel surface. Our experience [START_REF] Piwakowski | From high resolution land seismic imaging to very high resolution: state of the art, limits and fild examples[END_REF] shows that in order to perform a successful detection, the AN should be greater than 0.35 -0.5, depending on the site conditions. According to this model, if S c becomes equal to Sf, (i.e if AN =1) the gallery is sufficiently big and produces the same signal as reflected from a geological layer.

Results

The presented results are related to two HRS experiments carried out on underground marlpit quarries in Haute Normandie. The first survey was carried in 2002 [START_REF] Driad | Localisation et reconnaissance de l'état des cavités souterraines par sismique réflexion Haute Résolution -Application aux marnières de haute Normandie[END_REF] and the second in 2006. The measurements were performed on three sites along six seismic profiles. Acquisition was done using the 48-channel Strata View seismograph and end-off geometry. Table 1 summarizes general parameters of each profile pointing out the void characteristics like its depth and the AN coefficient. Notice that except the profile GR, all voids have sufficient dimensions to expect their detectability. All profiles were carried out using in-hole "buffalo gun" (firing blank cartridges). The profile GO was measured twice:

i. the profile with buffalo source was limited in length due restricted experimental zone, ii. the new portable P vibrator (100 kg, 700 W) and its optimized sweep generation procedure developed in the frame of our research allowed new HRS measurements extend over the restricted zone (i.e. habited zone). This non-destructive source has been used in private ground without any damage or disturbances for the inhabitants. In order to check the "true" reliability of detection, the survey profiles AA and BB (Eturqueraye site) were conducted without a priori knowledge of the void position. • The geological structure of investigated sites is irregular and displays numerous natural anomalies. Additionally, the high ground absorption implies the necessity to use low frequencies that lower the resolution. These two factors make the detection of voids relatively difficult. • Despite the latter limitations (notice the relatively low frequencies on the seismic sections) the voids were however detected. The masking of the deeper markers and perturbations of the upper marker (if close to the void) were the dominant symptoms. The precision of detection is close or even much better than estimated lateral resolution of the survey. • The comparison of Buffalo and P vibrator sections shows the great utility of the nondestructive P vibrator. The obtained results are quasi identical but the lower-costs survey and non-destructivity are the advantages of vibratory source.

Fig. 2 .Fig. 3 .

 23 Fig.2.Site of Godedrville a) positions of profiles et and void limits; b) P vibrator mounted on an all terrain vehicle (quad) c) Section GO_B and interpretation d) Section GO_V and interpretation.

Acknowledgements

The work presented in this paper lies within the scope of research program proposed by INERIS and sponsored by the French research ministry.

No

Site of St Gilles de la Neuville (Fig.l) The section (a) shows the locations of profiles in relation the positions of voids and the general geological setting. The voids occur at dept of 35 m in chalk layer, covered by alternated chalk and clay. The profile GR is the reference section situated within the void-free zone and crosses a small tunnel of 7 m width (its AN=0.34). The obtained section shows numerous markers: 2, 3,... 7 and it can be observed that the obtained resolution is relatively low (i.e. f e too low). Notice also the important natural irregularities of the structure. The expected masking caused by the tunnel is practically not seen; indeed, taking into account its AN = 0.35 the tunnel is close to the detection limit. The profile SGA includes the void-free zones (CMP < 90 and CMP > 160) and the zone including the void (90 < CMP < 160). The void manifests itself by the following phenomena: -Within interval 75 < CMP < 120 & 150 < CMP < 185: perturbations of the marker 3 and nearly total masking of markers 4, 5, 6, 7.

-Within interval 75 < CMP < 135 we can observe the quite strange seismic behaviour S and diffraction D which might be interpreted respectively as the effect of a local fill of an old subsidence and the presence of filled in well. -In the contrary the effects seen within interval 150 < CMP < 185 are rather evident. The perturbations of 2 suggest that the void is collapsing there and reaches depth of 25 m Site of Goderville (Fig. 2) This study compares the results obtained with the explosive and vibratory source.

GO-B profile:

The presence of the void is clearly seen for CMP > 105 by means of the perturbations of upper marker 3 and the masking of deeper markers 4, 5, 6, 7. The precision of location of the void limit (2.5 m) is much better than expected (5 X =16m). GO-Vprofile .This profile is longer then the profile GO-B since the non-destructive source was used. It reveals the same markers 3 à 7 seen already in GO-B. Notice that the quarry effect is now in the middle part of profile (250 < CMP < 330) giving better imaging. The natural geological structure is located symmetrically on its both sides. Site of Eturqueraye (Fig. 3). This study is carried out without a priori knowledge of the marlpit position. The extremely high ground absorption, implied to use a very low fe (such as used in deep seismic!) which resulted in very low resolution seismic image. The proximity of a motorway and of the high voltage power line caused additional difficulties. The profile AA manifests a masking of marker 2 within the interval (65 -115) m. and less evident perturbations of 7. Thus this zone is interpreted as the effect of marlpit gallery. The profile BB indicates the similar results within the interval (50 -100) m. but perturbation of 7 zone is much larger (position of gallery probable but less evident) The positions of presumed voids are shown in Fig. 3.a The found positions agree with the known position of the void given (after interpretation) by the owner of the investigated site.


S Brohez

Fourneau G Marlair

& H Breulet

CONTROLLED ATMOSPHERE BENCH-SCALE CALORIMETRY REVISITED

The standard Cône Calorimeter has been designed with an "open configuration", allowing for testing of spécimens through use of freely driven room air for combustion. For testing spécimens in oxygen depleted atmosphères or in fuel rich combustion a modified apparatus working under controlled atmosphère can be used. To our Knowledge there is very few publications describing thé use of such modified cône calorimeters and providing data regarding thé effect of ventilation on thé fire properties. In thé open literature it was reported end of thé 1990's that substantial burning can occurred outside thé test chamber when such a device is used, thé amount of oxygen available to combustion exceeding thé amount that was fed to thé combustion chamber. In such a case (leading to post-buming outside thé test chamber), it has been proposed to correct thé expérimental data by replacing thé oxygen mass feeding rate by thé actual rate of oxygen consumption. This paper analyses thé proposed correction, and suggests that this might not be fully satisfactory by comparison to data obtained in another bench scale calorimeter with controlled atmosphère. The capacity of a Cône Calorimeter fïtted with a controlled atmosphère device will be more in depth investigated in a new research project starting in 2007.

INTRODUCTION

The Cône Calorimeter is commonly used for thé measurement of main fire properties of products and materials such as thé heat release rate, thé effective heat of combustion, thé mass loss rate, thé time to ignition 12 . The standard Cône Calorimeter has been designed with an "open configuration", allowing for testing of spécimens through use of freely driven room air for combustion. For testing spécimens in oxygen depleted atmosphères (air vïtiation effect) or in fuel rich combustion (ventilation effect) a modified apparatus working under controlled atmosphère can be used. To our knowledge there is very few publications describing thé use of such modified cône calorimeters and providing data regarding thé effect of ventilation on thé fire properties.

On thé one hand, a cône calorimeter for controlled-atmosphere studies in vitiated atmosphères has been constructed at NIST 3 in thé beginning of thé 1990's. The results obtained in this controlledatmosphere unit regarding thé effect of thé air vitiation on thé heat release rate and carbon monoxide and smoke produced by fiâmes were published by Mulholland et al 4 . It is important to notice that thé controlled-atmosphere NIST unit was used in a closed configuration. The combustion air was supplied at thé bottom of thé Pyrex enclosure and thé combustion products were removed from thé top of thé enclosure. There was no dilution of thé combustion gases before thé instrumentation section in thé exhaust duct. While some of thé changes between thé standard unit and thé controlled-atmosphere unit were minor, thé number of changes is large and affects nearly ail of thé Systems on thé apparatus (thé cost for constructing thé controlled-atmospheres unit was estimated to be more than double that for thé standard unit) 3 .

On thé other hand, a cône calorimeter fïtted with a controlled-atmosphere apparatus was constructed at thé laboratory of VTT Building Technology/Fire Technology to investigate thé effect of ventilation conditions on thé burning characteristics and fire effluents of chemicals 5 . Exhaust duct system, gas measurements and smoke measurements were thé same as in thé standard Cône Calorimeter method.

Under thé cône heater an enclosure to produce thé reduced ventilation conditions was constracted with a short chimney on top of thé cône heater in order to prevent air flowing into thé chamber from above (Fig. 1) 6 . The mixture of air and nitrogen was supplied at thé bottom of thé chamber with both flow rates which could be adjusted between 0.5 and 4 1/s. The maximum flow through thé chamber being 8 1/s, thé fire effluents were diluted with ambient air in thé exhaust hood (before thé measurement section). It was reported that substantial buming can occurred outside thé test chamber when such a device is used, thé amount of oxygen available to combustion exceeding thé amount that was fed to thé combustion chamber. In such a case (leading to post-burning outside thé test chamber), it has been proposed to correct thé expérimental data by replacing thé oxygen nïass feeding rate by thé actual rate of oxygen consumption. This paper analyses thé proposed correction using data obtained in thé Fire Propagation Apparatus. EXHAUST DUCT--

• FLOW RATE • SMOKE DENS1TY -OXÏGEN QEPLETIOM HOOCk • GAS 5AMPLES: • FTIR • ADSORBENTS CONE HEATER J 1 JfL^E XTINCTION WATEft UNE

LEARNINGS FROM THE USE OF FIRE PROPAGATION APPARATUS

Figure 2 shows a schematic view of thé calorimeter implemented in a purpose-built section of INERIS réaction to fire laboratory. The lower part of thé calorimeter is thé combustion chamber which comprises essentially thé sample holder System and associated weighing cell, thé ignition device and infra red heaters. In addition, thé combustion or propagation tests may take place in a controllèd volume physically delimited by a quartz tube made of two cylindrical superimposed parts. A range of three mass flow meters allow thé operator to set thé desired mass flow rate of air to thé required value (up to 300 NLmuï 1 ) and to modify and adjust thé composition of thé inlet flow (e.g. mixtures of air, CO2, N 2 , O 2 ) for research purposes. In particular, thé inlet air flow may be enriched or depleted in oxygen. The infra-red heaters System is designed in a way it can supply an even heat flux to thé spécimen surface at whatever desired value in thé range of 0 to 60 kw.m" 2 . The upper part of thé apparatus is thé exhaust System collecting ail combustion product releases and dilution air and comprising main instrumentation section (see figure 1).

The combustion chamber allows thé user to adjust thé fire ventilation of thé test in terms of fuel enrichment of thé combustion process. This is done in practice quantitatively through thé measurement of thé parameter called thé équivalence ratio <& (actual fuel-to air ratio normalized by thé stoichiometric value of same ratio), a parameter commonly adopted by fire scientists7 . In any experiment, thé équivalence ratio may be targeted at any desired level to feature well ventilated ,or under-ventilated fire conditions, in its simplest mode by varying thé air inlet flow rate. Similarly to thé cône calorimeter it has be shown that some conditions require a careful control of oxygen flows to déterminé thé true équivalence ratio when very low air flow rate is adjusted (underventilated fire conditions) 8 . In such a case, thé O2 consumed as taken from heat release data could be more important than air available by normal air distribution System in thé bottom part of thé FPA. Figure 3(a) illustrâtes such a situation in thé case of heptane, a highly flammable hydrocarbon where a control of thé actual oxygen consumption by thé fire process reveals that an extra supply of air other than normal inlet flow occurred in that experiment. Thé same analysis can be done for thé CO 2 yield (Fig. 4). Indeed thé carbon dioxide produced by thé combustion revealed to be more important than thé maximum theoretical yield due to thé unexpected air entrance in thé quartz tube. This unexpected additional air supply revealed to take place at thé top of thé quartz tube, in thé form of air stream entering in opposite direction of main upward gas flow, close to thé inner walls of thé quartz tube (convective movement induced by cold wall effect, see figure 5). In order to reduce this phenomenon a technical solution 8 (Fig. 5) consists in reducing thé tube outlet diameter, thanks to a disk-shaped refractory pièce placed on its top (thé diameter was reduced by a factor of ~3). This procédure proves to be a good solution as shown by comparison of thé graphs plotted in figure 2 for thé oxygen consumption (see also figure 4 for thé carbon dioxide yield). The comparison clearly shows that using such a component to prevent any counter flow of air froni thé top part of thé quartz tube is efficient.

EFFECT OF THE OXYGEN MASS RATE CORRECTION

Fuel-rich combustion of heptane has been studied on a Tewarson Calorimeter, in two différent configurations:

-Unmodified Tewarson apparatus (standard apparatus), allowing convective recirculation and air entrainment at thé top of thé quartz tube, and, thus, post-combustion phenomenon. -Modified Tewarson apparatus, where recirculation is made impossible (using an orifice plate made of minerai material at thé top of thé quartz pipe) and buraing only occurs with available oxygen (controlled mass rate at inlet).

One might wonder whether thé correction proposed by Hietaniemi et al applied to thé data obtained with thé unmodified Tewarson apparatus (by replacing thé oxygen mass feeding rate by thé actual rate of oxygen consumption) could lead to data which are similar to thé ones obtained with thé modified Tewarson apparatus. The results are presented in figure 4 for thé carbon dioxide yield. By considering only thé amount of oxygen that is fed to thé combustion chamber (D), thé CO2 production exceeds thé maximum theoretical yield in thé case of thé standard apparatus (post-combustion phenomenon). Hietaniemi et al. correction (X) solves this issue, but does not allow for testing highly fuel-enriched mixes as post-combustion still happens, in opposition with real controlled atmosphère measurements (A) (especially for heptane, a very flammable product which leads to high heat release rates).

In a similar way, thé data measured for carbon monoxide are presented in figure 6 for thé standard Tewarson apparatus and thé modified one. The correction proposed by Hietaniemi et al is also presented. When a post-combustion phenomenon is observed it comes that thé correction of Hietaniemi et al should be applied in order to obtain more realistic results. However, this correction might not be fully satisfactory by comparison to data obtained in thé modified Tewarson Apparatus. The remaining différence comes certainly from thé fact that thé oxygen mass feeding thé combustion chamber is certainly higher than thé actual rate of oxygen consumption.

CONCLUSION

Bench scale fire tests such as thé Cône Calorimeter equipped with ventilation controlled atmosphère or thé Fire Propagation Apparatus can be used for thé establishment of expérimental corrélations between chemical species yields and thé équivalence ratio which can be used as input data in computer models for thé prédiction of thé fumes composition. However, a practical issue may anse to calculate thé actual équivalence ratio in experiments with bench-scale apparatuses like thé Cône Calorimeter and other fîre calorimeters, since oxygen consumed as derived from heat release data could be more important than thé theoretical limit of oxygen supply introduced at thé bottom of thé test chamber. In fact, secondary combustion air may be brought and participate in thé combustion process under some circumstances at ignorance of user from thé dilution air stage that occurs before thé effluents enter thé collecting hood. In such a case, thé correction proposed by Hietaniemi et al should be applied in order to obtain more realistic results. However, thé proposed correction might be not fully satisfactory since thé oxygen mass feeding thé combustion chamber is certainly higher than thé actual rate of oxygen consumption. The objective of this project will be to improve thé confined atmosphère testing equipment for thé Cône Calorimeter with proper ventilation control to reproduce thé whole range of burning conditions for différent materials.

Figure 1 .

 1 Figure 1. Schematic view of thé ventilation controllèd cône calorimeter constracted at VTT, Finland (from réf. 5)

Figure 2 .

 2 Figure 2. Schematic of thé INERIS Fire Propagation Apparatus Averaging Pitot tube. Thermocouple

Figure 3 .

 3 Figure 3. Time évolution of thé incoming and consumed oxygen mass flow rates for heptane bura tests in under-ventilated fire conditions, (a) Standard apparatus, (b) Môdified apparatus with a section restrictor at top of quartz tube 0,41

Figure 4 .

 4 Figure 4. CO 2 yields and maximum theoretical yield versus équivalence ratio.

Figure 5 .

 5 Figure 5. Schematic of thé natural convective movement occurring in thé upper part of thé combustion chamber

Figure 6 .

 6 Figure 6. CO yields versus équivalence ratio for heptane tires.

ISO 5660-1, Fire tests -Réaction to Fire-Rate of heat release from building products, International Organization forStandardization, Geneva (1993)

ASTM E1354, Test method for heat and visible smoke release rate for materials and products using an oxygen consumption calorimeter, ASTM Standards, American Society forTesting and Materials, West Conshohocken, PA, 750-767 (1999)

Babrauskas V., Twilley W.H., Janssens M. and Yusa S., 1992. A cône calorimeter for controlledatmosphere studies, Fire andMaterials, 16,[37][38][39][40][41][42][43]

 4 Mulholland G., Janssens M., Yusa S., Twilley W. and Babrauskas V., 1991. The effect of oxygen concentration on CO and smoke produced by fiâmes. G Cox and B. Langford éd. Fire Safety Science, Proceedings of the Third International Symposium, 8-12 July 1991,

 Hietaniemi J.,Kallonen R. and Mikkola E., 1999. Burning characteristics of selected substances: production of heat, smoke and chemical species. Fire and Materials, 23, 171-185. 6 Mikkola E., Kallonen R., 1994. Cône calorimeter experiments. Industrial Fires II, 17-18 May 1994, Cadarache, France. 7 Pitts W. M., 1995. The global équivalence ratio concept and thé formation mechanisms of carbon monoxide in enclosures Fires. Prog. Energy Combust. Sel, 21, 197-237 8 Brohez S., Marlair G. and Delvosalle C, 2006. Fire calorimetry relying on thé use of thé fire propagation apparatus. Part I: Early learning from use in Europe. Fire and Materials, 30, 131-149


EXPERIMENTAL ANALYSIS OF JET FIRE IMPINGEMENT ON INDUSTRIAL PIPE

Thé "smoke-point" is a minimum heat release rate at which smoke just escapes from thé flame tip.

INTRODUCTION

In industrial plants, jet fîres and pool fïres can increase hazards when they impinge and engulf on pipes or vessels. Then, thèse structures may also become themselves thé centre of major accidents (domino effects). Therefore, as part of hazard surveys and more particularly survey of domino effects, some questions are asked about, for example: thé relevance to consider thé explosion of such or such tank as a resuit of thé contribution of heat since a close fire considered besides, or again thé quantitative contribution expected by thé implementation of materials of heat insulation or thé implementation of means of cooling. Thus a research program supported by thé French Ministry for Ecology and Sustainable Development focuses on thé thermal impact of fïres on industrial pipes and tanks. Its main objective is to develop, to validate and to produce one or several tools of calculation satisfying needs mentioned above. This paper présents an expérimental campaign aiming to thé analysis of thé heat transfers exerting on a pipe impinged by a jet fire. Thus, an expérimental apparatus was set up making it possible to déterminé on thé one hand, precisely thé characteristics of jet fire and on thé other hand, thé thermal response of thé steel pipe crossed by water flow. First of ail, to characterise jet fire, measurements of gas températures, gas velocities and heat fluxes are performed for three gases that are thé méthane, propane and ethylene and for various gas release rates. Additionally, test monitoring has also been done with video caméra. Thèse measurements make it possible to define dimensions of jet fires, its surface emissive power as well as thé hot gas velocities for finally deducing thé heat transfers received by thé pipe. The expérimental data are compared with thé SHELL model which is a semi-empirical model [START_REF] Chamberlain | Developments in design methods for predicting thermal radiation from flares[END_REF] modified by [START_REF] Cook | Size and radiative characteristics of natural gas flares. Part II: empirical model[END_REF]. In thé second time, thé pipe crossed by cold water is subjected to thèse various jet fires and thé thermal response of pipe is quantified by monitoring thé pipe with thermocouples. This second test campaign aims to quantify thé influence of thé hot soot conduction in thé heat transfers.

EXPERIMENTAL APPARATUS

A first expérimental campaign consisted in determining precisely thé characteristics of jet fire and a second campaign made it possible to define thé thermal response of thé pipe impinged by a jet fire. Figure 1 présents a sketch of thé global expérimental apparatus. The expérimental campaigns were realised within thé closed INERIS fire gallery that provides a confined médium. Thus, there is no influence of meteorological conditions such as wind. An expérimental apparatus was set up making it possible to characterise initially thé phenomenon of jet fire for three various gases chosen for their différent propensity to produce soot which are méthane, propane and ethylene. Figure 1 présents this apparatus which is made up of a gas cylinder and a gas heat exchanger to allow thé flowmeter to work in its range of opération. This flowmeter is used to control thé exit gas velocity (nozzle diameter dj being unchanged during ail thé tests) in order to obtain a jet fire in stationary régime. A mass flow rate and an exit température define thé gas jet. Then, in order to characterise jet fire in term of geometry (lift off, flame length...) but also radiative power, various instruments of measurements are used such as: thermocouples placed in thé axis of thé jet fire to measure thé hot gas températures T g along thé flame, an anemometric bi-directional probe moving along thé axis of thé flame to measure thé hot gases velocity U g , radiative fluxmeters located on thé sides and above thé flame measuring thé radiative flux, a video caméra system to measure dimensions of thé flame (by visualisation).

Figure 1 -Sketch of thé expérimental apparatus. For thé second expérimental campaign, thé steel pipe is subjected to thèse various jet fires and thé thermal response of pipe is quantified by monitoring thé pipe response with thermocouples (Figure 2). It should be noted that measurements are done on thé part of thé pipe directly impinged by jet fire and symmetrically on thé part located in thé drag of thé flame. The pipe has thé following characteristics: internai diameter 22 mm and external diameter 34 mm. The installation is made of three sections of measurements, thé section B located in thé axis of jet fire, section A 10 cm upstream and section C10 cm downstream. The thermocouples directly impacted by jet fire are noted AX1, AX2, BX1, BX2, CY3 and CY4 and those in drag noted AY3, AY4, BY3, BY4, CXI and CX2 (Figure 2). In addition, a collector was also necessary to place thé whole of thé connectors, and also to ensure thé clearing of thé extension cables towards outside (Figure 2). An internai fluid that is water at ambient température flows in thé pipe. This water flow can be modulated until obtaining a maximum mass flow rate of 12 kg/min. The water température is measured using thermocouples upstream and downstream from thé sections of measurements.

Measurements are done with a rate of 2 seconds acquisition and make it possible to obtain an évolution of thé steel pipe températures. The variable parameters are as follows: thé jet fire (various gases and thé variation of heat release rate), thé water flow within thé pipe (water velocity going from 0 to 0,5 m/s).

Figure 2 -Sketches and picture of thé steel pipe monitored with thermocouples and thé collector of connectors.

'Thermocouoles 3 sections of température measurements

Collector of thermocouples nnectors

STRUCTURE OF FLAME

Whatever thé gas tested, thé visualisation by video caméra shows that jet fire takes a général shape of cône (Figure 3) which characterises fully turbulent jet fiâmes whose thé Reynolds number is greater than 2000 (Table 1). But thé structure of flame differs according to gas. Indeed, thé méthane flame compared to thé propane and ethylene fiâmes has a blue aspect and is very lifted off from thé nozzle.

The blue color of this flame is characteristic of thé radiation in thé field of visible of thé carbon dioxide and thé water vapor. The méthane flame is generally considered as a nonluminous flame and soot radiation can be neglected [START_REF] Marracino | Radiation modelling in non-luminous nonpremixed turbulent fiâmes[END_REF]. The soot production in a méthane flame is very weak even null under our conditions of tests. At thé opposite, thé propane and ethylene fiâmes known as luminous are characterised by their yellow color because of their important soot concentration. Indeed, thé ethylene and propane hâve a greater propensity to produce soot (see thé f s fraction in Table 1).

3 -Photos of différent gas fiâmes.

Moreover, thé température measurements on thé axis of jet fire also shows a différence between méthane and thé two other gases, ethylene and propane. Indeed, at thé flame tip, thé températures are included between 500 and 600 °C for jet fires of ethylene and propane, whereas for méthane, they are rather of 900 °C. The température range of 500-600 °C corresponds to thé empirical criterion given by Mac [START_REF] Caffrey | Purely Buoyant Diffusion Fiâmes: Some Expérimental Results[END_REF] to defme thé average flame. Physically, this criterion is explained by considering thé spectral distribution of thé emissive power of thé black body (Planck's law). For thé ethylene and propane fiâmes, thé radiation is emitted in thé field of visible by thé soot particles comparable with black bodies. The Planck's law shows that thé black body emits radiation in thé short range wavelengths of thé field of visible (0,4 -0,8 um) only when it reaches températures higher than 500-600 °C. Below this limit, thé black body does not émit any more but in thé infra-red one. No radiation is received coming from thé soot particles below 500 °C. Consequently, it is cohérent that this criterion does not apply to jet tire of méthane because thé structure is différent, thé steam and CO2 being thé only radiant bodies (semi-transparent bodies) in this flame.

RADIANT ENERGY OF FLAME

The fraction of combustion energy radiated î] r is important in thé calculation of thé radiative flux received by a target. To estimate it in experiments, a calculation is carried out while being based on thé values of radiative flux given by thé fluxmeters.

Figures 4 and5 show thé comparison between experiment and SHELL model for thé fraction of combustion energy radiated rj r and for thé radiative power Q r (Q r ~Tj r Q) according to thé Fraude number Fr. O.OOEtOO 2.00E<O4 4XEHH 6.00E4Û4 8.00E4O4 1.00E4O5 1.2O&O5 1.«E« 0.00&00 2.00BO4 4.00&W &00E+O4 B.00E+04 1.00&05 1.20&05 1.«6tO5

In a général way, thé expérimental and modelling radiative fractions tend to decrease when thé gas jet velocity increases. This observation is a characteristic of thé turbulent jet fires rather controlled by thé forced convection induced by thé gas jet. Even if thé fraction of combustion energy radiated î] r is reduced, thé radiative power Q r increases with thé exit gas velocity. Indeed, thé more thé mass flow rate grows and thé more thé flame is going to radiate (Figure 5). In addition, thé radiative fraction of thé méthane flame is systematically lower than thé radiative fractions of propane and ethylene. Indeed, thé radiation of a méthane jet tire cornes exclusively from thé water vapor and carbon dioxide which are bodies known as being "semi-transparent". Their émission is very weak compared to thé émission of a black body. Conversely, ethylene and propane jet fires hâve important concentrations of soot, particles radiating as black bodies.

In addition, except for ethylene, thé SHELL model (modified by [START_REF] Cook | Size and radiative characteristics of natural gas flares. Part II: empirical model[END_REF]) gives values of radiative fraction which are at least thé double of thé expérimental values. For a given surface of flame, this would imply a radiative flux received at a given distance multiplied by two. Moreover, thé SHELL model estimâtes that jet fires of propane hâve a highest radiative fraction than those of ethylene whereas thé tests showed thé opposite. Indeed, thé calculation is based on thé molecular weight of thé gas: more it is important and more thé gas will hâve a high radiative fraction. The radiation of thé propane and ethylene fiâmes is due mainly to their conséquent soot concentration.

The alkenes (ethylene) hâve a greater disposition to produce soot than thé alkanes (propane) [START_REF] Rasbah | Fundamentals of smoke production[END_REF]. The more thé fiâmes are concentrated of soot and thé more they tend to radiate until they are saturated with particles. It is completely logical to obtain experimentally a radiative fraction of propane flame weaker than thé ethylene one.

Consequently, thé calculation of thé radiative fraction instead of being based on thé molecular weight should rather be a function of thé propensity of thé gas to form soot. An analysis carried out by [START_REF] Delichatsios | Thé effects of fuel sooting tendency and thé flow on flame radiation in luminous turbulent jet fiâmes[END_REF] and based on thé smoke-point heat release rate Q sp 3 allows to define thé radiative fraction for jet fires whose radiation is induced mainly by soot. In this model, Delichatsios defines a maximum radiative fraction îj r mai[ corresponding in a jet fire saturated with soot. Moreover, it defines thé radiative fraction as a function of thé modifïed Fraude number Fr f , thé smoke-point heat release rate Q sp and thé gas mass flow rate riif such as:

Vr i '-= fcn 0^-298) Q sp m, Z sl (Q,SFr f 2 ) 13
[1]

where:

Frf = U u j 15 0.5 0.25 (Pfuel)

{ Pair J

To i : Adiabatic flame température (K), Z st : stoichiometric ratio (-).

Figure 6 présents a comparison of thé expérimental and modelling results. On thé one hand, thé évolution of thé radiative fractions obtained in experiments is in adequacy with thé Delichatsios model. On thé other hand, a variation remains between thé expérimental and modelling results. This différence is due to thé taking into account in thé model of a measured adiabatic température and non theoretical flame (for ethylene, 2370 K instead of 2637 K). The first tests realised with jet fires showed thé différences existing between tested gases in term of soot concentrations. The second expérimental campaign based on thé jet fire impingement of thé steel pipe was performed to apprehend how jet fire interacts with thé engulfed equipment. With this intention, Figure 7 présents thé thermal response of thé pipe impinged by thé fiâmes of three gases (méthane, propane and ethylene). The pipe is located at thé centre of jet fire and has a water flow of 12 kg/min. The méthane mass flow rate is 3,81 g/s, thé propane one is 4,48 g/s and thé ethylene one is 2,48 g/s (Fraude number is thé same for propane and ethylene). First of ail, Figure 7 shows that thé température of thé pipe lises very fast. This is caused by its thermal inertia which is very weak. This weak thermal inertia is due mainly to thé thermal diffusivity of thé steel which is high and about 1,55.10 5 m 2 /s. Consequently, in less than one minute, thé pipe subjected to thé méthane fire reaches a thermal equilibrium characterised by an asymptotic température of 120 °C. This thermal response is logical since with thermal equilibrium, absorbed heat flux (contributions by radiation and forced convection) and evacuated heat flux (losses by forced convection of water) by thé pipe are compensated. It should be noted that this is valid only if absorbed and evacuated heat fluxes remain constant. The pipe impinged by propane and ethylene flame does not reach a thermal equilibrium. Indeed, after having reached a température peak, thé thermocouple returns a température which decreases during time instead of stagnating. The forced convection induced by thé water flow remaining unchanged during thé test, only a modification of thé heat absorbed by thé pipe can be at thé origin of such a phenomenon. The photographs taken after tests showed that thé méthane fire had caused an oxidation of steel due to thé condensation of thé combustion steam coupled with thé high température in thé flame. The formation of this ferrie oxide residue did not hâve any impact on thé thermal response of steel. On thé other hand, after thé propane and ethylene tests, it appeared on thé pipe a conséquent soot deposit. Thus, we deduced from it that this deposit was at thé origin of thé température decrease. This phenomenon is called "thermophoresis" (Me [START_REF] Enally | Soot volume fraction and température measurements in laminar nonpremixed fiâmes using thermocouples[END_REF] and corresponds to a laminar transport by which thé particles (soot) go upstream a température gradient. Indeed, thé opaque particles (strongly absorbing) follow usually thé heat gradient while escaping from thé hot zones to go towards thé cold zones. Soot would corne to deposit preferentially on thé cold pipe and to insulate thé pipe thermally as thé deposit thickness evolves in thé course of time. A test carried out over one forty minutes duration showed that thé pipe température could go under a température of 40°C after having reached a température peak of more than 140 "C. The soot particles always remain in place condensing and agglomerating on thé pipe in thin layer then in thé form of aggregates.

Moreover, this soot deposit plays thé same rôle in thé long term as a fireproof material because of a very low thermal conductivity of soot.

CONCLUSION

In order to better characterise thé thermal domino effects, which can occur on industrial plants, it is thus necessary to be able to precisely assess thé thermal aggression and thé thermal response of thé impinged equipment. Accordingly, our expérimental research related to thé thermal impact of jet fire on a pipe with cooling flow and more particularly, on thé part of soot in thé heat transfers.

In fact, thé important flame radiation is due to soot. The more thé fiâmes are concentrated of soot and thé more they tend to radiate. Each hydrocarbon has a différent propensity to produce soot. For example, thé alkenes hâve a greater disposition than thé alkanes. However, in thé calculation of thé radiative fraction of jet fires (SHELL model), this data is not taken into account. The radiative fraction is an important parameter of thé calculation of thé thermal consequence-zones. Then, it rnust be precisely given. The tests carried out within thé framework of research program made it possible to clarify this problem of propensity then to test and validate thé corrélation of Delichatsios based on thé theory of thé "smoke-point". This corrélation permits to déterminé in a more suitable way thé radiative fraction.

If soot generated at high température produces an important radiative flux, its settlement on thé pipe by a thermophoresis phenomenon tends to thermally insulate thé pipe from thé exteraal aggression. In accidentai conditions, soot as well as a fireproof material would make it possible to protect thé équipaient and would act like a passive safety barrier. With thé différence of thé fireproof material, which can worsen in fire, thé soot insulating capacity increases during thé fire with thé growth of its deposit.

Figure 4 :Figure 5 :

 45 Figure 4: Fraction of combustion energy radiated 7] r

Figure 6 :

 6 Figure 6: Comparison between experiments and Delichatsios model for thé radiative fraction.

Figure 7 :

 7 Figure 7 : Evolution of thé thermocouple directly impinged by jet fire and photos showing thé conséquences of jet fire.

  Thé plan of tests is presented inTable 1 which indicates for ail gases, thé ranges of thé gas mass flow rate m f , of thé heat release rate Q, of thé exit gas velocity Uj, of thé Reynolds number Re s , of thé Fraude number Fr and thé effective diameter of thé jet D s . The Froude number is often considered to define thé characteristics of jet tire.

						Steel pipe with
						cooling water flow
	Gas cylinder:	Gas heat exchanger before thé
	Méthane	flowmeter
	Ethylene
	Propane
		Table 1 -Characteristics	of jet fires tests.
	Gas	m f (g/s)	Q(kW)	Uj (m/s)	D s ' (mm)	vi	ïï	u; gD s	()
	Méthane (CR,) /, 2 =18,9%	1,02-3,81	51-191	25-93	6,6	10000 -37330	9600-134030
	Propane (C 3 H 8 ) /. = 17,6 %	1,23-5,31	62 -296	11-47	10,9	27150-117200	1130-21060
	Ethylene (C 2 H 4 )	1,32-6,27	57 -246	18-87	8,7	18790-89260	3970 -89530

p r -J : s ( i Re,

D s : Effective diameter of thé gas jet such as : D s = d,

f s : Fraction which represents thé fuel mass fraction at which carbon particles begin to form[START_REF] Beyler | Fire hazard calculations for large open hydrocarbon fires[END_REF].


S Huguet

G Sarret

A Laboudigue ' '

V Barthès

V Bert

Is thé hyperaccumulating plant Arabidopsis halleri a good candidate for phytoextraction?

Keywords: Arabidopsis halleri, cadmium (Cd), hyperaccumulation, phytoextraction, speciation, sédiment

Ahstract

Thé cleaning of waterways by regular dredging générâtes great volumes of sédiments and, owing to human activities, thèse sédiments often contain large amounts of metals (Cd, Zn, As, Pb) which are potentially toxic for plants and animais. Phytoextraction could be a solution to treat this kind of sédiments. This work focuses on thé mechanisms of Cd accumulation in Arabidopsis halleri, a Cd and Zn hyperaccumulator, and thé effects of this species on a métal polluted sédiment.

Introduction

In thé north part of France, thé maintenance of waterways by regular dredging opérations générâtes large volumes of sédiments that often contain large amounts of metals ( Cd, Zn). The absence of effective and low cost technologies to treat polluted sédiments créâtes thé need to develop innovative technologies for remediation. Since thé last ten years, many studies were dedicated to thé potential use of plants in order to extract, contain or immobilize metals in contaminated soil. Some plants called hyperaccumulators are able to accumulate high amounts of metals in their aboveground parts. This interesting plant property could be used for phytoextraction. The lack of knowledge of thé mechanisms involved in métal hyperaccumulation is a major restraint for phytoextraction development This project is focused on Cd accumulation mechanisms in thé Zn and Cd hyperaccumulator Arabidopsis halleri and combines physics, physicochemical and biological approaches.

Materials and methods

Sédiment-. Dredged sédiment was collected from thé Scarpe canal in thé Nord Pas de Calais Région. This area is heavily polluted with Cd (around 140 mg • kg" 1 ). Sédiment was air dried and mechanically homogenized to reduce its water content. Pots (41) were filled with sédiment and equipped to collect leachates (Photo 1).

Plant material -. A. halleri developed natural populations on both métal contaminated and uncontaminated soils and sédiments in France and Belgium (Bert et al. , 2002). Seeds of A. halleri from a metallurgical waste (pH= 6. 8 -Auby, Fr) and from an uncontaminated soil (Hautes Fagnes, Be) were germinated on compost for 4 weeks. Seedlings were transferred to thé sédiment pots after roots hâve been washed carefully with deionized water (Photo 1). Seedlings of white mustard (Brassica napus) were grown in thé same conditions as a non-accumulator control. Seedlings were also transferred to pots filled with agricultural soil to hâve a plant growth control. The design of thé experiment is one seedling per pot and three replicates per origin and plant species. Soil and sédiment moisture was maintained at 80% field water capacity with additions of regular de-ionised water after weighing. Plants were grown for 6 months in a controlled environment growth room (12h photo period; 20/16°C day/night température; relative humidity). Pot experiment % Before thé start of thé experiment, total métal concentrations in thé sédiment were measured by inductively coupled plasma atomic émission spectroscopy (ICP-AES) after microwave HC1/NO3 digestion. Once a month, leachates were collected, pH was measured, and their composition was analysed. Cadmium phytoavailability was performed once a month using DGT probes (Nolan ét al. , 2005) and Ca ( No 3 ) 2 extraction. Health status and plant growth were regularly monitored by counting new leaves and measuring thé size of thé rosette. Total Cd concentration in leaves was measured once a month by ICP-AES.

Cd Autoradiography

: A. halleri ( Auby) plants previously studied in Sarret étal. (2002) were grown in hydroponics added with 20juCi/L 1 09 Cd and various concentrations of non-radioactive Cd (0, 10 and 50/iM) , non-radioactive Zn (0, 30fjiM and 2 mM) for various times (2, 3 and 5 weeks). Each experiment was done in triplicate.

Another experiment was designed and is in progress. In thé nutrient solution, 20juCi/L 109 Cd was added in each pot Cadmium (0, 5 and 20JLIM) and/or Zn (30, 300/JVD were added in thé pots depending on thé aim of thé experiment Each experiment was done in triplicate too, with three plants growing in thé same pot After various times of exposition (1, 2, 3 and 9 weeks), aboveground parts of plants were eut and arranged as flat as possible on a paper film and covered with a polyethylene film. Tb obtain autoradiographs of adaxial side, SR autoradiography films (Packard) were placed against thé polyethylene film. After overnight exposition, films were developed using a Cyclone Storage Phosphor System, and obtained autoradiographs were treated with Optiquant and ImageJ softwares.

Results

Pots experiment : Thé experiment is still in progress. The aim of thé experiment is to quantify thé impact of thé growth of A halleri from two origins (metallicolous and non metallicolous) on a métal contaminated sédiment in terms of Cd accumulation in leaves and Cd speciation in thé sédiment.

Cd distribution in leaves of Arabidopsis halleri {Auby, preliminary results )

The distribution of Cd and Zn was firstly studied at thé scale of thé whole plant at various exposure times. After 2 weeks of exposure to Cd only, Cd was accumulated mostly in new leaves and veins of oldest leaves. After 5 weeks, Cd was still distributed in new leaves, but also in ail tissues of thé oldest leaves.

When plants were exposed to Cd and Zn, a more homogeneous distribution of Cd among new and oldest leaves was observed.

Thé distribution of métal was then investigated at thé leaf level. After 3 weeks of exposure, trichomes of A. halleri were enriched in Cd (Figure 2) and showed a four-fold higher activity than thé leaf tissue ( 1. 68. 10 6 Digit Light Units (DLU) per mm 2 and 4. 44. 10 5 DLU/mm 2 , respectively) .

Trichomes represent 2. 5 % of thé total leaf area, which corresponds to 8% of Cd, thé rest being sequestered in thé leaf tissue. Therefore, in A. halleri trichomes represent a minor compartment of Cd accumulation, which is consistent with previous observations (Sarret et al. , 2002).

Discussion

Autoradiography was used in very few studies on métal accumulation in plants. Preliminary rests showed that autora" diography was an interesting too! to visualize Cd distribution and accumulation zones in thé leaves with a good latéral résolution, and quantify Cd activity in single leaves. However f this technique did not allow a précise quantification of total Cd content in thé plant. This latter parameter will be measured by ICP-AES in.a parallel experiment with stable Cd and Zn. Zhao étal (2006) observed that Zn inhibited short-terni uptake of Cd in metallicolous A. halleri. This resuit will be compared with our results obtained by autoradiography. The effect of an increase in Cd concentration will be investigated too. Thèse différent phenomena will be observed on a longer time (9 weeks), and compared with thé non-metallicolous A. halleri species.. Variation in Cd accumulation among différent populations may be expected (Bert étal. , 2002).

Figure 1 .

 1 Figure 1. Arabidopsis halleri "Auby" growing on contaminated sédiment in thé growth room and non vegetated pots (sédiment control) -

Figure 2 .

 2 Figure 2. Autoradiographs of leaves of A halleri exposed to lO j JVI Cd, 2mM Zn and 20fiCi/L 109 Cd for 3 weeks (a) and for 5 weeks (b). Black spots are trichomes.

culture

  Cuttings from a plant from Auby and from a plant from Hautes Fagnes were grown in hydroponics with thé following basai nutrient solution (0. 5 mM MgSO 4 • 7 H 2 O, 1 mM NH 4 H z PO 4 , 2 mM Ça (NQ, ) 2 • 4 H 2 O, 3mM KNO 3 , 0. lfxM (NH4) 6 Mo 7 O Z4 , H z O, 0. lfxM CuSO 4 • 5 H 2 O, 25jbtM H 3 BQ,, 2 p M MnSO 4 • H 2 O, l ( M KC1, 0. ljM NaCl, 30fxM ZnSO 4 • 7H 2 O and 20fxM Fe(ffl)-EDDHA). White mustard was also cultivated in hydroponics as a non-accumulator plant control. Clones were used in two experiments; one aims at quantifying Cd accumulation in leaves, thé other one aims at localizing Cd distribution at thé plant scale by autoradiography. Cadmium was added as CdCl z • 2. 5H 2 O in thé nutrient solution after 4 weeks of growth in hydroponics.

	Hydroponic

Acknowledgements

This work was supported by thé Nord-Pas de Calais Région and Voies Navigables de France, FEDER funds through French research program: Programme de Recherche Concert es (PRC "Sites et Sols Poilu s, Environnement et Activit Humaines").


S Huguet
email: shuguet@obs.ujf-grenoble.fr

V Bert

A Laboudigue Za

M P Isaure

G Sarret

Cd localization and speciation in a contaminated sédiment and in thé Zn and Cd hyperaccumulating plant Arabidopsis kalleri

Keywords: sédiment, Cd speciation, EXAFS, XANES, XRF, SEM-EDS

The purpose of this work was to characterise thé chemical speciation of Cd in a Zn-and Cd-contaminated dredged sédiment subjected to a phytoremediation treatment with thé hyperaccumulator plant Arabidopsis halleri. The investigations were perforrned using analytical chemistry, scanning électron microscopy and synchrotron techniques including X-ray microfluorescence and X-ray absorption spectroscopy (EXAFS and XANES). The paper focuses on thé initial state of thé sédiment before thé beginning of thé phytoremediation treatment. months in order to reduce its water content. Thereafter, thé sédiment was mechanically homogenized several times. Macroscopic characterization of thé bulk sédiment included thé détermination of major and trace élément concentrations, granulometry and physico-chemical parameters.

Physical methods

. Some samples of thé freeze-dried sédiment were embedded in epoxy resin, eut to 30 m-thick thin sections, micro-polished and mounted on glass slides. Thèse sections were examined by environmental SEM-EDS and by ,uXRF, Cd I^-edge juXANES and S K-edge juXANES spectroscopy on thé beamline LUCIA

Introduction

In thé Northern part of France, thé maintenance of waterways by regular dredging générâtes large volumes of metalpolluted sédiments Thèse materials are usually deposited on landfill sites ( 180 sites in thé Nord-Pas de Calais région). Phytoremediation could be a way to treat thèse polluted sédiments. However, to our knowledge, there are few investigations into phytoextraction using hyperaccumulating plants on contaminated sédiments. This study is part of a larger project investigating thé modifications of cadmium speciation in a contaminated sédiment planted with thé Zn and Cd hyperaccumulator Arabidopsis halleri. The goal of this study was thé characterisation of thé contaminated sédiment in its initial state.

Metals are generally présent in a variety of différent chemical species and phases ( co-précipitâtes, adsorbed species, etc. ) in soils and sédiments, including micro-and nanoparticles. Laterally resolved synchrotron techniques with micrometer-scale résolution offer thé opportunity to study thèse heterogeneous and complex Systems in détail. Hère, we used électron microscopy coupled with energy dispersive X-ray microanalysis (SEM-EDS) and synchrotron-based techniques including micro X-ray fluorescence ( XRF), micro-and bulk Xray absorption spectroscopy (Cd Lf-edge fxXANES, S Kedge XANES and Cd K-edge EXAFS) to study thé localization and thé chemical form(s) of cadmium in thé sédiment.

Materials and methods

Sampling area and characteristics of thé sédiment

The sampling area is located in thé North of France, about 30 km south of Lille. This région is among thé oldest and largest industrial areas in Europe. Past and présent contamination by non-ferrous métal processing has released huge amounts of ore particles and slags into thé environment (Thiry et al. , 2002). Five hundred kg of sédiment were collected by dredging thé Scarpe River in an area known to be heavily polluted with Cd (around 140 ppm) . The sédiment was mixed and left to drain, protected from rainfall, for 7 (SLS, Vdligen, Switzerland) with a spot of 3X3 pcm.

Résulte and Discussion

EXAFS analyses on bulk sédiment

Linear combination fits of thé bulk sédiment spectrum showed that greenockite provided thé closest référence spectrum, but thé two spectra showed some différences. Adding a second component did not improve thé fit, suggesting that our database of Cd référence compounds did not contain thé species présent in thé sédiment. The sédiment spectrum was then treated by FEFF simulations. The first shell was correctly simulated with 3. 9 S at 2. 52A. The second shell was not correctly simulated with Cd only (Figure la-b). The fit was improved by adding Zn in thé 2nd shell (not shown). Thé best fit was obtained with a mixture of Zn, Cd and Fe (7. 2 Zn, 2. 6 Cd and 1. 4 Fe at 2. 5lÂ, 3. 88Â, 4. 18Â and 3. 69Â, respectively, Figure lc-d). This suggests that Cd was présent in form of a mixed Cd,Zn,Fe-sulfide. This is not surprising since pyrite and sphalerite hâve been identified before in similar sédiments (Isaure étal. , 2001).

SEM-EDS and jxXANES analyses on bulk sédiment

SEM-EDS was used to study geochemical associations of Cd in Cd-rich régions of thé sédiment samples. The bright grains on thé backscattered électron image shown in Figure 2a contain associations of Cd, Fe, Zn and S (Figure 2c-f) , which is consistent with thé EXAFS results. The comparison of fxXANES spectra recorded on Cd-rich régions with référence spectra shown in Figure 3a suggests thé . occurrence of CdS. This conclusion should still be refined by comparing the ^XANES spectra with a mixed sulfide référence. Sulfur was not only présent in reduced forms. Indeed, also oxidized S species were found in Cd-poor and S-rich régions, (Figure 3b). 3.54 3.56 3.58

Photon energy (KeV) Normalized absorption 6.0 .

4.o :~

: '• • • -' ' "' " ^-- (a)
CdCO.

-

Conclusion & Perspectives

The électron microscopy and X-ray absorption results obtained at thé Cd and S edges were consistent with thé présence of a mixed sulfide (Cd, Zn, Fe)S as thé major Cd species. Further microanalyses (in progress) should provide more information on minor phases.

In subséquent experiments, we will grow hyperaccumulator plants on thé sédiment and study thé impact of thé plants on Cd speciation in thé substrate. In particular, we will look into métal sulfide oxidation and Cd redistribution between thé various phases.

Figure 1 .

 1 Figure 1. (a,b) Cd K-edge EXAFS spectrum for thé bulk sédiment and its and Fpurier transform (blue line) and FEFF simulation with a S first shell and a Cd second shell (a-red line). (c,d) Same spectrum simulated with a S first shell and a Cd, Zn, Fe second shell.

Figure 2 .

 2 Figure 2. (a) backscattered électron SEM image and (b) EDS spectrum of a Cd-rich spot of thé sédiment thin section, (c-f) FJemental maps for Cd, Fe, S and Zn of this région.

Figure 3 .

 3 Figure 3. (a) Cd Liedge fiXANES spectra of a Cd-rich région of sédiment and référence compounds and (b) S Kedge jzXANES spectra recorded on two sédiment samples (one Cd and S rich région and one S rich région)

Acknowledgements

Patrick Degrugilliers is thanked for thé préparation of thin sections and Philippe Recourt for his assistance during SEM analyzes. Anne-Marie Flank, Pierre Lagarde, Olivier Proux and Nicolas Geoffroy are acknowledged for their assistance during synchrotron experiments. This work was supported by thé Nord-Pas de Calais Région and Voies Navigables de France, FEDER founds through French research program: Programme de Recherche Concert es (PRC " Stes et Sols Poilu s, Environnement et Activit Humaines")