INERJS, BP J P Pineau
email: philippe.pineau@ineris.fr

Risk analysis for equipment and protective systems intended for use in potentially explosive atmospheres

Keywords: risk assessment, explosive atmospheres, equipment, protective systems

EU Directives 98/37/EC (machinery directive) and 94/9/EC (ATEX 100a) have to be applied by manufacturers of equipment and protective systems intended for use in potentially explosive atmospheres. These Directives include Essential Safety Requirements and place an onus on manufacturers to carry out a risk assessment for the intended use of their equipment. In order to help manufacturers in this task, the European Standards organisation, CEN, TC 305 has mandated its WG 4 (terminology and methodology) to write a standard on the risk assessment of equipment and protective systems intended for use in potentially explosive atmospheres. The RASE project was set up as a prenormative research work to define the requirements for developing such a standard as specified in the dedicated call of the European Commission's Standards Measurement and Testing programme concerned with subjects relating to the standardisation activities of CEN -Explosive atmospheresrisk assessment of unit operations and equipment. The project (December 1997-May 2000) was co-ordinated by INBUREX with the participation of FSA Germany, INERIS France, HSE England, NIRO Denmark and CMR Norway. Since March 2000, WG 4 (TC 305) is actively involved in preparing the final draft of this standard. This paper describes the objectives and the results obtained to date in RASE project and in WG4. An outline is given of the contents of the standard being developed for the risk assessment of equipment and protection systems intended for use in potentially explosive atmospheres.

INTRODUCTION

The Essential Safety Requirements relating to EU Directives 98/37/EC (machinery directive) and 94/9/EC (ATEX 100A) are to be applied by manufacturers of equipment and protective systems intended for use in potentially explosive atmospheres. Current standards (e.g. EN1127-1 and 2) only consider the basic concepts and methodology dealing with explosion prevention and protection respectively for groups II and I equipments. There is a lack of a common methodology which can be used by manufacturers facing the design of the wide variety of equipment and protective systems (both electrical and non-electrical) intended for use in explosive atmospheres. CEN/TC305 has mandated (december 1994) its working group 4 (terminology and methodology) to write a specific European standard dealing with risk assessment of equipment for use in potentially explosive atmospheres before end 2001. This means that there is an urgent need for a standard on risk assessment. In order for manufacturers to meet the Essential Safety Requirements, it is necessary that they carry out a risk assessment of their products including its intended use. Current Risk Assessment Methodology standards, for example EN 1050, provide a good general overview of the techniques and the concepts involved for application of the machinery directive. However they need to be extensively and clearly extended to cover the specific situation and problems associated with risk assessment of equipment and protective systems intended for use in potentially explosive atmospheres. Thus it is necessary to develop a flexible and comprehensive unified methodology that will assess the process parameters including those of equipment and protective systems to identify the hazardous situations and evaluate the risks. This methodology needs to provide a link between the risk, its severity and probability of occurrence and the consequences whilst allowing the evaluation of mitigating effects arising from both the design and construction of the equipment and also the provision of additional protective systems (risk reduction). The RASE project was set up to meet the requirements for developing such a standard as specified in the dedicated call of the European Commission's Standards Measurement and Testing programme concerned with subjects relating to the standardisation activities of CEN -Explosive atmospheres -risk assessment of unit operations and equipment. The objective of this project is to develop a comprehensive flexible Risk Assessment Methodology for identifying potential hazardous situations in equipment such as reactors, dryers, mixers, storage systems intended for use in potentially explosive atmospheres in various industries (chemical, oil, food and provender, metallurgy etc.). The developed Risk Assessment Methodology will help manufacturers of such equipment fulfil their obligations under the ATEXlOOa (Equipment for use in potentially explosive atmospheres, 94/9/EC) Directive, i.e. it will be related to the equipment groups and categories defined in this Directive and has been produced in a form that can be readily discussed as an input for a European Standard. The project has been developed to ensure a close relationship with the work performed in CEN/TC305 and CENELEC/TC31, the European Standards bodies concerned with this topic.

As a consequence of this scientific objective, the following technical objectives will be achieved:

• harmonisation of a comprehensive approach of hazardous situations between manufacturers, consultants, competent authorities and users. • the user should consider the safety in operational conditions on the basis of risk assessment performed at the design stage by the manufacturer. • estimation of the residual risk (if any) • improvement of the choice of equipment referring to safe operating conditions • reduction of production losses during operation (including malfunction) of the equipment and total loss of equipment from an accidental explosion • use of the results of the application of the risk assessment for the training of operators of equipment.

As the proposed project has been planned to be accomplished in close co-operation with CEN/TC305 and CENELEC/TC31, the end result has been a methodology that can be used as an input for the work to be performed by CEN/TC305/WG4 which will enable manufacturers to simply and quickly assess the risks associated with the intended use of their products, thus contributing to the improvement of Health, Safety and Environment in Europe.

The work (WI 00305061) mandated to WG 4 in TC 305 is concerning a methodology for risk assessment of equipment and protective systems for intended use in potentially explosive atmospheres.

The proposed scope is the following :

This standard will give guidance on risk assessment related to dangerous (hazardous) situations arising from potentially explosive atmospheres.

This includes : •

The evaluation of the likelihood and consequences of an explosion •

The mitigation of explosion effects •

The selection of equipment and/or protective systems (including components) •

The information for safe use and maintenance.

I WORK PROGRESS IN RASE PROJECT (December 1999-May 2000)

A draft version of a risk assessment methodology which can be used by manufacturers of equipment designed for use in potentially explosive atmospheres was produced in May 2000. This methodology was established as an end product after completion of four discrete work packages : Final improvement of the methodology.

Inquiry on Current Experience from Manufacturers

The starting point has been the existing experience of manufacturers and users. An inquiry was carried out through questionnaires (respectively for manufacturers and users). Included in these questionnaires were aspects such as the intended use, the level of training of operators, the degree of automation of the equipment, the choice of safety measures used, the severity of harm, the probability of occurrence of hazardous situations, the reliability data of equipment and safety measures, the efficacy of the safety measures, the maintenance, the lessons learnt from accidents, the knowledge of existing national regulations, standards and codes of practice, the safety rules specified in the instructions for use and whether and how manufacturers currently carry out risk assessments.

These questionnaires were translated into French, German, Danish and Norwegian and sent to firms in England, Ireland, France, Belgium, Germany, Switzerland, Austria, Denmark, Sweden and Norway. The distribution was mainly to manufacturers (mainly non-electrical but also some electrical) as well as to some users of equipment for use in both gas and dust explosive atmospheres. Both large and small companies were approached as well as Engineering Contractors. Unfortunately due the time constraints of the project, it was not possible to cover Southern European countries. Approximately 200 responses were received and the results reported using an Excel spread sheet specially developed to aid with the evaluation of the results. The main conclusions that can be drawn from this survey were:

• most respondees have little awareness of the European Directives dealing with potentially explosive atmospheres, however the majority are aware of national legislation in this field. • in many instances, manufacturers do not consider that it is their responsibility to define hazardous zones and assess risks, however customers specifications are taken into account. They do not seem to use the results of any risk assessment which would appear to contradict the response that the majority consider 'intended use'. • the risk of occurrence of explosive atmospheres is assessed by Users with a large diversity of methods. Both potential gas/vapour and dust explosive atmospheres are taken into account. For this risk assessment, topics such as flammability and explosivity characteristics of products, hazardous areas classification, protective and preventive methods are considered. • 1/3 of manufacturers are aware of accidental explosions involving their equipment. • 1/2 of users had had explosions in their plant ; protective systems were present in the majority of these incidents. • a large variety of safety measures were used by users however surprisingly such safety measures were chosen as a result of a risk assessment in only 50% of the cases. • with respect to efficacy, there were a lot of standards used by manufacturers either related to the equipment in general and for specific protective measures but only 50% of the users said that they received such information. • ca. 85% of the users consider reliability of equipment and protective systems as a part of their risk assessment whereas only ca. 50% of manufacturers consider this aspect.

The questionnaires identified that both manufacturers and users are still looking for suitable tools to use for risk assessment.

Additionnally, incident data have been collected and evaluated to determine relevant aspects which would have a bearing on the proposed risk assessment methodology. The review included approximately 750 dust explosion accidents and 20 gas explosion incidents.

The investigation revealed the following with respect to the cause and effects of dust explosions:

• 26 % of the accidents are caused by human action (based on German records, UK records indicate that only 7 % of the accidents are caused by human action) • 28 % of the accidents are caused by poor design • 12-14 % of the accidents is caused by poor maintenance • 2-7 % of the consequences of the accidents were worsened due to human action • in 19-21 % of the accidents poor design can be pointed out as a factor for worsening the effects • it was found that in almost all cases knowledge of ignition properties of the respective dusts would not have been able to prevent the accidents from happening. Explosion protection was applied in many cases but worked satisfactory in only a fraction of the cases that it was applied.

With respect to the causes of gas explosions it was found that: « 33-67 % of the accidents can be attributed to human action (respectively offshore and onshore) • both offshore and onshore design errors are responsible for approximately 33 % of the accidents « poor maintenance appears to be responsible for 11 and 17 % of the accidents occurring offshore and onshore respectively however, 46 % of the accidents concerned mechanical failure. >» in all investigated gas explosion accidents the design was too poor to withstand the gas explosion effects.

Overall the review showed that important issues in risk analysis are: human factor, plant design and maintenance and that these factors should be taken into account in the development of the risk assessment methodology.

Development of Risk Assessment Methodology

According to the responses to the questionnaires and the types of equipment involved, a review was carried out of existing methodologies for risk assessment which will enable a methodology to be developed so that it is flexible enough to be simply applied to the equipment considered but comprehensive enough to deal with the above mentioned aspects. The objective is the development of integrated explosion safety through the choice of reliable and effective safety measures. The review of existing methodologies considers not only current European standards but also national standards, guidelines and current practices. In addition accident literature was reviewed to ensure that any lessons to be learnt are incorporated in the methodology. The scope of the risk assessment methodology was based on the requirements identified from the responses to the questionnaire. The results of the review of existing methodologies for risk assessment together with the responses from the questionnaire and the review of gas and dust explosion incidents that have occurred allowed to develop a methodology which is flexible enough to be simply applied to the equipment considered but comprehensive enough to cover all aspects required by the Directives. The scope of the methodology has been extensively discussed by the project partners. In particular, the intended breadth of application of the methodology i.e. whether it is intended just for simple pieces of equipment or also for more complex assemblies of apparatus was a difficult point to resolve. Limiting the scope of application to simple single items of equipment has the advantage that the resulting methodology would be relatively simple to describe, however, this will prevent from a fulfilling the requirements of the project which specifically states that the methodology should be applicable to all equipment which fall under the ATEX 100a directive. At present the methodology attempts to cover all equipment covered by the ATEX 100a Directive. It is primarily targeted at design and manufacturing however it also covers uses of equipment to ensure a common format/language between the two aspects. Often the severity/consequences of an incident can only be defined by the user and a link is needed between these aspects. The methodology concentrates on risk analysis i.e. hazard identification, risk estimation and risk evaluation and also includes details of the relevant tools/techniques which can be used. In addition, ways to identify possible deviations have also be included. Risk reduction, which is not a part of risk assessment has not be included, however, a section on risk reduction options analysis has been included to ensure that the risk assessment considers the effect of any risk reduction measures that were taken. An extensive list of existing risk assessment techniques has been included with a short description of each and reference to more detailed information. It became apparent that a critical stage in the process of risk assessment was the definition of the scope of the intended use of the equipment being studied. The methodology includes a novel procedure for the preparation of an 'Equipment/Process Flow Diagram' to ensure that the intended use of the equipment is correctly defined. This procedure helps specify the conditions within the equipment during its use by the inclusion of energy (i.e. temperatures, pressures etc.) levels for each phase of the equipment's operation which are then used to consider/define the status of the materials being handled and the equipment itself. Such a flow diagram not only helps to define the intended use but is also used as the key part of the iterative risk assessment process. A large amount of effort has been expended in trying to achieve both a clear logic flow through the risk assessment procedure and also the arrangement of information in a structured way. Logic diagrams have been included to make the methodology more useable. Flow charts for deciding the which data/tests are required for gas/vapour flammability properties and for the explosibility of dusts have been developed and included. The methodology provides ways to consider the risk of damage to people, the environment and property and a separate section has been included discussing residual risk. In order to help the user of the methodology, tables with a prescribed format have been included for recording the results of the hazard identification step and also the new 'Function/State Analysis' step. These also help achieve data transparency between manufacturer and user. Although quality assurance is not felt to be a part of the methodology, the specific requirements for documentation which have been included would allow an audit of the results to be carried out where necessary. The final document will contain examples of the use of the methodology and will include information to help manufacturers classify their equipment as defined in the 94/9/EC Directive.

Identification of hazards, hazardous situations and hazardous events

There is rarely, if ever, a single cause of a hazardous situation or hazardous event. Although the immediate cause may be a simple hardware failure or operator error, other events will have also occurred which contribute to the development of the accident. Such events include undetected failure of protective systems, ergonomie problems or an organisation in which safety is not given priority. In many ways, hazard identification is the most important part of any risk assessment. In order to successfully carry out this step the previous step must have accurately defined the equipment in sufficient detail. Once a hazard has been identified, the design can be changed to minimise it, even though the degree of risk may not have been estimated. A full understanding of the equipment intended use and foreseeable misuse is of prime importance during this step. A project or a process has an acceptable safety design when one judges that adequate preventive or protective measures have been taken. The term "adequate measures", refers to generally accepted safety, engineering, scientific, production, operational, and maintenance procedures with view to the location in which the risk might occur. The main aim of hazard identification is that all possible hazards are found and none are missed. This may be facilitated by the use of more than one method and/or technique. The main output from the hazard identification stage is a numbered listing of hazardous events recorded as in Figure 2, which could result from the equipment involved and is used as an input to the risk estimation stage. Hazard identification can also produce subsidiary outputs, for example, a list of possible protective measures against the hazards which have been identified. Such lists can then be used in the risk evaluation and risk reduction steps. In the assessment of the combustion properties and the likelihood of occurrence of a hazardous explosive atmosphere logic diagrams are useful tools and several have been included in the proposed standard, for example, for flammability limits or relevant data characterising the behaviour of the explosive atmosphere, and for the exclusion of ignition sources. The ignition capability of the ignition sources should be compared with the ignition properties of the flammable substances. The likelihood of occurrence of the effective ignition sources is assessed following EN 1127-1 and 2 taking into account those that can be introduced e.g. by maintenance and cleaning activities.

Risk Estimation

In principle, Risk Estimation shall be carried out for each explosion hazard or every hazard event by determining the elements of risk after Hazard Identification. The risk associated with a complete machine or process is derived from a combination of these individual risks. Risk in terms of explosion safety is fundamentally made up of two elements: the severity of the possible harm and the probability of occurrence of that harm.

The seventy or consequence of an explosion can often be adequately characterised however the probability of its occurrence is usually more difficult to quantify. Risk is usually expressed in one of 3 ways: • Qualitatively for example as high, medium, low tolerable, intolerable, acceptable; • Quantitatively by calculating the frequency or probability of some determined event occurring; • Semi-quantitatively where elements of risk such as consequence, exposure and likelihood are given a numerical score which are then combined in some way to give a pseudo-quantitative value of risk which allows risks to be ranked one against another. In many situations it is not possible to exactly determine all the factors that effect risk, in particular those which contribute to the likelihood of a specified event occurring. Thus risk is often expressed in a qualitative rather than a quantitative way. Severity can be expressed as defined levels, one or more of which can result from each hazardous event. Thus in terms of injuries, damage to health or system damage severity can be expressed as shown in Table 2. In order to estimate the frequency of each severity level a screening technique can first be applied to determine the probability of each hazardous event in terms of both the occurrence of an ignition source and the explosive atmosphere. The frequency of occurrence can be qualitatively expressed as shown in Table 3:

Table 2 : Definition of severity levels

In order to estimate the frequency of each severity level a screening technique can first be applied to determine the probability of each hazardous event in terms of both the occurrence of an ignition source and the explosive atmosphere. The frequency of occurrence can be qualitatively expressed as shown in Table 3. The risk levels represent a ranking of the risk which enables an evaluation of what further actions are needed if any. Four risk levels are used ranging from 'A' representing a high risk level to 'D' a low risk level. The matrix linking frequency and severity is shown in Table 4. Following the estimation of the risk, Risk Evaluation is carried out to determine if Risk Reduction is required or whether the required degree of safety has been achieved. It is evident that if the risk estimation results in a risk level of A, the risk is so high as to be intolerable and additional risk reduction measures are required. Similarly a risk level of D can be considered to be acceptable and no further risk reduction is required. Thus the risk can be described either as 'Intolerable' -if the risk falls into the first ranking then appropriate safety measures must be taken to reduce the risk, or as 'Acceptable' -if the risk falls into the second category then no Risk Reduction is required and the Risk Assessment is complete. Risk levels B and C are intermediate levels and will normally require some form of risk reduction measures to make the risk acceptable. However, the degree of these measures will be smaller and in the case of a risk level C, organisational risk reduction measures will often be sufficient. Alternatively the process of Risk Evaluation can be carried out by comparing the explosion risks associated with equipment and unit operations with those of similar equipment. In this case it is essential that the following are comparable:

Frequency of Occurrence

Frequent

• hazards and elements of risk • type of equipment, its technology and operational limits • intended use and the conditions of use The application of the comparison method does not preclude the need for conducting a Risk Assessment for the specific conditions of use.

Risk Reduction Option Analysis

Risk can seldom in practice be reduced to zero except by eliminating the activities, however, risks can often be further reduced. Options which address the hazardous events that make the greatest contributions to the total risk have the greatest potential to reduce risk. Effectiveness in reducing risk always starts with changes to the design concept, i.e. an inherently safe design. Once the risk has been estimated and evaluated the risk reduction option analysis leads to the final decision as to whether or not the solution found reduces the risk to an acceptable level. This decision includes both the technological and economical point of view based on an appropriate classification of equipment category. If not, the iterative process has to repeated after amending the safety concept. It is necessary to deal with residual risks after all measures have been taken to reduce the probability and consequence of a specific hazardous event. The residual risks are those against which risk reduction by design and safeguarding techniques are not, or not totally, effective.

The user of the equipment must be informed about residual risks. Instructions and warnings, for example, prescribe the operating modes and procedures to overcome the relevant hazards.

In many cases, it is unlikely that any one risk reduction option will be a complete solution for a particular problem. Often, a combination of options are needed to get positive effects on safety.

Methods and/or techniques that could favourably be applied

The proposed standard also includes a section describing the different methods that are available for risk assessment and their applicability to different situations. There is no golden rule as to which method and / or technique ought to be adopted. Figure 3 gives some typical consideration in selecting type of analysis and depth of the study.

By using more than one technique the possibility of overlooking any relevant hazards is minimised. However, the additional time employed in using more than one technique needs to be balanced against the increased confidence in the results.

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APPLICATION OF THE METHODOLOGY FOR VARIOUS TYPES OF EQUIPMENT AND PROTECTIVE SYSTEMS

Six examples were extensively developed :

• exhaust system of gas engine <» paint spray booth • oil seed extraction unit • protective system : an explosion venting door. <» pneumatic powder transfer system ' » spray dryer for milk.

During these trials many manufacturers found that the document contains a great deal of useful information but from a practical point of view it was difficult to navigate. It was not easy to read, too extensive, doesn't spell out in word of one syllable what manufacturers have to do, what is link between methodology and directives etc. In applying the methodology it was found that the sections on risk estimation and evaluation were not consistent and required further development.

However following the application of the methodology with the help of the project partners, it was found that the use of the proposed pro formas helped to clearly summarise the results. Similarly, the methodology provided a good framework to pull together existing safety studies forcing the consideration of the intended use / limitations of the machines.

It was clear from the trials that had been carried out that most manufacturers found the methodology difficult to use. This in part reflects the complexity of the subject but also because the manufacturers have little idea what is involved in carrying out a risk assessment and what they have to do to meet the requirements of the Directives. When guided through the process by project participants, it was clear that the methodology produced a satisfactory risk assessment with the advantage of the results being transparent.

COMPARISON OF RESULTS AND IMPROVEMENT OF METHODOLOGY

The above mentioned trials have shown that the basic framework of the developed methodology is suitable and that when the suggested proformas are used for recording the results, the risk assessment which has been carried out can be clearly followed. However it is clear from the trials that manufacturers have extreme difficulty in applying the methodology. This is partly to be expected as the subject of risk assessment is extremely complex and it is unlikely that someone without experience in the field can simply take the proposed draft and directly apply it to their problem. In order to improve the 'useability' of the methodology the project team has decided to develop and include a 'User-Guide' which will contain detailed examples of the use of the methodology for assessing the risk associated with different types of equipment, unit operations and protective systems. Once this is completed, the revised draft will be considered as the input for CEN TC305.

WORK PROGRESS ON RISK ASSESSMENT METHODOLOGY IN CEN TC 305, WG4

Since mid 2000, four meetings were held with the active participations of representatives of the following countries : France, Germany, Sweden, United Kingdom, after a call for experts in the 15 EU countries.

A rearrangement of the the existing RASE project was proposed by experts and is under discussion.

The existing document should be adapted to be aligned with ISO/IEC guide N 51 " Safety aspects. Guidelines for their inclusion in standards.

The standard will follow the iterative process of risk assessment as given in EN 1050 « Risk assessment » used for the requirements of machinery directive (and used in the RASE project).

Further to discussions on the various parts of the RASE project, a revision of the work item dealing with risks assessment will be submitted for acceptance at the next CEN TC 305 plenary meeting in November 2002.

CONCLUSIONS

The RASE project is finished since May 2000 and has successfully achieved its objectives. A methodology for the risk assessment of equipment and unit operations intended for use in potentially explosive atmospheres has been developed. It is based on the results of a review of existing methodologies for risk assessment together with the responses from a questionnaire of manufacturers and users on their current experiences and a review of gas and dust explosion incidents that have occurred. The draft methodology has been tested with six manufacturers and the results from these trials have been used to produce a methodology which is flexible enough to be simply applied to the equipment considered but comprehensive enough to cover all aspects required by the Directives.

As the project is being carried out in close co-operation with CEN/TC305 and CENELEC/TC31, the end methodology is now an input for the work under progress by CEN/TC305/WG4 which will enable manufacturers to simply and quickly assess the risks associated with the intended use of their products, thus contributing to the improvement of Health, Safety and Environment in Europe.

Figure 1 :

 1 Figure 1 : Functional Analysis of Unit Operations

Figure 2 :

 2 Figure 2: Example of Hazard Identification Record Form

  LOSS. SEVERE INJURY, SEVERE OCCUPATIONAL ILLNESS, OR MAJOR SYSTEM DAMAGE. MINOR INJURY, MINOR OCCUPATIONAL ILLNESS, OR MINOR SYSTEM DAMAGE. LESS THAN MINOR INJURY, OCCUPATIONAL ILLNESS OR SYSTEM DAMAGE.

Figure 3 :

 3 Figure 3 :Typical considerations in selecting type of analysis and depth of the study

Due to slow bucket speed

	Re	Explosive	Frequency	Location	Potential	Occurrence	Probability	Effectiveness
	f	atmosphere	of	of	of	of	of	of ignition
			Release	Explosive	Ignition	Ignition	Ignition	sources
				atmosphere	source	sources	sources
	1	Mixture with	for a short	outside	stirrer	during	likely to	High;
		air of	period only	filling part	motor	malfunction	occur during	as surface
		flammable			surface	(overload)	malfunction	temperature
		gas						> ignition
								temperature
	2	Cloud of	Present	inside	Friction	buckets	likely to	Low;
		combustible	frequently	elevator	sparks in	rubbing on	occur
		dust	in normal	housing	bucket	housing	occasionally
			operation		elevator		in normal
							operation

Table 3 :

 3 Qualitative Description of Frequency

Table 4 :

 4 Frequency-Severity Matrix relating to risk levels

	1.2.6 Risk Evaluation

Acknowledgements

Part of the work described RASE project) in this paper was partly funded by the European Commission under contract number SMT4-CT97-2169. The author acknowledges the contributionsby the coordinator of the RASE project and by colleagues from the other project participants namely, FSA Germany, HSE England, NIRO Denmark and CMR Norway without whom this project would not have been possible. INERIS and the previous organisations funded also this project. Another part of the work is under progress in CEN, TC 305WG4/subgroup 3 and the author acknowledges the contributions by the members of this group.

Contents of the proposed standard

The proposed methodology has been written in the format of a standard and its contents are shown in Table 1. The Introduction outlines the requirements of both the Machinery and ATEX 100a Directives in terms of producing a safe machine and describes the applicability of each Directive. Thus in order to comply with the Essential Health and Safety Requirements of the Machinery Directive, it is necessary to comply with the ATEX Directive. If there is an explosion risk which is outside of the scope of the ATEX Directive then the original Machinery Directive will apply. Following a brief description of explosion risk and the influencing factors in section 4, the main body of the proposed standard is contained in section 5 which describes the proposed risk assessment methodology. What is the chain of events which could lead to harm? «> Can we tolerate the potential consequences at the estimated likelihood? <» What are the benefits and costs of alternative technologies?

For the purpose of the proposed standard, risk assessment comprises in principle four steps following the determination of intended use and the methodology proposed follows this sequential approach: • Determination of intended use (Functional / State-Analysis) <» Identification of hazards, hazardous situations and hazardous events <• Risk estimation (consequences / likelihood) • Risk evaluation <» Risk reduction option analysis.

The first three steps of risk assessment (determination, identification, estimation) are often referred to collectively as risk analysis. Risk assessment is an iterative process. If, after risk has been evaluated, the decision is made that the risk needs to be reduced it is necessary to re-estimate the risk. A decision can then be made as to whether the measures taken have reduced the risk to an acceptable level. It is also essential to check that the measures used to reduce risk have not themselves introduced any new hazards. Therefore a feedback loop from Risk Reduction Option Analysis to Hazard Identification has to be made.

Determination of intended use (Functional / State-Analysis)

As mentioned above, the trials of the methodology with manufacturers showed that this aspect was often poorly defined particularly in terms of nature of the explosive atmosphere that may be present. A functional state analysis procedure has therefore been developed by the project team and included in the proposed standard. In this respect it is an advantage to establish an Equipment / Process Flow Diagram in the light of a Functional / State-Analysis with the inclusion of energy levels (i.e. temperatures, pressures etc.) for each phase of the equipment's operation. Such a diagram helps the assessor to consider and/or to define the status of the materials being handled and the status of equipment itself, see Figure 1.

In addition, such a flow diagram not only helps to define the intended use but also can be used as the key part of the iterative risk assessment process. It refers the ATEX product characteristics to energies involved and/or the operating state as well as the physical state of the substance. Thus the analyst is able to determine what, why and how things can happen, especially when dealing with complete machines or more complex products. The diagram is based on the fact, that any ATEX product has limits to its functionality and to its use, especially the intended use, its lifetime and space it occupies (configuration). These limits form part of constituent elements or parameters which need to be taken into account in any phase of the Functional/State-Analysis. These constituent elements could serve as a screen to register, for example


G Marlair
email: guy.niarlair@ineris.fr

A Tewarson

EFFECTS OF THE GENERIC NATURE OF POLYMERS ON THEIR FIRE BEHAVIOR

Keywords: flammability, fire properties, ignition, combustion, and fire propagation behaviors of generic polymers, release of heat, CO 2, CO and smoke, fire propagation apparatus

Fire behavior of four aliphatic and two aromatic C, H, O, N, S, and Cl atom containing polymers has been examined. Experiments were performed in three ASTM E 2058 Fire Propagation Apparatuses. The differences in the ignition behavior of polymers were found to be mainly due to differences in the ignition temperature. Chemical effects appear to contribute about 25 % towards the ignition resistance of the polymers. For thermoplastics, formation of polymer melt and its burning as a pool fire was found to increase the fire intensity by factors of two to four. The combustion efficiency and generation efficiency of CO 2 were found to decrease and the generation efficiencies of CO and smoke were found to increase by changes in the generic nature of the polymers (aliphatic to aromatic to halogenated). About four times as much carbon atoms in the polymers converted to smoke than converted to CO. Large-scale fire propagation behavior of polymers was characterized by a Fire Propagation Index (FPI). The FPI values of melting type thermoplastics (showing rapid-fire propagation behavior) were high, whereas they were low for the engineered charring type and halogenated polymers (showing either slow or decelerating fire propagation behavior).

INTRODUCTION

Polymers are macromolecular organic materials manufactured by the modification of natural products or by synthesis from suitable intermediates. The number of basic polymers is large, the list is growing, and variations and modifications to these basic polymers, and co-polymers are quite large. Almost all the polymers consist of hydrogen (H), oxygen (O), nitrogen (N), sulfur (S), chlorine (Cl), fluorine (F), and silicone (Si) atoms bonded alone or in combination with other atoms to the polymer backbone of carbon (C) atoms with different types of chemical bonding. Polymers can be predominantly crystalline, amorphous or a combination of both the natures. In predominantly crystalline polymers, chains are packed together more efficiently and tightly than in the amorphous polymers [START_REF]Physical Properties of Polymers Handbook[END_REF]. Polymers with higher crystallinity have higher thermal stability than amorphous polymers. All these differences are reflected in wide variations in the fire behavior of polymers.

In our study, we have attempted to examine the differences in the fire behavior of polymers because of variations in their generic nature and physical and chemical properties. Four aliphatic and two aromatic polymers with H, O, N, S, and Cl atoms bonded to the polymer backbone of C atoms were examined. Independent experiments were performed in the three ASTM E 2058 Fire Propagation Apparatuses [START_REF] Astm E | Standard Test Methods for Measurement of Synthetic Polymer Flammability Using a Fire Propagation Apparatus (FPA)[END_REF], one at INERIS and two at the Factory Mutual Research (FMR).

EXPERIMENTAL POLYMERS USED IN THE STUDY

The following polymers were examined as sheets from original resins, without any additives, except those used for processing: 1. Polyoxymethylene, POM (aliphatic: C, H, O atoms, M mono : 29 g/mole, melting type ); 2. Poly(methylmethacrylate), PMMA (aliphatic: C, H, O atoms; M mono : 100 g/mole, melting type); 3. Nylon 6,6 (aliphatic: C, H, O, N atoms; M mono : 226 g/mole, melting type); 4. Poly(vinylchloride), PVC, rigid (aliphatic: C, H, Cl atoms; M m0I10 : 62 g/mole, charring type), 5. Polycarbonate, PC (aromatic: C, H, O atoms; M mmo : 238 g/mole, charring type); 6. Polysulfone, PSF (aromatic: C, H, O, S atoms; M mono : 442 g/mole, charring type).

The measured elemental composition and net heat of complete combustion are listed in Table 1. The data indicate that the resins are relatively pure with negligible amounts of impurities or additives. Additional information on the polymer samples, data analysis and experimental facilities are described in Ref [START_REF] Marlair | Evaluation of the performance of three ASTM E 2058 and NFPA 287 Fire Propagation Apparatuses[END_REF]. For the analysis of experimental results, these data along with the literature data listed in Table 2 were used.

APPARATUS, EXPERIMENTS, AND MEASUREMENTS

V! f

i h -* i i
Figure 1. The INERIS Fire Propagation Apparatus [START_REF] Astm E | Standard Test Methods for Measurement of Synthetic Polymer Flammability Using a Fire Propagation Apparatus (FPA)[END_REF] One of the three ASTM E 2058 Fire Propagation Apparatuses used in this study is shown in Fig. 1. Three types of experiments were performed: 1) ignition, 2) combustion, and 3) fire propagation. For ignition and combustion experiments, 100-mm square and 10-mm thick horizontal sheets were used. The sample surface was painted black. For fire propagation experiments, 300-mm long, 100mm wide and 10-mm thick vertical sheets were used. The sides and back of all the samples were tightly covered with ceramic paper and aluminum foil as described in the ASTM E 2058 standard. Cross wires across the surfaces were used for all the samples, because some of the samples expanded when exposed to external heat flux due to charring. Ignition experiments were performed under quiescent normal airflow condition with a small pilot flame close to the surface. The entire sample surface was exposed to external heat flux in the range of 10 to 60 kW/m 2 . Combustion experiments were performed under co-normal airflow rate of 158-mm/s (volumetric flow rate of 2.9 x 10"^ nr/s) with entire surface exposed to 50 kW/m 2 of external heat flux. The fire propagation experiments were performed in 40 % oxygen concentration in the co-air-oxygen mixture flowing at a rate of 158-mm/s (volumetric flow rate of 2.9 x 10 nrVs). Only the 120-mm bottom part of the sample was exposed to 50 kW/m 2 of external heat flux in the presence of a pilot flame in the fire propagation experiments.

In the ignition experiments, ignition-time was measured as a function of the external heat flux. In the combustion and fire propagation experiments, measurements were made for the release rates of polymers vapors, heat, and products.

IGNITION

In the experiments, ignition-time, defined as the appearance of a sustained flame, was measured visually by a stopwatch. The measured ignition-time at each flux from the three laboratories varied between 3 to 15 % of the average value for the non-charring and non-expanding POM, PMMA, and nylon and between 4 to 31% of the average value for the charring and expanding PC, PSF, and PVC. The variations were higher at lower heat fluxes than for heat fluxes > 30 kW/m 2 , where the variations were only between 3 to 10% of the average value for all the polymers, a range used to obtain the ignition properties of the polymers.

The ignition-time and external heat flux relationship shown in Fig. 2 for POM is very similar for all the polymers and has been analyzed using the following well known relationship for thermally thick conditions [START_REF] Delichatsios | The use of time to ignition data for characterization the thermal inertia and minimum energy for ignition or pyrolysis[END_REF][START_REF] Quintiere | Surface Flame Spread[END_REF]: The term (T ig -T a J^/kpc is defined as the Thermal Response Parameter (TRP) of the polymer [START_REF] Tewarson | Generation of Heat and Chemical Compounds in Fires[END_REF]. q cr is the minimum heat flux at or below there is no sustained ignition, which is about 10 kW/m 2 in Fig. 2. The TRP value is derived from the inverse of the slope in the range of që > 30 kW/m 2 . qj! r and TRP values derived in this fashion are listed in Table 3.

The TRP values from the three laboratories vary between 6 to 11% of the average value. There is no variation in the q c r values. The values are lower for the aliphatic polymers compared to the aromatic and aliphatic halogenated polymers. 3 and for many polymers listed in the literature [START_REF]Physical Properties of Polymers Handbook[END_REF][START_REF] Domininghaus | Plastics for Engineers-Materials, Properties, Applications[END_REF][START_REF] Abu-Isa | Thermal Properties of Automotive Polymers I. Thermal Gravimetric Analysis and Differential Scanning Calorimetry of Selected Parts from a Dodge Caravan[END_REF][START_REF] Abu-Isa | Thermal Properties of Automotive Polymers II. Thermal Conductivity of Parts Selected from a Dodge Caravan[END_REF][START_REF]Handbook of Plastics and Elastomers[END_REF] show that the ykpc component of TRP is approximately constant with an average value of 0.72 ± 19 %. The differences in the TRP values in Table 3 thus are mainly due to the differences in the T ig values. This is supported by the estimated1 ykpc values also listed in Table 3, which are very similar to the calculated -y/kpc values. The T jg values of polymers depend on the chemical bond dissociation energies and generic nature of the polymer vapor in addition to thermal effects [START_REF] Tewarson | Flammability of Polymers[END_REF][START_REF] Tewarson | Characterization of the Ignition Behavior of Polymers Commonly used in the Automotive Industry[END_REF]. For ordinary polymers, T ig « vaporization (T v ) or decomposition temperature (T d ), which supports the influence of the bond dissociation energy on the ignition behavior [START_REF] Tewarson | Flammability of Polymers[END_REF][START_REF] Tewarson | Characterization of the Ignition Behavior of Polymers Commonly used in the Automotive Industry[END_REF]. For high temperature and highly halogenated advanced engineered polymers, T ig » T v /T d suggesting the influence of both bond dissociation energy as well as of the generic nature of the polymer vapors [START_REF] Tewarson | Flammability of Polymers[END_REF][START_REF] Tewarson | Characterization of the Ignition Behavior of Polymers Commonly used in the Automotive Industry[END_REF]. It is estimated that chemical factors contribute to some 25 % in the TRP value [START_REF] Tewarson | Flammability of Polymers[END_REF].

Data in Table

It is, therefore, necessary to account for factors such as energies associated with chemical bonds and chemical nature of the vapors in addition to thermal effects to describe the ignition behavior of polymers.

COMBUSTION

In the experiments, release rates of polymer vapors, heat, and fire products were determined2 . In the experiments at 50 kW/m 2 , the 10-mm thick melting type polymers (POM, PMMA, and nylon) burned as liquid pool fires, whereas the 10-mm thick charring type polymers (PVC, PC, and PSF) burned as solid polymers. Thus, the data for POM, PMMA, and nylon are for the combustion of polymer melts whereas the data for PVC, PC, and PSF are for the combustion of solid polymers. The polymer vapors, heat and product release rate profiles and steady state (maximum) values from the three laboratories were in excellent agreement, such as shown by the data in Fig. 3 for the heat release profiles for POM and by the steady state data in Table 4 3 ' 4 . 2 For the determination of the heat release rate from the Oxygen Consumption (OC) and Carbon Dioxide Generation (CDG) Calorimetries, net heat of complete combustion per unit mass of oxygen consumed and CO and CO 2 generated were obtained from the data in Table 1.

Combustion efficiency (%) is defined as the ratio of the chemical (actual) heat of combustion to the net heat of complete combustion [START_REF] Tewarson | Generation of Heat and Chemical Compounds in Fires[END_REF]. 4 Generation efficiency (fj ) of a product is defined as the ratio of the yield of the product to its maximum possible stoichiometric yield based on its elemental composition [START_REF] Tewarson | Generation of Heat and Chemical Compounds in Fires[END_REF]. For example for the calculation of the maximum possible stoichiometric yield of CO, it is assumed that in the combustion all the carbon atoms in the polymer are completely converted to only CO.

Release Rates of Polymer Vapors, Heat, and Products

For the combustion experiments at q e = 50 kW/m 2 , the release rates of polymer vapors, heat, and products can be expressed as:

M=(qe+qf~qr r )/AH (2)
Q* =(AH ch /AH g Kq> qï -q; r ) = X (AH T /AH g )(q; +^ -q" rr )

: q;) = f J (T J /AH,)(q" e + q" f -q rr ) ( The measured range of m" values in Table 4 for the three charring type polymers (PVC, PC, and PSF) is similar to the predicted range. The measured range for m values for melting type polymers (POM, PMMA, and nylon), however, is significantly higher than the predicted range for the solid polymers, but similar to that for the generic similar liquids. For example, the predicted m" values are 50, 55, 93 x 10" 3 kg/m 2 -s for methanol, hexadecane, and butanol respectively at 50 kW/m 2 [START_REF] Tewarson | Flammability Properties of Engine Compartment Fluids Part I. Combustion Properties of Fluids Containing Carbon, Hydrogen, and Oxygen[END_REF].

The measured range of m " values for the melting type polymers (POM, PMMA, and nylon) are similar to the predicted m range at 50 kW/m 2 for genetically similar liquids. These observations suggest that formation, flow, and burning of polymer melt as liquid pool fires are critical stages in fires in thermoplastics (thickness <10mm for q e > 50 kW/m 2 ). The importance of these behaviors was also found critical in large-scale fires of 3 to 5mrn thick polymer parts of a minivan [START_REF] Ohlemiller | Burning Behavior of Selected Automotive Parts from a Minivan[END_REF].

Combustion Efficiency and Generation Efficiency of Products

Data in Table 4 and Figs. 4 and5 indicate that % » f C cn, that these two parameters are inversely proportional to f C o and f sm and that there is a linear relationship between fCo and f sm . The data also show that % and fCo2 decrease and fCo and f sm increase as the generic nature of the polymers changes from aliphatic to aromatic to halogenated. About four times as much carbon atoms are converted to smoke compared to the conversion to CO. Molecular weight of 0 100 200 300 400 500 600 700 800 Time (second) of the atoms in the structure. The implications of variations in the %, fCm, fco and fsm values are reflected in the expressions for the release rates of heat and products in Eqs. 3 and4.

FIRE PROPAGATION

Vertical fire propagation experiments were performed in 40 % oxygen concentration, with bottom 30 % of length exposed to 50 kW/m in the presence of a pilot flame. The 40 % oxygen concentration simulates flame radiative heat flux transferred to the surface in large-scale fires [START_REF] Tewarson | The Influence of Oxygen Concentration on Fuel Parameters for Fire Modeling[END_REF]. The fire propagation experiments thus are simulation of large-scale upward fire propagation.

In the experiments release rates of heat and products during upward fire propagation and initial and final weight of the sample were measured. Fire propagation was very rapid for POM and PMMA, but was slowfor PVC, PC, and PSF. Fire propagation experiments could be not be performed for nylon 6,6 due to rapid melting. The heat and product release rate profiles during fire propagation, from the three laboratories, were in excellent agreement, as shown in Fig. 6 for PMMA.

For examining the upward fire propagation behavior of polymers, theoretical expression for the flame spread velocity [START_REF] Quintiere | Surface Flame Spread[END_REF][START_REF] Fernandez-Pello | Controlling Mechanisms of Flame Spread[END_REF][START_REF] Drysdale | An Introduction to Fire Dynamics[END_REF][START_REF] Delichatsios | Upward Fire Spread: Key Flammability Properties, Similarity Solutions and Flammability Indices[END_REF] was utilized. With an assumption that the forward heat transfer from the leading edge of the flame is proportional to [START_REF] Quintiere | Surface Flame Spread[END_REF][START_REF] Fernandez-Pello | Controlling Mechanisms of Flame Spread[END_REF][START_REF] Drysdale | An Introduction to Fire Dynamics[END_REF][START_REF] Delichatsios | Upward Fire Spread: Key Flammability Properties, Similarity Solutions and Flammability Indices[END_REF] suggest the following expression for the upward fire propagation velocity:

.QI 5 Ê o F M R' I I "H 2 (Q/w) n , flame spread theories
, 1/2 X (Q r /w) n /(T ig -T a )(kpc p ) 1 /2 (5) Based on the correlation between small-scale and large-scale upward fire propagation experiments, Eq 5 is modified as follows [START_REF] Tewarson | Fire Propagation Behavior of Electrical Cables[END_REF][START_REF] Tewarson | Flame Propagation for Polymeric Materials in Cylindrical Configuration and Vertical Orientation[END_REF][START_REF] Tewarson | Flammability of Clean Room Polymeric Materials for the Semiconductor Industry[END_REF]:

The Q ch values from the fire propagation experiments and the (T jg -Ta)-v/kpc values, defined as TRP, from the ignition experiments are used in Eq. 7 to calculate the FPI values. Based on the visual observations in small-scale and large-scale fire propagation experiments, the following behaviors have been observed [START_REF] Tewarson | Generation of Heat and Chemical Compounds in Fires[END_REF][START_REF] Tewarson | Flammability of Polymers[END_REF][START_REF] Tewarson | Fire Propagation Behavior of Electrical Cables[END_REF][START_REF] Tewarson | Flame Propagation for Polymeric Materials in Cylindrical Configuration and Vertical Orientation[END_REF][START_REF] Tewarson | Flammability of Clean Room Polymeric Materials for the Semiconductor Industry[END_REF]]:

• For FPI < 6: flames are close to extinction conditions and fire propagation is limited to the ignition zone (area where surface is exposed to external heat flux in the presence of a pilot flame); • For 6 < FPI< 10: fire propagation is decelerating and stops short of the sample length; • For 10 <FPI< 20: there is fire propagation beyond the ignition zone; • For FPI > 20: fire propagation beyond the ignition zone is very rapid.

PVC

Excellent correlation has been found between the FPI values from the small-scale and large-scale tests [START_REF] Tewarson | Generation of Heat and Chemical Compounds in Fires[END_REF][START_REF] Tewarson | Flammability of Polymers[END_REF][START_REF] Tewarson | Fire Propagation Behavior of Electrical Cables[END_REF][START_REF] Tewarson | Flammability of Clean Room Polymeric Materials for the Semiconductor Industry[END_REF]. The FPI concept thus has been adopted for the acceptance of polymers in the clean rooms of the semi-conductor industry by Factory Mutual Research (FMR) and Underwriters Laboratories (UL) [START_REF]Clean Room Materials Flammability Test Protocol[END_REF][START_REF] Ul | Standard Test Method for Determining the Combustibility Characteristics of Plastics Used in Semiconductor Tool Construction[END_REF], and for electrical cables and conveyor belts by FMR [START_REF]Specification Standard for Cable Fire Propagation[END_REF][START_REF]Approval Standard, Class 1 Conveyor Belting[END_REF]. Thus, we have also used the FPI concept in this study to describe the fire propagation behaviors of the selected polymers.

Since there is an excellent agreement between the three laboratories for the heat release rate profiles and TRP values, FPI values from the three laboratories also show excellent agreement as indicated in Fig. 7.

The FPI value of PMMA [START_REF] Ul | Standard Test Method for Determining the Combustibility Characteristics of Plastics Used in Semiconductor Tool Construction[END_REF] suggest rapid propagation that is confirmed by the data from the large-scale parallel tests [START_REF] Tewarson | Flammability of Polymers[END_REF][START_REF] Tewarson | Flammability of Clean Room Polymeric Materials for the Semiconductor Industry[END_REF] and many large-scale vertical wall fires [START_REF] Orloff | Upward Turbulent Fire Spread and Burning of Fuel surfaces[END_REF][START_REF] Orloff | Burning of Large-Scale Vertical Plastic Surfaces[END_REF][START_REF] Quintiere | Wall Flames and Implications for Upward Flame Spread[END_REF][START_REF] Wu | Pyrolysis Efficiency in Upward Flame Spread[END_REF]. The FPI value for POM is 13 for which fire propagation was observed to be rapid. For char forming polymers (PC and PSF) and halogenated polymer (PVC), the FPI values were in the range of 6.9 to 8.4, for which fire propagation was observed to be either slow or decelerating. Thus, all the factors that influence the variations in the ignition and combustion behaviors of polymers are also responsible for the differences in the fire propagation behavior. SUMMARY 1) Under similar experimental conditions, differences in the ignition, combustion, and fire propagation behaviors of polymers are found to be influenced by the generic nature and molecular weight of the monomer; 2) Ignition temperature appears to be the main factor affecting differences in the ignition behavior of polymers.

The -^/kpc values are weakly dependent on the generic nature of the polymers. About 25 % of the ignition resistance is due to differences in the generic nature of the polymers;

3) The combustion efficiency and generation efficiency of CO 2 decrease and the generation efficiencies of CO and smoke increase as the generic nature of polymers changes from aliphatic to aromatic to halogenated. The combustion efficiency and generation efficiencies of products are closely related. A direct linear relationship is found between the generation efficiencies of CO and smoke, whereas an inverse non-linear relationship is found between the generation efficiency of CO 2 and that of CO and smoke; 4) About four times of the carbon atoms in the polymer are converted to smoke than to CO; 5) Generation rate of vapors for polymers that burn as solids is well predicted from the heat of gasification and surface reradiation loss at high external heat flux values where flame heat flux is negligibly small. The generation rate of vapors for polymers that burn as liquid pool fires however is under-predicted, suggesting that heat of gasification values for liquids rather than that of solid polymers need to be used. 6) Large-scale fire propagation behavior of polymers is well characterized by a Fire Propagation Index (FPI).

Melting type ordinary thermoplastics have high FPI values and have been observed to have rapid-fire propagation. The FPI values for the engineered charring type and halogenated polymers are low and have been observed to have either slow or decelerating fire propagation beyond the ignition zone.

NOMENCLATURE c

Heat capacity (kJ/kg-K) fj Generation efficiency of product j (yjAPj) Gj Generation rate of product j per unit polymer surface area (kg/m

Figure 2 .

 2 Figure 2. Relationship between ignition-time and external heat flux based on Eq. 1 and ignition data for POM measured in the ASTM E 2058 apparatuses.

  In the combustion experiments, flames were completely lifted off the surface due to high release rate of polymer vapors. Under this condition, q f value can be assumed negligibly small and m values can be predicted from AH c h/AH g and q rr values.Assuming q f = 0, the predicted m values for ordinary polymers are in the range of about 20 to 30 x 10' 3 kg/m 2 -s for q^ = 50 kW/m 2 .

Figure 3 .Figure 4 .

 34 Figure 3. Heat release rate in the combustion of POM in normal air at 50 kW/m 2 in the ASTM E 2058 apparatuses.

Figure 5 .

 5 Figure 5. Relationship between the generation efficiencies of smoke and CO for the wellventilated combustion of polymers.

Figure 6 . 2 [

 62 Figure 6. Heat release rate profile for the upward fire propagation at 40 % oxygen concentration for

Figure 7 :

 7 Figure 7 : Fire Propagation Indices of Polymers

Table 1 : Measured Elemental Composition and Net Heat of Complete Combustion of Polymers Polymer

 1

			Elemental Composition (% weight)		H T
		C	H	O	N	S	Cl	MJ/kg
	Polyoxymethylene, POM	41.40	6.91	51.40	0.15	<0.04	<0.02	15.7
	Polymethylmethacrylate, PMMA	60.10	8.56	32.14	<0.1	<0.04	<0.02	24.8
	Nylon 6,6	61.86	10.25	17.82	11.98	<0.02	<0.02	29.2
	Polyvinylchloride, PVC (rigid)	38.90	4.77	4.33	<0.1	0.36	49.00	19.3
	Polycarbonate, PC	75.70	5.50	18.40	<0.1	<0.04	<0.02	29.9
	Polysulfone, PSF	72.90	4.82	14.39	<0.1	8.2	0.02	30.4

Table 2 : Thermophysical Properties of Polymers from the Literature 3

 2

	Polymers	kxlO 3 (kW/m-K)	p x 10" 3 (kg/m 3 )	c (kJ/kg-K)	AH ch /AH g (MJ/MJ)
	POM	0.28	1.42	1.46	6
	PMMA	0.18	1.19	1.47	17
	Nylon 6,6	0.23	1.14	1.70	12
	PVC (rigid)	0.25	1.38	1.41	2
	PC	0.21	1.20	1.17	7
	PSF	0.28	1.24	1.30	5
	a: data are taken from Refs. 1,4,5,6,7, 8 and 9.

Table 3 . Ignition Properties of Polymers

 3

	Polymer	Laboratory	TRP (kW-s 1/2 /m 2 )	4cr (kW/m 2 )	(kpcf 2 (kW-s 1/2 /rn 2 -K From Table 2 Estimated
		INERIS	238			0.67
	POM (aliphatic C,H,O atoms)	FMR-1 FMR-2	286 294	10	0.76	0.81 0.83
		Average	204 + 11%		Average	0.77
	PMMA (aliphatic C,H,O atoms)	INERIS FMR-1 FMR-2 Average	200 196 217 204 ± 6%	10	0.56 Average	0.56 0.55 0.61 0.58
	Nylon 6,6	INERIS	263			0.62
	(aliphatic C,H,O,N	FMR-1 FMR-2	244 278	15	0.67	0.58 0.66
	atoms)	Average	262 ± 6 %		Average	0.62
	PC (aromatic C,H,O atoms)	INERIS FMR-1 Average	323 313 318	25	0.54 Average	0.62 0.60 0.61
		INERIS	333			0.60
	PSF (aromatic C,H,O,S atoms)	FMR-1 FMR-2	357 313	30	0.67	0.64 0.56
		Average	334 ± 7%		Average	0.60
		INERIS	333			0.79
	PVC (aliphatic C,H,C1 atoms)	FMR-1 FMR-2	357 385	15	0.70	0.85 0.91
		Average	358 + 7%		Average	0.85

Table 4 . Release rates of Polymer Vapors and Heat, Heat of Combustion and Yields of Products in the Combustion of Polymers

 4 -ventilated conditions due to extremely high burning rate at 50 kW/m. CO is unusually high and heat release rate, heat of combustion, and CO 2 and smoke yields are low; b: data not recorded properly.

	Polymer POM aliphatic: C, H, O atoms	Laboratory INERIS FMR-1 FMR-2 Average	m " x io 3 (kg/m 2 -s) 52 39 43 44	Qch (MW/m 2 ) 0.75 0.59 0.66 0.67	AH ch (MJ/kg) 15.1 15.2 15.4 15.2	CO 0.002 0.001 0.001 0.001	Yield (kg/kg) co 2 1.46 1.47 1.49 1.47	Sm 0.001 0.001 0.001 0.001
	kimono ~ 2" g/mole			Combustion Efficiency Generation Efficiency 0.97	0.001		0.969	0.002
	PMMA aliphatic: C, H, O atoms M mono -100 g/mole	INERIS FMR-1 FMR-2 Average		84 80 78 81 Combustion Efficiency 1.81" 1.83 1.80 1.82 Generation Efficiency 21.6 a 23.0 23.2 22.8 0.92	(0.050) a 0.012 0.024 0.018 0.013	1.94 a 2.02 2.03 2.00 0.912	0.022 a 0.030 0.022 0.025 0.038
	Nylon 6,6 aliphatic: C,H,O,N atoms M mono 226 g/mole	INERIS FMR-1 FMR-2 Average		46 56 54 52 Combustion Efficiency 1.21 1.53 1.54 1.43 Generation Efficiency 23.8 24.0 25.0 24.3 0.83	0.026 0.017 0.029 0.024 0.015		2.04 2.06 2.14 2.08 0.825	0.037 0.058 b 0.048 0.080
	PVC aliphatic: C,H,C1 atoms M mono -62 g/mole	INERIS FMR-1 FMR-2 Average	20 21 28 23 Combustion Efficiency Generation Efficiency 0.16 0.17 0.20 0.18	7.9 8.2 7.8 8.0 0.42	0.086 0.071 0.091 0.083 0.079		0.551 0.570 0.520 0.55 0.372	0.094 0.128 0.116 0.113 0.323
	PC aromatic: C,H,O atoms M mono = 238 g/mole	INERIS FMR-1 FMR-2 Average		23 31 28 27 Combustion Efficiency 0.43 0.51 0.49 0.48 Generation Efficiency 18.9 17.1 18.3 18.1 0.60	0.046 0.032 0.049 0.042 0.024		1.73 1.57 1.67 1.66 0.594	0.117 0.146 0.086 0.116 0.142
	PSF aromatic: C,H,O,S atoms M mono = 442 g/mole	INERIS FMR-1 FMR-2 Average		20 20 22 21 Combustion Efficiency 0.44 0.45 0.39 0.43 Generation Efficiency 17.2 17.2 16.5 17.0 0.56	0.045 0.079 0.085 0.070 0.040		1.59 1.59 1.52 1.57 0.543	0.098 0.079 0.085 0.087 0.119
	a: slightly under

The ^/kpc values of polymers were estimated from the expression: ^/kpc = TRP /[{(që r ) 0-25 x364} -293], where it is assumed that heat losses are mainly due to surface reradiation, polymer surface acts as a black body and the ambient temperature is

°C.

ACKNOWLEDGEMENTS

The financial support provided for this work (as part of the evaluation of the INERIS FPA) by the French Ministry for Land Use Planning and the Environment is gratefully acknowledged by one of us (GM).


R Meininghaus
email: roman.meininghaus@ineris.fr

E Bastin

N Gonzalez-Flesca

A Cicolella

A WEIGHTED SUM PARAMETER TO SIMPLIFY DISCUSSION ON ALDEHYDE EXPOSURE

Keywords: TVOC, sensory irritation, personal exposure, passive sampler, microenvironments

In the present work, the personal exposure of a French urban population to several aldehydes is assessed. For this purpose, a weighted sum parameter is used which takes into account the differences in sensory irritation of aldehydes. The personal exposure of 17 volunteers was assessed with personal passive samplers during one week. Simultaneously, aldehyde concentrations were determined in different microenvironments. The results show that formaldehyde is the most important sensory irritant of the aldehydes included in this study, due to a particularly high sensory irritation and because it is a ubiquitous compound found at high concentrations. Personal exposure is strongly linked to indoor exposure (homes and offices). By using a weighted sum parameter, the discussion of large data sets is considerably simplified. This sum parameter could be easily extended to other strong sensory irritants, leading to a weighted TVOC value for sensory irritation.

INTRODUCTION

The indoor air can contain a large number of Volatile Organic Compounds (VOC), which are held responsible for health effects like irritation of the eyes, skin and upper respiratory tract (sensory irritation). A sum parameter based on the sum of all measured VOC concentrations (Total VOC, TVOC) is frequently used for a first evaluation of the indoor air quality (ECA-IAQ, 1997). However, TVOC values are often not comparable when obtained with different analytical techniques [START_REF] Uhde | Suitability of direct reading instruments for the measurement of VOC concentrations in emission test chambers[END_REF] and the different health effects of different compounds are neglected.

Indoor VOC with strong sensory irritation typically contain one or more functional groups (for instance diisocyanates, organic acids, or aldehydes) and many of them show a high chemical reactivity. Reactive compounds are rarely detected indoors, because of their short lifetime, and because conventional sampling and analytical techniques are not appropriate [START_REF] Wolkoff | Are We Measuring the Relevant Indoor Pollutants?[END_REF][START_REF] Wolkoff | Organic compounds in indoor air -their relevance for perceived indoor air quality?[END_REF]. Simple aldehydes, however, are relatively stable compounds, for which standard sampling and analytical techniques have been established. Aldehydes were subject of several personal exposure studies (for instance [START_REF] Ullrich | Seasonal and Diurnal Variation in Formaldehyde and Acetaldehyde Concentrations along a Highway in Eastern Finland[END_REF]) and numerous emission sources have been identified indoors (for example furniture) [START_REF] Salthammer | Organic Indoor Air Pollutants -Occurence, Measurement, Evaluation[END_REF]) and outdoors (for example photochemical reactions) (Viskari et al., 2000).

In the present work, the personal aldehyde exposure of a French urban population is evaluated. For this purpose, a weighted sum parameter is used, taking into account the differences in sensory irritation of aldehydes.

METHODS

Weighted Sum Parameter. A weighted sum parameter KRDSO is formed by taking the sum of weighted aldehyde concentrations (Equation 1):

K RD50
The compound-specific weighing factors v,- [START_REF] Tenbrinke | Development of New Volatile Organic Compound (VOC) Exposure Metrics and their Relationship to "Sick Building Syndromes[END_REF] are based on the sensory irritation of a compound, which in turn can be expressed by its RD50 value. RD50 is the concentration of a compound inducing a 50 % decrease in respiratory rate in mice [START_REF] Alarie | Irritating properties of airborne materials to the upper respiratory tract[END_REF]. It has been shown that RD50 is predictive of human responses. A slight irritation would occur at a concentration of 0.1 *RD5o, and minimal or no effect would occur at 0.01 * RD50 [START_REF] Jensen | VOCBASE 2.0[END_REF].

Weighing factors v, are formed by dividing the compound-specific RD50 value by the RD50 value for formaldehyde, the most abundant of all aldehydes studied. RD50 values and weighing factors are summarised in Table 1. Note that RD50 for acetaldehyde is particularly high compared to its homologues. RD 50 values are not available for heptanal and octanal, but since v,-values for propanal, butanal pentanal and hexanal are in the order of magnitude of 0.001, it was decided to apply the same weighing factor for heptanal and octanal [START_REF] Tenbrinke | Development of New Volatile Organic Compound (VOC) Exposure Metrics and their Relationship to "Sick Building Syndromes[END_REF]. K.RD50 includes the compounds listed in Table 1. When assuming additivity of the irritating effects [START_REF] Flemming | Sensory irritation to mixtures of formaldehyde, acrolein, and acetaldehyde in rats[END_REF] -which seems reasonable given the low concentrations typically encountered-, KRDSO can be considered as a concentration in [ug/m3] of an aldehyde mixture having the same sensory irritation as formaldehyde at the same concentration.

Experimental. Average concentrations of several aldehydes (formaldehyde, acetaldehyde, acroleine, benzaldehyde, furfural, pentanal, hexanal, heptanal and octanal; averaged over 5 days) in various urban environments and with personal samplers were obtained. Due to analytical limitations, crotonaldehyde, propanal and butanal were not quantified.

Passive sampling devices [START_REF] Cocheo | High Uptake Rate Radial Diffusive Sampler Suitable for Both Solvent and Thermal Desorption[END_REF]) equipped with dinitrophenyl hydrazine (DNPH) sampling cartridges and ozone scrubbers [START_REF] Bates | Atmospheric Volatile Organic Compound Monitoring. Ozone Induced Artefact Formation[END_REF], were used to sample the compounds listed in Table 1. Preliminary uptake rates were experimentally determined for butanal, pentanal, hexanal, heptanal, octanal, nonanal, furfural and benzaldehyde.

The measurement campaign was carried out in a medium-sized French town and consisted of two parts. The weather conditions during the first part were characterised by rain episodes. Throughout this part, 22 samplers were exposed at outdoor background sampling sites. In addition, samplers were installed at 8 sites where people spend more of their time.

During these first five days, 17 volunteers carried a personal sampler on them. Half of them were office workers and the other half worked outdoors (gardeners). All participants installed samplers indoors in their sleeping rooms (were the participants are supposed to spend most of their time at home) and in their offices.

After this first part, the campaign lasted for another five days, where 10 samplers were installed outdoors. This time, the weather was dry and rather sunny.

Analytical and further technical details are given in [START_REF] Meininghaus | Indoor and outdoor aldehyde concentrations in a medium-sized French town[END_REF].

RESULTS

AND DISCUSSION

Influence of aldehydes other than formaldehyde. Crotonaldehyde and furfural were never detected. Acroleine was present in only two samples and benzaldehyde in 12 samples, whereas the other compounds were frequently detected. Concentrations of individual compounds were already published [START_REF] Meininghaus | Indoor and outdoor aldehyde concentrations in a medium-sized French town[END_REF].

Figure 1 shows a very good linear correlation between KRDSO values obtained from all samplers and the corresponding formaldehyde concentrations. The figure clearly illustrates that formaldehyde is by far the most important compound, due to a particularly low RD50 value (high sensory irritation) and because it is a ubiquitous compound found at high concentrations. Aldehydes with high sensory irritation (in particular acroleine and crotonaldehyde) were rarely detected and only at very low concentrations (this may be due to limitations of the sampling and analytical techniques). On the other hand, other frequently detected aldehydes show relatively high RD50 values. Although KRDSO values could be simply replaced by formaldehyde concentrations, they will be used throughout this paper, in order to illustrate how a weighted sum parameter -which could be easily extended to other compounds -helps to simplify the discussion on exposure to complex mixtures.

Comparison of Microenvironments.

KRDSO values (minimum, median, average and maximum values) are presented in Table 2 for different environments and time periods and allow for comparing different environments. Statistically significant differences (Mann-Whitney rank sum test, p < 0.05) were observed between outdoor and indoor KRDSO data sets, and between outdoor and personal sampler data sets. The results confirm that highest aldehyde concentrations prevail indoors, even with weather conditions favouring aldehyde formation by photochemical reactions. Personal exposure will hence mostly be determined by indoor exposure.

Aldehyde Exposure. The time spent in a microenvironment t env multiplied by the respective value is an exposure in this microenvironment (Equation 2):

Exposure m = x K m50em (2)
The time t env was obtained from a questionnaire distributed among the participants.

An estimated total exposure may be formed by summing up individual exposures of different microenvironments. This may then be compared to the calculated total exposures based on personal sampler measurements.

Figure 2 contains exposures of individual microenvironments and calculated exposures (personal sampler) of the participants. The total aldehyde exposure is strongly related to the exposure at home and to a lesser extent to exposure in the office. Outdoor exposure is negligible, even for the participants working outdoors (1-u). Differences between estimated and calculated exposure may be due to the fact that not all the relevant microenvironments (transport, shopping mall, bar...) were included in this study. Moreover, the selected sampling sites (close to emission sources like furniture) may not be representative for the microenvironment.

CONCLUSIONS

By using a weighted sum parameter, the discussion of large data sets is considerably simplified.

With regard to personal exposure, formaldehyde is the most important sensory irritant of the aldehydes included in this study, and the exposure at home is much more important than outdoor exposure.

The weighted sum parameter contains information on the physiological effect of a mixture of compounds (aldehydes) and could be easily extended to other strong sensory irritants. This would finally result in a weighted TVOC value for sensory irritation.

Figure 1 .

 1 Figure 1. KRDSO values of all samplers over formaldehyde concentrations of all samplers

Figure 2 :

 2 Figure 2: Aldehyde exposure in different environments and personal exposure.

Table 1 .

 1

	: RD50 values and weighing factors v
	aldehyde	RD 50 / [mg/m 3 ]	weighing factor
		(Jensen and	V
		Wolkoff, 1996)
	Formaldehyde	5	1
	Acetaldehyde	6700	0.0007
	Propanal	5800	0.0008
	Butanal	3700	0.001
	Pentanal	4100	0.001
	Hexanal	4500	0.001
	Heptanal	-	0.001
	Octanal	-	0.001
	Benzaldehyde	1600	0.003
	Furfural	1000	0.005
	Crotonaldehyde	12	0.42
	Acroleine	4	1.25

Table 2 .

 2 : Minimum, median and maximum KRDSO values of different microenvironments and

	time periods
	environment		KRD5o/[ng/m J ]
		minimum	median	average	maximum
	outdoors: background sites part I	0.7	1.2	1.3	1.9
	outdoors: frequently visited sites part I	1.3	1.9	2.0	2.6
	Outdoors: part II	1.0	1.3	1.4	1.9
	Indoors: sleeping rooms	6.4	14.4	27.6	127.4
	Indoors: offices	5.8	HA	14.5	24.2
	Indoors: personal samplers	6.4	14.5	16.7	38.2

ACKNOWLEDGEMENTS

Thanks are due to J.-C. Pinard and S. Bourdet for their substantial contributions to the pilot study, and to D. Granier for the analytical work and for fruitful discussions.


L Delery

A Cicolella

HEALTH RISK ASSESSMENT OF PCE EMISSIONS FROM DRY CLEANING ACTIVITIES IN FRANCE

Keywords: PCE, dry cleaning, risk assessment, public health

Tetrachloroethylene (PCE) is a solvent used mostly in the dry-cleaning and metal degreasing industries in Europe. Neurological and renal effects are the main non-cancer human health effects caused by chronic inhalation exposure of PCE. PCE is suspected to be probably carcinogenic to humans by IARC. During dry-cleaning processes, people are likely to be exposed to the chemical in a variety of ways because PCE emissions are not currently regulated in France. Exposed persons include workers, residents living in co-location with dry-cleaning establishments and the general population. This paper presents a literature review assimilating human exposure data to assess public health risk from dry-cleaning emissions. At the average indoor air level of 2 mg/m 3 , there is concern for health risk to co-located residents living above dry cleaning establishments. A personal exposure of 15 ug/m 3 of PCE should not cause adverse effects on the health of normal population.

INTRODUCTION

The European Union directive UE/13/1999 concerning the reduction of the emissions of volatile organic compounds requires a special limit value to regulate atmospheric PCE emissions of dry cleaning activities in European countries. PCE (CAS 127-18-4) is currently the main solvent used in dry cleaning processes in Europe. To formulate national regulations necessary to comply with this directive, the French environment ministry asked INERIS to assess health risks associated with PCE exposure. A preliminary study was carried out from available data in scientific literature to analyze the need to conduct exposure surveys to refine the associated health risks at a national level.

METHOD

The methodology used is based on the human risk assessment process formalised in 1983 by the National Research Council (NRC) of the American National Academy of Sciences (NAS). It aims, within a structured and transparent framework, at providing a decision-tool for risk managers to assess the risks connected with environmental sources of exposure. For health risk assessment, the NAS describes a four-step paradigm. For each step, the relevant and scientifically reliable information is evaluated. In addition, the related uncertainties are described. a) Hazard identification -determination of whether a particular chemical is or is not causally linked to specific health effects, b) Dose-reponse assessment, the determination of the relation between the magnitude of exposure and the probability of occurrence of the health effects in question, c) Exposure assessment, the determination of the extent of human exposure before or after application of regulatory controls d) Risk characterisation, the description of the nature and magnitude of human risk including related uncertainty.

In France, the guidelines for health risk assessment have been published by the National Institute for Public Health Surveillance [START_REF] Invs | Institut de Veille Sanitaire, Guide pour l'analyse du volet sanitaire des études d'impact[END_REF] and the National Institute for Industrial Environment and Risks [START_REF] Ineris | Evaluation des Risques Sanitaires liés aux substances chimiques dans l'Etude d'Impact des Installations Classées pour la Protection de l'Environnement[END_REF] within the framework of the French regulation of industrial activities with environmental impact.

RESULTS

HAZARD IDENTIFICATION (ATSDR, 1997), (INERIS, 2000) Inhalation is the most significant route for human exposure to PCE.

In humans, PCE is known to be toxic to central nervous system and kidneys (such effects were observed in dry cleaning workers following chronic inhalation of PCE). Several cases of human acute intoxication by inhalation are reported following the use of coin-operated dry cleaning machines in France [START_REF] Gamier | Coin-operated dry cleaning machines may be responsible for acute PCE poisoning[END_REF]. Carcinogenic effects of PCE are also suggested by numerous epidemiological studies, but are not clearly established. The International Agency for Research on Cancer has classified PCE as a Group 2A carcinogen (probably carcinogenic to humans) on the basis of experimental data (kidney tumours in male rat, hepatic tumours in mice and possibly mononuclear cell leukaemia in rats) and epidemiological data (oesophageal and cervical cancers and non-Hodgkin's lymphoma) (IARC, 1995). Some studies reported the existence of spontaneous abortions among women exposed to PCE in the workplace. Human data remains however inconclusive regarding PCE potential to cause developmental and reproductive effects.

Available animal data indicate that PCE itself is not mutagenic but some PCE metabolites have been shown to be mutagenic (perchloroethylene epoxide, trichloroacetaldehyde...).

DOSE-REPONSE ASSESSMENT

The manner in which dose-reponse relationships are expressed mainly depends on the endpoint of concern for human health. A key distinction between cancer and other toxicological effects is that most carcinogens are generally assumed to have no dose threshold i.e. no exposure level below which a significant adverse effect is not expected to occur). This leads to use two different estimates to assess dose-reponse :

• Reference concentration for the chronic non-cancer effects to estimate daily exposure to human population including sensitive subgroups that is likely to be without appreciable risk of adverse effects during a lifetime, • Inhalation « unit risk » for the chronic cancer effects to estimate the chemical's carcinogenic potency through the upperbound excess lifetime risk per ug/m 3 average daily inhaled.

In this way, for non-carcinogenic effects, two reference concentrations have been derived for chronic inhalation exposure to PCE, based on the effects observed among workers exposed to PCE at their workplace :

• WHO (WHO 2000) proposes an air quality guideline value of 0,25 mg/m 3 for critical effect on kidney.

-ATSDR (ATSDR 1997) recommends a chronic Minimum Risk Level of 0,28 mg/m 3 for neurotoxic effects.

For the carcinogenic effects, epidemiological data are not sufficient to develop a doseresponse relationship. The animal data, therefore, are the only source to approach the carcinogenic risk in humans.

Hazard assessment shows that there exists an uncertainty regarding the relevance in man of PCE carcinogenic mechanism of action in animal. Indeed, the effects observed in animal seem to be species-specific and humans would probably be more sensitive than the rodents.

However, two American organizations have assessed PCE carcinogenic dose-response relationship on the basis of the results of the National Program of Toxicology (NTP) of 1986. The California EPA (CalEPA, 1999) has derived a unit risk of 5,9.10" 6 (|ag/m 3 ) 'l in 1992 from male mouse hepatocellular adenoma and carcinoma incidence data using a linearized multistage procedure and PBPK model dose adjustment.

The federal Environmental Protection Agency (US EPA, 1998) has defined a provisional unit risk value of 7,1.10" 7 (p.g/m 3 ) ~l from mice liver adenomas and/or carcinomas and rat mononuclear cell leukaemia incidence data using a linear-at-low-doses approach. Toxicity values for use in PCE risk assessment are shown in table 1. The populations potentially exposed to PCE emissions from dry cleaning activities (Figure 1) include workers and the general population, with specific sub-populations for the latter (individuals who are residing in apartment buildings co-located with PCE dry-cleaning facilities, people working near drycleaners, coin-operated dry cleaning machines users, infants nursed by mothers working in a dry cleaning plants; families of workers...).

In this paper, only general population (non-worker) exposure is presented for inhalation specific pathway which appears most relevant to PCE kind of emissions. Chronic inhalation exposure is examined in our study as to determine the probability of occurrence of long-term effects. In this way, when available, central tendency (median or average) and high-end exposure descriptors were used to show the variability of estimated exposure. Analysis of literature shows that on one hand no French exposure data were to be found and that on the other hand monitoring studies for which appropriate PCE exposure data were available mainly focused on co-located residents and general people exposure.

Exposure received by co-located residents has been monitored by several studies. Two studies were chosen for use in exposure assessment: Fast (1992), quoted by EPA (1998), measured a median concentration of 2,2 mg/m 3 (90 th percentile: 17,8 mg/m 3 ) and [START_REF] Garetano | Factors influencing PCE concentrations in residences above dry-cleaning establishments[END_REF] reported a mean concentration of 2 mg/m 3 (range 0,47-4,2) in 12 residential sites of New Jersey. The value of 2 mg/m 3 was thus retained as average concentration of exposure with the high-end estimate of 17,8 mg/m 3 . To calculate inhaled concentrations, it was assumed that exposed individuals live 20 hours/day in their apartments, 365 days/year for 30 years.

With regard to the general population exposure, data were chosen from the Total Exposure Assessment Measurement (TEAM) study [START_REF] Wallace | Comparison of risks from outdoor and indoor exposure to toxic chemicals[END_REF]. This study was carried out at four sites in the USA and reported 24 hours concentrations of PCE from about 1000 personal samples. Personal sampling over a 24 hours period allowed to reflect exposure consequent to a variety of exposure patterns. The arithmetic mean exposure was 15 ug/m 3 . In this study, this scenario exposure is assumed to occur over an individual's entire lifetime, so duration of exposure is 24 hours/day, 365 days/year for 70 years Exposure estimates used in our risk assessment are summarised in table 2. To assess cancer risk, exposure estimates must be averaged over a lifetime as to be compatible with cancer risk values.

Table 1 . Chronic toxicity values for PCE risk assessment

 1

	Organization	Toxicity	Toxicity value	Critical organ or	Species	Key study
	name	value name		effect
					Human
	WHO, 2000	Air quality Guideline 1 year	0,25 mg/m 3	Renal	occupational study (10 years, mean exposure	Mutti et al, 1992
					level 100 mg/m 3 )
	ATSDR,	Chronic	0,28 mg/m J	Nervous central	Human	Ferroni et
	1997	Minimum		system	occupational	al., 1992
		Risk Level			study (10 years,
					mean exposure
					level 100 mg/m 3 )
	US EPA,	Unit risk	7,1.10" 7	Liver adenoma and	Mouse and rat, 2	NTP,
	1998		(ug/m 3 ) -1	carcinoma	years	1986
				Mononuclear cell
				leukaemia
	EXPOSURE ASSESSMENT

Table 2 : Estimated exposure received by populations studied

 2

	Population scenario	Co-located residents	General population
	PCE average	2 mg/m 3 (17,8 mg/m j )	15 |ig/m 3
	concentration in air
	(high-end)
	Average daily	1,67 mg/m 3 (14,8 mg/m 3 )	15 ug/m 3
	concentration inhaled
	(high-end)
	Lifetime Average daily	715 u.g/m J (6,3 mg/m 3 )
	concentration inhaled
	(high-end)

RISK CHARACTERIZATION

Two expression of risk are widely used. Cancer risk estimates are expressed as the incremental probability of developing a cancer for an individual over a lifetime of exposure to the chemical. Cancer excess risk is calculated by multiplying the estimated exposure level by the reference risk value. For toxic effects other than cancer, the expected human exposure considered is compared to the reference concentration value. The comparison is expressed as a ratio called Hazard Quotient. Hazard Quotient values above 1 are considered less likely to be free of adverse effects.

The following tables present calculated risk for non-cancer (table 3) and cancer effects (table 4). 3 indicate that there is concern for non-cancer risk to co-located residents living above dry cleaning establishments. For the general population, there is not any particular concern of non-cancer risk for a lifetime inhalation exposure at the average daily level of 15 ug/m 3 measured in the TEAM study. Regarding human exposure, as no French data are currently available, foreign studies had to be used to asses PCE health risk. Available monitoring studies do not cover the entire population exposure scenario such as coin-operated dry-cleaning machine customers so this risk assessment is not comprehensive. Risk conclusions are based on a limited number of exposure estimates. It is not known how well they represent French exposures since variation in the machines type (vented or nonvented transfer or dry-to-dry), maintenance and control operations, sampling duration, season and location may influence exposure levels reported.

CONCLUSION AND IMPLICATIONS

On the basis of a first literature review, PCE health risk assessment shows that there is a health risk concern for non-cancer and cancer effects among residents living in co-location with dry-cleaning establishments. Co-located residents could be even more at risk since they experience general public ways of exposure such as wearing dry-cleaned clothes or using households products containing PCE. The general population lifetime exposure to PCE 15 ug/m 3 is safe but should remain at public health policy watching in view of the number of exposed persons. This work has led the INERIS to propose to the French Environment Ministry to carry out an exposure survey near dry-cleaning establishments located in a shopping centre and near coinoperated dry-cleaning facilities located in a residence building. These measures will make it possible to reassess the health problem in the French context.