O Bour

I Zdanevitch

RISK ASSESSMENT AND COMPARISON OF SHORT-TERM AND LONG-TERM EMISSIONS FOR DIFFERENT TREATMENT AND DISPOSAL PHASES OF MSW

a research program including a comparison between short term and long term emissions of MSW landfill started in 2006. The goal of that program was to access the human health chronic risk of three different waste disposal processes (anaerobic with/without leachate recirculation, with/without aerobic pretreatment) and to provide new criteria for the disposal site. A methodological approach using both calibration of the short term fluxes by in situ measurements and the prediction of long term fluxes by the use of exponential decreasing functions was explored. The identification of contaminant species was made by qualitative and quantitative concentration measurements done in a first stage on the landfill gas, and the collection of chemical leachate load measurements. At this stage of the study, the work did not show specific chemical contaminant species for the different waste disposal.

INTRODUCTION

French regulation on waste disposal do not prescribe specific requirements concerning mechanical biological treatments and disposal phases for non-hazardous waste. The lacks of data concerning the behaviour of these types of waste during the disposal phase do not allow the definition of specific criteria and highlight the need of new tools for the assessment of chronic risks during the disposal phase. The developments of leachate recirculation also produce new time scale for the appreciation of the waste stabilization. Risk assessment concerning the human health chronic risks coming from these new types of waste will encounter new difficulties, especially concerning the definition of the major contaminant species, the fluxes rates of these compounds and the comparison between the equivalent stabilization time steps achieved. It is necessary to take into account the natural attenuation of the diffuse emissions of biogas and leachate. A better treatment of the diffuse emission could partialy balance the goals of the treatment before the disposal.

In order to build the comparison approach of these new types of waste management, a research program started in 2006, which includes the comparison of short-term and long-term emissions for three different treatments (anaerobic disposal with/without recirculation, aerobic pretreatment followed by anaerobic disposal) with the focus on the disposal phases of MSW. This program aims to use the combination of waste description parameters, the collect of new data coming from the analysis campaign on biogas and leachate, and available modelling tools concerning the emission of biogas and leachate. As previous work done concerning the gaseous emissions of closed landfills, the goals are to determine some combination of criteria in order to minimize the human health chronic risks and made feasible some comparison between the different type of waste disposal with the usual disposal regulation requirements. This paper presents the first results of that program conducted on four disposal facilities.

DESCRIPTION OF THE METHODOLOGICAL APPROACH

General approach

The methodological approach focuses on in situ landfills measurements in order to avoid the scaling difficulties coming from the direct use of the data coming from laboratory researches. In a first phase 8 different disposal facilities were visited, in order to collect different data and to define the more appropriate landfills for the characterization phase. A selection of 3 landfills was made in order to conduct new gaseous emission characterisation campaigns of VOC and major compounds. The identification of the contaminants for the three different types of waste disposal was done in a first step on each landfill.That step requires the collect of data from the litterature as well as new data issuing from old and new cells in order to define the short term and long term emissions of contaminants.

For each landfill disposal this work includes the identification of the major fluxes and trace compounds which lead to a health chronic risk and the selection of parameters in order to characterise the organic fraction and the stabilization processes.

The second step will use the results from in situ characterisation in order to select the more appropriate available tools coming from the laboratory research results in order to predict the evolution of the fluxes and stability parameters. The objective of that step is to provide informations concerning the assessment of the decreasing fluxes of the major compounds and contaminants for the three types of treatment and disposal in the short and long term perspectives.

The last step will be the risk assessment for the three types of waste, and key time steps during the exploitation phase and the aftercare periods. A special attention will be given at this point to compare the waste stabilization for equivalent time duration.

Identification of the health chronic risk contaminants

The quality and the composition of both the biogas and leachate evolve with time, and depend on the main intrinsic waste characterization.

Leachates may be classified respectively by young, intermediate and aged ones according to the different compositions; however the distinction between the different trace contaminants present into the landfill biogas (LFG) with the time scale and the type of waste is more scarce in the literature (UK EPA ( 2004), [START_REF] Hillier | Assessment of trace components in Landfill Gas from "Typical" UK Sites[END_REF]. The more recent work conducted in France was undertaken by FNADE (2007) and present the characterisation of the LFG coming from ten different landfills. This recent work gives new data for LFG trace contaminants without attenuation by the cover. These informations can be used to determine the quality of the biogas issued by the leaky biogas wells. We usually have LFG concentration measurements concerning the VOCs only in the LFG main line, which are not representative of the emissions occurring in a new cell during exploitation and just after the completion of temporary cover. The lack of these data is partially reduced with the release of the results of the ELIA program [START_REF] Lornage | VOC's emissions during a mechanical and biological pre-treatment (MBP) of MSW prior to landfilling[END_REF] for recent waste, and the data collected previously from "old" landfills [START_REF] Bour | Determination of guidance values for closed landfill gas emissions[END_REF]. The data coming from three new old landfills and new cells of pretreated MSW will complete this set of data and will help to do some selection of the major trace compounds. Previous studies concerning the attenuation of sulphide and BTEX compounds in the landfill top cover showed that a large fraction of these compounds can be oxidised

Definition and modelling of the contaminant fluxes decrease

Surface flux emission rate campaigns were realized on three landfills without LFG collection. In order to provide qualitative and quantitative data concerning the methane, carbon dioxide and TVOC emissions, the flux box campaigns were conducted on a deposit aged selection area of these landfills. Scarce data concerning the quality of leachate were also collected and a more complete data set concerning leachate load will be collected in 2007. The first goals will be to use data coming from the LFG and leachate characterization without those coming from the solid fraction of waste which are more difficult to sample in the case of closed cells with a final cover. All these data will allow to compare the LFG major compounds fluxes and make first assumptions for the scheme of the decreasing emissions used for the risk assessment study (See figure 1).

If the decrease of the LFG methane production during the anaerobic stage is well known, the importance of the flushing provided by the leachate recirculation will need some simplifications for the uses of the previous LFG production model. For example, the recirculation of the leachate will generally increase especially the fluxes in the preferentially flows pathways and provide an accelerated degradation of only a waste fraction.

Concerning the mechanical biological pretreatment, the focus will be put on the aerobic pretreatment which is the more frequent case in France. This treatment not only allows a fast decrease of the methane potential but also allows an increase of the organic fraction which is available for the anaerobic stage. The combination of the two processes could produce more LFG emissions in the short term period of the disposal if the duration of the aerobic treatment does not provide a sufficient decrease of this organic fraction. Parameters of the leachate like BOD, TOC, NTK will be measured in order to calibrate the amount of organic fraction available for the anaerobic phase. A focus will also be made on the natural attenuation of gaseous and leachate emissions emitted by the landfill body

Risk assessment for the short term and long term emissions of the disposal phase

Contrary to the long term emissions which are usually only limited by passive attenuation, short term emissions depend on the efficiency of the active LFG and leachate collection and treatment. An early optimized LFG collection will drastically decrease the gaseous emissions. Some assumptions concerning the percentage of biogas collection must be done in order to build an equivalent generic scenario for each type of waste. The in-situ measurements done in the previous stage on each type of waste will not reflect the median emissions without a correction factor concerning the site specific exploitation phase.

Concerning the long term emissions, the regulation requirements give a framework for each scenario. Depending on French regulation, only must be considered scenarios for the final cover and the passive barriers system at the bottom of the landfill.

We also need to use data related to the evolution of heavy metals. Due to the low concentrations of heavy metals in waste, and the high variability associated with the low concentration naturally occurring, we prefer to consider the level of protection offered by the thickness and the clay content of the layers, which usually better control the migration of the heavy metals by the adsorption processes.

We need to use both qualitative and quantitative parameters in order to compare both situations.

The study will also consider parameters describing the maturing process of the organic fraction, in order to compare the evolution of non-treated waste and composted waste during the long-term landfilling.

Finally the human health risk assessment will be done in order to make comparisons between the different waste type of disposal for the short term and long term period.

PRELIMINARY RESULTS

Identification of the health chronic risk contaminants and definition of the contaminant fluxes

Experimental data gathered from the characterization of three old landfills was used to describe the behaviour of MSW in the long term for two types of waste.

The waste of the first old MSW landfill was crushed and landfilled in narrow thickness layers for the old cells aged of more than 10 years. This type of disposal could be compared with an aerobic pretreatment followed by an anaerobic stage. In situ LFG trace concentration measurements in these old cells provided a TVOC concentration of less than 2 ppmv in the LFG wells. Hydrogen sulphide concentration was less than 5 ppmv.

The waste of the second old deposit was more rapidly landfilled and the exploitation phase of each cell was approximately one year. Due to the lack of clay cap in the first decades, the level of leachate had allowed a saturation of more than 30% of waste volume. The non saturated zone of this type of waste could be compared with an anaerobic area. Some hazardeous waste was mixed with the non-hazardeous waste. The theoretical surface flux of the cells aged of more than 20 years is estimated of approximately 5 m 3 CH4/h/ha. The LFG surface flux campaign realised on a selection of area does not show methane and TVOC fluxes but the measurements in the screening part of the boreholes which pass through the cover revealed a few spots of TVOC and the presence of methane. Trace of chlorine solvents was also be found in the leachate.

LFG surface fluxes measurements was also conducted on another old MSW landfill with a waste thickness of less than 10 meters and a1m soil cap. We also did not measure significant surface LFG fluxes of methane and TVOC. Laboratory measurements of the BTEX and chlorine solvents did not show any significant concentrations of these compounds.

For two old MSW disposals, with a theoretical production of methane of less than 5-10m 3 CH4/h/ha, the LFG surface fluxes VOC emissions were not significant for an approximately 10m waste thickness disposal, aged of more than 20 years, and with a1m soil cap thickness.

A surface fluxes campaign was also conducted on the early anaerobic phase of a pretreated waste disposal with an aerobic phase of approximately 6-10 weeks followed with a maturation phase of 10-20 weeks.

Due to the recent disposal of the waste (3 weeks) and the mixing of the different fractions of the composted waste, the surface fluxes of methane and carbon dioxide remain relatively high (methane surface fluxes average of more than 100 ml CH4/min/m 2 ) and show numerous peaks of carbon dioxide surface fluxes of more than 200 ml CO2/min/m 2 . These "hot spots" of carbon dioxide fluxes give also some evidence of a residual aerobic phase in the first 50 cm of the disposal.

Laboratory measurements were realized on gas sampled in the flux box located just on the surface of the waste. The qualitative measurements gave a lot of peaks without predominant chemical species. Quantitative measurements done on BTEX and chlorine compounds do not exhibit any significant concentrations. These LFG sampling campaigns will continue in 2007 with the leachate chemical load concentration measurements. These first results do not exhibit new contaminants for the chronic risks at this stage concerning the pretreated waste, but this must be confirmed with other sites.

Modeling the decrease of the contaminant mass fluxes

The goals of the first steps are the definition of the site specific parameters and simple models which can be used in order to qualify the decrease of the global load (COD, BOD or TOC , total N) in the leachate and the decrease of LFG emissions. The specific contaminant mass fluxes will be linked to the global load of the leachate and to the LFG emissions. The LFG emissions can be assess in the short and long term by the French LFG production model (ADEME, French environment agency) based on first order kinetic equations. A calibration of the model results with the LFG collected is necessary to reduce the uncertainty of the LFG production predictions.

Although the liquid/solid ratio can be used for the long term (Allgaier G. & Stegmann R., 2003), in the short term period the leachate collected will depend a lot on the different surface area contributing to infiltration. This modeling phase must also handle the scarce data which are usually available. In order to comply with that constraint, a calibration of the leachate load with in situ measurements will be chosen. The use of a specific kinetic for the decrease of that load in the short term will need accelerated laboratory tests. Due to the large variation of the rainfall inputs, the in-situ measurements of the leachate contaminant load during one year are not expected to give sufficient informations to extrapolate an exponential decrease.

Concerning the long term evolution of the leachate load, the rainfall data will be used with an hydrologic simulation in order to give an estimation of the infiltration rate in the landfill body. This value will be used in order to extrapolate the decrease of the leachate load by flushing [START_REF] Heyer | Landfill after care -scope for action, duration, cots and quantitative criteria for the completion[END_REF].

The coupling of organic fraction decrease due to both the anaerobic degradation and the flushing will need a lot of assumptions concerning the kinetics of the different processes (hydrolysis, acetogenesis). This work could not be conducted for the three waste types, then a non coupled approach was chosen for the first steps of this work

CONCLUSION

If the general decreasing tendency of the contaminant emissions can be assessed with site specific parameters in the long term for the three type of waste, the prediction of the decrease in the short term period will need data gathering on more parameters, a complete characterization of the waste and of the succession of the operation phases. The building of a generic scenario for the human health risk assessment for the three type of waste (anaerobic disposal with/without leachate recirculation and aerobic pretreatment) will need input data in order to calibrate the load of contaminant in the gas phase and the liquid phase during the short term period. Concerning the contaminants, the qualitative and quantitative measurements done on a specific site with a pretreatment, and three others sites, do no show new chemical compounds. The range of the chemical species seems to be narrow but these first measurements should be confirmed with new measurements performed on another site. The source separation and the sorting provide a large range of the quality of waste.

As previously mentioned (Heyer K-U, Hupe K. & Stegmann R., 2005), in the case of old shallow disposal, the relative high waste humidity level provided by a medium rainfall volume of 600 -1000 mm per year allows a quick degradation of the waste (with a relatively uniform circulation of the infiltration). With deeper disposal, some parts of the disposal exhibit a slower rate of degradation.

LFG emissions through the cover of one meter of soil on old landfill will decline rather quickly. We generally cannot measure significant LFG fluxes on old shallow waste deposits. The quality of the leachate evolves slower in the landfill body with a clay cap. An attenuation of the leachate load is compatible with the French regulation requirements for the second layer of the passive barriers (5 m thickness with a permeability lower than 1 10 -6 m/s). A back analysis of the migration of the leachate load, taking into account the clay content and the CEC of that layer, should be done to improve the prediction of the model. An emphasis must also be done in the near future on attenuation processes in the nearest barriers layers, in order to compare the waste disposals.

Figure 1 .

 1 Figure 1. Scheme used for the calibration and the decreasing of the emissions for the risk assessment of the three different waste type

ACKNOWLEDGEMENTS

The work presented here in this paper is supported by the French Ministry of Environment and sustainable development and ADEME.

Views expressed in this paper are those of the authors and do not necessarily represent those of any organisation.


I Zdanevitch

O Bour

A Budka

Y Ogor°

D Pailler °°

CHARACTERIZATION OF TOXIC GASEOUS EMISSIONS FROM INDUSTRIAL SOLID WASTE LANDFILLS

In France, Hazardous Industrial Waste, once stabilized, are buried in specific landfills. As for all polluting activities, these facilities must report to the EPER Register their toxic gaseous emissions, expressed in mass per year, as soon as they exceed threshold limit values. Campaigns were conducted on two different hazardous waste landfills in order to establish if these facilities needed to report to EPER Register. Global fluxes of gaseous components were measured by means of an FID (hydrocarbons) and a PID (halocarbons, aromatics and some non-organic compounds). Specific concentrations of aromatic (BTEX) and chlorinated hydrocarbons were also measured. Gaseous emissions were generally very low. Emissions were only detected for young and medium-aged layers, between 1 day and 3 months old. Due to these low emissions, and to the small surfaces involved, the two landfills do not fall under the EPER emission Register.

INTRODUCTION

In France, Hazardous Industrial Waste, once stabilized, are buried in specific landfills. As for all polluting activities, these facilities must report to the EPER Register their toxic gaseous emissions, expressed in mass per year, as soon as they exceed threshold limit values. A lot of compounds can be emitted by industrial waste. Depending on the type and age of waste, type and concentration of gaseous emissions can be very different, which would take a lot of time and money to characterize. Therefore, the study was limited to a few gases, which are good tracers for risks assessment : VOC, and among them, BTEX and chlorinated compounds. The aim of this study was to establish the fugitive VOC emission of two industrial waste landfills, representative of the French sites. The sites measurements were of two kinds :

• total gaseous emissions measured with a static flux chamber, on different parts of the landfills, in order to evaluate the participation of parts of different ages to the global emissions, • b) VOC sampling and identification in order to calculate toxic gases fluxes to be reported to EPER (benzene, toluene, xylenes, halogenated compounds).

EXPERIMENTAL STUDY

Materials and methods

Fluxes measurements

Fluxes of total hydrocarbons + aromatic and chlorinated compounds were measured through a static flux chamber (Savanne et al, 1997) equipped with flame ionisation and photo-ionisation detectors. Measurements were performed every 5 to 20 meters, depending on the surface area to be explored. A minimum of 10 points were analysed on the smallest zones. The flux chamber (INERIS patented) covers a surface of 0.25 m 2 . The minimum flux detected by this method is 0.01 ml/m 2 /min, and the precision of the method is 0.05 ml/m 2 /min. This chamber is generally used for exploring surface methane emissions on MSW landfills.

The flame ionisation detector used with this chamber is non-selective and responds to all hydrocarbons. On MSW landfills, surface emissions consist mainly in methane, which is not the case here. In order to improve the selectivity of the method, a photo-ionisation detector, which responds to lesser gases, was added to determine mainly aromatic hydrocarbons, halocarbons, hydrocarbons with double or triple bonds, and some inorganic gases like ammonia.

The flame ionisation detector is calibrated with methane, compound which gives the smaller response to the FID. The major organic compounds identified on the two sites, analysed by gas chromatography/mass spectrometry, are hydrocarbons with 5 to 8 atoms of carbons. FID measurements were corrected to give fluxes in equivalent-pentane, compound which gives the higher -and therefore the worst -values for the total flux.

The photo-ionisation detector is calibrated with iso-butylene. Other compounds give response which can be either bigger or smaller than iso-butylene, therefore no correction was made.

VOC identification and measurement

To quantify toxic gases, soil gases were sampled on each zone which was studied, except the ones with no surface fluxes. Sampling was done in evacuated canisters (US EPA TO14A, TO15) in order to quantify benzene, toluene, xylenes, vinyl chloride, tri-and tetrachlorethene by gas chromatography/flame ionisation detector. Sampling was performed on the flux chamber, at the end of a flux measurement, and monitored by either the FID or PID (Figure 1).

In addition, on each site, two samples of surface gases were taken on different zones. These samples on adsorption tubes were analysed by thermal desorption/gas chromatography/mass spectrometry, in order to identify the major VOC.

Sites description

Depending on the site, hazardous waste which are landfilled are mainly constituted of:

• dispersed waste which is stabilized with cement-type material, such as MSW incinerator fly ashes, • stable waste like mineral oxides, • dispersed waste, such as asbestos, contained in large bags. Large bags are only deposited on site 1. On site 2, only stable or stabilized waste are deposited.

Landfills are organised in partial compact layers, approximately 1.5 meters high, 2-10 m large, up to 50 m long, which represent one day of disposal. These daily disposals are made one beside the other, for up to one month. Then, another layer is started over the top of this arrangement. Large bags layers are sometimes covered by a thin layer of soil which was previously bioremediated on-site. The surface covered by each layer is not large, but the total height of the disposal can be high, up to 20 meters and more above the ground. Once completed, the section is covered with a geomembrane and a 1 meter-thick layer of clay.

Partial layers of wastes of different ages were investigated separately: from 1-2 days, up to 2-3 years old.

RESULTS AND DISCUSSION

Recent layers (2-8 days)

Due to the deposition process (engine movements) and the unsteadiness of new layers, it was not possible to make fluxes measurements over layers less than 2 days old. Nevertheless, fluxes of hydrocarbons measured by the FID over this type of layers were very low (Table 1).

Fluxes measured by the PID are smaller than those with the FID on site 1, which means that gaseous fluxes are constituted of hydrocarbons. It is not the case on site 2 : response are higher on the PID than on the FID. The number of organic compounds which respond to the PID being smaller than on the FID, the larger signal on the PID probably originates from the measurement of inorganic compounds like ammonia or nitric oxides. These fluxes remain small compared to surface emissions of biogas on certain MSW landfills.

Recent layers represent a small area, where fluxes are low. Therefore, total fluxes over theses areas are limited, though fluxes of possible inorganic gases are measured over site 2.

BTEX and halogenated compounds concentrations were analysed on samples taken in the flux chamber, at the end of fluxes measurements over young layers, for the 2 sites. Results are given in Table 2. On the soil gases samples taken in the flux chamber after flux measurements, concentrations of the target compounds are very low, and comparable to the values measured in ambient air [START_REF] Zdanevitch | Ambient air measurements related to traffic : evolution of VOCs over three years[END_REF]. Benzene is only detected on one sample on site 2, at a concentration which is below the European Limit Value to be attained in 2010 in ambient air (5 ng/m 3 : EC Directive, 2000). Trichlorethene is only encountered on site 1, but on the two samples. No tetrachlorethene and no vinyl chloride are detected on any sample.

Medium-aged layers (15 days -1 month)

On site 1, two zones which were 1-month old were attainable. On site 2 there was only one medium-aged zone. The age of the waste disposal vary from one part of the layer to the other part, from 3 months to a few days. This layer is also constituted of two parts : one with only stabilized waste (on the left on Figure 2), the other is a mix between stable and stabilized waste. Results of the flux measurements are given in Table 3. Analysis of soil gases sampled at the end of flux measurements are given in Table 4.

On site 1, emissions from the two 1-month old zones are similar. Fluxes measured by the PID are a little higher (5 to 10 times) than those measured by the FID. This behaviour can come from hydrocarbons which give a higher response on the PID than on the FID, or from the presence of compounds which do not give a response to the FID, like inorganic compounds. Nevertheless, emissions are so low that it is difficult to determine the origin of the signal. However, we have sampled the soil gases on the flux chamber to characterize the presence of VOC.

On site 2, fluxes measured by the PID are higher than values determined by the FID, but there is a different behaviour on stable and stabilized waste (Figure 2). FID values are generally similar to PID values on stable waste, though PID values are more dispersed, probably because the limit of detection and response time are better on the FID. On stabilized waste (with cementlike material), PID values are generally higher than FID values. This may be due to the presence of either inorganic compounds or organic compounds with a higher response to the PID. On this zone, the higher values of flux corresponds to fractures of the surface. Mean flux values are still low, but the surface of this zone is larger than the younger ones, so the total flux for this zone is a little more important, though still below 1 litre/min. On 1-month old layers, several sampling points show emissions below quantification limits of the FID and PID. Nevertheless, BTEX and chlorinated compounds were sometimes detected in the canisters samples, but with concentrations not much higher than those of a typical urban air, except for the chlorinated compounds. Tetrachlorethene is the only compound measured with a slightly higher value, and only on site 1, but on both samples taken on two different zones. This corresponds to a higher value also for trichlorethene, on one sample.

On site 2, only 2 compounds are quantified on each sample. Xylenes are present on one sample, taken on a 1-month deposit, and benzene and vinyl chloride are measured on the sample taken on a 2-month deposit. The higher response of the PID cannot be explained on site 2 by the presence of aromatic or chlorinated hydrocarbons. It is more probable than this response is due to inorganic compounds, which were not searched specifically.

Old layers (6 months -1 year)

For site 1, only one old zone could be explored : this zone is more than 2 years old, and has been rehabilitated with a geomembrane, covered by a thick layer of clay, soil and grass. On site 2, the two older zones were respectively 4 to 6 and 6 to 8 months old and made of stabilized waste. The surface of the younger zone is very dry and dusty.

Values of fluxes measured over these zones are given in Table 5. Analysis of one soil gas sample for site 2 is given in Table 6.

On site 1, no emissions were measured over the rehabilitated zone: all fluxes were null. On site 2, the two zones show a slightly different behaviour. The younger zone show no emission, though the older zone show a small mean flux on the PID values. The surface of this zone is rather small, so the total flux is very low. Nevertheless, soil gas was sampled in a canister (Table 6).

On the older zone of site 2, which show a very low flux on the FID (but not on the PID), some aromatic and chlorinated compounds are present: all the xylenes and vinyl chloride. Their concentrations are as low as the ones usually measured in ambient air. The presence of these compounds can be linked to the fluxes measured, though the concentrations are too low to explain the PID response.

Large bags

Large bags are only deposited on site 1. Large bags are deposited in layers: the deposition of a layer takes several days. When a layer is more or less full, a temporary cover, made of contaminated soil which is biologically treated on site, is deposited on the top. Older layers are covered by a thick layer of clay. No measurement was possible directly on the large bags, so the younger zone with temporary cover and the older zone with clay cover were explored. Results of flux measurements are presented in Table 7. Soil gases were also sampled in canisters at the end of a flux measurement on each zone: results are given in Table 8.

Most points of the recent zone show hydrocarbons fluxes measured by the FID. Only some of those points show a response on the PID. It may be concluded than the measured gases are probably a mixture of hydrocarbons containing a part of alcanes, which do not respond to the PID. Sampling of soil gas was made in order to verify this point. There are also points on this zone where emissions are null. Therefore mean fluxes are small. As the surface of this zone is small, emissions due to this deposition are still very low.

On the old aged large bags zone, which is covered by a layer of clay, only a few points showed very small fluxes, in the order of magnitude of the smaller flux detected. Therefore, the mean flux for this zone is close to zero.

On the recent large bags zone, for the soil gas sample, all target compounds are present except vinyl chloride, and in higher concentrations than those found in ambient air (Zdanévitch et al, 2006). The most abundant compounds are the chlorinated ones, showing the presence of residues of solvents. These emissions can come either from the waste disposed in the large bags, or from the soil used as a temporary cover, which has undergone a biological treatment on the site. Though values seem to be high, they are still low compared to those measured during fluxes measurement: they are in the high ppbv range, when flux measurements are in the ppmv range. As a consequence, the flux measured by the PID on this point is null, since the sum of the gas concentrations (BTEX and chlorinated) is below the PID detection limit. On the old aged zone, though the sample was taken on a point where the flux was not null, no target compounds are measured in the soil gas. Only toluene is detected, but it stands below quantification limits. Other compounds are not detected by the method.

CONCLUSIONS

The gaseous surface emissions of two industrial dangerous waste landfills in France were studied, by two means of measurements : FID analyser which responds to all hydrocarbons, and PID which respond to less hydrocarbons (alcene, aromatic, chlorinated..) and to inorganic gases such as nitrous oxides and ammonia. The measured emissions were generally low, and as could be expected, were higher on recent disposal zones than on older ones. Differences between the spatial distribution of the FID and PID values were identified, depending on the nature of the waste. Aromatic and chlorinated toxic compounds have been quantified on soil gas samples taken on the flux chamber. Though they were often present on the samples, their concentrations were usually very low, and comparable to those found in ambient air. These concentrations do not explain totally the fluxes measured on the PID analyser. Therefore, some inorganic compounds, which were not specifically searched, should be present. Relatively high hydrocarbon concentrations were only reported on the big bags recent zone, which is covered by a layer of biotreated soil.

Due to low mean fluxes, very low concentrations of toxic VOC and to the small areas of the sites, total emissions of those sites are low enough, and the sites do not have to report their emissions to the EPER register.

Figure 1 .

 1 Figure 1. Gas sampling for VOC analysis on the flux chamber

Table 1 .

 1 Gaseous fluxes measured on recent disposal zones

		Age of	Mean fluxes,	ml/m 2 /min	Surface	Total fluxes	, ml/min
		layer	FID	PID	area, m 2	eq. pentane	eq. iso-
							butylene
	Site 1	2 days	0.06	0	100	5.6	0
		2 days	0.07	0.04	50	3.5	1.8
	Site 2	2-8 days	0.03	0.8	150	2	120
		2 days	0.01	4.8	48	0.6	230

Table 2 .

 2 Gas analysis for recent disposal zones Concentrations,

		Site1		Site 2
	Benzene	ND*	ND	ND	4.70
	Trichlorethene	4.23	1.88	ND	ND
	Toluene	1.72	<QL**	ND	1.47
	Tetrachlorethene	ND	ND	ND	ND
	Ethylbenzene	0.69	0.70	ND	ND
	m+p Xylene	1.20	1.67	ND	1.77
	o-Xylene	ND	1.11	ND	3.55
	Vinyl chloride	ND	ND	ND	ND

* ND: not detected, ** QL: quantification limit

Table 3 .

 3 Gaseous fluxes measured over medium-age disposal zones

		Age of	Mean fluxes,	ml/m 2 /min	Surface	Total fluxes	, ml/min
		layer	FID		PID		area, m 2	eq. pentane	eq. iso-
								butylene
	Site 1	1 month	0.001	0.006		1350	1.35	8
		1 month	0.002	0.03		375	0.8	11.3
	Site 2	1-3 months	0.15		0.43		1420	213	610
	0 lo 0.D05
	o aos to D.O1
	O.01 to 01
	0 1 ta D.S
	0.S tt 1
	1 to 10
	I
	Figure 2. Interpolation of gas fluxes measured by	FID (left) and PID (right). Site 2, zone aged
	1 to 3 months
	Table 4. Gas analysis for medium-age disposal zones
	Concentrations,		Site1			Site 2
		|ag/m 3
		Benzene	<QL**	5.19	<QL**	3.51
		Trichlorethene		2.44		15.79	ND*	ND
		Toluene		3.02		8.81	<QL*	ND
		Tetrachlorethene	35.17	56.11	ND	ND
		Ethylbenzene		1.46		8.26	ND	ND
		m+p Xylene		2.07		8.66	1.11	ND
		o-Xylene		1.99		11.33	1.76	ND
		Vinyl chloride		ND*		ND*	ND*	5.13

* ND: not detected, ** QL: quantification limit

Table 6 .

 6 Soil gas analysis for old disposal zones

	Concentrations,	Site 2
	lig/m 3
	Benzene	ND*
	Trichlorethene	ND
	Toluene	ND
	Tetrachlorethene	ND
	Ethylbenzene	ND
	m+p Xylene	3.97
	o-Xylene	2.77
	Vinyl chloride	5.30

* ND: not detected

Table 7 :

 7 gaseous fluxes measured over large bags disposal zones

		Age of	Mean fluxes	, ml/m 2 /min	Surface	Total fluxes	, ml/min
		layer	FID	PID	area, m 2	eq. pentane	eq. iso-
							butylene
	Site 1	Recent	0.05	0.03	270	13.2	8.4
		Old	0	0	500	0	0
	Table 8 : gas analysis for large bags disposal zones
		Concentrations,		Site1
			Hg/m 3	Recent		Old
			Benzene	71.54		ND*
		Trichlorethene	816.88		ND
			Toluene	139.51		<QL**
		Tetrachl orethene	219.57		ND
		Ethylbenzene	64.00		ND
		m+p Xylene	49.28		ND
			o-Xylene	37.60		ND
		Vinyl chloride	ND		ND

* ND: not detected, ** QL: quantification limit

ACKNOWLEDGEMENTS

This study was initiated by ADEME and FNADE. The Authors wish to thank Guillemette Jantolek and Francis Guillot for on-site measurements.


Ruddy Branka
email: ruddy.branka@ineris.fr

CONSIDERATIONS ABOUT MARKET SURVEILLANCE AND QUALITY CONTROL OF FIREWORKS

A basic characteristic of the supply chain of fireworks is that most manufacturers are located in the Far East. Considering control results on tests made by CERL and INERIS on fireworks coming from this area (mainly from China), and taking into account that a new Directive has been published in 2007 in Europe for the certification of pyrotechnic articles (including fireworks), it seems clear that it is necessary to put in place an additional system for checking and certifying the fireworks, when importers of fireworks cannot check the imported batches by themselves according to the existing or newly arriving standards. This system could be applicable to manufacturers not belonging to the European Union or to control laboratories, and can be extended to any other country wishing to improve the safety of use of fireworks.

We present in this paper our views concerning such a system; -a comparison between the checking procedure applied by the Canada (CERL)i.e. on all imported batches -and those made by France (INERIS)i.e. on samples taken on the spot in the importers warehouses on imported fireworks from the far east, and some results some proposals on criteria of minimal competence (qualified or accredited testing laboratory, competent people, testing equipment, testing procedures, …) to put in place in order to qualify the manufacturers exporting into Europe, or local control bodies.

INTRODUCTION

Market surveillance, the verification of products to ensure that they meet the essential safety requirements, is an essential tool for enforcing "so called" New Approach European directives. It will allow non-compliant products to be brought into compliance and sanctions to be applied when necessary. There is an obligation for Member States to organise and carry out market surveillance, not only to protect the interests of consumers, workers and other users, but also the interests of economic operators from unfair competition.

A new European Directive 2007/23/EC of 23 May 2007 [1] on the placing on the market of pyrotechnic articles, including fireworks, published on 14 June 2007 in the Official Journal of the European Union, establishes the essential safety requirements which pyrotechnic articles must fulfil with a view to their being placed on the European market. This Directive explains in its article 4 that the responsibility of guaranteeing the compliance with these essential safety requirements (ESR) lies within the duties of the manufacturer, or if it is not established within the European Community, of the importer. The ESRs are described in Annex I of the Directive, the compliance of fireworks with these ESR is generally done during the so-called module B, the complete process of certification is achieved after application of a quality module (C, D, E, except for module H).

MARKET SURVEILLANCE IN FRANCE

After certification (e.g. initial approval procedure), each Member State shall take all appropriate measures (market surveillance according to article 14) to ensure that fireworks may be placed on the market, by carrying out regular inspections of fireworks on entry, at storage and on manufacturing site. In France, for pending the implementation of the Directive 2007/23/EC, the market surveillance is organised under the responsibility of the Ministry of Industry, by the way of samples arbitrarily taken on the spot by inspectors (DRIRE) in the importers warehouses.

The tests performed on the samples consist of measuring dimensions, total and net explosive contents of sub-elements, functioning observation, height of explosion, sound level and full composition analysis if applicable, and labelling. These results are compared to the original test results obtained during the agreement process and a decision is taken.

In the following Table 1, a summary of the full test results obtained during the 5 last years on theses samples is presented:

AUTHORISATION APPROVAL IN CANADA

The Canadian Fireworks Standard lays out the requirements for fireworks to be "authorised" in Canada. It also lays out a plan for deciding if samples are required for testing. If a manufacturer applies to have 100 products authorised, only about 10 products would be requested for testing and the authorisation of the complete set of products will be based on the results of those 10 products.

All testing is performed at CERL. Testing has not been contracted out to any other government or private laboratory or the manufacturers. Test procedures exists for consumer and display fireworks, such as measuring dimensions, masses, likelihood of toppling over, attachment of fuses and bases. The charge masses are also dismantled and measured, and chemical analysis are tested, mainly for ClO 3 , Pb and other heavy metals, one composition per product.

In the following Table 2, a summary is presented, the percentage of failure is similar than for the France market surveillance. At present, CERL is wrestling with high failure rates. Ideally, CERL would like the submitter to ensure that the product meets the Canadian standards before sending the samples. One way were to ask to the Chinese manufacturers to get their products pre-tested by an independent laboratory before sending the samples to Canada. To date, this has only been partially successful because Chinese manufacturers have only contracted to perform a limited set of tests in order to minimise the costs, and recent samples at CERL have failed on some relatively basic criteria like fuse times or their physical integrity which were not tested by the independent laboratory. The percentages (see Table 3) and causes of non conformities are very similar between both countries, which seems reasonable as basically same producers are supplying both markets.

COMPARISON BETWEEN THE 2 COUNTRIES

QUALITY MODULES OF THE 2007/23/EC DIRECTIVE

Considering these very poor results (only one half of the products pass the criteria), it seems clear that any given standard or specification that are used in the initial approval procedure cannot guarantee the essential safety requirements for the consumers. Therefore, it is necessary to put in place in any case an additional system for checking and certifying the fireworks manufacturers or importers. This is the goal of the new 2007/23/EC European directive concerning the CE marking of pyrotechnic articles. This directive applies to all pyrotechnic articles (except articles covered by other directives or not intended for general consumption), which are principally fireworks. Fireworks shall be classified in 4 categories and the manufacturers shall ensure that all fireworks placed on the European market comply with the essential safety requirement described in Annex I of the directive. If the manufacturer is not established in the Community, the importer shall ensure that the manufacturer has fulfilled his obligations, or assume these obligations himself, and may be liable by authorities with regard to those obligations. Distributors shall verify that the fireworks comply with the CE marking and are accompanied by the required documents. To obtain the CE marking, the manufacturers shall submit the fireworks to a notified body who performs an examination according to one of the following procedures:

an EC type examination of the product (checking of the conformity to the essential safety requirements -ESRs -according to module B) and an examination of the quality system applied by the manufacturer according to a module (C, D or E) depending on the level of his quality system. Figure 1 hereafter give an idea of the quality levels according to the modules. -A verification of each unit (module G) -A verification of the quality system only in case of full quality assurance (module H) and for category 4 fireworks only.

Degree of quality modules Figure 1: quality control process according to EU directive modules

INCOMING PROBLEMS

The main problems likely to be faced are that ;

very few manufacturers in China (a large majority of fireworks used in Europe comes from China) have a quality system certified by a body accredited by the CNAS (Chinese member of IAF [2] ): modules D and E cannot be applied, module C implies taking samples on the spot and testing them very few importers are ISO 9001 certified in Europe (20% in France for example), only module C can be applied there is no list of known distributors in the majority of European states, how to verify their duties ? -the number of Chinese manufacturers is huge and the number of future European notified bodies will remain low (10 to 20), the number of tests to be performed for the module B by the NBs is therefore extremely high (the number of fireworks already agreed in Europe according to the national existing procedures can be estimated to more than 100 000, including variants), and in addition module C tests should be organised in a majority of cases the application of modules D and E needs not only a verification of an existing quality system but also a verification of the procedures for manufacturing, testing and archiving corresponding records the existing independent Chinese laboratories able to perform tests on fireworks are generally not positioned for testing all the lots manufactured by local applicants, and are generally not fully equipped to perform the required tests for CE marking (according to ESRs)

PROPOSAL

According to the current situation described in the previous sections, it can be proposed in the following tables, according to the levels of quality of the applicants, different fields of interventions of the NB, taking in account the different possibilities concerning certification, accreditation, quality ensured by an importer,…This is only a proposal, to be discussed. Importer, if the importer ensure the quality system of a non European manufacturer, it should be certified according to an ISO9000 series standard EU:

Origin of applicant

European Union Module G: Unit verification Module B: Checking of the ESRs by the NB or an independent laboratory Module C: Conformity to type, with samples taken on the spot by the NB and tested by the NB or an independent laboratory Module D: Production quality assurance Module E: Product quality assurance Module H: Full quality assurance, category 4 fireworks only Testing procedures during manufacturing: taking sample on each manufactured lot according to a recognised international standardi.e. ISO2859 for example Minimum requirements for an independent laboratory:

accreditation as a testing laboratory according to ISO17025 by a body accredited in accordance with international accepted rules (like ILAC [3] ), -periodic audits from a NB in order to check their availability and capability to performed the necessary tests for ensuring the ESRs having personnel with proven experience concerning the fireworks technology for manufacturing, handling and testing

Table 1 :

 1 Summary of test results from France

	2002	2003	2004	2005	2007
					(6 month)

Table 2 :

 2 Summary of test results from Canada

	2003	2004	2005	2006

Table 3 :

 3 Comparison of test results from France and Canada

	FRANCE	CANADA

  International Laboratory Accreditation Cooperation), for example CNAS in China (China National Accreditation Service). If the manufacturer or importer is accredited for testing fireworks, the tests results can be taken in account by the NB for modules B or C

	ISO 9000 series certified Yes Yes No No Yes* ISO 9000 series certified Yes* Yes* Yes* ISO 9000 series certified No No * i.e. applying a quality system certified by a body accredited in accordance with international accepted rules (like IAF -International ISO17025 accredited Quality control ensured by importer Modules possibly applied (choice of applicant) Periodic audits performed by Quality system to be applied EU Yes n.a. G, B+E, B+D, H NB -Full quality system certified -Laboratory accredited for fireworks testing -Testing procedures during manufacturing checked by NB -ESRs checked by NB or independent laboratory (checked by the manufacturer for module H) -CE marking, archiving and labelling procedures -having personnel with proven experience concerning design, manufacturing and testing the fireworks (module H) EU No n.a. G, B+E, B+D NB -quality system certified -Testing procedures during manufacturing checked by NB -ESRs checked by NB or independent laboratory -CE marking, archiving and labelling procedures EU Yes n.a. G, B+C NB -Laboratory accredited for fireworks testing -Quality system checked by NB -Testing procedures during manufacturing checked by EU No n.a. G, B+C NB NB -CE marking, archiving and labelling procedures -Testing procedures during manufacturing checked by -ESRs checked by NB -Laboratory accredited for fireworks testing NB Non EU No No G, B+E, B+D NB -quality system certified -Testing procedures during manufacturing checked by -CE marking, archiving and labelling procedures -Quality system checked by NB -ESRs checked by NB or independent laboratory -CE marking, archiving and labelling procedures NB and I (different periodicity) -ESRs checked by NB or independent laboratory -Testing procedures during manufacturing checked by NB Origin of applicant ISO 17025 accredited Quality control ensured by importer Modules possibly applied (choice of applicant) Periodic audits performed by Quality system to be applied Non EU Yes** Yes G, B+E, B+D, H NB + I -Full quality system certified -Laboratory accredited for fireworks testing -Testing procedures during manufacturing checked by NB and I (different periodicity) -ESRs checked by NB or independent laboratory (checked by the manufacturer for module H) -CE marking, archiving and labelling procedures -having personnel with proven experience concerning design, manufacturing and testing the fireworks (module H) Non EU Yes** No G, B+E, B+D NB -quality system certified -Laboratory accredited for fireworks testing -Testing procedures during manufacturing checked by NB -ESRs checked by NB or independent laboratory -CE marking, archiving and labelling procedures Non EU No Yes G, B+E, B+D NB + I -quality system certified -ESRs checked by NB -CE marking, archiving and labelling procedures Origin of applicant ISO 17025 accredited Quality control ensured by importer Modules possibly applied (choice of applicant) Periodic audits performed by Quality system to be applied Non EU No Yes G, B+C NB + I -Quality system checked by NB -Testing procedures during manufacturing checked by NB and I (different periodicity) -ESRs checked by NB or independent laboratory under the responsibility of the importer -CE marking, archiving and labelling procedures Non EU No No G, B+C NB -Quality system checked by NB -Testing procedures during manufacturing checked by NB -ESRs checked by NB -CE marking, archiving and labelling procedures Accreditation Forum Multilateral Recognition Arrangement (MLA) Signatories, for example CNAS in China -China National Accreditation Service ** i.e. accreditation as a testing laboratory according to ISO17025 by a body accredited in accordance with international accepted rules (like NB: Notified Body ILAC -NOMENCLATURE I:

  [1] Directive 2007/23/EC of the European Parliament and of the Council of 23 May 2007 on the placing on the market of pyrotechnic articles, Official Journal of the European Union, page L154/1-21, published 14 June 2007 [2] IAF -International Accreditation Forum: Accreditation reduces risk for business and its customers by assuring them that accredited bodies are competent to carry out the work they undertake. Accreditation bodies which are members of IAF are required to operate at the highest standard and require the bodies they accredit to comply with appropriate international standards. Certificates issued by bodies accredited by members of the IAF Multilateral Recognition Arrangement (MLA) are relied upon all over the world because the MLA assures customers that the certificate is credible. [3] ILAC -International Laboratory Accreditation Cooperation, equivalent to IAF for testing and calibration laboratories


Yves Dien

Nicolas Dechy

Eve Guillaume

Accident Investigation: from Searching Direct Causes to Finding In-Depth Causes. Problem of Analysis or / and of Analyst?

Keywords: Accident, Industrial Safety, Organisational Analysis, Event Root-Causes

Current operating feedback Systems in industry show some limits as, in numerous industrial companies, thé numbers of events do not decrease anymore and as similar events seem to recur. Our assumption is that weaknesses corne from analysis methodology used. After a description of analysis methodology history, we focus on interest of applying an organisational analysis of events, familiar to scholars but not yet in industry, and we describe its main characteristics. Then we highlight rôles of analysts who are not neutral in using event analysis method, assuming that thèse rôles could be a block to progress of event analyses.

Introduction

One of thé ordinary goals of high-risk industries is to operate in a safe manner. Industrial policy for fulfïlling this goal involves, amongst others: safety oriented equipments design, relevant organisation (i.e. awareness of interactions needs between company Departments, of staffïng quality and quantity requirement, of educational background of employées, of training, of ...), compliance with régulations, ... This set of measures cannot prevent occurrence of every event1 and high-risk industries hâve to cope with minor events. In order to learn from thèse events, i.e. for preventing that thé same or a similar event happens again, industries set up operating feedback System (OFS) as part of their safety management process. Methodology used by every OFS generally implies several steps: (i) détection, identification of event, (ii) data collection, (iii) event analysis -causes finding -, (iv) définition of corrective measures, (v) decision-making regarding measures, (vi) implementation of corrective measures, (vii) vérification and validation of corrective measures, (viii) storage of information dealing with thé treatment of this spécifie event, (ix) diffusion of information and lessons. Considérable resources are devoted by industries for running OFS. OFS is one of the pillars of safety management process as it is seen as an essential tool in thé framework of prévention.

Nevertheless, numerous experts express concerns regarding limits of OFS. It is getting harder to establish convincing corrective action plans. Indeed, in spite of substantial efforts put for running OFS, thé same human errors or séries of similar technical breakdowns seem to recur [START_REF] Dien | Effects of the Columbia Space Shuttle Accident on High Risk Industries or: Can We Learn Lessons from Other Industries?[END_REF]. Once could say that, concerning safety, industries hâve reached a limit and are "dancing tango on asymptote" [START_REF] Frantzen | Tango on Asymptote, 13 * SRA-E Annual Conférence[END_REF], meaning that numbers of annual safety records are either slightly higher or slightly lower than thé ones of thé previous year, but are more or less thé same since several years.

Are we subjected to be satisfied with thèse weaknesses of current OFS? Does prévention hâve to find new paths? Some specialists implicitly reject event analysis and advocate either to analyse daily routine situation in order to figure out factors of opération strengths and reliability (e.g. [START_REF] Rochlin | The self-designing highreliability organization: aircraft carrier flight opérations at sea[END_REF][START_REF] Laporte | Working in practice but not in theory: theoretical challenges of "High-Reliability Organizations[END_REF] or, at thé opposite side of the spectrum, to be prepared to manage crisis because accident occurrence is inévitable (e.g. [START_REF] Lagadec | La gestion des crises, Ediscience international[END_REF]).

Fundamental question is: what has to be reappraised? The whole OFS [START_REF] Dechy | Les échecs du retour d'expérience dans l'industrie : problèmes de verticalité et/ou de transversalité ? -Papiers de la conférence IMdR -GRID des 13-14 décembre 2007 à Paris relative à la protection contre la malveillance et l'information de gestion[END_REF]) ? Event analysis itself or analysis methodology ? Furthermore can we define analysis methodology only in terms of set of conditions to follow. or to fulfil or can we extend définition up to rôle and features of thé ones who applied thé methodology? Indeed, could we consider that implementation of a methodology is "neutral" disconnected from, for instance, position in thé safety management process and/or self-interests of persons in charge of carrying out thé analysis, investigation.

After a brief description of analysis méthodologies évolution grounded on a better understanding of what is an event, what is at stake when dealing with organisational dimensions of socio-technical Systems, this paper will propose a way to improve event investigation by thé use of organisational analysis approach and will (try to) show how rôle of analysts2 is as important as methodology used itself.

Evolutions of Understanding of What is an Event and What constitutes Safety

Event investigations intend to figure out causes of event occurrence in order to define and to implement corrective measures in order to improve safety level of the plant. As part of thé safety management process, event investigation methodology is closely linked with thé way safety-related concerns were taken into account. [START_REF] Reason | Managing thé Management Risk: New Approaches to Organisational Safety[END_REF] described three periods regarding main focus of safety. [START_REF] Wilpert | Safety Related Interventions in Mer-Organisational Fields[END_REF] added a fourth one: Thèse periods are "time-marked" periods, i.e. that vision of safety sources of problems has changed with time. This évolution can, for example, be seen on thé nuclear industry.

Through thé '70s safety was mainly based upon technical reliability. Human Performance (i.e. human capabilities and human weaknesses) was not taken into account. Mitigation of potential or proven process failures resulted from technical changes and/or improvements.

During thé '80s, after thé TMI-2 accident, concept of "human error" has emerged. A positive effect of it is, that "thé operator(s)" was (were) inserted in thé loop of process opérations. It allowed improvements in domains of human-machine interface and operating procédures design, of training,... During this décade, "Operational Feedback" Systems were set-up in order to promote lessons learned. We hâve to highlight that event analyses were operator-error oriented.

After thé Chernobyl accident, during thé '90s, concept of "Safety Culture" emerged.

The safety culture of a company comprises thé beliefs, behaviours, norms, and work practices of employées and management as well. Safety culture refers to what an organisation is like in terms of safety. This concept is of the first importance because it acknowledges for thé first time that management activities are part of safety process -it means that managers could be seen, as thé operators, accountable for occurrence of events -.Nevertheless it is, to us, less operational that it seems. Indeed, according to International Nuclear Safety Advisory Group (INSAG) a safety culture could be ensured in an enterprise (i) if rôle and responsibilities of everyone are clearly defined and known and (ii) if thé relevant question is asked at thé right person at thé right time. In other words, "safety culture" can be seen as thé willingness to work on behaviour through organisation [START_REF] Insag | Safety Culture, Safety Séries n°75-INSAG-4[END_REF].

In parallel, specially thanks to [START_REF] Reason | The Age of Organisational Accident[END_REF][START_REF] Reason | Managing thé Management Risk: New Approaches to Organisational Safety[END_REF][START_REF] Reason | Managing thé Risks of Organizational Accidents[END_REF], concept of organisational event "came into thé world". It widens event analysis potential scope. So, this décade is moving toward a taking account of "Organisational Factors". From a conceptual point of view, "Organisational Factors" cover Socio-technical and Interorganisational relationship as well.

Results of évolution we briefly described are cumulative, non exclusive -from "technical aspects" to "human factors" and then to "organisational aspects" -. No-one aspect has to be ignored in favour of another. This statement can be seen as thé "Onion skin theory": Approaches (skins) are prioritised from thé core to outsider (i) technical approach, (ii) human factors approach, (iii) organisational approach. Each approach gives results, and thé whole set of results allows to hâve a better vision -a better understanding -of the (causes of occurrence of the) event.

3. Towards an Organisational Analysis of Event CAIB 2003). Due to flawed analysis, i.e. actual root causes of thé event are not figured out, correctives measures defined and implemented do not match "requirements" of thé situation and a "similar" event is ready to (re)occur 5 .

The CAIB also points out a side effect of a weak analysis: "Putting thèse corrections 6 in place leads to another mistake -thé belief that thé problem is solved" (CAIB 2003) As Turner said (1997), this kind of belief about thé world and its hazards are culturally accepted within thé organisation (i.e. thé company). So, organisation will live, according to Turner's expression (1997), an incubation period: a period during which some events occurring will remain unnoticed because they are at odds with current beliefs about existing hazards 7 .

Nevertheless, some events were analysed from an organisational point of view: collision of trains in England [START_REF] Cullen | The Ladbroke Grove Rail Inquiry, Part 1 and Part 2 Reports[END_REF], loss of Columbia space shuttle (CAIB 2003), accident in a plant manufacturing explosives (Le Coze and Lim 2003), 3 We do not say that investigation of event within thé industry do not address at ail human and organisational factors, but, rare are thé investigations which really go beyond technical aspects and "human error paradigm" and very rare are thé ones which refer to thé organisational analysis paradigm. 4 Emphasis added.

5 See for instance similarity between Challenger Space Shuttle and Columbia Space Shuttle accidents ("Echoes of Challenger" in CAIB, 2003). 5 i.e. fixing thé technical problem and replacement or retraining of the individual responsible.

7 Using a médical metaphor, we can say that if diagnosis (analysis) is weak (only deals with direct causes), associated treatment (corrective measures) will only treat symptom(s), not thé disease. For instance, patient's température will go down and virus is still potentially active. Furthermore as symptom is deleted, sick person (doctors and physicians as well) will think he/she is in good shape, while a virus is waiting to act again.

destruction of part of an altemator in a nuclear power plant [START_REF] Dien | Montée en température de l'Excitatrice de l'alternateur le 17 mai 2004 : un événement inscrit dans l'organisation[END_REF], explosion in a refmery (US CSB 2007).

What is currently at stake, is to define organisational analysis features in a way it could be disseminated in industry culture.

Challenging thé Event Chain Analysis Methodology

Currently, event analysis are mainly based upon an Event Chain approach. Event Chain Analysis methodology aims at directly "Connecting" every single event to its cause(s). It means "in thé other direction" that every action leads to direct consequence(s) and yet studies of accidents hâve shown that effects of some décisions (hère seen as actions) are visible several years after they are made, and thé way between décisions and consequence(s) is not direct (see for instance [START_REF] Vaughan | The Trickle-down Effect: Policy Décisions, Risky Work, and thé Challenger Tragedy[END_REF].

Studies of accidents hâve also shown that factors causing an event are often interlinked, overlap each other. They can be présent at thé same time with effects of mutual strengthening or réduction [START_REF] Dien | Première synthèse de la veille[END_REF].

Some scholars, as [START_REF] Perrow | Normal Accidents. Living with High-Risk Technology[END_REF], argue that roots of an accident are embedded in thé system itself and that ways taken for coming to, reaching occurrence of event are so complex, that it is almost impossible to describe them by a "set of arrows joining (single event) boxes".

Main Assumption

Any event is generated by direct or immédiate causes (technical failure(s) and/or "human error(s)") nevertheless its occurrence and/or its developing is considered to be induced, facilitated or accelerated by underlying organisational conditions (complex factors) [START_REF] Dien | Les facteurs organisationnels des accidents industriels[END_REF].

To Understand or To Explain?

Goal of an organisational analysis is not necessarily to explain an event from an expert point of view resulting in list of (more or less numerous) direct causes leading to conséquences (with, at thé end thé fatal conséquence). This approach brings some potential improvements in terms of, for instance, human machine interface, training, communication procédures (!!), ... Nevertheless, it leaves into shadow context of the event (i.e. a set a various phenomena as organisation, régulation, général and spécifie to thé event decision-making processes, company beliefs and culture, ...). Very often "explaining approach" is operator oriented and takes poorly into account managers actions (for instance "decision-making") and its rôle in occurrence of event -indeed, management actions hâve, generally, no direct effects, impacts concerning occurrence -. In contrast, organisational approach tries to understand events in/by taking account of context and to highlight its relevant features (i.e. history, every actor, entity potentially involved, It allows to propose corrective measures with broader effects. Thèse measures are usually less "technical", and could be related to cultural aspects and it could take times before their effects are felt.

Purpose of organisational analysis is to understand how organisation is working: it leads to (try to) understand weaknesses and vulnerabilities of/coming from daily, routine, day-to-day, ..., functioning.

Event organisational Analysis Main Features

According to [START_REF] Reason | Managing thé Risks of Organizational Accidents[END_REF], a System producing an event is made of three levels:

•

The person (having carried out thé unsafe acts, thé errors); •

The workplace (local error-provoking conditions); •

The organisation (organisational factors inducing thé event).

Development of event is "bottom-up", i.e. direction causality is from organisational factors to person. In thé event analysis, direction is opposite. "Gâte" -starting pointof analysis is direct and immédiate causes of bad outcome (event). Then, step by step, analysis considers, as far as possible, how and when defences failed.

In addition to results obtained by scholars in thé field of organisational studies, real event organisational analyses carried out allow us to define thé three main axis of an innovative approach, helping to go from direct causes to root organisational causes [START_REF] Dien | Méthode d'analyse et de diagnostic organisationnel de la sûreté[END_REF]):

• Historical dimension; • Organisational network; • "Vertical relationships" in thé organisation.

We hâve to note that, if thèse dimensions are introduced in a independent way, they are interacting and an analysis has to deal with them in parallel.

a) Historical dimension

As Llory states (1998): "accident does not start with triggering of final accidentai séquence; therefore, analysis require to go back in time, [...]" in order to put in prominent place détérioration phenomena. Analysis has to "go upstream" in thé History of thé organisations involved for highlighting significant malfunctioning aspects: what was not appreciated in real time has to "make sensé" when risk was confirmed (i.e. when event has happened). Vaughan reminds (2005): "The O-ring érosion that caused thé loss of Challenger and thé foam débris problem that took Columbia out of thé sky both had a long history. " Early warning signs hâve to be looked for and detected long before time event occurrence.

We hâve to note that one chapter of the CAIB report ( 2003) is named: "History as A Cause". Few years before, Presidential Commission on thé Space Shuttle Challenger Accident (1986) has entitled one chapter of its report: "An Accident Rooted in History". So taking account of past is important to understand thé event. Goal is to go back in time for comprehending and analysing relevant processes and trends which' led to thé event. Numerous industriel events show that weakness of operational feedback could be incriminated for their occurrence -i.e. that previous relevant event(s) was/were not taken into account or poorly treated after their occurrence -.

Analysts hâve to pay a spécifie attention at incidents, faults, malfimctioning occurred prior to thé event.

Analysis of thé "historical dimension" is parallel to detailed examination of parameters, of variables of context which allow understanding of events.

Analysis of thé "historical dimension" has to avoid a "rétrospective error". Fine knowledge of event scénario -i.e. séquences of actions and décisions which led to it -allows to assess actual mid and long term effects of each action and décision.

Analysts hâve to keep in mind that this évaluation is easier to make after thé event than in real time. In other words, analysts hâve to avoid a blâme approach.

b) Organisational network

Within an organisation, entities8 communicate: they exchange data, they make common décisions -or at least they discuss for making a décision -, they collaborate, ... So it is of thé first importance to "draw" organisational network between entities concerned in thé event. This network is not thé formai organisation chart of entities. It is a tool for showing numerous and complex interactions involved for occurrence of event. It is a guideline for carrying out thé analysis; it is built ail along analysis itself.

Organisational network is hardly defined once and for ail for a given organisation. It is draft according to thé analysis goals. Parts of organisation can be ignored because they were not involved in thé event.

Organisational network allows visualising complexity of functional relationships between entities, and sometimes, it highlights absence of relationships which had to be présent.

c) "Vertical relationships" in thé organisation

This dimension is a part of organisational network on which a spécifie focus is needed. It covers top-down and bottom-up communications. It is essential to isolate it since it makes easier understanding of interactions between various management levels, experts and "field operators". We hâve to remind an obviousness often forgotten during event analysis: organisation is a hierarchical System.

The main interests of this dimension are: modes of relationships, of communication, of information flows and modes of co-operation between hierarchical layers. Real events show that détérioration of thèse modes are cause of their occurrence.

At least, thanks to this dimension, causes of an event cannot be focussed only on field operators.

Some Other Concepts of Organisational Analysis

Organisational and structural features are of importance to understand thé nature of Accident Analysis. However, we could also take other dimensions into account. Social sciences provide interesting findings to understand people's action in risky situations. Spécial attention has to be paid during investigations/analyses to thé two following issues. They are not thé only ones but seem of particular importance.

a) Weak signais

Notion of "weak signais" arose from Vaughan's work (1996). She defined a weak signal as "information informai and/or ambiguous, so that threat to the flight safety 9 was not clear". In other words, we can say that a weak signal is either a technical or a human phenomenon which is not the/one direct cause of an event but which is meaningful regarding potential weakness, fragility of thé socio-technical system in domain of safety.

b) Whistle blowers

Sometimes "whistle blowers" make thé effort of writing to signal a malfunction and express their concern for safety. Thèse written exchanges occur among some operational staff-members, or their management, who sound thé alarm about persistent malfunctions, thé treatment of which falls to others, and they often underline thé accident-generating conséquences of thèse situations. Thèse persons take their responsibility and also take risks through personal involvement, especially regarding their careers. Their objective is to reach thé décision making centres in order to remedy thé situation they are concerned with [START_REF] Llory | Ce que nous apprennent les accidents industriels[END_REF].

Some Principles for Applying Organisational Analysis a) Field Analysis

Even if an organisational analysis could be carried out from documentation (having high quality), usually it is implemented through a field analysis with contacts with every actor (operators, managers, ...) and with every entity (company where event occurred, safety authority "in charge", ...). In order to collect "true" information analysts hâve to hâve an empathie attitude toward people met during analysis 10 , and to insure an understanding approach.

b) Background Knowledge

"We only find what we are looking for" ! ! An organisational analysis cannot do without a set of background knowledge related to méthodologies, main findings of organisational approach. Indeed, as some root

9 She spoke about thé Space Shuttle Challenger accident 10 Collecting "true" information does not mean to take what it is said as "holly words". Analysts hâve to understand speeches according to thé context, thé rôle of thé speaker(s), ... Information collected hâve to be cross-examined as well.

causes could be "hidden" in thé past or by thé situation, analysis is based upon assumptions to be confirmed or denied.

Background knowledge are a général framework for (fîeld) analysis and are usefui as well for making a synthesis and for drawing conclusions.

Knowledge of day-to-day opérations is also part of background knowledge required for an organisational analysis.

c) A "Thick" Description of An Event

First output of an organizational analysis is a "story" as detailed as possible which is, as said Geertz (1998), a dense description, a thick description of the situation having led to thé event. For synthesis, story is expurgated in order to highlight on thé one hand main technical and organizational processes "responsible" and, on thé other hand spécifie organisational factors involved in thé situation.

Analysts and Organisational Analysis

Historical and Sectorial Developments of Organisational Analysis

The understanding and explicit formalisation of thé human and organisational dimensions of events and safety came with public reports upon some major accident investigations and work of scholars. It implies that thé différent industrial sectors (and in particular their analysts and thé available méthodologies) are at différent stages of knowledge and practice of thèse new paradigms. Very recently, it seems that thé CAIB report and posture constitutes a turning point on thé organisational paradigm. This investigation has integrated some of thé latest developments proposed by scholars, has used them explicitly and has criticised thé approach in other investigations (too much focused on technical factors or human error oriented). This investigation is producing a 'trickle down effect' [START_REF] Vaughan | The Challenger Launch Décision. Risky Technology, Culture, and Déviance at NASA[END_REF] on other sectors such as in thé process industries with US CSB investigation (2007) of Texas City accident and CCPS 11 learning lessons process on thé Columbia case (2005). We can see hère, thé important rôle of independent safety boards and independent ad-hoc commissions in thé development of this paradigm. Some analysts in those sectors and safety boards are now more familiar with those concepts.

Position of Analysts Within thé Organisation and Epistemological Barrier

It was shown by J. [START_REF] Rasmussen | Risk Management in a Dynamic Society: A Modeling Problem[END_REF] that several "layers" are involved in hazardous processes -Work, Staff, Management, Company, Authority, Government. We assume that causes of an accident could stem from flaws in several layers. Event analysts usually belong to one layer. Their problem is to be able to detect and to take àccount of thé whole set of event causes. For instance, CAIB (2003) showed that "American political system" (i.e. thé White House and thé House of Représentatives) played a rôle in loss of Columbia space shuttle in cutting down thé NASA budget. This budget decreasing, with no parallel changes in thé goals of NASA led to staff downsizing, time schedule pressure, ... which weakened thé "space shuttle system". Some root causes of an event could be outside of the company "affected" by it. Could an analyst or a team of analysts members of a company, be able to detect such root causes or are they beyond their reach?

In addition "culture of efficiency" will lead analysts to emphasise on controllable and manageable causes for which corrective measures are within thé organisation boundaries analysts could reach. According to A. [START_REF] Hopkins | Lessons from Longford. The Esso Gas Plant Explosion[END_REF], analysts can be driven by "stop rules" in their investigation. Study of several event analyses reveal that often analysts implicitly hait searching causes to causes they handle, i.e. to causes for which they can propose corrective measures in order to prevent them. That means, for instance, if analysts belong to "management layer", they could "put aside" causes implicating "company layer" because décisions concerning corrective measures hâve to be made at thé corporate level. That is a reason why, very often, analyses do not go far enough.

So, position of analysts within thé organisation influences their vision of situation and therefore their analysis. It seems that, in order to take an event in its broad scope, analysts hâve to be in position enabling them to catch thé "big picture" of thé event and to catch thé comprehensive -organisational -situation prior to it.

Furthermore, position of thé analysts towards thé event, gives them implicit or explicit goals for thé analysis. In other words, depending on position of analysts, results of analysis could be tremendously unlike each other. Thus, [START_REF] Hopkins | Lessons from Longford. The Esso Gas Plant Explosion[END_REF] shows, in analysing investigations carried out after an explosion in a gas plant in Australia, that results, and therefore définition of causes, were différent according to thé company owning thé plant and according to thé courts. In performing his own investigation of this event, Hopkins figured out a third set of results, of root causes having led to thé accident.

In addition and at thé basis also, [START_REF] Llory | L'accident de la centrale nucléaire de Three Mile Island[END_REF] talked about an epistemological barrier for some actors, in particular with engineers, to think about organisational dimensions of accidents. The behaviourist model is still in mind to conceive thé human factors despite thé fact that they can refer to organisational, communication problem to explain some of thé situations they face. And at thé other end of thé socio-technical System, thé justice also uses this underlying worldview.

Analysts as Political Actors

An event analysis can be sum-up as séries of decision-making (what is important, what to look for, what to take account of, ...). Now, décision makers in any organisation "are not perfectly rational individuals. They are collections of normal human being, constrained by common cognitive and organizational limits on rationality [START_REF] Sagan | Toward a Political Theory of Organizational Reliability[END_REF])".

Effects of organisation/company culture, self interests of analysts, ... can hâve an impact on results of event investigation: " organizational blind spots can hid failures modes. Organizations often hâve taboo subjects which cannot be discussed , because to do so hurts thé morale and self-image of the organization [START_REF] Sagan | Toward a Political Theory of Organizational Reliability[END_REF])".

Llory (1999) referring to Crozier (1995) analysing French failures of top décision making "Obstacles are not only epistemological and cultural, they are grounded on an organisational and hierarchical System that bans thé accountability of executive élites13 ".

Does it lead to promote investigation carried out by "external" experts -in thé sensé not belonging to organisation/company affected by thé event -? It is not either thé "pure" solution. Indeed external experts hâve also their limits to rationality. For instance, [START_REF] Sagan | Toward a Political Theory of Organizational Reliability[END_REF] refers to a study made by Hawkins showing that safety "inspectors tend to report problems only when they believe there is a good chance that they can win a case against thé violators, rather thon focusing on thé actual effects on thé hazards."

This goes back to thé independence as a political factor facilitating thé tackling and explicit formalisation of those political factors (organisational, hierarchical, managerial, power, responsibility). However, there is no perfect situation as addressed by [START_REF] Bourdeaux | Procédures de REX, d'apprentissage et de vigilance organisationnelles : approches croisées[END_REF]: thé external (a priori more independent) person will hâve less difficulties to ask questions not asked by thé insiders, and an insider could hâve thé advantage of understanding thé power relationships. A way of improving thé whole situation is to protect thé analyst, to institute thé bénéficiai rôle of Cassandra's in high risk industries [START_REF] Dien | Cassandre au pays des risques modernes, Présentation au 29ième[END_REF] and look for analyst with will not be complacent under contractual or hierarchical pressure.

Analysts and Organisational Data

Such organisational analysis requires spécifie methodological approaches, spécifie data and resources, to conduct interviews, to analyse collected data, that are far from thé resource allocation currently observed for incident analysis within industrial organisation. This is a reason among others why, those analyses hâve often yet been performed by scholars, researchers and independent safety boards or commissions.

Furthermore, thé access to thé needed data is not that obvious. As a first comment, [START_REF] Llory | Accidents industriels : le coût du silence, Opérateurs privés de parole et cadres introuvables[END_REF] pointed out in his book titled "Industrial accidents: thé Cost of Silence --Operators Deprived of Speech and Untraceable Managers". Most often, thé accidents are not described from thé point of view of actors and thé work of managers and experts is not described in those analyses. The technical factors of accidents are politically more neutral.

Following an accident, an a posteriori assessment of the real work of actors should be performed but is hard to conduct. First, this assessment is perceived as suspicious according to thé risk with thé use of those information to allocate blâme, to find a scapegoat and to assess individual performance of actors in human resources perspective [START_REF] De Gaulejac | La société malade de la gestion[END_REF]. Indeed, it implies to address real work versus formai work which is a well known subject [START_REF] Bourrier | Le nucléaire à l'épreuve de l'organisation[END_REF]. But in normative perspective in this context, a secrecy culture is establishing [START_REF] Llory | L'accident de la centrale nucléaire de Three Mile Island[END_REF][START_REF] Dejours | L'évaluation du travail à l'épreuve du réel[END_REF]. In addition, this access to real work assumes to hâve access to tacit skills and as stated by [START_REF] Dejours | L'évaluation du travail à l'épreuve du réel[END_REF] "professional intelligence, in rule, is in advance on Us knowledge and symbolisation". Spécifie methodological approaches to collect data hâve to be practised, such as clinical approaches defined in social science. They are also facing power dimension due to thé stratégie knowledge of thé real work (Crozier and Friedberg 1977) and individual or group "défensive idéologies" [START_REF] Llory | L'accident de la centrale nucléaire de Three Mile Island[END_REF][START_REF] Dejours | L'évaluation du travail à l'épreuve du réel[END_REF]) that can be observed in particular after accidents, when actors are fearing allocation of blâme or a responsibility towards thé justice litigation.

Sélection and Training of Analysts

Sélection and training of analysts is an issue that will hâve to be strengthened in thé next years as we hâve not seen yet many actions regarding this dimension.

Organisational analyst compétence can be seen at thé intersection of two competencies, thé first one in accident investigation (and by extension in learning from expérience) and thé second one in human and organisational approaches of safety.

In human and organisational dimensions of safety, différent sectors since thé eighties hâve selected human factors specialist (ergonomics, psychology) following thé impact of "human error" discovery ... Very few industrial organisation hâve integrated more organisational dimensions expert (sociology political science, ...) when thinking about safety management

In investigation and learning from expérience, despite this field of safety has been implemented for several years, in France we know only one school on learning from expérience and none on investigation. With thé independent accident investigation boards, some developments are observed such with NTSB14 academy. However thé training proposed are still more focused on technical dimension of investigations with forensics techniques for example.

Transferring tools and methods on organisational analysis ?

One of thé issue that is underlying hère is thé gap between some knowledge of scholars, researchers, and experts in thé field of organisational analysis and thé industrial practices of incident analysis. An operational transfer of those concepts is lacking [START_REF] Bourrier | A la recherche d'un second souffle pour les facteurs humains et organisationnels[END_REF]. Some perspectives of developing framework, approaches, tools adapted to an industrial context with insights coming from lessons learned in organisational analysis hâve been proposed (Bourrier 2004, Le Coze and[START_REF] Coze | Stratégie de développement des approches organisationnelles dans l'industrie[END_REF].

Accident Analysis: A Social Product and Analyst Sensé Making

As earlier mentioned, social sciences provide interesting findings to understand • people's action in risky situations. This theoretical approach is worthwhile in terms of accident prévention, based on a posture of doubt, critical analysis of knowledge acquired and tools implanted. We consider Macrae's study (2007) as an interesting way to explore and operate this notion. He argued that "in modem, complex and hazardous organizations such as airlines, risks are rarely self-evident. They must be actively identified and interpreted, often in a context rich with weak or equivocal signs of potential problems'". Risk managers and experts hâve to try to pièce together signs in order to give sensé to them. The capacity of analysts or safety managers to detect, interpret and take thèse early signs of potential problems lies in a posture of doubt; of learning from their own ignorance. In addition to thé necessary a posteriori reconstruction of those processes, we believe that this approach could be of interest for investigation a posteriori. Indeed, an issue to address is how this doubt prone behaviour (gained during daily opérations and a priori analyses) could influence analysts during an event investigation?

Analyst' Judgement and Memory of Analysis of Organisations

One of thé issue in organisational analysis (prior to thé event or after) is thé judgement that arises after thé thick description and analysis when dealing with fmdings. A posteriori, it is necessary to avoid both thé restropective bias as thé historian and to avoid thé 'rétrospective illusion of fatality' [START_REF] Llory | Accidents industriels : le coût du silence, Opérateurs privés de parole et cadres introuvables[END_REF][START_REF] Llory | Les leçons des risques industriels : répétitions insistantes et illusions rétrospectives, Papiers du colloque Risques industriels majeurs[END_REF]. A priori, thé issue is to be able to judge complex factors, pathogenic factors and latent conditions and detect an incubation period.

In both situations, a judgement as a conclusion of analysis is pronounced by thé analyst. The judgement of complex factors (with feedback loops, non linearity, counter-intuitive effects,...) is not trivial, even after thé event, and relies on underlying assumption of models of safety), on a modelling of thé accident (thick description provided by organisational analysis) and on accident cases to support judgement. Indeed, thé médical metaphor was used by [START_REF] Llory | Accidents industriels : le coût du silence, Opérateurs privés de parole et cadres introuvables[END_REF] to explain thé need for référence cases to judge potential pathogenic conditions or behaviours of dynamic socio-technical Systems. Furthermore, to study organisational pathogenic patterns, [START_REF] Llory | Accidents industriels : le coût du silence, Opérateurs privés de parole et cadres introuvables[END_REF], referring to S. Freund metaphor regarding dreams and unconscious, has recalled that accident investigations are thé 'royal road' (versus "normal" situations analyses) for understanding organisations.

Conclusions

It appears that use of organisational analysis for event investigation could break current limits of OFS and improve safety since potential causes of incidents or accidents are looked for in a wider scope than thé one of analysis methodology generally used in industry.

One of thé issue, for thé methodological dimension, would be to work on doser bridges between scholars and industries. In spite of many in depth studies on thèse issues, many scholars still regret that accident analysis are too technical and not deep enough. We could say that some efforts are still to make in thé capacity of scholars to translate and transfer thé intellectual and practical tools to thé industries. This work requires taking industrial constraints into account -production, people's background, market conditions, ... If scholars and researchers tend to be doser to industries concems, bridges should be built in a more concrète and stronger way. It will imply also serious sélection and training of analyst on those approaches.

Nevertheless, analysts either could not be able -i.e. to be in a "wrong" position within organisation -to address thé whole scope or do not hâve self interest to extend scope of investigation. They could also face difficulties to hâve access to relevant organisational data and to make sensé of it.

Furthermore, practical corrective measures hâve to be derived from investigation and they hâve to be implemented. However, some corrective measures are out of sphère of compétence and responsibilities of persons in charge of drafting corrective measures, and of persons in charge of decision-making regarding their implementation. So, main improvements concerning effects of event investigations hâve to be sought with future studies of position and rôle of analysts and of decisionmakers of implementation of corrective measures.

One promising, but expensive in terms of resource and time, is to promote a "check and balance" approach for investigation, meaning a collective building of results deriving from several parallel organisational analyses. Results of each analysis could be compared and discussed in order to defïne one set of shared results allowing to gain a "global vision" of the event. This approach could be worth for major accidents.

3.1 Status of Event Investigation

	Unfortunately, if concept of organisational accident is already familiar to scholars, it
	is more récent in industry, and so not applied 3 . Indeed, it was noticed by thé
	Columbia Accident Investigation Board (CAIB) in its investigation concerning
	accident of the space shuttle Columbia occurred on February 1, 2003. CAIB states:
	"Many accident investigations do not go far enough 4 . They identify thé technical
	cause of the accident, and then connect it to a variant of "operator error "[...]. When
	thé détermination of the causal chain is limited to thé technical flaw and individual
	failure, typically thé action taken [...] are also limited [...]" (

By event we mean every type of malfunctioning with effects on either process availability or process safety: from minor and major incident to accident and disaster and also crisis.

This point is developed further (section 4) but we would like to précise thé importance of the analyst in thé construction of identification, interprétation and analysis of the Accident..

"Entity" means a part of organisation more or less important in terms of size, staffîng. It could be a small amount of people or even an isolated person (for instance a whistle blower).

' Center for Chemical Process Safety at http://www.aiche.org/CCPS/index.aspx

Emphasis added.

of the country

National Transportation Safety Board (USA).

Chemical Safety and Hazard Investigation Board