Guy Marlair

Patricia Rotureau

Hervé Breulet

& Sylvain Brohez

BIOFUELS FOR TRANSPORT IN THE 21 st CENTURY: WHY FIRE SAFETY IS A REAL ISSUE

Years after pioneering development of sugar cane éthanol in Brazil (started in thé mid 70's), with thé new century venue we are assisting of a booming industry regarding biofuels for transportation in général, at international level. However, fire safety has not appeared so far as a potential bottleneck for future sustainable development, nor has it been anticipated that fîre safety misleading judgements or lack of safety management might act as a non technical barrier for sustainable development. This paper is a fîrst contribution to discuss thèse issues within thé fîre safety community aiming at identifying research needs and bring a first overview based on life cycle and whole value chain perspectives of biofuels for transport. This contribution is a fîrst output from a National research program named BIOSAFUEL piloted by INERIS, comprising a fîrst analysis of fîre risk typology presented by socalled in Europe l st génération technologies of biofuels. When thé first statement is to consider that fire safety aspects are not likely to be that much critical on a technical point of view, thé analysis is showing that safety related issues -and more especially fîre safety related issues-with biofuels are not correctly summarized by simply saying that fuel éthanol is a flammable product whereas biodiesel is not, from a regulatory point of view. A more in-depth analysis is needed, that will, in addition, hâve to consider significant changes in biofuel technologies in thé future.

INTRODUCTION

Nobody from both sides of thé Atlantic Océan can ignore by now what biofuels are and represent in terms of alternative fuels for thé automotive sector, considering nearly daily média reporting regarding that tremendous activity actively. Indeed, biofuels had a long and chaotic history in thé past, thé development of which was more or less killed by thé dominance of thé cheap oil era. However, say since thé 2000's, a new phase, that everyone hopes sustainable, is currently supported by a number of key drivers. Thèse key drivers vary slightly from country to country, most common being:

-using biofuels secure or diversify fuel supplies (USA, Western Europe...) biofuels are assumed to hâve very limited -if any-impact on global climate change (CO 2 émissions are compensated by photosynthesis at level of thé growing biomass) and induce, as oxygénâtes, improved combustion properties limiting pollutant émissions biofuels offer opportunities for developing or diversifying rural economy (source of employment) tax incentives or other financial supports for farmers, biofuels producers, or users other policy driven regulatory frameworks (ex. clean fuel act in thé USA, Directive 2003/30/CEintheEU...)

In addition, regular sharp increases in oil prices are reminding to western countries associated geopolitical issues of fossil fuels reserves and inéluctable diminution of relating ressources (hâve we passed through thé so-called oil peak ?).

Consequently, a tremendous research effort to develop and improve biofuels production and use has been implemented for years, however, very limited considération of safety issues has been given so far (apart from material compatibility issues at thé level of vehicles). Aren't there any real new challenges regarding safety, and fire safety in particular ? At time France is going a step forward in boosting thé use of biofuels on thé National market, INERIS has been granted to produce a first overview of thé question. This is in thé scope of a three years research project called BIOSAFUEL® 1 ' 2 started in January 2006.

GENERAL FACTS AND FIGURES ABOUT AUTOMOTIVE BIOFUELS

The conventional biofuels, namely foel éthanol or biodiesel, both derived from energy crops (sugar containing and starch containing plants, or oil seeds, respectively) hâve reached an industrial development in Brazil, in thé USA, and in a few countries in Europe for at least two décades or more, whereas big expectations are anticipated for thé new routes of production of biofuels under development from biomass (lignocelMosic resources). Given thé vast availability of that renewable resource, thé current debate that raises potential conflicts such "fuel versus food ? " or thé risk of biodiversity would no longer exist when such production routes will be commercially available. The readers may refer to a number of very récent books to appraise how far is thé interest of thé scientific community for thé global biofuels activity and related market [START_REF] Ballerini | Biofuels : State of thé Art, perspectives & development issues[END_REF] ' 10 ' 11 ' [START_REF]The biodiesel handbook[END_REF] ' [START_REF]Biodiesel thé comprehensive handbook[END_REF] . The tremendous number of conférences dedicated to biofuels issues is also very impressive, as largely revealed by a brief web search or by reading dedicated newsletters of joumals [Licht reports on éthanol and biofuels][IEA task 39 newsletters]. S'orii 1 ? lïrjesr ettsaool pEKÎaser ,ini esparsvidâtes s'Jumdat lera'ea astfvel drêèkçsd Hofiisl 3aia.pi!rta:iaa mSiKCncniiï. lioâesaï "it-fto ' iBCîBtly dev«iop«l mé pstmud by ïsieL'eiii îïiCTrailtBaiicû iraïa^îadl?) EÎT sidjKpiiij siciiîl; Biiciia-ui>-?:t«5 is La-^îtoK ui E^s-ÈiiWnes aid liîjps to sr*atg a3arb*ï aiflesfiïelcar? l"#lmcte ownership sacxeaîîd &10*» m iut âerade oeiinj Jtasî doetsaai'* and ôt nesd ftar !fr"nuRkefoelr ClanaspshcvsjEtioiael: sill «rïdY Passant fhs iswlcpKiettt«ïbisi&«l! CE a s'cbal :casa. aicenti;"e p39^raïï3ïne«-for eibacel.

(courtesy UNCTAD secrétariat)

Quantities of biofuels put on thé market drastically increased in récent years, as indicated in figure 1. This sharp increase translates thé émergence of a real world market for biofuels, with current major actors being mentioned in tables 1 and 2. It is worth to notice that thé USA will hâve overturned Brazilian production of bioethanol in 2006 for thé fîrst time, as a resuit of promotion policies at both State and Fédéral levels that resulted in many new plants for processing bioethanol from corn. It must also be outlined that many émergent countries, generally located in thé tropical area are involving themselves in thé biofuel industry due to climate opportunities (for example for producing palm oil and derived biodiesel). China, dramatically lacking fossil oil, and India are also becoming, as can be seen, major actors on thé fuel éthanol side. Table 3 complète général information on thé biofuel market indicating thé current context in a sélection of countries.

Classification of biofuels

There is no unique classification of biofuels accepted at international level. There are currently basically two major types of fuels, corresponding to current major industrial pools of fossil liquid fuels: bioethanol, which may be blended in various proportions with unleaded gasoline for use in gasoline fuelled cars or in so-called flexfuel vehicles, and biodiesel, which can be blended with diesel for use in diesel cars. In this paper, we focus on liquid biofuels, representing thé vast majority of currently commercialized biofuels. In his final report 5 , regarding thé élaboration of a research agenda for biofuels in thé European Union, thé BIOFRAC proposed thé following conventional classification schème (see table 4 and5) for biofuels of current and future interest for thé automotive transport.

Fire safety général considérations

At évidence, fire safety considérations pertaining to thé biofuels industry must take into account: : a) safety data of thé concerned products; b) safety data of thé whole list of substances that may intervene on thé whole value chain if we want to evaluate safety issues with a life cycle analysis perspective; c) process safety considération; d) organizational aspects; e) storage and transport issues; f) any other related pertinent topics.

As an example of thé latter point, and not necessarily easily perceived, thé analysis of fire safety issues must take into account différences that are pertaining to local conditions of development and use. Fire safety expérience accumulated so far by thé biofuels industry (and very poorly valorized in thé open literature in our view) is not necessarily directly transférable from one place to another, due to différences in production technologies, environmental constraints and many technical détails, including significant différences in safety culture. As an example, Brazil has accumulated some 30 years of expérience with thé production and use of sugar cane éthanol and has implemented by now some 30,000 stations delivering 100% éthanol (hydrated) and gasoline/anhydrous éthanol blends up to 25% rich in éthanol. The extensive use of dedicated vehicles using hydrated éthanol is a unique expérience in Brazil. Moreover, Brazilian model of FFV (Flex-fuel vehicles) that has now reached a commercial status since 2003 in replacement to dedicated vehicles for thé use of hydrated pure éthanol is simply not applicable in Europe, due to thé présence of a secondary fuel tank installed in thé engine compartment (see fig. 2). In addition, Brazil recently announced brand new plans for developing biodiesel micro-units and related use for developing rural economy, as well as a long term plan for éthanol aiming at weighing some 10% of thé world market in 2025, inducing many technical modifications at many levels of thé life cycle of éthanol (sugar cane production and pretreatment, bioethanol processing, technical schemes for exports.. .). By contrast, elsewhere (USA, Europe... ) thé development of E8 5 as an alternative fuel has been chosenin addition to ethanol/gasoline blends with low concentrations in éthanol (E5, E10). The (modem) FFV vehicles delivered in thé USA and in Europe are designed to be able to work with any ethanol/gasoline mixture with up to 85% in éthanol, but thé expérience with distribution networks for E85 keeps so far very limited (some 300 refuel stations available in Sweden, which looks impressive for such a small country, but only 49 refuel E85 stations available for ail US States of America, for a corresponding vehicles fleet capable of using it of 30000 in 1999, according to réf. [START_REF] Rivkin | Alternative fuels for Vehicles[END_REF] ). In thé USA by contrast, thé development is more piloted by thé need to secure fuels supply, and an ambitious expansion plan of biofuels production has been suggested (in particular from thé promising route involving cellulose éthanol): Developing cellulose éthanol at industrial scale is currently perceived by US politicians as a good part of thé solution. To finalize this idea that local considérations are of importance, let us report on récent moves in France and Belgium. France has pioneered thé industrial production of biodiesel from vegetable oil by homogenous catalysis transesterification (first unit operating since 1992 in Compiègne), and has started to use fuel éthanol in diluted blends for some ten/fifteen years. France keeps one of thé leaders, at European level, for bio fuel production (râpé seed methyl ester in particular), however, no spécifie distribution network for delivering biofuels is currently existing: France, for a number of reasons, has opted so far to limited (and not registered at thé pump) incorporation of biodiesel in thé diesel pool and of bio-ETBE (thé éther derived from sugar beet éthanol by synthesis with isobutene) in thé gasoline pool. But thé French Government offîcially announced thé promotion of an E85 network in last September, and official authorization of this new fuel by l st January 2007, with thé ambition of implementing some 500 E85 dispensing stations by 2008. Belgium, on his side was until recently far below thé objective fixed by thé EU in 2005 (as many European countries) but has by now started internai production. Some 5/8 projects are currently under development (or in construction) to procure a reasonable production capacity which will hâve to be completed by imports. Safety issues relating to storage and transport (notably by water streams) are likely to be there of major importance for such a heavily densely inhabited country.

E25 aux. réservoir

BIOFUELS TECHNICAL DATA IN RELATION WITH THE FIRE PROBLEM

Table 6 présents important data regarding fuel éthanol and related gasoline/ethanol blends constituents. MTBE (Methyl Tert Butyl Ether), also mentioned, has been banned in 18 States of USA. This situation is at the origin of thé initial promotion of éthanol as an octane enhancer (anti-knock) substance as a substitute. Butanol data are also provided, as sometimes considered as a potential alternative fuel presenting some advantages compared to éthanol (such as a heating value doser to gasoline). However, thé général view is that butanol from fermentation of biomass is not yet compétitive. Some récent projects however are reactivating thé interest of butanol 8 .Table 7 gives similar data for biodiesel (fatty acid methyl or ethyl esters of vegetable oils). (a) 36.1 (a) 19.9

22.4-22.9

A32

LEL-UEL : Lower explosion limit -Upper explosion limit (vary according to réf. température) Table 6 essentially illustrâtes basic flammability parameters of éthanol, showing in particular that flammability is a real issue that differs from thé gasoline case. Whereas from table 7, it can be stated that biodiesel is a fuel reasonably comparable with conventional diesel in terms of fîre risks, in a first glance. However, thé fîre risk is much more complex with éthanol that thé simple expanded flammability range (on thé reach side) that appears from thé data in table 6. The global fîre risk with thé end use product must take account of thé following additional considérations: a) although moderately volatile (relatively high boiling température and heat of vaporization 2.5 higher than for gasoline), éthanol in blends with gasoline, has thé capacity of forming low boiling azeotropes with gasoline components of low molecular weight that leads to critical volatility issues with thé blends, b) electrical conductivity is 35,000 times higher than for gasoline, c) éthanol is a polar solvent, and as such requires spécial fire-fighting procédures to tackle significant fires, d) thé product présent significant corrosivity (to metals and plastics), e) éthanol is hydroscopic, fully miscible with water, but in blends with gasoline and traces of water, demixtion problems exist (e.g. phase séparation may occur, depending on concentrations of thé three components): this is particularly important with blends with low éthanol contents. Some of those properties are implementing indirect tire risks at level of storage of éthanol blends, and enduse of éthanol blends in cars, due to potential leakage through material attack by corrosion. The question of thé right sélection and location of flame arresters in cars and in refueling stations for thé use of E85 is still an open question, as shown by some récent work [START_REF] Brandes | Safety Characteristics of Ethanol/Automotive Petrol Mixtures[END_REF] ' [START_REF] Weyand | Flame Arrester Evaluation for E-Diesel Fuel Tanks[END_REF] . Limited expérience of E85 distribution networks at thé EU level currently justifies careful examination of thèse issues in France, as well as in thé USA [START_REF]Fuel Dispenser Components containing Ethanol & Other alcohol Blended Fuels[END_REF] . Naturally, considering thé full life cycle of biofuels, this section would gain benefit through pertinent data acquisition regarding other materials and chemicals intervening in thé life cycle of biofuels. As an example, some 10 chemicals (including gasoline) are in thé list of potential éthanol fuel dénaturant in Europe, distillation residues like fusel oils, of important value, also présent fîre risks due to flammability properties. The list of potential catalysts in use or currently tested for biodiesel production is still much higher. Products in use for odour réduction, maintenance purposes, or alcohol rectification or other treatment (desulfurization using potassium permanganate), or fuel additives (like anti-oxidizers) are other families of chemicals that deserve interest from thé fire safety point of view. One major problem to look further on thèse compounds is bound to thé fact that many of them are proprietary.

AN ANALYSIS OF THE TYPOLOGY OF THE FIRE RISK BY BIOFUELS FROM AGRO-RESSOURCES SUPPLY TO END USE AND RELATED ACTIVITY

Bioethanol life cycle analysis and thé fîre risk issue

From a life cycle perspective, thé fire safety engineer may need to consider éthanol processing as well as side aspects that may play significant rôles as well, such as conditions of feedstock supply, storage, handling and pre-treatment, import and export issues, management of by or co-products that differ according to biomass feedstock under considération. Some of thé feedstock are directly releasing sugars or sugar based co-products like molasses, that are directly fermentable by use of micro-organisms (generally yeasts) into éthanol (e.g. sugar beets or sugar cane). Starch containing crops, like potatoes, wheat or corn, require more sophisticated break-down of thé feedstock, by processes that may involve cooking and adding enzymes. Although processes thus vary from one case to thé other, thé core of thé fuel éthanol process remains based on same basic chemical processes (or biological processes) like hydrolysis (acidic, enzymatic or combined), saccharification (optional), fermentation, distillation, refining and rectification (such as P and S removing, or dénaturant addition). In those processes, thé risk pattern is very closely related with conventional edible alcohol or industrial distilleries, at least at thé process level, which suggests that major achievements terms of fîre risk management with those other ethyl alcohol uses might be helpful for assisting thé development of thé biofuel industry. The treatment of co-products, for use in thé animal feed (plant residues) or for other purposes (fusel oil components valorization) maybe more spécifie. Let us add as well thé dehydration step, required for fuel éthanol in most vehicles capable of running with ethanol/gasoline blends for a number of reasons. Vapour is used to do this final step, a source of significant heat

As an example, Figure 3 summarizes thé main steps of bioethanol processing from corn, referring to thé socalled dry milling process, thé most popular one in thé USA today, for reasons of limited investment costs. The analysis of thé flowsheet helps in identifying potential fîre risks, like: self heating of raw material or derived crushed products (during corn mashing) création of explosive atmosphères (vapour or dust) and related explosion risk in tanks fîre risk induced from excessive heat transfer to products due to malfunctioning of handling Systems or cookers (treated feedstock) or dryers to products (co-processing of by-products to obtained dried distiller grains...) operational problems on thé distillation process (see for instance paper from Kvaalen [START_REF] Kvaalen | Alcohol distillation: Basic principles, equipment, performance relationships, and safety[END_REF] ) use and storage issues of various flammable products use of other dangerous substances (acids, bases) storage of gas (CO 2 ) under pressure.

Those risks are quite conventional and relatively well known, but they are real issues, more or less well addressed according to régulation background and existing safety culture. One should also be very cautious of thé analysis of conséquences of requested flexibility of an éthanol process plant in terms of : a) various grades of feedstock that will hâve to be treated, b) various options defîned for thé valorization of coproducts, as thé type and form of "in" and "off" substances will clearly influence pertinence of storage and handling equipment and procédures, in terms of safety management. Naturally, thé way fuel éthanol is introduced after production in thé gasoline pool (transportation issues: road, rail, pipelines...), blending issues, ethanol/gasoline dispensing stations safety equipment, equipment compatibility for storage and at level of thé car manufacturers are typical spécifie issues that deserve interest of thé scientists.

Going further on thé end use side, it must be noted that éthanol could also be considered in thé future as a candidate for use as a component in blends with diesel, and why not biodiesel: thé US DoE has carried out a testing program in thé area for about 10 years, for a potential use on heavy duty engines; there is also a spécial interest in Europe like in France or Germany, countries in short of diesel and too large in gasoline, for technical reasons (existing refmeries configurations and local consumers attraction for diesel cars). However, with ethanol/diesel blends (so called E-diesel or bioE-diesel), many challenges are still existing [START_REF] Hansen | Ethanol-diesel fuel blends-a review[END_REF] , including in relation with fîre safety (stability of thé mixtures, protection of car tanks and fuel distribution line to thé engine...).

In thé future, other technical challenges pertaining to thé fuel bioethanol industry that will also interact with fire safety management will also entail thé development of new routes of production, more intégration of biofuel production into biorefinery concepts (where thé full valorization of thé energy crop or thé biomass feedstock will be thé global objective) or even thé use of éthanol as a source for biohydrogen processing.

Biodiesel life cycle analysis and thé fîre risk issue

There also, addressing properly thé fîre issue globally, starts by considering much more input than thé limited combustibility properties of vegetable oils or fats (thé needed material to process biodiesel by chemical three steps réaction called transesterifîcation (see figure 4)) and thé biodiesel by itself.

Quick examination of thé main réaction process (figure 4) and thé global process flowsheet (figure 5) reveals why flammability is also a key issue: thé fire danger may arise at least from two major products intervening in thé chemical process: thé main reactant in thé chemical réaction that converts thé triglycérides into fatty acid alkyl esters: most of thé time methanol is chosen, giving thé conversion of thé oil into fatty acid methyl esters or FAME (see table 6 for methanol flammability properties), and thé catalyst generally necessary to reach satisfactory conversion rate or conversion time duration. Catalysts may be selected in thé following family list 9 : a) alkali métal hydroxides or methylates, alkali métal or transition métal soaps, alkylguanidines b) acid catalysts (minerai acids, sulfonic acid, ion exchange resins, zeolites c) others like titane alcoholates, diverse métal oxides.

O : o CH-O-C-* * o CH r OH O Qttaiyst g 3 t'0H -* 3 H-0-C-R 4 CH-0H OL-OH Triacyij^ycero! Akohat AJkyte«ter Glycerol (Vejetable o il)

Figure 4: thé chemical réaction of transesterification

As can be seen, a number of dangerous materials is involved in thé sole réaction at thé core of bio diesel production, notwithstanding other materials in used in other parts of thé biodiesel life cycle.

Oil extraction & semi-refining

Vegetable oil

Extraction solvent Catalists: Sodium or Potassium methylates, thé most commonly used catalysts with sodium hydroxide présent thé particularity of being solid at normal température and pressure. Dissolution of thé methylate powder in methanol is then a key "dangerous" step in thé process, as it leads to potentially highly exothermic réaction and gives rise, in thé same time of a potentially explosive composite (vapor + dust) atmosphère. Such an opération generally requires adapted préventive measures [START_REF] Glor | Transfer of powders into flammable solvents overview of explosion hazards and préventive measures[END_REF] . Apart from thé transesterification process, figure 5 also reveals other potential fire related risks, regarding methanol recovery from thé crude glycerin tank, pre-esterification steps by use of acids, or refining processes of both glycerin and crude biodiesel that may require distillation phases. Oil seed processing, that can be done in biodiesel plants or in specialized oil refineries, also présent spécial fire risks, such as thé use of n-hexane as for complementary solvent extraction from seed cakes after screw extraction. The next section which essentially provides two lists of significant incidents, classified by type of biofuels, is a consolidation of our analysis.

KOH or NaOH or rr.ethyiate K ou Na

Recycled oils or fat

A REVIEW OF RECENT INCIDENTS

Tables 8 and9 présent a sélection of récent accidents of particular interest to consolidate our analysis. A Word of caution is needed however.

Known facts about thé incident

Fire initiated and contained in a bag-house filter, collecting dust from corn drying process. Fire extinguished by fire brigades in 30 min. Blast in a distillation plant (wet milling process), followed by alcohol tank fire. Hopefully, major alcohol tank farm was separated from thé process plant area Massive Explosion of a 40,000 gai. Of corn mash, may be additional explosions. Parts of thé tank flew away, one hitting a tank truck getting loaded with fuel éthanol, 75 feet away, another dropped through roof of an adjacent processing room An odor-reduction equipment (thermal oxidizer) overheating caused a fire in thé insulation of thé roofing materials. 3 rd fire reported at this plant... Major éthanol tank fire (4,000,000 liters) in a petroleum terminal, after initial explosion that blew away thé 5 tons tank roof. Fire-fighting opérations made difficult due to polarity of EtOH, damage on plastic part s of cars up to 50 m away. Fire put out after more than 20 hours using alcohol résistant foam drops by helicopter. On its way from NY to Houston, thé Bow Mariner, a 3.5 min gallons Ethanol tanker exploded and sank 50 miles off thé coast Fire at thé éthanol process plant, handled up to arrivai of fire-brigades by thé facility sprinkler System. Fire reported due to equipment malfunction Fire at level of a dryer (for thé production of DDGs) at a 40,000 gai 2peopl éthanol dry milling unit Fire declared in a sugar producing &distillery complex, outside of thé éthanol tanks farm, at level of a dénaturant storage unit. The fire is reportedly due to electrical malfunction of thé heating system Fire on board of tugboat thé "Pacifié Reliance", pushing a barge full of éthanol, on its way to Baltimore by thé Hudson River: fire was in thé engine compartment and was put out within 20 minutes Very short flash fire at an éthanol plant, during routine maintenance work (replacement of old pipe at filling station area of thé facility) On its way from Chicago to New Jersey, A freight train derailed over a bridge, not far from Pittsburgh. The train was conveying some 85 tank cars of éthanol, 24 No statistical analysis of thé level of risk shall be driven from those tables in order to rank biofuel producers (in terms of companies or even countries): for example, thé absence of any incident originating from Brazil (thé leading country in fuel éthanol production and use until 2005!) simply translates thé diffîculty to get appropriate information in existing database, as it is more that likely that accidents hâve and may be still do happen sometime.

Although considérable expérience was existing with éthanol distillation before thé émergence of thé fuel éthanol market and although biodiesel is hardly ignitable, thé careful examination of data in table 8 and 9 clearly shows that both alternative fuels hâve suffered significant incidents considering their life cycle and also illustrâtes thé wide variety of scénarios. Owing to thé flammable character of éthanol, it is not surprising to see that explosion and fire scénarios involving éthanol fuel stocks hâve indeed occurred in some of thé incidents recorded in table 8, either as thé initial event, or as a "domino" effect. One may also see that incidents are material related or equipment related or both. The well known Port Kembla tank fire (#5 in table 8) présents some similarities with a former éthanol tank blaze that happened in thé Netherland on thé 18 February 1998 in Bergen op Zoom 23 . Those two scénarios hâve clearly illustrated that emergency response to be given to fuels tanks added with significant amounts of éthanol deserve spécial considérations. As a matter of fact, a modification of thé UN recommendations for Transport of Dangerous Goods (thé so-called "Orange Book") has just been adopted end of 2006, that créâtes a new UN number to identify fuel blends containing more than 10% of éthanol, to facilitate adéquate emergency response plans in case of a fire.

Known facts about thé incident

Fire declared in a cooling tower, associated to biodiesel processing plant Multiple car crashes after sunflower oil leak from tank truck on motorway close to airport. No fire but very difficult cleaning procédure due to frost A biodiesel récent plant suffered a violent fire during several hours, as a resuit of a outside methanol fire that spread into thé process plant. Ignition of methanol occurred due to leakage (electrostatic discharge ?) Tank of homemade biodiesel left unattended caught a fire due to overheating of heating device. Destruction of shed and surrounding equipment Major fire involving canola biodiesel stock erupted at small biodiesel processing site. Difficult fire fïghting. An explosion occurred, followed by a fire, in a brand new biodiesel small plant. The explosion is consécutive of unsafe welding opération above a glycerin tank under refining process Banal "chimney fire" at thé historié first biodiesel production unit in France. Some related "societal acceptance" issues. Among thé lessons learnt from thé listed incidents is thé significance of thé risk during transports. Massive transports of vegetable oil and fuel éthanol, by road, rail and maritime routes is likely to occur in thé future, and those incidents, even not necessarily followed by a fire (a number of récent train derailment or tank truck overturns had occurred without consécutive fire incidents in a reported number of cases in North America 21 before thé occurrence of incident #12 in table 8), are potential events that require emergency preparedness. Table 9 listing of incidents regarding biodiesel clearly illustrâtes that thé fire risk with biodiesel may be linked with thé product itself, and to flammability issues of other materials used to process it like methanol or mixtures of glycérine and methanol. At last, Biodiesel processing is increasingly popular as a "hobby" at home: a situation that recently led thé Health and Safety Executive to address a safety warning on their web site [START_REF] Hse | Domestic Production of biodiesel -health and safety warning", Health and safety Executive web site, February 2006 25 unknown[END_REF] : low cost batch reactors can be supplied from various companies and ordered on thé internet. However, consumers are rarely aware that normal dwellings are not necessarily suitable places for biodiesel processing, owing to signifîcant quantities of dangerous materials involved in thé process and to usually inadéquate house environment.

Conséquences

FINAL DISCUSSION

A first and certainly incomplète overview of l st génération biofuels safety issues arising on their whole life cycle has been proposed, as a contribution of thé INERIS BIOSAFUEL project. The typology of risk has been briefly reviewed, at thé light of process and side opération flowsheets, as well as at thé light of an accident review. Although currently industrialized biofuels, fire safety issues pertaining to thé biofuel industry keeps a real issue, and sustainable development of biofuels as a Worldwide market will require assistance from western and other experienced countries to implement adéquate safety culture in émergent countries, taking account of thé many peculiarities that may rely to selected energy crops, and processes. The relatively high number of significant incidents reviewed likely reflects thé high mutation in thé biofuels market that increases sharply for a number of years, statistically multiplying thé number of potential abnormal situations for a given level of risk control. An increasing number of them outlines handling and transportation issues : an emerging risk, recently recognized by specialists in logistics 25 . To our view, in thé field of fire safety, research needs cover topics like: -examination of fire related and other safety issues pertaining to 2 nd génération types of biofuels, for which no industrial expérience is still available -follow-up of technical development in thé field of valorization of by and co-products of thé biofuel industry: a key issue for final cost competitiveness that leads to wide variety of potentially new chemicals derived from glycerin for instance -data production on: a) combustion species from materials relating to thé biofuels industry liable to be involved in accidentai fîres, including raw materials themselves; b) stability of biofuel characteristics versus time; c) situation of thé conventional phys-chem properties of materials currently involved in thé biofuel industry according to new regulatory frameworks under implementation due to arrivai of REACh and GHS; d) for consolidation of safety measures needed from production to use of E85 in modem fleet; e) consolidation of learning from lessons from past accidents on a word wide basis; f) safety impacts in case of use of biofuels in other transport Systems (rail, marine, aircrafts). LITERATURE

Figure 1 :

 1 Figure 1: history of production of fuel éthanol and biodiesel from thé early 1980's up to 2006-12-21 adapted from réf. 3

Figure 2 :

 2 Figure 2: auxiliary gasoline fuel tank (E25) located in engine compartiment of a typical Brazilian Flex-fuel car

Figure 3 :

 3 Figure 3: insight on thé most common fuel éthanol process from grains (corn) in thé US

Figure 5 :

 5 Figure 5: général flowsheet for biodiesel processing using homogeneous catalysis

Table 1 :

 1 top 5 producers of éthanol

	Data 2005, Source: C. Berg (after réf. 3 )

Table 2 :

 2 top 5 producers of biodiesel

	Data 2005, Source: KO. Licht (after réf. 3 )

Table FtoâiifïtoB

 FtoâiifïtoB

		C005 Boe-rsj
	Eilatioi	Sioilfeel
	1?B	:SGM*
	S50H"
	16B

Z.ÏB 12504}

Table 4 : biofuels of first génération : adapted from réf. 5 Biofuel type Spécifie name Biomass feedstock Production process Bioethanol

 4 Ethyl Tert Butyl EtherNaturally, biogas, obtained from wet biomass residues, is also a reality, but is of limited, and generally local, use. Safety issues are naturally pertaining also to such a gaseous fuel: thé fire risk is présent, as with ail other flammable gases. Moreover, a dramatic accident at thé process level that took place recently in Germany reminded us also of potential toxicity related issues with biofuels 6 .

				Sugar beet, sugar cane, Hydrolysis and fermentation
				grains (corn, wheat, barley),
				potatoes, ...
	Vegetable oil	Pure Plant Oil (PPO), also Oil crops (e.g. râpé seed, Clod pressing/extraction
		called Straight Vegetable Oil sunflower seed... )
	Biodiesel	Biodiesel from energy crops Oil crops (e.g. râpé seed, Cold pressing/extraction &
		Râpé seed methyl ester sunflower seed...)	transesterification
		(RME), fatty acid methyl
	Biodiesel	Biodiesel	from	waste Waste/cooking/frying	(optional) pretreatment	&
		FAME/FAEE		oil/animal fat	transesterification
	Biogas			(wet) biomass	Digestion and refming
				Bioethanol (etherified)	Chemical synthesis

Note: ':

Table 6 :

 6 safety characteristic data of major products involved in bioethanol production N.B.: figures from various sources, such as ref.9 to 13 orMSDS; (a) estimâtes fromréf.14

	Products	Vapor	Boiling	Flash	AIT	Density	LEL-UEL	LHV
		Pressure (kPa)	point CO	point (°C)	(°C)	(g/cm 3 ) (20°C)	(% air)	(MJ/kg)
	Ethanol	5.8(20°C)	78.4	12	363-425	0.79	3.3-19	26.8
		15.9(37.8°C)	78	13	400	0.794	3.1-27.7	26.8
		29.4 (50°C)			423	(15°C)	4.3-19
		15.9 (38°C)					3-19
	ETBE	21 (25°C)	73	-19	-310	0.75	1.2-9.1	35.9
								36.3 (a)
	MTBE	27 (20°C)	55.3	-28	224-460	0.746	1.5-8.4	35.2
		33 (25°C)						35.9
	Butanol	0.67 (20°C)	118	35	340	0.81	1.4-11.3
	Methanol	3.8 (0°C)	65	12	464	0.791	5.5-31
		12.3 (20°C)		11	455
		34.4 (40°Q
	E85	38-83 (38°C)	35.5-76.7	-45-10	257.2	0.78-0.79	1.4-19
		41-83	49-80	slightly	> gasoline	(15°C)	between
				higher than			éthanol and
				gasoline			gasoline
	Gasoline	48-103 (38°C)	30-190	-40	257	0.73-0.76	0.6-8.6
		50-100	27-225	-43		0.69-0.79	1.4-7.6
						(15°C)	1-8

Table 7 :

 7 safety characteristic data of products involved in biodiesel production

	Products	Viscosity	Boiling point	Flash	AIT	Density	LEL-UEL	LHV
		(40°C) (mm 2 /s)	(°C)	(°C) point	(°C)	(g/cm 3 ) (20°C)	(% air)	(MJ/kg)
	Rapeseed	30.2	n.a.	300-324	n.a.	0.92	n.a.	39.7
	Oil			> 320°C				(HHV)
	RME	4.5	170-366	170-180	n.a.	0.88	n.a.	37.4 ( *>
		4.83	320-350	153-179		0.883 (15°C)		42
		4.46		179
	FAEE	6.17	358	185	n.a.	0.876 (15°C)	n.a.	40
				175-185
	Diesel	2-4.5	160-350	70	316	0.82-0.86	1-6	42.6
			188-343	74		0.82-0.845		42.9
						(15°C)
	FT diesel	2.4	211-297.7	95.5	n.a.	0.77 (15°C)	n.a.	-43
	(synthetîc)

N.B.: figures from various sources, such as ref.9 to 13 or MSDS; (*): value for FAME

Table 8 :

 8 incidents relating to bioethanol fuel industry that occurred in thé 2000's N.B.: figures from various sources, such as ref.21 and many press releases

	#	Date & location
	1	21/03/2000, South
		Bend (USA)
	2	14/09/2002,
		Atchison, KA (USA)
	3	22/10/2003, Benson,
		Minn. (USA)
	4	26/07/2003, St Paul,
		Minn. (USA)
	5	28/01/2004, Port
		Kembla, (Australia)
	6	29/02/2004, near
		Porthmouth, VA
		(USA)
	7	16/05/2005, Groton,
		SD (USA)
	8	22/09/2005, West
		Berlington, Iowa
		(USA)
	9	15/02/2006, Lillers,
		(France)
	10	22/05/2006, New
		Hemburg, (USA)
	il	15/06/2006, Shively
		KY (USA)
	12	20/10/2006, New
		Brighton, PEN,
		(USA) 22

  of them were involved in thé derailment over thé Beaver River; 9 of them turned into explosion & fire scénario conséquences

	No injury, $20,000
	damage
	4 workers injured
	1 killed, 1 injured
	1 fire-fighter injured;
	$15,000 damage
	estimate
	2 injured
	21 crew out of 27
	members killed or
	lost
	No injury; minor
	damage
	2 people suffered
	minor injuries
	No injury;
	Existing
	Contaminent basin
	limited fire spread
	No injury nor
	pollution
	2 people treated for
	burns
	No one injured,
	significant damage
	with rolling stock,
	river pollution

Table 9 :

 9 incidents in relation with thé biodiesel industry N.B.: figures from various sources, such as ref.21 and many press releases

	#	Date & location
	1	04/08/2003, Grand-
		Couronne, (France)
	2	11/01/2006, Brussel
		Ring, (Belgium)
	3	17/02/2006,
		Bakersfield, ÇA
		(USA)
	4	07/05/2006,
		residential area,
		Colorado (USA)
	5	23/06/2006, Canby,
		OR (USA)
	6	07/07/2006, New
		Plymouth, ID (USA)
	7	17/7/2006, Venette,
		(France)


Lionel Perrette

Henri Paillere

Guillaume Joncquet

Presentation of the French national project DRIVE: Experimental Data for the Evaluation of hydrogen Risks onboard vehicles, the Validation of numerical tools and the Edition of guidelines

The everyday use of hydrogen in the transport sector requires high safety standards. Safety requirements must be addressed as a key issue for fuel cell car development. Therefore, it becomes crucial to have experimental data on hand in order to provide realistic and reliable risk assessment and to be able to really know the extent of safety margins taken. In such a context, the National Institute of Industrial Environment and Risks (INERIS) along with the French Atomic Energy Commission (CEA), the French automotive manufacturer PSA PEUGEOT CITROËN and the research Institute on unstable phenomena (IRPHE) recently started a research programme entitled DRIVE. This programme aims at providing experimental and numerical results for the safe design of hydrogen vehicles. Fields of investigation cover the whole range of phenomena that can be encountered in hydrogen accidents, from leakage to dispersion, ignition and finally combustion. The work programme and early results are presented in this article.

INTRODUCTION

The everyday use of hydrogen in the transport sector requires high safety standards. Safety requirements must be addressed as a key issue for fuel cell car development. It is therefore a necessity to fully understand and investigate explosion and fire hazards associated with the use of hydrogen and to come up with practical and realistic means to control these hazards. Although the experience and safety record of hydrogen as an industrial gas is significant, it turns out not to be applicable to the future decentralised use of moderate quantities of hydrogen. Data specific to that use are becoming crucial in order to provide realistic risk assessment and to be able to specify expected safety performances.

PROGRAMME OBJECTIVES

This project which gathers together industrial expertise of the car manufacturer PSA PEUGEOT CITROËN as well as technical and scientific skills of CEA, IRPHE and the co-ordinator INERIS aims at providing experimental and numerical results to better assess hazards when handling hydrogen onboard vehicles. Results will contribute to strengthen risk assessment studies in terms of hazard quantification as well as to propose innovative solutions for the handling of hydrogen in cars compatible with public use.

The work programme is split into 4 items: the automotive system, hydrogen dispersion, hydrogen ignition and combustion and finally results dissemination. The second and the third items focus on the hazardous phenomena one would consecutively encounter when dealing with hydrogen accidents. The accidental chain is illustrated by the figure below. The list below indicates some of the safety challenges that face car manufacturers:

• Safe pressurised storage design (thermal insulation, use and location of pressure relief devices (PRD), enclosed or open compartment for storage...) and location of the pressurised storage in order to prevent burst due to thermal and mechanical aggressions as well as to control consequences of accidental leakage or PRD releases. • Adequate control of standing flames fed by minor undetected leaks, • Appropriate equipment design (choice of material and technology) and location (segregation,, enclosure,...) in order to control ignition sources whether mechanical, electrical or electrostatic in normal operations, • Safe handling of hydrogen purged outside vehicle, • Effective control of explosive atmospheres in confined or semi-confined spaces on-board vehicles (engine compartment) or outside the vehicle (underbody, garages...). That also includes ensuring that hydrogen will never penetrates into the passenger compartment.

Aside from the items above, one of the great challenges consists in setting an appropriate limit to segregate tolerable accidental releases versus unacceptable ones. Such a limit would contribute to set the expected performance of the leak detection and leak interruption systems whether based on atmospheric detection or on direct measurement such as flow or pressure drop. Ideally, a vehicle should be able to run without leak detection systems having in mind that reliability of such detection system is so far moderate and that maintenance is rather constraining. Chronic leakage is also an issue since the no-leak objective does not seem to be realistic. Therefore, upper tolerable limit should also be specified for chronic leakage along with design measures to ensure that hydrogen can never accumulate to form an explosive mixture.

Finally, CFD tools currently and intensively used by car manufacturers to design vehicles (aerodynamic studies for instance) should also be able to provide reliable results when computing normal or accidental release scenarios for hydrogen vehicles.

Safe design practices should finally be shared among manufacturers to promote the high safety standard expected for the public use of hydrogen.

DETAILED PRESENTATION OF THE WORK PROGRAMME AND EARLY RESULTS

WORK PROGRAMME

This project started early 2006 in the framework of the first call for proposals of the National Research Agency (ANR). It will last for three years. Its work programme is made of 4 main modules:

• vehicle safety, • hydrogen release and dispersion, • hydrogen ignition and combustion (explosion or jet flame), • and finally results compilation and dissemination.

The vehicle safety module includes a thorough risk assessment in order to identify hazardous situations (causes, consequences). Outputs from this module will shape the content of the experimental and modelling work in terms of hazardous situations to investigate with the objective of obtaining better quantification and therefore better risk assessment and risk control. The vehicle safety module that concentrates on hydrogen equipment and potential ignition sources onboard vehicles goes down to component level.

Within the hydrogen release and dispersion module, we will then experimentally look at hydrogen component leakage in order to quantify them. Both chronic and accidental hydrogen leakage, as well as hydrogen emissions (purges, pressure relief systems) will be considered. These values will then serve as references to build the test matrix for hydrogen releases (free and impinged) on board the vehicle as well as in confined spaces.

These release experiments will be carried out with helium as well as with hydrogen. The size and location of explosive atmospheres will be monitored for various leaking rate and location. Within the third module, we will concentrate on hydrogen ignition with vehicle components as well on hydrogen combustion (flame or explosion). Ignition potentiality of car components (fans, electronic cards, electric engines, braking systems...) will be investigated through practical testing. In parallel, explosion experiments will be undertaken in order to assess the destructive potential of explosive atmospheres (in accordance with hydrogen dispersion findings) in more or less obstructed environments. In a later stage, combustion tests will take place on board vehicles. Hydrogen flames will also be considered at two different scales; on one hand, effect of large hydrogen flame resulting for instance from a PRD release and on the other hand, standing flames fed by minor leaks. For the latter point we will look at the ease with which ignition can occur as well as flame sustainability depending on upstream pressure and leaking orifice size. Excessive fire hazards due to the use of hydrogen can possibly be more critical than explosive atmospheres themselves that concentrate most of today's concerns. In the frame of the last module, experimental learning will be turned into practical graphs to facilitate risk quantification. Recommendations on best practices for vehicle design will also be drafted. Topics such as maximum allowable explosive volume, control of ignition sources and location of hydrogen components... will be addressed in final public reports. Results will be discussed during dedicated seminars. This project will not investigate the safety of highpressure hydrogen storage in terms of potentiality for catastrophic failure when exposed to mechanical aggression or external fire. Issues such as fuse location on tanks or thermal insulation will not be looked at in the frame of this project. However, potential leaks as well as PRD releases consequences (explosive atmosphere under vehicle, jet fire) will be experimentally considered. Leakage during refuelling will not be considered either.

More detailed content and progress of some of the work themes is given below.

WORK TOPICS

Objectives, methodology, tools, basic background information and early results will be presented for each of the topics below:

VEHICLE RISK ASSESSMENT

OBJECTIVE

Risk assessment helps to evaluate and demonstrate through a systematic and consistent approach that a hydrogen vehicle whether of a prototypic or a series production type is as safe as a conventional one. Within this project this early work will help us to select hazardous situations to be studied and therefore to shape the experimental programme.

STEPS

Usual risk assessment steps are the following:

• identify unwanted events and associated causes and consequences, • e va I u ate th e i r criti city, • and take appropriate actions to bring risk down to an acceptable level.

TOOLS

Four tools are mainly used to contribute to the risk assessment studies: functional analysis preliminary risk analysis, fault trees and then Failure Mode and Effect Analysis (FMEA).

First of all, a functional analysis was undertaken. It helps to identify system functions and associated internal and external constrains. Then a preliminary risk assessment was carried out. This simple methodology helps to highlight the most unwanted events and to initiate discussions on severity and severity levels. For each vehicle mode (running, stand by, maintenance...) the following unwanted events are investigated:

• shift in internal system functions and system constrains, • impact from the system on its environment, • and finally, impact from the environment on the studied system.

All identified unwanted events were then ranked according to severity criteria. The severity scale consists of four levels. The highest ones 4 and 3 are those further considered in the study. Level 4 is associated with death or injury on people and level 3 means that the vehicle can no longer be used because of a break down. Level 3 and 4 unwanted events were then further investigated using the fault tree methodology. This graphical methodology helps to visualise steps and failure combinations that lead to the top unwanted event.

Finally, a failure mode and effect analysis (FMEA) was carried out. This systematic and inductive methodology helps:

• to assess consequences of component failures (loss or alteration of associated function) on the vehicle and its user, • to identify component failure modes that can impact safety, • and finally to propose corrective safety actions in the course of the design process.

A typical FMEA table similar to the one used in the project is pictured below:

o Q. 0)
<ô a:

CD > E Hi | P .E ô t E = E 5 SSI CO CD Bel .2 .2 ;>, [DOE. E Q..S E x ai <D Ë S « • Q o) 2 2 2 c IS °O) (J is < 0) > T3 D-

II

CO CD

I a Table 1: FMEA table used in the risk assessment process

EARLY RESULTS

Identified unwanted events when using hydrogen onboard vehicle include:

• fire onboard vehicles,

• explosive atmospheres and ignition wherever onboard or outside the vehicle, • the burst of the pressurised tank, • high pressure jets.

All the selected unwanted events are linked either with the use of hydrogen or with the handling of pressurised gas. Unwanted events associated with high voltage or other non specific hazards are not considered in this programme.

LEAK QUANTIFICATION

OBJECTIVE

The objective of this task consists in experimentally measuring chronic and accidental leak rates (external aggression, human error...) associated with key components of the hydrogen feed line and the hydrogen conversion system. Accidental leaking rates to be evaluated include likely situation such as bad fitting (insufficient clamping), erroneous fitting, missing or damaged sealant. Ageing will be looked at through repeated dismantling of hydrogen connections. Leak caused by organic failures of components (quality issues, internal ageing) quantification will be forwarded to component manufacturers. Design related hydrogen emissions (PEMFC purge, PRV...) will also be taken into consideration. Investigated pressures will cover the full range from the 700 bar working pressure for the highpressure line down to few bars for the hydrogen conversion system. Both hydrogen and helium gas will be used in order to assess the appropriateness to use helium for leak quantification.

These realistic and practical figures gained from these tests will serve as input parameters for further hydrogen dispersion and combustion experiments. These values will also be of a great help for risk assessment studies.

STEPS

The study includes four main steps. The first one consists in extracting and referencing leak scenarios from the risk assessment study. The next one will consist in selecting components and test conditions (pressure, damage free / damaged equipment). Selection criteria include for instance likelihood and severity of leak, lack of data from manufacturers or gas component not initially designed for hydrogen use. Then, tests will be carried out with the experimental set up shown further down. Finally results will be recorded and analysed.

BACKGROUND INFORMATION

(Cfcp 1 [START_REF]Support facilities for hydrogen fuelled vehicles-Conceptual design and cost analysis study[END_REF]) with an average value around 10-20 g/min. It is interesting to notice that these values vary in a large domain. Besides, except for the BMW tests, there is not any obvious link between investigated cases and specific component leakage.

Regarding component leakage the Cfcp document indicates that the fill up point and the pressure relief point are considered as the only way for the hydrogen tank to leak out. As far as other components are concerned, the pressure regulator, piping and fittings were considered as components able to leak out whatever the operating pressure (high-pressure and low-pressure). The value of 20 CFM (12.77g/min), referenced in this document, is based on the assumption that that the onboard computer is capable of shutting down hydrogen flow upon receiving a signal detecting a flow larger than 20 CFM when the engine is off. The Japanese regulation for hydrogen vehicle 2 proposes a leak threshold of 11,8 g/min (or 131 L/min) that should not be reached in case of leakage after vehicle collision. This leakage is assumed to have the same calorific value as today's admissible value for gasoline. However, associated explosive atmosphere and consequences have not been taken into consideration. The same document indicates that helium can be used instead of hydrogen for leak tests as long as a 1.33 multiplication factor of the leak volumetric flow is used.

Regarding purge management, the Japanese regulation indicates also that no purged gas in excess of 4% of hydrogen concentration shall be discharged or leaked to the atmosphere.

As far as the GRPE Informal Group on Hydrogen/Fuel Cell Vehicles work is concerned [START_REF]on Hydrogen/Fuel Cell Vehicles[END_REF], no maximum allowable leakage value or leakage value to be detected is proposed.

The work carried out in the framework of the DRIVE project will propose some realistic data specific to hydrogen components and hydrogen fittings. These data will enrich somehow empirical data proposed so far.

TOOLS

Components will be connected to pressure sources according to the figure below. Components will be placed inside a closed 2 m3 insulated sphere inside where both pressure and temperature are monitored.

Component leak rate measurement is directly linked to pressure variation inside the sphere.

Literature shows that various vehicles related leak rates have been investigated in the frame of dispersion experiments. As shown in table 2, these investigated rates vary from 0.5 g/min (BMW [START_REF] Dr Fùrst | Safety of Hydrogen-fueled motor vehicles with IC engines[END_REF]) up to 100 g/min 1 California Fuel Cell Partnership 2 Attachment 100 -Technical standard for fuel systems of motor vehicles fueled by compressed hydrogen gas At least, the following components will be tested: hydrogen connections, pressure regulator, phase separator, hydrogen pump, solenoid valve & components made of polymeric or plastic type materials.

HYDROGEN DISPERSION ON BOARD AND OUTSIDE VEHICLE (CONFINED SPACES)

OBJECTIVES

The objectives of this study are to investigate, experimentally and numerically, different types of leaks and the dispersion of hydrogen either inside the vehicle or outside the vehicle in the most critical situation, that is when the vehicle is parked in an enclosed space such as a private garage. The mechanisms for the build-up of a potentially explosive mixture of hydrogen and air will be studied in detail, and effects of confinement and ventilation will be assessed.

STEPS

The experimental programme will consist of leak and dispersion tests in a full-scale garage as well as onboard a vehicle. Both helium and hydrogen will be used. The test matrix will be elaborated from the leak quantification tests, the preliminary risk assessment study, and some pretest calculations using CFD (Computational Fluid Dynamics) codes will be performed to optimise the instrumentation set-up (location, number of sensors). After the tests have been performed, the CFD tools will be validated on a series of experiments, including some involving passive or active ventilation. Finally, the CFD tools will be used to perform parametric studies and to identify worse case scenarios and how they can be mitigated (for example by design of passive or active ventilation).

BACKGROUND INFORMATION

The table below summarises past hydrogen leak hypotheses and dispersion experiments in confined spaces. The assumption is that the on-board computer is capable of shutting down hydrogen flow upon receiving a signal detecting a flow larger than 20 cubic feet per minute (CFM) flow, 'leak', when the vehicle is dormant. This leak rate corresponds to a fuel cell power output of about 50 kW It was found that with change in release speed (0.1, 0.2 and 3.4 m/s (corresponding exit diameters are 46, 33 and 8 mm respectively) there was a moderate variation in the horizontal hydrogen diffusion along the bottom surface and in the lift of the 4%+ combustible mixture 1 g/min is considered to be the maximum escape volume of hydrogen in the event of a fault. 0,5 g/s concerns less severe cases. Hydrogen is stored under cryogenic form. These values are based on hydrogen boil off.

No indication given on why these data have been chosen.

Table 2: Hydrogen leak cases in confined spaces extracted from the literature

Compared with existing experiments and data, DRIVE will investigate wider leak rates and release conditions spectrum with more elaborate measurement techniques, in terms of gas concentration and velocity and turbulence measurements. The new tests will be the most detailed and finely instrumented tests for the study of hydrogen leaks. The objective is clearly to produce data both for risk assessment purpose, and to validate CFD tools, which are now well recognised to be potentially the most accurate and reliable computational tool for assessing consequences of accident scenarios.

TOOLS

The development of a full-scale garage and a quasi nonintrusive (due to their small size) sensor network (catharometric measurement type) is currently in progress. Mass flow controller of various ranges will be used in order to control leak flow. Hydrogen or helium concentration will be measured with the help of the catharometric sensors grid. Non intrusive velocimetry measurements will be undertaken through particle image velocimetry (PIV) and Laser Doppler Velocimetry (LDV). Transparent walls will be mounted on the garage to allow measurements. Ventilation will be managed with the help of either an extractor or a fan. The dimensions of the garage are those of a typical European garage for a single vehicle, and it is fitted with an overhead pivoting door. The garage will be fitted with vents which can provide either passive or active ventilation or extraction.

Computational Fluid Dynamics tools will be used for pretest calculations, as well as to analyse the tests once the CFD codes have been completely validated. One of the CFD outputs that will be of most use for safety assessment is the time-evolution of the volume of explosive atmosphere (for example the volume of gas mixtures above 4% of H2). The effect of leak location, direction, impingement on nearby obstacles as well as presence or absence of ventilation on the evolution of this cloud will be investigated in detail.

HYDROGEN IGNITION BY VEHICLE COMPONENTS

OBJECTIVE

The objective of this work is to assess the ignition potential of some of the electrical and mechanical components and to identify best practices for the design and the positioning of vehicle components.

STEPS

Though not applicable to vehicles, the same strategy as the one of the ATEX 94/9CE [9] & ATEX 99/92CE [10] is followed. Basically, it consists in demonstrating that components have no ignition potential under normal circumstances whenever an explosive atmosphere can form accidentally.

The first step therefore consists in listing mechanical and electrical components in the vicinity of hydrogen systems. Then, some of them will be selected to undertake ignition tests in dedicated chambers. Based on results, recommendations will be made regarding the design and the location of the components.

BACKGROUND INFORMATION

In the course of this project, we have been looking at cross-experiences from natural gas vehicles (NGV) as well as from industrial vehicles that could accidentally drive into an explosive atmosphere (fork lift trucks).

Regarding NGV vehicles, no recommendation at all is found regarding protection or segregation of electrical equipment [11]. As far as forklift trucks are concerned (category 3 vehicle for type 2 zone), the EN 1755 [12] standard gives a few hints which include:

• minimum distance to prevent mechanical frictions or limit speed at which friction can occur (brakes, clutch,...), • bounding of all mechanical parts to ensure same electric potential, • enclosing of electrical equipment to limit combustible gas ingress whenever the forklift drives through an explosive cloud, • installing gas detection onboard forklift truck. A 10% LFL concentration triggers an alarm. A 25% LFL concentration stops the forklift, • and also, limiting maximum surface temperatures when in use. Now, looking at GRPE [START_REF]on Hydrogen/Fuel Cell Vehicles[END_REF] latest draft provisions, one could notice quite a few recommendations on electrical equipment. That includes:

• preventing hydrogen ingress into power supply connections where hydrogen leaks are possible (paragraph 14.11.4.), • providing sufficient insulation of electrical components to ensure that no current passes through hydrogen containing parts (paragraph 6.5.1)

• & ensuring that electrical connections and components in the gas tight housing are constructed such that no sparks are generated (paragraph 14.10.3.)

TOOLS

Tests will be carried out inside an explosion chamber dedicated to test electrical or mechanical equipment.

The picture below features a typical test chamber. So far, the following components have been selected for practical testing:

• the hydrogen compartment fan,

• the electric motor that drives the vehicle,

• the electrical converter,

• and the braking system.

Moreover, some non-conductive material components have been selected in order to check whether or not they can lead to an electrostatic ignition hazard.

Regarding early recommendations for the design of vehicle components in order to control ignition sources in normal use, the following can be proposed so far:

HYDROGEN COMBUSTION

OBJECTIVE

This work aims at defining maximum tolerable explosive volumes for various leakage environments and providing straightforward pressure/effect prediction rules for risk assessment. Test results will also be useful to evaluate the prediction potential of CFD tools.

STEPS

This experimental programme will first investigate pressure effects caused by the ignition of moderate and calibrated explosive volumes for various levels of confinement from free environment up to congested environment similar to those we can find onboard vehicles. Pressure prediction rules will be derived from these early tests. Then explosions will be carried out onboard vehicle following leakage flows and locations consistent with those found in the earlier work programme. These tests will also help us to evaluate the destructive potential of onboard vehicle explosions.

BACKGROUND INFORMATION

Although not wanted, leaks will inevitably occur onboard vehicles. It is therefore a necessity to work on a maximum allowable explosive volume with tolerable associated effects. Once this limit is set, it will be a significant input to size safety barriers for leak detection and interruption. So far, the only "tolerable explosive volume" we found come from the industry. The European guide document for the implementation of ATEX 99/92CE directive [10] indicates, independently of the combustible gas considered that:

• an unconfined explosive atmosphere should always be considered hazardous when its volume is above 10 litres, • and an explosive atmosphere in a closed room should always be considered hazardous when its volume is greater than 1/10 000 of the room volume.

Other work [15] investigated the limit of acceptable explosive volumes in natural gas turbine casings. The recommended safety criterion is that the natural gas flammable cloud volume should be less than 0.1% of the net enclosure volume. In addition to the above condition on the allowable size of a flammable gas cloud relative to the net enclosure volume, the flammable gas cloud volume should also be less than 1 m 3 in all cases, irrespective of the enclosure volume. Safety systems have to be designed (detection, ventilation) in order to insure that these limits are never exceeded. One should mention that people would not be present inside the enclosure volume but are expected to stand nearby. Proposed acceptable explosive volumes are not susceptible to cause casing rupture and blast injuries.

Examples above illustrated confined and unconfined explosions as well as explosion with and without direct exposure of people. These various cases will be taken into consideration.

Regarding existing data on explosion experiments for moderate and calibrated explosion volumes in more or less confined environment, the review has not yet started. However, similar experiments will be carried out by FZK 3 in the framework of the HySafe network.

For explosion onboard vehicles, we can mention experiments carried out by the Motor Vehicle Fire Research Institute USA [START_REF]IEA Task 19 meeting[END_REF] where they investigated hydrogen leakage in the engine compartment. They investigated various release rate and ignition delay. Test showed that the maximum engine compartment overpressure was 220 mbar. This maximum overpressure that caused the hood to bend was obtained for a 64 sec release of 51 g of hydrogen. Shorter released produced overpressure of 10 mbar to 152 mbar.

TOOLS Forschungszentrum Karlsruhe

These tests are planed for 2007. The experimental set up has not been designed yet. Tests will most probably be combined with those undertaken by FZK in the framework of the HySafe network.

HYDROGEN FLAME OBJECTIVE

This work aims on one hand at providing data on hydrogen flame length and on hydrogen flame radiation for some severe scenarios (significant leak under the hood, hydrogen escaping through the thermal fuse). Besides these tests, less severe cases will be investigated in order to study conditions under which a hydrogen flame cannot be sustained. Ease of ignition shall also be investigated for high and moderate pressures with various leak orifices. These latter cases address minor / non detectable leakage that do not cause any explosion hazard but could however cause a significant fire hazard whenever the vehicle is parked or driven.

STEPS

The work programme includes both an experimental and a numerical part. The first step will consist in selecting a set of realistic scenarios/situations to be investigated. The experimental set up for flame length and flame radiation has not yet been designed. Regarding flame length, both free and impinged jets will be looked at. Seeding will probably be used to visualise flames. As far as micro leaks are concerned, we will look at leak orifices most probably below 1 mm for various values of pressure.

BACKGROUND INFORMATION

It has been established experimentally that hydrogen discharges through circular orifices larger than a critical diameter sustains stable lifted flames irrespective of the reservoir pressure driving the release. At smaller diameter however, stable burning will only be achieved at operating pressures higher than a particular, diameter-dependant threshold [16].

Regarding vehicle related literature contributions, we can mention two practical contributions to the topic. First of all, we can mention the experimental work from the Motor Vehicle Fire Research Institute USA [START_REF]IEA Task 19 meeting[END_REF] where jet flames in the engine compartment have been investigated. Some more data was previously released by the Japan Automobile Research Institute [START_REF] Hayashi | Hydrogen Safety for Fuel Cell Vehicles[END_REF]. JARI compared for a given leakage rate (11.8 g/min for hydrogen and 28.6 g/min for natural gas/methane) critical diameter under which a gas flame was not sustained. They found out that the methane flame became no more viable with a rather large diameter of 2.00 mm or less. On the other hand, the hydrogen flame was sustained at the leak orifice even with a nozzle diameter of 1.0 mm. Authors concluded that the favourable stability of hydrogen flames is advantageous as a means to avoid explosion. Needless to say that the 1 mm orifice considered is rather large. Much smaller leak orifice could be expected without being noticed. They could eventually cause a fire hazard. It is therefore necessary to investigate leak orifices smaller than 1 mm. The DRIVE project will investigate these situations.

Moreover, this research institute also investigated the flame behaviour of hydrogen released from 350 bar hydrogen tanks. They found out that the hydrogen flame released upwards reached its maximum height of 7-8 meters in 5 to 10 seconds. This flame length is very significant and could cause severe hazards for cars occupants as well as for rescue services. It is therefore of a prime importance to provide advice on how this release should be dealt with (upward, downward under the vehicle...). The DRIVE project will also address this issue within this work programme.

RESULTS AND DISSEMINATION

The DRIVE project aims at investigating experimentally and numerically hydrogen vehicle related accidental scenarios in order to strengthen risk assessment as well as to promote safe hydrogen handling solution onboard vehicle. Three documents will be produced:

• the first one will address hazard quantification results and hazard quantification tools for hydrogen vehicles. Hazardous phenomena will be explained. Issues such as flame length or explosive atmosphere volume versus pressure and diameter will be detailed, • the second one will address best practices when using CFD tools to predict hydrogen behaviour when released accidentally or under normal situation, • and the final one will address best practices when handling hydrogen onboard vehicles. Its content will include both generic risk assessment as well as best practices for the design of hydrogen vehicles.

These results will be presented in the course of open seminars.

CONCLUSIONS

Field of investigation covers the all range of phenomena that can be encountered in hydrogen accidents from leakage, to dispersion, ignition and finally combustion. This programme aims at providing experimental and numerical results in order to provide realistic risk assessment and to be able to specify precisely expected hydrogen vehicles safety performances. DRIVE outputs will be turned into practical graphs to facilitate risk quantification. Recommendations on best practice vehicle design will also be drafted. Actually, topics such as maximum allowable explosive volume, control of ignition sources and location of hydrogen components will be addressed.

This project has just started. However preliminary reviews of existing experimental data and guidelines have been performed, to better define the expected results of the project. These reviews and early thoughts and findings represent important contributions to the elaboration of safety guidelines for hydrogen vehicles. We can without any doubt consider today that DRIVE outputs will be of a great help for designing safe hydrogen vehicles.

Figure 1 :

 1 Figure 1: Experimental set up for leak quantification

Figure 3 :

 3 Figure 3: Front view of a typical test chamber to test ignition potential of equipment EARLY RESULTS

Table 3 :

 3 State of the art design to control ignition sources for some key components

ACKNOWLEDGMENTS

Authors would like to thank the French National Research Agency ANR, and its hydrogen programme PAN-H, which financially supports this project.

[9] ATEX 99/92/EC -Equipment and protective systems intended for use in potentially explosive atmospheres

[10] ATEX 99/92/EC -Minimum requirements for improving the safety and health protection of workers potentially at risk from explosive atmospheres [11] Regulation No. 110 -Uniform provisions concerning the approval of: 1. Specific components of motor vehicles using compressed natural gas (CNG) in their propulsion system; 2. Vehicles with regard to the installation of specific components of an approved type for the use of compressed natural gas (CNG) in their propulsion system

[12] EN 1755 : Safety of industrial trucks -Operation in potentially explosive atmospheres -Use in flammable gas, vapour, mist and dust

[13] EN 50021 : Electrical apparatus for potentially explosive atmospheres -Type of protection "n".

[14] Guide de bonne pratique à caractère non contraignant pour la mise en oeuvre de