Guv Marlair

Margaret Simonson

Richard G Gann

ENVIRONMENTAL CONCERNS OF FIRES : FACTS, FIGURES, QUESTIONS AND NEW CHALLENGES FOR THE FUTURE

Keywords: fire, environment, emissions, organic pollutants

The effect of fires on the environment has been increasingly in the public eye since the chemical warehouse accident in the Sandoz facility in Schweizerhalle in November 1986. This paper presents a discussion ofthis accident together with a representative sample of other environmentally important case studies related to fires. Modes of interaction with the environment and potential transfer mechanisms are discussed. The impactof fire effluents in both the short and long terms and activities on the quantification of the environmental effect of fires are also presented. Some ofthe current environmental debates that are interacting withfire prevention and fire firefighting techniques are also discussed, outlining challenging remaining issues. Finally, insight on international action in response to these incidents and related standardisation activities under progress is presented.

INTRODUCTION

Community awareness of the fact that large fires may present dramatic and persistent adverse effects on the environment has been accentuated by a number of high impact incidents over the past half century, as indicated by a few review papers l i 2' 3 ' 4 ' [START_REF] Fowles | The ecotoxicity of Fire Water Runoff-Part I : Review of the Literature[END_REF] . Perhaps the most instructive example of these was the chemical fire in an industrial warehouse near Basel Switzerland in November 1986, best described in references ''. This fire presented major challenges in terms of fire fighting tactics, emergency response management, crisis communication with concerned nearby countries (France and Germany), air pollution in a highly urbanised area, and water pollution. Large amounts of extinguishing water contaminated by pesticides and other toxic chemicals ran off directly into the river Rhine, killing aquatic life for several hundreds of kilometres. Moreover, the environmental problems caused by fires go far beyond pollution by run-off waters as stated as early as 1994 by Hôlemann [START_REF] Holemann | Environmental Problems Caused by Fire and Fire-Fighting Agents[END_REF] . The serious consequences of these disasters have confirmed that the environmental impact of fires is a real threat that urgently needs to be treated by a more systemic approach. In particular, the hazard from the emission and re-deposition in the environment of some fire effluent components having carcinogenic or mutagenic properties, and sub-lethal exposures to toxic compounds are a matter of intensive debate. Hôlemann [START_REF] Holemann | Environmental Problems Caused by Fire and Fire-Fighting Agents[END_REF] previously pointed out some of the difficulties associated with this problem and the size of appropriate mitigation measures. However, we need to better understand the relationship between these phenomena, and develop scientifically sound tools for identification ofthe hazard, the assessment of risk, and the implementation of fire prevention and protection measures. Such work is just beginning within ISO/TC92/SC3 under its mandate to consider notjust the local effect of fire effluent on people but also its effect on the environment [START_REF] Cox | Developments on the Standardisation of Fire Safety within ISO[END_REF] . A very limited number of papers have focussed on the environmental issues of fires until recently [START_REF] Fprf | Proceedings of 'Fire Risk and Hazard Assessment Research Application Symposium[END_REF] . On the one hand, environmental issues of fires can be somewhat negatively summarised by reporting them in terms of a history of conflict among fire safety, health and environment quality conservation u . This view is largely supported by several examples such as the long term use of asbestos, or decades of use of fire resistant PCBs (polychlorobiphenyls) in electric transformers followed by PCBs being progressively phased out, fire fighter training on abandoned houses, soil contamination at fire training academies, wildland fire management, hazardous material incident responses, water conservation measures, halon replacements that are greenhouse gases, fire retardant chemicals that are used in furniture, cables and appliances, alternative fuels and increased use of plastic materials in the automotive industry. On the other hand, remaining "old problems" (such as contaminated water runoff) and emerging ones (determination of the degree to which fire effluents contribute to POPs, persistent organic pollutant, -production) need to be clearly identified, weighted and treated in the most relevant way. The challenge in the future is not to raise public awareness of the environmental impact of fires or the importance of fire prevention or mitigation ; but to improve the interaction between these facets of fire science to ensure that toxicity, eco-toxicity and fire safety are dealt with together in a single holistic approach. It is only through such an approach that we can optimise any fire related situation to ensure that neither is fire safety obtained at an unacceptable cost to the environment, nor is environmental safety obtained at an unacceptable cost to fire safety. This paper will provide some background to this discussion based on experience from some environmentally significant fire accidents, important modes of environmental impact and relevant legislation and standardisation activities.

THE SANDOZ FIRE LEGACY

On the 1 st November, 1986, at 00.19 hours a fire was discovered in the Sandoz warehouse (B956) in Schweizerhalle near Basel in Switzerland, simultaneously by traffic police and a Sandoz Ltd employee. Although the commander of the Sandoz fire brigade and several fire fighters were on the scene within minutes, the fire had already engulfed approximately one quarter of the warehouse and was spreading rapidly. Reinforcements were quickly brought in and one hour later 15 fire brigades and 200 firemen were in action. The warehouse contained some 1300 tons of organic chemicals, largely for agricultural use. Initial efforts were focussed on preventing the fire from spreading to neighbouring buildings and an adjacent open air barrel storage facility. Attempts to extinguish the fire with foam were ineffective and large quantities of water were used (up to 25 m V min being directed towards the central warehouse building). In total an estimated 20 000 m 3 of water were used in the mitigation and extinguishment activities. This water, highly contaminated with organic compounds, was then able to drain into the Rhine (through drains) and to seep into surrounding soil. Numerous studies have been made of this catastrophic warehouse fire and it is often cited as the first major fire to receive significant publicity focussed largely on its effect on the surrounding environment. This is no doubt due to a combination of factors, both scientific and political. The fire in itself did not cause significant air pollution over and above the levels of air pollution from other sources on a typical winter day, but did cause significant pollution of the Rhine river and the land surrounding the warehouse site. While the Rhine is an important central European river its pollution would perhaps not have received such international attention had it not served as the border between several countries. Thus, the environmental effects of an accident in Switzerland had immediate consequences for its neighbours (Germany and France) and subsequent consequences even for neighbours downstream. (Polluted water reached The Netherlands on the 13 th November). Indeed, all drinking water extraction downstream from the accident to the North Sea had to be temporarily shut down. This international aspect of the disaster has almost certainly heightened awareness of the accident and interest in monitoring its consequences. To understand all the environmental implications of that fire, the best reference is likely to be the special issue of Chemosphere*'. Worth noting is that the fire occurred in a highly urbanised area justifying some interesting screening investigation of sub-lethal exposure to carcinogenic and mutagenic species that could have been emitted by the fire, owing to the chemicals in storage. No evidence of such a threat was reported as the main conclusion in that particular case. While the recovery of the Rhine was possible within about 5 years its devastation during the initial period after the fire was significant. Several changes were made to German legislation as a direct result of this accident requiring the installation of catchment basins for run-off water surrounding large chemical storage facilities. Further, several European-funded research projects were initiated specifically to investigate the products from combustion of chemicals in storage facilities, in terms of emissions to the air, water and soil [e.g., the STEP, Toxfireand Mistral projects [START_REF]Industrial Fire III Workshop[END_REF] ]. Perhaps the single most important and positive results of the Sandoz fire, however, is the role it is playing in raising international awareness of the importance of fires as significant point sources of pollution to the air, water and soil. This has, in turn, promoted useful safety storage guidance documents that address such techniques as incompatible chemical segregation principles, limitation of stored quantities and requirements for fire water containment 13 ' 14 .

CASE STUDIES

A large number of fire catastrophes have occurred historically which have had a significant effect on the environment. The present presentation does not aim at an exhaustive collation of these accidents. Rather a small number of representative fires are discussed to illustrate the international nature of this issue and the ubiquitous nature of the environmental effects. Table 1 contains a summary of the fires briefly discussed. The chemical warehouse fire that was referred to worldwide ' , initiated debate of the environmental issues of fires, and was a source of progress in the area (see dedicated section). 10 years after this ecological disaster, eels that were restocked the Rhine were still not consumable. A chemical warehouse storing inorganic fertilisers suffered a major blaze due to self-sustained decomposition of 20 t of N-P-K products, releasing a massive toxic plume that eventually dispersed over the ocean 5 . 15,000 people were evacuated as a precaution. Afterwards, an experimental assessment of the plume toxicity confirmed the toxicity of the effluents 47 . Sherwin-Williams paint warehouse fire in environmentally sensitive area (see dedicated section) [START_REF] Copelandt | Sherwin-Williams Paint Warehouse Fire[END_REF] Known as the Protex fire, that chemical fire spread vigorously due to close proximity of flammable and toxic products. The plume zone was some 30 km long and 12 km large (fire plume zone) and provoked a major pollution of the river Brenne. Two of the numerous large-scale tire waste fires that have taken place in North America [START_REF] Poole | Scrap and shredded tire fires -Special report[END_REF] .Tire fires last several days to several months. They lead to massive air, soil and water pollution and to extreme difficulties in fire fighting. Evacuation of people is required in some cases, and fresh water is sometimes disrupted for long periods. Lessons learned led to the production of useful guidelines in Europe and North America 15 ' 17 . As a result of the Iraqi invasion of Kuwait, oil wells were systematically damaged with explosives resulting in uncontrolled gas and oil blowout fires of some 700 wells. The environment contamination by both oil leakage and fire gases was severe, in relation with the tremendously important and long lasting releases of pollutants that have affected air and soils (equivalent to some 7,400,000 bbls/day), according to NIST evaluation reported in 1994 3 ' [START_REF] Evans | Flame Heights and Heat release Rates of 1991 Kuwait Oil Field Fires[END_REF] A major pollution of the aquatic environment resulted from the runoff of some 16,000 m 3 of contaminated water used to fight the fire in the plant of a chemical manufacturer named Allied Colloid in Bradford : the UK reference in matter of pollution by contaminated water run-off in fresh water streams. The origin was the proximity of storage of incompatible chemicals. Polypropylene warehouse fire on a BASF chemical complex, raging for 12 hours, due to fault in the lighting system.

Wildland foes

Massive fire of a sulphur stockpile used by three different companies in industrial applications in the era of the South African embargo19 . A unique proof that fire toxicity may be a lethal threat, even in the open environment Paper mill containing PCB transformers. An foe accident with considerable difficulties in the emergency response management, that required the medical survey over 1 year of some 100 people (including journalists), liable to have suffered some exposure to PCDDs (dioxines) and PAHs (polycyclic aromatic hydrocarbons). A case study that reveals that until the phase out of a banned product is fully effective, the threat is remains. A very instructive report was produced on the aftermath of that foe and made public by the French Authorities [START_REF] Gabier | Unseen hazards of fire fighting[END_REF] Large release of toxic effluents arose from warehouse storing inorganic fertilisers (NPK), a quite similar scenario to the one which occurred in Nantes (1987) [START_REF] Fowles | The ecotoxicity of Fire Water Runoff-Part I : Review of the Literature[END_REF] Significant concerns worldwide, massive foes lasting weeks long, inducing multiple fire deaths and large property losses in urbanised areas, or causing sanitary problems or temporary closures of airports due to large levels of pollutants emitted on long periods (USA, Australia, Indonesia, Southern

Europe...)

Many of the events reported briefly in table 1 have been the subject of detailed studies reported in the open literature, following the fire investigations. This paper provides additional description of two of these, the Sulphur fire at Somerset West and the Sherman Williams Paint Warehouse Fire in Dayton, as they illustrate particularly well some of the specific issues of the environmental dimension of large fires.

The Sulphur fire at Somerset West (Western Cape Province in South Africa, December 1995) 2 -19 -20 ' [START_REF] Batterman | Estimation and Evaluation of Exposures from Large Sulfur Fire in South Africa[END_REF] This massive fire hit an impressive stockpile of sulphur, the size of which was a consequence of the local government's response to the anti-Apartheid sanctions. The raw material was a key product for three major companies producing munitions and fertilisers. Surprisingly, this fire has remained relatively unknown in the fire literature except on the local level, where the Ministry of the Environment 20 made the full enquiry report available to the public (Commission DESAI report). Indeed, this accident provides some important lessons for the fire community. In particular it reinforces the idea that industrial fires of non-hydrocarbon combustibles (i.e., those containing a significant amount of hetero-atoms in the organic chemicals involved or involving non-organic materials) may behave quite differently from hydrocarbon fires in terms of the nature of emissions and how they threaten the environment. In the early stages of this incident, the fire was wrongly identified as a bush fire, yet it emitted some 14,0001 of sulphur dioxide .

The fire was a tragic demonstration of shortcomings in hazard management and emergency response, leading to : disorganised evacuation, in a panic, of several thousands of people, congestion of all emergency services and transportation routes, agricultural impacts that ranged over a broad area extending to 30 km from the fire site, and last, but not least, SO 2 levels in the nearby Macassar town (30,000 inhabitants), that far exceeded the safety threshold over 20 h of exposure, resulting in multiple deaths in the open environment at distances quite remote from the fire site. Although the actual number of deaths attributed to this incident is controversial this does present a unique reference to such a threat, to our knowledge.

The Sherwin Williams Paint Warehouse Fire (Dayton, Ohio May 27 1987) M8 This major chemical blaze had to be faced by the concerned fire services and local authorities only 6 months after the Sandoz case, pioneering after a time of hesitation the use of the still controversial 'let it burn option'. The fire brigades were confronted with a fully engulfed fire, raging in a warehouse containing over 6 million litres of paint and other toxic chemicals located over the aquifer. The local source of fresh water was supplying one third of the 400,000 people living in the countryside. Due to the absence of any capacity for water containment, it was agreed that the environmental threat would have been more severe (in terms of deep water pollution) if extinguishing operations were used instead of allowing the fire to consume all combustible material and release pollutant emissions into the air. The property itself was estimated to be a total loss before this strategic decision was taken in full agreement with all stakeholders.

FIRE EMISSIONS AND TRANSFER MECHANISMS

The interaction between a fire and its surroundings or environment is best illustrated in Figure 1. This figure shows how fires effect the environment through:

-Direct gaseous and particulate emissions to the atmosphere (fire plume) Spread of atmospheric emissions Deposition of atmospheric emissions Soil contamination Aquifer contamination

This contamination can be due to emissions of numerous, time and product dependant effluents from the fire itself (primarily source term) or those associated with the fire brigade activities that may even influence the nature of airborne emissions 23 . The effect of these various emissions depends in part on the transfer mechanism (i.e., atmospheric emission of gaseous species or soil and aquifer contamination) and on the specific species (i.e., small gaseous compounds, large particles and the range of species in between). A wide variety of toxic effluents are generally emitted in fires. These effluents may follow a number of pathways to impact human and ecological receptors. Risk assessments may not be possible for all potential impacts but contingency planning should take account of appropriate "worst-case" scenarios. In assessing the potential environmental impacts of toxic releases from fires, the following major zones of impact are generally considered.

Fire zone

This area is defined by the direct fire damage and the corresponding emergency response. The primary response generally relates to preserving the health and safety of individuals who may be within this zone, with secondary consideration for the structure and its contents. The environmental impacts are typically less critical with minor exceptions.

Fire plume zone

The fire plume zone is an area over which the smoke/vapour plume from the fire disperses. Within this zone there is the potential for harm from inhalation of and surface exposure to the airborne toxic gases and particles within the plume. For intense plumes, there is also the potential for decreased visibility, although this is generally of little environment significance. PM10, airborne particles with a mass median aerodynamic diameter under lOum present an important potential environmental problem both due to their direct effect on the respiratory system and due to their transport of other potentially carcinogenic organic species (e.g., polycyclic aromatic hydrocarbons, dioxins and furanes).

Both local topography and meteorological conditions (wind speed and air stability characteristics) have an influence on the characteristics of dispersion and the extent of the fire plume zone. Short-term environmental impacts are most significant in this zone. Valleys, basins, high buildings and street canyons, adjacent to or surrounding the fire can effect the dispersion of the plume. Low wind speed, temperature inversion and conditions that promote rapid plume grounding all limit plume dispersion. The combined effects of topographical features and meteorological conditions that result in restricted dispersion are generally additive and result in higher air pollutant concentrations within the fire plume.

As stated by Gann et al. 34 , in homes fires, far more occupants are likely to be exposed to fire smoke than those actually suffering consequences, either immediate to the fire incident or afterwards. Thus it might appear that single smoke exposures outside the immediate fire vicinity (see fig. 1) might seem inconsequential. However, single exposure to the plumes from atypical fuels (e.g. chemical fires involving pesticides [START_REF] Marlair | Experimental Evaluation of the Fire Hazard of Organophosphorous Insecticides by use of Various Test Methods[END_REF] , high sulphur content materials, fertilisers, pool chemicals, etc) poses special risks and repeated exposure to sub-lethal concentrations of fire gases have been reported as potentially responsible for chronic diseases or specific pathologies among firemen populations [START_REF] Rechenbach | Fires today : risks and protection for fire-fighters[END_REF] .

Plume deposition zone

The fire plume is affected by complex thermal, mechanical and chemical transfers that leads in turn to final sedimentation processes as mentioned in figure 1. Atmospheric releases may thus also affect terrestrial and aquatic environments through deposition of pollutants from the fire generated plume. Many thermal degradation products can condense on, or be adsorbed by, the soot particles and be transported with the smoke. There may also be deposition on structures, leading to corrosion, particularly from acidic decomposition products. These effects on building materials, machinery and electrotechnical equipment are much like those from acid rain. Health and ecological damage can arise from exposure to deposited pollutants through a variety of pathways including aerial deposition to water and land and accumulation in the food chain and subsequent consumption of contaminated food.

Water runoff zone

As exemplified in a number of case studies, fire-fighting water runoff presents the major potential threat to the aquatic environment from toxic releases from fires in the short term although some threat to the aquatic environment is present through deposition of airborne pollutants into aquatic receptors. The threat from fire-fighting water runoff is strongest where runoff waters directly enter aquatic habitats in surface waters (e.g., rivers, streams, ditches), within the immediate vicinity of the site, and where levels of toxic releases are particularly high.

Short-term impacts may arise where fire-water runoff infiltrates drinking-water supplies during or immediately following a fire. The risk is higher local to the fire, where the runoff water is potentially most highly contaminated with ash / soot / decomposition products, and relatively undiluted. The likelihood of such water being directly ingested is limited, but such surface water bodies do represent a potential hazard. Impact on the aquatic environment will be exacerbated where the contours of the land are such that runoff is conducted directly to surface waters (non-contained) and where dilution effects are limited (low flows, small water volumes within the receptor, and a short source-to-receptor pathway). Toxic, carcinogenic, and exotic organic compounds in surface waters can directly affect freshwater habitats and species. Marine habitats and species may also be affected, though owing to dilution, the impacts are likely to be diminished.

The assessment of the level and area of contamination of the various eco-systems as a follow up of any accidental emissions is a quite complex procedure and thus it is rare that such studies have been performed so far in the fields. Reference 36 provides good reference material concerning this aspect.

ENVIRONMENTAL IMPACT OF FIRE FIGHTING TACTICS AND FIRE PREVENTION

Challenging issues as regard fire safety and the fast growing environmental concerns have sharply increased since the early 1990s. Several of the major activities are discussed below:

The progressive phase out of halons Since the 1950s, there had been great expansion of the use of the halon (halogenated hydrocarbon fire extinguishing fluids. These chemicals quench flames with high efficiency, low toxicity, and no residue. They thus became the agent of choice for protecting sensitive (e.g., computer rooms) and valuable (e.g., aircraft) properties.. The most prevalent fire suppressant halons are also potent depleters of stratospheric ozone. They are no longer in production and their use has been restricted to those few applications where no alternative yet exists. Replacements have been developed for most applications. These generally dilute and cool the flame environment below the flame-propagation limit, without the strong chemical action of the halons..

Water containment basins

The problem of water basins for run-off water in the event of a fire is internationally recognized and some industrial countries such as Switzerland, Germany, France, the Netherlands, and the UK, as well as some international groups of experts from the chemical industry, insurance and fire service and administration sectors have provided useful guidelines, and sometime controversial recommendations. In particular the sizing of the containment basins as well as the overall design and management of containment systems have received attention in some countries (e.g., references. [START_REF]Best Practice Guidelines for Contaminated Water Retention and Treatment Systems[END_REF] -44 -45 )5 although in a quite diverse manner.

Many industrial sites in the chemical industry are equipped with containment basins. However, to date, existing regulatory texts (the existence of which is patchy at best) are based largely on "magic" compliance rules as no universally recognized fire engineering technique has been made available. This has resulted in, as exemplified by Vandonkelaar 7 , sizing rules giving containment basin capacity characteristics that vary by up a factor of 10 for a given industrial facility, according to location of the facility. France has initiated a number of initiatives to update current technical knowledge to promote a more engineering sound approach, both on a National and international level.

Fire fighting foams

On 16 th May 2000, 3M™ Corporation, in agreement with the US Environmental Protection Agency (EPA), announced officially its decision to cease marketing its AFFF series of firefightingfoams, a fact which illustrates the voluntary code of practice more popular in the US. The decision was justified by the potential long term environmental impact of a single substance PFOS, perfluoroocanyl sulfonate, a manufacturing process intermediate bound to the so-called Simons' electro-fluorination method. 25 Useful updates on the environmental issues of all firefighting foams (including FP/FFFP and AFFF) have been published by R. Harman [START_REF] Harman | Focus on foam[END_REF] and W. H. Ruppert et al , together with the regulatory frameworks pertaining in this matter in Europe and the US. This decision by the manufacturer has created a void for those applications (e.g., liquid fuel fires on airport runways, ship decks) where these foams are used.

It is now clear that in summary one can make the following statements :

The water polluting effects of a firefighting foam must be considered as a condition for its use. Indeed, none of the available firefighting foam can to be considered as environmentally benign Due care should be taken when running training operations with foams, to avoid their release into the environment It is clear that fire protection/suppression benefits are too great (in particular for type B fires) to phase out foams Environmental impacts of foams must be mitigated, new formulations are desirable to fill the void, but will not be the complete answer.

Flame retardants and the environmental issues

Over several decades, a variety of flame retardant (FR) chemicals have been developed to lower the ignitability and flame spread performance of both plastics and natural materials used in construction and furnishings. The widespread use of these chemicals has led to significant reduction in the number and severity of unwanted fires, and thus sustainable development of flame retardants production and use remains a key issue. However, concerns have been raised concerning a variety of FR chemicals (e.g., halogenated -brominated as well as chlorinated-FRs, antimony trioxide, etc). Recently both the State of California and the European Union have announced required phase-outs of two brominated flame retardant (BFR) groups : pentabromodiphenyl ethers and octabromodiphenyl ethers. Belonging to the same family of BFRs, Decabrominated diphenyl ether (see figure 2), which is fully brominated is currently extensively used in the cable industry, in particular in North America. It is also under consideration for restriction.

There is at present no consensus regarding any health and environment significant issues with this FR, justifying the additional studies that are underway to clarify remaining uncertainties 30 ' [START_REF] Harriman | Environmental Challenges and Materials Restrictions in Coated Wire and Cable[END_REF] . Much of the debate surrounding BFRs has originated from massive accidental (and non-fire related) exposure to PBBs in 1973 2 through the food chain, that occurred in Michigan (USA). A useful document [START_REF] Beard | Flame Retardants -FAQs[END_REF] was recently published that provides a good overview of technical and societal aspects pertaining to FR chemicals, in general. A more scientific overview of the current understanding issues and remaining challenges on current BFRs in use has been provided in the special issue of Chemosphere 2 . Other papers of interest are those of E.Harimann et al [START_REF] Harriman | Environmental Challenges and Materials Restrictions in Coated Wire and Cable[END_REF] and G. L. Nelson 32 , both presented at a recent FPRF symposium. Extensive reviews of toxicological properties of several flame retardants are underway, in particular in Europe, as a result of the legislation. Figure 3 illustrates the complexity of appropriately addressing the question of effective exposure to chemicals in our environment and in particular flame retardants, reflecting the whole life-cycle of the product, including the accidental exposure through fires.

Total human body burden

Fire LCA models for for other LCA studies about FR products

From the extensive discussion preceding and following this legislation, it is clear that addressing the environmental health and safety issues of flame retardants while maintaining high firesafety performance is no simple and straightforward process. Unfortunately, much of the debate has been politicised and little information was initially available to make a quantitative comparison between flame retardants that were questioned and alternatives (whether these were alternative flame retardants or entailed a reduction in the fire performance of the material used in specific products).

In 1998 the first attempt was made to define a quantitative model to establish the environmental impact of choosing between high fire performance or low fire performance products, or between different flame retardants [START_REF] Simonson | The incorporation of fire considerations in the life-cycle assessment of polymeric composite materials : a preparatory study[END_REF] . The Fire-LCA model is based on a holistic approach to calculating the environmental impact of fires using a life-cycle assessment model supplemented by emissions from fires and the cost of replacement of products involved in fires [START_REF] Simonson | a life-cycle assessment (LCA) model for cables based on the fire-LCA model[END_REF] . The model has been applied in three separate case studies and shows the importance of including the environmental impact of fires when calculating the environmental impact of the use of flame retardants. Indeed, a product's impact on the environment in a general way must be considered for its entire life cycle, as stated by Ahrens et al [START_REF] Ahrens | Fire and the Environment: Issues and Events[END_REF] .

EXAMPLES OF THE TECHNICAL AND REGULATORY FRAMEWORK THAT AFFECTS THE FIRE PROBLEM

The Stockholm Convention on Persistent Organic Pollutants (POPs).

The Stockholm Convention is a global treaty to protect human health and the environment from POPs, which are described as chemicals that remain intact in the environment for long periods, become widely distributed geographically, accumulate in the fatty tissue of living organisms and are toxic to humans and wildlife. POPs circulate globally and can cause damage wherever they travel. In implementing the Convention, governments will take measures to eliminate or reduce the release of POPs into the environment.

UN Convention on the Transboundary Effects of Industrial Accidents

Since the early 1990s the United Nations Economic Commission for Europe has concentrated its efforts on preventing industrial accidents and especially their transboundary effects.

Major accidents at Seveso in Italy in 1976 and Basel in Switzerland in 1986 caused significant environmental damage. In Seveso, the release of dioxin contaminated the surrounding area, and in Basel, the pollution of the Rhine ~ in France and Germany, as well as in Switzerland ~ following a fire at a chemical warehouse killed thousands of fish. The objectives of this global convention are to protect human health and the environment from persistent organic pollutants. The Convention contains six annexes which form an integral part of the document. Annex C lists POPs which may be produced and released unintentionally as the result of combustion processes.

Seveso H Directive (96/082/EEC)

The Seveso II Directive applies to a wide range of activities including the storage, use and manufacture of large quantities of dangerous chemicals. It places additional responsibility on operators of establishments to document their major-accident prevention policy and to ensure that it is properly implemented. Operators are also required to produce a safety report to document those procedures put in place to prevent major accidents or, in those instances where accidents have occurred, to limit their consequence for man and the environment. Such safety reports shall be made publicly available.

Montreal Protocol

The Montreal Protocol on Substances That Deplete the Ozone Layer is a landmark international agreement designed to protect the stratospheric ozone layer. The treaty was originally signed in 1987 and substantially amended in 1990 and 1992. The Montreal Protocol stipulates that the production and consumption of compounds that deplete ozone in the stratosphere-chlorofluorocarbons (CFCs), halons, carbon tetrachloride, and methyl chloroform-are to be phased out by 2000 (2005 for methyl chloroform). Some 180 countries have ratified the Protocol at this time.

Precautionary Principle

The Precautionary Principle is generally defined in terms of the 1998 Wingspread Statement: "When an activity raises threats of harm to human health or the environment, precautionary measures should be taken even if some cause-and-effect relationships are not fully established scientifically."

One of the most important expressions of the precautionary principle internationally is the Rio Declaration from the 1992 United Nations Conference on Environment and Development, also known as Agenda 21.

The declaration stated that in order to protect the environment, the precautionary approach shall be widely applied by States according to their capabilities. Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation. Nonetheless, the subjective nature of this principle hampers its uniform and egalitarian application.

EPA reglations 40 CFR Part 82, subpart A, Subpart E, Subpart G and Subpart H 39

These texts, in accordance with the Clean air Act, sets the rules as regards the problem of the ozone depletion process (e.g. phase out of halons)

STANDARDISATION ACTIVITIES BS 7982

In response to several incidents in the UK in the 1990's (in particular the Cleveland warehouse fire in 1995) the British Standards Institution (BSI) committee responsible for developing standards on the burning behaviour of plastics initiated [START_REF] Purser | Assessment of Environmental Hazards from Fires and Draft Guidance in British Standards[END_REF] the development of a standard to categorise the environmental impact of such events. The first version of the standard (BS7982) was made available for public comment in 2000 and all comments were taken into account before a final version was published in September 2001. This standard is intended to be a ready reference both on information and guidance pertaining to large scale fires involving plastics. It does not provide any guidance on how to quantify the environmental impact any given fire has had after the fact.

ISO TC92 SC3

Traditionally ISO/TC92/SC3 has focussed on the effect of fires on humans. This is leading to the creation of several standards determining and defining the toxic effect of fire effluents, and using that information in a fire hazard or risk analysis. Recently 9 , the mandate of this sub-committee was extended to include the effect of fires on the environment. In October 2002 a workshop was held at SP Swedish National Testing and Research Institute in Boras entitled: "Fire Threat to the Environment" [START_REF] Gann | The ISO TC 92 SC3 Initiative on Fire Threat to the Environment[END_REF] . In this workshop the delegates identified some general principles to guide possible ISO TC92 standardisation activity in the field.

• The focus should be on the consequences of large unwanted fires, such as in industrial buildings and other large occupancies, rather than the consequences of small individual fires and combustion in incinerators or power stations.

• While fires may effect the environment in many ways SC3 can only be concerned with aspects of this environmental effect that are appropriate for standardisation.

After the meeting in Boras a Task Group (TGI) was set up and commissioned to bring forward one or more topics for further development. This Task Group has met on two occasions in conjunction with TC92/SC3 meetings to define the best path forward. Presently work is ongoing in two specific areas: a) the creation of a Guidance Document on the Environmental Impact of Fires; and b) the creation of a Guidance Document on the Sizing of Water Basins. It is expected that these will lead to new work items within a year, resulting in Technical Specifications or Technical Standards.

CONCLUSIONS

Environmental concerns arising from human activities have long been identified in many areas. Fires and fire safety issues are no exception. The scientific knowledge to support decision making processes in the trade-offs between local safety and global environmental preservation is still limited and requires further and urgent attention. As is evident from the information presented in this paper, potential environmental concerns associated with fires are diverse. Some control over the environmental effect of fires has been obtained with variable success through national and/or international regulation and voluntary codes of practice. Since some of the fire-generated environmental effects cross national boundaries, there is a real challenge in the field for international standardisation committees, such as ISO, to establish consensual approaches and appropriate tools to address these issues. Such an effort is now underway in ISO TC 92 SC3, Fire threat to People and the Environment.

Figure 1 :

 1 Figure 1: Emission pathways from fires.

Figure 2 :

 2 Figure 2 : Structure of Deçà bromodiphenyl ether, one of the PBDEs in extensive use

Figure 3 :

 3 Figure 3 : A Holistic approach for the assessment of human body exposure to chemicals (adapted from Wenning's paper 30 )

Table 1 : A selection of important case histories with established environmental outcomes.

 1

	Date	Place	Comments
	1962	Centralia, USA	Coal mine fire, burning continuously since 1962. At that time the local
			population was some 1100 most of them had to relocate progressively.
	Nov. 1986	Basle,
		Switzerland
	Oct. 1987	Nantes, France
	June 1987	Ohio, USA
	June 1988	Near Tours,
		France
	Feb. 1990	Hagerville,
	&	Ontario,
	May 1990	Saint-Amable,
		Quebec,
		Canada
	1991	Kuwait
	July 1992	South Bradford
		(UK)
	Oct. 1995	Wilton (UK)

Table 1 A selection of important case histories with established environmental outcomes (cont'd)

 1

	Date	Place	Comments

  They are either mixtures of inciting gases (N 2 /Ar/CO2), or single gases interfering with the combustion reactions like C 3 HF 7 (HFC 227 ea), CHF 3 (HFC 23) or C 4 F 10 (FC 3-1-10)48 . Significant problems were anticipated and mitigated to foster the sustainable protection of property without compromising fire protection primary goals. Indeed, existing alternatives to halons no longer contribute to the ozone depletion process, i.e., their ozone depletion values (ODP) are zero. However, they are contributors to global warming and may present other adverse potential effects to the environment due to their environmental persistence. (See table 2.)

Table 2 :

 2 halon 1301 and some commercial alternatives : environmental parameters

		ODP	GWP	Atmospheric
			(100 years vs CO2)	lifetime (years)
	Halon 1301	16	4900	77
	HFC 227ea	0	2050	31
	FC 3-1-10	0	5500	2600
	HFC 23	0	9000	280

Tewarson A. & Marlair G., "Liquids and chemicals", Chapter 8 in C. Harper's (Ed) 'Handbook of building materials for fire protection', Me Graw Hill, ISBN 0071388915, 2003, p8.1 -p8.43

Aresu de Seui H. , "Instructive Fire", Sandoz in Schweizerhalle (Switzerland) (In French), Revue Belge du feu,


C Lagny

Z Pokryszka

M Prince

Modeling of Gas Extraction from Closed Coal Mines

The closed coal mines carry on releasing firedamp. In some cases, the quantity of gas released is not negligible and it can induce an overpressure in old works. A means to avoid hazards related to these gas emissions at the surface is to put in drainage installations and to keep the pressure of the underground reservoir under the atmospheric one. This practice has been used in several mines in France like in the Lorraine basin. A mathematical model has been developed by INERIS in order to improve operation of such installations. This model needs to determine 4 main parameters of reservoir. After its calibration, it is possible to forecast daily variations of pressure and methane content in drained gas as a function of daily extracted gas flow rate. Validations were made for several years. This model is able to evaluate firedamp quantity which may be extracted for a given period and to characterize the extraction conditions allowing an optimal production and its durability.

INTRODUCTION

One way to prevent efficiently firedamp migration from closed mines towards the surface is to extract gas and keep the old mining works in depression. This partial depression of underground reservoir can be obtained by means of global industrial gas drainage from the surface. Some installations of this kind exist in France in Nord-Pas-de-Calais and Lorraine coal basins. One of those operates in Saint-Charles closed mine located in the Lorraine basin, in the East of France (figure 1). This site was closed down in June 1991 mainly with closing of two shafts (Saint-Charles 1 and 3). The gas extraction installation is connected to the reservoir using pipelines through the old shaft Saint Charles 2 closed by a concrete dam. This site is isolated from nearby workings. It is still in exploitation with a mean methane volume of 10'106 m3 extracted each year. Each day, the gas exploitation data are registered:

-standard gas rate flow; methane content; reservoir pressure (measured in shaft head) ; atmospheric pressure.

This global firedamp drainage needs a good operationplanning. Indeed, after a temporary or permanent stoppage of the gas drainage, the reservoir pressure increases up to an equilibrium pressure greater than the atmospheric pressure. As a result, gas can escape uncontrollably to the surface. The analytical modeling can help in an optimal and safe management of industrial gas drainage from the surface.

PRESENTATION OF THE MODEL

Principles of the model

The old mine workings with the entire strata volume destabilized by exploitation are assumed to represent a firedamp reservoir. This reservoir will be of given volume, VR, but defined limits or strata will not materialize it. Usually, the volume V R corresponds to the residual volume of exploitation cavities and spaces due to neighbor strata cracking and porosity.

The firedamp is stored in free form in this volume, and principally under an adsorbed form on the coal seems. This reservoir will be connected to drainage surface installations through old shafts or drainage boreholes. In such installations, the reservoir pressure value, the quantity of the captured gas and its methane content are usually registered.

The pressure of this volume will vary with the outgoing flow rate of mine drainage and the "produced" gas flow rate.

The "produced" gas flow rate is the contribution of two phenomenon which are:

incoming flow of firedamp desorption, QD incoming flow of atmospheric air, QA QD is regarded during a rather short period of time as a decreasing linear function according to the pressure within the reservoir. By introducing the parameters a and P, QD is equal to:

(1)

QA is related to the depression of the reservoir relatively to the atmosphere, noted AP, by the following law:

AP=RQA'(2)

with R, equivalent aeraulic resistance of reservoir cover strata and %, coefficient; value of this coefficient is 2 for a turbulent flow and 1 for a laminar flow.

Assumption is made on the flow laminar nature (Darcy flow). By introducing parameter y, it is then possible to write:

QA=YAP (3)
So, the total incoming flow of gas is the sum of the two flows and is expressed as:

(4)

with: a, the firedamp desorption capacity depending on the reservoir pressure (3, the firedamp desorption capacity independent of the reservoir pressure Y, th6 atmospheric air inflow capacity of the reservoir.

Modeling

Calculation of the pressure in the reservoir

The calculation of the pressure variations is possible with the knowledge of:

-the drainage mine gas quantities (measured data) -the incoming gas quantities (formula 1 and 3) -the evaluation of the reservoir volume, V R This assessment reiterated with a given time step permits a dynamic modeling of the pressure evolution within the reservoir.

Calculation of methane content in drained gas

The same method is used to model methane content of the drained gas. The methane content in the drained firedamp is assumed to be equal to real seam value (usually 100 % on the studied coal deposit conditions). Then, a mass balance is made between firedamp desorption and drained methane quantities (based on measured data).

Calibration and initialization

In a first step of modeling, the model needs to be calibrated. These validation consists in the determination of 4 parameters of the reservoir: a, p, Y and VR (see §2.1), using the past experimental data.

To ensure this validation, the calculated and the measured parameters (pressure of the reservoir and methane content in drained gas) are compared.

The parameters are considered as satisfying when the absolute average error between measured and forecast data is below to 10%. However, attention must be paid on the type of measured data used for calibration. For example, periods of drainage stoppage are not appropriate to validation of methane content calculation. Indeed, in this situation the methane content measured in the connection devices between the reservoir and pumping station may not be as representative of real reservoir methane content as during an extraction period.

The comparison of the data can require another calibration of the parameters and a new initialization of the calculations. The model parameters have to be adjusted until the less discrepancies are obtained between the measured and calculated results.

Kind of modeling

The knowledge of the reservoir's behavior and particularly its capacities of methane production is of prime interest for the operator. This knowledge can be improved using the model by simulation of various operation situations, for example: -reservoir response to gas extraction: this type of information can be useful for the operators to understand the long-term behavior of the reservoir at a given and periodic rate of exploitation. It will be useful to determine the production capabilities of a reservoir;

-reservoir pressure evolution after temporary or permanent gas drainage stoppage: the application of the model is expected to forecast the time necessary for an increase of pressure within the reservoir up to the atmospheric pressure. This information is essential for safe management of firedamp reservoirs, since it gives the period of drainage cutoff collection not to be exceeded.

EXAMPLES OF MODEL APPLICATION

In the past, the model has been validated and used with a good result on some closed mines drained reservoirs in the French coal basins (Couillet et al.

1998).

In this paper, some examples of model application on the case of Saint-Charles reservoir in Lorraine coal basin (see § 1.2) are presented.

Calibration

For this reservoir, the first calibrations of the model were operated in the previous study using the operating data of 1995and 1996(Couillet, 1998)). Table 1 shows the value of the parameters determined for that period. Table 1. Saint-Charles reservoir. Parameters determined for year 1995.

Parameters

A detailed analysis (CECA 2003) using the new registered data from the period 1997-2002 has shown that the characteristic of the reservoir did not change a lot even after 7 years. It must be specified that in this area, water rising has not yet started, so reservoir volume is unchanged. Methane desorption capacity and air inlet characteristics did not change really too.

The preliminary modeling of reservoir pressure and methane content in drained gas, using the reservoir parameters from 1995, has shown very limited discrepancies between calculated and measured values. Thus, the calibration of the model and new evaluation of reservoir parameters was not necessary to obtain a good forecast of the pressure and methane content So, parameters determined in 1995 were used to forecast the reservoir behavior in the future.

Modeling of the behavior in the gas extracting phase

The simulated gas production program predicted by operator are: collected gas flow of 1.110 m/day during operating periods (9 months) followed by a cessation of drainage for three months.

Two configurations were considered: -an optimistic forecast -a pessimistic forecast

The optimistic forecast consists on taking exactly all parameters as defined in table 1. The pessimistic forecast consists on taking all parameters as defined in table 1, except P (firedamp flow rate). It is in fact possible that desorption capacity of reservoir decrease in the future. Following this hypothesis, the desorption flow rate is taken equal to half the value defined in table 1 (P = 10 000 m 3 /day).

Methane content and pressure were modeled. Only the results relative to the optimistic forecast are presented on figures 2 and 3. It can be seen that reservoir pressure reduces quickly after drainage beginning. Methane content drops quickly and remains below 50% even in the second year of operation. This level of methane content in collected gas is just sufficient for drainage continuation, but operating margins are low. In the case of the pessimistic forecast, methane content is much lower. It quickly drops below the limit of 30%. In this situation, continuous exploitation of the reservoir is not possible.

These simulations show that methane content in the captured gas can drop until it is too low to operate the system in safe conditions. This predicted rate of exploitation will not necessarily be reliable in the long term.

Other simulations have to be carried out so that the capacities of the reservoir can be used satisfactorily, with reduction in the collection flow or prolonging stoppage periods.

Study of the cessation of gas drainage

Pressure variation after the cessation of gas drainage was modeled taking the initial pressure equal to the pressure that occurs in the reservoir during a stable pumping period. The simulations carried out indicate (Fig. 4) that reservoir pressure can increase rapidly after firedamp drainage stoppage.

In one month, reservoir pressure becomes higher than the atmospheric one. In this situation, there is a risk that gas could rise to the surface uncontrollably. This information must be taken into account in the planning of duration of periodic exploitation stoppages. The research carried out at INERIS resulted in a reliable and appropriate method for firedamp drainage modelling from die closed mines reservoirs. The method has already been applied in an operational manner for several French drainage installations. The results of the simulations carried out indicate that analytical modelling is a very useful tool for improving our knowledge of firedamp reservoirs behaviour and for optimising the gas drainage processes.

The methodology is intended to forecasting of drainage parameters (reservoir pressure and methane content) in the function of planned level of collected gas flow rate.

It can be also used for predicting reservoir pressure evolution after periodic or definitive drainage stoppage. In the case of studied firedamp drainage site from Lorrain coal basin, the simulations carried out show that the reservoir pressure increases up to an equilibrium pressure greater than the atmospheric pressure about 1 month after drainage stoppage.

ACKOWLEDGEMENTS

FigureFigure 3 .

 3 Figure 2. Modeling in the pumping phase -Reservoir

  Figure 4. Cessation of gas drainage -Reservoir Saint-Charles -Reservoir pressure


Jon P Busby

Gloria Senfaute
email: senfaute@mines.u-nancy.fr

Jean Christophe Gourry
email: jc.gourry@brgm.fr

James Lawrence

Stig A S Pedersen

Rory Mortimore
email: r.n.mortimore@bton.ac.uk

Mr

Developing Tools for thé Prédiction of Catastrophé Coastal Cliff Collapse

The érosion of coastal cliffs is inévitable. The cliff collapses are a hazard, a problem for coastal land use planners and limit thé use of thé coastline as an amenity. Techniques to increase our knowledge of coastal cliff failure and provide pre-cursors to impending collapse are presented. The rock mass cracks before a collapse and thé cracking générâtes high frequency seismic signais. An increase in emitted seismic energy has been recorded on accelerometers, in boreholes within a cliff, during thé fifteen hours before a cliff fall. Comparison of thé seismic signais with those generated in thé laboratory has identified a number of collapse mechanisms that occur during différent phases of thé fall. A second technique assumes that in cliffs composed of a highly fractured rock, any sub-vertical fractures will gradually dilate with time before a collapse. The electrical résistance of thé rock varies with azimuth reflecting thé dominant fracture orientation. A factor of anisotropy, calculated from thé measurements, was found to change dramatically due to a cliff fall. Large values of anisotropy prior to thé fall were interpreted as évidence of dilating fractures. In addition, thé research has demonstrated thé existence of a cliff parallel fracture adjacent to thé cliff edge. It is likely that cracking within this fracture set is responsible for thé seismicity and thé variations in thé measured anisotropy. Laboratory analysis has identified a significant weakening of thé rock due to sait crystals within thé matrix. The intégration and implications of thèse results are discussed.

INTRODUCTION

The érosion of nard rock cliffs is inévitable and to-date it has been considered to be relatively unpredictable. A large proportion of thé European coastline is subject to érosion and cliff récession. A considérable body of data has been collected on thé nature and lithology of coastal cliffs that has enabled geologists and engineers to develop a better understanding of cliff collapse mechanisms and thé factors that déterminé rates of érosion. The only measuring tools commonly implemented are displacement transducers and inclinometers used to detect movements of blocks. However, thèse techniques cannot be used at large spatial scales because they are too expensive and they monitor only single blocks or a small area. There has been very little research into physical property changes within thé rock mass behind a cliff face prior to collapse. If any such changes can be quantifîed they could be used as pre-cursors to impending collapse.

It is to be expected that in cliffs composed of a highly fractured rock such as chalk, any sub-vertical fractures near thé top of thé cliff will gradually dilate with time. The downwarddeveloping dilatancy will alter thé stress régime within thé cliff until a shear is initiated that séparâtes thé base of thé tension fracture from thé cliff face. This fresh crack will generate high frequency seismic signais known as acoustic crack émissions. An increase in emitted seismic energy would be expected as a collapse approaches.

Since fractures often occur in sets with a preferred orientation they impose anisotropic physical properties to thé rock mass. It has been shown that thé apparent resistivity of thé rock will vary with azimuth reflecting thé dominant fracture orientation. A factor of anisotropy can be calculated from resistivity measurements collected on thé cliff top that would be expected to vary with time if thé fractures are dilating.

DATA COLLECTION

Developing large scale monitoring tools to predict coastal cliff collapses was thé main aim of thé current study. It was undertaken by a collobo-rative project, PROTECT (PRediction Of The Erosion of Cliffed Terrains) that was supported by thé European Union 5 th Framework Reseach and Development Programme. The project, involved nine partners from five différent countries [START_REF] Busby | Can we predict coastal cliff failure with remote, indirect measurements[END_REF].

Five test locations were established on chalk sea cliffs in order to collect microseismic and apparent resistivity data over a two-year period. Thèse were at Beachy Head and Birling Gap on thé East Sussex coast of thé UK, Mesnil-Val on thé Normandy coast of France and two locations on thé island of Mon, at Mons Klint, on thé Baltic coast of Denmark.

Geological description of thé test locations

The cliff at Beachy Head is composed of Seaford Chalk in thé upper part of thé cliff, underlain by Lewes Nodular Chalk. Seaford Chalk is characterised by sub-vertical fractures with mapped dominant fracture orientations of 70° and 150°( relative to British National Grid co-ordinates) The site is on a westerly facing slope that has undergone deep periglacial weathering that might hâve created randomly orientated fractures near surface and a variety of dissolution features. The site is on thé northerly limb of thé Beachy Head Anticline and dips at 15° to 20° to thé north-west. The Birling Gap site is approximately 2.5 km west from thé Beachy Head site. Due to thé northwesterly dip of thé chalk thé Seaford Chalk that is exposed at thé top of Beachy Head is found at about 20 m below thé top of thé cliff at Birling Gap. The entire cliff is composed of Seaford Chalk and is characterised by sub-vertical fracturing. The strata at Birling Gap are approximately horizontal.

The cliff at Mesnil-Val is composed of Lewes Nodular Chalk. The fracturing is sub-vertical and two conjugate fracture sets hâve been mapped striking at 30° and 127° (relative to l'Institut Géographique National grid). The south-facing slope of thé research site has been subjected to some periglacial weathering. This has resulted in a number of linear cryoturbated lobes filled with silty material that strike at ~150°. Some of thé fractures at Mesnil-Val hâve been observed to be filled with loess.

The chalk of Mons Klint has been highly deformed by glaciotectonics. The chalk originated from thé Baltic and was moved by northerly flowing ice before being deformed again by an ice sheet from thé east. As a resuit, thrust sheets of chalk lie over and are intermingled with slabs of glacial till. The cliffs at thé test locations contain no till. The glaciotectonics has generated a highly fractured chalk with many fracture sets, but with low persistence and high frequency.

Microseismic data collection

The émission of a seismic signal when thé rock cracks has been efficiently used to detect cracks in deep coal mining [START_REF] Senfaute | Spatial Distribution of Mining Tremors and thé Relationship to Rockburst Hazard[END_REF][START_REF] Sato | Induced Seismicity Associated with Longwall Coal Mining[END_REF] in abandoned mines [START_REF] Senfaute | Qualification of thé microseismic monitoring technique applided to thé risk of collapse in iron ore mines[END_REF] and in hot dry rock geothermal projects [START_REF] Niitsuma | Acoustic analyses of a geothermal réservoir and its application to réservoir control[END_REF]. The challenge in this research was to adapt thé microseismic technique to cliffs where thé overburden stresses induced by thé rock mass are lower than in underground deep mines. The induced crack signais are likely to be weaker than in underground mines and are disturbed by noise.

Acoustic crack émissions are measured with accelerometers and geophones. Since thé wavelengths of thé seismic signais generated during thé rupture of chalk are not known, a broad frequency band-width was selected. A network of five microseismic stations (accelerometer and geophone) was installed in thé cliff at Mesnil-Val. Anticipating strong atténuation of thé seismic signal in chalk, a maximum spacing of about 50 m was chosen between stations. The network comprised two stations in vertical boreholes, drilled from thé top of thé cliff, and installed to a depth of 10 m and located 10 m from thé cliff edge. And three stations in horizontal boreholes, drilled from thé cliff face to a depth of 6 m. Data were recorded continuously from January 2002 to May 2004. In addition thé cliff was equipped with température and humidity sensors, extensometers and a weather station was established on thé cliff top. Due to thé cost of thé installation, microseismic data were only collected at Mesnil-Val and not from thé UK and Danish locations.

Azimuthal apparent resistivity data collection

An apparent resistivity measurement is made by imposing a low energy direct current between two électrodes implanted into thé ground surface. The résultant distribution of ground electrical potential is measured between additional pairs of stainless steel électrodes. Sub-vertical, parallel fractures will often impose anisotropic physical properties that resuit in a variation of apparent resistivity with thé orientation of thé resistivity measuring array [START_REF] Taylor | Characterizing jointed Systems by azimuthal resistivity surveys[END_REF]. By rotating thé array it is possible to estimate thé dominant strike direction of thé fracture set and to calculate a coefficicient of anisotropy, A. For thé Square resistivity measuring array used in this study (Habberjam and WatMns, 1967) this is defined as thé ratio of thé apparent resistivity perpendicular to thé fracture set (thé maximum value) to thé apparent resistivity parallel to thé fracture set (thé minimum value). If thé fractures dilate as a cliff collapse approaches then thé value of A would be expected to be time dépendant.

On each cliff top, three sites perpendicular to thé cliff face were established and a control site was setup approximately 50 m from thé cliff (cf. Figure 1). Those sites near thé cliff edge (Sites A, B and C) should sample ground that is likely to be affected by fracture dilatancy. The maximum électrode spacing (referred to as 'a' and equal to thé side of thé square) for thé three sites near thé cliff face was set so that thé nearest approach of an électrode to thé cliff edge was about one to two mètres. Some temporal variations are likely to be observed due to influences such as seasonal changes in saturation levels, but thèse should also be observed at thé Control Site. A time séries was built up by repeating thé measurements every two months for a period of two years at thé five test locations. Detailed geological data hâve been collected from ail locations that consists of mapping of thé lithology and stratigraphy, mapping of fracture density, fracture orientations and fracture persistence and laboratory strength testing of samples under varying levels of saturation. Topographical surveying grids were also established at each location in order to detect any small ground movements near thé cliff edge.

RESULTS

Microseismics

Signifîcant seismic activity was recorded twice per day at Mesnil-Val, at thé hours when thé sea was highest for periods of 2 to 3 hours. Analysis confîrmed a strong corrélation between tide and seismic triggering. Hence, it is possible to conclude that thèse recordings are related to thé action of high tide on thé face of thé cliff. Microseismic events were also recorded at low tide. Thèse events are considered as independent of thé action of thé sea. Spectral analysis of thé signais showed signifîcant différences between thèse events and those recorded during high tide.

A cliff collapse occurred on 23 rf June 2002 at Mesnil-Val. An estimated 2700 m 3 of chalk dropped from a maximum height of around 50 m. It occurred at thé center of thé monitored zone (cf. Figure 2). In thé 15 hours preceding thé collapse strong seismic pre-cursors were recorded on one of thé accelerometers (cf. Figure 3). This accelerometer (AH4) was damaged by thé collapse and ceased to function. The collapse occurred during a low tide, and most of thèse seismic pre-cursors can therefore be considered to be independent of thé action of thé sea. From thé measured apparent resistivity anisotropy, fracture orientations hâve been estimated. Away from thé cliff edge, thé derived fracture orientations correspond to thé tectonic fractures and are consistent with thé mapping of fractures at thé cliff face. At thé French and UK locations, thé fracture orientation obtained adjacent to thé cliff is sub-parallel to thé cliff face. At Beachy Head and Birling Gap it occurs in a zone about 10 m wide, but at Mesnil-Val it widens to about 20 m. At thé Danish locations no consistent fracture orientations were obtained. The chalk hère has been highly deformed by glaciotectonics and thèse results are consistent with thé geological mapping that indicates a highly fractured rock mass with many fracture sets at différent orientations, but of low persistence.

A plot of thé variations of thé coefficient of anisotropy (À) against time at Birling Gap is shown in Figure 4. A cliff fall occurred between 5 * March and 23 rd April 2002 and is associated with a large decrease in X at Sites A and B, which are situated adjacent to thé cliff edge. There is no associated réduction in X at thé Control Site, away from thé cliff. A further cliff fall at Birling Gap occurred on 9 * January 2003, but there is no indication of it in thé time séries of À,. weight of thé sample was measured after removing surplus water, and thé dimensions were measured with a vernier gauge. The sample was then prepared and tested in thé triaxial rig.

The cernent works samples in de-aired water had thé highest average axial stress peak strength of 4.9 MPa and thé Birling Gap coastal samples had thé lowest average axial stress peak strength of 2.9 MPa. The sait saturated samples from thé cernent works had an average axial stress peak strength of only 3.4 MPa. This is évidence that thé weakness in thé coastal samples is at least partly due to thé influence of thé sait from thé sea on thé chalk. At Beachy Head and Mesnil-Val there is a strong seasonal variation in X (cf. Figure 5). Values peak in thé summer with minimum values in thé winter. The cliff fall at Mesnil-Val is not apparent in thé variations of À,.

Laboratory sample testing

Laboratory based investigations hâve been carried out to better understand thé mechanical properties of thé chalk cliffs in relation to thé effects of sea sait saturation on thé strength and stability of thé sea cliffs. This will help to better understand thé causes, processes and mechanics involved in chalk cliff collapse. The laboratory testing involved a séries of undrained triaxial tests to establish stress paths for chalk cliffs in thé Cuckmere Bed of thé Seaford Chalk Formation. Chalk samples from Birling Gap were compared with samples collected of thé same stratigraphy from an inland cernent works. The coastal Birling Gap samples were placed in a desiccator and saturated in stages under vacuum with de-aired water for at least 7 days. A set of samples from thé chalk quarry were saturated with saline water, whilst another set of identical samples from thé quarry were saturated in de-aired water. After saturation thé samples were dried in an oven at 60° C, this process was repeated 3 times. The saturated

ANALYSIS AND DISCUSSION

Microseismics

Frequency analysis of thé seismic signais measured before thé collapse at Mesnil-Val has identifîed a number of seismic event families that each contains one spécifie frequency spectrum. Each family is associated with a différent phase of thé collapse and thus indicates two phases of failure. This has been investigated further by measuring thé acoustic émissions emitted by chalk samples collected from thé Mesnil-Val cliff, under laboratoty uniaxial compression tests. The failure strength obtained for each sample was between 3 and 6 MPa. The total porosity of thé chalk is very high (42 to 45 %) suggesting a low mechanical strength, which is confïrmed by thé low values of thé failure strength obtained during thé tests. The laboratory results show similar changes of thé seismic behaviour before thé final rupture of thé samples, and thé collapse of thé cliff. There is an exponential increase in thé number of seismic events and in thé energy released. The frequency spectra evolve towards higher frequencies that are associated with thé formation of new cracks. In thé hours before thé collapse of thé cliff, high frequencies were recorded one hour before thé collapse and at thé time of thé collapse itself (cf. Figure 6). Hence, thèse peaks are most likely associated with thé création of new cracks. Lower frequencies emitted after thé fîrst peak are most likely associated with thé extension of cracks. The identification of a signifîcant increase in released seismic energy and of high frequencies may be a pre-cursor for thé imminent catastrophic failure of thé cliff.

Azimuthal apparent resistivity

Of thé three cliff falls that occurred during thé period of monitoring, only thé one from Birling Gap in thé spring of 2002 generated a significant variation in thé temporal variation of thé coefficient of anisotropy. The interprétation of this resuit is that considérable fracture dilatancy was occurring in thé cliff parallel fracture set prior to thé fall. This collapse occurred from thé part of thé cliff over which thé resistivity measurements were made, whilst in thé other two collapses thé ground lost was several mètres from thé measurements. Since thé latéral extent of thé falls is largely constrained by thé tectonic fractures, it is likely that thèse tectonic fractures also constrain thé latéral extent of thé fracture dilatancy. Température and extensometer data collected at Mesnil-Val are shown in Figure 7. The average monthly air température shows, as expected, a peak in thé summer and a trough in thé winter. The température sensors within thé cliff demonstrate that rock température is being driven by thé air température. It is well known that to depths of around 15 m, rock température changes are driven by atmospheric températures. There is a phase shift of 1 to 2 months between thé température variations at thé cliff face and those at a depth of 3 m and 4 months between thé cliff face and those at a depth of 6 m. From thèse différences an average thermal diffusivity of 5.98 x 10" 3 cm 2 s 1 has been calculated, which is consistent with fractured chalk. In turn, rock température is driving an expansion and contraction of thé rock mass that has been measured by thé extensometers. The movements are extremely small, but there is a clear maximum expansion in February and minimum contraction in September. Hence, it would appear from thé seasonal variations in thé coefficient of anisotropy (peak in thé summer and trough in thé winter) that thé expansion of thé rock mass is taken up by a contraction of thé fractures. The différent magnitudes of thé seasonal variations observed in X at différent locations are unclear, especially, when as at Beachy Head and Birling Gap, they are on thé same Chalk stratigraphy and are only 2 km apart.

CONCLUSIONS

The research presented has been successful in identifying changes within thé rock mass behind thé cliff face prior to a collapse. The joint interprétation of a number of data sets has enabled thé following conclusions to be drawn.

The microseismic data hâve demonstrated that there is a significant increase in seismic energy emitted from cracks within thé rock mass in thé hours before a cliff collapse.

Analysis of thé sesismic data indicates that différent phases of thé failure can be identified by distinct seismic families. Comparisons with laboratory induced acoustic crack émissions has demonstrated that high frequency seismic signais are emitted as thé rock cracks and that this might be used as an indicator that a collapse is imminent.

The high porosity of chalk was found to lead to rapid atténuation of thé seismic signais. The distance between accelerometers in a monitoring network on a chalk cliff would hâve to be less than 30 m.

Comparisons of thé azimuthal apparent resistivity data with geological mapping indicate that tectonic fracture orientations are being measured at thé Control sites. Towards thé cliff edge at thé UK and French locations, thé analysis indicates a cliff parallel fracture set that is thought to develop in response to thé free face at thé cliff This occurs in a zone adjacent to thé cliff edge, 10 to 20 m in width. In Denmark, at Mons Klint, thé results are more uncertain, reflecting thé glaciotectonised nature of thé chalk. It is likely that acoustic crack émissions are being generated as thé cliff parallel fracture set develops.

The 2002 cliff fall at Birling Gap, where ground from within thé circle of measurement was lost, produced a large temporal change in thé coefficient of anisotropy. This has been interpreted as a réduction in fracture dilatancy as a resuit of thé cliff fall.

The Mesnil-Val and Birling Gap 2003 cliff falls did not show temporal changes in thé coefficient of anisotropy. Ground outside of thé circle of measurement was lost and it is possible that thé tectonic fractures limit thé extent of both thé fall and thé dilating fractures.

Some sites showed seasonal variations in thé measures of anisotropy with peaks in thé summer and troughs in thé winter. The Mesnil-Val température monitoring suggests a corrélation between thèse variations and rock température. The thermal diffusivity of thé rock is such that thé maximum expansion of thé rock mass occurs six months after thé maximum air températures. The data indicate that thé expansion leads to fracture contraction with associated minimum values of anisotropy in thé winter.

The laboratory testing of chalk samples saturated with saline water has demonstrated a significant weakening of thé samples. It has been noted how frequently collapses occur along coastal sections, yet inland quarries of similar chalk appear relatively more stable. Hopefully this study goes some way to proving that sait is a major contributing factor to thé weakening of chalk coastal cliffs.

The techniques described hère would need to be improved and optimised before they could be used as tools for predicting cliff collapses, especially on lithologies other than chalk. However, cliff failures affect local communities and thé wider participation of ail groups of people who use thé cliffs as an amenity. Planners and local government authorities need to be assured of thé safety of thé cliffs. With further improvements to thèse methods, networks could be installed by thé appropriate authorities within cliff collapse highrisk zones. Thèse would contribute to preventing risks and decreasing insurance costs of vunerable properties.

Figure 1 :

 1 Figure 1: Four centres for azimuthal apparent resistivity measurements on thé cliff top. Site A: 'a' = 5 m, Site B: 'a' = 5, 10 m, Site C: V = 5, 10, 20 m, Control: 'a' = 5, 10, 20 m. Where 'a' = thé side of thé square.

Figure 2 :

 2 Figure 2: Mesnil-Val cliff collapse that occurred on 23 * June 2002.

Figure 3 :

 3 Figure 3: Cumulative seismic energy recorded over eight months at Mesnil-Val. AV are stations in vertical boreholes, AH are in horizontal boreholes.

Figure 4 :

 4 Figure 4: Temporal variation of thé coefficient of anisotropy at Birling Gap.

Figure 5 :

 5 Figure 5: Temporal variation of thé coefficient of anisotropy at Mesnil-Val.

FreqFigure 6 :

 6 Figure 6: Frequency spectrum of seismic events recorded during thé cliff collapse at Mesnil-Val.

Figure 7 :

 7 Figure 7: Air température, rock température and extensometer data from Mesnil-Val. The rock température sensors were emplaced in a horizontal borehole drilled into thé cliff face.

ACKNOWLEDGEMENTS

This research was supported by thé European Union 5 Framework Research Programme (Contract EVK3-CT-2000-00029). This paper is published by permission of thé Director of thé British Geological Survey (NERC).


Khalidbelghazi
email: khalid.belghazi@u-picardie.fr

Laurent Ghyselen

Elmountacer Billahelabbassi

Jean-Pierre Libert

INFLUENCE OF NEONATE'S BODY POSITION WITH AND WITHOUT A PLASTIC BLANKET ON BODY HEAT LOSS ASSESSED FROM A THERMAL MANNEQUIN

INTRODUCTION

The present study aimed at assessing the net gain of body heat storage induced by a transparent plastic blanket draped over small premature neonates in the prone and the supine positions. Thermal stress is particularly important in premature and small-for-gestational-age infants characterized by high values of the ratio between skin surface area and body mass, the greater this ratio, the greater the body heat exchanges. The large skin permeability enhances body water loss. The risk of hypothermia is particularly increased at birth and during operations on naked neonates implying opening of the canopy (surgical operation, blood sampling and gastric aspiration). In the first day of life, the rate of evaporation can reach 100 g.h"'.m' 2 in very preterm infants. To prevent the large amount of water loss it is sometimes recommended to cover the neonate with a plastic blanket. In closed incubator Fanaroff et al. <3) pointed out that a transparent plastic heat shield reduces the insensible water loss of 44 % in low birth weight neonates lower than 1250 g and postnatal age less than 10 days. For postnatal age greater than 10 days, the magnitude of this reduction was only 19 %. Bell et al. (2> also reported that the addition of a heat shield in an incubator decreased the water loss by 10 % in infants with mean birth weight of 1570 g. However the efficiency of this solution which depends on the physical environment but also on the inter individual difference in the ability to exchange heat with the environment remains questionable and the use of a plastic blanket is still a controversial topic.

The total heat loss of premature infants depends on various factors such as gestational age, nutritional state, mean skin temperature, body hydromineral balance, vigilance state, metabolic rate and of the postnatal age which modifies the skin keratinisation. Thus, it is difficult to obtain homogeneous data base that takes into account all these factors and there are conflicting data on the effectiveness of plastic blanket. To rule out these confounding factors we use a sweating mannequin the advantage of which is that it measures directly the total heat loss with the environment without interference with these factors.

METHODS • Mannequin:

The multisegment anthropomorphic, sweating mannequin (Belghazi et al.) [START_REF] Belghazik | Assessment of whole body and regional evaporative heat loss coefficients in very premature infants using a thermal mannequin: Influence of air velocity[END_REF] represents a small-forgestational-age newborn with a body surface area of 0.086 m 2 and a simulated birth weight of 900g (Fig 1). It was cast in copper and painted matt black (surface emissivity = 0.95). Temperatures at various points of the outher surfaces were measured by attached thermistors (CTN Siemens 10 kQ at 25 °C, precision ±0.1 °C after calibration) protected from radiant energy by an aluminium foil patch. To take into account the regional thermal heterogeneity of the surface, each segment was separately heated to reach a set point temperature. The temperature of the surface of the head was set to 36.4 °C, the trunk to 36.6 °C and the upper and lower limbs to 33.3 and 35.5 °C, respectively. These values corresponded to those currently recorded for neonates nursed at thermoneutrality in closed incubators.

• Simulation ofsweating:

Contrary to most models found in the literature which only assess dry heat exchanges, the present mannequin can simulate skin water loss. A black cotton stocking water was tightly held onto the surface so as to eliminate any air trapped between the fabric and the mannequin surface. A pumping system was used to supply water to the mannequin surface (i.e. simulated skin hydration). It consisted of two peristaltic pumps (MS-CA 4 cassettes, B32089, 40 rpm and Mini-S 3 canaux, B32067, 40 rpm) which were designed for transferring water with a high degree of speed stability and a low pulsation level. Each pump consisted of a rotor with rollers pressing a flexible tube: the water was thus pumped by a peristaltic effect. The mannequin's segments (head, trunk, two lower limbs, two upper limbs) were separately supplied with water.

Preliminary trials have shown that to perform water evaporation close to the level observed at birth, the mass of water supplied to the nude mannequin could be 4.1 g and 12.5 g (evaporative rates from the mannequin's surface of 117g.rf'.m" 2 and 244 gh^.m' 2 , respectively). The ratio between these measured evaporative rates and the maximal evaporation recorded for a fully wetted surface (352 g.h" '.m" 2 ) corresponds to the surface wettednesses about 30 % and 70 %, respectively. To reach these levels of skin wettedness over each segment, the mass of water supplied was 1.3 g and 4 g for the head, 0.8 g and 2.4 g for the trunk, 0.6 g and 1.8 g for each lower limb and 0.4 g and 1.2 g for each upper limb.

At thermal equilibrium the heat exchanges between the mannequin and the surrounding (expressed in W) can be described by the body heat balance equation:

P=±K±C±R-E

The heating power (P)supplied to the mannequin balances the total heat losses by conduction (K), convection (C), radiation (R) and evaporation (E).

EXPERIMENTS

The experiments were performed to simulate the first day of life during which skin water loss is very high. The mannequin was lying in a relaxed supine or prone position on a mattress in a single-walled, convectively heated incubator for intensive care or outside the apparatus to simulate surgical operations. The air temperature was 33 °C, air humidity 50 %, air velocity 0.02 m.s" 1 in the incubator and 25 °C, 50 %, 0 m.s" 1 outside the apparatus. In each experimental condition the mannequin was nude or covered by a flexible plastic blanket (except the head and an upper limb).

RESULTS AND DISCUSSION

The heat loss from the whole mannequin under the various experimental conditions and the changes in mean body temperature AT b due to the covering are shown in table 1 AT b (in °C.h"') was calculated from the equation of body heat storage AS = mb x C p xAT b (where AS is the body heat storage increase induced by the placement of the plastic blanket in W, m b is the mass of the tissues in kg, C p is the approximate specific thermal capacities of body tissues in 1 W-kg^^C 1 ).

For the covered mannequin, statistical analysis showed that the body position did not significantly modify the heat loss from the whole mannequin inside or outside the incubator whatever the level of the surface wettedness. On the contrary, for the nude mannequin, the total heat loss was significantly reduced (P < 0.0001) by the prone position in all the experimental conditions.

As expected lower heat powers are required to maintain a thermal equilibrium where the mannequin was covered by the plastic blanket. The reduction of heat loss was significant (P < 0.0001) in all experimental conditions. Covering the mannequin prevents a fall of mean body temperature ranging from 3 to 13 °C.h ~ 1 . The plastic blanket is particularly efficient where the mannequin was placed outside the incubator and for high levels of surface wettedness.

CONCLUSION

The present data points out that this simple device night be useful in very preterm small for gestational age neonates to avoid sudden body hypothermia in the first hours after birth particularly in situations during which large amounts of water can be loss during surgical operations implying the opening of the canopy.

Fig. l :

 l Fig.l :Thermal mannequin lying on the mattress of the incubator

Table . l

 . : Total heat loss from the mannequin in the different experimental conditions.

				Total heat loss (W)
		Wettedness	Supine	position	Prone	position
		surface(%)	Nude	Covered	Nude	Cover
		30%	15.0±0.7	10.1±0.4	12.9±0.9	9.7±0.4
	Inside
	incubator	70o	20.4±0.3	11.2±0.3	17.3±0.4	10.8±0.2
		30%	23.5±0.3	16.8±0.2	20.5±0.5	16.4±0.3
	Outside
	incubator	70%	31.5±0.5	19.5±0.5	28.8±0.4	18.8±0.7