Annals qf the MBC - vol. 3 - n' 2 - June 1990

FOREST FIRES: TYPOLOGY, PREVENTION, AND PROTECTION OF FIRE-FIGHTERS

Bovio G.

Istituto di Selvicoltura e ASsestamento Forestale, Universita di Torino, Italia

SUMMARY. After a brief introduction that underlines the extent and gravity of the problem of forest fires, a description is made of the kinds of forest fires that may actually occur in the Mediterranean area. The nature of the particular forest environment is closely related to the characteristics of the fire-front. Precautions to control the fire involve environmental modifications that must be planned with a view both to maximizing the possibilities of extinction and to guaranteeing the safety of the fire-fighting squads. A distinction is made between the kind of fire that can be attacked directly and indirectly. Particular reference is made to firebreaks, where fire-fighting squads can take up their positions. An account is given of the temperatures that have to be faced in the vicinity of the fire, as also of the protective clothing that must be worn. If adequate safety is to be guaranteed many dangers have to be considered, the most serious of which is burns.

In the 1980s the problem of forest fires in Italy was characterized by the alternation of a year of greater interest in the subject followed by a year of reduced interest. In 1988 there were 13,500 fires affecting an area of 186,000 hectares, 60,000 of which were woodland. The average area of each fire was 14 hectares, i.e. an extent requiring considerable efforts in order to extinguish the fire.
On the basis of these average figures it has been calculated that the loss of timber production has amounted to 68 billion lire.
These statistics do not give an idea of the more serious fires. Many examples can be cited. In August 1988, on Mt Gargano (Puglia), flames destroyed 350 hectares of pine-forest and 400 holiday-makers had to be evacuated. In August 1981 a serious fire broke out on Mt Argentario (Tuscany) affecting an area of 1,700 hectares, of which 600 hectares consisted of woodland of particular landscape and environmental value, the rest being bushland. Between the end of December 1980 and mid-January 1981 a fire covered 900 hectares in the communes of Givoletto, Valdellatorre and Varisella (Piedmont), and in the same period there was another serious fire that affected 1,700 hectares in the Orco Valley (Piedmont).
Not all these events, however, had the same effect on public opinion. For example, much more was said about the Argentario fire than the Piedmont fires, even if these afTected a much greater area of woodland. This shows that public opinion is not always struck by the real gravity of such fires.
Many more or less evident factors are involved here, but the most important regard personal danger and the physical harm caused to individuals.
To complete the statistical picture it is as well to recall that other countries face the same problem. In 1985 Spain had 12,284 fires affecting 486,000 hectares. In France in 1986 50,000 hectares were burned, with 12 victims and 200 houses destroyed. In 1988 in Greece 80,000 hectares were swept by fire. These figures are high, but there are in fact even worse situations. In Australia in 1983 600,000 hectares were swept by fire, with 71 dead and 2,000 injured. In 1988 in Yellowstone Park (USA) 400,000 hectares were burned, although even this seems little compared to the single fire which in 1987 in China swept through 1,300,000 hectares, leaving 50,000 people homeless.

Forest fires, regardless of their extent, have different typologies that depend in particular on the biomass exposed to fire (tons per hectare) and the density and distribution of the combustible material.
It is advisable in the planning stages to predict the characteristics of the possible fires that may occur. This prediction is based above all on a floristic analysis of the species that are most liable to spread the fire. The quantity of combustible available and the actual vegetable species are the main factors determining heat emanation in the event of a fire.
The spreading of the fire front, on the other hand, is effected by the density and the distribution of the combustible. In order to determine the probable behaviour of a forest fire, special attention must also be paid to the horizontal continuity of the combustible, i.e. the distance between the foliage of the individual trees that create the forest coverage. It is also necessary to know the vertical continuity of the combustible, which is determined by the distance between the lowest levels of the tree foliage and the shrub level of the ground cover. It will thus be possible to estimate if the fire is likely to spread at ground level, only burning the ground cover, or if it will succeed in reaching the foliage of the trees.
Knowledge of the typology of the combustible is necessary for the realization of planning measures.
In the modern approach to fire prevention plans it is considered acceptable, much more than was the case in the past, for a fire to sweep through some areas of a larger territory that is protected by a fire prevention plan. This concept has come to be accepted in the light of research which has shown that in some cases the passage of the fire-front does not damage the vegetation and may indeed even be beneficial to it. For economic reasons it would be unrealistic to prepare a plan that would with absolute certainty prevent all fires in a given territory, and it is therefore more practical to accept that a fire-front with pre-determined pyrological characteristics may be allowed to pass through certain areas and certain well-defined forest coverings.
Therefore, for the preparation of a forest fire prevention plan on the basis of the maximum admissible burns surface, it is necessary to establish the area of woodland where fire will be tolerated as well as the power and the height of the flame-front.
The determination of a value for the maximum admissible burn surface and for the maximum admissible heat emanation corresponds synthetically to the objective that the application of the plan was intended to achieve.
Calculation of the possible extent of fires is therefore at one and the same time both a planning option and an estimation of the effects that the prescribed measures will achieve.
In areas where the passage of fire is not to be tolerated specific fire protection measures must be realized that do not require a precise assessment of the intrinsic burning capacity of the combustible material. This is because in this case it is sufficient to predict the characteristics of any fires that may occur so that fire-fighting teams will be aware of the danger they have to face.
The steps to be carried out as regards the combustible material in the areas where fire is to be tolerated have the principal aim of maintaining the quantity of burnable biomass within limits that permit extinguishing of the fire. The effectiveness of these prevention measures must be lasting, i.e. they must not be based merely on the actual situation but must also take into account the foreseeable development of the silviculture in the territory.
All operations to manage the burnable biomass must therefore be carried out with a view to the actual situation and to the possible future modifications in the composition of the territory and the natural growth and evolution of the tree coverage.
The typology of forest fires is extremely variable, in relation to the characteristics of the territory, and through planning it is possible in part to predict and in part to manage the extent and the consequent dangerousness of the fires.
Numerous procedures are normal in forest fire prevention planning. We shall here consider operations directly related to fire extinguishing and in particular to the activities of the fire-fighting teams.
Firebreaks are among the most important of these precautionary measures, often being planned with a view to reducing the power of the fire-front but not to completely stopping it. The purpose of the firebreak is to create an area where a direct attack can be launched on the fire-front by working directly on the flames which, if not limited in their power by the firebreak, could not be tackled by the fire-fighters who would be compelled to combat the fire by creating fire barrages some distance away, i.e. mounting an indirect attack.
It will thus be necessary to plan for the presence of fire-fighting teams wherever the firebreak reduces the power of the fire below the number of kcal/m that prevents any approach.
This consideration inevitably means that there must be a close relationship between the distribution of the firebreaks, their construction characteristics and the organization of the fire-fighting squads. In fact, given a reduction of the spread of the fire due to the firebreaks, it will or will not be be possible to stop the fire according to the possibilities to intervene directly and to the equipment at the disposal of the rescue teams.
The firebreaks must therefore ensure the transformation of foliage fire to surface fire, and a flame-front that in all cases is less than the width of the firebreak.

Fire-fighting must therefore be preferentially fought along these firebreaks, which therefore represent a vital structure in the prevention of spreading of any fire. In areas without firebreaks any direct attack must be carried out where thermic emanation is limited, Accurate firebreak planning also makes it possible to predict the behaviour of any fires that may occur. The presence of such firebreaks also makes it possible to predict the temperatures that fire-fighting teams will have to face.
However, even if specific planning measures are non-existent, there are certain general rules that make it possible to have some indications about the heat conditions that will have to be faced in the extinguishing of a fire. It is known for example that the temperature becomes high only in the vicinity of the flame-front and that peak temperatures are always to be found in the highest part of the vegetation.
Measurements (Trabaud, 1979) performed using thermocouples in brushwood fires indicated that the temperature reached varies from 800 to over 1200 'C, depending whether the fire occurs in spring or in autumn. In other vegetational conditions (Countryman, 1969) temperatures were recorded in the 1040-1370 'C range. Experimental trials show that the thermal field can vary considerably and that extremely high temperatures can be reached. These high levels usually occur however only where the combustible vegetable mass has a high surface area/volume ratio. When surface area is high compared to volume there is an increased possibility of gas exchanges with the atmosphere. Where such conditions exist fires develop in which extinguishing operations become difticult not only because of the heat emanated but also because of the speed with which fire spreads. Environments exist, e.g. the African savannahs and the grassy Australian outback, where the fire-front can advance as fast as 300 em/sec. Elevated heat production may also occur in Mediterranean and Alpine environments, usually in areas where the density of the vegetation makes fire-fighting operations extremely difficult.
Other experimental work has demonstrated that with less dense vegetation the difficulties encountered also depend on the season of the year when the fire occurs. Also, temperature varies in relation to the distance between the ground and the point considered, Temperatures were measured (Pitot Masson, 1951) of 90-140 'C at ground level, 285-560 'C at a height of 5 cm, and of 140-375 'C at 140 cm. Fire-fighters can face only the lowest of these heat levels. Flame-fronts emanating temperatures above 500 'C at the highest part of the vegetation prevent any direct attack, i.e. fighting the fire in the vicinity of the flames. Thus, whenever such high temperatures occur, indirect extinguishing techniques must be used until the fire reaches an area that is more suitable for a direct attack. Protective clothing must therefore be manufactured with features guaranteeing safety only with regard to heat conditions which the individual can reasonably tolerate. In fact, any clothing that gave total protection in any kind of fire would have to be able to resist such high temperatures that its size and weight would make it unusable.
It is important to remember that temperatures of over 500 'C may occur in situations where the fire-fighter is involved in direct operations. In these cases the highest heat levels develop above the vegetation and are of very short duration. It is known that the heat flow disperses vertically and that only a small part of it contributes to the spreading of the flame-front. The greater part is dissipated vertically by convection and radiation. The fire-fighters must always be positioned in the zone where they can attack the fraction of radiant heat necessary for the propagation of the flames.
A different situation arises when flame, which is simply a mass of burning gas, is blown by the wind towards the fire-fighting team. In this case there is a much higher heat transfer than the fire-fighter normally has to face. However exposure to heat is limited in time, and in any case the doses of heat received do not raise thermal levels above those reached as a consequence of radiation, which though lower in temperature has to be tolerated during fire-fighting operations for considerably longer periods.

Fire-fighting and the protection of the individual

Depending on heat production, fire-fighting operations may consist of direct or indirect attacks, which may be by land or by air, and very frequently even simultaneous. If the local orography is irregular and the fire-front is advancing rapidly, it is advisable to adopt an indirect approach, also using chemical retarding agents to create barrages that will slow down the fire. The indirect attack always includes removal of combustible material or a counterfire. The latter method consists in creating at an appropriate distance a flame-front that will approach the main fire. Theoretically one should be absolutely certain that the counterfire will spread towards the main fire-front but in practice that does not always happen. The counterfire must always start from a safety line which may be natural (roads, water courses, watersheds without vegetation) or specially created by opening them up through vegetation using appropriate equipment.
When possible however an attack is mounted directly on the fire at close quarters.
The methods of action are numerous and they vary according to circumstances. For the same reason various types of equipment are commonly used. Even the direct attack on the fire varies in space and in time. For example, in a ground fire that develops along the floor of a broad-leaf forest in autumn, before the leaves have been compacted by atmospheric precipitations, it is advisable to avoid the use of equipment intended to suffocate combustion. This kind of equipment, which is not meant to be used on light-weight combustible material, would only stir up burning foliage and vegetable matter. In such cases the most suitable apparatus is a motor-fan, usually shoulder-held. This sends out a violent blast of air which easily removes the vegetable matter along a strip which will either slow the fire down or stop it completely if it is very weak. When the fire is spreading through compact materials or ground cover the most appropriate piece of equipment is the fire-beater, an instrument consisting of strips of material attached to a long handle.
When the vegetation is bushy the fire-rake can be used. This is a stout form of rake which is robust enough to smash down the bushes, enabling other operators to complete clearance work with other equipment. Shoulder-held, manual or motor pumps may also be used to direct powerful jets of water on to more violent fires, in order to reduce the level of the flames and to enable operators with other equipment to work more easily.
All the equipment so far described is extremely simple but quite indispensable. This manual and easily transported apparatus is prevalently used in areas where there are few forest paths and the fire has to be reached on foot. If access is possible also for motor vehicles various types of equipment can be used to spray liquids that are usually highly effective but difficult to transport across rough terrain.
All fire-fighting operations involve a risk factor and fire-fighters must therefore be as well protected as possible. The most serious risk is burns. To prevent these, specially made equipment must be used: fire-suits, helmets, goggles, antismoke mask, gloves, boots.
This equipment is indispensable not only to ensure operational functionality but also to limit the risk of accidents. Fire-fighting accidents do however frequently cause injuries and even fatalities.
Every year the official statistics report many deaths and injuries. In 1988, in Italy, there were 6 deaths and 80 persons injured. However the general picture offered by the statistics is always incomplete because they do not include a large number of accidents which may cause severe burns even though the fire is of very limited extent. This happens for example in the case of fires lit for silvicultural or agricultural purposes by persons - often elderly - who are then unable to control the spreading of the fire.
In Italy, until law N' 47 was passed in 1975, fire extinguishing was the responsibility of the National Fire Brigade, which employed equipment suitable for city and industrial fires that could be used in the vicinity of roads. The second half of the 1970s saw the formation of volunteer squads which obtained their equipment through regional government contributions. Very soon the need was felt of personal defence, something which in the past had been neglected. The squads began to wear fire-suits. There were however no precise regulations governing the technical features of protective clothing. Choices were based on what technology had to offer, and attempts were made to observe the measures laid down by Law N' 547 of 1955, which sets norms for the prevention of accidents and in particular establishes that appropriate protective clothing must be worn by operators engaged in dangerous work. There was however no specific experience in the field of forest fire-fighting. At first green and even camouflaged fire-suits were worn. These were however soon discarded because it was found that they hampered localization of the operators, especially as helicopters began to be used more frequently and pilots found it difficult to localize the fire-fighting squads. Accordingly colours were adopted that can be seen in vegetation even from considerable distances.
A further step forward concerned the fire-resistant quality of the protective clothing. This was necessary because cases occurred of persons being burned not only by the fire itself but also by the combustion of the protective clothing they were wearing. Wide use was made of fireproof materials which were not however sufficient in themselves to guarantee personal safety because they did not prevent heat transmission.
A great deal of technical progress has been made with regard to types of clothing that can be used in heat defence. Protective clothing was developed that slowed down inward heat transmission for a sufficient length of time. These characteristics were obtained using very thick insulating materials which were however neither light-weight nor pervious to air. This is important because fire-fighters must not sweat because of the clothing they are wearing. If they do sweat at the fire-front where temperatures are high their physical performance is impaired and the danger of accidents increases proportionally. Also, sweating may induce the operator to neglect the norms governing the use of protective clothing so that he wears it unbuttoned or incomplete. Another important feature to be respected is that the operator must be able to perceive any slow and gradual increase in heat so that he has time to abandon the area. The best protection is provided by fire-suits of variable structure that protect the various parts of the body in proportion to their vulnerability and their capacity to recuperate.

RÉSUMÉ. L'Auteur analyse la typologie des incendies de forêt qui peuvent se produire dans la région méditerranéenne. Les charactéristiques de la forêt déterminent le développement de l'incendie. L'Auteur décrit la manière directe et indirecte de combattre l'incendie. Les coupe-feu ont une importance particulière. Les températures élevées constituent un grand danger pour les pompiers et il faut avoir des vêtements protectifs appropriés. Pour garantir la sécurité de tous ceux qui combattent les incendies, il faut considérer beaucoup de dangers, dont le plus grave est la brûlure.

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