AU724899B2 - Method and device for fighting fires from the air - Google Patents

Description

PCT/DE96/01510 WO 97/06858 Method and .device for fighting fires from the air In recent years, a continual increase in the number of forest fires and extensive blazes recorded worldwide has been observed. Simultaneously with this trend, the size of the area destroyed in each fire is continually increasing. These fires primarily affect regions of the Northern hemisphere, in particular the northern coniferous forests of Canada and the tundra of the Eurasian land mass, and to a less significant extent the pine stands in the Mediterranean region. The global volume of harmful emissions resulting from forest fires has in the meantime been estimated to be approximately of the overall volume.

Current methods of fighting major fires, in particular forest fires, which exhibit a strongly chaotic character and spread rapidly in the manner of an advancing front, have hitherto been insufficient to extinguish the fires in question quickly and completely.

Hitherto, even in the most favourable scenario, it has only been possible to check forest fires. The reasons for this are extremely diverse. For example, the ground-based fighting of major fires is essentially carried out using the same equipment and in the same manner as when extinguishing buildings within a residential area with a fully developed infrastructure. However, in the case of forest fires one cannot as a rule assume either a sufficient supply of water or sufficiently numerous and adequately constructed approach routes for the fire-fighting vehicles. The latter deficiency is frequently also accompanied by a general inaccessibility of the source of the fire and in each case means that one can only act at isolated points against the front-like fire, preventing the complete extinguishing thereof.

Although firefighting from the air, which has been developed over a relatively long period of time, does improve the accessibility of the source of the fire, it has to date not contributed to decisive progress.

Raining down or dropping water from the air by means of WO 97/06858 2 PCT/DE96/01510 aircraft or helicopters has proved inefficient despite high financial outlay, since, firstly, this type of fighting is carried out only on an extremely isolated basis and, secondly, makes dropping extremely inaccurate.

Due to the considerable formation of smoke and turbulence, moreover, there are continual obstacles during deployment from the air, which makes it impossible to come close enough to the fire from the air and thus in many cases to succeed with the extinguishing.

A fundamental problem, which in view of the scarceness of water when fighting forest fires has a particularly disadvantageous effect, is the inefficiency of the deployment of extinguishing water, because using the methods customary hitherto only about 10% of the extinguishing water actually has an extinguishing effect.

A large proportion of the water used drains away, unused, into the earth or remains inaccessible, in the form of large pools, for any further extinguishing operations on the ground. This affects both the deployment of air support and also that of fire-fighting vehicles.

The object of the invention is to improve firefighting from the air such that both a significantly higher extinguishing effect of the water used and also a considerable enlargement of the area of the fire extinguished using one such aerial deployment are achieved, accompanied by an inherently improved accuracy and the possibility of ensuring a maximal level of safety for the firefighting personnel required for the aerial deployment.

This object is achieved by the method according to the invention in that the extinguishing water is introduced into the source of the fire by means of aircraft, preferably helicopters, by being atomized to form a cloud-like mist of microscopic droplets just above the source of the fire by means of an explosion. This method is preferably carried out such that a container filled with the extinguishing water having a wall which can be burst, in which container an explosive charge with a fuse is arranged within the extinguishing water, is exploded WO 97/06858 3 PCT/DE96/01510 just above the source of the fire. In this method, the container is preferably a drop-shaped or bubble-shaped bag made of plastic, which is also referred to below as "exploding bag".

The exploding bag can be brought to the explosion location just above the source of the fire by means of the helicopter, hanging from a long holding cable, and can then be detonated. However, it is exposed to the heat of the fire for a relatively long time, with the risk of being damaged and losing the water even before detonation. Also, fundamental safety regulations may stand in the way of exploding a load hanging from the helicopter.

It is therefore more advisable to uncouple from the helicopter the exploding bag, which is hanging from the helicopter by means of the holding cable, in a safe position well above the source of the fire, to allow it to fall freely in the direction of the source of the fire and then to detonate it just above the source of the fire.

The invention places airborne firefighting on a completely new footing. In contrast to all known methods, in which the extinguishing water is ultimately introduced into the source of the fire "en masse", the invention provides for the introduction of the extinguishing water in an extremely finely divided form. High pressures (e.g.

of several thousand bar) are formed inside the homogeneous medium water in the exploding bag as a result of detonating the explosive charge, which pressures burst the exploding bag and suddenly project the water into the environment in microscopically fine droplets at a high initial speed of over 5000 Due to dissipation of the blast wave formed during the explosion, due to the air resistance and possibly due to striking obstacles situated in the vicinity of the detonation site, these droplets are decelerated after a short time, so that a completely atomized extinguishing region is formed, in the centre of which the exploding bag was situated. Owing to the immensely large number of extremely small water droplets and the associated enormously large total wo 97/06858 4 PCT/DE96/01510 surface area of these droplets in the direct vicinity of the burning substances, there is an an [sic] immediate heat transfer, that is to say a heat transfer which is complete even within a few fractions of a second, between the vaporizing water droplets and the fire. The heating of the water droplets to their boiling temperature, the boiling method consuming a high heat of vaporization and the further heating of the steam formed withdraw such high quantities of energy from the burning environment that the temperature suddenly falls by several hundred degrees. In addition, a considerable proportion of the atmospheric oxygen which is initially still present in the detonation environment is forced out of the extinguishing region by the quantities of steam formed.

The resulting oxygen deficiency in the extinguishing cloud has a suffocating action on the fire.

Since the temperature in the region of the suddenly mistcovered fire is simultaneously forced to a comparatively low level, the formation in this area of combustible vapours, for example from essential oils, resins or other gaseous emissions from the wood, is brought to a virtual standstill and the temperature falls below the ignition temperature required to (re-)ignite these vapours or combustible organic materials (wood). Together, all this leads to a spontaneous successful extinguishing which makes it possible for ground firefighters to gain access to the extinguished source of the fire and carry out secondary extinguishing operations, for example beating out remaining fire pockets using fire beaters.

The following calculation example is cited in order to illustrate the excellent .extinguishing efficiency of the method according to the invention: If it is assumed that an exploding bag with a capacity of 1000 1 of water is used and the explosive charge is metered such that, following detonation in the centre of the bag, a cloud of water having a radius of between 20 and 30 m is formed, then this cloud has a volume of from 33,500 to about 113,000 m 3 The heat of vaporization of water is 539 kcal/kg, which for 1000 1 of WO 97/06858 5 PCT/DE96/01510 water results in a heat of vaporization of about 2,256,000 kW/s. A sudden withdrawal of a quantity of heat of 100 kW/s has been calculated as the requirement to extinguish a burning forest of small pole trees measuring 100 m long, 6 m wide and 6 m high. This corresponds to about 0.17 kJ/m 2 A water cloud of 30 m radius wets a surface area of about 2,800 m 2 which corresponds to a mean heat of vaporization required to vaporize the water of about 789 kJ/m 2 It can therefore be assumed that there is a disproportionately high excess of heat which can be taken up by the finely atomized water, which results in a sudden extinguishing of almost 3000 m 2 of burning forest, especially if it is also borne in mind that heat is also required to heat the water to boiling temperature. Such a high level of extinguishing efficiency has not been known hitherto.

If the method according to the invention is carried out in a suitable manner, there is no risk of any hazard to people or equipment. 3 kg of a highly brisant and high-dose explosive are required to atomize the quantity of 1000 1 of water assumed in the calculation example, "highly brisant" being understood generally to mean an explosive charge which produces a detonation wave with a propagation rate of more than 5000 metres per second, and a "high-dose" explosive charge being present if more than two kilograms of explosive are used per 1000 1 of water. The detonation pressure of such an explosive charge is dissipated so strongly that, at 30 m distance from the detonation site, it is then only about 0.063 kp/cm 2 As a result, it is possible to eliminate any hazard for the helicopter and its crew. It may be mentioned, in order to illustrate this low detonation pressure, that a person standing upright at 10 m distance from the detonation site would only feel a strong squall and would not be thrown to the ground or injured in any way.

Preferably, a highly brisant modern explosive, which is water-resistant, can be stored for almost unlimited periods of time and is scarcely combustible, is WO 97/06858 6 PCT/DE96/01510 used for the explosive charge. The latter property is important for use in the immediate vicinity of the fire.

Modern explosives of this kind can additionally withstand strong mechanical effects and are thus insensitive to shocks and impacts even when handled roughly. In addition, they have a high level of safety during handling, so that the risk of accidents resulting from unintentional, premature detonation can be virtually eliminated. In a test, an exploding bag filled with 1000 1 of water and provided with 3 kg of such a highly brisant explosive charge was allowed to fall to the ground from a helicopter from a height of 150 m without prior activation of the fuse without the explosive detonating on impact. Any hazard to firefighting personnel and the environment is thus reliably eliminated in the event of such an undesired, premature release of the exploding bag.

The enormously high extinguishing efficiency, the high level of safety for people and materials when carrying out the extinguishing operation, and the possibility of a very accurate deployment of the extinguishing medium are not the only advantages provided by the method according to the invention.

The method according to the invention can be used to fight forest fires and extensive blazes without causing ecological harm. The extinguishing deployment leaves scarcely any traces, but by contrast, owing to the high extinguishing efficiency, the destruction of biological substance, which can never be completely avoided in the event of a forest fire or extensive blaze, is reduced to a minimum. There is no additional impairment to the ecosystem, such as for example scarring of the ground when using ground-based explosives.

The scarcity of water which often occurs on site and the inaccessibility of the site of the fire, which is frequently encountered, combined with the lack of infrastructure in forest areas, is optimally counteracted by the method according to the invention. Due to the high mobility and speed of the helicopters used, the water- WO 97/06858 7 PCT/DE96/01510 filled exploding bags can be picked up at a considerable distance from the site of the fire, at locations which contain natural sources of water or which are easy to reach for fire-fighting tenders. In addition, there is no longer any need for the previously required times to fill helicopter tanks with water, for which actions the helicopter was previously always forced to land first.

For the method according to the invention, it is sufficient if the helicopter flies down to a sufficient height to be able to suspend the exploding bag from the helicopter. Equipping the exploding bag with extinguishing water, explosive charge, fuse and holding cable and setting the fuse can be carried out in the absence of the helicopter "in stock" and at a safe distance from the site of the fire, so that firstly the time for one deployment is limited to the flying time alone and the very short equipping period, and secondly maximum safety is ensured for the firefighters working on the ground.

The rapid, problem-free loading of the helicopter with an exploding bag is particularly advantageous for forest fires, where a relatively narrow fire front extending over relatively great lengths is typical. This is because a single helicopter can effectively extinguish the fire front in sections along its length with a short cycle time. Naturally, it is even quicker if two or more helicopters undertake extinguishing by sections in a rolling, that is to say successive, deployment. As an alternative, two or more helicopters may also drop their extinguishing load simultaneously at the distance of one effective width apart and detonate it, preferably coordinated by radio, one effective width being understood to be the mean diameter of the extinguishing cloud formed on detonation.

The application of the method according to the invention is not limited just to forest fires and extensive blazes but may also be used for all conceivable fires which can be fought from theair. Owing to the very high extinguishing efficiency and the high level of safety of the method, it can be used particularly advan- WO 97/06858 8 PCT/DE96/01510 tageously for very hazardous fires and those which are difficult to extinguish. These may be, for example, fires in fuel tanks, oil tower fires or fires occurring during aircraft accidents, without seeking to restrict the use of the invention to these cases. It is recommended here to use for the extinguishing operation in question a quantity of water of 500 1 (bush fires, buildings, warehouses), 1000 1 (forest fires) or 2000 1 (tank fires, refinery fires, oil rig fires).

The water used for extinguishing does not have to be pure water, but may also contain retarders. These are chemical substances which inhibit or at least delay the ignition of combustible solid materials and which are introduced into the burning material together with the water on explosion of the extinguishing bag. Subsequent re-ignition of the suddenly extinguished burning material as a result of any remaining pockets of embers becomes at least less likely if a retarder is present. Various types of retarder are known and act in different manners depending on their composition. Salt-based retarders form a crust on the burning material, which on the one hand inhibits gaseous emission therefrom and on the other hand denies the oxygen in the ambient air access to the burning material. Other retarders absorb large amounts of water in a similar manner to a gelling agent and store this water. On burning material which is finely coated with such water stores, "the fire dies out". However, particularly for forest fires, such retarders are not normally necessary and are also not advisable, owing to the inevitably accompanying pollution of the ground. They may, however, have an extremely positive effect on other fires.

The invention is explained in more detail below in exemplary embodiments with reference to the drawings, in which: Fig. 1 diagrammatically shows an exploding bag suspended from a helicopter, Fig. 2 diagrammatically shows the dropping of the exploding bag onto the source of a WO 97/06858 9 PCT/DE96/01510 fire, Fig. 3 diagrammatically shows the triggering of an extinguishing cloud, and Fig. 4 shows an example of a detonating device.

Figs. 1 3 diagrammatically illustrate the procedure for an extinguishing attack on the flame front of a forest fire. A water-filled, drop-shaped exploding bag 1 is suspended from the lifting hook 7 of a helicopter 10 (Fig. 1) by means of a holding cable 4 made of synthetic material nylon) or steel, the length of which may be 3 50 m. The exploding bag has a capacity of about 1000 1 of water and consists of thin-walled plastic polypropylene), the wall thickness of which is sufficient to carry the water but small enough to burst on explosion.

An explosive charge 2, which is provided with a delayed-action fuse, is expediently likewise drop-shaped or bubble-shaped in accordance with the exploding bag and is held in position by a short cable 5, is situated within the water 3 in the exploding bag, and preferably centrally. The lower side, facing the fire, of the exploding bag may be provided with a heat-protective layer 8 which reflects thermal radiation, e.g. an aluminium foil, which is intended to prevent the exploding bag being locally destroyed by the fire in the event of exposure to excessive heat and the extinguishing water thus being largely lost for the action of the subsequent detonation.

The holding cable 4 may have different designs, so that it is either dropped together with the exploding bag 1 or remains on the helicopter. In the example of Figs. 1 and 2, it is assumed that the holding cable is released from the lifting hook 7 and dropped together with the exploding bag. In this case, it should be provided with a spliced loop at the upper end situated on the lifting hook, in order to prevent twisting of the holding cable under load on the lifting hook of the helicopter, since this could possibly impede dropping from the hook. The load should in no event be taken up by WO 97/06858 10 PCT/DE96/01510 means of a clevis on the hook itself, since the relatively heavy clevis would overtake the exploding bag in free fall after being released from the hook and thus would undesirably rotate the said bag through 1800. For even better stabilization during the fall, it is advisable to fix one or two small braking parachutes 6 (Fig. 2) to the holding cable directly below the upper end, which parachutes are dimensioned such that they do not brake the falling motion of the exploding bag but merely prevent the holding cable from destabilizing the position of the exploding bag during the fall.

As an alternative, however, the holding cable 4 may also be provided at its lower end with a remotecontrolled lifting hook 18 (only indicated diagrammatically), which makes it possible to release the exploding bag from the holding cable from the helicopter and to drop it on its own. As a result, the holding cable remains on the helicopter and is available for reuse.

Lifting hooks controlled remotely from the helicopter are known and are used, for example, in forestry for feeding wild animals.

When the helicopter has reached the site of the fire and has positioned the exploding bag at a predetermined height above the source of the fire, the exploding bag (with or without holding cable) is dropped and moves towards the source of the fire in free fall (Fig. As soon as it has then reached a height just above the source of the fire a few metres above the treetops), the explosion is triggered. This may be carried out by remote detonation which is triggered from the loading helicopter 10 or a special fire-chief helicopter or an observation station on the ground by means of a radio signal. Since remote ignition requires high concentration and quick reactions from the operator, in view of the high falling rate of the exploding bag, it is generally more expedient to effect detonation of the explosive charge in the exploding bag by means of a delayed-action fuse, which is activated at the same time as the exploding bag is dropped and detonates the WO 97/06858 11 PCT/DE96/01510 explosive charge at a specific time after the drop, when the exploding bag is situated at the desired height above the source of the fire.

Preferably, delayed-action fuses with two safety means are used here in order to satisfy safety requirements under aviation law. These U-detonators, which are nowadays produced on an industrial scale, have tolerances of only a few milliseconds, so that the required dropping height for the explosive charge can be calculated very precisely and also maximum safety is provided for the aircrew. By way of example, a fuse which has proven to be well suited is one which can be set in up to 18 intervals of 250 milliseconds each, so that falling times until detonation following activation of the fuse of from 0.25 to 4.5 seconds can be set, corresponding to a falling height of half a metre to just under a hundred metres, disregarding the air resistance. The height of the helicopter above the detonation site at the moment when the exploding bag is dropped is composed of this falling distance plus the length of the holding cable.

Fig. 4 shows an example of a triggering of the delayed-action fuse which is particularly acceptable in terms of safety. A twin-core detonation cable 11 is led from the delayed-action fuse, out of the exploding bag 1, along the holding cable 4 as far as just beneath the bottom of the helicopter 10. There, the detonation cable is connected to a direct voltage source 17, situated in the helicopter and serving as detonation source, by means of a plug-in connection 12, for example comprising a flat plug (on the end of the detonation cable) and a flat socket (fixed firmly on the bottom of the helicopter).

A

tumbler switch 13 is arranged in the line between the flat socket and the detonation source. The detonation cable is provided after a relatively short distance, slightly below the flat plug, with a further switch 16, which contains two contact springs which are separated from one another by a plastic flat key and contact one S another when the plastic flat key is removed. The plastic flat key, which is suspended in the lifting hook 7 or a WO 97/06858 12 PCT/DE96/01510 different hook on the helicopter by means of a short traction cable 14, is inserted into the switch 16 and thus interrupts the electrical connection of the delayedaction fuse to the detonation source. The detonation cable is fastened to the holding cable 4 by a clamp just below the switch 16. During the approach flight of the helicopter from the pick-up point for the extinguishing bag to the drop point, the connection between detonation source 17 and the plug-in connection 12 is likewise interrupted by the tumbler switch 13, in order to prevent the detonator being activated prematurely as a result of the plastic flat key unintentionally slipping out of the switch 16.

When the helicopter is situated at the site intended for the drop, at the height corresponding to the length of the holding cable, the duration of the delay for the fuse and the desired detonation height above the ground, voltage is firstly applied to the plug-in connection 12 by actuating the tumbler switch 13. The holding cable 4 is then unlatched from the lifting hook 7 of the helicopter. Due to the fact that the detonation cable is fixed to the holding cable by means of the clamp the plastic flat key, which is retained by its connection to the helicopter, is firstly pulled out of the switch 16 by the falling movement. As a result, there is electrical contact between detonation source and delayed-action fuse, and the fuse is activated. A short time later, the continuing falling movement pulls the flat plug out of the flat socket, as a result of which the so-called in-cockpit component, comprising detonation source, tumbler switch, line and flat socket, is not mechanically loaded by the drop and is immediately available again for the next extinguishing deployment.

Attention merely has to be paid here to the fact that the traction cable 14 for fastening the plastic flat key should be selected to be so short that the plug-in contact is only initiated after the key has been pulled out of the contact clamp. Otherwise, the fuse would not be electrically activated and the exploding bag would not WO 97/06858 13 PCT/DE96/01510 be detonated as desired.

As already described, the detonation of the explosive charge in the exploding bag results in a mist of extremely finely divided water droplets, also referred to as an extinguishing cloud. This extinguishing cloud expands essentially spherically. Movement of water droplets upwards away from the source of the fire is generally not desirable, however, and an essentially hemispherical extinguishing cloud, in which all the water droplets are directed downwards towards the source of the fire and its environment, is much more effective. Such an essentially hemispherical extinguishing cloud is illustrated diagrammatically in Fig. 3; it can be achieved by covering the extinguishing water 3 within the exploding bag 1 with a thin film 9 of plastic, paper or the like (Fig. This film may be placed loosely on the extinguishing water, but may also be attached to the exploding bag at points such that a sufficient opening remains for filling the extinguishing water into the exploding bag.

Claims (12)

1. Method of fighting fires from the air, in which extinguishing water is introduced by means of aircraft, perferably helicopters, into the source of the fire, characterized in that the extinguishing water is atomized to form a cloudlike mist of microscopic droplets just above the source of the fire by explosion.

2. Method according to Claim 1, characterized in that a container which is filled with the extinguishing water, has a wall which can be burst and in which an explosive charge with a fuse is arranged within the extinguishing water is exploded just above the source of the fire.

3. Method according to Claim 2, characterized in that a highly brisant explosive is selected as the explosive charge in an amount which is sufficient to impart to the water droplets an initial speed of at least 5,000 m/s. 15

4. Method according to Claim 2 or 3, characterized in that the container is dropped from a helicopter above the source of the fire and in that the explosive charge is detonated during the free fall just above the source of the fire.

Method according to Claim 4, characterized in that two or more helicopters simultaneously each drop one container at a distance apart of one effective width of the extinguishing cloud and detonate it, preferably coordinated by radio.

6. Device for carrying out the method according to one of Claims 1 to Socharacterized by an exploding bag made of thin-walled plastic in the shape of a bubble or a drop for receiving the extinguishing water and an explosive charge, with fuse, which is held approximately centrally within the extinguishing water and is likewise bubble or drop-shaped, it being possible to suspend the exploding bag from a helicopter by means of a holding cable such that it can be dropped.

7. Device according to Claim 6, characterized in that a reflective heat- •protective layer is arranged on the lower side, facing the fire, of the exploding bag.

8. Device according to Claim 6 or 7, characterized in that the 30 extinguishing water is covered with a thin film within the exploding bag.

9. Device according to one of Claims 6 to 8, characterized in that the fuse of the explosive charge is a delayed-action fuse which can be set to a predetermined falling height, is connected to a detonation source in the helicopter via a detonation cable, which can be separated from the helicopter, and can be activated at the same time as the exploding bag is dropped.

Method according to one of Claims 6 to 9, characterized in that at least one small braking parachute is attached to the holding cable near the upper end of the holding cable, which parachute prevents the holding cable from overtaking the exploding bag during the falling phase. [N:\LIBW08255:GMM

11. A method of fighting fires from the air, the method being substantially as hereinbefore described with reference to the accompanying drawings.

12. A device for extinguishing fires from the air, the device being substantially as hereinbefore described with reference to the accompanying drawings. Dated 8 May, 1997 Winfried Rosenstock Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON 5e *S 0 o O S° S [N:\LIBW]08255:GMM