Thanks to preventive fire protection, typical residential fires are declining, while at the same time, climate change is exacerbating prolonged droughts in the natural environment. As a result, the danger of forest and vegetation fires increases more and more.
These types of fires have always existed, of course, and in certain regions of the world, annual ‘fire seasons’ are nothing unusual. However, it can be observed that the forest-fire season is getting longer from year to year and the fires are getting more and more intense. Consequently, the demands on mobile extinguishing technology are also increasing. It must be possible to fight the fires quickly while using as little water as possible.
In many cases, the technology and tactics are mainly designed for fighting fires in urban areas. The flame front of forest and vegetation fires, however, usually does not run along well-prepared roads including water mains and hydrant networks, but off-road on field, forest and farm tracks with a wide variety of topography.
A forest or vegetation fire that extends over several hectares brings its own rules with regard to spreading speed, temperature, wind strength and direction. Fighting and containing such fires requires a high degree of mobility.
The ability to proceed quickly and in a mobile manner with as little water as possible can quickly determine the success of the operation. In forest and vegetation fires away from urban infrastructure, water is a valuable good that must be used in a targeted and economical way. In this case, economical means a maximum water delivery of between 25 and 50 l/min, delivered in bursts. This amount of water corresponds to approx. two D-size hollow jet pipes.
Use of wetting agent for more effective use of water as an extinguishing agent
An increase in the effectiveness of extinguishing is possible with the use of wetting agent added to the water, and in some cases it is also indicated, in particular when burning into the ground is taking place or a lot of dead wood is present. Wetting agent added to the extinguishing water reduces the surface tension and soaks much deeper into the substance on fire or the ash layer.
The foam agent industry has provided suitable foam agents for the field of forest and vegetation firefighting. According to the manufacturers’ own statements, these foam agents are harmless to the environment when used as intended, and they are 100% biodegradable. In addition to generating wetting agent for vegetation fires, they are also suitable for fighting Class A and B fires with wetting agent and/or foam. The proportioning rates vary greatly and these in turn have a significant impact on logistics and effectiveness at lower proportioning rates.
Electronic pressure proportioning systems
Today, there is a large number of pressure proportioning systems on the market, which are permanently installed in fire trucks and are driven by the 24V on-board voltage of the vehicles. These systems have become established in the vehicles, also because of the DIN 14430 pressure proportioning systems. These electronic proportioning systems are now comparatively inexpensive to purchase. However, a look at the technical data and the corresponding working diagrams reveals that the proportioning and working range is limited. The generation of foam with a foam pipe of 400 l/min flow and a 1% or 3% proportioning rate is no problem for all pressure proportioning systems.
The situation is different for the generation of wetting agent with only a low extinguishing agent output. A guaranteed and constant proportioning of foam concentrate for the generation of wetting agent in the range of 0.1% to 0.3% can only be ensured by most electronic proportioning pumps from a water delivery of at least 100 l/min and more. In the case of interval extinguishing by repeatedly opening and closing the jet pipes, deviations in proportioning can occur, which then leads to ‘overdosing’ of the mixture. The electronic systems are adjusted to the water flow by a measuring section (inductive measurement of the flow rate). Due to the fluctuating delivery of extinguishing water, the dosage is not exact and for a certain period of time no wetting agent is produced, but foam.
Mechanical pressure proportioning systems
Purely mechanical systems represent an alternative to electronic pressure proportioners. The foam pump is not driven by a 24V electric drive but by the discharged extinguishing water. This water flows through a closed water motor with a turbine wheel (the principle is similar to the mill wheel in a water mill). This turbine wheel in turn drives the foam pump, i.e. in the form of a piston pump. The system (drive turbine and foam pump) is thus purely mechanical and the proportioning of wetting agent is always automatically controlled as a direct function of the volumetric flow rate.
The foam agent is thus added in exact proportion to the water flow. This means that the turbine wheel in the water motor turns faster or slower depending on how large or small the water flow rate is. Accordingly, more or less foam agent is added by the foam agent / proportioning pump. Overdosing is not possible.
This results in the following operational advantages for the application in vegetation firefighting:
- Purely mechanically driven pressure proportioning systems do not require any external power.
- Thus, they are not only suitable for vehicles but can also be used independently, e.g. on a roll-off container, trailer or mobile in connection with a portable fire pump.
- Depending on the size, the unit can be comfortably carried to the scene by firefighters.
- Large hose distances can be overcome without the water/foam premix segregating.
- Loading on carts, roll-off containers or even trailers is possible without any problems.
A useful field of application for mobile systems is the filling of external firefighting water tanks for helicopters. In some cases, these tanks are partially filled by ground personnel if the approach to the next suitable water intake point is too far. Here, too, it makes sense to add wetting agent or gel to the water to achieve a better extinguishing result. If necessary, a dye can also be added to mark drop zones. This task is much more complicated or even impossible with conventional pressure proportioning systems. Incidentally, the turbine proportioning systems described above were developed for the chemical industry, where very precise proportioning, sometimes of several media at the same time, is very important.
Conclusion
Fighting forest fires effectively depends on the right technology. By using wetting agent, water can be used more economically and effectively as an extinguishing agent in many cases. Compared to electrically driven pressure proportioners, mechanical systems offer some advantages not only for this application.
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About the Author
Tristan Reitz Dipl.-Ing. (FH) is Market Manager Fire Service and Mobile Fire Protection at FireDos.
