This schematic shows a dual fire supression system designed for an engine compartment.

For decades, A:B:C dry chemical has been the standard firefighting agent of choice across the professional vehicle fire suppression industry. It is known for a fast knockdown of flames and for the fact that it fills a volume of space, which makes it perfect for use in enclosed areas like engine compartments. As a result of this 3-D coverage, pound for pound, dry chemical agent is very efficient. These attributes make it as ideal for keeping a fire from spreading today as they did 50 years ago. This is also why the vast majority of handheld fire extinguishers continue to be filled with A:B:C powder, as it is proven and can be used effectively against debris, fuel and electrical fires.

In certain circles, A:B liquid has been made out recently to be some sort of ultimate agent, an assertion that under scrutiny doesn’t hold up. Due to its physical makeup, a wet agent can only put out a fire it is directly sprayed on, unlike a dry agent that engulfs the engine compartment with firefighting material. Based on independent laboratory testing, it has been proven that, to provide an equal amount of coverage to a dry chemical system, a wet system needs more nozzles. This requires more agent to supply them, which in turn requires more or larger tanks to contain the liquid. From a logistical standpoint, a liquid-only system is more involved and expensive to install and more costly to maintain.

Additionally, the larger/more numerous tanks required to hold the needed liquid agent are more expensive for the end users. This type of system also takes up more space on the machine it is protecting, it adds weight, and it is not appropriate for Class C (electrical) fires. This last fact is especially concerning as this type of fire is the cause of a significant percentage of vehicle fires on mobile heavy equipment each year.

These factors aside, there are advantages to incorporating a liquid agent to a suppression system. In addition to its ability to suppress fire, it has the distinct advantage of lowering the surface temperatures of the engine components on which it is being used. This cooling ability is especially helpful when it comes to the next generation of Tier 4 engines, which are quite a bit larger than traditional engines and have very high operating temperatures. By reducing the temperature of the engine components, like the afterburner and turbocharger, the likelihood of a fire reflashing after having been suppressed is dramatically limited. (This is predominantly why dual agent systems incorporate A:B liquid.)

Clearly, each of the agent types has important advantages, but when used together they are even more effective than when used separately, as they cover for each other’s shortcomings. This is why dual-agent fire suppression systems have become more popular than ever among end users in many of the heavy industries, including mining and forestry.

A dual-agent system is actually two different fire suppression systems, a dry chemical and a liquid, which are actuated at the same time. Each of these systems has its own delivery system, which is routed separately throughout the machine. The nozzles of each agent type are directed at specific engine areas based upon their firefighting capacity. (In general, the liquid agent is aimed at extremely hot surfaces and the dry chemical is used to flood the protected area as well as address specific components, like the starter.) The two share detection and actuation networks. When discharged, these tandem systems each suppress the fire in keeping with their own strengths, contributing to a well-rounded, more thorough approach than either separately is capable of.

When all these individual facts are weighed, it becomes clear that a dual-agent system is the better solution than liquid-only when looking to protect heavy equipment from the threat of fire.

This article was supplied by AFEX Systems.