Fire Suppression Basics: Control Systems

In case you missed any of the previous posts in the Vehicle Fire Suppression Basics series…

Part 3 of 8: Control Systems

Extinguishing agents and detectors are key components of any fire suppression system, but it is the control module that co-ordinates and dictates the response to fire. While the subject of control systems is worthy of a book in its own right, in this post we will briefly outline the control system process and the features currently available.

How Control Modules Work

Control modules essentially receive the information relayed by the sensors and detectors, then process this information to decide whether there is a fire. They then deploy the necessary measures to ensure operator and equipment safety.

The simplest, manual systems only provide fire warning, therefore requiring the operator to stop the vehicle, shut down the engine, manually operate the fire suppression system and then evacuate the vehicle. However, more complex systems offer automatic 24-hour stand-alone protection. Of these systems, the most sophisticated can electronically monitor the actuation, power, release and communication circuits, and interface signalling measures such as engine/fuel shutdown, isolating the main battery, stopping the engine fan, activating a high decibel alarm, deploying a fire suppressing agent and venting the hydraulic system.

In line with the EU Machinery Directive 2006/42/EC, the operator must always be in control of the machine. The operator must therefore be able to delay the activation of the fire suppression system and engine shutdown sequence, until he deems it safe to do so. In automatic systems, this is achieved by a delay button in the control module that allows the operator the postpone the system discharge for a pre-programmed period of time.

Wherever possible, the control module should be mounted where it is visible to the operator, but manual deployment controls should be available both in the cab and, if applicable, at ground level or outside.

Detection Time

In almost all vehicles, an engine fan is used to cool the air around the engine. This can produce air flow speeds of 2.5 to 11.5 m3/s. In order to achieve optimum coverage by the suppressing agent, the fan needs to be stopped before the fire suppression system discharges. When running at maximum rpm, it can take some fans up to 10 seconds to completely stop. The same applies for hydraulic system venting. As hydraulic fluids are often flammable and under high pressures, they can increase the likelihood of fire or reignition and therefore need to be removed if deemed necessary.

The total time between the detection of fire and full deployment of the suppression agent can vary depending on the type of vehicle and the quality of the system, but here is an indication:

  • Automatic detection or manual actuation of the fire suppression system -> 2 – 5 seconds -> engine shut down signal, battery isolation, engine fan slowing down, hydraulic venting, fuel valve closing -> 10 seconds -> Suppression agent(s) discharging from nozzles

Self-Contained Control Modules

Control modules are sometimes self-contained units. This means that the equipment does not need to be connected to the vehicle power supply and has its own independent supply. In the event of the main battery being damaged or disconnected, then power will still be available and surges cannot damage the control unit.

Electrical faults are the single largest cause of vehicle fires and so it is also recommended that an automatic battery isolator is installed. This ensures the main battery power is switched ‘off’ on activation of the fire suppression system, thereby reducing damage to wiring looms and the possibility of fire re-ignition.

Next blog post in the Vehicle Fire Suppression Basics series: Suppression Agent Tanks

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