Suppression Systems: Active

Manual activation

The manually activated extinguishment systems may be a hand-held tank-type extinguisher, or an extinguisher mounted in the engine compartment but activated by the operator in the driver’s seat. For systems activated remotely by the driver, there will be a switch or button actuator in on the instrument panel a suppressant agent storage container in the vehicle, possibly piping to direct the agent where needed and one or more dispersal nozzles. The installed systems are analogous to the automatically activated system, differing only by their means of activation. The components will be further described in the automatic activation section.

Automatic Activation

Once the sensors signal for suppressant system activation, one of several strategies may be initiated.

1. Immediate release of the suppression agent. For this approach, no processing component is necessary for the system.
2. Delay in activation for an amount of time (for the vehicle operator to bring the vehicle to rest) or until vehicle sensors indicate the vehicle is below a preset speed. By delaying for a slower or stopped vehicle, the airflow is likely reduced and a greater amount of the suppressant agent remains in the area of need.

The control module pictured above is a sample of the type used in transit bus applications and generally located in the operator’s area. [1]

When suppression systems are fixed in the vehicle, components remaining after the fire may include:

1. Nozzles for dispersal of dry chemical or clean (gaseous) agents. Often the nozzles have a similar appearance to water-based systems found in buildings.
2. Suppressant agent reservoirs. The reservoirs often have appearances similar to small fire extinguisher cylinders.
3. Valves on reservoirs that may be activated by solenoid (electric control) or pyrotechnic detonators (squib).
4. Less commonly, there may be an un-pressurized agent reservoir and a pressurized cylinder of gas to expel the agent when needed.
5. Piping between the nozzle(s) and reservoirs and wiring to detectors or alarm signal processor.

An extinguisher bottle as used in commercial vehicle suppression systems.

Example of a System in a Transit Bus

This diagram shows a fire suppression system used in a transit bus. A detection system and both manual and active actuation systems are described [2].

References

1. Photographs on page courtesy of Kidde Dual Spectrum.
2. Reproduced with permission of Port Authority of Allegheny County, Pennsylvania.