Fire suppression
For a more general treatment of the subject of fire suppression, see Chapter 4. The risk of a vehicle fire during chassis dynamometer running is quite high, since the air cooling, even with supplementary fans, is likely to be less than that experienced on the road. Underfloor exhaust systems, in particular, can become very hot and could ignite fuel vapour, whatever its source. A fixed fire suppression system is more difficult to design than in an engine test cell because of both the large size of rolling road cells and the more difficult access to the seat of the fire, which may
be within the vehicle body. All vehicle test facilities should be equipped with substantial handheld or hand-
operated fire extinguishers and staff should be trained in their use. One method of fire protection is to fit the test vehicle with a system of the type designed for rally cars which enables the driver or control room to flood the engine compartment with foam extinguishant. Automatic gas-based systems of the type used in some engine test cells are less effective in vehicle cells in view of the greater difficulty in ensuring that all personnel, including the driver, have been evacuated before they are activated. The modern trend is towards water fog suppression systems, which may include discharge nozzles mounted beneath the vehicle and thus near the seat of most potential fires.
There must be a clear and unimpeded escape route for any test driver and the impairment in vision from steam or smoke must be taken into account, particularly in the case of anechoic cells, where the escape door positions should not be camouflaged within the coned surface.
The effect of roll diameter on tyre contact conditions