Whilst smoke detectors can be mounted at various heights they can never exceed 10.5 metres above floor level. In many modern office buildings there are triple volume areas, especially at reception which may exceed this height. In industrial environments many warehouses have high roofs that exceed this measurement. In addition to detectors not working correctly they are also very difficult to maintain, requiring specialist lift equipment to perform the routine maintenance. There are specialist detection system that can perform above these heights. If you observe a standard ceiling mount type detector on a ceiling above 10.5m chances are the system has not be fitted correctly.
Reason: As smoke leaves a fire it rises, doing so it looses some of its heat for each meter it rises. This reduces the speed of the smokes accent resulting in two issues:
- The smoke disperses horizontal as it rises (becomes less concentrated)
- Time taken to reach a detector above this level is too long.
The net result is that the amount of smoke required at fire source to generate a smoke alarm activation is too great and would impair peoples escape at floor level before the fire alarm would raise the warning.