Sprinklers are designed to suppress automatically small fires on, or shortly after, ignition or to contain fires until the arrival of the fire service.
Sprinkler head exploding.
Photograph courtesy of Wormald Ltd.
In Europe most sprinklers work on the exploding bulb principle. The water nozzle is sealed by a glass bulb containing a volatile liquid. When heated by the fire, the liquid expands and breaks the bulb thus activating the sprinkler head (Figure 10 & Figure 11). As only individual sprinkler heads affected by the hot gases from the fire are activated, water damage is minimised. Research has shown that over 90% of fires are suppressed by four sprinkler heads or less.
Figure 10: Typical sprinkler head configuration. The red colour of the volatile liquid indicates that the glass will break at 68°C. This is the most common activation temperature.
In Approved Document B to the 1991 Building Regulations for England and Wales, a reduction of 30 minutes in the required fire resistance may be applied to most types of non-domestic occupancies less than 30 metres in height when an approved sprinkler system is installed. All non-domestic buildings over 30 metres in height are now required to have sprinklers. This trade-off between passive and active systems has given an impetus to their use in England and Wales; it is widely seen to be a positive development since statistical experience shows that the use of sprinklers provides a significant improvement in life safety, and also has considerable social and economic benefits.
The major cause of fatalities in fire is smoke and most deaths occur long before there is any significant risk of structural collapse. In addition the major costs of fire typically result from destruction of building contents, finishes and cladding and from the consequential losses. Structural damage is normally of secondary importance. By suppressing fire and smoke, sprinklers are an extremely effective means of enhancing life safety and reducing financial losses.
More information on the benefits of sprinklers, both in terms of life safety and property protection can be obtained from the British Automatic Sprinkler Association (BASA)
This publication contains detailed cost examples which indicate that the value of trade-offs in passive fire protection. Larger allowable compartment sizes, reduced number of fire fighting lifts and shafts etc. can cancel out any additional costs incurred in installing sprinklers.