After a number of large fires on construction sites involving timber frame construction, the risk of both high radiation emissions due to the high fire load from the wood on the construction site and ember transportation causing secondary fires has been recognised. The HSE has started to address these concerns by producing new guidance on construction sites using timber frame construction, incorporating the lessons learnt from recent fires.
However, less well known and published is the specific risk posed by timber frame construction in completed buildings. There are two main issues specific to timber frame buildings, the quality of construction with regard to fire stopping, and fire fighting issues. Compartmentation, an essential safety feature in a completed timber frame building, is present only if the fire stopping has been provided according to the design. In typical brick and mortar type buildings, if fire stopping is not 100% correct and a fire occurs which spreads into a void, the brick is inherently non combustible so the potential for fire spread through the void and a large fire developing is less likely. However in timber frame buildings, if a fire occurs and a weakness in the fire stopping is present, fire can spread into a void. The void then contains timber which is inherently combustible and therefore fire can potentially spread within the void to other areas of the building, causing a large fire. In essence, if the fire stopping is not installed correctly then timber frame buildings are more susceptible to minor ignition events becoming large fires than in typical brick and mortar type buildings.
The second issue with timber frame construction is the fire service not being able to identify the type of construction when they arrive to fight a fire. Timber frame buildings can be virtually impossible to identify from a visual inspection of a building. The various different types of cladding on the outside of a building mask the fact that the building has a timber frame. In some cases a brick facade is used and it is impossible for the fire service to know whether a building is timber framed. If the fire service had the knowledge that the building was timber framed, their approach to fighting the fire would be modified. They would also consider the best way to prevent the specific risk of potential fire spread within the voids of the building.
What needs to happen next? Some people, especially within the insurance industry are wanting a blanket use of sprinklers with timber frame buildings. In our opinion, installing a suppression system is a generic solution but is not the only solution to providing a safe timber framed building. At Innovation Fire Engineering, we prefer to develop a solution that addresses the specific risks within the individual building we are working on. This ensures fire safety is not compromised but the package of fire safety measures is not over specified, hence are clients are not lumbered with unnecessary costs.
As timber frame is here to stay, the long term strategy should include the following:
Controlling the quality of construction in timber frame buildings during construction.
Education of trade persons on the subtle differences of fire stopping requirements on timber frame buildings. Development of a clear and simple system for the fire service to identify timber frame construction, to assist fire fighting operations. This education element of the solution will take time, but in our opinion this will be more effective as a long term solution than the government changing Approved Document B to incorporate sprinklers in all timber frame buildings. There is currently no political will to amend Approved Document B, the cost to developers of using sprinklers may be prohibitive in this economic climate and the use of sprinklers may not be the most cost effective solution to address the fire safety issues in this type of building.