Fire Safety Science Digital Archive

A study has been made of the behavior of roofs of buildings in which large fires occurred. Owing to the small numbers involved no firm conclusions can be drawn but certain indications can be discerned. In approximately one fifth of the number of large fires occurring during one year the roof played an important role in the development of the fires, and one third of these originated within the roof. Supposed causes of fire were unknown in about one half the cases considered. Fires involving wooden roof structures were noted on 22 occasions and metal on 14, half of the latter were covered with bituminised metal sheeting and the fire was often aggravated by drops of burning bitumen falling on the contents below. Wooden framed roofs may not be easily ignited but fire spreads rapidly once it has obtained a hold. Most of the fires were said to have spread rapidly in the roofs and most of the roofs covered compartments of large area. Smaller compartments with walls taken through the roof could prevent fire spread. Maximum roof damage was not necessarily associated with the maximum damage to the building. Felt and fibreboard roof linings tended to assist the growth of fire in the few cases in which they were reported. Venting of the fire can in certain circumstances reduce the rate of spread but there may be conditions in which the opposite effect occurs. Mansard and Belfast roofs can from the nature of their construction assist in spreading the fire. Combustible material adhering to roof members enables easy spread of fire, regular cleaning of the roof structures would minimise fire spread by this means.