How Does Building Construction Impact Fire Behavior?

The shift in fire behavior is accompanied by a shift in building materials. The use of 2x8, 2x10, 2x12 dimensional lumber as framing for structures changed to the use of 2x4 roof and floor trusses. Wooden I-joists are now used for floor systems to provide wide spans without supporting posts.

This construction simply does not perform well with a fire that progresses to flashover within five minutes. Lightweight construction allows fire to spread, and the structure loses its integrity with little to no warning. The days of floors sagging or feeling soft are in the past. I personally benefited from older construction when soft floors and a soft roof signaled me and my crew to move to safety. 

The newer construction fails catastrophically and offers no warning. As a result, there is a reluctance on the part of fire departments to commit staff inside a building unless they are able to immediately control the fire from outside.

Open Floor Plans

The design trend of open floor plans also aggravates fire spread. With a reduced number of interior partitions, the fire can easily overtake a large area of the building. The open floor plan is also a factor in commercial design. Tenability in modern open spaces is a life safety challenge. The higher property losses follow when there are little internal fire divisions to slow fire spread.

Storage Hazards

 The size and volume of storage facilities is also a new development. When I entered the insurance business in the early 1980’s our diagrams routinely included firewalls and fire doors in storage facilities. Since a single sprinkler valve can protect 40,000 square feet of high piled storage, it was common to find fire divisions inside buildings that were close to the single sprinkler riser maximum area. Twenty-foot heights were considered very high piled storage exposures.

Today’s warehouses with open areas exceeding 250,000 square feet and storage heights over fifty feet are more common. There have been large fire losses where these buildings burned to the ground despite having sprinkler systems.

The design of storage systems outstrips the pace of code development for fire protection. Codes are generally at least three years behind the building designs being constructed.  Add in the delay in governments adopting the codes and you can be six years behind the curve.

Where in the code is there any consideration of hose line advancement inside these huge buildings? I have seen warehouses whose depth exceeded the amount of hose available on the first due engine company. Interior hose stations in warehouses are too little, too late.

Fire behavior in these structures has no comparison to the older buildings that make up the vast majority of loss data. The current construction classifications in the insurance world lacks the ability to differentiate between old traditional construction and new construction.

Frame is Frame until is is not

Looking back at loss data in buildings that are not being built anymore does not create an effective tool for predicting the future. The most appropriate focus would be to use loss data from the past 25 years as the benchmarking tool. Specific construction designators for lightweight construction and open floor plans would help identify the impact of these changes on property risks.