The National Research Council (NRC) is the Government of Canada's organization for research and development. Following previous studies of unprotected floor/ceiling assemblies under basement fire scenarios, a subsequent program was undertaken to investigate the performance of protected floor/ceiling assemblies and the tenability conditions in a test facility representing a two-story detached single-family house.

Most of us are familiar with the Underwriter Laboratories (UL) study of unprotected lightweight/engineered wood assemblies in basement fire scenarios. The UL tests revealed that these unprotected structures collapse as early as six minutes from the onset of fire, representing a great danger to home occupants and an even greater danger to firefighters who may arrive at or after the six minute threshold.

The NRC experiment used a simple and repeatable fuel package consisting of a mock-up sofa and wood cribs representing the typical additional fire load to sustain the fire. The structures were protected with gypsum or a fire sprinkler system.
The data was analyzed to determine the following:
- fire performance of the protected floor/ceiling systems
- tenability conditions in the floor areas above the fire, and
- timeline for fire initiation, smoke alarm activation, onset of untenable conditions, and structural failure.
Smoke obscuration was the first hazard to arise. Even though smoke obscuration is not considered an incapacitating factor, it does disorient people; slowing down their escape and exposing them to other untenable conditions for a longer period.
Untenable (incapacitation) conditions were reached shortly after smoke obscuration. Heat exposure reached incapacitation doses after 4 minutes; CO exposure reached the incapacitation doses on the second story after 5 minutes. The structural performance was improved significantly with the gypsum board protected floor assemblies.
The single sprinkler activation was able to control the fire quickly and keep the temperature in the fire room close to the ambient level. Tenability limits were not reached. There was no structural damage to the test floor assembly.
The NRC tests reveal that although protection of lightweight ceiling/floor assemblies with gypsum in basement fire scenarios extends the structural stability of these assemblies, they do little to nothing to affect tenability. “Among the protection measures studied, the sprinkler protection was the only measure that provided both the structural protection and the tenable conditions for the safety of occupants.” Firefighter are also protected by fire sprinkler systems.
Read the NRC report