New Study: Performance of Protected Ceiling/Floor Assemblies and Impact on Tenability

Blog Post created by ryan.quinn Employee on Jul 8, 2011

The National Research Council Canada (NRC) has released a report on its latest study -Performance of Protected Ceiling/Floor Assemblies and Impact on Tenability with A Basement Fire Scenario. In addition to testing the structural integrity of engineered wood assemblies under fire conditions, testing included smoke alarm performance, fire development, sequence of events, and tenability in relation to evacuation of occupants.Structural_stability_strip

The results of the NRC research project are considered critically important to dispel the perceived notion by numerous stakeholders that protection of engineered floor assemblies constitutes equivalency to fire sprinklers.

http://nfpa.typepad.com/.a/6a00d8351b9f3453ef01543394b4f3970c-piProtection of engineered floor assemblies is included in the 2012 IRC. This requirement in the model codes is in addition to the requirement of fire sprinkler installation of the entire dwelling. There are very good reasons for this; protection of engineered floor assemblies, while extending the time to structural instability and collapse under fire conditions, does nothing to prevent the fire from growing or to become deadly for occupants and responding fire crews; as supported by the NRC report.

The following common floor structural beam assemblies were exposed to full scale fire scenarios and protected on the basement side:

  • Engineered wood I-joist – ½ in. gypsum board, suspended ceiling, and 1 or 2 sprinklers
  • Steel C-joist – ½ in. gypsum board
  • Metal- web wood truss – ½ in. gypsum board and 1 sprinkler
  • Solid sawn wood joist – ½ in. gypsum board.

The testing facility consisted of a typical two-story detached single-family home with a basement. The fuel package consisted of a mock-up sofa with exposed polyurethane foam placed on a metal frame and wood cribs, to simulate a typical living room configuration.

NRC fire testing Thermocouple arrays were used to measure temperatures at different heights above the floor installed in numerous areas. Flame sensing devices and floor deflection devices (measured at 9 locations) were used on the first floor, and smoke and gas measurement devices were installed on the first and second floor. Gas sampling ports were included at the quarter point and the center of the second story corridor and connected to infrared Carbon Monoxide/Carbon Dioxide gas analyzers, Oxygen gas analyzers, and smoke density meters.

Although passive protection of solid-sawn wood joists, wood I-joists, steel c-joists, metal web trusses with gypsum board increased structural stability for longer time periods, the structures always failed and collapsed after a certain time during the experiments. The same applies to suspended ceilings. Most importantly, the structural failure of the test assembly occurred well after the untenable conditions were reached.

The test assemblies protected by residential fire sprinklers retained their structural integrity and did not collapse. Conditions that would cause incapacitation did not exist, or were quickly reversed by sprinkler activation. Tenable conditions remained throughout the structure.

Based on the results of this study, passive protection of engineered wood assemblies by gypsum and suspended ceilings will do little to increase life safety in the event of fire in the home, especially for susceptible (high risk) persons. These high risk groups; young children, adults older than 65 and disabled persons are disproportionately incapacitated earlier in fire events by untenable conditions reached when the structures are not protected by fire sprinklers.

Maria Figueroa