(NIST) Structural Collapse Fire Tests: Single Story Wood Frame Structures

(NIST) Structural Collapse Fire Tests: Single Story Wood Frame Structures

Synopsis

This study examines the feasibility of predicting structural collapse in single story wood frame structures. The study is based off of a series of fire tests conducted by the Phoenix Fire Department as part of a training video.

Experiment Design

·  Multiple fires were set in four structures with different roof constructions.

·  Temperatures were measured at specific intervals of time in four locations within each structure.

·  Furniture items were placed in the front and back of each structure to simulate living room and bedroom areas.

·  The living room and bedroom areas of each structure were ignited simultaneously using electric matches.

Findings

·  In all of the tests, the roof of each structure collapsed approximately 17 minutes after ignition.

·  Flashover occurred in the living room spaces approximately three to four minutes after ignition.

·  Prior to collapse, peak temperatures in the attic spaces were approximately 930 °F (500 °C).

·  The fires broke through into the attic spaces six to eight minutes after ignition. Flashover in the attic space occurred approximately five-and-a-half minutes after the fire broke through the ceiling, or 12 minutes after ignition. As the attic space approaches flashover, temperatures under the roof rapidly change (within a few seconds) from near ambient 100 °F (37 °C) to 1000 °F (540 °C).

·  The thermal signature of fire coming through the roof as seen on infrared cameras is washed out by radiation from smoke or fire plumes or was obscured by water spray or rain.

Takeaways

·  This limited set of burn tests indicated that infrared cameras and thermal images may not be able to adequately predict structural collapse in residential structures.[1]

·  Collapse happens within operational timeframe.

·  Regardless of the fire source or ventilation, firefighters can fall through floors and can get caught in the flow path between the basement and upper levels.

·  Sounding and sagging are not an indication of stability; Firefighters must verify the stability of the platform on which they operate.

Read the Report

http://fire.nist.gov/bfrlpubs/fire04/art018.html

[1] Stroup, Bryner, Lee, McElroy, Roadarmel, & Twilley, March 2004