Structural Collapse Prediction Technology Research

This USFA/National Institute of Standards and Technology (NIST) research partnership examined structural collapse prediction technologies on the fireground. This project examined modern construction, the effect of weight loading, as well as thermal exposure. Development of prediction technology for information transfer to the fire service for operational use was addressed as part of this project.

NIST examined data collected by NFPA on firefighter fatalities due to structural collapse from 1979 through 2002 (not including those firefighters lost in the 2001 collapse of the World Trade Center). The analysis included, but was not limited to, the following factors: firefighter's age, rank, experience level, and activity at the time of the incident. The types of property involved, cause and nature of death, and the time of incident were also examined.

Among the trends discovered in the data was that the number of fire fighters lost annually in residential collapses has tripled since the 1980's even though there has been a decrease in the average number of annual fatalities during the same time period.

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Wood Frame Structures Live Fire Testing

Photo showing live fire test on a residential wood frame structure.

Four wood frame residential-like structures with different roof constructions were used in a series of fire tests conducted in cooperation with the Phoenix, AZ Fire Department. The roof construction was the primary difference between each structure: asphalt shingles and plywood, asphalt shingles and oriented strand board, cement tiles and plywood, or cement tiles and oriented strand board. Each structure contained an attic space and two furnished rooms: a living room and a bedroom.

Multiple fires were initiated in each structure to facilitate collapse. The fires were allowed to burn until the portion of the roof supporting two firefighter mannequins failed. Temperatures were measured at various locations in the structures. Peak temperatures obtained during the tests ranged from approximately 800 ºC (1500 ºF) to 1000 ºC (1800 ºF). The roof of each structure collapsed approximately 17 min after ignition.

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Block and Brick Warehouse Construction Live Fire Testing

Fire venting through roof.

Another series of experiments were conducted in Phoenix, Arizona using a brick and block warehouse structure with a "traditional" wood frame roof assembly. This set of two experiments included measurement of temperatures and carbon monoxide inside the structure. The building was approximately 150 feet long by 50 feet wide. Infra-red (IR) cameras were used on the outside of the building to evaluate their usefulness in structural collapse prediction by incident commanders. In addition, vibration sensors were attached to the structure to "listen" for signs of structural collapse.

A firewall was constructed to divide the warehouse into two fire compartments. Stacks of wood pallets were used as the primary fuel source and were ignited using paper and an electric match. Some combustible debris and the building structural elements provided the remainder of the fuel load. Each portion of the structure was allowed to burn until the roof was completely destroyed.

Peak temperatures obtained during the tests ranged from approximately 300 ºC (570 ºF) to 800 ºC (1470 ºF). Peak carbon monoxide measurement reached 4 % in the first test and 5 % during the second test. The roof of the front half of the structure burned through approximately 18 minutes after ignition of the fire. The roof of the back half of the structure began burning about 15 minutes after the start of the second test.

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A DVD, Structural Collapse Fire Tests, containing the reports and video clips of some of the fire experiments is available by contacting David W. Stroup of NIST at 301-975-6564 or david.stroup@nist.gov.

Light-Frame Construction Live Fire Testing

Kinston, North Carolina Live Fire Testing Photos

As part of this project initiative, full-scale fire experiments were conducted in Kinston, North Carolina. Ranch style homes with traditional frame roof construction were used in this experiment done in partnership with NIST and the Bureau of Alcohol, Tobacco and Firearms (ATF). ATF used this experiment to study the investigation of house fires having substantial destruction by fire to the point of roof collapse or burn off. Houses were burned with and without extra loading on the roof. The movement of the roof and other parts of the structure were measured during the fire using advanced laser range finding technology.

The feasibility of measuring changes in position of the roof during the fire as an advanced indicator of collapse was examined. All of these tests showed very little or no motion of the roof during the house burns. There were also many difficulties in obtaining reliable position measurements. In one of the tests, extra roof loading, provided by a water tank, was used to force a well-defined collapse event. Temperature histories were recorded close to these wood supports to document the history of the high temperature exposure.

Shopping Mall Live Fire Testing

Woodbridge, Virginia Live Fire Testing Photos

The final set of experiments was conducted on May 8-10, 2002. These tests involved USFA and fire engineers from NIST and Harvey Mudd College as well as the ATF. This set of experiments tested the ability of highly sensitive motion detectors to detect pre-collapse building vibrations at an abandoned shopping mall (note photos) in Woodbridge, Virginia. Vibration sensors that give early warning to building collapse could provide firefighters time to escape. These controlled fire tests examined the vibration characteristics of lightweight steel frame building construction (note photos) during fires large enough to cause collapse of steel deck roofs. (View photos of Initial Stage of Roof Collapse, Roof Fully Collapsing, and Remains After the Fire.).

Previous initiatives to investigate the integration of the predictive capabilities of computer-based fire models with various non-intrusive sensing techniques will continue. Enhanced live operational testing using different types of construction and the results of such efforts will be targeted in future efforts.

Tiny Vibrations Provide Warning of Collapse

Harvey Mudd College in Claremont, California conducted building vibration sensing during several of the live fire tests (Phoenix warehouse, light frame construction, and shopping mall). Professor Ziyad Duron at Harvey Mudd College is studying the minute vibrations in burning structures for ways to provide reliable advanced warning of collapse. Preliminary analysis of the results seemed promising.

Using micro-accelerometers attached to the walls, Professor Duron measured the vibrations of the exterior wall caused by the pulsating flames from furniture fires within the structure. Vibrations of the house taken during the Kinston test indicated that warning signs of collapse could be detected about three minutes before a water filled tank fell through the partially burned roof. The researchers hope to develop a methodology for interpreting the vibration data to enable the development of warning devices. A future warning device that uses this technology could be attached to burning buildings by firefighters or installed into the structure permanently.

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