| Firefighting With Fog - Inside Science
Reported January 2006
BACKGROUND: A new strategy for combating fires has been embraced by firefighters in Sweden and Great Britain, and is starting to gain acceptance in the United States. Called 3-D firefighting, the tactic takes into account not just the structure of the fire, but also the gases that fill a room. Firemen can gauge a blaze with thermal-imaging equipment and then use split-second pulses of fog to attack or control and extinguish the blaze.
THE OLD WAY: In the United States, firefighters are trained to kick down doors and douse flames with water pumped through massive hoses. One of the oldest rules in the business is, don't put water on smoke, especially if firefighters are nearby, because the water will turn to steam and cause burns. But fires can now project their energy much farther from their cores. This makes them more dangerous and difficult to extinguish.
THE NEW WAY: Bursts of delicate fog cool the gases and contain the fire. The water is broken into tiny droplets and deployed in extremely brief bursts, so instead of turning to steam, the moisture's expanded surface area will cool the gases in the smoke. Then firefighters can move closer to the blaze -- instead of ducking for cover. Once they are close enough, revert to the old method of smothering the blaze with a massive application of water.
GASSY ELEMENTS: House materials inside and out have changed dramatically over the last three decades -- most are now made from synthetic materials rather than wood or metal. This causes today's blazes to produce two- to three-times as much energy as a typical fire did in 1980, and most of that energy is released as flammable gases. The invisible gases produced in a fire can be much more dangerous than the flames, especially in enclosed spaces. Newer buildings are well insulated and tightly sealed. That means gases in newer buildings can become superheated, flammable and highly mobile. The result is extreme fire behavior, marked by life-threatening backdrafts, flashovers and gas explosions. Scores of firefighters die each year because they use old outdated methods against this volatile mix of physics and fire gases.
THE RESULTS: In Sweden, the number of firefighter deaths was cut in half from 1986 to 2005. The United Kingdom adopted the 3-D firefighting approach in 1997 with even more impressive results. Britain lost 12 men to extreme fire behavior from 1990 to 1996, but from 1997 to 2003, they didn't lose any. France has since made the 3-D technique its official training methodology.
The American Society of Civil Engineers and the American Society of Mechanical Engineers contributed to the information contained in the TV portion of this report.
If you would like more information, please contact:
Fire Protection Publications
Headquarters for the International Fire Service Training Association
930 N. Willis
Stillwater, OK 74078
(405) 744-5723
For more information on engineering, contact:
The American Society of Civil Engineers
1801 Alexander Bell Drive
Reston, Virginia 20191-4400
(800) 548-2723
http://www.asce.org
American Society of Mechanical Engineers
(800) 843-2763
(973) 882-1170
infocentral@asme.org
http://www.asme.org |
