Fires and Explosions

Two incidents recently point to the hazards presented by explosions which may occur during firefighting operations.

Pittsburgh, PA

On March 25, 2009, firefighters in Pittsburgh, Pennsylvania were operating at a fire in a three-story apartment building of ordinary construction when an explosion occurred on Floor 2 while WPXI was videotaping fireground operations. Watch the video and see what you think?

• Did you observe any indicators of potential backdraft prior to the explosion?
• Do you think that this was a backdraft?
• What leads you to the conclusion that this was or was not a backdraft?
• If you do not think this was a backdraft, what might have been the cause of the explosion?

A news reporter quotes a chief officer, providing the following explanation: [Backdrafts] occur when a fire causes a buildup of pressure inside a building. When a firefighter enters a pressurized area, an influx of oxygen can cause the fire to explode. Note: comments reported in the press are not always an accurate representation of what was said.

While the comments reported are not completely inaccurate, they do not accurately describe the mechanism by which a backdraft occurs.

Cleveland, OH

On April 2, 2009, in Cleveland, Ohio an explosion occurred while firefighters were operating at a fire in a 2-1/2 story, wood frame dwelling. The fire, which had originated on the exterior of the structure, extended into the building and to the upper floors through void spaces in the balloon frame walls. According to news reports, the explosion occurred shortly after firefighters conducting primary search opened an attic door. The force of the explosion blew the two firefighters down the stairs to the second floor. Both firefighters received burns to the neck and face. News reports represented the phenomena involved in this event as a smoke explosion or backdraft.

• Based on the limited information provided in the news reports, which of these phenomena (backdraft or smoke explosion) do you think was most likely?
• What leads you to the conclusion as to which of these phenomena was most likely to have occurred?

A WKYC news report quoted a chief officer as stating “When they opened up the door to the attic that flow of oxygen allowed that fire to ignite, and it actually explodes.” Watch the video of this interview. This is a simple, but incomplete explanation of how a backdraft occurs. However, it does not explain the smoke explosion phenomena.

While smoke explosion and backdraft are often confused, there are fairly straightforward differences between these two extreme fire behavior phenomena. A smoke explosion involves ignition of pre-mixed fuel (smoke) and air that is within its flammable range and does not require mixing with air (increased ventilation) for ignition and deflagration. A backdraft on the other hand, requires a higher concentration of fuel that requires mixing with air (increased ventilation) in order for it to ignite and deflagration to occur. While the explanation is simple, it may be considerably more difficult to differentiate these two phenomena on the fireground as both involve explosive combustion.

While definitions are often ambiguous and the lines between various extreme fire behavior phenomena are a bit fuzzy, it is useful to examine even the limited information provided in news reports and give some thought to what might have happened. Are reported conditions consistent with the reported phenomena and what alternative theories might explain what happened?

Ed Hartin, MS, EFO, MIFIreE, CFO

Tags: Add new tag, backdraft, Extreme Fire Behavior, fire behavior, reading the fire, smoke explosion