Flashover & Backdraft: What Cops Need to Know
Police action in the first moments of a fire can be critical, but sometimes the best action to take is to recognize your own limited experienceBy Scot DuFour | Mar 20, 2018
Cops and firefighters like to make good natured fun of each other. I’ve heard cops call firefighters “second responders,” and every cop knows the look of sleepy firefighters just called out of bed in the middle of the night. I bring up these examples because they speak to this truth: Cops can get themselves seriously injured when they feel they can’t wait for the fire department to arrive.
When a structure fire gets called in to 911, the police and fire department often receive those calls simultaneously. Because cops are out prowling the streets anyway, it’s often the case that they will be first on scene. The problem is, there are many important aspects of compartment fires that cops are ignorant about—aspects that could get us killed.
It would be prudent to understand a little bit about how fire works so we can protect ourselves and others and hopefully preserve as much evidence as possible for the fire investigators.
Backdraft is a type of explosion called a deflagration that occurs when fresh air is suddenly introduced into a compartment containing products of incomplete combustion.
What does that mean to a cop? Fire needs only a few things to burn: fuel, oxygen, and heat. Sometimes a fire may be contained to one compartment in a house—a bedroom, for example—where the fire has become oxygen deficient. The compartment may maintain enough heat and fuel to continue burning, but it just needs the reintroduction of oxygen to start up again. When you, the cop, kick open the bedroom door or smash out the window, oxygen to rushes into the room and in many cases an explosion is the result.
Many police officers might not realize that smoke is itself combustible. We often think of smoke as only the byproduct of combustion, but the smoke contains many unburned products of combustion that will burn, given the chance.
Everybody has heard that smoke is the most dangerous part of the fire. It’s true: Smoke inhalation is deadly and kills more people than fire itself. But the danger of the smoke, often called the hot gas layer, is much more dangerous than cops might think.
Flashover is a recently understood phenomenon even in the firefighting world, one that’s unlikely to be known by most cops. Flashover is the name for a sudden transition in a compartment fire in which the hot gas layer plays a vital role. Firefighters sometimes refer to flashover as the transition from a “fire in a room” to “a room on fire.” The following video makes that expression come to life.
Flashover is an important concept for cops to understand because the room can transition almost immediately. As the hot gas layer spreads throughout a room or house it radiates an incredible amount of heat down onto items far from the actual flames. That radiant heat can start a process called pyrolysis on solid fuels not even near the flames. Once the radiant heat reaches a certain heat flux measurement (20 kW/m2) then flashover can occur.
Flashover causes flaming combustion to all combustible fuels in a compartment—even if they aren’t near flame. A heat flux of 20kW/m2 will ignite crumpled newspaper not in contact with flame. Once flashover occurs, the heat flux reading increases rapidly to as high as 170 kW/m2. For some context, a heat flux of 6.4 kW/m2 will cause second-degree burns and blister human skin in about 18 seconds. That is not a survivable environment.
Lessons from Firefighters
I have personally responded to many structure fires during my career as a police officer. It’s the reality of the situation that police often arrive at the fire scenes minutes before the fire department and officer actions during that time are critical. Police and fire departments have started training together a great deal to enhance their ability to respond to active shooter and mass-emergency situations, but this should be expanded. Fire instructors should be given some time with police academies to educate police recruits on the dangers of fire and the proper response to structure fires.
Police officers must be incredibly careful if they find themselves at the scene of a structure fire. Deciding to go inside the structure can mean causing backdrafts or being caught inside when flashover occurs. Additionally, causing backdrafts or accelerating a fire to flashover means potentially destroying a lot of evidence fire investigators use to determine cause and origin. Rescuing people takes precedence, of course, but recognizing our own ignorance of fire dynamics might mean avoiding becoming an additional victim or destroying evidence.
Scot DuFour began his career in law enforcement with the Phoenix, Ariz., Police Department in 2004 and worked primarily on patrol in South Phoenix. In 2008, Scot moved to Colorado and transferred to the Aurora, Colorado Police Department where he worked until 2018. Scot is currently a criminal investigator for a district attorney’s office in the Denver area.
Scot has an AAS in Law Enforcement Technology with honors, a BA in Philosophy with a concentration in ethics, magna cum laude, and a Master’s Degree in Criminal Justice with honors.