Firefighters Need to Know the Four Hostile Fire Events
Be Wise to Extreme Fire Events and Behaviors
I am going to put on my fancy cape and become Captain Stating-the-Obvious. Fire is in and of itself hostile. It lacks any form of hospitality or compassion. As firefighters, we know that it is nature's most destructive medium. We train on fire behavior hoping to understand the beast.
I always tell my crew to look at fire as a conversation. Listen to what fire is telling you, and look for its non-verbal communications. We must know the best way to respond to the conversation in the event we are caught in its path.
In this installment of Let's Talk Fire, we will explore four occasions when that conversation can go south: backdraft, flashover, smoke explosions, and rapid fire spread.
These hostile fire events, or "extreme fire behaviors," kill firefighters. We can't think "what if"; we need to think about "when." This article shows you key indicators of hostile fire events and how to protect yourself and your crew.
Backdraft is created by a fire contained in a compartment that has used up all of the air. This oxygen-deficient fire will stop producing flames and enter what we call the "soldering stage." Great amounts of heat will still be present, but the flames will be little to none. This creates a paradoxical concept: for too many untrained firefighters, the lack of flame means safety. This is far from the case.
Recall Fire Behavior Day One: you know you need heat, fuel and an oxidizing agent to sustain combustion. Take one away and you cripple the fire. The catch-22 here is: add that element back and guess what you do?
Let's say we have a fire in a closet that has burned out its air supply and is simply waiting behind the door. A firefighter opens the door unknowingly and suddenly all hell breaks loose, and now your chief is filling out an accident report, or—worst case scenario—someone is not going home after the fire.
Backdraft will generally be quick and fierce, first pulling in that fresh air and then pushing out tremendous amounts of energy. Backdraft does not have to be immediate. You may pop a hole in a roof on the C side of the fire and be giving oxygen in small doses to the A side. Suddenly without warning you have a backdraft.
Flashover occurs when every object in a room has reached its point of combustion. Everything in the compartment catches fire at the same time. Let me really go hard on that one word, everything. That includes you, buttercup.
When the warning signs of flashover present themselves, you need to start looking for a point of egress and quickly. Flashover does not give you time for a clean escape.
Warning Signs of Flashover
- Rollover. Rollover is kind of like the salad to the steak of flashover. When you start to see heavy roll over across the ceiling you know you are getting ready for a bad day.
- Fingering or ghosting. We have all seen fire kind of wisp through smoke. It is spooky and in a very unsettling way beautiful. It is also dangerous.
- Sudden increase in heat. When you feel that room get significantly hotter, get yourself moving.
Sadly, as our gear improves, we get placed in more danger. We can go deeper into the fire now but by the time we feel that heat on our bodies it may be too late to get to safer conditions. Be aware of indicators other than heat to key in on flash potential.
Another concern is the short time in which a fire can flash. Years ago when dealing with legacy furnishings we did not have to worry about flash occurring in the first few minutes we were on scene. We knew we had a little time to get in there, "get the seat," and get the hell out and go have a cold one with the boys. This is not the case now. Modern furniture is more focused on cost, weight, and convenience, and the result is a large number of products on the market that are polyfoam-based. These give off tremendous heat in a hurry.
This means flash is happening a lot faster than we ever thought it could. Quicker flash means we have to react faster. That's why crews now really need to study and understand modern fire behavior. We are not fighting the fires we fought a decade ago.
III. Smoke Explosion
We all know that smoke is the product of incomplete combustion and is, therefore, fuel. This fuel gathers in pockets and stirs about eagerly awaiting two things. The first is a way out: an opening that will let the smoke seek a cooler atmosphere and vacate the building. The second is an ignition source. This source could be a faint spark.
Once the source is discovered the the smoke will ignite with great force and power. The result resembles a backdraft and is often mistaken for one. The real difference is that backdraft requires air to do its damage, while smoke explosion needs an ignition source.
The risk is greater in a small compartment or void not yet involved in the fire. You need to look for the risk factors: cooler temperatures inside the fire, and accumulations of large amounts of smoke.
Ventilation is the key to preventing smoke explosion. Ventilate well, and coordinate with attack crews to maximize efforts.
IV. Rapid Fire Spread
This one may seem not to fit in as well as the other three but I assure you this is an issue. For me the main concern with rapid fire spread is for us to catch the things that can cause it before we let it happen. Balloon frame construction, inadequate holes made by plumbing or remodeling, and of course stairwells.
Other factors can contribute to rapid fire spread. Finishings on wood are big movers of fire. A varnish will act as an accelerant much like gasoline or other flammable liquids. Rapid fire spread can cause a fire to get away from us and make our jobs difficult if not impossible.
As firefighters we need to handle this one by being on the top of our game. Get in there and get the job done before the fire can get that head start on you, know the elements of a home or structure that will cause rapid fire spread, and know how you can counter them if possible.