Backdraft is a sudden explosion of hot gases caused by fresh oxygen entering an enclosed, steaming room. Signs of a potential backdraft include yellow or brown smoke and puffs of smoke around door or window frames. Firefighters can use ventilation tools to reduce the chances of a backdraft.
One of the most dangerous situations firefighters can face is a rare but powerful effect called backdraft. While definitions of backdraft vary somewhat, in general it is a sudden explosion of hot gases as fresh oxygen enters a steaming airtight room. Professional firefighters are trained to recognize the signs of a potential flashback, but even the most experienced firefighter can be caught off guard.
Fire requires both fuel and oxygen to keep burning, so if a fire breaks out in an enclosed area, it can use up its entire supply of oxygen before using up flammable objects as fuel. The room would still be extremely hot, but there would be very few visible flames. Instead, a thick cloud of smoke, often yellow or brown in color, would fill the room. Firefighters recognize the presence of yellow or brown smoke as a sign of incomplete combustion. This is a classic warning sign of a potential backdraft.
Because the fire is starved of oxygen to keep burning, the air pressure inside the room can be significantly different from the air pressure outside the room. Fire wants to draw more oxygen through any available opening, which often results in puffs of smoke suddenly appearing and disappearing around door or window frames. The difference in air pressure can also cause the windows outside the room to vibrate or rattle. These are other signs of a potential backdraft that firefighters are trained to look out for.
If the door to a burning airtight room is suddenly opened, a fresh supply of oxygen is supplied directly to the smoldering fire. The heat from the room also warms the volatile gases and the result is often a powerful explosion and instantaneous flames. This is the dreaded backdraft and can injure or kill anyone who enters the room. Thankfully, backdrafts are rare events, but one is all it takes to restart a fire or cause more structural damage.
If a potential backdraft is suspected, firefighters can use tools to ventilate the room from the highest point possible, such as the top of a door. This allows heated gases to escape without absorbing enough fresh oxygen to create combustion. Once the hot gases have been vented, the chances of drafts are greatly reduced. The fire could still be rekindled with the addition of oxygen, but a catastrophic gas explosion is much less likely.
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