The Simple Reason Why Firefighters Break Windows

 The estimated number of firefighters working in the United States is just over one million, the majority of which are volunteers in small towns. Each year, firefighters respond to over 1.25 million fires of which 500,000 are residential structures. Their job first and foremost is to save the lives of those trapped in the building followed by minimizing property damage and extinguishing the fire.

The simple reason why firefighters break windows is to let the smoke escape. The smoke from a fire is made up of many toxins but the two biggest concerns are the build-up of hydrogen cyanide and the high concentration of the flammable gas, carbon monoxide. If a building fills with dense smoke, the results could be catastrophic.

Breaking windows to let the smoke escape helps to clear the air making it easier for firefighters to see where they are going when they enter a building. The hot smoke is replaced by cooler fresh air bringing temperatures down just slightly and making it easier for people trapped inside to breathe. Ventilating the hot smoke allows the firefighters to get to the people inside and makes it possible to approach and put out the flames of the fire.

Horizontal and Vertical Ventilation

Horizontal ventilation is a method used by firefighters to keep the fire contained within the room of origin. By breaking a window in the room that is on fire, the flammable smoke will travel out the window instead of spreading throughout the building where it could ignite. The cost of replacing a broken window is far less expensive than the costly damage a spreading fire would cause.

Firefighters use the method of vertical ventilation when battling a fire that is in the center of a building. They will cut holes in the roof and break windows as needed to direct the smoke and heat upward. This helps cool the building from below and improve visibility needed for rescue efforts and getting closer to the fire.

Ventilation techniques are used to control which direction the fire is traveling. When fire moves, it travels upward first before it begins spreading outward. Firefighters are trained in strategic ventilation to direct fire away from people in need of rescue. In addition, firefighters are able to reduce the amount of property damage by coordinating the breaking of windows for ventilation with where they need to get hose lines in place to battle the blaze.

The Simple Reason Why Firefighters Break Windows

Backdraft and Flashover

Breaking windows and cutting holes in the roof to let the heat and smoke escape also reduces the risk of backdraft and flashover. These two phenomena have a comparative outcome, a large fire that encompasses the entire area or room. However, how backdrafts and flashovers happen and why they occur differ in several ways.


When fresh air meets a churning fire, superheated gases reach their ignition temperature resulting in an explosion known as a backdraft. As a fire grows, it consumes everything in the room and begins to burn itself out as it uses up all the oxygen. When the oxygen level drops below 14 percent the amount of visible flames is reduced and contents have reached their ignition temperature.

If oxygen is introduced at this point, the room and all of its contents will burst into flames and the superheated gases will explode. These backdraft explosions can erupt so violently they can burst windows, knock down walls, or cause bodily harm to firefighters or others trapped in the building. Backdrafts can occur at any time during the final stages of a fire if the flammable gases haven’t cooled which is why it’s important to know the warning signs.

One of the warning signs of a potential backdraft is heavy dense smoke or smoke that is being drawn back into the building in a puffing fashion. These signs of smoke are best seen at a distance away from the building. This is why the Chief sets up the command post across the street, to keep an eye out for signs of backdraft.

Other signs a backdraft is about to occur are small smoldering fires and stained or cracked glass. Unfortunately, these signs are often overlooked by firefighters who are zoned in on getting into the building to put out the flames. The only way to prevent backdraft is by ventilating the fire from above letting the superheated gases escape before introducing oxygen from below.


Flashovers are defined as a sudden floor to ceiling engulfment of fire caused by thermal radiation feedback. When the fire’s energy radiates back into the room’s contents, the rising temperature will cause everything in the room to reach its ignition temperature. This causes a sudden and simultaneous igniting of the room’s contents, including the floor, wall, and ceiling.

A flashover indicates the fire has reached the full development stage.

There are four factors that determine whether a flashover will occur during a fire. The size of the room is the first indicator. A small sized room will heat up much quicker than a large room with lots of space. The next aspect that affects flashover potential is the combustibility of the room’s contents. A room full of highly combustible material will create more fire resulting in more heat which produces more radiated energy and a greater chance of a flashover event.

The third ingredient that influences a flashover is the air supply of the room. The majority of fires are driven by air. Most rooms have enough burnable material (fuel) to create a large fire but without a constant supply of oxygen, the fire will eventually choke itself out. The final factor involved in a flashover event is how well or poorly a room is insulated. If a room is well insulated the heat can’t escape and the level of thermal radiation increases.

Other than the size of the room, firefighters are not going to know these factors as they approach the flames so they need to be aware of the warning signs for a potential flashover. The first warning flag is the intense heat from the combination of the fire and the thermal radiation. In addition to the extreme heat, firefighters look for two other signs: black smoke and rollover.

The black smoke is so black that no other colors can be seen. The reason it is so black is because of how much unburned carbon it contains making it highly flammable. Firefighters know this black-black smoke as black fire because of its volatility. Rollover is the fire seen within the black smoke often resembling snakes of flames that dart out of the smoke. Firefighters can prevent a flashover by properly ventilating the room or by cooling the hot black smoke with the hose line.

The Simple Reason Why Firefighters Break Windows

Composition of Smoke

The smoke from a fire is comprised of the chemical compounds created when the structure, furnishings, plastics, and polymers are burning. The burnable items, or fuel sources, are made of carbon, hydrogen, sulfur, and nitrogen. However, when they are set ablaze they create hydrogen sulfide, sulfur dioxide, hydrogen chloride, ammonia, carbon monoxide, and hydrogen cyanide, just to name a few.

Black soot forms from the carbons that don’t burn completely and contains more than one hundred toxins. Venting the smoke reduces the risk of death from the toxicity of smoke inhalation. It also decreases the possibility of injury to the eyes, skin, and lungs caused by the intense heat of the smoke and fire.

With so much for firefighters to worry about, you might be wondering if they can wear glasses? Check out this article to find out:

Carbon Monoxide and Hydrogen Cyanide

Carbon Monoxide (CO) and Hydrogen Cyanide (HCN) are two of the most dangerous chemical compounds found in the smoke of a fire. Carbon Monoxide attaches to the blood’s hemoglobin and prevents the delivery of oxygen to the body. It also hinders the body’s ability to remove carbon dioxide from the bloodstream. The result of this lack of oxygen and overabundance of carbon dioxide is asphyxiation. CO also causes substantial damage to the heart and nervous system.

Hydrogen Cyanide is a colorless flammable liquid that is extremely poisonous. Hydrogen Cyanide attacks the body at the level of the cells. Its primary focus is the nervous system of the body where it immediately terminates cell functions. Cyanide poisoning kills brain cells and is believed to be the cause of heart attacks experienced by firefighters.

Related Questions

How effective are fire sprinkler systems at saving lives and reducing the amount of damage caused by the fire?

When a fire sprinkler system is activated by the heat of the fire in residential facilities the death rate drops by more than 80%. Sprinkler systems in manufacturing facilities reduce the rate of death by almost 90%. As for reducing the amount of property damage, sprinkler systems are found to decrease the rate of damage by 65-75% when functioning properly.

What is the leading cause of fires in both residential and non-residential blazes?

Cooking is the number one cause of fires in residential buildings at almost 52% of all fires. In nonresidential buildings, cooking is the cause of 30% of fires.

Who dies more often in fires, men or women?

Sixty percent of deaths from a fire are men while only thirty-nine percent of deaths are women. Men are also injured more often than women at a rate of almost 60% compared to 40% who are women.

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