You don’t have much time to react when a fire starts. It doubles in area every three seconds. While different materials have different combustion times, the determining factor is the fire’s temperature which correlates to how long it has been burning. Due to the variety of materials found in residential structures and the toxic gases that each type of material produces when burning, breathing the smoke can result in loss of life before the fire is visible. Fire damage to lungs and other organs can result in a fatal injury in 3-5 minutes. Breathing high levels of hydrogen cyanide, a by-product of burning certain nitrogen-based plastics, can be fatal even faster.
Once a fire reaches the flashover temperature of 900 to1500 degrees Fahrenheit, depending on the composition of the flammable gas, general destruction of the room contents and escape of the fire into adjacent spaces occurs. That is why fire sprinklers are designed to become operational at very low temperatures, so that the fire does not have the opportunity to reach those temperatures.
What is flashover?
In its simplest form, flashover is when the combustible gases released during a fire event reach a temperature that allows the gas itself to ignite. With all the plastics, wood and other materials available to a fire, gases are generated very quickly. These gases are explosive, flammable, and toxic. You can equate a flashover to what happens when you turn on your gas BBQ grill for a few seconds and then hit the ignition button. That big poof of flame and hot air is flashover. There are a number of sub-definitions, according to whether the combustible gas is low to the floor or high to the floor, but the thing to remember is that the whole room explodes in flames. Anything that wasn't actively burning before will burn extremely quickly now. Additionally, much like the BBQ grill, there is pressure generated as the gas ignites. This super-heated air blows out of the room with tremendous force, breaking windows and blowing doors off their hinges. The air introduced when that happens further feeds the flames.
That is why fire safety instruction emphasizes not opening the door or windows in a room that is burning. Not only do you not want to introduce more oxygen into the room because oxygen feeds the fire, but if the room is close to the flashover point, the in-rush of oxygen will cause ignition of the gas. Don't enter a room that is smoke-filled, or open a door that has smoke coming in under the door. Get out, and call the fire department.
How long do you have?
Let's look at a typical fire scenario. It's your living room. You light a scented candle with a match. You shake out the fire on the match and mean to flip the match into a glass dish next to the sofa, but it accidentally lands on the sofa cushion. You shut the door to the living room to let the candle fragrance permeate the room. You exit in route to clean the bathroom. The smoldering match begins to char the fabric on the couch cushion.
The clock starts.
0:30 seconds The small charred section of fabric now shows an active flame.
1:04 The entire cushion is burning, giving off gas-filled smoke.
1:35 The air around the sofa exceeds 190 degrees Fahrenheit. Smoke fills the room and descends from the ceiling into the room.
1:50 The hall smoke alarm goes off. You hear it, but don't see or smell smoke. You think it must be a malfunction. You finish cleaning the bathroom sink.
2:30 You start back up the stairs to shut off the alarm, and now you smell smoke. The temperature in the living room is now over 400ºF. You see the smoke coming under the living room door, and jerk it open to see what is burning.
2:38 A wall of thick, hot, acrid smoke and air rushes into the rest of the house. You can't see, and you can't breathe standing up. The temperature in the living room is now over 500ºF. You push the door shut and drop to the hall floor, fighting for cleaner, cooler air.
3:00 A neighbor sees the fire through the living room window and calls 911.
3:03 The entire hall is engulfed in smoke. You are disoriented, you can't even see the walls, and you can't breathe. You know you need to get out, but where is "out"? You are desperately crawling down the hallway, feeling the walls, looking for an exit. If you were still downstairs you would not be able to get to the main floor.
3:20 Every room is now smoke-filled. There is no safe room to be in.
3:41 The living room temperature is 1400º. The superheated gases ignite in a flashover, blowing the partially shut door open. Now everything combustible in the living room is fully engulfed.
3:50 You finally hear people screaming and go toward the sound. They are at the back door. You finally reach it and your neighbors pull you from the house.
4:00 The 911 dispatcher has finally gotten the location information from your panicked neighbor and sends the alarm to the closest fire station.
4:33 Two minutes and 43 seconds from the time the smoke alarm went off, the flames are now visible from outside the house. If anyone was still in the house, it is likely they could not be rescued. The fire department, located just five miles away, is getting ready to leave for the scene. (Adapted from homefiredrill.com)
5:43 The first fire engine leaves for the scene. You are lucky. They have a straight shot to the fire, with little traffic to negotiate, but they still have to drive five miles.
10 minutes The fire engine is now one mile away. Your house is fully engulfed in flames, but thankfully, no lives are lost.
Fire department response times
Fire department personnel cannot sit around in full gear in a fire engine with the engine idling 24/7. Even if you have an alarm system that dials the fire department automatically, there is a lag between the time the fire begins to ignite and the time the alarm goes out. If someone on the scene has to call 911, even if it is you, by the time the fire is discovered, it will already be well into its timeline.
Generally, fire department personnel have a "wheels rolling" call response time of one to two minutes. That is the length of time it takes to receive the call, get into their gear, jump into their stations on the trucks, start the engine on the fire trucks, and pull out of the fire house. Once they leave, they are at the mercy of traffic, road configurations, road conditions and distance. Even when the station is close to your home, it can take a substantial amount of time for them to arrive on scene. As you can tell from our timeline, if the fire is burning unchecked, there can be extensive property damage or even loss of life before the engines reach you.
What can you do today to mitigate the risk and prepare?
The key to minimizing property damage and injury or loss of life is to slow down or extinguish the flames as soon as possible. It is crucial to maintain a functioning, tested fire extinguisher in the kitchen, near the bedrooms, and in work spaces. Take it a step further and have your family or employees get trained to use the extinguishers by the local fire department or fire extinguisher service company.
Make sure your smoke alarms are working – replace the batteries today, even if you think you just did it.
And finally, seriously consider a home or business fire sprinkler system. It is the only way to have near-certain peace of mind.
Consider this case study from Pennsylvania.
Comparing fire sprinkler protected homes with non-sprinkler protected homes from 1988 to 2010, it concludes that fires in homes without fire sprinklers experienced over $100,000 in more damage and used 5,500 more gallons of water to extinguish the blaze. Over that time period, not one person living in a sprinkler protected home died.
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