Smoke, like a fingerprint, is unique to each fire

Where there’s fire, there’s smoke. And that smoke is every bit as deadly as the flames. According to the Centers for Disease Control and Prevention, most fire victims die from smoke or toxic gases and not from burns.

House fires killed approximately 3,055 people in the U.S. last year. Safety experts believe the death toll could be greatly reduced if they knew more about how fires burn and what’s inthe smoke they create.

The just-completed Smoke Characterization Project was designed to get those answers. This year-long study was funded by Underwriters Laboratories and the Fire Protection Research Foundation.

When you or I look at smoke, we notice its color and density. You hear news reporters do that all the time. “The thick, black smoke could be seen for miles.”

UL researchers found that smoke is not only complex, it’s unique to every fire based on the materials that are burning.

“There is no such thing as average smoke,” says Tom Chapin, director of research at UL. “Smoke, like afingerprint, is unique to each fire.”

‘Fingerprinting’ smoke
Most homes today have fewer natural materials in them and more synthetics than they did 20 years ago. There is less cotton, linen and silk — and more nylon, polyester and acrylic. That changes the way fires burn and the types of smoke they generate. 

For this study, researchers burned 27 natural and synthetic materials commonly found in today’s homes. These materials included vegetable oil, pillows, mattresses, sofas and plastic coffee makers. UL engineers burned them separately and in combination to analyze the composition of their smoke and how the fire behaved.

“We learned that synthetic materials burn faster and hotter than natural materials,” says John Drengenberg, UL’s manager of consumer affairs. This has reduced the time you have to respond when the smoke alarm goes off before the fire is out of control — what firefighters call “flashover.”

“At one time you had approximately 17 minutes on average to get out of the house after the alarm sounded before flashover,” Drengenberg tells said. “Today that time frame has been reduced to as little as three minutes in certain situations. So when that alarm goes off, you don’t investigate; it’s time to get out.”             

According to Kathleen Almand, executive director of the Fire Protection Research Foundation, the study data should help firefighters understand the movement of smoke as they enter burning buildings. That should help them get more people out safely.

The data collected should also result in more fire-resistant materials in the home and better smoke detectors.

Building a better smoke alarm
Smoke from synthetics is significantly different from smoke created when natural materials burn. Because of the UL study, we now know the particles are smaller — 1/500th the diameter of a human hair. They’re also more buoyant, so they move around more quickly.

“Now that we know what smoke is, engineers can design detectors to identify smoke when it happens,” UL’s Chapin says.

The result will be smoke alarms that soundmore quickly — seconds can make the difference between life and death — and detectmore accurately.  Future detectors should do a better job of distinguishing between burnt toast and a burnt sofa.

“It is very important that we don’t have smoke detectors that alarm at the drop of a hat, because people will pull their batteries out and won’t use their detectors,” Almand says. 

Where to locate smoke detectors
The Smoke Characterization Project also raises questions about where smoke detectors should be located. The current recommendation is for detectors to be placed on the wall or ceiling.

But will the smoke reach a unit mounted up there? If the smoke doesn’t get to the detector, it’s not going to go off. In some of the UL test fires — especially smoldering fires — the smoke never rose to the ceiling. “We saw a settling of the smoke,” Chapin says.

Almand says there were situations where the alarm sounded and then stopped. The smoke was still around, she says, but lower than the ceiling. “So this is something that is going to be looked at, that’s for sure.”

How to play it safe
Smoke detectors are still the best way to prevent fire deaths. A working smoke alarm can reduce your changes of dying in a fire by 50 percent.

Most homes have at least one smoke alarm. But you may need more than one. UL recommends a smoke alarm on every level of the home and outside every sleeping area.

If you have smoke detectors on more than one floor, it’s a good idea to get the kind that connects wirelessly. That way, if you’re asleep upstairs and smoke sets off the alarm downstairs, the one outside your bedroom will also sound.

There are two types of smoke detection sensors. Photoelectric sensors are generally more effective at detecting smoldering fires. Ionization sensors are more sensitive to open flames. You can also find alarms that have both kinds of sensors. That’s what I use for the obvious reason that two sensors are better than one.                                                        

One more tip: Smoke alarms only last about 10 years before they need to be replaced. So if your detectors are that old, it’s time for new ones.

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