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This Derry house fire from May 2011 shows the advantage of "ventilating" a blaze by punching a hole in the roof: It releases deadly smoke and gas, making it safer to fight the blaze inside the building. In some cases, however, ventilation can cause more harm than good by introducing oxygen and causing a flash fire.
Monday, July 9, 2012

Fighting fire can be considered the world’s biggest chemistry experiment

David Brooks

When you’re watching from the street, fighting a house fire seems pretty straightforward: rescue people, pump water.

Heroic and dangerous, certainly, but not very complicated.

Just goes to show how wrong appearances can be.

Here are some of the things firefighters have to consider as they race up to, and perhaps inside, a burning building: Was the home built before 1946? Is the couch stuffing synthetic or natural? Is the door to the basement open or shut?

That’s a lot of variables to juggle when lives and property are at stake, which explains why departments have long, detailed “standard operating guidelines” to help teams make decisions on the fly at the command of the senior officer on scene, known as the incident commander.

“The incident commander is much like the conductor,” said Michael O’Brien Sr., deputy chief of Nashua Fire Rescue. “He’s calling for certain things, deciding about going in, deciding where and when to lay the lines.”

Helping the conductor explains why the New York City Fire Department recently conducted what might be called a super-colossal chemistry experiment: stuffing 20 abandoned townhouses full of furniture and igniting them. And it explains why local departments are interested in what comes of the tests.

“Probably six to eight months down the road, we’re going to see a pretty comprehensive model from this, see whether there should be any change in response matrixes,” said Robert Buxton, deputy chief of operations for the Hudson Fire Department.

“We’re excited to look at those NYC results,” agreed O’Brien, adding a little wistfully, “In Nashua, we can’t have that same amount of research and development.”

The New York experiment was designed to test whether modern fabrics are forcing a rethink of firefighters’ habits.

When a room is full of smoldering natural materials, it usually makes sense to quickly ventilate it – punch a hole in the roof or wall with an axe – to release deadly gases and smoke, reducing the danger of smoke inhalation and making it easier for firefighters to direct the spray of water.

But synthetic materials, which are usually made from petroleum, burn faster and hotter than cotton, wool and other natural fabrics.

So if the room is full of smoldering synthetic materials, the onrush of air from ventilation might cause a fast and dangerous increase in the size of the fire, almost an explosion. That situation has been blamed for at least two firefighter deaths in New York City, plus a horrendous furniture-store fire in South Carolina that killed six people.

Hence last week’s townhouse tests, to determine how much of a difference synthetics make.

No matter what New York finds, however, the conclusions may not fit here.

For example, Buxton noted, a big fire department in a crowded city like New York can count on fast backup by lots of firefighters, so they can be more aggressive in entering buildings because someone else is always right behind with hoses and other equipment. Less urban departments have to take a different approach.

“What works for the city of Nashua may not work for the town of Hudson, and that may not work for town of Litchfield,” Buxton said.

But it will add to the surprisingly large body of work that guides fire-fighters.

The National Institute of Standards and Technology has an entire department devoted to studying fire fighting, making recommendations or rules about protection equipment, procedures, and detailed decisions about how spray angle and patterns from fire hoses affect heat dispersal in both compartmentalized and non-compartmentalized structures.

If that’s not geeky enough, the institute uses fluid dynamics, about as complicated as mathematical formulas get, to understand “positive pressure ventilation.” And for electronics fans, NIST is also testing whether RFID radio tags and ultra-wideband broadcasting via mesh networking might be used to help find firefighters in smoky environments. Neat stuff.

Speaking of neat stuff, you may be wondering about that reference to homes built before 1946. That refers to the post-World War II introduction of fire-resistance standards in construction materials, including the switch from plaster to drywall, and changes in construction that make it harder for flames to shoot up inside walls.

Granite Geek appears Mondays in the Telegraph, and online at www.granitegeek.org. David Brooks can be reached at 594-6531 or dbrooks@nashuatelegraph.com.