Putting out a fire means more than throwing water on a flame. Fighting fires involves science, says Robert Pearson, head training officer at the District of Columbia Fire and Emergency Medical Services Department in Southwest.
“Four things must be present at the same time in order to produce fire oxygen, heat, fuel and a chemical reaction,” Mr. Pearson says. “If you take any one of these things out, the fire goes out.”
Especially during the Christmas season, all four abound. Homeowners deck the halls, stringing electrical wires for tree lights and other illumination. They light candles for fragrance and that warm and fuzzy glow. They haul in fireplace wood or wax-laced logs for cheer. They cook more, stirring sauces on the stove top and roasting big birds in the oven. Every one of those added attractions is potential fuel. Each year, fires occurring over the holidays injure about 2,000 people and cause more than $500 million in damage.
It all adds up to more work for firefighters, who must undergo extensive training to learn the most effective ways to put out a fire safely. This training teaches them how to protect themselves and how to cause the least amount of damage to property.
Mr. Pearson, who trains about 100 recruits a year, says firefighters must learn first that not all fires are the same. Fires are classified according to the type of fuel. Class A fires involve solid combustible materials that are not metals, such as wood, paper, cloth, trash and plastics. Class B fires contain flammable liquids and gases, such as gasoline, oil, grease and acetone. Class C fires are electrical fires, and Class D fires occur with metals such as potassium, sodium, aluminum, and magnesium.
If you attack the fire with the wrong agent, you make matters worse.
“For a Class A, you use water to extinguish the fire,” Mr. Pearson says. “For Class B, you use a foam agent. For Class C, you try to remove the electrical current and treat it as a Class A fire. If you can’t remove the current, you use carbon-dioxide gas. For Class D, you use dry chemical.”
The D.C. Fire and EMS Department attacks fires through “offensive firefighting.” Firefighters enter the burning building with hoses and go directly to the base of the fire. This method, though it involves hoses, generally causes less water damage to property than drenching an entire building with water.
“We considered using the ‘defensive’ method,’” Mr. Pearson says. “It’s the ‘surround and drown’ approach. But there are too many historical buildings in the area. The more water you put into a structure, the more damage you’ll have.”
Mike Walko, a probationary District firefighter, says training classes have taught him how quickly flames can engulf a room. A dry Christmas tree that catches fire can set an entire room ablaze in 40 seconds. A cigarette in a flame-retardant couch can smolder for about a day, but when the flame grows, it will destroy the room in about three minutes. In about five minutes, an entire floor of an office building with flame retardant materials will be engulfed.
Darryl A. Green, training officer at the District’s Fire and EMS Department, says he teaches recruits to be aware of the color of the flames and smoke in a burning building. This helps firefighters determine the type of fire in progress and what stage it has reached.
“The more complete the combustion process, the less smoke and less toxic gases will be present,” he says. “A blue flame means the fire is gas-fed. When you have a blue flame, you don’t have smoke. You will have a hotter fire, and it will ignite the items around it.”
He says using the correct hose nozzle is also important. Firefighters try to avoid creating steam so it’s easier to see and to breathe.
“When you use a narrow stream of water, you disrupt the thermal layering in the room less than you would if you use a fog pattern of water,” he says. “Thermal layering” refers to the way heat and gases rise in a room.
“The hottest gases are at the ceiling. Depending on the situation, interrupting it could be good or bad, he says.”
Charles Gibbs, training captain of the Arlington County Fire Department, says his firefighters study the construction of the buildings in their response area to prepare for possible fires. This helps them locate “fire extension” throughout a structure.
“There are void spaces that are inherent with construction,” he says. “There are pipe [encasings] and heating and air-conditioning ducts. It is good to know the void spaces in relation to the fire. If you don’t know them, you might have to pull down more ceiling and walls than necessary to look for fire in hidden spaces.”
Fires progress through several stages, says Mike Clemens, assistant chief of training at Montgomery County Fire and Rescue Service in Rockville. Each stage ignition, growth, rollover, flashover, full development and decay has its own dangers.
“Temperatures at flashover are 900 to 1,200 degrees Fahrenheit,” he says. “That’s the most dangerous time for a firefighter to be in a house because the flames are about to engulf the entire room. You don’t want to be in there. If it occurs, you have about five seconds to get out. If the ceiling is high, you might have more time.”
Back draft, which is not as common as flashover, involves an area with low oxygen and high heat that is smoldering. Opening a door or a window, which allows oxygen to enter the area, will make the room explode like a bomb.
“The fire is starving for oxygen,” he says. “You start seeing pressurized smoke coming out of small openings. It’s a dense gray-and-yellow smoke. The glass or wall becomes very hot, but you don’t see a flame. Before you make entry, you ventilate the highest area you can and get out of the way.”
Even though ventilating an area can create back draft, Bill Troup, fire program specialist at the U.S. Fire Administration in Emmitsburg, Md., says ventilation is key to suppressing a fire. If the gases have no place to go, the blaze becomes more difficult to extinguish. Firefighters usually cut a hole in the roof and use fans to move the smoke.
“If you try to push the heat to the roof and there is no ventilation, the heat will bank down and cause you to be burned,” he says. “You try to ventilate ahead of the hose stream of water so you can actually push the smoke somewhere.”
Dan Madrzykowski, a fire-protection engineer at the National Institute of Standards and Technology in Gaithersburg, says protective fire-resistant clothing, self-contained breathing apparatus and personal-alert safety systems are important pieces of technology for firefighters.
“PASS, personal alert safety systems, start beeping if a firefighter stops moving so other firefighters can know someone is down,” Mr. Madrzykowski says. “The devices are about the size of a pack of cigarettes, usually a bright color. Typically, they will have a flashing light. They are watertight. They are usually worn on the front of a firefighter’s coat. The newer designs integrate them into the self-contained breathing apparatus. Some of the devices have thermal sensors in them to warn that the conditions are increasing to a hazard level, beyond what their gear can handle.”
Imploding structures are another danger firefighters must consider. Instinct and experience serve as the best gauges for evacuation, says Glenn Corbett, professor of fire science at John Jay College in New York City.
“Any building movement is a gigantic sign that a building will collapse,” he says. “The signs are not specific. It’s a risk-management situation.”
Mr. Corbett says one of the best improvements in technology has been thermal imaging cameras. The devices are hand-held cameras that originally were used by the military. They detect heat from bodies and fires through doors, walls and smoke.
“The cameras make distinctions between different materials in the rooms,” Mr. Corbett says. “Hollywood fires are a lot different than real fires. There is a lot of smoke, and you can’t see anything.” The cameras, he says, can “speed up the process of finding people.”
Obtaining money to purchase the thermal imaging cameras is a difficulty in some fire departments across the country, Mr. Corbett says.
“The technology is there,” he says. “Our problem is finding the resources to buy it.”
The professional firefighters at the District’s Fire and EMS Department say civilians need just a few tips.
“If there is a fire, stay low to breathe the good air,” Mr. Walko says. “If you stand up, you could burn your nasal passages or ears.”
Mr. Pearson says average civilians should not attempt to put out fires if they don’t know what is burning. If the fire is spreading rapidly beyond the spot where it started, it could be a life-threatening situation.
“We want to emphasize the importance of calling 911 as quickly as possible,” he says. “Get out and call for help.”