A new grenadelike gadget—designed to quickly extinguish flames in small quarters, thereby limiting injury to victims as well as firefighters—is becoming an important part of firemen's arsenals.

More than 37 fire departments along the U.S. east coast now carry Vancouver-based ARA Safety's FIT-5 (for fire interruption technology). The device, available to firefighters since December, is a means of knocking down or even extinguishing fires in rooms, basements and attics. The FIT-5 (price tag: around $1,300) is a nine-pound (four-kilogram) red disk that resembles a land mine and is deployed like a grenade: A firefighter pulls its cord and tosses the disk into the area engulfed in flames; within seconds the FIT-5 releases a wispy cloud of potassium carbonate, a flame retardant that suppresses combustion and disrupts fire at the molecular level.

The company says the device can fully extinguish a class B (fuel-based) fire in a room 2,100 cubic feet (60 cubic meters) or less and reduce fire temperatures from 1,000 to 300 degrees Fahrenheit (540 to 150 degrees Celsius) in less than 10 seconds. The FIT-5 is also designed to control class A (wood-based) fires enough so that firefighters can douse them with water. Firefighters in New York State and New Jersey have successfully contained three fires (in a room on the third floor of a house and two in basements) with the FIT-5 since it hit the market.

The FIT-5 is designed to be most effective in a contained space—the larger the area, the less effective, which is why it is not a good candidate for squelching, say, wildfires.

Most handheld fire extinguishers sold at hardware stores for home use are pressurized with nitrogen or carbon dioxide to propel powdery potassium bicarbonate, liquid water or a fluorocarbon at a fire. In addition to allowing firefighters to control fires from a safe distance, the FIT-5 could also replace halon fluorocarbons, an effective fire-fighting tool until they were banned in 1994 after it was discovered that they destroy Earth's ozone layer.

Because halon displaces oxygen, it extinguished electrical, grease and other fires that water alone could not, says Robert Kaul, ARA Safety's technical director. When a firefighter approaches a fire and pulls the rip cord located on the side of the FIT-5 device, this generates a spark of heat that leads to a thermal reaction within the FIT-5. Within 10 seconds the container releases a white cloud of potassium carbonate aerosol that expands to fill an enclosure (room, basement, attic). A FIT-5 grenade is unlikely to leak and works when wet because it is not pressurized and has a sealed outer casing that keeps moisture out. In addition, even if the rip cord is not pulled, the device will automatically dispense the when placed in temperatures exceeding 500 degrees F (260 degrees C).

"Once the FIT-5 is done, you're left with potassium carbonate powder, which can be vacuumed or swept clean," says Michael Gardner, ARA Safety's director of marketing.

Of course, potassium carbonate, used in the production of soap and glass, must be handled carefully; it can be dangerous if inhaled (by irritating the respiratory tract and causing coughing and shortness of breath) or swallowed, potentially damaging the gastrointestinal tract and causing nausea, vomiting and diarrhea. The odorless chemical can also severely irritate the eyes or skin if it comes in contact with either.

Andrew Schmidt, chief of Morris County, N.J.'s Jefferson Township Fire Department (about 45 miles northwest of New York City) used a FIT-5 in April to contain a basement fire in the nearby town of West Milford. Because most of the fire departments in the area are volunteer, Schmidt was unable to marshal much of a firefighting squad at 3 P.M., when most of his volunteers were working their day jobs. On arriving at the burning basement, he broke one of the windows and tossed in an FIT-5, which held the flames in check until the fire trucks arrived.

"When you don't have a truck, and you don't have water, you've got to do something," he says, adding that West Milford ended up using less than 200 gallons (750 liters) of water to extinguish a fire that easily could have required 6,000 gallons (22,700 liters) to put out. Schmidt was so impressed that he has become trainer and consultant for ARA Safety.

The company is now exploring developing a larger version of the device and hopes to within the next year offer a fixed system for homes and businesses that could be mounted on a wall or ceiling like a smoke detector and switched on when needed. This would be particularly useful in rooms containing lots of computers or other electronic equipment that would be ruined if water was used to douse the flames.