Spray on the Mist to Snuff the Fires
Clouds of water vapor sometimes more efficient than sprinklers with less collateral damage
Suddenly an oil fire breaks out in a turbine engine on a cruise ship plying the waters of the North Sea.
Overhead, small nozzles are activated by the heat of the fire. A cloud of thick mist envelopes the turbine, snuffing the fire in about 80 seconds.
Water from standard sprinklers could have warped the turbine (as the cold water hit the hot engine). But the misty blast saved the costly turbine, stopped the fire quickly, used less water than a sprinkler, and did less damage.
Could this misty cloud be the ''magic bullet'' that radically changes how fires are extinguished from engine rooms to bedrooms in the future? If the mist proves to douse fires under all circumstances, will it help reduce America's arson and fire death rate, one of highest among industrialized nations?
''Probably every major fire research organization or lab around the world now has some kind of water-mist fire-suppression research going on,'' says Carl Miller, CEO of Factory Mutual Research Corp. in Norwood, Mass., the world's largest fire research center.
''I don't want to call it the panacea for fire problems,'' says Larry Maruskin, a fire protection specialist with the United States Fire Administration in Maryland, ''but it has the potential. The US Navy and the Coast Guard are looking into it, and corporations are looking into it for hotels, condos, and manufactured homes.''
Water-mist fire-suppression systems differ from widely used sprinklers in several ways. Technically, mist-producing nozzles use pressure up to 4,000 pounds per square inch, and produce mist.
Sprinklers simply spray water on a fire much like a thumb held over the end of a water hose. And they often cause high collateral water damage.
Experts say water-mist suppression has proven to be effective under some circumstances, so far mostly in marine environments, for three basic reasons:
* The intense mist increases the total surface area of the water available to absorb the heat of a fire. This maximizes the evaporation rate of the water and takes heat away from the flames.
* The expanding water vapor reduces the amount of oxygen in the vicinity of the fire, thereby reducing or extinguishing the flames.
* Because the mist is suspended in the air, it reduces the heat transfer between the flames and nearby objects by scattering or absorbing the heat.
In Europe a number of cruise ships and passenger ferries have added water-mist systems in machinery rooms, cabins, and dining rooms with good results.
''Water-mist systems require smaller pipes and smaller water storage [tanks], and this adds up to a weight savings in ships,'' says Robert Solomon, senior fire protection engineer at the nonprofit National Fire Protection Agency (NFPA). NFPA establishes standards for most of the fire codes for communities across the US.
Although water-mist fire suppression has been around since the 1920s in basic form, what has prompted renewed interest are new international maritime regulations and the need to find an alternative to Halon, a chemical widely used in extinguishing fires, but recently banned because it depletes the ozone layer.
The International Maritime Organization (IMO) now requires that all passenger vessels must have fire protection systems. This requirement created an interest in low-cost, effective systems that can be easily retrofitted. Although water-mist nozzles are still more expensive than sprinkler heads, their performance advantages make them attractive.
Because water-mist systems began appearing in the marketplace several years ago, NFPA established a Water Mist Standards Committee a year ago to determine how and where water-mist suppression systems can be used in the US.
People on the committee come from a variety of backgrounds, says Mr. Maruskin, who is a member. ''Some are from the insurance sector, some from engineering and from industry. Once the standards are made public in 1996, then the marketplace [will] take over.''
Jerome Peppi, Vice President of Research and Development for Grinnell in Exeter, N.H., and the largest manufacturer of sprinklers in the US, says, ''In addition to the marine market, I see a good future for water-mist technologies in special hazards applications like computer rooms, electronic environments, libraries, and other places where there is a need to minimize water discharge. I don't think the world will be covered with mist nozzles, but six or seven years from now, they could reach 10 percent of the entire fire protection market.''
Wide use of water-mist systems depends on the results of the research under way in industrial and residential applications, and, of course, cost is a factor.
''Where a structure is built out of combustible materials, like my home,'' Mr. Miller says, ''I'm not sure a fine-mist system is the solution. If the system could be designed so that it could react fast enough to catch a fire in the incipient stage before the structure is involved, it might work. Right now it's a matter of the fire research community getting the knowledge to know the limits and boundaries of mist systems.''
Although the US fire death rate has dropped considerably in the last 20 years, it still hovers at about 18 per million, or 4,635 deaths in 1993, and $8.5 billion in property loss. Unlike European countries, where preventing fires is more of a personal responsibility, fire prevention in the US relies more on fixed protection such as sprinklers.
Interest in water-mist systems here is high, experts say, because the technology is evolving from sprinklers. ''In Germany and France,'' says Joe Hankins, manager of the protection section of Factory Mutual Research in Norwood, Mass., ''fire service perceives sprinklers as questioning their capabilities. By installing sprinklers you are saying you don't trust the firefighters. In the US, the building has to be safe from fires, and nobody has the responsibility. It's the building's responsibility.''