FAA Hunts for New Firefighting ‘Wonder Gas’ : Air safety: Halon saves lives, but it also erodes the ozone layer. Fire experts are searching for a substitute, so far without success.
When an electrical fire broke out on a Delta Air Lines jet on a 1991 transatlantic flight, the “wonder gas” known as halon helped save 231 lives.
The blaze started beneath the floor and was beginning to spread to the cabin of the Atlanta-bound L-1011 on March 17 when flight attendants used portable extinguishers to spray Halon 1211. The fire was doused and the plane landed safely in Goose Bay, Labrador.
Halon, the generic name for a variety of halogenated hydrocarbons containing fluorine and bromine, provides a safety net that made flying safer for more than 30 years.
But there is a problem: Halon erodes the ozone layer. Its production in the United States and other industrialized countries was banned beginning in 1994 because of environmental concerns.
Now scientists, aerospace engineers and aviation-industry fire experts are searching for a replacement for the substance known in the industry as “the instant firefighter” and “the wonder gas.”
In a box-shaped test bay at a Federal Aviation Administration research facility 12 miles northwest of Atlantic City, experts are developing tests for substitutes for Halon 1301 and Halon 1211, the most widely used halons in the industry.
The goal is to develop performance standards so that when current halon supplies dwindle or its use is banned--both scenarios are years away--the government will be able to certify the safety and effectiveness of a replacement.
The U.S. military and aviation companies such as Boeing are known to have stockpiles of halon that will last for many years. In addition, it can be recycled, so the supply is not expected to run out any time soon.
The work by the FAA researchers began in early 1993 and is being watched by aviation industry insiders the world over.
“So much is at stake, it needs leadership on a worldwide basis,” said DuPont fire-suppression expert Daniel Moore in Wilmington, Del. “This is what FAA is doing. I don’t know anyone else in the world who’s taking this leadership. But they’re all eagerly listening.”
In aviation, halon is used in fire-suppression systems in engines, cargo compartments, bathrooms and portable extinguishers.
A liquid when contained under pressure, a gas when released into air, halon is dispensed from sphere-shaped steel balls through a nozzle. Its beauty is in its per-unit efficiency. It is light, potent and poses no threat to those who inhale its fumes in routine circumstances. It isn’t corrosive like some dry powders and doesn’t harm machinery.
A blast of halon gas can snuff out a raging gasoline fire in a fraction of a second. It can be used to suppress deep-seated fires in cargo compartments too tightly packed for anything but a remote fire-suppression system. And it can prevent a fire from flaming up again for up to three hours.
Finding another chemical, gas or mixture suitable for use on airplanes is proving difficult, said Constantine Sarkos, manager of the fire safety branch at the FAA Technical Center.
“There’s four things you need from a halon replacement. Effectiveness on a unit-weight basis, low toxicity, it must be clean and volatile and it must be environmentally acceptable,” Sarkos said.
“To determine how effective an agent is, you have to conduct realistic tests, and that’s what we do in this building,” he said, pointing to the bay, which is 180 feet long, 70 feet wide and 50 feet high.
Inside, FAA engineers test would-be replacements on a 130-foot “TC-10,” which is actually the fuselage of a DC-10 with a custom-made steel-and-aluminum addition.
Its 2,500-cubic foot cargo compartment needs 50 pounds of halon for fire extinguishing. To protect the same area with water would require 60 gallons--weighing 480 pounds.
FAA aerospace engineer Tim Marker has worked on a water spray system that would recycle water, lessening the amount needed. “It would drip into a pipe beneath the belly and be channeled back around for use again,” he said.
The FAA is working with experts in the United States and abroad in establishing criteria for halon replacements. The FAA spent $500,000 in 1994 on the tests, not including the salaries of five people involved, Sarkos said.
The FAA brings expertise and objectivity to the project.
“They’re not suspect as a manufacturer or someone trying to make a profit. They lend that degree of third-party impartiality,” said Moore.
Researchers hope to have settled on an evaluation process for halon replacements for all facets of aviation use by 1998, Sarkos said.
Whatever substance replaces halon, it probably won’t be suitable for the extinguisher systems in place in airplanes.
“So far, we haven’t seen any agent that can just be dropped into existing systems. We will have to make modifications or come up with a totally new system, we don’t know yet,” said Harry Mehta, a propulsion engineer for Boeing Co. in Seattle.
