Aviation Department Tech Tips Logo of USDA Technology & Development Program
February 1996
5700 9657 1301 - SDTDC



Halon and Its Replacements for Fire Suppression Systems in Aircraft
Eric C. Shilling, Mechanical Engineering Technician

What is Halon?
Halon (short for halogenated hydrocarbon) is a liquefied gas that is used to extinguish fire by chemically interrupting the combustion chain reaction. It is nonconducting and described as a "clean agent," as it leaves no residue after being discharged. Halon fire extinguishing agents, approved for use by the Federal Aviation Administration (FAA), include Halon 1211, Halon 1301, and a combination of the two (Halon 1211/1301). The four-digit number represents, respectively, the number of carbon, fluorine, chlorine, and bromine atoms present in one molecule. (Reference 1)

Both Halon 1211 and 1301 have Class A, B, and C ratings and have relatively low toxicity and electrical conductivity, making them the agents of choice for extinguishing the type of fires most prevalent in aircraft. Halon 1211 is a "streaming agent," and more commonly used in hand-held extinguishers because it discharges mostly as a liquid stream.

Halon 1301 is a "flooding agent," and discharges mostly as a gas, allowing it to penetrate tight spaces and behind obstacles and baffles. This property makes it ideal for use in engine nacelles and other tightly enclosed spaces commonly found in aircraft.

The Trouble with Halon
Halons have been found to be an ozone-depleting substance, harmful to the Earth's stratospheric ozone layer, and have an unacceptable "global warming potential." As of January 1, 1994, under the Clean Air Act, the United States has banned the production and import of Halons 1211 and 1301 in compliance with the Montreal Protocol On Substances That Deplete The Ozone Layer. (Reference 2)

This ban does not eliminate the use of halons as fire suppressants. It does, however, significantly affect the cost and availability.

Current Status of Availablity
The following information is from a U. S. Environmental Protection Agency (EPA) publication titled, Questions and Answers on Halons and Their Substitutes. (Reference 2)

  • 1. It is legal to continue to use your existing halon system and to purchase recycled halon to recharge your system.
  • 2. There are currently no laws prohibiting halon emissions, however, discharge testing is strongly discouraged.
Recycled halon can be purchased from many halon and fire protection equipment distributors or directly from owners who are decommissioning their halon systems. The Halon Recycling Corporation (HRC) may be able to provide information on such sellers. HRC phone numbers are: 800-258-1283 and 202-223-6166.

The United States owns 40 percent of the world's supply of Halon 1301. Fire protection consultants and EPA believe that there will be enough of the chemical to service existing critical needs for several years.

Replacement
Currently, there is no "drop-in" replacement for fire suppressant halons. A task group from the International Halon Replacement Working Group (IHRWG) has recommended several agents for the development of FAA testing protocols for on-board aircraft use. In their report, Chemical Options to Halons for Aircraft Use, the IHRWG defines halon replacements as halocarbon agents that are chemically similar to the present halons, but with low environmental impacts, acceptable toxicity, and, of course, they must be effective as fire extinguishants. (Reference 3)

The FAA is currently developing tests for candidate replacement agents. Once the tests are developed, manufacturers wishing to have their product approved by the FAA will have standardized tests by which they can be evaluated. According to officials at the FAA Technical Center in Atlantic City, NJ, the test procedure for hand-held extinguishants is close to completion, but it might be another year or two before those for cargo bays and engine nacelles have been finalized.

The Air Force, at Wright Patterson Air Force Base, has conducted extensive testing with engine nacelle applications and is working on design parameters for the hardware to accommodate agent HFC-125 (trade name DuPont "FE-25"). This agent, along with FIC-13I1 or CF3I (trade name Pacific Scientific "Triodide" or West Florida Ordnance "Iodoguard") and HFC-227ea (trade name Great Lakes "FM-200") are showing the most promise.

It is still early in the halon replacement process. As long as halons are available, they will continue to be used by the aviation community. It took many years for halons to be developed and approved, and they are not likely to be replaced with great speed.

Recommendations
With all the ongoing research and testing, it is too early to change to a halon replacement agent. Halon is legal to use, available from current or recycled stocks, and will be for at least the next few years. It is recommended that halon continue to be used until a permanent replacement is approved by the FAA and accepted by the rest of the aviation community. The San Dimas Technology and Development Center (SDTDC) will keep apprised of the latest information and pass along any significant new developments.

References
1. Hand Fire Extinguishers for Use in Aircraft (U.S. Department of Transportation, Federal Aviation Administration, Advisory Circular No. 20-42C, March 7, 1984)

2. Questions and Answers on Halons and Their Substitutes (U. S. Environmental Protection Agency, Office of Air and Radiation Stratospheric Protection Division, September 7, 1994, Rev. 7)

3. Chemical Options to Halon for Aircraft Use (U.S. Department of Transportation, Federal Aviation Administration, Report No. DOT/FAA/CT-95/9. February 1995)

4. Halon: Searching for Solutions (NFPA Journal, November/December 1995, pages 47-53)

5. Halon and Beyond: Developing New Alternatives (NFPA Journal, November/December 1994, pages 40-54)

6. Cockpit Fire Extinguishers (Aviation Consumer, April 1995, pages 12-15)


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For Additional Information Contact:
Aviation Program Leader
San Dimas Technology and Development Center
444 East Bonita Avenue, San Dimas CA 91773-3198
Phone 909-599-1267; TDD: 909-599-2357; FAX: 909-592-2309
E-mail: mailroom_wo_sdtdc@fs.fed.us

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