Fire suppression in cargo components

Fire Suppression in Cargo Compartments By Fred Workley May-June 1998 Fred Workley is the president of Workley Aircraft and Maintenance Inc. and director of Aircraft Appraisals at AvSOLUTIONS, both in Manassas, VA. He is on the technical...

Class E - A cargo compartment used only for the carriage of cargo. Typically, a Class E compartment is the entire cabin of an all-cargo airplane. A smoke or fire detection system is required. In lieu of providing extinguishment, means must be provided to shut off the flow of ventilating air to or within a Class E compartment. In addition, procedures such as depressurizing a pressurized airplane are stipulated in the event that a fire occurs (something you can't do on a passenger-carrying airplane).

The overhead storage areas and certain other areas in the cabins of passenger-carrying airplanes are considered "stowage" compartments rather than cargo or baggage compartments. They are not required to meet any of the above standards.

The standards for liners are found in Part III of the Appendix F of Part 25. In addition, Section 121.314(a) permits the ceiling and sidewall panels to be constructed of materials that meet the test requirements of Part III of Appendix F, or of glass fiber reinforced resin. Section 121.314(a) also permits the continued use of ceiling and sidewall panels constructed of aluminum, provided they were approved prior to March 20, 1989.

Section 25.858, adopted Sept. 11, 1980, (Amendment 25-54, 45 FR 60173) requires the smoke or fire detection systems of Class B, C, and E compartments to provide visual indication to the flightcrew within one minute of the start of a fire. Since the installation of detection systems alone would provide only a small incremental increase in safety, both detection and suppression systems must be installed in Class C compartments.

The changes from Class D to Class C compartments to Part 121 will require compliance within three years, that is, March 19, 2001. Every Class D compartment, regardless of volume, must meet the standards of a Class C compartment unless the aircraft is an all-cargo carrier, in which case it may meet the standards of a Class E compartment.

The easiest and cheapest time to make the conversion would be during a C-check when many areas of the plane are easily accessible. Of course, after installation these systems must be maintained and inspected.

This will include:

1) leaks check
2) visual inspection of the system
3) sensor test
4) hydrostatic check of the fire bottles

The first three checks could be accomplished at each C-check. A hydrostatic check will involve removing and replacing the fire bottle and will occur every five years. The fire bottle, containing the inerting agent, will be returned to the provider where it will be recharged and checked for leaks. This inerting agent could be carbon dioxide or nitrogen.

The Montreal Protocol of 1987 prohibits the manufacture or import of new halon as of Jan. 1, 1994. However, there is no restriction on the use of existing supplies of halon. The Environmental Protection Agency (EPA), which is responsible for the regulation of halons, advised the FAA in a letter of May 8, 1997, that it does not intend to ban the use of halon in installed fire suppression systems for the life of the airplanes. Further, it can support the use of stockpiled halons to retrofit aircraft holds, and it can support these policies in international negotiations related to aircraft or environmental matters. This support from EPA came in the political climate following the Valujet crash. This support is conditional on airline and aircraft industry support of on-going efforts to develop alternatives to halon for use in future aircraft. Nitrogen doesn't seem practical because of the large tank size required to support the range of some aircraft.

The Aviation Rulemaking Committee of the FAA has a Fuel Tank Inerting Task Group #3. This group is looking into the fuel tank explosion on TWA 800 center tank and in Manila, an aircraft incident involving the explosion of a wing tank. They have heard presentations on using carbon dioxide as an alternative to Halon. The same technology, as inerting in fuel tanks, can be used in cargo compartments. Cargo compartments and lower deck fires or explosions could be combated with a two step approach.

Step One: An alarm system can be installed using state-of-the-art oxygen analyzers. When smoke or a flame is detected, the crew will be alerted and automatically CO2 will be metered into the compartment in just enough quantity to change the oxygen level so it cannot support combustion and the fire will go out immediately. The advantage of utilizing CO2 is that the gas will penetrate baggage and cargo containers. CO2 is also drawn to the heart of the fire with the oxygen as it is being consumed in the fire. CO2 causes less clean up.

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