Fire Suppression in Cargo Compartments
By Fred Workley
The FAA has finalized its Revised Standards for Cargo or Baggage Compartments in Transport Category Aircraft. This was effective Feb. 17, 1998, for 14 CFR Parts 25 and 121. At the same time, the FAA requested additional comments from Part 135 operators. The FAA on or before May 18, 1998, must have received comments on the proposed changes to cargo/baggage compartments for Part 135 certificate holders.
The effect of this final rule is to change the primary means of preventing uncontrolled fires in Class D compartments in passenger-carrying aircraft from containment to suppression. The necessity to revise the standards was prompted by uncontrolled fires in cargo or baggage compartments that have caused accidents and loss of life, and also by the increased danger of explosion and fire caused by aerosol cans in passenger luggage. The aerosol cans now manufactured use a mixture of propane, butane, and isobutane for propellant. These aerosol cans are widely used and are found in a high percentage of checked baggage.
Tests conducted by the FAA Technical Center found that this type of aerosol can explodes in burning luggage with such force that the compartment liners are ruptured. With the liner no longer intact, an unlimited supply of oxygen is available to support the fire that can now spread throughout the aircraft. However, in a Class C compartment in which an extinguishing agent has been released, the aerosol propellant does not ignite and explode.
The goal of requiring a "fire suppression system" is not the same as a "fire extinguishing system." The suppression system is to suppress the fire until it can be completely extinguished by ground personnel following a safe landing. To achieve this goal, the FAA proposed in Notice 97-10 to amend Part 25 to eliminate Class D compartments altogether. Compartments in passenger-carrying airplanes that can no longer be approved as Class D compartments must be retrofitted to meet the standards of Class C compartments. Compartments in all-cargo airplanes that can no longer be approved as Class D compartments must be shown to meet the standards of Class E compartments in lieu of those for Class C compartments.
A brief overview of the different classes of cargo or baggage compartments will help in understanding the required changes.
Class A - A compartment in which the presence of a fire would be easily discovered by a crewmember while at his or her station, and where all compartments are easily accessible in flight. No compartment liner is required.
Class B - A compartment with a separate, approved smoke or fire detection system to give warning to the pilot or flight engineer station and with sufficient access in flight to enable a crewmember to effectively reach any part of the compartment with a hand fire extinguisher. A liner meeting the flame penetration standards of 25.855 and Part III of Appendix F of Part 25 must be provided to prevent the fire from spreading.
Class C - Class C compartments differ from Class B compartments primarily in that built-in extinguishing systems are required for control of fires in lieu of crewmember accessibility. Smoke or fire detection systems must be provided. An approved liner is required.
Class D - This is the class that must be changed. In lieu of providing smoke or fire detection and extinguishment, Class D compartments were designed to control a fire by severely restricting the supply of available oxygen. The capability of the liner to resist flame penetration is especially important. As discussed, exploding aerosol cans can rupture the liner so that the supply of oxygen can no longer be restricted.
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