Aviation Investigation Report A98H0003
1.14.3 Designated Fire Zones and Smoke/Fire Detection and Suppression
The occurrence aircraft met the regulatory requirements, and was consistent with industry standards for smoke/fire detection and suppression equipment. No regulatory requirement existed for built-in smoke/fire detection or suppression devices in those areas not specified as either a designated or potential fire zone, which are referred to in this report as non-specified fire zones. Non-specified fire zones included areas such as the cockpit, cabin, galleys, electrical and electronic equipment compartment, attic spaces, areas behind side walls, and areas behind electrical panels.
Smoke/fire detection and suppression in non-specified fire zones is dependent on human intervention. However, in the MD-11 and other transport category aircraft, the airflow within the aircraft is such that air moved from some of the inaccessible areas to the occupied areas is first filtered by highly efficient aircraft ventilation and filtering systems that can effectively remove most of the combustion by-products of small fires. Therefore, a fire may ignite and propagate in an inaccessible area and its detection could be delayed.
Designated fire zones were identified as such because they were recognized as having both potential ignition sources and flammable materials. Although flammable materials existed in the non-specified fire zones, the threat of ignition was considered minimal. There was no recognized need to train aircraft crews for firefighting in other than the interior cabin areas, or to design aircraft to allow for quick and easy access to hidden non-specified fire zones for firefighting purposes.
Fire suppression in aircraft cabin areas is largely accomplished with hand-held fire extinguishers, located in such areas as the cockpit and galleys. For small, accessible fires, hand-held fire extinguishers have proven to be adequate. It has not been demonstrated that aircraft crews using hand-held fire extinguishers can be consistently effective in accessing and extinguishing fires in less accessible areas, such as attic areas or avionics compartments, also known as electrical and electronic equipment bays.
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