Handheld Fire Extinguishers
For over 45 years, halogenated hydrocarbons (halons) have been practically the only fire extinguishing agents used in civil transport aircraft. However, halon is an ozone depleting and global warming chemical and its production has been banned by international agreement. Although halon usage has been banned in some parts of the world, aviation has been granted an exemption because of its unique operational and fire safety requirements. Under Federal Aviation Administration (FAA) sponsorship, the International Aircraft Systems Fire Protection Working Group (IASFPWG) has developed Minimum Performance Standards (MPS) that describe the full-scale fire tests, which the FAA will accept to demonstrate that an environmentally acceptable replacement agent is equivalent to halon in fire-extinguishing effectiveness.
Halon has been the fire-extinguishing agent of choice in civil aviation because it is extremely effective on a per unit weight basis over a wide range of aircraft environmental conditions, is a clean agent (no residue), is electrically nonconducting, and has relatively low toxicity. Two types of halons are employed in aviation: Halon 1301, CBrF3, a total flooding agent and Halon 1211, CBrClF2, a streaming agent.
With the signing of the Montreal Protocol on Substances that Deplete the Ozone Layer, the production of halons ceased in developed countries on January 1, 1994, although the use of halons was not prohibited for aviation uses. At that time the FAA convened an informal working group, the International Halon Replacement Working Group (now called the International Aircraft Systems Fire Protection Working Group) to develop MPSs for each of the four aircraft applications: lavatories, hand-held extinguishers, engines/auxiliary power units and cargo compartments.
The main purpose of each MPSs is to define full-scale fire tests to demonstrate that a replacement agent is equivalent to halon in terms of fire extinguishment/suppression effectiveness. Moreover, the full-scale fire tests can be used to derive certification criteria to allow for the approval of new agents/extinguishers/systems by the regulatory authorities.
Minimum Performance Standard for Hand-Held Extinguishers
The purpose of the MPS is to ensure that extinguishers using halon replacement agents pose no reduction in safety, both in terms of effectiveness in fighting onboard fires and decomposition product toxicity the passengers and crew. The MPS specifies two extinguisher tests that replacement agents must pass: a hidden fire and a gasoline-drenched seat fire . Halon replacement agents found to be compliant to date include the halocarbons HCFC Blend B, HFC-227ea, and HFC-236fa.
The hidden fire test evaluates the flooding characteristics of the agent against a hidden in-flight fire. This test determines the ability of a streaming agent to function as a flooding agent. [1,2]. The test is comprised of 20 n-Heptane cup fires in a three-dimensional array separated by perforated baffles in an enclosure. The cup fires are allowed to burn for 30 seconds before the extinguisher is discharged. The number of fires extinguished is compared to the number extinguished using a Halon 1211 extinguisher. It was determined that the effectiveness of the agent was affected by the hardware used to deliver it. Therefore, approval is granted on an agent/hardware unit basis.
The seat fire/toxicity full-scale fire test measures the agent's ability to extinguish a triple-seat fire in an aircraft cabin and assesses the toxicity of the decomposition products [1,2] [DOT/FAA/AR-01/37]. An experienced firefighter extinguishes the fire as efficiently as possible, following the prescribed 30 second pre-burn. Agent concentration and agent decomposition gas concentrations are measured.
FAA Advisory Circular AC 20-42D
Working with experts in the IASFPWG, the FAA developed extensive guidance material on the selection and use of hand extinguishers in aircraft. A draft FAA Advisory Circular (AC) has been developed which provides Halon 1211 equivalency guidance by referring to the MPS. When used, it replaces the canceled AC 20-42D and is intended to be applied to new installations. AC 20-42D establishes the halocarbons HCFC Blend B, HFC-227ea, and HFC-236fa as FAA-approved replacement agents to Halon 1211. Existing installations can continue to follow the cancelled AC 20-42C. The AC prescribes the quantities of halon replacement agents that can be safely discharged from a hand-held extinguisher to extinguish an in-flight fire in any civil aircraft, with due consideration given to volume, ventilation rate, and cabin pressure
This maximum safe W/V guidance was developed to minimize the risk of adverse health effects (cardiac sensitization and anesthetic effects) from potential exposure of compartment occupants to an extinguishing agent. The tables and plots developed indicate the maximum extinguisher charge weights that could be safely used. Additional guidance is provided for minimizing exposures to low-oxygen concentrations resulting from displacement of oxygen when the agent is discharged into small compartments. Guidance for each aircraft installation is based on the maximum certificated pressure altitude of that aircraft. Perfect mixing is assumed. The safe-use guidance is sufficiently conservative to ensure safe use of this agent. The basis document for the safe use guidance can be found in DOT/FAA/AR-08/03  and .
Papers / Reports
- Webster, Harry, "Development of a Minimum Performance Standard (MPS) for Hand-Held Fire Extinguishers as a Replacement for Halon 1211 on Civilian Transport Category Aircraft, Federal Aviation Administration Report No. DOT/FAA/AR-01/37, 2002.
- Chattaway, A., The Development of a Hidden Fire Test for Aircraft Hand Extinguisher Applications,. Civil Aviation Authority Paper No. 95013, London 1995, November 1995.
- Speitel, Louise C. and Richard E. Lyon, "Guidlines for Safe Use of Gaseous Halocarbon Extinguishing Agents in Aircraft", Federal Aviation Administration Report No. DOT/FAA/AR-08/3, 2009.
- Lyon R.E., Speitel, L.C., A Kinetic Model for Human Blood Concentrations of Gaseous Halocarbon Fire Extinguishing Agents. Inhalation Toxicology, 22(14), pp. 1151 - 1161.