Bits and Pieces
About Fire Extinguishers (For Amateur-Built Aircraft Owners)
By Jack Dueck
As homebuilders, we need to contend with the CARs that regulate our amateur-built aircraft. And even if most of our attention is directed to the nuts and bolts of building, we often grind up against the rules and regulations that affect many aspects of homebuilding. Hence, the following review on fire extinguishers.
549 of the Airworthiness Manual - Airworthiness Standards - Amateur-built Aircraft, Appendix A, sets out the regulation requiring fire extinguishers under Part III, Design Standards, Equipment and Instruments, Para (26) Unless otherwise indicated in an applicable part of this appendix, amateur-built aircraft shall have the following minimum equipment and instruments:
b) a portable fire extinguisher.
Under Part II, Construction Standards, General, (again, Appendix A),
Para (8) - The builder shall be responsible for ensuring that the materials and methods of construction of the aircraft are adequate for the purpose.
So you the builder must decide the type of unit, material of the assembly, and the manner in which it is mounted to the airframe.
Para (9) - The methods of construction and assembly, and the workmanship employed, shall be appropriate to the aircraft design and shall conform to accepted aviation standard practices.
Probably a quick look at AC-43 will help. You, the builder, must decide how and where to mount the unit, in accordance with accepted aviation practices.
Para (10) - Materials shall be appropriate to the aircraft design and should conform to aviation quality specifications.
Again, the choice is left to the builder. However, here it becomes apparent that a fire extinguisher mounted to a plastic frame and exposed to a hot fire, can quickly become detached and out of reach in an emergency. Common sense, (as well the probable expectation of the MD-RA Inspector) will suggest that a metal supporting frame is a necessity.
Fires are defined in four classes:
Class A fires involve ordinary combustibles such as wood, cloth, paper, rubber, and some plastics. In other words, “fires that can be expected to flourish in a wood or fabric covered aircraft.” Water is an ideal extinguishing agent for a Class A fire because of its soaking and penetrating ability. On other fires, however, it can be dangerous. A multi-purpose dry chemical can be used as well because it melts and forms an oxygen- excluding coating over the solid burning materials. We can also use a foam extinguishing agent that blankets and smothers the fire.
Class B fires involve ordinary flammable or combustible liquids, flammable gasses, greases, and similar materials such as gasoline, oil, paint, and natural and propane gases. Again, substances that would exist in all aircraft. A dry chemical is used here, because it is a flame interrupting agent. A multi-dry chemical is also suitable. We can also use carbon dioxide, a gas that effectively suffocates the fire and leaves no residue, or we can also use a blanketing and smothering foam.
Class C fires usually involve both Class A and Class B fires, but also involve energized electrical equipment including wiring and electrical appliances. Here we would use a dry chemical, a multi-purpose dry chemical, or a carbon dioxide gas. We should not use a foam extinguishing agent, since foams can be electrically conductive.
Class D fires involve combustible metals such as magnesium, sodium, potassium, etc. On such fires we use a dry powder that acts as a coating and smothering agent. It is not suited for use on other classes of fire.
The type(s) of fires the extinguisher is designed for is indicated by the following symbols on the label.
How to Know Which Extinguisher to Use?
Class A Fires: The symbol is a triangle enclosing the letter A,
Class B Fires: The symbol is a square enclosing the letter B,
It will be found on dry chemical, multi-purpose dry chemical,
Class C Fires: The symbol is a circle enclosing the letter C,
It will be found on dry chemical, multipurpose dry chemical,
Class D Fires: The symbol is a star enclosing the letter D,
It will be found on special dry powder extinguishers.
With the above descriptors, the most common choice for use in your amateur-built aircraft will be a combination A, B, and C, or a Halon fire extinguisher.
As required by CAR Part VI and VII, hand-held fire extinguishers shall contain a type and quantity of extinguishing agent suitable for the kinds of fires likely to occur in the compartment where the extinguisher is intended to be used. For crew and passenger compartments, hand-held fire extinguishers shall be designed to minimize the hazard of toxic gas concentrations.
Refer to AMA 500C/4A dated March 25, 1987, for guidance regarding the different types of extinguishers, minimum capacities, and hazards of toxic gas concentration.
Acceptable equipment Standards will carry one of the following labels:
- Underwriters Laboratories of Canada, ULC
- British Civil Aviation Authority, BCAA
- Federal Aviation Administration, FAA
- Underwriters Laboratories Inc., U.L.
- US Coast Guard
- Approved for aircraft by the airworthiness authority of any country, whose standards are accepted by the Minister
We have already discussed the ‘builders’ responsibility to select, and install ‘suitable’ equipment ‘in accordance with accepted aviation practices.’ CAR instructions go on to state:
The installation of hand-held fire extinguishers shall be such that when properly secured in its mounting:
- the extinguisher will remain secure when subjected to the ultimate inertia loads established by the aircraft basis for certification, but not less than the following ultimate load factors: forward - 9
So if we take the weight of a typical fire extinguisher containing a capacity of 2 or 3 pounds of agent, to be as high as 10 lbs., the securing load would reach 90 lbs. This then suggests the mount consists of fasteners that will withstand this load, and prevent the extinguisher from becoming a flying object to add to the unpleasantness associated with any accidental or sudden stop.
From the above I would suggest the following considerations:
- Type: Combination A,B, & C, or Halon
- Size: 2-3 pounds of agent
- Mounting Bracket: Steel or other metal, to withstand 9g.
- Location: Preferably upright, within reach of pilot or passengers when seated and seat belts fastened
- Currency: Extinguisher tested and certified within time frame as specified under STD 625 Appendix C.
This will hopefully take some of the mystery out of, and add to the common sense, of meeting the requirement for a suitable fire extinguisher in your amateur-built aircraft.