(v) Specialized Dry Powder extinguishers for Class D fires. Solid materials in powder or granular form are designed to extinguish Class D combustible metal fires by crusting, smothering, or heat-transferring means. The recommendations of the manufacturer for use of those extinguishers should be followed because of the possible chemical reaction between the burning metal and the extinguishing agent. (Amendment 25-0) NOTE: Carbon dioxide is noncorrosive and will not injure food or fabric. Extinguishers must be winterized if they are to operate at temperatures below -40 °F. Approved unit capacity ranges upwards from two lbs. These extinguishers have only limited value for the extinguishment of a Class A fire, the action of the agent being to blanket the fire by excluding oxygen. Certain antifreeze agents may be corrosive. Approved extinguishers are either protected against freezing to -40 °F. or must be handled as any other unprotected water on the airplane. Technical Standard Order (TSO)-C19a covers a minimum l-3/8 quart capacity approved water extinguisher. Water extinguishers of the kinds currently on the market are not acceptable for flammable liquid or electrical fires.
Vaporizing liquid extinguisher agents are not normally corrosive to airplane structure and approved units will be satisfactorily protected against freezing to at least -40 °F. Up to the effective date of this guidance, no vaporizing liquid extinguisher with Underwriters' Laboratories toxicity rating higher than Group 4 is commercially available. Approved units have a minimum capacity of one quart. They are of only limited value for the extinguishment of Class A fires, having a cooling effect of about one-tenth that of water. When using dry chemical extinguishers the powder is nontoxic and noncorrosive, and approved units are protected against freezing to at least -40 °F. Minimum capacity of approved units is two lbs.
(4) Paragraph (a)(2). Class of fires. (Amendment 25-0)
(i) Class A fires. Fires in ordinary combustible materials where the quenching and cooling effects of quantities of water, or solutions containing large percentages of water, are of first importance. (Amendment 25-0)
(ii) Class B fires. Fires in flammable liquids, greases, etc., where a blanketing effect is essential. (Amendment 25-0)
(iii) Class C fires. Fires in electrical equipment, where the use of a nonconducting extinguishing agent is of first importance. (Amendment 25-0)
(iv) Class D fires. Fires which involve combustible metals, such as magnesium, titanium, zirconium, sodium, lithium, and potassium, and require extinguishing agents of the dry powder types. (Amendment 25-0)
(5) Paragraphs (a)(2) and (a)(3). For further guidance, refer to National Fire Protection Association (NFPA) 10, "Standards for Portable Fire Extinguishers." (Amendment 25-0)
(6) Paragraph (a)(2). A fire extinguisher containing at least five (5) lbs of Halon 1211 may be used in lieu of a water extinguisher to combat Class A fires. Alternatively, two (2) fire extinguishers containing at least 2.5 lbs of Halon 1211 each, installed in close proximity to each other, may be substituted for one water fire extinguisher. In locations where one Halon and one water extinguisher are installed and replacement of the water extinguisher is desired, the above guidance will apply, however, the existing Halon extinguisher is not part of the substitution; i.e., three (3) 2.5 pound Halon extinguishers are equivalent to one (1) 2.5 pound Halon and one (1) water extinguisher. The resulting configuration from the replacement of a water fire extinguisher with Halon fire extinguishers must not result in unhealthy, toxic gas concentration. (Amendment 25-0)
602. AMENDMENT 25-54, Effective October 14, 1980.
a. Regulation.
(a) Hand fire extinguishers. For hand fire extinguishers the following apply:
(1) Each hand extinguisher must be approved.
(2) The types and quantities of each extinguishing agent used must be appropriate to the kinds of fires likely to occur where used.
(3) Each extinguisher for use in a personnel compartment must be designed to minimize the hazard of toxic gas concentrations.
(4) A readily accessible hand fire extinguisher must be available for use in each Class A or Class B cargo compartment.
[(5) There must be at least the following number of hand fire extinguishers conveniently located in passenger compartments:
Passenger capacity:
Minimum number of hand fire extinguishers 7 through 30 1 31 through 60 2 61 or more 3
(6) There must be at least one hand fire extinguisher conveniently located in the pilot compartment.]
(b) Built-in fire extinguishers. If a built-in fire extinguisher system is required-
(1) The capacity of each system, in relation to the volume of the compartment where used and the ventilation rate, must be adequate for any fire likely to occur in that compartment; and
(2) Each system must be installed so that-
(i) No extinguishing agent likely to enter personnel compartments will be hazardous to the occupants; and
(ii) No discharge of the extinguisher can cause structural damage
b. Guidance.
(l) Paragraph (a)(1). Standards for approval. An approved type fire extinguisher includes those approved by the Underwriters' Laboratories, Inc., Factory Mutual Laboratories, Underwriters' Laboratories of Canada, or any other agency deemed qualified by the Administrator, or approved by the Administrator in accordance with the provisions of § 21.301.
(Amendment 25-0)
(2) Paragraphs (a)(2) and (a)(3). When selecting a hand held fire extinguisher for use in airplanes, consideration should be given to the most appropriate extinguishing agent for the type and location of fires likely to be encountered. At least one extinguisher appropriate for a Class A fire should be provided. Consideration should also be given to the extinguisher agent’s ratio of extinguishing ability to quantity required, toxicity, corrosive properties, freezing point, and to the unit's gross weight, ease of operation, and maintenance requirements. Airplane hand held fire extinguishers using extinguisher agents having a rating in toxicity Group 4 or under should not be installed in airplanes for which an application for a type certificate was made on or after March 5, 1952. (Amendment 25-0) NOTE: The toxicity ratings listed by the Underwriters' Laboratories and the halon and freon number for some of the commonly known fire extinguisher chemicals are as follows:
Group Number Halon Number* Freon Number Bromochloromethane 3 1011 --- Bromotrifluoromethane 6 1301 13B1/FE1301 Carbon dioxide 5 --- --- Carbon tetrachloride 3 1040 --- Dibromodifluoromethane 4 1202 12B2 Methyl bromide 2 1001 --- * The halon number is defined as follows: the first number is the number of carbon atoms; the second, fluorine; the third, chlorine; and the fourth, bromine in the extinguisher agent’s chemical formula.
Some older transport category airplanes, due to their type certification bases, are not required to comply with § 25.851. For such airplanes, it is recommended that hand held fire extinguishers
492 employing agents in toxicity Group 4 or higher be installed when renewing or replacing hand held fire extinguishers employing toxic agents. (Amendment 25-0)
(3) Paragraph (a)(2). Types of extinguishers. (Amendment 25-0)
(i) Carbon dioxide extinguishers. Carbon dioxide extinguishers are acceptable when the principal hazard is a Class B or Class C fire. Portable carbon dioxide installations should not exceed five lbs of agent per unit to ensure extinguisher portability and to minimize crew compartment carbon dioxide (CO2) concentrations. (Amendment 25-0)
(ii) Water extinguishers. Water extinguishers are acceptable when the principal hazard is a Class A fire and where a fire might smolder if attacked solely by such agents as CO2 or dry chemical. (Amendment 25-0)
(iii) Vaporizing liquid extinguishers. Vaporizing liquid type fire extinguishers are acceptable when the principal hazard is a Class B or Class C fire. (Amendment 25-0)
(iv) Dry chemical extinguishers. Dry chemical extinguishers are acceptable where the principal hazard is a Class B or Class C fire. The extinguisher should not be used in crew compartments because of interference with visibility during discharge and because of the possibility of the nonconductive powders being discharged on electrical contacts not otherwise involved. (Amendment 25-0)
(v) Specialized Dry Powder extinguishers for Class D fires. Solid materials in powder or granular form are designed to extinguish Class D combustible metal fires by crusting, smothering, or heat-transferring means. The recommendations of the manufacturer for use of those extinguishers should be followed because of the possible chemical reaction between the burning metal and the extinguishing agent. (Amendment 25-0) NOTE: Carbon dioxide is noncorrosive and will not injure food or fabric. Extinguishers must be winterized if they are to operate at temperatures below -40 °F. Approved unit capacity ranges upwards from two lbs. These extinguishers have only limited value for the extinguishment of a Class A fire, the action of the agent being to blanket the fire by excluding oxygen. Certain antifreeze agents may be corrosive. Approved extinguishers are either protected against freezing to -40 °F. or must be handled as any other unprotected water on the airplane. Technical Standard Order (TSO)-C19a covers a minimum l-3/8 quart capacity approved water extinguisher. Water extinguishers of the kinds currently on the market are not acceptable for flammable liquid or electrical fires.
Vaporizing liquid extinguisher agents are not normally corrosive to airplane structure and approved units will be satisfactorily protected against freezing to at least -40 °F. Up to the effective date of this guidance, no vaporizing liquid extinguisher with Underwriters' Laboratories toxicity rating higher than Group 4 is commercially available. Approved units have a minimum capacity of one quart. They are of only limited value for the extinguishment of Class A fires, having a cooling effect of about one-tenth that of water. When using dry chemical extinguishers
493 the powder is nontoxic and noncorrosive, and approved units are protected against freezing to at least -40 °F. Minimum capacity of approved units is two lbs.
(4) Paragraph (a)(2). Class of fires. (Amendment 25-0)
(i) Class A fires. Fires in ordinary combustible materials where the quenching and cooling effects of quantities of water, or solutions containing large percentages of water, are of first importance. (Amendment 25-0)
(ii) Class B fires. Fires in flammable liquids, greases, etc., where a blanketing effect is essential. (Amendment 25-0)
(iii) Class C fires. Fires in electrical equipment, where the use of a nonconducting extinguishing agent is of first importance. (Amendment 25-0)
(iv) Class D fires. Fires which involve combustible metals, such as magnesium, titanium, zirconium, sodium, lithium, and potassium, and require extinguishing agents of the dry powder types. (Amendment 25-0)
(5) Paragraphs (a)(2) and (a)(3). For further guidance, refer to National Fire Protection Association (NFPA) 10, "Standards for Portable Fire Extinguishers." (Amendment 25-0)
(6) Paragraph (a)(2). A fire extinguisher containing at least five (5) lbs of Halon 1211 may be used in lieu of a water extinguisher to combat Class A fires. Alternatively, two (2) fire extinguishers containing at least 2.5 lbs of Halon 1211 each, installed in close proximity to each other, may be substituted for one water fire extinguisher. In locations where one Halon and one water extinguisher are installed and replacement of the water extinguisher is desired, the above guidance will apply, however, the existing Halon extinguisher is not part of the substitution; i.e., three (3) 2.5 pound Halon extinguishers are equivalent to one (1) 2.5 pound Halon and one (1) water extinguisher. The resulting configuration from the replacement of a water fire extinguisher with Halon fire extinguishers must not result in unhealthy, toxic gas concentration. (Amendment 25-0)
(7) Paragraph (a)(5). The quantities of extinguishers noted above are the absolute minimum permitted. Virtually all airplanes with 61 or more passengers will require additional extinguishers due to interior amenities (galleys, lavatories etc.) and division of cabins. Refer to AC 20-42C, “Hand Fire Extinguishers for Use in Aircraft,” dated 3/7/84, for guidance on acceptable fire extinguishers. (Amendment 25-54)
603. AMENDMENT 25-72, Effective August 20, 1990.
a. Regulation.
(a) Hand fire extinguishers.
494 [(1) The following minimum number of hand fire extinguishers must be conveniently located in passenger compartments Passenger capacity:
Minimum number of hand fire extinguishers 7 through 30 1 31 through 60 2 61 or more 3
(2) At least one hand fire extinguisher must be conveniently located in the pilot compartment.
(3) A readily accessible hand fire extinguisher must be available for use in each Class A or Class B cargo compartment.
(4) Each hand fire extinguisher must be approved.
(5) The types and quantities of each extinguishing agent used must be appropriate to the kinds of fires likely to occur where used.
(6) Each extinguisher for use in a personnel compartment must be designed to minimize the hazard of toxic gas concentration.
(b) Built-in fire extinguishers. If a built-in fire extinguisher is provided-
(1) The capacity must be adequate for any fire likely to occur in the compartment where used, considering the volume of the compartment and the ventilation rate;
and,]
(2) Each system must be installed so that-
(i) No extinguishing agent likely to enter personnel compartments will be hazardous to the occupants; and
(ii) No discharge of the extinguisher can cause structural damage.
b. Guidance.
(l) Paragraph (a)(1). Standards for approval. An approved type fire extinguisher includes those approved by the Underwriters' Laboratories, Inc., Factory Mutual Laboratories, Underwriters' Laboratories of Canada, or any other agency deemed qualified by the Administrator, or approved by the Administrator in accordance with the provisions of § 21.301.
(Amendment 25-0)
(2) Paragraph (a)(1). The quantities of extinguishers noted above are the absolute minimum permitted. Virtually all airplanes with 61 or more passengers will require additional extinguishers due to interior amenities (galleys, lavatories etc.) and division of cabins. Refer to AC 20-42C, “Hand Fire Extinguishers for Use in Aircraft,” dated 3/7/84, for guidance on acceptable fire extinguishers. (Amendment 25-54)
(3) Paragraph (a)(5) and (a)(3). For further guidance, refer to National Fire Protection Association (NFPA) 10, "Standards for Portable Fire Extinguishers." (Amendment 25-0)
(4) Paragraph (a)(5). When selecting a hand held fire extinguisher for use in airplanes, consideration should be given to the most appropriate extinguishing agent for the type and location of fires likely to be encountered. At least one extinguisher appropriate for a Class A fire should be provided. Consideration should also be given to the extinguisher agent’s ratio of extinguishing ability to quantity required, toxicity, corrosive properties, freezing point, and to the unit's gross weight, ease of operation, and maintenance requirements. Airplane hand held fire extinguishers using extinguisher agents having a rating in toxicity Group 4 or under should not be installed in airplanes for which an application for a type certificate was made on or after March 5, 1952. (Amendment 25-0) NOTE: The toxicity ratings listed by the Underwriters' Laboratories and the halon and freon number for some of the commonly known fire extinguisher chemicals are as follows:
Group Number Halon Number* Freon Number Bromochloromethane 3 1011 --- Bromotrifluoromethane 6 1301 13B1/FE1301 Carbon dioxide 5 --- --- Carbon tetrachloride 3 1040 --- Dibromodifluoromethane 4 1202 12B2 Methyl bromide 2 1001 --- * The halon number is defined as follows: the first number is the number of carbon atoms; the second, fluorine; the third, chlorine; and the fourth, bromine in the extinguisher agent’s chemical formula.
Some older transport category airplanes, due to their type certification bases, are not required to comply with § 25.851. For such airplanes, it is recommended that hand held fire extinguishers employing agents in toxicity Group 4 or higher be installed when renewing or replacing hand held fire extinguishers employing toxic agents. (Amendment 25-0)
(5) Paragraph (a)(5). Types of extinguishers. (Amendment 25-0)
(i) Carbon dioxide extinguishers. Carbon dioxide extinguishers are acceptable when the principal hazard is a Class B or Class C fire. Portable carbon dioxide installations
496 should not exceed five lbs of agent per unit to ensure extinguisher portability and to minimize crew compartment carbon dioxide (CO2) concentrations. (Amendment 25-0)
(ii) Water extinguishers. Water extinguishers are acceptable when the principal hazard is a Class A fire and where a fire might smolder if attacked solely by such agents as CO2 or dry chemical. (Amendment 25-0)
(iii) Vaporizing liquid extinguishers. Vaporizing liquid type fire extinguishers are acceptable when the principal hazard is a Class B or Class C fire. (Amendment 25-0)
(iv) Dry chemical extinguishers. Dry chemical extinguishers are acceptable where the principal hazard is a Class B or Class C fire. The extinguisher should not be used in crew compartments because of interference with visibility during discharge and because of the possibility of the nonconductive powders being discharged on electrical contacts not otherwise involved. (Amendment 25-0)
(v) Specialized Dry Powder extinguishers for Class D fires. Solid materials in powder or granular form are designed to extinguish Class D combustible metal fires by crusting, smothering, or heat-transferring means. The recommendations of the manufacturer for use of those extinguishers should be followed because of the possible chemical reaction between the burning metal and the extinguishing agent. (Amendment 25-0) NOTE: Carbon dioxide is noncorrosive and will not injure food or fabric. Extinguishers must be winterized if they are to operate at temperatures below -40 °F. Approved unit capacity ranges upwards from two lbs. These extinguishers have only limited value for the extinguishment of a Class A fire, the action of the agent being to blanket the fire by excluding oxygen. Certain antifreeze agents may be corrosive. Approved extinguishers are either protected against freezing to -40 °F. or must be handled as any other unprotected water on the airplane. Technical Standard Order (TSO)-C19a covers a minimum l-3/8 quart capacity approved water extinguisher. Water extinguishers of the kinds currently on the market are not acceptable for flammable liquid or electrical fires.
Vaporizing liquid extinguisher agents are not normally corrosive to airplane structure and approved units will be satisfactorily protected against freezing to at least -40 °F. Up to the effective date of this guidance, no vaporizing liquid extinguisher with Underwriters' Laboratories toxicity rating higher than Group 4 is commercially available. Approved units have a minimum capacity of one quart. They are of only limited value for the extinguishment of Class A fires, having a cooling effect of about one-tenth that of water. When using dry chemical extinguishers the powder is nontoxic and noncorrosive, and approved units are protected against freezing to at least -40 °F. Minimum capacity of approved units is two lbs.
(6) Paragraph (a)(5). Class of fires. (Amendment 25-0)
(i) Class A fires. Fires in ordinary combustible materials where the quenching and cooling effects of quantities of water, or solutions containing large percentages of water, are of first importance. (Amendment 25-0)
(ii) Class B fires. Fires in flammable liquids, greases, etc., where a blanketing effect is essential. (Amendment 25-0)
(iii) Class C fires. Fires in electrical equipment, where the use of a nonconducting extinguishing agent is of first importance. (Amendment 25-0)
(iv) Class D fires. Fires which involve combustible metals, such as magnesium, titanium, zirconium, sodium, lithium, and potassium, and require extinguishing agents of the dry powder types. (Amendment 25-0)
(7) Paragraph (a)(5). A fire extinguisher containing at least five (5) lbs of Halon 1211 may be used in lieu of a water extinguisher to combat Class A fires. Alternatively, two (2) fire extinguishers containing at least 2.5 lbs of Halon 1211 each, installed in close proximity to each other, may be substituted for one water fire extinguisher. In locations where one Halon and one water extinguisher are installed and replacement of the water extinguisher is desired, the above guidance will apply, however, the existing Halon extinguisher is not part of the substitution; i.e., three (3) 2.5 pound Halon extinguishers are equivalent to one (1) 2.5 pound Halon and one (1) water extinguisher. The resulting configuration from the replacement of a water fire extinguisher with Halon fire extinguishers must not result in unhealthy, toxic gas concentration. (Amendment 25-0)
604. AMENDMENT 25-74, Effective May 16, 1991.
a. Regulation.
(a) Hand fire extinguishers.
[(1) The following minimum number of hand fire extinguishers must be conveniently located and evenly distributed in passenger compartments:
Passenger Capacity Number of Extinguishers 7 through 30 1 31 through 60 2 61 through 200 3 201 through 300 4 301 through 400 5 401 through 500 6 501 through 600 7 601 through 700 8
(2) At least one hand fire extinguisher must be conveniently located in the pilot compartment.
(3) At least one readily accessible hand fire extinguisher must be available for use in each Class A or Class B cargo or baggage compartment and in each Class E cargo or baggage compartment that is accessible to crewmembers in flight.
(4) At least one hand fire extinguisher must be located in, or readily accessible for use in, each galley located above or below the passenger compartment.
(5) Each hand fire extinguisher must be approved.
(6) At least one of the required fire extinguishers located in the passenger compartment of an airplane with a passenger capacity of at least 31 and not more than 60, and at least two of the fire extinguishers located in the passenger compartment of an airplane with a passenger capacity of 61 or more must contain Halon 1211 (bromochlorodifluromethane CBrC1F2), or equivalent, as the extinguishing agent. The type of extinguishing agent used in any other extinguisher required by the section must be appropriate for the kinds of fires likely to occur where used.
(7) The quantity of extinguishing agent used in each extinguisher required by this section must be appropriate for the kinds of fires likely to occur where used.
(8) Each extinguisher intended for use in a personnel compartment must be designed to minimize the hazard of toxic gas concentration.
(b) Built-in fire extinguishers. If a built-in fire extinguisher is provided-
(1) Each built-in fire extinguishing system must be installed so that-
(i) No extinguishing agent likely to enter personnel compartments will be hazardous to the occupants; and
(ii) No discharge of the extinguisher can cause structural damage.
(2) The capacity of each required built-in extinguishing system must be adequate for any fire likely to occur in the compartment where used, considering the volume of the compartment and the ventilation rate.]
b. Guidance.
(l) Standards for approval. An approved type fire extinguisher includes those approved by the Underwriters' Laboratories, Inc., Factory Mutual Laboratories, Underwriters' Laboratories of Canada, or any other agency deemed qualified by the Administrator, or approved by the Administrator in accordance with the provisions of § 21.301. (Amendment 25-0)
(2) For further guidance, refer to National Fire Protection Association (NFPA) 10, "Standards for Portable Fire Extinguishers." (Amendment 25-0)
(3) Paragraph (a)(1). The quantities of extinguishers noted above are the absolute minimum permitted. Virtually all airplanes with 61 or more passengers will require additional extinguishers due to interior amenities (galleys, lavatories etc.) and division of cabins. Refer to AC 20-42C, “Hand Fire Extinguishers for Use in Aircraft,” dated 3/7/84, for guidance on acceptable fire extinguishers. (Amendment 25-54)
(4) Paragraph (a)(6). When selecting a hand held fire extinguisher for use in airplanes, consideration should be given to the most appropriate extinguishing agent for the type and location of fires likely to be encountered. At least one extinguisher appropriate for a Class A fire should be provided. Consideration should also be given to the extinguisher agent’s ratio of extinguishing ability to quantity required, toxicity, corrosive properties, freezing point, and to the unit's gross weight, ease of operation, and maintenance requirements. Airplane hand held fire extinguishers using extinguisher agents having a rating in toxicity Group 4 or under should not be installed in airplanes for which an application for a type certificate was made on or after March 5, 1952. (Amendment 25-0) NOTE: The toxicity ratings listed by the Underwriters' Laboratories and the halon and freon number for some of the commonly known fire extinguisher chemicals are as follows:
Group Number Halon Number* Freon Number Bromochloromethane 3 1011 --- Bromotrifluoromethane 6 1301 13B1/FE1301 Carbon dioxide 5 --- --- Carbon tetrachloride 3 1040 --- Dibromodifluoromethane 4 1202 12B2 Methyl bromide 2 1001 --- * The halon number is defined as follows: the first number is the number of carbon atoms; the second, fluorine; the third, chlorine; and the fourth, bromine in the extinguisher agent’s chemical formula.
Some older transport category airplanes, due to their type certification bases, are not required to comply with § 25.851. For such airplanes, it is recommended that hand held fire extinguishers employing agents in toxicity Group 4 or higher be installed when renewing or replacing hand held fire extinguishers employing toxic agents. (Amendment 25-0)
(5) Paragraph (a)(6). Types of extinguishers. (Amendment 25-0)
(i) Carbon dioxide extinguishers. Carbon dioxide extinguishers are acceptable when the principal hazard is a Class B or Class C fire. Portable carbon dioxide installations
500 should not exceed five lbs of agent per unit to ensure extinguisher portability and to minimize crew compartment carbon dioxide (CO2) concentrations. (Amendment 25-0)
(ii) Water extinguishers. Water extinguishers are acceptable when the principal hazard is a Class A fire and where a fire might smolder if attacked solely by such agents as CO2 or dry chemical. (Amendment 25-0)
(iii) Vaporizing liquid extinguishers. Vaporizing liquid type fire extinguishers are acceptable when the principal hazard is a Class B or Class C fire. (Amendment 25-0)
(iv) Dry chemical extinguishers. Dry chemical extinguishers are acceptable where the principal hazard is a Class B or Class C fire. The extinguisher should not be used in crew compartments because of interference with visibility during discharge and because of the possibility of the nonconductive powders being discharged on electrical contacts not otherwise involved. (Amendment 25-0)
(v) Specialized Dry Powder extinguishers for Class D fires. Solid materials in powder or granular form are designed to extinguish Class D combustible metal fires by crusting, smothering, or heat-transferring means. The recommendations of the manufacturer for use of those extinguishers should be followed because of the possible chemical reaction between the burning metal and the extinguishing agent. (Amendment 25-0) NOTE: Carbon dioxide is noncorrosive and will not injure food or fabric. Extinguishers must be winterized if they are to operate at temperatures below -40 °F. Approved unit capacity ranges upwards from two lbs. These extinguishers have only limited value for the extinguishment of a Class A fire, the action of the agent being to blanket the fire by excluding oxygen. Certain antifreeze agents may be corrosive. Approved extinguishers are either protected against freezing to -40 °F. or must be handled as any other unprotected water on the airplane. Technical Standard Order (TSO)-C19a covers a minimum l-3/8 quart capacity approved water extinguisher. Water extinguishers of the kinds currently on the market are not acceptable for flammable liquid or electrical fires.
Vaporizing liquid extinguisher agents are not normally corrosive to airplane structure and approved units will be satisfactorily protected against freezing to at least -40 °F. Up to the effective date of this guidance, no vaporizing liquid extinguisher with Underwriters' Laboratories toxicity rating higher than Group 4 is commercially available. Approved units have a minimum capacity of one quart. They are of only limited value for the extinguishment of Class A fires, having a cooling effect of about one-tenth that of water. When using dry chemical extinguishers the powder is nontoxic and noncorrosive, and approved units are protected against freezing to at least -40 °F. Minimum capacity of approved units is two lbs.
(6) Paragraph (a)(7). Class of fires. (Amendment 25-0)
(i) Class A fires. Fires in ordinary combustible materials where the quenching and cooling effects of quantities of water, or solutions containing large percentages of water, are of first importance. (Amendment 25-0)