Class A fires. Fires in ordinary combustible materials, such as wood, cloth, paper, and rubber.

Class B fires. Fires in flammable liquids, gases, and greases.

Class C fires. Fires which involve energized electrical equipment where the electrical nonconductivity of the extinguishing media is of importance. (When electrical equipment is deenergized, extinguisher for Class A or B fires may be used safely.)

Class D fires. Fires in combustible metals, such as magnesium, titanium, zirconium, sodium, and potassium.

Classification of portable fire extinguishers: Portable fire extinguishers are classified for use on certain classes of fires and rated for relative extinguishing effectiveness at a temperature of plus 70°F by nationally recognized testing laboratories. This is based upon the preceding classification of fires and the fire extinguishment potentials as determined by fire tests.

Class A rating—Wood and excelsior fires excluding deep-seated conditions.

Class B rating—Two-inch depth gasoline fires in square pans.

Class C rating—No fire test. Agent must be a nonconductor of electricity.

Class D rating—Special tests on specific combustible metal fires.

Light hazard. A situation where the amount of combustibles or flammable liquids present is such that fires of small size may be expected. These may include offices, schoolrooms, churches, assembly halls, telephone exchanges, etc.

Ordinary hazard. A situation where the amount of combustibles or flammable liquids present is such that fires of moderate size may be expected. These may include mercantile storage and display, auto showrooms, parking garages, light manufacturing, warehouses not classified as extra hazard, school shop areas, etc.

Extra hazard. A situation where the amount of combustibles or flammable liquids present is such that fires of severe magnitude may be expected. These may include woodworking, auto repair, aircraft servicing, warehouses with high-piled (14 feet or higher) combustibles, and processes such as flammable liquid handling, painting, dipping, etc.

Sprinkler system. For fire protection purposes, is an integrated system of underground and overhead piping designed in accordance with fire protection engineering standards. The system includes a suitable water supply, such as a gravity tank, fire pump, reservoir, or pressure tank and/or connection by underground piping to a city main. The portion of the sprinkler system above ground is a network of specially sized or hydraulically designed piping installed in a building, structure or area, generally overhead, and to which sprinklers are connected in a systematic pattern. The system includes a controlling valve and a device for actuating an alarm when the system is in operation. The system is usually activated by heat from a fire and discharges water over the fire area.

Sprinkler alarm unit. An assembly of apparatus approved for the service and so constructed and installed that any flow of water from a sprinkler system equal to or greater than that from a single automatic sprinkler will result in an audible alarm signal on the premises.

Class of service—Standpipe systems: Standpipe systems are grouped into three general classes of service for the intended use in the extinguishment of fire.

Class I: For use by fire departments and those trained in handling heavy fire streams (2 1/2 inch hose).

Class II: For use primarily by the building occupants until the arrival of the fire department (small hose).

Class III: For use by either fire departments and those trained in handling heavy hose streams or by the building occupants.

Class I service. A standpipe system capable of furnishing the effective fire streams required during the more advanced stages of fire on the inside of buildings or for exposure fire.

Class II service. A standpipe system which affords a ready means for the control of incipient fires by the occupants of buildings during working hours and by watchperson and those present during the night time and holidays.

Class III service. A standpipe system capable of furnishing the effective fire streams required during the more advanced stages of fire on the inside of buildings as well as providing a ready means for the control of fires by the occupants of the building.

Standpipe systems. Usually of the following types:

- A wet standpipe system having a supply valve open and water pressure maintained at all times.

- A standpipe system so arranged through the use of approved devices as to admit water to the system automatically by opening a hose valve.

- A standpipe system arranged to admit water to the system through manual operation of approved remote control devices located at each hose station.

- Dry standpipe having no permanent water supply. See also (11) of this section.

Type I storage. That in which combustible commodities or noncombustible commodities involving combustible packaging or storage aids are stored over 15 feet but not more than 21 feet high in solid piles or over 12 feet but not more that 21 feet high in piles that contain horizontal channels. Minor quantities of commodities of hazard greater than ordinary combustibles may be included without affecting this general classification.

Type II storage. That in which combustible commodities or noncombustible commodities involving combustible packaging or storage aids are stored not over 15 feet high in solid piles or not over 12 feet high in piles that contain horizontal channels. Minor quantities of commodities of hazard greater than ordinary combustibles may be included without affecting this general classification.

Type III storage. That in which the stored commodities, packaging, and storage aids are noncombustible or contain only a small concentration of combustibles which are incapable of producing a fire that would cause appreciable damage to the commodities stored or to noncombustible wall, floor or roof construction. Ordinary combustible commodities in completely sealed noncombustible containers may qualify in this classification. General commodity storage that is subject to frequent changing and storage of combustible packaging and storage aids is excluded from this category.

Approved. Listed or approved by: (a) At least one of the following nationally recognized testing laboratories: Factory Mutual Engineering Corp.; Underwriters' Laboratories, Inc., or (b) federal agencies such as Mine Safety and Health Administration (MSHA); the National Institute for Occupational Safety and Health (NIOSH); Department of Transportation; or U.S. Coast Guard, which issue approvals for such equipment.