30 CFR § 75.1107-9 Dry chemical devices; capacity; minimum requirements.
(a) Dry chemical fire extinguishing systems used on underground
equipment shall be of the multipurpose powder-type and shall include the
following:
(1) The system including all hose and nozzles shall be
protected against the entrance of moisture, dust, or dirt;
(2) The system shall be guarded against damage during
operation of the equipment protected;
(3) Hose and pipe shall be as short as possible; the
distance between the chemical container and furthest nozzle shall not exceed
50 feet;
(4) Hose, piping, and fittings between the actuator and
the chemical container shall have a bursting pressure of 500 pounds per
square inch (gage) or higher; the hose, piping, and fittings between the
chemical container and the nozzles shall have a bursting pressure of 300
pounds per square inch (gage) or higher and
(5) The system shall discharge in 1 minute or less, for
quantities less than 50 pounds (nominal)1 24 and in less than 2
minutes for quantities more than 50 pounds;
1 Many dry chemical systems were originally designed for sodium
bicarbonate before all-purpose chemical (ammonium phosphate) was shown to be
more effective. Sodium bicarbonate is denser than ammonium phosphate; hence,
for example, a 50-pound system designed for the sodium bicarbonate will hold
slightly more by weight than all-purpose dry chemical (ammonium phosphate) by
weight. The word "nominal" is used in §75.1107-9 to express the approximate
weight in pounds of all-purpose dry chemical.
(b) On unattended underground equipment, the number of pounds of dry
chemical employed by the system shall be not less than 1 pound per square
foot of top surface area of the equipment; however, the minimum amount in
any system shall be 20 pounds (nominal). The discharge shall be directed
into and on potentially hazardous locations of the equipment.
(c) On attended underground equipment, the number of pounds (nominal)
employed by the system shall equal 5 times the total number of hazardous
locations; however, the minimum amount in any system shall not be less than
the following, except that systems on haulage vehicles installed prior to the
effective date of this section may contain 20 pounds (nominal).
