d. Electrical Equipment (arcs and sparks or overheating). Inspect and use only explosion-proof
electrical equipment that complies with Underwriters' Laboratory Incorporated standards when there is the
possibility of flammable vapors.
e. Spontaneous Combustion (self-ignition of combustible materials caused by accumulation of heat
though slow oxidation of its own material; for example, oil or paint-soaked waste and rags). Place waste and rags
in airtight metal containers.
f. Welding and Cutting. Clean and vapor-free equipment to be welded or cut.
g. Static Electricity (electricity generated by friction between two unlike substances). Prevent sparks by
(1) Bonding is an electrical connection between metallic containers or equipment to equalize their
(2) Grounding is an electrical connection between one or both of the bonded transfer units and the
ground. This action dissipates electrical potential into the ground through the use of a conductive wire and a
grounding rod. In some warm areas, rocky or sandy soil makes it hard to get a good ground because such soil has
low conductivity. Chemicals, to include sodium chloride (common table salt), can be used to condition the soil to
raise its conductivity. To use table to raise conductivity follow this method:
(a) First, dig a hole about 1 foot deep and 3 feet across.
(b) Mix 5 pounds of salt with 5 gallons of water.
(c) Pour the mixture into the hole, and allow it to seep in.
(d) Install the ground rod and wire, and keep the soil moist around the rod.
(3) Lightning s a massive discharge of static electricity. Cease all operations immediately whenever
there are lightning discharges within the vicinity.
Classes of Fire.
Fires are divided into four main classes. The Underwriters' Laboratories, Incorporated, groups fires into Classes
A, B, and C. The National Fire Protection Association groups them into Classes A, B, C, and D. These classes
are based on the combustion characteristics of the ignited material. In most cases, installation fires are
combinations of at least two and sometimes all of these classes.
a. Class A. Fires occur in ordinary combustible materials such as bedding, books, cloth, wood,
brush, grass, and rubbish. This type must be dealt with by cooling (water) the fire below its ignition temperature.
All class A fires leave embers which are likely to rekindle if air comes in contact with them. Therefore, this type
of fire must not be considered extinguished until the entire mass has been cooled thoroughly.
b. Class B. Fires occur in flammable substances such as gasoline, jet fuels, grease, oils, paint, tar,
and other combustible substance which do not leave embers or ashes. A smothering or diluting agent is the best
agent for putting out class B fires.