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 MIL-HDBK-419A
mixtures exist in the proper ratio. In order for static to be a source of ignition of the mixtures, four conditions
must be fulfilled. These conditions are:
There must first be an effective means of static generation.
a.
There must be a means of accumulating the separate charges and maintaining a suitable difference
b.
of electrical potential.
c.
There must be a spark discharge of adequate energy.
The spark must occur in an ignitable mixture.
d.
The most common sources of static electricity are:
Steam, air, or gas flowing from any opening in a pipe or hose, particularly when the stream is wet or
a.
when the air or gas stream contains particulate matter.
Pulverized materials passing through chutes or pneumatic conveyors.
b.
Nonconductive power or conveyor belts in motion.
c.
Moving vehicles.
d.
e.
All motion which involves changes in relative position of contacting surfaces (usually of dissimilar
substances, either liquid or solid), of which one or both must be a poor conductor of electricity.
Static electricity can be controlled in a variety of ways. The most effective means are:
Bond all metallic parts of a system to prevent the existence of a statically-induced potential
a.
difference between any two metallic objects in the system.
Ground all metallic systems to prevent the accumulation of static charges.
b.
Increase the relative humidity to 60% - 70% to increase the moisture content and thus the
c.
conductivity of insulating materials such as fabric, wood, paper, concrete, or masonry.
Use ionizing devices to ionize the surrounding air so that it becomes sufficiently conductive to bleed
d.
off static charges.
Use conductive materials for rugs, flooring, belts, etc. where nonconductive materials might
e.
otherwise be used.
9-4
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