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 MIL-HDBK-1038
Class I, hazardous environment; and Type 9 for Class II, hazardous environment as
classified by NEC. Trolley and runway electrification must be in the form of
covered conductors, either festooned or reeled.
6.3.4
Background. The highest probability of spark creation is at the
make/break contact surfaces of electrical equipment. These spark-producing sites
localized and are isolated from the hazardous environment by standard approved
designs of electrical enclosures. The possible sites of mechanical/impact spark
creation on exposed surfaces are of a type that cannot be shielded by isolating
enclosures, and there are no materials that are definitely non-sparking and have
the required mechanical properties for crane applications. Only a limited number
of practical materials with low-sparking characteristics are available for use on
cranes.
Military specifications were developed for hand tools for "use in the
presence of flammable gases, dust, and explosives" in the 1960's. The term
"nonsparking" was used in their titles and the phrase "low sparking hazard" in
their text. These tools included such high impact items as scrapers, cold
chisels, and hammers. The prescribed materials for these hand tools were heat-
treatable copper-beryllium alloys 172 and 173. The acceptance test for confirming
the low sparking property of the tool involved pressing the tool (or sample of
tool material) against a knurled carbon steel wheel with a hardness of Rockwell
C60 to 65 and rotating at 10,000 revolutions per minute. The test was conducted
in a chamber with oxygen-enriched air mixture and evaporated gasoline. To be
acceptable, the tool specimen subjected to this test was not to cause an explosion
on three successive runs to be acceptable.
American Petroleum Institute funded a research project to be conducted at
Underwriters' Laboratories, Inc. under the sponsorship of the Committee on
Accident Prevention and Fire Protection. The results of the project were
presented in an API publication PSN 22114, Spark Ignition Properties of Hand
Tools, October 1980. The conclusion:
"In the 24 years since the publication of Sparks from Hand Tools, nothing
essentially new has been learned. Sparks produced by violent contact between some
substances and others, including some of the metals ordinarily termed nonsparking
can, in fact, produce ignition of gases or vapors if sufficient energy is
dissipated in the impact. However, such conditions are far removed from the
actual conditions in which hand tools are used. The fire records of more and more
companies that have never used or have ceased to use the nonsparking tools amply
confirm and support the position taken by the Safety Committee of the API Board of
Directors in 1956:
The Institute's position is that the use of special nonferrous hand
tools, sometimes referred to as nonsparking tools, is not warranted as a fire
prevention measure applicable to oil and gas operations."
6.4
Hot (Molten) Metal Service. These cranes are popularly known as "hot
metal cranes" but in Navy service they only handle ladles with molten lead or
copper alloys. (Cranes that lift solid hot castings or forgings are classified as
general purpose service cranes.) The most common cranes in this service are OET
and underrunning types. The following design features apply to hot metal cranes:
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