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 MIL-HDBK-1038
b)
All exposed fasteners and other items of hardware that may loosen or
become dislodged, must be captivated by means of applied thread locking compound,
installed lock wire, or attached chain. Items such as equipment nameplates and
their fastening rivets must be removed or the rivets replaced with captivated
threaded fasteners. On OET, underrunning, cantilever, gantry and semi-gantry
cranes the entire hoist, trolley, or hoist/trolley unit must be captivated.
Additionally, bridge drives that pass over open reactor compartments, must also be
captivated. On portal, floating, and mobile cranes, the outer section of the boom
(as defined above) requires captivation. (Structural bolts tensioned or torqued
in accordance with the structural design requirements do not require captivation.
The practice of tack welding structural bolts or nuts is prohibited.)
c)
Devices containing elemental mercury are prohibited, unless they
provide double containment for the mercury. (HID and fluorescent lamps are among
such prohibited devices, but may be used if the lamps are within sealed lenses or
refractors, which serve as the second means of containment for the mercury.)
d)
Devices containing fluids, including bumpers and components of
hydraulic systems, are prohibited.
6.3
Hazardous/Explosive Environment. Cranes operating in hazardous
environments require features which minimize the possibility of creating a spark
by impact or by electric arcing. The extent of anti-sparking provisions is
limited by the boundaries of the hazardous region, usually defined as a distance
above the floor. In the majority of cases, the hazardous region encompasses only
the hook blocks, wire ropes, and the pendent pushbutton station; in rare cases,
the entire crane must be made low-sparking. Standard commercial varieties of
electrical equipment are available to comply with the National Electrical Code
requirements for all formally defined classes of hazardous environments, but there
are no comparable criteria for the mechanical components. The material
restrictions for hazardous environments given below are the traditional Navy Crane
Center requirements for materials with low sparking potential (when struck) and
with adequate mechanical (strength) properties as engineering materials.
6.3.1
Minimum Anti-Spark Protection. As minimum protection against creation of
sparks by impact, the load hook is required to be either bronze (any alloy) or
stainless steel (any alloy). In this application, cast hooks are acceptable;
other mechanical properties should be approved by NCC. The pendent pushbutton
station must be Type 7 for Class I, hazardous environment; and Type 9 for Class
II, hazardous environment, as classified by NEC.
6.3.2
Additional Anti-Spark Protection. An additional degree of protection can
be obtained with a bronze or stainless steel hook block or by covering the exposed
surfaces of the hook block with thin bronze, stainless steel, or aluminum covers
attached with similar fasteners. (Sheaves and other internal components are not
required to be spark resistant.) To complement the hook block materials,
stainless steel wire rope should be used.
6.3.3
Maximum Anti-Spark Protection. When the hazardous region envelops the
entire crane, all electrical equipment on the trolley and bridge, and runway
electrification require anti-sparking protection. Trolley and bridge travel
wheels should be bronze, electric motors and disc brakes must be of the totally
enclosed type (shoe brakes may not be used), all electrical enclosures must be
Type 7 for
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