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 TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
If these tests indicate the presence of an explosive
when carbon monoxide is present. By comparing the
mixture in the structure, an injection of carbon di-
change in color with the color chart furnished, the
oxide (CO,) into the structure may be made, before
concentration can be determined. Tests of this type
ventilating, to reduce the possibility of an explosion.
can be made in less than one minute.
Ventilation is best provided by a power-driven por-
c. Asbestos-cement fireproofing. Follow instruc-
table ventilating blower. Before the structure is
tions for handling in chapter 15, section II.
d. Ventilation. Even when tests indicate there are
purged with a blower, or CO, is injected into it,
personnel in connecting structures should be
no combustible or toxic gases, it is good practice to
warned, as the gas may be blown through the ducts
force-ventilate a manhole or vault whenever person-
into connecting structures. If CO, is used, the struc-
nel are in it. This is especially important if cable
ture must be purged with fresh air before it is en-
splicing is being performed.
tered by personnel.
e. Protection of open structures. Open structures
b. Toxic gases. A calorimetric indicating gel tube
should never be left unguarded. A barricade should
manufactured under specifications of the National
be placed around the structure opening prior to re-
Bureau of Standards, commonly referred to as the
moving the structure cover.
NBS carbon monoxide detector, is available to test
f. Ladders. Portable ladders used for access to
for toxics. It is used by breaking the seals of the
manholes or vaults should be checked before use to
tubes and aspirating gas to it from the atmosphere
ensure that they are firmly placed and will not
to be tested. Chemicals within the tube change color
wobble or tilt.
Section III - INSPECTION
5-5. Frequency of underground system in-
intended. Look for signs of traction on cable termi-
spections.
nations or direct-burial cable which may be a result
of expansion and contraction of the cable.
The frequency of inspection is largely determined by
a. Cable supports. Check mountings and sup-
the importance of the equipment or facility it serves
ports to ensure they are secure. Remove rust and
or contains. Inspections can vary in frequency from
corrosion and clean and repaint supports with
6 months to 5 years, but a 2-year cycle of inspection
corrosion-resistant paint.
is recommended. Records should be kept of each
b. Duct entrances. End bells are usually used to
inspection.
prevent cable damage at duct entrances. If they
5-6. Structure inspections.
were not installed, or are damaged, strips of hard
rubber or similar material should be used to protect
Inspect structures and check their cleanliness and
the cable at the duct entrance.
their physical condition, such as cracking of walls,
c. Testing. Cable insulation integrity cannot be
roofs, or floor slabs, spalling of concrete, and the
visually checked; it requires some type of insulation
condition of frames and covers. Inspect for corrosion
testing to determine whether the cable is reaching
of pulling eyes; driven grounds; and other miscella-
an insulation breakdown that will lead to a cable
neous fixtures such as cable racks, arms, and insu-
fault. Testing is described in section VII.
lators.
d. Cable faults. Inspection alone may reveal the
5-7. Cable inspections.
location of a cable fault or it may be a more compli-
cated process requiring test equipment. Visual and
Walk the route of underground direct-burial cable
test procedures are covered in section V.
circuits to inspect for changed conditions. Changes
in grade caused by washouts can expose cables to
5-8. Underground equipment inspections.
damaging conditions. Adjacent new construction
Special maintenance for such distribution equip-
should be closely monitored. Examine connections
ment in underground locations includes the follow-
to equipment terminals or cable terminations,
ing:
whether in the structure or above-ground. Check in
a. Keep items clean and protected from corrosion.
structures for the condition of duct entrances, fire-
b. Check equipment covers to be sure that their
proofing, splices, cable tags, and ground connections
gasketing is water-tight.
to cable shielding and sheathes. Anchors for subma-
rine cables should be inspected occasionally to be
c. Keep nuts and bolts free from rust by applica-
sure they are in good condition and functioning as
tions of paint or heavy grease.
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