4210 Flow Meter
Appendix C General Safety Procedures
C-2
C.1.2 Deteriorated Rungs Manhole steps may be corroded and not strong enough to support
a man. It may be difficult to inspect the rungs because of poor
lighting.
C.1.3 Traffic Whenever manholes are located in the traveled way, barricades
and warning devices are essential to direct traffic away from an
open manhole.
C.1.4 Falling Objects Items placed near the manhole opening may fall and injure a
worker in the manhole. All loose items should be kept away from
the manhole opening. This applies to hand tools as well as
stones, gravel and other objects.
C.1.5 Sharp Edges Sharp edges of items in or near a manhole may cause cuts or
bruises.
C.1.6 Lifting Injuries Unless proper tools are used to remove manhole covers, back
injuries or injuries to hands or feet may result.
C.2 Planning Advance planning should include arrangements for test
equipment, tools, ventilating equipment, protective clothing,
traffic warning devices, ladders, safety harness, and adequate
number of personnel. Hasty actions may result in serious
injuries. Time spent in the manhole should be kept to a
minimum.
C.3 Adverse Atmospheres [Refer to the table of Hazardous Gases at the end of this
appendix.] Before workers enter a manhole, tests should be made
for explosive atmosphere, presence of hydrogen sulfide, and
oxygen deficiency. Combustible or toxic vapors may be heavier
than air, so the tests on the atmosphere must be run at least
3
/4 of
the way down the manhole.
Whenever adverse atmosphere is encountered, forced ventilation
must be used to create safe conditions. After the ventilating
equipment has been operated for a few minutes, the atmosphere
in the manhole should be retested before anyone enters the
manhole.
When explosive conditions are encountered, the ventilating
blower should be placed upwind to prevent igniting any gas that
is emerging from the opening. When a gasoline engine blower is
used, it must be located so that exhaust fumes cannot enter the
manhole.
If testing equipment is not available, the manhole should be
assumed to contain an unsafe atmosphere and forced ventilation
must be provided. It should never be assumed that a manhole is
safe just because there is no odor or the manhole has been
entered previously.
C.4 Entering Manholes Since the top of the manhole is usually flush with the sur-
rounding surface, there may not be anything for the person who
is entering the manhole to grab on to steady himself. Persons
who are entering manholes should not be permitted to carry any-
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