Teledyne 4220 - Manual (Page 174)

4220 Flow Meter
Appendix D General Safety Procedures
D-2
“Lifting Injuries. Unless proper tools are used to remove
manhole covers, back injuries or injuries to hands or feet may
result.
“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.
“3. Adverse Atmosphere. [Refer to Table D-1, 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 atmo-
sphere must be run at least
3
/ 4 of the way down the manhole.
“Whenever adverse atmosphere is encountered, forced venti-
lation must be used to create safe conditions. After the venti-
lating 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.
“4. Entering Manholes. Since the top of the manhole is usually
flush with the surrounding 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 per-
mitted to carry anything in their hands as they enter the
manhole, to ensure that their hands will be free to hold on or
grab if they slip. A good method for entering a manhole is to sit
on the surface facing the manhole steps or ladder, with the feet in
the hole and the arms straddling the opening for support. As the
body slides forward and downward, the feet can engage a rung,
and the back can rest against the opposite side of the opening. If
there is any doubt about the soundness of the manhole steps, a
portable ladder should be used.
“A person should never enter a manhole unless he is wearing
personal safety equipment, including a safety harness and a hard
hat. Two persons should be stationed at the surface continuously
while anyone is working inside a manhole, to lift him out if he is
overcome or injured. One man cannot lift an unconscious man
out of a manhole. The persons stationed at the surface should
also function as guards to keep people and vehicles away from