Page 581 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

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14.16 Safety and Hazards Prevention 537
Special attention is given to the integrity of the force main surface and pipeline con-
nections, unusual noise, vibration, pipe and pipe joint leakage and displacement, valving
arrangement and leakage, lift station operation and performance, discharge pump rates and
pump speed, and pump suction and discharge pressures. Depending on the overall per-
formance of the force main/lift station system, the extent of grease buildup and the need for
pipeline pigging are also assessed.
If there is an excessive increase in pump head and the head loss increase is caused by
grease buildup, the pipeline is pigged. Corrosion is rarely a problem since pipes are prima-
rily constructed of ductile iron or plastic, which are highly resistant to corrosion.

14.16 SAFETY AND HAZARDS PREVENTION
Safety and hazards prevention during the construction and operation of sewer works can be
prevented by taking the appropriate and safety measures starting from the initial design
phase. Six case studies are discussed below to illustrate several hazardous conditions and
how to avoid them.
14.16.1 Municipal Sewer Maintenance Worker Drowns Inside Sewer Wet Well in Illinois

A 35-year-old male municipal sewer maintenance worker (victim) drowned inside a sewer wet
well. The victim was part of a four-man sewer maintenance crew assigned to clean out a sewer
wet well, which was 20 ft deep and 6 ft in diameter (6.1 m deep and 1.83 m in diameter). The
victim entered through a 24-in.-diameter (600-mm-diameter) manway and climbed down on
fixed steel rungs that extended to the bottom. The wet well atmosphere had not been tested nor
ventilated before entering. The victim was wearing a full-body harness (secured to a winch
cable) and a supplied-air respirator. After descending 8 ft (2.44 m) to a grating platform, the
victim installed an inflatable sewer plug into the end of an 18-in.-diameter (450-mm-diameter)
inlet sewer pipe 2 ft (0.60 m) below ground level. After inflating the sewer plug, the victim
climbed down to the bottom of the wet well and began cleaning out the wet well with an 8-in.-
diameter (200-mm-diameter) sewer vacuum hose. Within a few minutes the victim removed
the respirator face piece, complaining to a coworker that the respirator was in his way.
Approximately 30 minutes later, the sewer plug gave way, causing sewage to flood the wet well.
On hearing the noise, the foreman ran to the manway and yelled for the two workers to
get out. Another coworker turned on the winch and began raising the cable. Within 15 sec-
onds the level of sewage inside the wet well was up to the grating. The coworker who was
standing on the grating reached down through the opening in the grating and made an un-
successful attempt to grab the victim who was submerged. During this rescue effort, the
winch cable became entangled in the grating support beams. As the sewage level continued
to rise, the coworker was forced to climb up further and was ultimately helped out of the wet
well by other coworkers. An attempt was also made to start up the pumps inside the lift sta-
tion. However, the pumps were air-locked and, therefore, would not pump the sewage out.
The fire department rescue squad was notified and arrived within 10 minutes. By this
time the sewage was about 2 ft (0.60 m) above the grating. Fire department rescuers en-
tered the wet well, freed the entangled winch cable, removed the victim, and began admin-
istering cardiopulmonary resuscitation. The victim revived and was transported to the in-
tensive care unit of a local hospital where he died approximately 11 hours later.
The public works department has a safety policy and confined space entry procedures,
but no confined space rescue procedures. The director of the public works department is
responsible for the safety program. Public works employees attend monthly safety meet-
ings where job safety issues are discussed and training is occasionally given. The victim
had previously attended a 1-hour training session on confined space safety, and a 1-hour