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544 Chapter 14 Design of Sewer Systems
stumbled 3,000 ft (914.4 m) to the outside to report the worker was down near the pump.
The only ill effect experienced by the foreman was a severe headache.
Seven workers went into the pipe in an attempt to remove the downed worker. At the
same time the state inspector got into his truck and drove to manhole 2, where he removed
the plywood cover and entered the sewer. The state inspector proceeded toward the area
where the worker had been reported down. The underground superintendent also entered
the sewer at manhole 2 but exited after 2 or 3 minutes. Six of the seven workers who en-
tered the pipe at the portal exited at manhole 2. The seventh man reached the worker but
was unable to remove him. The company safety director entered the sewer at manhole 2
and reported passing the seventh worker and reaching the deceased. Shortly after, the sev-
enth worker and the safety director exited the sewer manhole 2.
At this time three firefighters arrived at the scene and entered manhole 2. The firefighters
were equipped with 30-minute self-contained breathing apparatus (SCBA). In addition to
the bulkiness of the SCBA, they were hampered by the curved and slick inner surface of
the sewer. Initially, the firefighters were told the victims were down approximately 150 ft
(45.72 m) into the sewer. However, they had to travel 500 to 600 ft (152 to 183 m) to reach
the victims. As their air supply decreased, the firefighters placed one SCBA on the victim
(the state inspector) who was still breathing, and resorted to buddy breathing to exit. The
state inspector was removed through manhole 2. He was pronounced dead at the scene.
Subsequent autopsy indicated his carboxyhemoglobin level was 50% and his pO was 0%.
2
The laborer was removed later through manhole 2. He was also pronounced dead at the
scene. His carboxyhemoglobin level was 56% and pO level was not available.
2
Combustible gas measurements and oxygen and carbon monoxide levels were taken
22 hours later at the incident site by an industrial hygienist. Oxygen level was 19% and
concentrations of CO were 600 ppmv. The industrial hygienist estimated that concentra-
tion of CO next to the pump on the day of the incident was 2,000 ppmv. An air sample
taken the following day revealed readings of 19% to 20% oxygen. Trace amounts of H S
2
were also recorded.
Given the industrial hygiene survey results and the toxicologic findings, the cause of
death was determined to be exposure to high concentrations of CO, a by-product of the
gasoline-powered pump, in an area with no natural ventilation, that is, in a confined space.
While the following list of recommendations is not exhaustive, it does cover some of
the salient points which, if implemented, could have prevented this fatal incident:

1. When the existing sewer was activated (passing through manhole 1), no plans were
made to prevent the sewage from flowing into the newly constructed sewer. An
analysis of the conditions surrounding the connection at manhole 1 should have
generated several safe alternatives for an effective temporary barrier in the new
sewer, which also considered safe atmospheric conditions.
2. A gasoline-powered pump was installed inside the sewer (a confined space), which
was known to have almost no ventilation. Neither workers nor pump could have
operated efficiently in the sewer. The rich mixture created by depletion of O in-
2
creased the levels of CO. The pump should have been located on the outside of the
sewer with a hose running to the sewage via an access hole or an electric
motor–driven pump should have been considered.
3. A static ventilating condition was created when the plug was installed in the new
sewer next to manhole 1. Because it was necessary for workmen (either those serv-
icing the pump or those planning to do the grouting) to enter the sewer, adequate
ventilation should have been provided. If ventilation could not create a safe atmos-
phere, the use of SCBA should have been mandatory.