Operator Safety - Wastewater Operators - page 37

There is also no room for poor judgment in performing excavation
and trenching operations. Before beginning to trench or excavate, cer-
tain conditions must be checked, such as the location of utility installa-
tions (e.g., telephone, fuel, electric, water lines) or any other underground
installations that reasonably may be expected to be encountered during
excavation work prior to beginning an excavation.
Several other conditions must be checked before excavation is
attempted, including soil, weather, and climate conditions. These fac-
tors will determine the amount and degree of sloping that should be
used. Moreover, the strength of trenching support members (bracing
and shoring) is based on soil type and weather conditions. Failure to
properly support walls for a trench or excavation may cause disaster.
Often, trenching and excavation jobs are driven by cost and time saving
requirements. At other times, the supervisor in charge of the operation
might determine that the trench or excavation will only be open for a
short period and that proper shoring is not needed. What this supervisor
is really doing is taking a chance on a shortcut … perhaps a shortcut to
disaster.
When auditing various plant excavation programs it is not unusual
to find a weak link in the program. This weak link can usually be attrib-
uted to a lack of supervisor and worker knowledge. The auditor often
finds that workers are not aware of the hazards involved and the precau-
tions necessary to minimize the hazard. A trenching and excavation
training program should provide the information necessary to ensure
that supervisors and workers know the hazards. They should know
that the major hazard is cave-ins, which can crush or suffocate them.
They should know that trenches and excavations can contain poisonous
gases. There is also the very real possibility of uncovering a pocket of
combustible vapors or gases. For example, when digging around inter-
ceptor lines, it is not unusual to run into a pocket of methane, leading
to the danger of fire or explosion. Supervisors and workers also need to
know that OSHA requires excavations to be protected from cave-ins by
an adequate protective system that is designed to resist without failure
all loads that are intended or could reasonably be expected to be applied
or transmitted to the system.
Trenches and excavations can be full of additional obstacles; for
example, carelessly placed tools and equipment or excavated material
can cause injuries due to slips, trips, or falls. After explaining the gen-
eral hazards that are present with any trenching or excavation job, the
person performing the training needs to inform the workers about the
causes of cave-ins—they need to know what to look for. Workers need to
understand that cave-ins occur when an unsupported wall is weakened
or undermined by too much weight or pressure or an unstable bottom.
One of the danger signs to look for in trenching or excavation work
is surface cracking. These cracks usually occur near the edge of the
trench or excavation. Overhangs and bulges are other signs of danger.
An overhang at the top or a bulge in a wall can cause soil to slide into
the trench or excavation. Whenever cracks or overhangs are discovered,
work should be stopped and the problem reported immediately.