Environmental Engineering Reference
In-Depth Information
In order to protect excavators against accidents, proper techniques and equipment
must be used in the trenching and shoring operation. Trench shoring material should
consist of sheeting, bracing, and jacks. Never use shoring materials that have not
been certified for use by a licensed professional engineer. After installation of the
correct shoring materials, these materials should be inspected daily before anyone
enters the trench or excavation.
When the decision is made to use ground sloping techniques to prevent cave-
ins, the sides of a trench or excavation must be sloped correctly so that soil will
not slide. Determining the
angle of repose
is critical in shaping the proper slope.
The angle of repose is the steepest angle at which trench or excavation walls will
lie without sliding. The more unstable the soil, the flatter the angle should be; for
example, the angle of repose for solid rock should be set at 90°. For average soil
an angle of 45° is recommended. For loose sand, the proper angle of repose should
be set at about 25°.
Several other safety considerations are necessary whenever a trenching or exca-
vation project is undertaken. Workers must understand that it is important to pro-
vide site protection. Site protection not only protects workers from rocks or other
objects kicked or thrown into the trench but also protects pedestrians who might
inadvertently fall into an open trench or excavation. Safety measures such as fences,
barricades, covers for manholes, flags, security guards, and warning signs may be
necessary. It is important to remember that lighting may be necessary so that safety
can be maintained at night.
Along with providing proper lighting so that excavators can see well enough to
work in an excavation, a stairway, ladder, ramp, or other safe means of egress must
be located in trench excavations that are 4 feet or more in depth so as to require no
more than 25 feet of lateral travel for workers.
As with any other dangerous operation, the plant safety official should ensure
that a contingency plan for emergency response is in place and is used. This con-
tingency plan must be made clear and understandable to all trenching and exca-
vation personnel. Emergency procedures are worthless if they are not common
knowledge. Someone should always be outside the trench or excavation to help,
if necessary. Emergency telephone and numbers should be readily available. As a
final precaution, the trench or excavation should be backfilled as soon as possible
when the work is completed.
As with many other work activities, OSHA requires that personnel involved with
excavation activities be trained and that this training be documented. Moreover,
OSHA also requires that the person in charge of the excavation be a
qualified
or
competent person
. When qualifying a qualified or competent person for excavation
and trenching operations, it is wise to assemble an excavation crew with a potential
qualified or competent person as the person in charge and to have the crew dig a
12-foot-deep hole in a practice area. Experience gained through actually perform-
ing the work can never be replicated by listening to a classroom lecture on the topic.
While observing the digging and shoring procedures, note whether or not the poten-
tial qualified or competent person is conducting the dig as required.
