On–the–Job Evaluation §1926.651(k)
The standard requires that a
competent person inspect, on a daily basis, excavations and the adjacent areas
for possible cave–ins, failures of protective systems and equipment, hazardous
atmospheres, or other hazardous conditions. If these conditions are
encountered, exposed employees must be removed from the hazardous area until
the necessary safety precautions have been taken. Inspections are also required
after natural (e.g., heavy rains) or man–made events such as blasting that may
increase the potential for hazards.
Larger and more complex
operations should have a full–time safety official who makes recommendations to
improve the implementation of the safety plan. In a smaller operation, the
safety official may be part–time and usually will be a supervisor.
Supervisors are the
contractor's representatives on the job. Supervisors should conduct
inspections, investigate accidents, and anticipate hazards. They should ensure
that employees receive on–the–job safety and health training. They should also
review and strengthen overall safety and health precautions to guard against potential
hazards, get the necessary worker cooperation in safety matters, and make
frequent reports to the contractor.
It is important that managers
and supervisors set the example for safety at the job site. It is essential
that when visiting the job site, all managers, regardless of status, wear the
prescribed personal protective equipment such as safety shoes, safety glasses,
hard hats, and other necessary gear.
also take an active role in job safety. The contractor and supervisor should make
certain that workers have been properly trained in the use and fit of the
prescribed protective gear and equipment, that they are wearing and using the
equipment correctly, and that they are using safe work practices.
Cave–ins and Protective Support Systems
Excavation workers are
exposed to many hazards, but the chief hazard is danger of cave–ins. OSHA
requires that in all excavations employees exposed to potential cave–ins must
be protected by sloping, or benching the sides of the excavation; supporting
the sides of the excavation, or placing a shield between the side of the
excavation and the work area.
One method of ensuring the
safety and health of workers in an excavation is to slope the sides to an angle
not steeper than one and one–half horizontal to one vertical (34 degrees
measured from the horizontal). These slopes must be excavated to form
configurations that are in accordance with those for Type C soil found in
Appendix B of the standard. A slope of this gradation or less is considered
safe for any type of soil. It is our policy to treat all soils as if
they are Class C (see table below).
MAXIMUM ALLOWABLE SLOPES
OR ROCK TYPE
ALLOWABLE SLOPES (H:V)(1) FOR EXCAVATIONS LESS THAN 20 FEET DEEP(3)
VERTICAL (90 Deg.)
3/4:1 (53 Deg.)
1:1 (45 Deg.)
1 1/2:1 (34 Deg.)
- 1.3 Excavations Made in Type C Soil
1. All simple slope excavations 20 feet or
less in depth shall have a maximum allowable slope of 1 ½:1.
2. All excavations 20 feet or less in depth
which have vertically sided lower portions shall be shielded or supported to a
height at least 18 inches above the top of the vertical side. All such
excavations shall have a maximum allowable slope of 1 ½:1.
VERTICAL SIDED LOWER PORTION
3. All other sloped excavations shall be in
accordance with the other options permitted in §1926.652(b).
- 1.4 Excavations Made in Layered Soils
1. All excavations 20 feet or less in depth
made in layered soils shall have a maximum allowable slope for each layer as
set forth below.
design method, which can be applied for both sloping and shoring, involves using
tabulated data, such as tables and charts, approved by a registered
professional engineer. These data must be in writing and must include
sufficient explanatory information to enable the user to make a selection,
including the criteria for determining the selection and the limits on the use
of the data.
At least one copy of the
information, including the identity of the registered professional engineer who
approved the data, must be kept at the worksite during construction of the
protective system. Upon completion of the system, the data may be stored away
from the job site, but a copy must be made available, upon request, to the
Assistant Secretary of Labor for OSHA.
Contractors also may use a
trench box or shield that is either designed or approved by a registered
professional engineer or is based on tabulated data prepared or approved by a
registered professional engineer. Timber, aluminum, or other suitable materials
may also be used. OSHA standards permit the use of a trench
shield (also known as a welder's hut) as long as the protection it
provides is equal to or greater than the protection that would be provided by
the appropriate shoring system.
The employer is free to
choose the most practical design approach for any particular circumstance. Once
an approach has been selected, however, the required performance criteria must
be met by that system.
The standard does not require
the installation and use of a protective system when an excavation: (1) is made
entirely in stable rock, or (2) is less than five feet deep and a competent
person has examined the ground and found no indication of a potential cave–in.
The standard requires the
employer to provide support systems such as shoring, bracing, or underpinning
to ensure the stability of adjacent structures such as buildings, wells,
sidewalks or pavements.
The standard prohibits
excavation below the level of the base or footing of any foundation or
retaining wall unless: (1) a support system such as underpinning is provided,
(2) the excavation is in stable rock, or (3) a registered professional engineer
determines that the structure is sufficiently removed from the excavation and
that excavation will not pose a hazard to employees.
Excavations under sidewalks
and pavements are also prohibited unless an appropriately designed support
system is provided or another effective method is used.
Installation and Removal
of Protective Systems §1926.652(e)
The standard requires the
following procedures for the protection of employees when installing support
Securely connect members of support systems.
Safely install support systems.
Never overload members of support systems.
Install other structural members to carry loads imposed on the support system
when temporary removal of individual members is necessary.
In addition, the standard
permits excavation of two feet or less below the bottom of the members of a
support or shield system of a trench if: (1) the system is designed to resist
the forces calculated for the full depth of the trench, and (2) there are not
indications, while the trench is open, of a possible cave–in below the bottom
of the support system. Also, the installation of support systems must be
closely coordinated with the excavation of trenches.
As soon as work is completed,
the excavation should be backfilled as the protective system is dismantled.
After the excavation has been cleared, workers should slowly remove the
protective system from the bottom up, taking care to release members slowly.
Materials and Equipment
The employer is responsible
for the safe condition of materials and equipment used for protective systems.
Defective and damaged materials and equipment can result in the failure of a
protective system and cause excavation hazards.
possible failure of a protective system, the employer must ensure that (1)
materials and equipment are free from damage or defects, (2) manufactured materials
and equipment are used and maintained in a manner consistent with the
recommendations of the manufacturer and in a way that will prevent employee
exposure to hazards, and (3) while in operation, damaged materials and
equipment are examined by a competent person to determine if they are suitable
for continued use. If materials and equipment are not safe for use, they must
be removed from service. These materials cannot be returned to service without
the evaluation and approval of a registered professional engineer.
Falls and Equipment §1926.651(e),(f)
In addition to cave–in
hazards and secondary hazards related to cave–ins, there are other hazards from
which workers must be protected during excavation–related work. These hazards
include exposure to falls, falling loads, and mobile equipment. To protect
employees from these hazards, OSHA requires the employer to take the following
materials or equipment that might fall or roll into an excavation at least 2
feet from the edge of excavations, or have retaining devices, or both.
warning systems such as mobile equipment, barricades, hand or mechanical
signals, or stop logs, to alert operators of the edge of an excavation. If
possible, keep the grade away from the excavation.
scaling to remove loose rock or soil or install protective barricades and other
equivalent protection to protect employees against falling rock, soil, or
employees from working on faces of sloped or benched excavations at levels
above other employees unless employees at lower levels are adequately protected
from the hazard of falling, rolling, or sliding material or equipment.
Prohibit employees under loads that are
handled by lifting or digging equipment. To avoid being struck by any
spillage or falling materials, require employees to stand away from vehicles
being loaded or unloaded. If cabs of vehicles provide adequate protection from
falling loads during loading and unloading operations, the operators may remain
Water Accumulation §1926.651(h)
The standard prohibits
employees from working in excavations where water has accumulated or is
accumulating unless adequate protection has been taken. If water removal
equipment is used to control or prevent water from accumulating, the equipment
and operations of the equipment must be monitored by a competent person to
ensure proper use.
OSHA standards also require
that diversion ditches, dikes, or other suitable means be used to prevent
surface water from entering an excavation and to provide adequate drainage of
the area adjacent to the excavation. Also, a competent person must inspect
excavations subject to runoffs from heavy rains.
Hazardous Atmospheres §1926.651(g)
Under this provision, a
competent person must test excavations greater than four feet in depth as well
as ones where oxygen deficiency or a hazardous atmosphere exists or could
reasonably be expected to exist, before an employee enters the excavation. If
hazardous conditions exist, controls such as proper respiratory protection or
ventilation must be provided. Also, controls used to reduce atmospheric
contaminants to acceptable levels must be tested regularly.
Where adverse atmospheric
conditions may exist or develop in an excavation, the employer also must
provide and ensure that emergency rescue equipment, (e.g., breathing apparatus,
a safety harness and line, basket stretcher, etc.) is readily available. This
equipment must be attended when used.
When an employee enters
bell–bottom pier holes and similar deep and confined footing excavations, the
employee must wear a harness with a lifeline. The lifeline must be securely
attached to the harness and must be separate from any line used to handle
materials. Also, while the employee wearing the lifeline is in the excavation,
an observer must be present to ensure that the lifeline is working properly and
to maintain communication with the employee.
Access and Egress §1926.651(c)
Under the standard, the
employer must provide safe access and egress to all excavations. According to
OSHA regulations, when employees are required to be in trench excavations
4–feet deep or more, adequate means of exit, such as ladders, steps, ramps or
other safe means of egress, must be provided and be within 25 feet of lateral
ramps are used as a means of access or egress, they must be designed by a
competent person if used for employee access or egress, or a competent person
qualified in structural design if used by vehicles. Also, structural members
used for ramps or runways must be uniform in thickness and joined in a manner
to prevent tripping or displacement.
Trenching and excavation work presents serious risks
to all workers involved. The greatest risk, and one of primary concern, is that
of a cave–in. Furthermore, when cave–in accidents occur, they are much more
likely to result in worker fatalities than other excavation–related accidents.
Strict compliance, however, with all sections of the standard will prevent
or greatly reduce the risk of cave–ins as well as other excavation–related