EXCAVATION
REQUIREMENTS EXERCISE
The first
part of the exercise is a summary general requirements, the second part is a
table explaining proper sloping of excavation walls and the third part is a
bullet outline of excavation requirements.
PART I
PLANNING
YOUR EXCAVATION
The estimated
location of utility installations, such as sewer, telephone, fuel, electric, water
lines, or any other underground installations that reasonably may be expected
to be encountered during excavation work, needs to be determined prior to
opening an excavation. When utility
companies or owners cannot respond to a request to locate underground utility
installations within 24 hours (unless a longer period is required by state or
local law), or cannot establish the exact location of these installations, the
employer is allowed to proceed, so long as the employer does so with caution,
and so long as detection equipment or other acceptable means to locate utility
installations are used.
When
excavation operations approach the estimated location of underground
installations, the exact location of the installations needs to be determined
by safe and acceptable means. Since
most utility companies provide markings that are supposed to be accurate to
within about two feet, hand excavation of the soil beginning just outside the
marked zone can be used to confirm the exact location of the underground
structure to assure that excavating equipment will not damage it and allow the
equipment to excavate nearer to the underground structure.
EMPLOYEE
ACCESS TO EXCAVATIONS
A stairway,
ladder, ramp or other safe means of egress must be located in excavations that
are 4 feet or more in depth so as to require no more than 25 feet of lateral
travel for employees to reach a means of egress. In the case of a trench, egress points must be placed no more
than 25 feet apart for the entire length of the trench. If an area of the trench is to be unoccupied,
placing physical barriers around the area that will not be occupied can
eliminate the requirement for placing means of egress within those areas of the
trench.
HEAVY
EQUIPMENT OPERATION
When mobile
equipment is operated adjacent to an excavation, or when such equipment is
required to approach the edge of an excavation, the operator must either have a
clear and direct view of the edge of the excavation, or a warning system needs
to be utilized. Examples of warning
systems include: barricades, hand or mechanical signals, or stop
logs/curbs. Where possible, the grade
should be away from the excavation.
MONITORING
OF EXCAVATIONS
Where oxygen
deficiency (atmospheres containing less than 19.5 percent oxygen) or a
hazardous atmosphere exists or could reasonably be expected to exist (OSHA does
not differentiate between evaluation of real versus potential risks), such as
in excavations in landfill areas or excavations in areas where hazardous
substances are stored nearby, the atmospheres in the excavation must be tested
before employees enter excavations greater than 4 feet in depth.
WATER
IN EXCAVATIONS
Employees are
not allowed work in excavations in which there is accumulated water, or in
excavations in which water is accumulating, unless adequate precautions have
been taken to protect employees against the hazards posed by water
accumulation. The precautions necessary to protect employees adequately vary
with each situation, but could include special support or shield systems to
protect from cave-ins, water removal to control the level of accumulating
water, or use of a safety harness and lifeline.
ADJACENT
STRUCTURES
Where the
stability of adjoining buildings, walls, or other structures could be endangered
by excavation operations, support systems such as shoring, bracing, or
underpinning are required to be provided to ensure the stability of such
structures.
EXCAVATED
SPOILS
Employees
need to be protected from excavated or other materials or equipment that could
pose a hazard by falling or rolling into excavations. This protection can be
provided by placing and keeping such materials or equipment at least 2 feet
from the edge of excavations, or by the use of retaining devices that are
sufficient to prevent materials or equipment from falling or rolling into
excavations, or by a combination of both if necessary.
INSPECTIONS
Daily
inspections of excavations, the adjacent areas, and protective systems are
required to be performed by a competent person. The competent person should look for evidence of a situation that
could result in possible cave-ins, indications of failure of protective
systems, hazardous atmospheres, or other hazardous conditions. An inspection
must be conducted by the competent person prior to the start of work and as
needed throughout the shift. Inspections are also required after every
rainstorm or other hazard increasing occurrence when employee exposure can be
reasonably anticipated (if no one will be occupying the excavation, the
inspection is not required).
SLOPING
AND SHORING
Excavation
edges 5 feet or greater in depth (4 feet in California) are required to either
be sloped or shored to prevent collapse when the excavation is to be
occupied. It is important to understand
that excavated material does not have to cover the nose and mouth to cause
suffocation. Excavated materials
surrounding the chest can cause a person to be constricted by the weight of the
surrounding material. With each exhaled
breath, the the volume of air that can be inhaled is reduced until suffocation
occurs. Additionally, depending on the
activity to be performed within the excavation, sloping or shoring of
excavation walls may be necessary at leeser depths. For example, a worker required to kneel within an trench to
perform work duties could be adversely affected by the collapse of excavation walls as little as three
feet in height.
PART
II
The
following table provides basic information on allowable slope
configurations. These slopes can be
accomplished with straight slope edges, simple benching and multiple benching
configurations. Additional sources for
information on excavations is provided in Department of Labor publication OSHA
2226, American Petroleum Institute Recommended Practice API RP1615,
and Petroleum Equipment Institute Recommended Practice PEI RP100.
MAXIMUM
ALLOWABLE SLOPES
______________________________________________________________
SOIL
OR ROCK TYPE | MAXIMUM ALLOWABLE
SLOPES (H:V)(1) FOR
| EXCAVATIONS LESS THAN 20
FEET DEEP(3)
____________________|___________________________________
STABLE
ROCK | VERTICAL (90 Deg.)
TYPE
A (2) | 3/4:1 (53 Deg.)
TYPE
B | 1:1 (45 Deg.)
TYPE
C | 1 1/2:1 (34 Deg.)
____________________|____________________________________
Footnote(1)
Numbers shown in parentheses next to maximum allowable slopes are angles
expressed in degrees from the horizontal. Angles have been rounded off.
Footnote(2)
A short-term maximum allowable slope of 1/2H:1V (63 degrees)is allowed in
excavations in Type A soil that are 12 feed (3.67 m) or less in depth.
Short-term maximum allowable slopes for excavations greater than 12 feet (3.67
m) in depth shall be 3/4H:1V (53 degrees).
Footnote(3)
Sloping or benching for excavations greater than 20 feet deep shall be designed
by a registered professional engineer.
PART III
EXCAVATIONS
BULLET
OUTLINE SUMMARY
ALL
EXCAVATIONS:
* PRIOR TO INITIALIZATION OF EXCAVATION ACTIVITIES
THE ESTIMATED LOCATION OF UTILITY AND OTHER UNDERGROUND INSTALLATIONS WHICH
COULD REASONABLY BE ANTICIPATED MUST BE ESTABLISHED
* AS EXCAVATION ACTIVITIES APPROACH THE
ESTIMATED LOCATION OF UNDERGROUND INSTALLATIONS, THE EXACT LOCATION IS TO BE
DETERMINED
* EMPLOYEES ARE NOT PERMITTED UNDERNEATH
LOADS HANDLED BY LIFTING OR DIGGING EQUIPMENT
* EMPLOYEES ARE REQUIRED TO STAND AWAY FROM
ANY VEHICLE BEING LOADED OR UNLOADED TO AVOID BEING STRUCK BY ANY SPILLAGE OR
FALLING MATERIALS
* EQUIPMENT WHICH MUST OPERATE NEAR OR
APPROACH THE EDGE OF THE EXCAVATION, WHERE THE OPERATOR DOES NOT HAVE A CLEAR
AND UNOBSTRUCTED VIEW OF THE EXCAVATION EDGE, SHALL BE USED IN CONJUNCTION WITH
AN ADEQUATE WARNING DEVICE OR SYSTEM
* EXPOSURE TO ATMOSPHERES GREATER THAN 20%
LEL ARE NOT PERMITTED
* EMERGENCY RESCUE EQUIPMENT MUST BE READILY
AVAILABLE WHERE HAZARDOUS ATMOSPHERIC CONDITIONS EXIST OR COULD REASONABLY
EXIST
* EMPLOYEES MUST NOT WORK IN EXCAVATIONS
WHICH CONTAIN ACCUMULATED WATER OR WHICH ARE ACCUMULATING WATER WITHOUT
ADEQUATE SAFE GUARDS
* STABILITY OF ADJACENT STRUCTURES
POTENTIALLY AFFECTED BY EXCAVATION OPERATIONS MUST BE DETERMINED
EXCAVATIONS
4 FEET DEEP OR GREATER:
* MUST BE EVALUATED BY A QUALIFIED PERSON WHEN
A HAZARDOUS ATMOSPHERE EXISTS OR COULD REASONABLY EXIST PRIOR TO ALLOWING ENTRY
INTO THAT EXCAVATION
* MUST HAVE STAIRWAYS, LADDERS, RAMPS OR
OTHER SAFE MEANS OF EGRESS LOCATED SO THAT EMPLOYEES WOULD REQUIRE NO MORE THAN
25 FEET OF LATERAL TRAVEL TO REACH THE NEAREST MEANS OF EGRESS
EXCAVATIONS
5 FEET OR GREATER (4 FEET IN CALIFORNIA) IN DEPTH:
* MUST BE SLOPED OR SHORED TO PREVENT THE
EXCAVATION WALLS FROM COLLAPSING ON INDIVIDUALS WORKING IN THE EXCAVATION
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