Excavation Safety
Objectives:
 Highlight the hazards of working in a excavation.
 How to protect employees from cave-ins.
 Factors that pose a hazard to employees working in
excavations.
 The role of a competent person at an excavation site.
Introduction:
Cave-ins are perhaps the most feared trenching hazard.
But other potentially fatal hazards exist including:
 Asphyxiation due to lack of oxygen in a confined space
 Inhalation of toxic fumes, drowning, etc.
 Electrocution or explosions can occur when workers
contact underground utilities.
Definitions:
Cave-In:
 Means the separation of a mass of soil or
rock material from the side of an
excavation, or the loss of soil from under
a trench shield or support system, and its
sudden movement into the excavation,
either by falling or sliding, in sufficient
quantity so that it could entrap, bury, or
otherwise injure or immobilize a person.
Definitions:
Excavation Falling onto the Personnel:
 A RELATIVELY SMALL COLLAPSE MIGHT
INVOLVE A CUBIC METRE OF SOIL, BUT
A CUBIC METRE OF SOIL WEIGHS OVER
A TONNE.
 PERSONNEL BURIED AT THE BOTTOM
OF THE TRENCH UNDER THIS VOLUME
OF MATERIAL WOULD BE UNABLE TO
BREATHE DUE TO THE PRESSURE ON
THEIR CHESTS, AND SO WOULD
QUICKLY SUFFOCATE AND DIE.
Anatomy of a Cave - In:
There is usually no warning before a cave-in
Definitions Continued:
 Excavation – a man-made cut, cavity, trench, or
depression formed by earth removal.
 Trench – a narrow excavation. The depth is greater
than the width, but not wider than 15 feet.
 Shield - a structure able to withstand a cave-in and
protect employees
 Shoring - a structure that supports the sides of an
excavation and protects against cave-ins
 Sloping - a technique that employs a specific angle of
incline on the sides of the excavation. The angle varies
based on assessment of impacting site factors.
Excavation Hazards:
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Surface encumbrances
Utilities
Access/Egress
Vehicle traffic
Falling loads
Mobile equipment
Hazardous atmospheres
Water accumulation
Adjacent structures
Loose rock or soil
Falls
Cave-in
General Requirements:
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Before any excavation actually begins, the employer must determine the estimated location
of utility installations: Sewer, telephone, fuel, electric, water lines, or any other under ground
installations that may be encountered during digging.
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A competent person will inspect, on a daily basis, excavations and adjacent areas for
possible cave-ins, failure of protective systems and equipment, hazardous atmospheres, or
other hazardous conditions.
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Takes prompt corrective measures to eliminate hazards.
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Adequate protective systems will be utilized to protect employees. This can be accomplished
through: Sloping, Shoring, or Shielding.
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Workers must be supplied with and wear any PPE deemed necessary to assure their
protection.
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Mechanical excavators and power tools should not be used within 0.5 m
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If a trench is 4 feet or deeper, stairways, ramps, or ladders will be used.
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The employees must not have to travel any more than 25 feet to reach the stairways, ramps,
or ladders.
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4 feet and more trenches – Toxic and hazardous atmosphere will be tested daily.
Access:
The ladder should extend 3
feet above the excavation
Access:
These two
ladders which
are lashed
together are not
an adequate
means of egress
The ladder
should extend 3
rungs above the
top of the
excavation
Ladder to be 1 Meter Above Wall:
Excavation Protection Systems:

There are three basic protective systems used in excavations and
trenches:
1. Sloping and Benching Systems
2. Shoring Systems
3. Shielding Systems
Simple Sloping:
Benching:
Shoring Systems:
 Support system for
trench faces used to
prevent movement of
soil, underground
utilities, foundations.
 There are two basic
types of shoring,
timber and aluminum
hydraulic.
Shoring Systems:
Timber Shoring Installations:
Hydraulic Shoring:
Pneumatic Shoring:
Shielding Systems:
A- Trench Boxes:
 The space between the
outside of the trench
box and the face of the
trench should be small
as possible, and
backfilled to prevent
lateral movement of the
box.
Excavation Inspections:
 Daily Inspections of ALL excavations by Competent Person
at Start of shift, or as needed, following rainstorms or other
hazard-increasing event:
 Possible cave-ins
 Protective system failure
 Water accumulation
 Hazardous atmospheres
Competent person has authority to remove workers
from
Causes of Cave – Ins:
Causes of Cave – Ins:
 When water is present
in an excavation it is
extremely hazardous to
enter. Also no head
protection
Causes of Cave – Ins:
 Note: telephone pole
adjacent to excavation,
not supported /
removed
Inadequate Protective System:
 This excavation has
inadequate support
posts and egress
access.
Inadequate Protective System:
 This worker is in a
trench with no
protective system, that
is not sloped or
benched and has no
means of egress.
Hazardous Condition:
 The weight and
vibrations of the
machinery above make
this a very hazardous
condition.
 They should not be
working under any
machinery.
Hydraulic Trench Support:
 Using hydraulic jacks the
operator can easily drop
the system into the hole.
 Once in place, hydraulic
pressure is increased to
keep the forms in place.
 Trench pins are installed
in case of hydraulic failure.
Hazardous Atmosphere:
 Test excavations more than 4
feet before an employee
enters the excavation for:
 Oxygen deficiency.
 High combustible gas
concentration.
 High levels of other
hazardous substances.
Means of Egress:
 A stairway, ladder, or
ramp must be present
in excavations that are
4 or more feet deep,
and within 25 feet of
the employees.
 The ladder should
extend 3 feet above the
excavation
Summary:
 The greatest risk in an excavation is a cave-in.
 Employees can be protected through sloping, shielding,
and shoring the excavation.
 A competent person is responsible to inspect the
excavation.
 Other excavation hazards include water accumulation,
oxygen deficiency, toxic fumes, falls, and mobile
equipment.
REMEMBER: