Excavation and Trenching Safety

References EM 385-1-1 Section 25 29 CFR 1926.650 ; Subpart P UFGS 01 35 29 (Latest) Manufacturer’ s

Recommendations Accident Abstracts

Potential Contractor Mishap Outcomes

Cave-ins Fires, Explosions, Electrocutions and Engulfment

due to utility hits Struck by falling objects Falls and Equipment rollovers Asphyxiation, toxic exposures, and explosions

due to hazardous atmospheres Leading to property damage, injury, death

A Trenching Tragedy

Had a false sense of security Knew they were out of compliance Thought the soil was stable Conditions

changed overnight

A worker died

Trenching Statistics

About 400 U.S. workers die in trench-related accidents each year

About 6,400 are seriously injured

What Is a Trench? A narrow excavation

that is deeper than it is wide

No more than 15 feet wide at bottom

Walls will eventually fail

Cave-ins are much more likely to result in worker fatalities than other excavation-related accidents.

90% of all violations related to lack of cave-in protection involved manhole installations

During inspections where these violations were cited, the excavations were nearly vertical

Introduction

Excavation/Trenching Plan

Excavation/trenching plan will be submitted and accepted by the GDA prior to beginning operations.

Conditions

Excavations/trenches < 5ft (1.5m) in depth,

AHA is required but Plan optional

Excavations/trenches > 5ft (1.5m) in

depth, AHA and Plan required

Identification and credentials of CP Diagram or sketch of area where work to be done indicating

adjacent structures Projected depth of excavation Projected soil type and method of testing Planned method of shoring, sloping and/or benching Planned method of confined space entry, access, egress,

and atmospheric monitoring process Location of utility shut-offs (if required) Method for preventing overhead utility line damage, tree to

remain, or other features to remain Management of excavated soil/asphalt/concrete Traffic control Digging permits UXO clearance certificate Controlled flooding plan.

Plan Contents

Fatal Mishap Trench was 7 ft.

deep and 4 ft. wide.

Backhoe was 30 ft. away straddling trench.

The operator saw the collapse.

No protective system

Worker died.

Remove all surface encumbrances

Determine location of all underground utilities before opening excavation

Use safe means to determine exact locations & protect underground utilities

If required, obtain “Digging Permit”

Excavation Requirements This image cannot currently be displayed.

Excavation Inspections

Competent person. Inspected daily. As needed through out shift. After every rainstorm or other

hazard- increasing occurrence. If cave-in hazard identified, work

stopped, workers removed !

Competent Person for Excavations:

• Training, experience, and knowledge

• Ability to detect.

• Authority to take prompt corrective measures to eliminate existing and predictable hazards and to stop work when required.

Definitions

Requirements for protective systems

Protective systems shall have the capacity to resist without failure all loads that are intended or could reasonably be expected to be applied or transmitted to the system.

25.A.03.e

Provide full worker protection from cave-ins except:

Requirements for protective systems

-Excavation completely in stable rock -Less than five feet deep & CP determines no potential for cave-in

Protection from Water

Precautions required before working for water in excavations

CP must monitor control measures If diverting surface water must take steps to prevent

water from entering trench

Trenching And Excavations Protection From Water-25.A.06

Water in excavation

Trenching And Excavations Protection From Water-25.A.06

Water in excavation

Trenching And Excavations Protection From Water-25.A.06

Water in excavation

Water in trench

Employees shall not work in excavations in which there is accumulated water or in which water is accumulating unless the water hazard posed by accumulation is controlled.

25.A.06.b

Falling Soil or Equipment

Protect workers from loose rock/soil that may fall from an excavation face

— Use scaling to remove loose soil — Use protective barricades, such as shoring

or shields Protect workers from material or equipment that

could fall into the excavation — Keep material/equipment 2 feet from edge — Use retaining devices

Protection from Falling Materials

Barricades and substantial stop logs for mobile equipment operating near excavations

Equipment-Vehicle Precautions

Excavating or hoisting equipment shall not be allowed to raise, lower, or swing loads over or adjacent to personnel in excavation without substantial overhead protection.

Equipment-Vehicle Precautions

25.A.08.c

No working on sloped or benched faces unless employees below are protected

25.A.09 - Requirements for protective systems

Safe Access - 25.B Workers, vehicles, equipment and the

public must be protected. The public,vehicles or equipment

require class I perimeter guarding. Greater than 6 feet or other hazard and

worker exposure requires class II guarding.

If none of the above, at least class III. See definitions for type I, II, III

guarding.

Safe Access-25.B.01 Perimeter Protection Required Class I - Members of the Public or

Vehicles Class II - Contractor Employees/>6’ or Contain Hazard Class III - <6’, No Hazard, No Routine Contractor Employee Exposed

Safe Access

Perimeter Protection Criteria Class I - Standard Guardrail/Barriers Withstanding Impact Loads Class II - Warning Barricades/Flagging Not Closer Than 6’ From Edge Class III - Warning Barricades/Flagging 6” to 6’ From Edge

Safe Access-25.B

.03 - Excavations shall be backfilled as soon as possible

.04 - Walkways or bridges with guardrails shall be provided where people or equipment are required or permitted to cross over excavations

Stairway, ladder, ramp or other safe means of egress shall be located in trench excavations that are 4 feet or more in depth to require no more than 25 feet of lateral travel for employees.

Safe Access

Every 25'

4' or greater

Safe Access-25.B.05/07

At least two means of exit shall be provided for personnel working in excavations

Width of excavation exceeds 100 ft 2 or more means of exit for each side

Excavations 20 feet or more in depth Ramps, Stairs, or mechanical personnel hoists

Ladders used as access ways Shall extend 3 feet above the surface

Access and Egress

These two ladders which are lashed together are not an adequate means of egress

The ladder should extend 3 feet above the top of the excavation

What is wrong/right with this picture?

Ramps solely for personnel access shall be a minimum width of 4 ft (1.2 m.) and provided with standard guardrails

Ramps for equipment shall be 12 ft min.

Ladders used as access ways shall extend 3 ft from bottom of excavation

Ramps

What Is a Cave-in?

Soil or rock that suddenly falls or slides into an excavation

Sufficient quantity to entrap, bury, injure, or immobilize

Soil gravitates downward, pressure pushes soil inward toward the trench

Bottom third of wall typically fails first Soil above the collapsed lower wall follows

Cave-in Injuries

Soil weighs 125 lbs. per cubic foot

A worker can be crushed by soil, rock, or an object

Suffocation—even if worker’s head is not buried, soil prevents chest expansion

Worker becomes immobilized by soil’s suction effect

Sloping and Benching Options

Excavations less than 20 feet deep, maximum slope shall be 34 degrees measured from the horizontal (1 1/2 horizontal to 1 vertical).

Design selected from tabulated data (OSHA’s standard, Mfg’s specification)

Designed or approved by registered professional engineer.

Sloping and Benching

Sloping: angling of walls at an incline Benching: series of steps to angle walls Soil type determines angle of slope/bench

— Type A: 3 feet horizontal to 4 feet vertical (3/4:1) — Type B: 4 feet horizontal to 4 feet vertical (1:1) — Type C: 6 feet horizontal to 4 feet vertical (1-

1/2:1) — Benching not permitted for Type C soil

Support System Options

Timber, hydraulic and mechanical shoring systems etc..

Designs drawn form manufacturer’ s tabulated data.

From tabulated data (such as tables and charts such as OSHA’ s Standard).

Designed or approved by a registered professional engineer.

Materials for protective systems free from damage & defects

Used according to manufacturers specifications

If damaged CP must determine suitability for continued use

25.D.02- Requirements for support systems

Support system members securely connected together

Installed & removed to assure employee safety

Support systems not subjected to loads exceeding their capacity

25.D.03 – Installation and Removal of Support Systems

Removal of support systems from bottom up

Backfilling progresses with the removal of shoring

125.D.03.e – Removal of Support Systems

Excavation of up to 2 feet underneath support system allowed only if: System designed for support of full depth No evidence of loss of soil loss behind or

below

1926.652 – Additional Requirements for Trenching

2'

Soil Classification 29 CFR 1926 Appendix A 1926.652(b)(2) – Sloping &

Benching

1926.652(c) – Protective Systems

Competent Person Visual Test Manual Test

Soil Classification 29 CFR 1926 Appendix A Visual Test Observe soil as it is excavated. Soil

that remains in clumps when excavated is cohesive. Soil that breaks up easily and does not stay in clumps is granular.

Manual Test Penetrometer, Shear Vane, Plasticity,

Dry Strength, Thumb Penetration.

Soil Classification

Grain size Saturation Cohesiveness Unconfined

compressive strength

Soil Types Type A (most stable)—dense and heavy clay Type B—silt, sandy loam, medium clay Type C (least stable)—gravel, loamy sand,

soft clay

Fatal Shoring Related Mishap

Good example of a poorly designed system.

8’ x15’ x3/4” Steel plates leaning at 30 degrees against bank.

No supports Not approved, no

tabulated data used.

Trench Shield

A trench shield was built around this work area

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

Materials and Equipment

• Equipment used for protective systems must not have damage or defects that impair function.

• If equipment is damaged, the competent person must examine it to see if it is suitable for continued use.

• If not suitable, remove it from service until a professional engineer approves it for use.

Summary Tone before you dig. Get a dig permit

where applicable. Classify soil and install proper protection

prior to entry of trench or excavation. Provide fall protection for employees

exposed to falls of 6 feet or greater. Provide members of the public protection.