Excavations & Trenching

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Definitions • "Excavation" means any:• 1. Man-made cut • 2. Cavity • 3. Trench • 4. Depression in an earth surface, formed by

earth removal.

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Definitions • Confined space is a space that, by design and/or

configuration has:• 1. Limited openings for entry and exit • 2. Unfavorable natural ventilation • 3. May contain or produce hazardous substances • 4. Is not intended for continuous employee

occupancy.

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.

General Requirements• 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.

• 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.

• Takes prompt corrective measures to eliminate hazards.

• Adequate protective systems will be utilized to protect employees. This can be accomplished through: Sloping, Shoring, or Shielding.

General Requirements• Workers must be supplied with and wear any PPE

deemed necessary to assure their protection.

• Mechanical excavators and power tools should not be used within 0.5 m

• If a trench is 4 feet or deeper, stairways, ramps, or ladders will be used.

• The employees must not have to travel any more than 25 feet to reach the stairways, ramps, or ladders.

• 4 feet and more trenches – Toxic and hazardous atmosphere will be tested daily.

Definitions• 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 (also called box).• 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.

Definitions

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.

Excavation Hazards

– Surface encumbrances– Utilities– Access/Egress– Vehicle traffic– Falling loads– Mobile equipment– Hazardous atmospheres– Water accumulation– Adjacent structures– Loose rock or soil– Falls– Cave-in

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.

Anatomy of a Cave - In:

There is usually no warning before a cave-inThere is usually no warning before a cave-in

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

Injury and Death

• Excavating is one of the most hazardous construction operations

• Most accidents occur in trenches 5-15 feet deep

• There is usually no warning before a cave-in

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Protection of Employees

• Employees should be protected from cave-ins by using an adequately designed protective system.

• Protective systems must be able to resist all expected loads to the system.

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Protect Employees Exposed to Potential Cave-ins

• Slope or bench the sides of the excavation.

• Support the sides of the excavation.

• Place a shield between the side of the excavation and the work area.

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Requirements for Protective Systems

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A well-designed protective system Correct design of:

- Sloping and benching systems - Support systems- Shield systems

- Other protective systems+

Appropriate handling of materials and equipment +

Attention to correct installation and removal =

Protection of employees at excavations.

Design of Protective Systems

The employer shall select and construct :→Slopes and configurations of sloping and

benching systems.→Support systems, shield systems and other

protective systems.• Shield - Can be permanent or portable. Also known as

trench box or trench shield.• Shoring - Such as metal hydraulic, mechanical or timber

shoring system that supports the sides. • Sloping - Formed sides of an excavation that are inclined

away from the excavation.

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Requirements for protective systems

• Protection of employees in excavations

• Design of sloping and benching systems

• Design of support systems, shield systems, and other protective systems

Materials and equipment Installation and removal

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Protection of employees in excavations• (1) Each employee in an excavation shall be protected from

cave-ins by an adequate protective system designed in accordance with paragraph (b) or (c) of this section except when: – (i) Excavations are made entirely in stable rock; or– (ii) Excavations are less than 5 feet (1.52 m) in depth and

examination of the ground by a competent person provides no indication of a potential cave-in.

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Cave-in Hazard

This excavation has inadequate

support posts and egress access.

Inadequate protective system

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Inadequate Protective System

•

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This worker is in a trench, with no

protective system, that is neither sloped nor benched, and has no means of egress.

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Factors Involved in Designing a Protective System

• Soil classification

• Depth of cut

• Water content of soil

• Changes due to weather and climate

• Other operations in the vicinity

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Shoring

• General

• Provides a framework in which to work

• Uses walls, cross braces and uprights

• Supports excavation walls

• Must know soil type

• Must know depth and width of excavation

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Trench Shield

A trench shield (also called a

trench box) was built around this

work area.

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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.

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Materials and Equipment

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

• If equipment is damaged, a 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.

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Trench Box

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Protection from Vehicles

• Install barricades

• Hand/mechanical signals

• Stop logs

• Grade soil away from excavation

• Fence or barricade trenches left overnight

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Hazardous Conditions

They should not be working under this crane.

The weight and vibration of the crane makes this a

very hazardous condition.

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Spoil Piles

• Don’t place spoils within two feet from edge of excavation.

• Measure from nearest part of the spoil to the excavation edge.

• Place spoils so rainwater runs away from the excavation.

• Place spoil well away from the excavation.

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Other Excavation Hazards

• Water accumulation

• Oxygen deficiency

• Mobile equipment

• Access/egress

• Toxic fumes

• Falls

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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

1. Shoring Systems

2. 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 fromthe excavation

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.

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Means of egress

• Means of egress from trench excavations: • 1. A stairway, ladder, ramp or other safe

means of egress shall be located in trench excavations that are 4 feet (1.22 mm) or more in depth.

• 2. A means of egress should require no more than 25 feet (7.62 m) of lateral travel for any employee to reach.

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Inspections• Daily inspections of excavations, the adjacent

areas, and protective systems shall be made by a competent person for evidence of a situation that could result in:

• 1. Possible cave-ins • 2. Indications of failure of protective systems • 3. Hazardous atmospheres • 4. Other hazardous conditions.

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Inspections Cont.

• An inspection shall be conducted by the competent person:

• 1. Prior to the start of work and as needed throughout the shift.

• 2. After every rainstorm or other hazard increasing occurrence.

• 3. These inspections are only required when employee exposure can be reasonably anticipated.

Safety considerations

• Excavation is one of the most hazardous types of work in the construction industry

• Accidents result from inadequate planning

• Build safety into pre-bid planning• Plan safety into the job. Consider:

– Traffic– Nearness of structures and their conditions– Soil

Safety considerations

• Plan safety into the job. Consider:– Surface and ground water– Water table– Overhead/ underground utilities– Weather

Jobsite safety and health programs

• Establish and maintain a safety and health program for the worksite

• Provide adequate systematic policies, procedures, practices

• Recognize job-related safety/health hazards

Jobsite safety and health programs

• Safety and health programs should reflect the unique characteristics of the jobsite

• Proper implementation depends on cooperation among:– supervisors– employee groups– individual employees

Locating utilities

• Employers must determine the estimated locations of utility installations

• Contact utility companies before starting excavation

• Utility owners must attempt to find exact location of utilities

• Proceed with caution if the exact location of utilities cannot be found

• Use safe and acceptable means to locate exact locations of installations

Safety starts at the surface

• Surface encumbrances that create hazards must be removed/supported

• Wear warning vests when near traffic• Employees must be trained to operate heavy

equipment• Stay away from loads being handled by lifting/digging

equipment

Safety starts at the surface

• Warn mobile equipment operators about the edge of the excavation site

• Keep the grade away from the excavation site

• Stay away from vehicles being loaded/unloaded

Employee access/egress from excavations

• Ramps must be designed by a competent person• Ramps must be structurally sound and not create a

tripping hazard• Use surface treatments on ramps to prevent slipping• Trenches 4 or more feet deep need a safe means of

egress– Stairway– Ladder– Ramps

• Means of egress must be fixed and secure

Employee access/egress from excavations

• Means of egress must be within 25 feet of workers

• Ladders must extend a minimum of 36 inches above the landing

• Use metal ladders with caution around utilities