Safety Guideline :- Digging & Excavation

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Chapter :- Construction Safety 

 

SAFETY AT DIGGING & EXCAVATION

1. Context:

The digging and excavation of trenches is considered to be a hazardous task due to the potential for unplanned contact with utilities/services and the potential for injury from the collapse /localized failure of trench walls. It is therefore critical to establish suitable risk controls to avoid fatal injuries resulting from material instability and inadvertent contact with underground services/utilities.

2. Purpose:

To detail the functions necessary to manage the design, planning and work method for the excavation of openings or trenches such that adequate safeguards are implemented to prevent contact with utilities and exposure to loose material.

3. Scope:

This element applies to the management of any task requiring the penetration of the ground to a depth deeper than 300 mm. Therefore the scope is wider than simply the digging of trenches. This element excludes bulk excavation work being performed in quarries, stockpiles and spoil piles.

4. Element Requirements

4.1 Hazard Identification Risk Assessment and Control

A procedure must be established for the issuing of an excavation permit. The procedure will ensure all digging and excavation work performed outside a quarry must be conducted under the authority of an excavation permit. The excavation permit must address the following key issues:

Type of  work being preformed:-

1. Identification of underground utilities and services including the requirement for verification by the appropriate person that the area has been checked for underground services/utilities.
2. Soil type (ground conditions)– hard rock, clay, soil or sand

General safety requirements:-

1. Barricading & signage
2. Segregation distances or barriers between personnel and mobile equipment and/or a loose digging face
3. Personal protective equipment
4. Locating of diesel/ petrol driven equipment
5. Name and Signature of authorizing permit issuer, including the date, time of issue of the permit.
6. Note: In situations where an excavation/trench is being dug to a depth >1 meter and wider > 0.5 meters or where the trench is being excavated for the purposes of conducting work on (installation repair) underground utilities/services a risk assessment must be performed before the excavation permit can be issued. 
7. Requirements of other FPEs must also be considered, e.g. confined spaces.

Risk assessments performed on digging and excavation work must consider the following and where identified assess the potential for injury or damage and define the risk controls:

1. Potential collapse of excavations or shoring
2. Potential collapses of spoil heaps, adjacent structures or roads
3. Potential for flooding from storm water, broken mains or ground water ingress
4. Potential ventilation hazards from exhaust fumes from operating equipment
5. Potential entrapments in confined spaces ( coffer dams, drains etc)
6. Potential for inadvertent contact or damage to live services and underground tanks or structures
7. Potential for workers being injured by falling objects, being struck by machinery or falling into the trench
8. Potential for persons to fall into the excavation
9. Emergency response requirements to recover personnel

The risk assessment shall be attached to the excavation permit prior to being submitted for approval by the authorized permit issuer

Changes to the method of excavation or design of the excavation/trench including the angle of repose to slopes/protective support systems must be submitted to the excavation permit issuer before the change can be implemented (refer management)

4.2 Selection, Training, Competency and Authorisation

The training and competency assessment system shall ensure competency standards are established and applied for personnel designated as excavation permit issuers. These competencies must incorporate the following functions:

1. Identification and characteristics of soil types and ground conditions
2. Identification of confined spaces
3. Common hazard during excavation (atmosphere, water inrush, collapse, Cobile equipment etc)
4. Protection methods
5. Simple slope excavation
6. Protective support systems (shoring, shielding, benching)
7. Identification of underground utilities/ services
8. Safety precautions when working or accessing underground utilities / services

Personnel designated as authorized permit issuers must receive refresher training at period not exceeding 3 years.

All personnel conducting risk assessments in relation to digging and excavation work must:

Excavation Safety

• Have completed excavation permit issuer training
• Have completed formal risk assessment training

Personnel responsible for the installation of protective support systems must be trained in the safe erection, maintenance and dismantling of the system being used.
An overview of the excavation permit requirements must be provided as part of the general induction program.

4.3 Communication and Awareness

Excavations/ trenches need to be identified by having a barrier erected around the perimeter of the area of excavation at a minimum distance of 2 meters from the edge of the opening.

Awareness information and/or instruction must be provided on a regular basis to personnel who may perform digging and excavation.  The following topics should be addressed:

• Definition of  digging and excavation
• Hazards presented by excavations/trenches/ holes, openings
• Range of underground services installed at the operation
• Permitting requirements
• Means for inspecting protective support systems and access points

4.4 Design, Purchase, Fabrication, Installation and Commissioning

The design of excavations/ trenches must consider the soil type and the duration the excavation/ trench will be left open. The application of  either slope excavation or protective support systems must address the following:

1. Slope excavation
2. Maximum slope angles for the various soil  types
3. Bench heights for the various soil types
4. Protective support systems
5. Trench shields are suitably designed for the expected compression load
6. Screw jacks, wales, clingers, braces and sheeting (separate and continuous) are suitably spaced for the intended load
7. Accumulated spoil from the excavation must not located closer than 2 meters from the edge of the excavation/trench
8. Designated access and egress points are provided for personnel
9. Segregation requirements are established where mobile equipment may operate or a loose digging face is present

In situations where water accumulation is expected the following aspects must be considered within the design of the excavation/trench:

• Requirements to prevent water accumulation from surface and ground water
• Dewatering pumps used are capable of dealing with, as a minimum,  25% above the expected accumulation rate
• Designated sump or drainage facility is provided for dewatering

4.5 Work Method and Condition Control

Digging and excavation is only permitted after written authorization is issued in the form of an excavation permit. The person supervising the task must ensure the following aspects are understood and applied by personnel involved in the task:

• Check the excavation/trench for tension cracks, surface water before permitting access to the area
• Erect barricading in the form of fencing/ barrier tape and signage around the perimeter of any open excavation/trench at a minimum distance of 2 meters from the edge of the opening.
• Personnel must use the designated access and egress points to an excavation or trench
• Personnel must not approach a loose digging face or mobile equipment excavating a trench
• Work involving repair to underground services/utilities, must have those services isolated and locked out before digging/excavation can commence (refer fatality prevention element for isolation and lockout)
• Diesel/ petrol driven equipment cannot be operated within a trench with personnel working. Atmospheric testing being performed prior to entry - (refer fatality prevention element confined space)

 4.6 Maintenance
 No requirement applies to this element

 4.7 Emergency Controls

Where digging and excavation requires personnel to access the excavation/trench a specific rescue plan must be in place and suitable rescue equipment must be available before entry into the excavation/ trench is permitted.
 
4.8 Monitoring, Inspections and Audits

An inspection of excavations/ trenches must be performed weekly or when any of the following situations arise:

1. Tension cracks, sloughing, undercutting, water seepage, bulging at the bottom, or other similar conditions occur
2. After inclement weather (rainstorm)
3. Change in the size, location, or placement of the spoil pile
4. Any indication of change or movement in adjacent structures
5. The inspection will be performed using a formal checklist and the findings recorded.  Inspection checklist shall be retained for a period of 6 months.

Annual audits must be performed to verify the quality and effectiveness of the requirements set out in this element. As a minimum this will include :

• Schedules for audits
• Audit verification of:
• Quality of the risk assessments performed
• Quality of the inspection program for digging and excavations
• Compliance to training, competency, and awareness requirements
• Compliance to excavation permitting requirements
• Feedback and reporting requirements

Task/job observations must be performed for the purpose of measuring compliance in regard to:

• Excavation permit issuing procedure
• Construction of protective support systems
• Work practices being performed within the trench/excavation

4.9 Reporting, Assessment and Corrective Actions

Processes must be in place for the reporting, assessment, and correction of hazards identified with equipment used for digging and protective support systems or trenching practices and must address:

• Actions required to stand down unsafe equipment or stop work
• The recording of actions taken to correct the hazard or defect

5. Glossary of Terms

Accountability 

The person designated to ensure that the assigned requirement is implemented. This person is held liable and answerable to the level of compliance against the stated requirement.

Authorised

Construction Safety

Permission granted by the relevant Manager or nominee to carry out specific tasks.

Angle of Repose
 
Angle (or incline) from the horizontal surface at which the excavation wall is cut.

Competent Person

A person having a combination of training, education, experience, acquired knowledge and skills enabling them with the capability to perform specified tasks to a pre-determined quality, which may be assessed against, defined criteria.

Bench (benching)

Method of protecting employees from cave-in by excavating the sides of an excavation to form one or more horizontal levels or steps, usually separated by vertical or near-vertical surfaces.

Contractor

A firm or person employed under a contract to provide services to firm as distinct from a contract of employment. 

Department Manager

The person nominated by the company as Manager under the organizational structure, also the most senior position within a firm contracting work to firm.

Excavation/ Trench

Man-made cut, cavity, trench or depression in the earth surface formed by the removal of soil and rock.

Personnel

Are all people including company employees, sub contractors, third party contractors and visitors which work within the firm managed operation and/or company employees which a performing work for the operation outside the lease area

Potential to cause a Fatality / Risk of a fatality

A hazard that has been identified that if not properly controlled will contribute to a fatal incident. This can be derived from previous fatal incident experience and /or having being identified by means of a risk assessment as having a consequence for fatal injuries.

Protective Support System

Method of protecting employees from cave-in, from material that could fall or roll from the face or wall into an excavation, or from collapse of adjacent structures. Protective support systems include support systems, sloping and benching, shields, and other devices or methods that provide necessary protection.

Sloping

Digging the sides at an incline away from the deepest part of an excavation to prevent cave-in. The angle required depends on factors such as soil type, environmental conditions (wet or dry soil), and equipment, structures, soil or other material near the edge of excavation.

Soil Type

Soils are characterized by their physical properties and type - A, B or C.

• Type A -are cohesive soils with an unconfined compressive strength of 1.5 tons per square foot (144 kPa) or greater.
• Type B- are cohesive soils with an unconfined compressive strength greater than 0.5 tons per square foot (48 kPa) but less than 1.5 (144 kPa).
• Type C -are cohesive soils with an unconfined compressive strength of 0.5 tons per square foot (48kPa) or less.