Excavation collapses can result in serious injuries or fatalities. This article will provide guidance on how to safely excavate. Relevant legislation is also included.

Soil does not always support its own weight especially if subjected to additional loads from plant and material. A cubic metre of earth weighs approximately 1.3 tonnes or more when wet. A small fall of earth can cause serious injury or death.

Adhering to the following recommendations will greatly reduce the risks associated with excavating:

Collapses

Excavation sides can be protected by:

• Battering the sides to a safe angle and supporting them with shuttering and sheeting.
• Using trench boxes or hydraulic support systems.

A person falling into the excavation

Substantial barriers (guardrail, intermediate rail, toe board), warning tape and signs should be erected where there is a risk of people falling 2 metres or more.

Materials falling into an excavation

Excavated soil and materials should be placed at a safe distance from the excavations as the extra weight can contribute to a collapse.

Overrunning vehicles

Stop blocks should be placed at approximately 1.5 metres from an excavation to prevent a vehicle from falling into the excavation and to minimize the risk of surcharging i.e. an excavation collapsing due to the weight of the vehicle.

Underground services

Underground services include electricity cables, gas pipes, water pipes, sewerage, other pipelines, and telecoms. It is necessary to physically locate all underground services because it is inadequate to rely on maps. Finding these underground services should always incorporate safe digging practices, cable detection equipment and metal detection equipment.

Access and egress

Safe access and egress to the excavation must be provided.

Hazardous atmosphere

Noxious or flammable gases could occur naturally in an excavation or be emitted from a nearby plant or pipes. Gas tests should be conducted before work starts and should be regularly performed throughout the project.

Undermining adjacent structures

If there is any reason to believe that an excavation could undermine an adjacent structure, an Engineer should be consulted prior to starting work.

Flooding

Groundwater, surface water and rainwater pose a risk of flooding an excavation and undermining its integrity. Ground de-watering systems can be used to lower the water table by drilling boreholes and draining the excess water into a drain or ditch.

Contamination

Soil can be contaminated from:

• Previous industrial activities.
• Biological contaminants such as Leptospirosis.
• Anthrax spores from farming, slaughterhouse or tanneries.
• Methane emitted from compost.

Therefore, it may be necessary to conduct land surveys and take soil samples prior to work, and to wear protective equipment and clothing. It must be noted that standard respirators do not prevent the inhalation of most gases.

Additional safety measures

• Comprehensive planning should be done when excavating under unfamiliar conditions.
• The sides of a trench should be more than 15 degrees from vertical.
• Bench or batter the sides.
• Excavator operators must be supervised.
• Supervisors must have the authority and means to prevent workers from entering the trench.
• Responsibly for the inspection of an excavation must be clearly designated.
• A work permit system must be fully implemented when applicable.
• Risk assessment for excavation must be extensive and include soil conditions, equipment and experience.
• Workers must be properly trained to perform their duties and to deal with potential risks.
• The competency of plant operators must be assessed, and plant operators should have all required competencies.
• Regular inspections and audits must include compliance with excavation laws and all aspects of operational procedures.
• Managerial and disciplinary procedures must be consistent.
• When new risks are identified, work must cease until a review of the risk assessment is completed by specialists, and the recommended measures are taken.

In addition to the guidelines provided above, it is vital for relevant personnel to adhere to the following excavation legislation:

OHS Act, 8 (2)(b) - Employers must take steps to eliminate hazards. Section 14 on General Duties of Employees at work; Every employee has a duty to (a) take reasonable care of themselves, (c) obey health and safety rules.

Construction Regulations; CR 9 Risk assessment; (4) ensure that employees are informed, instructed and trained by a competent person regarding hazards and related work procedures.

13. Excavation

(1) A contractor must -

(a) ensure that all excavation work is carried out under the supervision of a competent person who has been appointed in writing for that purpose; and

(b) evaluate, as far as is reasonably practicable, the stability of the ground before excavation work begins.

(2) A contractor who performs excavation work:

(a) must take reasonable and sufficient steps in order to prevent, as far as is reasonably practicable, any person from being buried or trapped by a fall or dislodgement of material in an excavation;

(b) may not require or permit any person to work in an excavation which has not been adequately shored or braced: Provided that shoring and bracing may not be necessary where -

(i) the sides of the excavation are sloped to at least the maximum angle of repose measured relative to the horizontal plane; or

(ii) such an excavation is in stable material: provided that -

(aa) permission has been given in writing by the appointed competent person contemplated in subregulation (1) upon evaluation by him or her of the site conditions; and

(bb) where any uncertainty pertaining to the stability of the soil still exists, the decision from a professional engineer or a professional technologist competent in excavations is decisive and such a decision must be noted in writing and signed by both the competent person contemplated in subregulation (1) and the professional engineer or technologist, as the case may be;

(c) must take steps to ensure that the shoring or bracing contemplated in paragraph (b) is designed and constructed in a manner that renders it strong enough to support the sides of the excavation in question;

(d) must ensure that no load, material, plant or equipment is placed or moved near the edge of any excavation where it may cause its collapse and consequently endangers the safety of any person, unless precautions such as the provision of sufficient and suitable shoring or bracing are taken to prevent the sides from collapsing;

(e) must ensure that where the stability of an adjoining building, structure or road is likely to be affected by the making of an excavation, steps are taken to ensure the stability of such building, structure or road and the safety of persons;

(f) must cause convenient and safe means of access to be provided to every excavation in which persons are required to work, and such access may not be further than six metres from the point where any worker within the excavation is working;

(g) must ascertain, as far as is reasonably practicable, the location and nature of electricity, water, gas or other similar services which may in any way be affected by the work to be performed, and must before the commencement of excavation work that may affect any such service, take the steps that are necessary to render the circumstances safe for all persons involved;

(h) must ensure that every excavation, including all bracing and shoring, is inspected -

(i) daily, prior to the commencement of each shift;

(ii) after every blasting operation;

(iii) after an unexpected fall of ground;

(iv) after damage to supports; and

(v) after rain,

by the competent person contemplated in subregulation (1), in order to ensure the safety of the excavation and of persons, and those results must be recorded in a register kept on site and made available on request to an inspector, the client, the client's agent, any other contractor or any employee;

(i) must cause every excavation which is accessible to the public or which is adjacent to public roads or thoroughfares, or whereby the safety of persons may be endangered, to be -

(i) adequately protected by a barrier or fence of at least one metre in height and as close to the excavation as is practicable; and

(ii) provided with warning illuminants or any other clearly visible boundary indicators at night or when visibility is poor,

or have resort to any other suitable and sufficient precautionary measure where subparagraphs (i) and (ii) are not practicable;

(j) must ensure that all precautionary measures stipulated for confined spaces as determined in the General Safety Regulations, 2003, are complied with by any person entering any excavation;

(k) must, where the excavation work involves the use of explosives, appoint a competent person in the use of explosives for excavation, and must ensure that a method statement is developed by that person in accordance with the applicable explosives legislation; and

(l) must cause warning signs to be positioned next to an excavation within which or where persons are working or carrying out inspections or tests.

Neil Enslin | Occupational Health and Safety Manager

Sources:

Occupational Health and Safety Act and its Regulations

Master Builders SA Construction Manual

Excavation manual