Excavations

The Manitoba Workplace Safety and Health Regulation defines “excavation” as a dug-out area of ground, including deep foundation excavations, trenches, tunnels and shafts.

The most common hazards that exist in excavation work include:

cave-ins or excavation collapses
excavated material falling into the excavation or affecting wall stability
equipment used in or near an excavation

Excavations and Tunnels in the Manitoba Workplace Safety and Health Regulation states that an employer must develop and carry out safe work procedures for the work to be done at an excavation, including the installation, use and removal of shoring, train workers in the safe work procedures, and ensure that workers comply with the safe work procedures.

Excavation-related hazards

Cave-ins or excavation collapses

Why do serious worker injuries and fatalities continue to occur in the excavation industry?

It is because both employers and workers often forget that when they remove earth from the ground it creates an opening, and the remaining earth surrounding the opening tends to relax. This increases the pressure on the walls of the opening and makes the ground collapse.

Water in the soil or ground also affects the stability of the walls by putting additional pressure on the walls and increasing the possibility of a cave-in. Unless a horizontal distance equal to the vertical depth of the excavation walls is maintained, engineering controls must be used (for example shoring and trench cages) to provide a safe and healthy workplace within the excavation area.

No one can predict that an excavation is safe to enter without ensuring the walls of the excavation are sloped at 45 degrees or using an engineered support structure.

Victims buried in an excavation collapse may suffocate. Even workers only buried up to their waist have died because of the pressure exerted by the soil on their bodies. Survivors often receive severe crushing injuries.

Excavations in or near backfilled (previously excavated) ground are especially dangerous since the previously disturbed soil is “loose” and not self-supporting.

In addition, clay can be extremely treacherous if dried by the sun. Large chunks of clay can break off a trench wall after being stable and solid for a long time.

Furthermore, during winter months, it is not safe to assume that an excavation is safe to enter because the walls are frozen. Frozen ground is not an alternative to temporary engineered support structures.

Excavated material falling into the excavation or affecting wall stability

Injuries may also occur in excavation work when excavated material on the surface of the excavation is too close to the edge and falls into the excavation or affects the structural stability of the walls of the excavation.

Equipment used near or in an excavation

Place tools and equipment used at the excavation site so that they cannot fall into the excavation or affect the structural stability of the walls. Use barriers to help keep tools and equipment at a safe distance from the edge of the excavation. Use ropes or other lowering devices to transport the tools or equipment into the excavation.

These are just three of the many hazards associated with excavation sites.

Other common hazards include:

hazards related to the use of powered mobile equipment on an excavation site
slips, trips and falls
hazardous atmospheres
flooding/water hazards
underground facilities that could be disrupted by an excavation (including electrical lines, oil and gas lines and water and sewer lines)

Legislation

Workers and employers must follow the safe work procedures developed for the work to be done at an excavation and be in compliance with Part 26 of the Manitoba Workplace Safety and Health Regulation.

Employers must register the work with the Manitoba Workplace Safety and Health Branch. Employers must notify the branch that they intend to do excavation work and receive a registration number from the branch. Employers must not begin any excavation work unless they have a valid registration number after submitting the following form.

A safety and health officer may revoke an employer’s registration number if the officer is of the opinion that the employer is performing excavation work in a manner that creates or may create a risk to the safety or health of a worker. When a registration number has been revoked, an employer may not be issued a new registration number unless a safety and health officer is satisfied that the employer will perform excavation work in accordance with the requirements of this part. (Part 26.3 of the Manitoba Workplace Safety and Health Regulation.)

Manitoba’s Workplace Safety and Health Act and associated regulations are in place to protect the safety and health of workers in Manitoba. Below is a link to the regulation part associated with this safety topic.

Part 26 Excavations and Tunnels General Matters Manitoba Workplace Safety and Health Act and Regulation