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Maintains Safe Work Environment

Chapter A6 – Maintains Safe Work Environment

Prerequisite Knowledge:

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Topic 1 – Identify Hazards When Working in Confined Spaces and Excavations

Confined Space Hazards

According OHS Regulations, a confined space is defined as an “enclosed or partially enclosed space that is not designed or intended for human occupancy except for doing maintenance work and has restricted means of entrance and exit”. There are two classifications of confined spaces: confined spaces (as described above) and hazardous confined spaces. Hazardous confined spaces fit the criteria listed but also contain harmful gases due to poor ventilation. Some examples of confined spaces are storage tanks, silos, manholes, under ground utility vaults, and septic tanks.

Workers who will be working in confined spaces require training to recognize hazards, how to take precautions against those hazards, and how to use protective and emergency equipment. Some hazards that may be present in a confined space are:

– Flammable or explosive atmosphere
– Lack of breathable air
– Toxic chemicals that pose a health risk
– Electrical shock
– Cave-ins
– Falling objects

When working in a confined space the contractor must ensure the following is done:

– Ensure there is a safe entrance and exit
– Ensure the structural safety of the space is secure (prevent risk of cave-ins)
– Ensure a competent person assesses the space for hazards including poisonous gases, flammable materials, and energy sources are locked out
  • If any of the above is present, personal protective equipment must be worn
  • Atmospheres are monitored using specific instruments

As part of working in confined spaces, the contractor must also ensure there is a confined space entry plan in writing. This plan includes:

– Results of air test
– Identification of all hazards present
– Means of ventilation
– Procedures for entry and exit
– Availability and use of PPE
  • This includes respiratory protection, body harness, and lifelines
  • Workers must wear a body harness at all times when the means of exit is from above to assist with rescue procedures in the event it is required
– Means to maintain communication with workers

Trenching and Shoring

While many trenches seem shallow and free from hazards, a trench that is less than even 6’ deep can pose a serious hazard to workers. The greatest risk when working in a trench is the potential for cave ins. The stability of the soil is the primary consideration made when evaluating a trenches safety and hazards. Type of soil, water table, and weather conditions are some of the factors which can affect the stability of the trench walls.

OHS Regulations lists four types of soils:

– Type I
– Type II
– Type III
– Type IV

Type I soils are the most stable for trenching whereas type IV is the least stable. The type of soil present is the number one factor in determining the trench design and protections against cave ins required. Cave ins can be prevented by a number of means:

– Sloping of trench walls. Depending on the type of soil, the trench walls may be sloped or terraced to prevent a cave in. For a more detailed explanation, see section 260 of OHS Regulations
– Trench Shoring, which may be either built in place or moveable shields. When movable shields are used, they can encompass the entire trench or be moved as required. Workers must remain inside the protected area at all times. Build in place shoring can be used instead of shields. It must be designed by a professional engineer and is usually constructed using sheathing or planks which are braced against uprights and walers.

If a trench is more than 1.2 meters deep, proper egress must be provided to the workers. OHS requires that a ladder is placed no more than 8 meters from a worker at any given time when working in a trench. A competent worker must also be stationed on the bank and in communication with the workers at all times to monitor the trench and aid in an emergency.

Once work is completed, a trench should be backfilled immediately to prevent water seepage. If a trench is left overnight, it needs to be barricaded.

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Carpentry Refresher Program Manual Copyright © by Saskatchewan Indian Institute of Technologies-Trades and Industrial is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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