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A worker was laying sewage pipe in a trench when a section of embankment gave away, burying him waist deep in soil. When even one cubic meter of dirt can weigh more than a car, a trench collapse becomes a race against time. In this case, the worker was quickly dug out by his fellow workers and escaped with a broken ankle. Despite advancements in engineering controls, protective equipment and safe work practices, excavation and trenching remain among the most hazardous construction operations.
Generally speaking, an excavation is a hole in the ground as the result of removing material. A trench is an excavation in which is deeper than it is wide and no wider than 4.5 meters. Recognizing the hazards and learning how to prepare and work safely can help prevent serious injury or death.
One of the biggest hazards related to trenching and excavation is the risk of cave-ins. An unstable trench or excavation can collapse, killing or injuring workers by suffocation or crushing from the falling soil. A number of factors such as the improper use or installation of a support system or trench box, soil type and moisture content, the activities carried out adjacent to the site, weather, vibration, depth of the trench, and the length of time the trench is left open can affect trench stability.
Sloping and temporary protective structures are two basic methods of protecting workers against cave-ins.
Sloping involves cutting back the trench wall at an angle that is inclined away from the work area of the excavation. The angle of slope required depends on the soil conditions. Benching is a similar method to sloping with the sides excavated in levels similar to steps.
Temporary protective structures
Saskatchewan Labour defines a temporary protective structure as "a structure or device in an excavation, trench, tunnel or excavated shaft that is designed to provide protection from cave-ins, collapse, sliding or rolling materials, and includes shoring, trench boxes, trench shields and similar structures."
Shoring is a system that supports the sides or walls of the trench. It involves installing aluminum, steel, or wood panels that are supported by screws or hydraulic jacks. Some systems can be installed without the workers entering the trench which provides additional safety for those workers. Wherever possible, shoring equipment should be installed as the excavation proceeds. If there is any delay between digging and shoring, no one should enter the unprotected trench.
Trench boxes are commonly used in open areas, away from utilities, roadways, and foundations, to protect workers in cases of cave-ins, but not to shore up or support trench walls. Trench boxes can support trench walls if the space between the box and the trench wall is backfilled with soil and compacted properly. Otherwise, a cave-in or collapse may cause the trench box to tilt or turn over. When used in excavation projects, trench boxes should have a wall height greater than or equal to the wall height of the surrounding trench.
BEFORE BEGINNING AN EXCAVATION
Employers and supervisors must take the necessary steps to identify all the hazards and risks before beginning any work, including:
Resources and Information:
Tips & Tools
Whether driving on the road to another city or soaring on a plane to a different country, travelling for work can be an exciting experience. Regardless of how they travel, or if it is in their own country or abroad, most business travellers do not expect trouble while away. Here are some tips to help workers be ready for potential risks when travelling.
Our mental health affects how we think, feel, act and work. As Canada’s largest employer with more than 250,000 people across 125 organizations, the federal public service plays an essential leadership role in supporting workplace mental health.
In 2015, the Government of Canada and the Public Service Alliance of Canada established a Joint Task Force to address mental health in the workplace. Together, they identified key areas of focus with the overarching need for the federal public service to create a culture that enshrines psychological health, safety and well-being in all aspects of the workplace through collaboration, inclusivity and respect. The strategy draws heavily on the work of the Joint Task Force and is designed to support public service organizational efforts to develop and implement mental health action plans.
Last year the Government of Canada adopted the Federal Public Service Workplace Mental Health Strategy, an important first step in its efforts to foster a healthy, respectful, and supportive work environment that strengthens the overall performance of the public service.
The government-wide Strategy focuses on three strategic goals:
Federal organizations will develop their own comprehensive action plans on mental health. Each plan will be unique, assuming that organizations may be faced with different challenges in addressing mental health in the workplace.
The Centre of Expertise, a joint initiative with federal and related bargaining agents established this year, will help guide organizations on their journey to building a healthy, respectful and supportive federal public service, provide access to resources, and collect and share best practices. Deputy Heads will be expected to demonstrate visible and sustained leadership commitment, engage senior management, managers and employees, and promote healthy workplaces and mental health at work activities.
For more information:
Health and Safety To Go
This month’s Health and Safety To Go! podcasts offer tips for mowing safely, and feature an encore presentation on minimizing risks when working at heights.
Feature Podcast: Mowing Safety
Whether you use them as part of your job, or when at home, mowers may seem simple enough to operate but there are serious hazards that come with operating any power tool. CCOHS offers tips for the safe use of power mowers.
The podcast runs 4:35 minutes. Listen to the podcast now.
Encore Podcast: Minimize the Risks When Working at Heights
For construction workers, roofers, window cleaners, painters, arborists and firefighters, working at heights is a part of their daily work experience. Avoiding the risk of falling from ladders, scaffolds, lifts, buckets, mast climbers, roofs, balconies and trees requires safety diligence by both worker and employer. CCOHS provides tips on how to work safely when working at heights.
The podcast runs 5:48 minutes. Listen to the podcast now.
CCOHS produces free monthly podcasts on a wide variety of topics designed to keep you current with information, tips, and insights into the health, safety, and well-being of working Canadians. You can download the audio segment to your computer or MP3 player and listen to it at your own convenience... or on the go!
What does the law state about acceptable work temperatures? What can workplaces do to support mental health? What do you need to know before wearing a respirator? These are just some of the newest questions addressed in CCOHS’ OSH Answers fact sheets. Learn how workplaces can access this reliable health and safety information resource.
The complete OSH Answers fact sheet collection, as well as the app and the badges, are available for free in English and French.
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The Health and Safety Report, a free monthly newsletter produced by the Canadian Centre for Occupational Health and Safety (CCOHS), provides information, advice, and resources that help support a safe and healthy work environment and the total well being of workers.
© 2020, Canadian Centre for Occupational Health and Safety
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