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:
- Identifying the soil type(s) related to the excavation or trench to be dug. Soil properties often vary widely within a single trench (e.g., the soil type changes from top to bottom and along the length of a trench).
- Locating all buried services.
- Grounding and isolating electrical cables or conduits.
- Identifying and locating overhead power lines.
- Checking areas adjacent to the site for potential hazards and sources that can impact the stability of soil. Nearby vehicles and equipment can cause the soil to vibrate and then collapse.
- Determining if nearby buildings or structures and their foundations may put pressure on the soil and affect the walls of the trench.
- Testing for hazardous gas, vapours, and dust before entering.
- Testing for oxygen levels in the space before entering, and during the work as required.
- Making arrangements to remove water from the excavation.
- Identifying appropriate personal protective equipment including high visibility apparel for vehicular traffic and making sure every worker wears them as required.
- Designating a worker above ground when a worker is working in the trench to warn of danger and to provide emergency help.
- Preparing work permits for work in confined spaces, as appropriate.
- Providing a means of exit from inside the trench, usually no more than 8 meters (25 feet) away than any worker in the trench.
- Preparing an emergency plan and rescue procedures.
- Educating and training workers about all existing and potential hazards and risks and appropriate safety measures.
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.
- Find out if you require immunizations. If you will be travelling internationally, consult a doctor or travel health clinic at least four to six weeks before travel so they can determine your need for immunizations and advise you on what preventive medication precautions to take to avoid disease.
- Arrive in daylight. It may not always be possible but when booking flights or travel times try to arrange to arrive at your destination in daylight. If you must arrive in the late evening or early morning, reserve a car service in advance to avoid having to find a cab.
- Don't forget your meds. If you take medication for a pre-existing condition, bring enough to last the trip, and some extra in case your return flight is delayed. As a precaution, have a copy of your prescription, or a doctor's note, in case you need to prove that the medication is necessary. Consider dividing your medication supply and keeping it in two different pieces of luggage, in case one piece of luggage is lost or stolen, or carry it with you.
- Protect your documentation. Make sure your passport does not expire before or during your trip. Some countries require that it be valid for up to six months after your return home, so check the expiry date. Keep photocopies of your passport and visa, and keep them separate from the original copies. Also keep a record of credit cards, bank cards, and contact telephone numbers, and leave copies with someone back home. At the hotel, store your passport, airline tickets, extra money and other documents in the hotel safe.
- Stay connected. Establish a check-in procedure and make sure your workplace, friends or family back home know where and how to reach you. Give someone at home a copy of your travel itinerary and check in with them when you arrive and periodically thereafter. It is also a good idea to find out ahead of time where to contact Canadian government offices abroad. Keep all necessary emergency numbers handy.
- Know your surroundings. Ask the hotel for advice on safe areas to visit or walk through in the neighbourhood. They will tell you which areas to avoid.
- Hide your valuables. Carry your passport, travel documents, plane ticket, credit cards and cash in a concealed money belt worn around the waist. Do not draw attention to yourself by displaying large amounts of cash, expensive jewelry or electronic equipment. If possible, use the bank machine more often or a credit card instead of large amounts of cash. Consider carrying a second "dummy" wallet, with some local currency, a small amount of US dollars, a few old receipts, and expired credit cards to make it look real. Keep some money in an outside pocket to avoid fumbling through your purse or wallet for tips and other small expenses.
- Watch your luggage. Do not leave your luggage unattended or in the care of a stranger. On your luggage tag, use only your first initial, not your full name. To further protect your identity, include your business address instead of your home address, and use a luggage tag that has a flap that hides your name and address.
- Safeguard your hotel room. Ask for a hotel room that is above ground level but no higher than seven stories up, within reach of most firefighting evacuation buckets and ladders. Ask for a room close to the elevators, and ensure it has a peephole, deadbolt and chain lock. Don't let anyone know which room you are staying in. Tell the hotel not to give your room number or name to anyone. If the hotel clerk accidentally says your room number out loud, ask to change rooms. Close the door securely when you enter or exit the room, and check that any sliding glass doors, windows and connection doors are locked every time. Do not invite strangers or acquaintances into your room or accept invitations to others' rooms. Arrange to meet in a public location such as the hotel lobby or restaurant.
- Prepare to act quickly. To avoid delays in hallways, have your room key or card ready to use.
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:
- Changing the culture to be respectful to the mental health of all colleagues
- Building capacity with tools and resources for employees at all levels
- Measuring and reporting on actions
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:
- Centre of Expertise on Mental Health in the Workplace
- Federal Public Service Workplace Mental Health Strategy, Treasury Board of Canada Secretariat
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.
- Visit the CCOHS website. For nearly 20 years, CCOHS has provided health and safety information free of charge on the web. Topics are based on questions that its Inquiries Service receives from workers, their families, health and safety committee members, employers, occupational hygienists, safety professionals, health care professionals, and the general public over the years. The number of fact sheets continues to grow as inquirers raise new questions and topics. View the collection online.
- Download the app. The OSH Answers app contains all the fact sheets from the CCOHS website – almost 600 in total. Organized by major subject areas, the app also includes a handy search box so you can find answers even faster. Once it is downloaded to a device, it can be used offline, in remote areas or manufacturing shop floors where wireless connectivity is absent or unreliable. The app is available for iOS and Android devices. Learn more and download the app.
- Add a badge. Add a badge to your website or intranet so your workers can quickly find answers to their health and safety questions. Choose from assorted designs to match the look and feel of your website. Simply right-click on any badge to download it, then link the badge to OSH Answers for convenient access to health and safety information. Download a badge.
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.
© 2017, Canadian Centre for Occupational Health and Safety
Length: 5:24 minutes
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