OHS Canada Magazine

Going Underground

January 14, 2014

Human Resources Construction Health & Safety Injury, Illness Prevention Training/Professional Development Workplace accident -- fatality Workplace accident -- injury

When Paul Villeneuve was 20, he was buried up to his waist in soil after heavy machinery nearby caused the trench in which he was working to collapse. Fortunately, he got out alive after his brothers, who were working on the job, dug him out...

When Paul Villeneuve was 20, he was buried up to his waist in soil after heavy machinery nearby caused the trench in which he was working to collapse. Fortunately, he got out alive after his brothers, who were working on the job, dug him out with shovels.

Villeneuve of Laval, Quebec was one of the lucky ones. Had the level of soil been a bit higher, he might not have lived to tell the tale.

When you’re buried up to your chest, you’re dead. There’s too much pressure,” Villeneuve says. Some 40 years after his work accident, Villeneuve now works for ASP Construction in Montreal, which teaches compulsory courses in safety and security — including a trenching and excavation component — to construction workers in Quebec.

One of the biggest hazards of trenching and excavation work is the risk of cave-ins. Trenching fatalities are primarily caused by cave-ins, with death occurring by suffocation or crushing when a worker is buried by falling soil, notes information from the Infrastructure Health and Safety Association in Mississauga, Ontario.

Trench stability is affected by a number of factors, such as soil type, moisture content, depth of the trench, length of time during which the trench is left open, previous excavations or soil disturbances and vibration and excessive weight from heavy equipment nearby. Trench-related fatalities can also be caused by falls, exposure to hazardous gases, drowning, falling equipment or materials and electrocution.


“People think they’re invincible. They don’t realize how extremely dangerous trenches and confined spaces can be,” Villeneuve says.

An excavation is a hole made in the ground of at least four feet, with the width of its base exceeding the depth. A trench, which is also at least four feet in depth, has a base that has a width equal to or less than the depth. Several effective methods that can help prevent accidents include sloping, shoring and using trench boxes. Sloping involves cutting back the trench wall at an angle inclined away from the excavation. Shoring systems that retain the walls are usually made of wood, aluminum or steel panels held apart by shoring screws or hydraulic jacks. Trench boxes or prefabricated shoring are used more frequently to hold trench walls in place while workers are inside them.

Despite these safeguards, fatalities and injuries still occur. Last September, a worker in Westmount, Quebec was buried in a trench next to a house when the wood retaining wall collapsed on him, as did soil and paving stone. Colleagues got him out in 90 seconds, but he succumbed to his injuries shortly afterwards.

That same month, two construction workers in Toronto were pulled out alive from a collapsed trench at a house under construction. The 90-minute rescue effort involved 60 firefighters.

But a worker who was installing a sewer service in Toronto last March was not so lucky: he was killed when he fell into a trench and was buried by a concrete slab.

Shifting Ground

Most trench and excavation fatalities occur on small, short-duration jobs and involve companies with fewer than 10 employees, notes information from Ontario’s Ministry of Labour (MOL). Small-scale projects, such as excavating houses to waterproof basements, typically attract smaller companies that provide little or no training and supervision of workers, says Mike Chappell, provincial coordinator of the construction health and safety program at the labour ministry in Toronto.

“They’re hiring workers from temporary help agencies or workers who don’t have a lot of experience, and they’re loosely supervising them,” he says. Chappell reports that accidents on small jobs typically involve only a back-hoe operator and the worker in the trench. The recommended shoring or sloping protection for trenches is often not in place. Some companies take the risk that the shallow holes, which are generally two to two-and-a-half metres deep, will not collapse in the day or two during which the job is being done.

“If you’re digging in the top layer of the soil, it will stand up [for] some period of time without falling in,” Chappell says. But vibration and water destabilize the soil, and eventually, it will collapse. “It’s not a question of if, but when.”

Workers caught in that situation have very little chance to survive. “The popular belief is that if you are buried in a trench, your co-workers can jump in and somehow dig you out in time. That is not the reality,” Chappell notes. “Soil is so heavy that when it collapses, it pushes all of the air out of the lungs of a worker.” One cubic yard of soil can weigh as much as a car and the pressure on the chest can make it impossible for a worker to breathe, even if his or her head is above the level of the collapsed soil.

“You only have four, perhaps five minutes realistically to rescue a worker, and if you are covered by three or four feet of soil and try to dig that out, it’s not going to happen. It becomes a recovery situation,” he adds.

Digging Safe

Workers engaged in trenching and excavation works are exposed to risks from both the top, such as cave-ins, and underground – with electrical utility services as an example. Apart from wearing the proper personal protective equipment, ensuring that workers have received proper training and making first-aid supplies available in the event of an incident, trade guidelines on excavation and trenching from the Construction Safety Association of Manitoba recommends the following safe work practices:

• Do not use pointed tools to probe for underground gas and electrical services;

• Protective barricades should be installed;

• The spoil pile must be placed at least one metre away from the edge of the excavation, while work materials and equipment must be at least two metres back from the edge;

• The trench must have adequate entrance and exit points every eight metres;

• Ladders must be placed within three metres of workers, secured and capable of extending at least three rungs above ground;

• If trench depth is more than one metre in height below the sloped sides, a support structure or adequate shoring must be provided; and

• No vehicles should be parked within a distance equal to the depth of the excavation or they may jeopardize the stability of the walls.

Chappell says such accidents continue to happen even though requirements for trenching and excavation safety have been in place for well over 20 years and employers are required to provide adequate training and supervision to workers.

David Law, partner at Gowling Lafleur Henderson in Ottawa and co-leader of the law firm’s national oh&s practice, says small employers who have not joined construction safety associations are more prone to unsafe practices in trenches. Even companies with adequate resources and training may have supervisors who have not bought into the safety program or may direct people to do work in a way that is unsafe, because they are under time pressure.

“A worker who knows they shouldn’t do something they think is dangerous is an employer’s best friend,” says Law, since these workers draw employers’ attention to safety concerns and bring about the opportunity to rectify them. “The missing piece, a lot of the time, is the unwillingness of individuals to say, ‘I’m not comfortable with that.’”

Horse Before Cart

A trench accident is like any other non-compliance issue, says Law, who has worked on many cases involving trenches in his 25-year career. “It’s pretty horrifying for a person to be trapped in that way, whether she lives or dies.”

Before digging even begins, On
tario’s Occupational Health and Safety Act (OHSA) requires debris and excavated soil near the excavation site to be removed. Workers must be protected from falling into an excavation and water-removal plans should be in place.

Apart from locating overhead power lines and underground infrastructure, such as gas and electric power lines, knowing the type of soil and the sloping, shoring or shielding required is critical. Having an emergency plan to deal with any unforeseen incidents is also required, notes information from the MOL.

But Chappell says Ontario does not stipulate the need for a full-time supervisor on jobs with fewer than five workers. On the other hand, “the greater the risk, the more the employer has the obligation to provide supervision.” Even for trench jobs with fewer than five workers, Chappell is of the mind that “it would be prudent to do due diligence” and provide full-time supervision.

Kimberley Labrecque, whose husband Fabien Guindon was killed by the collapse of a soil wall in Oka, Quebec in 2007 while repairing a conduit in a trench, says she continues to see trenches that are potentially dangerous. She vowed her husband’s death would not be in vain and agreed to appear in an accident prevention video for the Commission de la santé et de la sécurité du travail.

She believes that had her husband been protected by a trench box, he would not have been killed. “It’s unacceptable. Without trench boxes, trenches can become real coffins for the workers who are inside them.” Quebec’s guidelines require an experienced person who can detect faults, earth breaking or any other source of danger to be present at the ground level when employees are working in trenches.

Candice Brown, a safety and injury management advisor at the BC Construction Safety Alliance in New Westminster, British Columbia says employers planning to do trench or excavation work should call one-stop services, such as BC One Call in British Columbia and Info-Excavation in Quebec, to determine the location of underground utilities within the area. She adds that British Columbia and other provinces have the Common Ground Alliance, a non-profit organization that develops best practices and coordinates safe excavation activities near underground infrastructure.

Trench walls become less stable the longer they are exposed to rain, snow or dry weather. When trench accidents occur, firefighters are almost always called upon to rescue trapped workers. But only a minority of firefighters in Toronto have taken all three levels of trench-rescue courses available, says firefighter Geoff Boisseau, who sits on the executive of the Toronto Professional Fire Fighters’ Association. Boisseau is one of 60 firefighters who recently completed the top-tier technician level training, which deals with intersecting trenches. The first two levels — awareness and operations — deal with recognizing the general hazards associated with trench and excavation emergencies and understanding the need for protective systems to perform a safe rescue.

Silt or Sand

Understanding the type of soil, which determines the strength and stability of trench walls, can help supervisors and workers plan their protection accordingly. As soil types and conditions can change over very short distances, the Construction Regulation under the Occupational Health and Safety Act sets out soil types into the following categories:

Type 1: Often described as “hard ground to dig”, this type of soil, such as “hardpan”, consolidated clay and some glacial tills, is so hard that it is close to rock.

Type 2: This type of soil can easily be excavated by a backhoe or it can be hand-excavated with some difficulty. The sides of a trench will remain vertical for a short period of time. Examples include silty clay and less dense tills.

Type 3: This type of soil, when dry, flows through fingers and will not stand vertically. Sand, granular materials, silty or wet clays and all backfilled or previously disturbed material fall under this category.

Type 4: This type of soil must be supported and contained to be excavated to any significant depth. With its high moisture content, soil of this type is very sensitive to vibration and other disturbances. Examples include muskeg, quicksand, clay and silty clay.

Source: Infrastructure Health and Safety Association

The more training firefighters have, the closer they are allowed to get to the trench during rescues, says Boisseau, who was involved in a trench rescue a few years ago. Two men were waterproofing their basement from the outside when soil collapsed and pinned them against a wall. One man was rescued, but the other had to be dug out — fortunately alive — by crews.

Boisseau says Toronto Fire Services has a specialized trench-rescue truck with the equipment required to respond to accidents, although calls for rescues of this nature are few and far between.

Employer Liability

Cheryl Edwards, partner of Heenan Blaikie and labour and employment lead at the law firm’s oh&s and workers’ compensation practice group in Toronto, points out that employers can be charged with criminal offences in addition to occupational health and safety violations in the wake of a trench accident.

For example, charges were laid against Millennium Crane Rentals of Sault Ste. Marie, Ontario in connection with a sewer work accident in 2009, when a crane that was being repositioned rolled into an excavation, killing a worker. Five charges were laid against Millennium Crane under the OHSA. The company, the crane owner and the crane operator were also charged with criminal negligence causing death.

Edwards says this was the first time a corporation in Ontario was charged with this offence since amendments had been made to the Criminal Code in 2004. While the criminal charges were withdrawn as the Crown could not prove that a lack of maintenance caused the crane to roll into the excavation, the company was fined $70,000 last July for failing to ensure that the crane was maintained in a condition that would not endanger a worker.

“There can be significant liability under occupational health and safety legislation across Canada, under the Criminal Code of Canada, for excavation-related issues to employers, to general contractors, business owners and even workers and supervisors,” Edwards cautions.

She adds the Ontario Court of Appeal ruled in September that in appropriate cases, courts can fine a company into bankruptcy for a Criminal Code conviction. In that case, the court increased the fine from $200,000 to $750,000 for Metron Corp. after the company pleaded guilty to a charge of criminal negligence causing death. The case against Metron Corp. stemmed from the deaths of four migrant workers on Christmas Eve of 2009, when the swing stage on which they were working collapsed from a high-rise building in Toronto. Edwards says higher fines are sending a message to employers that “this is not acceptable.”

Chappell notes that Ontario is working on mandatory entry-level training that will make construction workers aware that trenching and working under the soil is inherently dangerous. “Workers often have no idea. They do as they’re told. They want to keep their job and that puts them in a situation of playing the game of chance — when will this collapse? Unfortunately, they don’t know.”

Law observes that compliance with safe practices in trenching and excavation works has improved considerably over the past two decades. That said, “it shocks me to think that we have 10 fatalities a year in this country when we are equipped to deal with this.” 

Danny Kucharsky is a writer in M

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