A group of construction workers in British Columbia were digging trenches to lay pipes in the basement of a large building. The walls were up, but no windows had been installed. Five workers in the trenches began to get breathing distress and headaches. They were all taken to the hospital, where it was determined they were suffering from nitrogen dioxide (NO2) poisoning.
While workers had been monitoring continuously for carbon monoxide, which did not reach a hazardous level, they had not been monitoring for NO2.
Excavations present many of the hazards associated with confined spaces. This is true whether they meet the regulatory definition of a confined space or, like the basement trench above, are only partially enclosed. Safety managers and workers should consider every excavation as a potential confined space. Doing so triggers additional procedural and equipment requirements that will help prevent incidents.
“Not all excavations are confined spaces. Each one has to be looked at on its own merits,” says Karren Kossey, president of Nanaimo, B.C.-based ORCA Health and Safety. “By definition, any excavation more than 4 feet deep should be looked at a confined space, unless they have some sort of staircase or sloping in that excavation that gives them decent access for rescue.”
Most federal and provincial legislation defines an area as a confined space if it:
• is enclosed or partially enclosed
• is not designed primarily for continuous human occupancy
• has restricted means of access or exit
• may become hazardous to a person entering it due to design, construction, location, atmosphere, the materials or substances in it or any other related hazards.
In Alberta, an area that meets only the first three criteria is defined as a “restricted space.” In Saskatchewan, the same kind of area is called a “confined space,” while one meeting all four requirements is a “hazardous confined space.”
There are important variations among regulations. For example, while federal and most provincial regulations state any space that meets the first three criteria and also has the potential to contain atmospheric hazards is a confined space, the definitions in B.C., Manitoba, Yukon, Northwest Territories and Nunavut do not have a specific requirement for toxicity.
Moreover, until recently in B.C., excavations were generally exempt from being identified as confined spaces, Kossey says. In April 2015, new guidelines were introduced that stipulated excavations could be exempted from confined space regulations only if they meet nine criteria, including the assurance of “clean respirable air at all times.” (See sidebar.)
“Now, as soon as they have the ability to go toxic, they are confined spaces. As soon as you’re going in the space to generate contamination, they are confined spaces,” she says. “It’s been a game changer for a lot of companies to start looking at some of these excavations and say, ‘What toxicity are you at?’ Many people just didn’t know the air quality in these excavations was as bad as the levels we’re finding.”
One of the greatest hazards of confined spaces — and one generally present in excavations — is air quality. This includes flammable or explosive gases, the presence and concentration of airborne chemical substances and oxygen enrichment or deficiency.
The most common toxic concerns include carbon monoxide (CO), nitrogen dioxide and hydrogen sulphide (H2S). If there has been a fuel spill, there may be a combustible gas, and an LEL (lower explosive limit) detector should be used, Kossey says.
The surrounding soil, which may contain organic material, substances from old toxic dumps or fuel leaks from old gas stations, can produce toxic atmospheres. Some of these gases, like nitrogen dioxide, are heavier than air and will sink into the excavation where they may endanger workers. Hazardous vapours can also come from sewers and from equipment and vehicles common in excavations, such as excavators, generators and plate packers.
In addition to hazardous gasses, workers face many other hazards when working in excavations, says Loy Gursky, advisory services manager at Saskatchewan Construction Safety Association in Regina. A common hazard is contacting buried service lines: electrical, natural gas, power, telecommunication, water and sewage mains. Another is unexpected collapse of the excavation, caused by improper cutbacks, spoil piles too close to the edge, improper soil classification, failure of support systems and vibration from nearby equipment or traffic. When a collapse occurs, restricted access and exit make rescue more difficult.
There are other common hazards, Gursky says, such as poor visibility and psychological issues from working in tight spaces, which should be identified before the worker goes into the site. In small excavations, lack of wind and predominance of dark materials can cause high temperatures and produce heat exhaustion. Workers should have regular breaks and maintain hydration.
Depending on weather and soil conditions, water can accumulate in the excavation, causing engulfment or even drowning.
Other physical hazards include:
• equipment falling onto workers
• material falling into excavations
• falling into the trench or excavation
• slips, trips and falls at access and egress points
• contact with heavy machinery
• contact with overhead electrical lines.
The particular tasks being carried out in an excavation, the processes and products used can also create harmful conditions, says Jason Hindson, senior safety consultant at Ronin Safety and Rescue in Coquitlam, B.C. A worker may be required to remove coal tar with asbestos from a utility pipe, for example. Welding in a confined space produces oxygen deficiency, which can cause dizziness, confusion, asphyxiation and death. When a sewer main is opened in an excavation, the space should be considered a confined space. Hazardous energy sources must be locked out.
Hindson says safety managers must always remember that even when an excavation does not meet the regulatory definition of a confined space, it may still contain many serious hazards.
“For example, when it comes to confined spaces, everyone thinks about atmospheric monitoring and ventilation. But a lot of construction companies think air monitoring and ventilation is only for confined space. Now you have an excavation. It’s not a confined space, but there are still atmospheric hazards in it, so you still need to ventilate and monitor to make sure your ventilation is working correctly,” he says.
Employers should have an effective health and safety management system, such as the Certificate of Recognition (COR) program, Gursky says. Such a system helps them identify all hazards and controls, ensure workers are properly trained in their tasks and responsibilities and ensure equipment is maintained and inspected. They should also set out safe job procedures and work practices that are detailed to the specific job and communicate these to the workers.
When an area has been identified as a confined space according to the regulatory criteria, the employer is required to fulfill certain obligations specific to confined spaces, says Jon Wright, EHS specialist at Waterloo, Ont.-based Acute Environmental and Safety Services. Some of these are tasks that must be completed before a worker is required to enter the space.
First, an employer must have a qualified person assess the site for hazards. The assessment is used to then create a plan that states all precautions, controls and personal protective equipment needed to render the area safe for the worker. In some provinces, including Ontario and Manitoba, regulations require the employer to have an entry permit; it serves as a checklist to verify everything in the plan has been put in place.
The plan must include an effective rescue, Wright says.
“If something goes wrong, what people and equipment do we need on the project site to get the person out as fast as possible? The rescue has to be ready for immediate implementation.”
At Edmonton-based PCL Construction, anytime they have to go 6 inches under the soil, a ground disturbance permit must be completed, says Eugene MacMahon, district health, safety and environmental manager. The permit system establishes roles and responsibilities and helps them determine if an excavation is a confined space.
“It establishes the level of risk before anyone goes anywhere near the ground. We’ll find out who’s doing it, what drawing they’re using, where it is and when it’s going to start. We get a competent person to fill out this checklist. They’ll determine what kind of soil it is. Or are you breaking rock? Is it close to buildings, footings or pilings? Is there a source of vibration nearby, like traffic? And have the utilities been located? Depending on where you are, you might have an explosive atmosphere around the excavation,” he says.
Using the permit, they also determine what controls they need. They consider the slope on the excavation; the size of the excavation and whether they need to re-route traffic; whether water removal operations will be needed; where the hoisting equipment should be placed; and how to vent exhaust away from the excavation.
“This gives us a lot of information to determine: Are we looking at a confined space situation here? If you’re going 2 feet down, it’s hard to call something a confined space. But if you’re going 80 feet down, as we did in downtown Edmonton, it makes a difference. How do you rescue someone from 80 feet underground? It’s a tough thing. All the hazards there are combined with the confined space,” MacMahon says.
As soon as an area space has been identified as a confined space, precautions against hazardous atmosphere must be taken. Prior to entry, the qualified person should test the air in the space. Then there should be continuous monitoring and ventilating while workers are in the space.
At PCL, MacMahon says, with areas deemed confined spaces, they typically have the workers wear a four-head gas monitor, which monitors oxygen, LEL, methane and H2S.
“You can have naturally occurring H2S, especially if you’ve had an open excavation for a long time and you’ve brought in vegetation.” In some excavations, he adds, they will send down gas detection systems that can be operated remotely from above.
Safety managers should also determine whether there are underground utilities in the digging area, Gursky says. Remember, line locates show approximate locations. Specific locations may have to be found by hydro-vacing or digging by hand. When the locations are known, the safety manager must determine the control zone, or safe area, in relation to the specific utility.
Cave-ins can be prevented through the use of sloping (or benching) and shoring. Sloping entails cutting back the trench walls at an angle slanted away from the excavation. Shoring systems consist of vertical planks placed against the excavation walls and held apart by shoring screws or hydraulic jacks. The structure, called a “shoring cage,” is usually of wood, aluminum or steel.
“The cage is engineered to hold back the soil in the event of a collapse. They are all engineer-certified, and you can’t modify them without approval from a certified engineer,” Gursky says. “Depending on the depth of the excavation, you may need to stack them a few times. They need to be at least a foot above the top of the excavation.”
Other controls include:
• installing an adequate number of exit ladders
• removing water from the excavation
• protecting workers from falling into the excavation
• replacing equipment to reduce carbon monoxide risk.
Once the location is identified as a confined space, everyone involved in the work needs to be adequately trained, Wright says. Workers need to know what procedures they should be following, what could go wrong and how they must respond in an emergency. Practise the rescue plan so everyone is sure of their role.
In Ontario, the rescue team must be trained in the procedure to be used, safe operation of any equipment deemed necessary in the plan (such as a breathing apparatus) and first aid, including CPR. Generally, confined space regulations require another standby worker be stationed above ground to provide rescue and watch for danger. Workers should also be aware they have a right to a gas monitor and rescue plan.
In the basement excavation, all five workers exposed to the toxic air were fine in the end. Ventilation systems were installed and the work continued. Serious incidents like this happen all the time, Kossey says.
“I don’t think people recognize what’s happening. In this case, there was very limited air flow and all the nitrogen dioxide. They had three excavators in the space and they had a large number of plate packers and cut-off saws running. So they had many pieces of equipment without enough ventilation,” she says. “Nobody recognized the hazards.”
Linda Johnson is a freelance journalist based in Toronto. She can be reached at firstname.lastname@example.org
Enclosed but not confined
In British Columbia, enclosed spaces that are not considered “confined spaces” must satisfy specific exclusion criteria. The spaces that may be excluded from Part 9 Confined Spaces of the Occupational Health and Safety Regulation, provided that all the below criteria are met, include swimming pools; crawl spaces under school portables or other non-industrial buildings; excavations; attic space; open, unconnected wet wells or dry wells for storm or sewer hookups at new construction sites; elevator shafts; HVAC plenums; and agricultural feed mixer wagons and trucks that are permanently open on top and empty.
• The design, construction, location and intended use of these spaces will ensure these spaces are characterized by clean respirable air at all times.
• The space must have an interior volume of not less than 64 cubic feet per occupant.
• The space must have openings to the atmosphere that are known to provide natural ventilation.
• There must be no potential for a high or moderate hazard atmosphere, as defined in section 9.1 of the regulation, to exist or develop immediately prior to any worker entering the space or during any work within the space.
• There must not be a need to mechanically ventilate, clean, purge or inert the space prior to entry for any reason.
• There must be no potential for a hazardous substance to migrate through any media (such as soil, conveyance, piping or structure) to infiltrate the space.
• The space must be free of residual material (such as water, sludge or debris) that if disturbed could generate air contaminant that could immediately and acutely affect a worker’s health.
• No risk of entrapment or engulfment to workers entering the space.
• The space must not contain, have introduced or be adjacent to tools, equipment or processes that could generate air contaminants that could immediately and acutely affect a worker’s health.
This article originally appeared in the August/September 2017 issue of COS.
© Copyright Canadian Occupational Safety, HAB Press. All rights reserved.
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