Canadian Occupational Safety

24 Canadian Occupational Safety | www.cos-mag.com group of construction workers in British Columbia were dig- ging 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 haz- ards associated with confi ned spaces. This is true whether they meet the reg- ulatory defi nition of a confi ned space or, like the basement trench above, are only partially enclosed. Safety manag- ers and workers should consider every excavation as a potential confi ned space. Doing so triggers additional pro- cedural and equipment requirements that will help prevent incidents. "Not all excavations are confi ned 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 confi ned space, unless they have some sort of staircase or sloping in that excavation that gives them decent access for rescue." Most federal and provincial legis- lation defi nes an area as a confi ned 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 fi rst three criteria is defi ned as a "restricted space." In Saskatchewan, the same kind of area is called a "con- fi ned space," while one meeting all four requirements is a "hazardous confi ned space." There are important variations among regulations. For example, while federal and most provincial regulations state any space that meets the fi rst three criteria and also has the potential to contain atmospheric haz- ards is a confi ned space, the defi nitions in B.C., Manitoba, Yukon, Northwest Territories and Nunavut do not have a specifi c requirement for toxicity. Moreover, until recently in B.C., excavations were generally exempt from being identifi ed as confi ned spaces, Kossey says. In April 2015, new guidelines were introduced that stipu- lated excavations could be exempted from confi ned 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 confi ned spaces. As soon as you're going in the space to generate contamination, they are confi ned 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 fi nding." HAZARDS One of the greatest hazards of con- fi ned spaces — and one generally present in excavations — is air quality. This includes fl ammable or explosive gases, the presence and concentration of airborne chemical substances and oxygen enrichment or defi ciency. The most common toxic concerns include carbon monoxide (CO), nitrogen dioxide and hydrogen sul- phide (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 endan- ger workers. Hazardous vapours can also come from sewers and from equipment and vehicles common in excavations, such as excavators, gen- erators 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 traffi c. When a collapse occurs, restricted access and exit make rescue more diffi cult. There are other common hazards, Gursky says, such as poor visibility and psychological issues from work- ing in tight spaces, which should be identifi ed before the worker goes into the site. In small excavations, lack of wind and predominance of dark mate- rials can cause high temperatures and produce heat exhaustion. Workers should have regular breaks and main- tain 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 confi ned space produces oxygen defi ciency, which can cause dizziness, confusion, asphyxia- tion and death. When a sewer main is opened in an excavation, the space should be considered a confi ned 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 defi nition of a confi ned 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 confi ned space. Now you have an excavation. It's not a confi ned space, but there are still atmospheric hazards in it, so you still need to ventilate and monitor to make sure your ventilation is working cor- rectly," he says. CONTROLS Employers should have an effective health and safety management system, such as the Certifi cate 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 specifi c job and communicate Considering every excavation as a potential confined space can expose hidden hazards By Linda Johnson

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