Canadian Occupational Safety

April/May 2016 17 sewage lagoon to check a valve on a feeder line. One worker entered the valve chamber and collapsed. The second worker went in to rescue him and also collapsed. The third worker called for help, but by the time the fi re department arrived, the two workers had died. Air samples determined H2S was in excess of the measuring instrument's upper limits. Carbon monoxide — a colour- less, odourless and toxic gas — is a concern in sewers due to the gasoline and diesel engines overhead. Expo- sure to concentrations exceeding 25 ppm may result in ringing in the ears, nausea, headaches and sleepiness. "If we were to enter a confi ned space with some of these gases pres- ent, it could overcome us and the person entering the space could pass out and eventually, if the gases were strong enough and potent enough, it could cause damage," says Pigott. Gases or vapours that are fl amma- ble or explosive pose a serious hazard for workers in sewers. Methane gas — a byproduct of backed up or slug- gish sewers — is one example as it is very fl ammable. Additionally, even very, very quickly down there. The sooner we can get out the better." Companies are required to main- tain their air monitoring test records — which are recorded on confi ned space entry permits — for a mini- mum of one year. Many keep them for two years, which allows them to review trends in worker health. "If a worker ends up being ill down the line, they can go back to those reports and say 'What was the exposure?'" says Cowan. If the gas detector alarms are sounding, employers should ven- tilate the space. Powered blower equipment must be used. According to the government of Alberta, venti- lation must continue until: • the oxygen content of the air is between 19.5 and 23 per cent by volume • the concentrations of toxic contaminants are below their occupational exposure limits • the concentrations of fl ammable contaminants are below their lower explosive limits. The City of Charlottetown sets up a forced air system of fans that blow large volumes of air into the confi ned space and remain operational for the duration of the project, says Pigott. "They do an air circulation and do that for a period of time and re- test the confi ned space to make sure everything is going to be safe." WET ENVIRONMENTS Slips, trips and falls are a common hazard among these workers because sewers are wet environments. Lad- ders going down into manholes or lift stations can be very slippery or rusted out, and the fl oors and walls can be slippery as well. "When we are down in the man- hole or well chamber, the conditions down there can be pretty bad, depending on where we are. There's excess grease down there that you have to watch for especially on the bench of the manhole. It's very slip- pery and there's human solid waste and stuff like that — those are the things you really have to watch for," says Parkman. To mitigate this risk, workers move as much of the debris out of the way as possible, which some- times means putting debris in a though it is against the law, gasoline, oil, paints and solvents are some- times fl ushed down into the sewer as a means of disposal either from residential properties or factories. Gasoline may also enter the sewer system from leaking underground storage tanks or inadvertent spillage. Explosive hazards are the most concerning, says Randy Cowan, president of Cowan Consulting in Bowmanville, Ont. "You can have all the protective equipment in the world on — you can have supplied air if there is a low oxygen content in there — but there's going to be no protection from the explosive limit if some- thing goes south pretty quickly in there," he says. The City of Charlottetown has a three-step process to test the air in a confi ned space to ensure it is safe for workers. Before the cover is even opened to the manhole, a universal pump probe (a wand-like attachment for the gas detector) is inserted through the access holes of the manhole lid to check for hazardous conditions, says Pigott. Once it's cleared, the cover to the confi ned space is opened up and a remote gas detector is lowered into the structure that checks for oxygen defi ciency, H2S, carbon monoxide and the lower explosive limit. As a fi nal precaution, the worker enter- ing the confi ned space has a gas monitor strapped to him. And if that monitor goes off for any reason — even if it's just a low battery warning — the worker needs to get out of the confi ned space right away. "We have been in situations where the monitors went off and we don't hesitate to get extracted out ASAP," says Parkman. "We don't want to take that chance. Things can change encounter rats, human feces, syringes every day on the job THE WORLD BELOW

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