'Rainwater mixed with silt and soil entered the trench, forming a slurry that accumulated rapidly'
Aecon Utilities Inc. has been fined $175,000 after a worker died when a trench rapidly filled with water and slurry during underground utility work at a residential property in King City, Ontario.
The incident occurred on July 30, 2024, at 2750 King Road, where the company was installing a new underground utility service. Excavation work had been carried out to expose an existing pipeline, and a trench shoring box system had been installed to support the walls of the excavation.
While a worker was inside the trench connecting the new service to the existing pipeline, weather conditions deteriorated and heavy rainfall began. According to the Ontario government, “Rainwater mixed with silt and soil entered the trench, forming a slurry that accumulated rapidly.”
The Ontario government stated that the worker “became trapped in the slurry and was fatally injured by the rapidly rising water.” Emergency response efforts were not able to prevent the fatality.
Court outcome and penalties
Aecon Utilities Inc., based at 105-20 Carlson Court in Toronto, was convicted following a guilty plea in the Ontario Court of Justice in Newmarket. The company was found to have failed to ensure that equipment was not used under weather conditions likely to endanger a worker, contrary to section 93(2)(b) of Ontario Regulation 213/91 and section 25(1)(c) of the Occupational Health and Safety Act.
On March 26, 2026, Justice Prutschi imposed a fine of $175,000 on Aecon Utilities in relation to the July 30, 2024 offence. Crown counsel in the matter was David McCaskill.
The court also imposed a 25 per cent victim fine surcharge under the Provincial Offences Act. According to the Ontario government, the surcharge is credited to a special provincial fund set up to assist victims of crime.
Findings of investigation
The Ministry of Labour, Immigration, Training and Skills Development investigated the incident. The investigation examined the engineering aspects of the trench, the pumping capacity used for dewatering and the site conditions at the time of the incident.
The ministry concluded that the amount of rainfall and sediment entering the excavation made it impossible to safely dewater the trench. The investigation found that the slurry formed by rainwater, silt and soil accumulated rapidly inside the excavation.
According to the Ontario government, Aecon Utilities Inc. failed to ensure that equipment was not used when weather conditions made its use likely to endanger a worker, contrary to the Occupational Health and Safety Act.
Slurry hazards
slurries pose serious and sometimes fatal risks to workers. The hazards vary depending on the slurry type (manure, concrete, mining tailings, drilling mud, industrial sludge), but several common dangers and control measures are well documented by Canadian occupational health bodies.
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Hazard |
What It Looks Like in Pactice |
What Employers Can Do |
Source |
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Toxic gas exposure (hydrogen sulphide, H₂S) |
Anaerobic decomposition in manure, sewage, and biogas slurries releases H₂S. Concentrations can spike from background levels to over 1,300 ppm during agitation; above 600 ppm a person can die in one or two breaths. The gas paralyses the sense of smell at ~100 ppm, removing any natural warning. |
Install continuous mechanical ventilation; require personal H₂S monitors; agitate only when workers and livestock are out of the building; post warning signs; train workers on H₂S risk; develop written standard operating procedures and emergency plans. |
CCOHS, "Hydrogen Sulfide" chemical profile; CCOHS Government of Ontario, "Hydrogen sulphide in livestock facilities" (Nov 2022); Ontario OHS Canada Magazine, "Do H2S Monitors Belong on Swine Farms?" (May 2017) Ohscanada |
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Slurry tanks, manure pits, digesters, sewers, and storage bins are classified confined spaces. Oxygen can be displaced by methane, CO₂, or H₂S; would-be rescuers without breathing apparatus often become secondary victims (the majority of H₂S poisonings happen in confined spaces, and many involve workers trying to help a downed co-worker). |
Implement a written confined-space entry program with permits; pre-entry atmospheric testing (oxygen, H₂S, methane, CO₂); forced ventilation; tripod/harness retrieval systems; a trained attendant outside; never permit unprotected rescue attempts. |
CCOHS, "Confined Space – Introduction"; CCOHS OHS Canada Magazine (May 2017) Ohscanada |
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Chemical burns from alkaline (cement/concrete) slurry |
Wet cement slurry reaches a pH of 12 or higher. Skin contact can cause irritant contact dermatitis, deep alkaline burns (sometimes only felt hours later), and in severe cases ulceration or amputation. Hexavalent chromium in Portland cement can also trigger allergic contact dermatitis. |
Provide waterproof, chemical-resistant gloves extending past the wrist, rubber boots, eye protection and coveralls; supply on-site wash stations with pH-neutral soap; train workers to remove cement-soaked clothing immediately; keep Safety Data Sheets accessible. |
WorkSafeBC, "Burns"; WorkSafeBC "Concrete Burns Stats and Facts" referencing CCOHS 2023 data and WorkSafeBC 2020–2023 construction fatality figures Safetynow |
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Respirable crystalline silica from dried concrete/mineral slurry |
When concrete slurry dries and is later cut, ground, swept, or disturbed, respirable crystalline silica becomes airborne. Inhalation causes silicosis (irreversible lung scarring) and increases lung-cancer risk. There is no effective treatment for silicosis. |
Eliminate or substitute lower-silica materials where possible; use engineering controls (wet cutting, local exhaust ventilation, HEPA-filtered vacuums); avoid dry sweeping; provide fit-tested respirators based on air monitoring; conduct medical surveillance; deliver worker training. |
CCOHS, "Silicosis"; CCOHS WorkSafeBC, "Silica" WorkSafeBC |
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Toxic-coating removal hazards (industrial slurry vacuuming) |
Removing lead-, cadmium-, or chromate-containing coatings before welding/cutting can generate highly toxic dust if done dry. CCOHS specifically recommends wet slurry vacuum removal rather than grinding. |
Use wet slurry vacuum techniques for removing very toxic coatings (do not grind); conduct risk assessments and occupational hygiene sampling; supply task-appropriate PPE based on exposure assessment; follow manufacturer’s instructions. |
CCOHS, "Welding – Fumes and Gases" CCOHS |
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Workers can fall through slats, covers, or unfenced lagoon edges into liquid manure or tailings. Even a shallow depth of slurry can cause drowning, and the toxic atmosphere directly above compounds the risk. |
Guard openings and edges; use covers rated for foot traffic; install fall protection where edges cannot be eliminated; restrict access during agitation; use the buddy system; post signage. |
Government of Ontario (Nov 2022); Ontario CCOHS, "Safety Hazards" (slips, trips and falls) Canadian Centre for Occupational Health and Safety |
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Slips, trips, and contact injuries on wet surfaces |
Spilled slurry creates slick walking surfaces around mixers, pumps, transfer points, and barn floors. Falls are among the most common construction-sector injuries in Canada. |
Apply the hierarchy of controls — engineering controls first (drainage, non-slip flooring, splash guards), then administrative controls (housekeeping schedules, safe work procedures), then PPE (slip-resistant footwear). |
CCOHS, "Hazard and Risk – Hierarchy of Controls"; CCOHS CCOHS, "Safety Hazards" Canadian Centre for Occupational Health and Safety |
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Many slurry incidents trace back to no formal risk assessment, no SOPs, and no worker training — not the slurry itself. The Institute for Work & Health notes that comprehensive injury-rate data in Canada is limited, which weakens prevention targeting. |
Conduct a documented risk assessment for every slurry-handling task; consult Safety Data Sheets; review incident records; train supervisors and workers; communicate findings; review controls regularly. |
CCOHS, "Hazard and Risk – Risk Assessment"; CCOHS Institute for Work & Health, comments from president Cameron Mustard cited in The Globe and Mail (Oct 2017) The Globe and Mail |
