A worker at a hardboard siding manufacturing operation in Nova Scotia has won his appeal for workers’ compensation after the tribunal found his respiratory symptoms and other health issues were caused by workplace exposure to hydrogen sulfide at the facility’s wastewater treatment plant.
The Workers’ Compensation Appeals Tribunal allowed the worker’s appeal of an August 2023 decision that had denied his claim. The tribunal determined there was sufficient evidence to establish the worker sustained a personal injury by accident arising out of and in the course of his employment caused by exposure to hydrogen sulfide.
The worker had been employed at the facility since 1985 and worked in the wastewater treatment plant from 2010 onward, typically on 12-hour shifts. He filed an injury report in February 2019 reporting burning eyes, facial rashes, headaches, nausea and nasal polyps, which he attributed to workplace exposures including hydrogen sulfide, ammonia, phosphoric acid, rust, mould and polymer.
Timing of symptoms and equipment failures
The tribunal found the timing of the worker’s worsened symptoms was significant. According to the evidence, symptoms intensified in 2017 and became worst in summer 2018, coinciding with the employer’s efforts to seal the wastewater treatment plant building from air leakage after failure of the HVAC system.
“I find a strong inference of causation from the timing of symptom onset and its correspondence with increased equipment failures,” the tribunal stated.
The tribunal noted an uncontested increase in equipment failures at the facility during the same period. The employer’s environmental manager testified that hydrogen sulfide corrodes metal within equipment, leading to failure. The tribunal found it reasonable to infer the increased equipment failures were caused by increased hydrogen sulfide levels resulting from reduced air leakage in the building.
Environmental testing results
Environmental testing conducted in 2018 showed elevated hydrogen sulfide levels in the lab area where the worker spent up to 10 hours per shift. Two of three samples exceeded the threshold limit value for an eight-hour workday, and all three samples exceeded the more stringent 12-hour threshold limit value of 0.7 mg/m3.
Testing in 2015 had also shown some elevated hydrogen sulfide levels around the dissolved air flotation tank, though recommendations at that time were not fully implemented. No personal protective equipment beyond basic safety gear was required until after the 2018 testing results.
The tribunal rejected the employer’s argument that the 2018 testing artificially inflated results because it was conducted with doors closed on a hot day while the mill was not operating.
“While the mill not being operational leading to less water flow through the WWTP may have had some impact on H2S levels, it would not have taken those levels from acceptable levels to unacceptable levels on its own,” the tribunal found.
Medical evidence
The worker saw multiple specialists after filing his claim, including physicians in otolaryngology, neurology and occupational medicine. A physician who examined the worker noted symptoms of throat irritation, eye irritation, facial rash and nausea, stating “it is clear that [the worker] has worked in an environment with significant chemical exposure, particularly to a number of irritants.”
The physician concluded the worker had become sensitized and should not return to the environment.
The tribunal gave little weight to an occupational medicine specialist’s opinion obtained by the workers’ compensation board, noting the specialist appeared to assume the worker would have been wearing a respirator throughout his time in the facility and did not adequately address the timing correlation between increased symptoms and equipment failures.
Scope of decision
The tribunal limited its finding to the initial respiratory, skin and eye irritations, as well as nausea and fatigue caused by hydrogen sulfide exposure. It declined to make findings on subsequent diagnoses including multiple chemical sensitivity and fibromyalgia, leaving it to the workers’ compensation board to determine what benefits flow from the decision.
The worker had testified that he would start to feel somewhat better by his fourth day off work and that some symptoms improved after leaving the facility, though facial burning persisted.
The tribunal applied section 187 of the Workers’ Compensation Act, which requires giving the worker the benefit of the doubt when disputed possibilities are evenly balanced on an issue of compensation.
For more information, see 2023-352-AD (Re), 2025 CanLII 134975 (NS WCAT).
