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New rules to reduce diesel exposure in Ontario mines

19 April 2023

The government of the Province of Ontario, Canada, introduced new rules to lower the occupational exposure limit to diesel particulate matter (DPM) in underground mines.

Effective September 1, 2023, the new exposure limit will be a time-weighted average exposure to elemental carbon (EC) of 0.12 mg/m3, replacing the current limit of 0.4 mg/m3 based on total carbon (TC).

Long-term exposure to diesel exhaust can be a significant cause of lung cancer in miners, the Ontario Labour Ministry said in a press release. The amendments respond to calls from unions for a reduction in DPM exposure limits in underground mines and follow recommendations from the Mining Health, Safety and Prevention Review.

Ontario’s allowable level of exposure to diesel particulates in underground mines will now be the most protective in North America, according to the Labour Ministry. In the United States, the Mine Safety and Health Administration’s (MSHA) DPM exposure limit for underground mining is 160 µg/m3 = 0.16 mg/m3 (TC).

The total carbon definition includes elemental carbon and organic carbon, i.e., TC = EC + OC. The OC fraction typically represents about 20% of total carbon emissions, but it can vary considerably depending on the diesel engine technology. The EC measurement also eliminates potential non-diesel sources of organic carbon particulates found in mines, such as oil mist.

DPM exposure in mines can be controlled by increased ventilation rates and/or the use of diesel particulate filters. However, according to the 2014 Underground Diesel Survey by the Labour Ministry and earlier data by CanmetMINING, the vast majority of occupational exposures in Ontario mines were already under 120 µg/m3. Hence, it would appear that most Ontario mines can meet the new DPM exposure limit without the need for any additional control measures.

Source: Ontario Ministry of Labour