How much is too much chemical exposure at work?

WorkSafeBC regularly revises Occupational Exposure Limits (OELs) for chemical substances. Manganese was one chemical substance discussed at the last review. 

Photo of welding metal in factory

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Potentially harmful chemicals are present in many workplaces. So how can employers know how much chemical exposure is too much? That’s where Occupational Exposure Limits (OELs) come in.

To learn more about OELs, I spoke with Mark Teo, senior policy advisor at WorkSafeBC and the chair of WorkSafeBC’s OEL Review Committee.

According to WorkSafeBC, an OEL is “the maximum allowed airborne concentration for a particular substance from which nearly all workers are believed to experience no adverse health effects over a working lifetime.”

To help employers understand how OELs apply in their workplaces, WorkSafeBC publishes a guideline (G5.48-2) that provides background information on chemical exposure. It also links to the Table of Exposure Limits and to a policy on exposure limit exceptions.

WorkSafeBC regularly reviews and updates OELs — a thorough process that involves getting feedback from different stakeholders, including employers, workers, and WorkSafeBC subject matter experts.

The OEL review team looks at:

  • The availability of air-sampling methods that can accurately and reliably measure the concentration of contaminants in the air.
  • A review of adverse health effects documented in epidemiological peer-reviewed studies.
  • Implementation issues — in other words, is it feasible for employers and workers to comply with these OELs?

For more information about how WorkSafeBC determines and reviews OELs, see Regulating Chemical Exposures (OELs) on

Manganese in the spotlight at OEL review

Mark tells me that manganese was the most-mentioned substance during the last OEL review. It’s a heavy metal, often encountered in welding and other metalworking processes.

“When workers do things like grinding or welding a metal alloy, there’s a very good chance they will be exposed to manganese in some form,” says Mark.

After its recent review, WorkSafeBC decided on a new OEL for respirable manganese. Mark explains that “respirable” particulates are so small that they can deposit and settle deep in the gas-exchange region of the lungs.

“Welders and other workers can be at risk of being exposed to elevated levels of the very small, respirable manganese particulates, and this can cause many adverse health effects.”

Manganese is also found in batteries, fireworks, matches, porcelain, fertilizers, and many other products. Prolonged exposure can lead to damage to the lungs, reproductive system, and central nervous system — health effects the new OEL will help prevent.

Says Mark: “The new B.C. OEL will help ensure worker exposure to manganese is maintained as low as possible so that workers can work in a safe environment.”

For more information, see WorkSafeBC’s page on Welding gases & fumes.

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