Carbon monoxide exposure limits for Canadian workplaces
Ontario, BC and Alberta list 25 ppm over eight hours for carbon monoxide. Compare short-term rules, OSHA's PEL and NIOSH recommendations for workplaces.
The official sources reviewed list carbon monoxide exposure limits in Ontario, British Columbia and Alberta at 25 ppm as an eight-hour time-weighted average (TWA). Short-term rules differ: BC lists a 100 ppm, 15-minute short-term exposure limit (STEL), while Ontario and Alberta apply general excursion rules.
Start with the jurisdiction. The three provincial values below are examples, not a complete Canadian survey. Keep the jurisdiction and averaging period beside each recorded value.
Carbon monoxide exposure limits chart for three Canadian provinces
| Jurisdiction | Eight-hour TWA | Short-term requirement |
|---|---|---|
| Ontario | 25 ppm | No CO-specific STEL or ceiling listed. General excursion rules apply. |
| British Columbia | 25 ppm | 100 ppm STEL, averaged over 15 minutes. |
| Alberta | 25 ppm, or 29 mg/m³ | No CO-specific STEL or ceiling listed. General excursion rules apply. |
The CCOHS carbon monoxide profile also reports an ACGIH TLV-TWA of 25 ppm. Its exposure-limit section cites the 2022 ACGIH publication. That reference is not a national legal limit or confirmation of the newest ACGIH edition.
Ontario's combined ministry table gives the practical lookup, but the regulation determines how the limit applies. For substances absent from its own table, Regulation 833 incorporates the 2017 ACGIH Adopted Values table. Do not assume Ontario automatically adopts each new ACGIH edition.
What is the short-term exposure limit for carbon monoxide?
In BC, the listed STEL is 100 ppm over 15 minutes. The BC regulation limits STEL exposures to four periods per eight-hour shift, at least one hour apart. The eight-hour TWA still applies.
A TWA controls the average over its stated period. A STEL controls a shorter average. A ceiling is a concentration that must not be exceeded at any time, unless otherwise specified. These terms are not interchangeable, as the NIOSH exposure-limit definitions explain.
BC's 100 ppm value is a STEL, not a ceiling. Nor does the 25 ppm eight-hour average mean every brief reading above 25 ppm automatically breaches that average.
But a blank STEL entry does not permit unrestricted peaks. Ontario's general excursion rules set three times the TWA for any 30-minute period and five times the TWA at any time. For CO, those values are 75 ppm and 125 ppm. They are not a listed CO-specific STEL or ceiling.
Alberta's Code also imposes general excursion controls. Its timing rules differ from Ontario's, so do not transfer Ontario's 30-minute wording into an Alberta assessment.
OSHA and NIOSH limits are different
For US general industry, the OSHA permissible exposure limit, or PEL, is 50 ppm. Under §1910.1000, this is an eight-hour TWA for an eight-hour shift in a 40-hour week. It is not a Canadian limit, and this general-industry figure should not be extended to every US sector.
The NIOSH Pocket Guide separately recommends a 35 ppm TWA and a 200 ppm ceiling. NIOSH's TWA covers up to a 10-hour workday within a 40-hour week. Its recommended exposure limit, or REL, is distinct from OSHA's legal PEL.
NIOSH also lists 1,200 ppm as immediately dangerous to life or health (IDLH). This is an emergency and respirator-selection benchmark. It is not a permissible workplace exposure or a safe 30-minute work allowance.
Choose the rule for your workplace
Before using a number, establish whether federal or provincial rules govern the workplace. Then check the applicable text for the averaging period, short-term controls and any sector or extended-shift provisions. Do not use the three-province chart to fill gaps for other jurisdictions.
Check the version, too. The Ontario text reviewed had a consolidation interval ending October 30, 2026. The BC text was current to October 27, 2026. Alberta's displayed consolidation was March 31, 2025. These source dates do not establish that the CO values changed then. Check current amendments before relying on these values.
RegAffairs AI's answer on workplace carbon monoxide limits in Canada provides a starting point for the jurisdiction lookup. For compliance decisions, use the applicable official regulation and its current amendments.