Carbon monoxide damages health at low as well as high levels. 

A growing body of research shows that adverse health effects occur at lower levels than had previously been thought.

• At levels as low as 10ppm, CO increases the risk of thrombosis, cardiac arrhythmia, release of oxidants, damage to vascular lining, and destruction of brain tissue.

• The unborn are especially vulnerable to low-level CO exposure, which is particularly toxic to the developing heart and brain.

• An ambient level of 25ppm (corresponding approximately to a COHb of 3.4 per cent) is sufficient to cause a measurable impairment in driving skills.

In September 2021, the World Health Organization (WHO) revised its air quality guidelines, lowering the recommended safe level of CO to just 4mg/m3 (3.49ppm). This was the first significant revision since 2005, following new research showing that adverse health effects occur at lower concentrations than previously thought.

As evidence accumulates of the harm that low-level CO can cause, we anticipate that occupational health safety limits will also be revised downwards.