At what concentration of carbon monoxide is it considered dangerous?

The consideration of carbon monoxide (CO) concentrations as dangerous is determined largely by its impact on human health. At a concentration of 25 parts per million (ppm), carbon monoxide can begin to produce adverse health effects after prolonged exposure. This level is significant because it is below the levels that might cause immediate symptoms but can still lead to problems such as headaches, dizziness, and impaired cognitive function over time.

In contrast, lower concentrations of 10 ppm and 0 to 25 ppm may not pose immediate risks but are still noteworthy, as they could indicate the presence of CO and a potential larger issue in the environment, warranting further investigation. Concentrations of 50 ppm and above are associated with more severe health risks, including more acute reactions, but the selection of 25 ppm as a dangerous threshold underscores the importance of monitoring and managing lower levels of CO to prevent cumulative, harmful exposure.