What is the permissible exposure limit for carbon monoxide (CO)?

• A. 5 PPM
• B. 35 PPM
• C. 100 PPM
• D. 50 PPM

Answer: (B)

CO exposure limits are set as a time-weighted average so workers aren’t exposed to harmful levels over a full workday. The value used in many navy safety references is 35 parts per million as an 8-hour time-weighted average. This relatively low limit reflects how CO binds to hemoglobin and reduces oxygen delivery, so even moderate, prolonged exposure can cause headaches, dizziness, or more serious effects. Among common standards, 35 ppm is the familiar REL used in safety training, whereas other figures like 50 ppm or 100 ppm come from different standards or shorter-term limits. Therefore, the permissible exposure limit is 35 ppm averaged over an 8-hour work period.