OSHA permissible exposure limit for carbon monoxide over an eight hour period is:

OSHA permissible exposure limit for carbon monoxide over an eight hour period is:

• A. 10 ppm
• B. 25 ppm
• C. 50 ppm
• D. 100 ppm

Answer: (C)

OSHA controls carbon monoxide exposure using an eight-hour time-weighted average, and the value for CO is 50 parts per million. This means the average concentration workers can be exposed to over a full 8-hour shift should not exceed 50 ppm; if exposure averages higher, protective measures are needed to bring it down. Carbon monoxide is dangerous because it binds to hemoglobin, reducing oxygen delivery to tissues, so keeping exposures at or below this level helps prevent symptoms like headaches, dizziness, and fatigue. There is also a separate short-term limit (a higher concentration allowed for a brief period), but the eight-hour standard is the one applied to normal work shifts. The other numbers listed aren’t the eight-hour OSHA limit: 10 ppm and 25 ppm are well below the limit, and 100 ppm would exceed it.

OSHA controls carbon monoxide exposure using an eight-hour time-weighted average, and the value for CO is 50 parts per million. This means the average concentration workers can be exposed to over a full 8-hour shift should not exceed 50 ppm; if exposure averages higher, protective measures are needed to bring it down. Carbon monoxide is dangerous because it binds to hemoglobin, reducing oxygen delivery to tissues, so keeping exposures at or below this level helps prevent symptoms like headaches, dizziness, and fatigue. There is also a separate short-term limit (a higher concentration allowed for a brief period), but the eight-hour standard is the one applied to normal work shifts. The other numbers listed aren’t the eight-hour OSHA limit: 10 ppm and 25 ppm are well below the limit, and 100 ppm would exceed it.