Permissible Exposure Limit (PEL) for ammonia is?

• A. 100 PPM averaged over an eight hour work day
• B. 50 PPM averaged over a 24 hour period
• C. 50 PPM averaged over an eight hour work day
• D. 5 PPM averaged over eight hours

Answer: (C)

A Permissible Exposure Limit is the maximum average airborne concentration a worker can be exposed to during a standard work shift without adverse health effects. For ammonia, this limit is 50 parts per million as a time-weighted average over an eight-hour day. That means the exposure averaged across the whole shift should not exceed 50 ppm to be considered compliant.

Why this matters: the PEL is about an 8-hour shift, not a single moment or a full 24 hours. The option that uses a 24-hour period would not represent how OSHA regulates occupational exposure. A value like 5 ppm is far below the actual limit and would imply more stringent protection than required. A higher value like 100 ppm would exceed the standard exposure limit when averaged over eight hours, which is not allowed. There is also a separate short-term exposure limit for brief peaks, which is higher than the eight-hour PEL, but that does not replace the eight-hour average.