Ceiling values refer to

• A. The average concentration over an 8-hour work day.
• B. The concentration that should not be exceeded during any part of the working exposure.
• C. The level used to determine PPE requirement.
• D. The peak concentration during a 5-minute period.

Answer: (B)

Ceiling values refer to the concentration that should not be exceeded during any part of the working exposure. They’re meant to protect workers from acute effects by stopping exposure spikes in real time. This differs from a time-weighted average, which averages exposure over a full period (like 8 hours), potentially hiding brief peaks. It also differs from a short-term exposure limit, which allows a higher concentration for a defined short duration but still has a limit. The ceiling concept isn’t about determining PPE by itself; PPE decisions come from the overall exposure and controls in place. A brief 5-minute peak aligns more with short-term exposure concepts, not a true ceiling.