What is the term 'ceiling value' in exposure limits?

• A. A concentration that should not be exceeded on average over the shift.
• B. A concentration that should never be exceeded during any part of the work shift.
• C. A concentration that should not be exceeded at the end of the shift.
• D. A concentration measured as a 10-minute average.

Answer: (B)

The concept being tested is how a ceiling exposure limit works. A ceiling limit is an absolute instantaneous threshold: the concentration should never be exceeded at any time during the work shift. It is more stringent than limits that are based on averaging over a period, such as an 8-hour time-weighted average, or short-term exposure limits that apply to brief intervals like a 15-minute window. If a spike occurs even briefly, it violates the ceiling limit, triggering immediate corrective action to bring exposure down. The other options describe averages over time or limits tied to a specific end point or short interval, which do not capture the idea of “never exceed at any moment.”