TLV/TWA describes the maximum concentration a person may be exposed to for how long?

TLV/TWA describes the maximum concentration a person may be exposed to for how long?

• A. The max exposure for 24 hours
• B. The max exposure for 15 minutes
• C. The maximum exposure that should never be exceeded
• D. The max exposure for 8 hours per day/40 hours per week

Answer: (D)

Time-weighted average captures the average airborne concentration a worker can be exposed to over a standard work period. For TLV/TWA, that standard period is eight hours per day, averaged over forty hours per week. It reflects how the body tolerates exposure when concentration may vary during the workday, by ensuring the overall average stays within safe limits. If exposure rises above this level but only for a short time, that would fall under a short-term exposure limit, which covers about 15 minutes. A limit that should never be exceeded at any moment is a ceiling value, which is a different concept. So the eight-hour day and forty-hour week is the correct interpretation.

Time-weighted average captures the average airborne concentration a worker can be exposed to over a standard work period. For TLV/TWA, that standard period is eight hours per day, averaged over forty hours per week. It reflects how the body tolerates exposure when concentration may vary during the workday, by ensuring the overall average stays within safe limits. If exposure rises above this level but only for a short time, that would fall under a short-term exposure limit, which covers about 15 minutes. A limit that should never be exceeded at any moment is a ceiling value, which is a different concept. So the eight-hour day and forty-hour week is the correct interpretation.