According to the ACGIH Guidelines for Heat Stress and Heat Strain: the Threshold Limit Value (TLV) for a job in the light workload category, with an 1-hour TWA metabolic rate of 180 Watts, is approximately 31.0 C WBGT. the Action Limit (AL) for a job in the moderate workload category, with an 1-hour TWA metabolic rate of 300 Watts, is approximately 25.0 C WBGT. O the Threshold Limit Value (TLV) for a job in the moderate workload category. with an 1-hour TWA metabolic rate of 300 Watts, is approximately 28.0 C WBGT. the Action Limit (AL) for a job in the light workload category, with an 1-hour TWA metabolic rate of 180 Watts, is approximately 28.0 C WBGT. all of the above are correct, and. technically, an AL and TLV can be mathematically calculated to determine exposure limits for jobs at any metabolic rate