Threshold Values (Nilai Ambang Batas, NAB) are 8 hour Time Weighted Average, TWA values based on a 40 hour work week. This regulation contains the time-weighted average of the Permissible Level of the chemical substance in the workplace air, in which there are workers who might be exposed to the chemical substance on a day-to-day basis for not more than 8 hours per day or 40 hours per week.