- Part Number:1910
- Part Number Title:Occupational Safety and Health Standards
- Subpart:1910 Subpart Z
- Subpart Title:Toxic and Hazardous Substances
- Standard Number:
- Title:Air contaminants.
- GPO Source:
Substances with limits preceded by "C"—Ceiling Values. An employee's exposure to any substance in Table Z-1, the exposure limit of which is preceded by a "C", shall at no time exceed the exposure limit given for that substance. If instantaneous monitoring is not feasible, then the ceiling shall be assessed as a 15-minute time weighted average exposure which shall not be exceeded at any time during the working day.
Other substances—8-hour Time Weighted Averages. An employee's exposure to any substance in Table Z-1, the exposure limit of which is not preceded by a "C", shall not exceed the 8-hour Time Weighted Average given for that substance in any 8-hour work shift of a 40-hour work week.
Acceptable ceiling concentrations. An employee's exposure to a substance listed in Table Z-2 shall not exceed at any time during an 8-hour shift the acceptable ceiling concentration limit given for the substance in the table, except for a time period, and up to a concentration not exceeding the maximum duration and concentration allowed in the column under "acceptable maximum peak above the acceptable ceiling concentration for an 8-hour shift."
E = (Ca Ta+Cb Tb+. . .Cn Tn)÷8
E is the equivalent exposure for the working shift.
C is the concentration during any period of time T where the concentration remains constant.
T is the duration in hours of the exposure at the concentration C.
The value of E shall not exceed the 8-hour time weighted average specified in subpart Z of 29 CFR part 1910 for the substance involved.
Two hours exposure at 150 ppm
Two hours exposure at 75 ppm
Four hours exposure at 50 ppm
Substituting this information in the formula, we have
(2 × 150 + 2 × 75 + 4 × 50) ÷8 = 81.25 ppm
Since 81.25 ppm is less than 100 ppm, the 8-hour time weighted average limit, the exposure is acceptable.
Em=(C1÷L1+C2÷L2)+. . .(Cn÷Ln)
Em is the equivalent exposure for the mixture.
C is the concentration of a particular contaminant.
L is the exposure limit for that substance specified in subpart Z of 29 CFR part 1910.
The value of Em shall not exceed unity (1).
To illustrate the formula prescribed in paragraph (d)(2)(i) of this section, consider the following exposures:
|Substance||Actual concentration of 8-hour exposure (ppm)||8-hour TWA PEL (ppm)|
Substituting in the formula, we have:
Since Em is less than unity (1), the exposure combination is within acceptable limits.
[71 FR 16673, April 3, 2006; 81 FR 16861, March 25, 2016]