VOSHA
Safety and Health Standards for General Industry
1910.1000
Air Contaminants - Permissible Exposure Limits
(adopted from the 1989 OSHA PEL Project)
1910.1000 Air contaminants
An employee's exposure to any substance listed in Tables Z-1-A, Z-2 or Z-3 of this section shall be limited in accordance with the requirements of the following paragraphs of this section.
(a) Table Z-1-A:(Click here for a complete list of PELs)
(1) Substances in Transitional Limits Columns with Limits Preceded by "C" - Ceiling Values. An employee's exposure to any substance in Table Z-1-A under the Transitional Limits columns, the exposure limit of which is preceded by a "C", shall at no time exceed the exposure limit given for that substance in Table Z-1-A under the Transitional Limits columns.
(2) Other Substances in Transitional Limits Columns-8-hour Time Weighted Average. An employee's exposure to any substance in Table Z-1-A under the Transitional Limits columns, 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 Table Z-1-A under the Transitional Limits columns in any 8-hour work shift of a 40-hour work week.
(3) Final Rule Limits Columns. An employee's exposure to any substance listed in Table Z-1-A shall not exceed the Time Weighted Average (TWA), Short Term Exposure Limit (STEL) and Ceiling Limit specified for that substance in Table Z-1-A under the Revised Limits columns.
(4) Skin Designation. To prevent or reduce skin absorption, an employee's skin exposure to substances listed in Table Z-1-A with an "X" in one or both of the Skin Designation columns, the designation "Skin" following the substance name shall be prevented or reduced to the extent necessary in the circumstances through the use of gloves, coveralls, goggles, or other appropriate personal protective equipment, engineering controls or work practices.
(5) Definitions. The following definitions are applicable to the Final Rule Limits columns of Table Z-1-A:
(i) Time Weighted Average (TWA) is the employee's average airborne exposure in any 8-hour work shift of a 40-hour work week which shall not be exceeded.
(ii) short term exposure limit (STEL) is the employee's 15-minute time weighted average exposure which shall not be exceeded at any time during a work day unless another time limit is specified in a parenthetical notation below the limit. If another time period is specified, the time weighted average exposure over that time limit shall not be exceeded at any tine during the working day.
(iii) ceiling is the employee's exposure which shall not be exceeded during any part of the work day. 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 over a working day.
(6) Additional Definition. The terms "substance," "air contaminant," and "material" are equivalent in meaning for 29 CFR 1910.1000.
(b) Table Z-2:
Table Z-2 is applicable for the transitional period and to the extent set forth in paragraph (f) of this section.
(1) 8-hour time weighted averages. An employee's exposure to any material listed in Table Z-2, in any 8-hour work shift of a 40-hour work week, shall not exceed the 8-hour time weighted average limit given for that material in Table Z-2.
(2) Acceptable Ceiling Concentrations. An employee's exposure to a material listed in Table Z-2 shall not exceed at any time during an 8-hour shift the acceptable ceiling concentration limit given for the material 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 ceiling concentration for an 8-hour shift."
(3) Example. During an 8-hour work shift, an employee may be exposed to a concentration of Substance A (with a 10 ppm TWA, 25 ppm ceiling and 50 ppm peak) above 25 ppm (but never above 50 ppm) only for a maximum period of 10 minutes. Such exposure must be compensated by exposures to concentrations less than 10 ppm so that the cumulative exposure for the entire 8-hour work shift does not exceed a weighted average of 10 ppm
(c) Table Z-3:
Table Z-3 is applicable for the transitional period and to the extent set forth in paragraph (f) of this section. An employee's exposure to any substance listed in Table Z-3 in any 8-hour work shift of a 40-hour work week shall not exceed the 8-hour time weighted average limit given for that substance in the table.
(d) Computation formula:
The computation formula which shall apply to employee exposure to more than one substance for which 8-Hour time weighted averages are listed in Subpart Z of 29 CFR Part 1910 in order to determine whether an employee is exposed over the regulatory limit is as follows:
(1)
(i) The cumulative exposure for an 8-hour work shift shall be computed as follows:
E = (CaTa + CbTb ……… CnTn) ¸ 8
- Where: 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 1910 for the material involved.
(ii) To illustrate the formula prescribed in paragraph (d)(1)(i) of this section,, assume that Substance A has an 8-hour time weighted average limit of 100 ppm noted in Table Z-1-A. Assume that an employee is subject to the following exposure:
- Two hours exposure at 150 p/m
- Two hours exposure at 75 p/m
- Four hours exposure at 50 p/m
Substituting this information in the formula, we have:
(2x150 + 2x75 + 4x50) ¸ 8 = 81.25 p/m
Since 81.25 ppm is less than 100 ppm the 8-hour time weighted average limit, the exposure is acceptable.
(2)(i) In case of a mixture of air contaminants an employer shall compute the equivalent exposure as follows:
Em = (C1 ¸ L1 + C2 ¸ L2) + . . . (Cn ¸ Ln)
Where: 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) .
(ii) To illustrate the formula prescribed in paragraph (d)(2)(i) of this section, consider the following exposures:
| Material | Actual concentration of 8-hour exposure (ppm) | 8-hr. TWA PEL (ppm) |
| Substance B | 500 | 1,000 |
| Substance C | 45 | 200 |
| Substance D | 40 | 200 |
Substituting in the formula, we have:
Em = 500¸ 1,000 + 45¸ 200 + 40¸ 200
Em = 0.500 + 0.225 + 0.200
Em = 0.925
Since Em is less than unity (1), the exposure combination is within acceptable limits.
(e) To achieve compliance with paragraphs (a) through (d) of this section, administrative or engineering controls must first be determined and implemented whenever feasible. When such controls are not feasible to achieve full compliance, protective equipment or any other protective measures shall be used to keep the exposure of employees to air contaminants within the limits prescribed in this section. Any equipment and/or technical measures used for this purpose must be approved for each particular use by a competent industrial hygienist or other technically qualified person. Whenever respirators are used, their use shall comply with Section 1910.134.
(f) Effective dates; start-up dates and transitional provisions:
(1) Effective date: The effective date for the permissible exposure limits specified in the Final Rule Limits columns of Table Z-1-A is November 30 IV. 1990.
(2) Start-up dates:
(i) The permissible exposure limits specified in the Final Rule Limits columns of Table Z-1-A shall be achieved by any reasonable combination of engineering controls, work practices and personal protective equipment effective November 30, 1990, through December 30, 1992.
(ii)
(a) The permissible exposure limits specified in the Final Rule Limits columns of Table Z-1-A shall be achieved by the methods of compliance specified in paragraph (e) of this section effective December 31, 1992, if by December 31, 1991 a final rule has been published in the Federal Register amending or determining not to amend paragraph (e) of this section.
(b) If no final rule has been published in the Federal Register by December 31, 1991, amending or determining not to amend paragraph (e) of this section, then the permissible limits specified in the Final Rule Limits columns of Table Z-1-A shall be achieved by the methods of compliance specified by paragraph (e) of this section effective December 31, 1993, and paragraph (f)(2)(i) of this section shall remain in effect through December 30, 1993.
(iii) The skin designations in the Final Rule Limits columns become effective September 1, 1989. The skin designations in the Transitional Limits columns are in effect from March 1, 1989 through November 30, 1990.
(3) Transitional provisions:
(i) The permissible exposure limits specified in the Transitional Limits column of Table Z-1-A, Table Z-2 and Table Z-3 shall continue to be achieved by the methods of compliance specified in paragraph (e) of this section through December 30, 1992. If paragraph (f)(2)(ii)(b) of this section takes effect, this provision is extended through December 30, 1993.
(ii) The permissible exposure limits specified in the Transitional Limits column of Table Z-1-A, Z-2 and Z-3 shall be applicable to the extent cross referenced in 29 CFR 1915, 1917 and 1918.
(iii) If any new or amended provisions or new or revised limits for any substance or substances are either administratively stayed or judicially stayed or vacated, then the existing provisions or limits for those substances specified in the Transitional Limits columns of Table Z-1-A, Table Z-2 or Table Z-3 shall remain in effect until such stay is lifted, or in definitely, if the limit is vacated.
(4) Enforcement of the limits are indefinitely stayed for: aluminum alkyls; ethylidine norbornene; hexafluoroacetone; mercury (alkyl compounds); oxygen difluoride; phenylphosphine; and sulfur pentafluoride; until OSHA publishes in the Federal Register a notice that a sampling and analytical technique is available.