OAR 437-003-1000: Oregon Rules for Air Contaminants

An employee's exposure to any substance listed in Oregon Tables Z-1, Z-2, or Z-3 of this section shall be limited in accordance with the requirements of the following paragraphs of this section. (1) Oregon Table Z-1. (a) Substances with limits preceded by "C" – Ceiling Values. An employee's exposure to any substance in Oregon 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. (b) Other substances – 8-hour Time Weighted Averages. An employee's exposure to any substance in Oregon 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. (c) Other Substances – Excursion Limits. Excursions in worker exposure levels may exceed 3 times the PEL-TWA for no more than a total of 30 minutes during a workday, and under no circumstances should they exceed 5 times the PEL-TWA, provided that the PEL-TWA is not exceeded. (d) Skin Designation. To prevent or reduce skin absorption, an employee's skin exposure to substances listed in Oregon Table Z-1 with an "X" in the Skin Designation column 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. (2) Oregon Table Z-2. An employee's exposure to any substance listed in Oregon Table Z‑2 shall not exceed the exposure limits specified as follows: (a) 8-hour time weighted averages. An employee's exposure to any substance listed in Oregon 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 substance in Oregon Table Z-2. (b) Acceptable ceiling concentrations. An employee's exposure to a substance listed in Oregon Table Z-2 shall not exceed the acceptable ceiling concentration for the given substance in the table at any time during an 8-hour shift except: Acceptable maximum peak above the acceptable ceiling concentration for an 8-hour shift. An employee’s exposure to a substance listed in Oregon Table Z-2 shall not exceed the acceptable maximum peak above the acceptable ceiling concentration, and shall not exceed the maximum duration for the given substance during an 8-hour shift. (c) Example. During an 8-hour work shift, an employee exposed to benzene may be exposed to an 8-hour time weighted average (TWA) of 10 ppm. Concentrations of benzene during the 8-hour work shift may not exceed 25 ppm, unless that exposure is no more than 50 ppm and does not exceed 10 minutes during an 8-hour work shift. Such exposures must be compensated by exposures to concentrations below 10 ppm so that the 8-hour time-weighted average is less than 10 ppm. [Oregon Table Example] (d) Skin Designation. To prevent or reduce skin absorption, an employee’s skin exposure to substances listed in Oregon Table Z-2 with an “X” in the Skin Designation column 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. (3) Oregon Table Z-3. An employee's exposure to any substance listed in Oregon 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. (4) Computation formulae. The computation formula which shall apply to employee exposure to more than one substance for which 8-hour time weighted averages are included in OAR 437, Division 2/Z, Toxic and Hazardous Substances, in order to determine whether an employee is exposed over the regulatory limit is as follows: (a) Cumulative Exposures. (A) The cumulative exposure for an 8-hour work shift shall be computed as follows: E = (CaTa + Cb Tb +... 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 remain 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. (B) To illustrate the formula prescribed in paragraph (4)(a)(i) of this section, assume that Substance A has an 8-hour time weighted average limit of 100 ppm (Oregon Table Z-1). Assume that an employee is subject to the following exposure: 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 [(2x150) + (2x75) + (4x50)] ¸ 8 = 81.25 ppm Since 81.25 ppm is less than 100 ppm, the 8-hour time weighted average limit, the exposure is acceptable. (b) Mixtures. (A) 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). (B) To illustrate the formula prescribed in paragraph (4)(b)(i) of this section, consider the following exposures: [Oregon Table Z 2.1] Substituting in the formula, we have: Em = (500 ¸ 1000) + (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. (5) To achieve compliance with paragraphs (1) through (4) 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 1910.134. [Table Z-1, Notes, Footnotes; Table Z-2, Note, Footnotes; Table Z-3, Notes, Footnotes.] [ED. NOTE: To view attachments referenced in rule text, click here to view rule.]