Subpart Z
The 8-hour TWA for benzene in Table Z-2 is 10 ppm and the acceptable maximum peak above the acceptable ceiling is 50 ppm for up to 10 minutes during an 8-hour shift. See the benzene row in Table Z-2 at 1910.1000TABLEZ-2. If the benzene-specific standard at 1910.1028 applies to your operations, follow that standard instead of this Table Z-2 entry.
The benzene entry in Table Z-2 applies to industry segments that are exempt from the benzene standard at 1910.1028. See the benzene footnote in Table Z-2 at 1910.1000TABLEZ-2 for that limitation.
Table Z-2 lists an 8-hour TWA of 2 µg/m3, an acceptable ceiling of 5 µg/m3, and a peak of 25 µg/m3 for up to 30 minutes for beryllium and beryllium compounds. This Table Z-2 entry applies only where the beryllium standard at 1910.1024 is stayed or otherwise not in effect; see the footnote in Table Z-2.
If a substance has its own OSHA-specific standard, employers must follow that specific standard unless that specific standard is stayed or otherwise not in effect—only then does the Table Z-2 entry apply. For example, Table Z-2 applies to cadmium only when the cadmium standard at 1910.1027 is stayed or not in effect, and the chromium entry applies only when the Chromium (VI) standard at 1910.1026 is stayed or not in effect; see the footnotes in Table Z-2 at 1910.1000TABLEZ-2.
The notation means formaldehyde is governed by its own specific standard, so employers must follow the formaldehyde standard at 1910.1048 rather than relying on a Table Z-2 value. See the formaldehyde row in Table Z-2 at 1910.1000TABLEZ-2.
When Table Z-2 lists only an "acceptable ceiling concentration," employers must ensure worker exposure does not exceed that ceiling at any time; there is no 8-hour TWA listed in that row. For example, chromic acid (as CrO3) has a ceiling of 1 mg/10 m3 in Table Z-2 at 1910.1000TABLEZ-2. If a substance also has a current specific standard (e.g., 1910.1026 for Chromium (VI)), follow that specific standard when it is in effect.
The unit “mg/10m3” means milligrams per 10 cubic meters; to convert to the common mg/m3 unit, divide by 10 (so 1 mg/10m3 equals 0.1 mg/m3). This unit appears in entries such as chromic acid and mercury in Table Z-2 at 1910.1000TABLEZ-2.
If Table Z-2 specifies a maximum peak with a time and a frequency qualifier (for example, "5 minutes in any 3 hrs."), the employer must ensure that any excursion above the ceiling does not exceed that peak concentration and that the excursion durations and frequency limits are met—for example, no single excursion longer than 5 minutes and not more often than allowed by the "in any 3 hrs." restriction. See the specific entries and their time/frequency limits in Table Z-2 at 1910.1000TABLEZ-2.
That Table Z-2 entry means a single 10-minute peak up to the listed maximum is allowed once per shift—and only if there are no other measurable exposures above the acceptable ceiling during that shift. Employers must ensure no additional excursions occur and must otherwise keep exposures below the ceiling. See the hydrogen sulfide entry in Table Z-2 at 1910.1000TABLEZ-2.
No—short-term peaks do not raise the 8-hour TWA allowable limit. The 8-hour TWA limit must be met across the shift, and any permitted short-term peaks must also meet the listed peak concentration and duration limits in Table Z-2 at 1910.1000TABLEZ-2. Employers must control both TWA and any short-term excursions as specified.
When Table Z-2 refers you to another rule, follow that rule: methylene chloride exposures are governed by 1919.52, so employers must comply with the requirements in that section for methylene chloride rather than rely on a Table Z-2 numeric entry. See the methylene chloride note in Table Z-2 at 1910.1000TABLEZ-2.
Table Z-2 lists an 8-hour TWA of 200 ppm for toluene, an acceptable ceiling of 300 ppm, and an acceptable maximum peak above the ceiling of 500 ppm for up to 10 minutes during an 8-hour shift. See the toluene row in Table Z-2 at 1910.1000TABLEZ-2.
When OSHA publishes and enforces a substance-specific standard, that standard governs exposures for covered operations; Table Z-2 entries apply only where the specific standard is stayed or not in effect as the footnotes state. Employers must comply with the current, operative OSHA standards—consult the specific standard URL (for example, 1910.1024 for beryllium) and Table Z-2 at 1910.1000TABLEZ-2 to determine which set of limits applies.
Table Z-2 gives carbon tetrachloride an 8-hour TWA of 10 ppm, an acceptable ceiling of 25 ppm, and an acceptable maximum peak above the ceiling of 200 ppm for up to 5 minutes in any 4 hours. That means each allowed peak may be up to 5 minutes long and such peaks are limited to the frequency implied by "in any 4 hrs."—see the carbon tetrachloride entry in Table Z-2 at 1910.1000TABLEZ-2.
Yes. If a Table Z-2 row lists an acceptable ceiling but no permitted peak, employers must prevent any excursions above that ceiling; no peak above the ceiling is authorized. See examples in Table Z-2 at 1910.1000TABLEZ-2.
Table Z-2 lists styrene with an 8-hour TWA of 100 ppm, an acceptable ceiling of 200 ppm, and an acceptable maximum peak above the ceiling of 600 ppm for up to 5 minutes in any 3 hours. See the styrene entry in Table Z-2 at 1910.1000TABLEZ-2.
Yes—Table Z-2 contains OSHA PELs (time-weighted averages, ceilings, and permitted peak excursions where shown) and is part of the permissible exposure limits in 29 CFR 1910.1000; view the detailed Table entries at 1910.1000TABLEZ-2. Employers must use these PELs unless a specific substance standard applies to their operation.
Table Z-2 lists an 8-hour TWA of 50 ppm for ethylene dichloride, an acceptable ceiling of 100 ppm, and a permitted peak of 200 ppm for up to 5 minutes in any 3 hours. See the ethylene dichloride entry in Table Z-2 at 1910.1000TABLEZ-2.
Table Z-2 lists an 8-hour TWA of 0.2 mg/m3 for cadmium dust (ceiling 0.6 mg/m3) and 0.1 mg/m3 for cadmium fume (ceiling 0.3 mg/m3). These Table Z-2 values apply only where the cadmium standard at 1910.1027 is stayed or otherwise not in effect, per the footnote in Table Z-2 at 1910.1000TABLEZ-2.
The employer must prevent exposures from exceeding the limits shown in Table Z-2—both the ceiling and any specified short-term peak. If an excursion would exceed either, the employer must implement engineering controls, work practices, or respiratory protection to reduce exposures to within the Table Z-2 limits. See the applicable exposure limits in Table Z-2 at 1910.1000TABLEZ-2 and the general duty to comply with OSHA standards under 29 CFR 1910.
Table Z-2 lists methyl chloride with an 8-hour TWA of 100 ppm, an acceptable ceiling of 200 ppm, and an acceptable maximum peak above the ceiling of 300 ppm for up to 5 minutes in any 3 hours. See the methyl chloride row in Table Z-2 at 1910.1000TABLEZ-2.