ABSTRACT
Determination of Compliance for Air Quality Standards. The following procedures and policies shall be followed to determine compliance with air quality standards (“Permissible Exposure Limits” or PELs).
Personal Exposure.
The determination of noncompliance with PELs requires measurement and documentation of an overexposure to at least one employee. For air contaminants having PELs sampling must be conducted within the breathing zone. (Some standards; e.g., beryllium and cotton dust, may necessitate area sampling.) OSHA defines the breathing zone to be a sphere approximately 2 ft in diameter surrounding the head.
In some instances (e.g., substances in 29 CFR 1910. 1002-1014) personal sampling is not necessary to establish the presence of the material in order to substantiate a violation.
Full-Shift Sampling. To eliminate error associated with fluctuations in exposure, full-shift sampling for air contaminants shall be conducted.
Full-shift sampling is defined to be a minimum of the total time of the shift less 1 hr; e.g., 7 hr of an 8-hr workshift or 9 hrs of a 10-hr workshift. Every attempt shall be made to sample the greatest exposure periods. Such exposure may occur during set-up and take-down.
Pumps may be changed to avoid pump failure due to excessive sampling periods.
Single or multiple samples should be taken to determine any 8 hr of exposure for comparison with the PEL. A separate sample should be used to determine any additional exposure beyond 8 hrs. (See Chapter XIII, Modification of PELs for Prolonged Exposure Periods.)
Calculation of Time-Weighted Average (TWA) Exposures.
Full-Shift Sampling (e.g., 7 hr or more for an 8 hr shift).
Professional judgment is necessary for making any conclusions or assumptions regarding the unsampled period (i.e. the set-up and/or take-down time which is not to exceed 1 hr). For example, if the workshift is 8 hr, and sampling was conducted for 7 hr and 15 min, the Industrial Hygienist needs to make some professional judgment regarding the unsampled 45-min period.
A zero exposure shall be assumed unless the Industrial Hygienist can defend a professional judgment on the magnitude of the exposure for the unsampled period. Thus, a TWA should generally be calculated by dividing the sample results by 8 hr rather than the actual time sampled.
274Given sufficient information, a professional judgment on estimated exposure for the unsampled period could be defended.
For example, if an 8-hr operation is continuous and the concentration of the substance would not be likely to vary substantially due to the process; and if the employee by virtue of the job could be assumed to be exposed continuously to essentially the same concentration, it would then be acceptable to assume that the exposure for the unsampled time would be the same as that measured for the actual sample time.
In this situation it would be acceptable to calculate a TWA by dividing the sample results by the actual time sampled and compare the resulting TWA with the 8-hr standard.
The Industrial Hygienist should carefully document the rationale for any professional judgment regarding unsampled exposure periods.
b. Less than Full-Shift Sampling (e.g., less than 7 hr of an 8-hr shift). If the employee is exposed for less than 7 hr, or if less than a 7-hr sample is collected, the unsampled time shall be calculated as zero exposure, and the sample results shall be divided by 8 hr. A determination that an employer is in compliance shall not be made in this case unless the sampled period is representative of the employee's normal exposure.
Grab Sampling for 8-Hr TWA Determination. If technology has not been developed to allow full-shift sampling, a series of “grab” or “spot” samples taken randomly throughout the workshift is acceptable. A defensible statistical approach should be used to design the sampling strategy. Assistance from the Assistant Regional Administrator (ARA) for Technical Support may be required.
Prolonged Work Shifts. To arrive at an adjusted PEL for prolonged exposures in excess of 8 hr, see Chapter XIII.
Lunchbreaks.
Generally it is not advisable to sample during lunch breaks unless lunches are eaten in areas where significant exposure exists. In most cases, the pump should simply be turned off by the Industrial Hygienist prior to lunch, and then turned on again after lunch.
Generally it is not necessary to remove the pump unless the employee leaves the company premises. Care should be taken to assure that contamination of the collection medium does not occur (i.e. the sample should be capped and/or removed).
If the pump is turned off for lunch, the time it is off should not be counted as sample time for calculation of the TWA.
Collection and Analytical Methods. All industrial hygiene samples must be collected and analyzed using OSHA standard methods, where available, or by methods developed in consultation with or approved by the Salt Lake City Analytical Laboratory (SLCAL). (See Chapter IX, Analytical Laboratory Policies and Procedures.)
Interpretation of 29 CFR 1910.1000, Tables Z-l, Z-2, and Z-3. Guidance 275regarding interpretation of Tables Z-1, Z-2, and Z-3 should be sought from the Regional Office.
Interpretation of 29 CFR 1910.1000, Table Z-1—Ceiling Standards. Materials in Table Z-1 of 29 CFR 1910.1000 preceded by a “C” are ceiling limits which theoretically should never be exceeded even instantaneously. Practically, the Industrial Hygienist should generally use a 15-min sampling period to evaluate compliance with ceiling standards, unless direct-reading instrumentation or methods with sufficient analytical accuracy are available.
Interpretation of Table Z-2.
Materials in Table Z-2 have both “acceptable ceiling concentrations" (column 2) and “maximum peak concentrations" (column 3) up to which exposures are allowed for the period specified in column 4. Generally a 15-min sample is used by OSHA to evaluate ceiling limits due to analytical accuracy.
All the time periods specified in column 4 are less than 15 min with the exception of beryllium, formaldehyde, and carbon disulfide. Therefore, if a 15-min continuous exposure (minus total error, see paragraph A. 11.) exceeds the ceiling value in column 2, noncompliance is established.
Where less than a 15-min sample is taken, a citation may be issued if one of two conditions exists:
Column 2 is exceeded and the sampling time is beyond the time allowed by column 4.
Column 3 is exceeded even instantaneously.
For the exceptions of beryllium, formaldehyde, and carbon disulfide, a continuous sample period in excess of 30 min should be used. If the exposure found exceeds the ceiling values in column 2, noncompliance is established.
The last two entries in Table Z-2, “mercury” and “chromic acid and chromates”, should be considered as 8-hr TWA standards and not ceiling standards.
Interpretation of Table Z-3.
The “talc (fibrous)” standard should not be enforced under der 29 CFR 1910.1000. Talc-containing tremolite (or any other “asbestos” as defined by 29 CFR 1910.1001(a)) shall be enforced under the asbestos standard, provided the laboratory can verify the presence of “tremolite fibers” or any other asbestos fibers.
The nuisance dust standard applies to both organic and inorganic dusts. The standard should not be used when evaluating an exposure to a substance listed in Table Z-1, Z-2, or Z-3.
Where toxicity information exists for a substance with no PEL and a serious hazard exists below the nuisance dust standard, a citation under Section 5(a)(1) of the Act should be considered.
In this case where the nuisance dust PEL is insuffi-
cient to protect the employee, correction for the 5(a)(1) citation will consist of requiring reduction of exposure to appropriate levels.Where the employee is exposed to combinations of silica dust (i.e. quartz, cristobalite, and tridymite), the additive effects of the mixture will be considered, as detailed in 29 CFR 1910.1000(d)(2).
276(a) For the PEL calculation specified in Table Z-3, the percent silica will be determined by doubling the percentage of cristobalite and/or tridymite and adding it to the percentage of quartz, according to the following formula. The PEL mixture pertains to the respirable fraction.
