![]() ![]() The effect of this screen on sampler efficiency is currently being studied by NIOSH. One sampler manufacturer has recently introduced a sampler with an inlet port shield by a perforated screen. NIOSH's HHE Report 94-0122-2578 used a deflector and found the device to be ineffective at shielding the sampler from abrasive blast grit. The effects of simply putting a deflector of unknown specifications at the opening of a sampling train are not well studied. The Agency's Salt Lake Technical Center is closely following the efforts to reach a consensus of which sampler configuration best represents the exposure of occupational concern. The Agency is aware of the continuing discussion of the particle-size-dependent efficiency of the different sampling devices and of the human body at inhalation or ingestion. OSHA adopted its current particulate methodology based upon a general consensus at the time. Further information is described in OSHA's Technical Manual, TED 1.15, Section 1, Chapter 1, a copy of which is enclosed for your convenience. The sampling procedure followed by OSHA Compliance Officers is to place the cassette outside of all personal protective equipment. There is specific information on analytical and sampling procedures listed by subject on the OSHA web site in the Chemical Information File, the OSHA Technical Manual, and the Analytical Methods. The collection efficiency of the sampler, in this case a 37mm closed face cassette containing a mixed cellulose ester filter, is assumed to represent the exposure of interest. Both of these errors are summed to derive the accuracy of the method of monitoring. Conventionally, the sampling error is plus-or-minus five percent to account for variations in pump flow. The analytical error is derived from both the recovery efficiency of the compound from the collection substrate and the precision of the analytical technique. The overall accuracy for monitoring, which is conducted in the field and analyzed in a laboratory, is customarily broken into two constituents: sampling and analytical error. The monitoring methods OSHA uses for lead, cadmium, and arsenic meet the accuracy requirements as stated in the standards. The study did not determine an effective method of sampling which would overcome this problem. It concluded that non-inhaleable particles of steel grit trapped in the cassette inflate the employee's airborne lead-exposure level. ![]() The HHE looked at the effect of blasting materials, specifically steel grit, on employee sampling results. The current, acceptable sampling method for determining employee exposure is to place the sampling cassette outside of all personal protective equipment. Measuring inside the shroud would create an artificially low exposure concentration as it would be composed of a mixture of the air passing out of the respirator and the contaminated air outside the hood. Therefore, while it is true that sampling inside the hood would eliminate particles driven into the cassette by the force of the blasting operation, it would also result in a measurement which is not representative of the employee's potential exposure. The standards were written to include protection from ingestion of these toxic metals. Particles which are too large to contribute to the employee's airborne exposure nevertheless contribute to the overall exposure through the potential for ingestion. Each of the standards you mentioned (Cadmium, Lead-in-Construction, and Arsenic) recognize ingestion as a route of exposure. This measurement will, in large part, determine the actions the employer must take to provide the employee with protection, such as appropriate personal protective equipment, medical monitoring, and hygiene facilities. Since OSHA is concerned with an employee's potential exposure, the cassette must also be located outside of any protective equipment. It should be as close as possible to the employee's nose and mouth, i.e., in a hemisphere forward of the shoulders within a radius of 6 to 9 inches. The correct placement for air sampling cassettes is near the breathing zone of the employee. Your questions, repeated below, related specifically to monitoring for abrasive blasting operations. We are in receipt of your letter of January 8, 1999, requesting assistance regarding exposure monitoring requirements for the Lead-in-Construction (.62), Arsenic (.1018), and Cadmium (.1027) Standards. ![]()
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