OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at https://www.osha.gov.

March 21, 2019

Ms. Pamela Persaud
Safety Links
1855 W. SR 434 STE 283
Longwood, Florida 32750

Dear Ms. Persaud:

Thank you for your letter to the Occupational Safety and Health Administration's (OSHA) Directorate of Enforcement Programs. You have requested clarification regarding the monitoring requirements in OSHA's Respirable Crystalline Silica (RCS) standard for general industry, 29 CFR 1910.1053. This letter constitutes OSHA's interpretation only of the requirements discussed and may not be applicable to any question not delineated within your original correspondence. Your paraphrased question and our response are below.

Background: In your letter, you state that you provide industrial hygiene services to a client that has workers who perform abrasive blasting. The client has implemented substitution and engineering controls, such as replacing the blasting media and isolating the area, as well as administrative and housekeeping measures, such as wetting down the areas, putting up boundaries, and minimizing the number of employees in the area during blasting. The employees also use airline respirators (blasting hoods with an assigned protection factor of 1,000) and full body suits.

In addition, you reference the following information from the RCS standard in your letter:

29 CFR 1910.1053(d)(3)(iv) Where the most recent exposure monitoring indicates that employee exposures are above the PEL, the employer shall repeat such monitoring within three months of the most recent monitoring.
29 CFR 1910.1053(d)(6)(ii) Whenever an exposure assessment indicates that employee exposure is above the PEL, the employer shall describe in the written notification the corrective action being taken to reduce employee exposure to or below the PEL.

You were contacted by my staff for further clarification and you explained that the employees work in a large open space and clean and polish very large pieces of pre-cast concrete, using beaded glass as the blasting media. You also stated that the employer has conducted exposure monitoring on a few occasions during blasting, and that these monitoring data demonstrate that employees' 8-hour time-weighted average (TWA) exposures are consistently above the permissible exposure limit (PEL) for silica. Employee exposures are controlled to below the action level (AL) by use of airline respirators.

Question: Does the employer still have to monitor employees every three months, given that the sampling results will probably not vary significantly for the follow-up exposure measurements (i.e., they will still exceed the PEL without the use of airline respirators)?

Response: Under the RCS standard's scheduled monitoring option, employers must conduct initial monitoring to assess the 8-hour TWA exposure for each employee, on the basis of one or more personal breathing zone air samples that reflect the exposures of employees on each shift, for each job classification, and in each work area; employers must then conduct follow-up monitoring at specified intervals, based upon the results of the initial monitoring. 29 CFR 1910.1053(d)(3). If your client chooses to proceed under the scheduled monitoring option in 29 CFR 1910.1053(d)(3), monitoring must be performed every three months as long as exposures remain above the PEL. 29 CFR 1910.1053(d)(3)(iv). However, your client could switch from the scheduled monitoring option to the performance option in 29 CFR 1910.1053(d)(2), provided that the air monitoring data your client has collected are sufficient to accurately characterize current employee exposures. See 81 FR 16763 (March 25, 2016). Whether an employer's air monitoring data accurately reflect current exposures depends on several factors, including the degree to which exposures vary by day, shift, or process; the work practices used; and the condition of the equipment. Where an employer uses the performance option or the scheduled monitoring option and finds exposures to be above the PEL after implementing all feasible engineering and work practice controls, the employer is required to provide the appropriate level of respiratory protection, per 29 CFR 1910.1053(g)(1)(iii). You might also find it helpful to review the Frequently Asked Questions (FAQs) for occupational exposure to RCS in general industry on OSHA's website,1 specifically FAQ 7.

Both the performance and scheduled monitoring options in the RCS standard require that the employer reassess employee exposures following any changes in the production, process, control equipment, personnel, or work practices that may reasonably be expected to result in new or additional exposures to RCS at or above the AL, or when the employer has any reason to believe that new or additional exposures at or above the AL have occurred. 29 CFR 1910.1053(d)(4). OSHA's response to FAQ 15 in the general industry RCS FAQs1 provides additional information on an employer's ongoing duty to assess employee exposures under the performance option.

Thank you for your interest in occupational safety and health. We hope you find this information helpful. OSHA's requirements are set by statute, standards, and regulations. Our letters of interpretation do not create new or additional requirements but rather explain these requirements and how they apply to particular circumstances. This letter constitutes OSHA's interpretation of the requirements discussed. From time to time, letters are affected when the Agency updates a standard, a legal decision impacts a standard, or changes in technology affect the interpretation. To assure that you are using the correct information and guidance, please consult OSHA's website at www.osha.gov.

If you have any further questions, please feel free to contact the Office of Health Enforcement at (202) 693-2190.



Patrick J. Kapust, Acting Director
Directorate of Enforcement Programs

1 Occupational Exposure to Respirable Crystalline Silica 29 C.F.R., § 1910.1053, Frequently Asked Questions for General Industry, January 2019, https://www.osha.gov/dsg/topics/silicacrystalline/generalindustry_info_silica.html.