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.

April 15, 2021

Mr. Henry McDermott, President
H.J. McDermott, Inc
128 Longfield Place
Moraga, CA 94556-2127

Dear Mr. McDermott:

Thank you for your letter to the Occupational Safety and Health Administration (OSHA). You requested clarification regarding whether a powered-air purifying respirator (PAPR) with an assigned protection factor (APF) of 1,000 used in welding operations is allowed under the Respiratory Protection standard, 29 CFR § 1910.134, Footnote 4.1 This letter constitutes OSHA's interpretation only of the requirements discussed and may not be application to any question not delineated within your original correspondence. Your paraphrased questions and our responses below.

Question 1: Does OSHA play any part in the testing of devices or the evalutation of data developed and/or submitted by respirator manufacturers that the manufacturers use to justify an APF of 1,000 for PAPR welding helmets?

Response: No, OSHA does not test, approve, or certify any personal protective equipment, including respiratory protection. OSHA's 2006 APF final rule (71 FR 50121-50192, August, 2006) states, "Consistent with Section 5 of the OSH Act (29 U.S.C. 654), which places the responsibility for employee protection on employers, Footnote 4 in the final rule clearly places the responsibility for proper respirator selection on employers. Accordingly, employers may use a respirator at an APF of 1,000 only [emphasis added] when they have appropirate test results provided by the respirator manufacturer demonstrating that the respirator performs at a protection level of 1,000 or greater."2 The employer could gather the evidence either from the manufacturer or from an independent testing facility. In addition, the employer shall ensure that the respirator is used in accordance with the manufacturer's specifications to attain the APF of 1,000.

Question 2: If the answer to the question one is "yes," is there a written summary of OSHA's program or procedures relating to the APF of 1,000 designated in the Federal Register or other written format?

Response: OSHA does not have a program of procedure that summarizes the APF of 1,000 designation.

Question 3: Has OSHA issued any specific guidance on what would, or would not, meet the requirements in Footnote 4 for "evidence provided by the respirator manufacturer that testing of these respirators demonstrates performance at a level of protection of 1,000 or greater, other than the current wording in Footnote 4?"

Response: Evidence for APF typically comes from workplace protection factor (WPF) and/or simulated workplace protection factor (SWPF) studies. WPF studies are conducted under actual conditions of use in the workplace that measure the protection provided by the properly selected, fit-tested, and functioning respirator, when the respirator is worn correctly, and used as part of a comprehensive respirator program that is in compliance with OSHA's Respiratory Protection standard, 29 CFR § 1910.134. Measurements of the concentration of an airborne contaminant outside (Co) the respirator and the concentration inside (Ci) the respirator are obtained only while the respirator is being worn during the performance of normal work tasks (i.e., samples are not collected when the respirator is not being worn). As the degree of protection afforded by the respirator increases, the WPF increases. SWPF studies are conducted in a controlled laboratory setting, in which the C0 and Ci sampling are performed while the respirator user performs a series of set exercises. The lab setting is used to control many of the variables found in workplace studies, while the exercises simulate the work activies of respirator users. This type of study is designed to determine the optimum performance of respirators by reducing the impact of sourcess of variabliity through maintenance of tightly controlled study conditions.

Question 4: Does OSHA maintain a list of PAPR welding helmets with APFs of 1,000 that is separate from the NIOSH listing of approved respirators?

Response: No, OSHA does not maintain such a list. However, the National Institute for Occupational Safety and health (NIOSH), National Personal Protective Technology Laboratory (NPPTL), does have an online Certified Equipment List of approved respirators. This list can be used to help determine if the respirators being used or considered are NIOSH-certified and appropriate for the hazard(s) they are exposed to.3 The NIOSH certified Equipment List can be found, at:

Question 5: Is there any other information on points that we have not considered (based on our questions) that might be helpful to us as we investigate use of APFs of 1,000 for welding helmets to protect our welders?

Response: Please refer to OSHA's Assigned Protection Factors for the Revised Respiratory Protection Standard (OSHA 3352-02 2009), at: www.osha.gov/sites/default/files/publications/3352-APF-respirators.pdf, or the NIOSH Respirator Selection Logic Guide (2004), at: www.cdc.gov/niosh/docs/2005-100/pdfs/2005-100.pdf, for more information on APFs.

As you may be aware, California is one of 26 states plus Puerto Rico and the Virgin Islands that operates its own occupational safety and health program under a plan approved aned monitored by federal OSHA. Employers in California must comply with state occupational safety and health requirements. As a condition of plan approval, State Plans are required to adopt and enforce occupational safety and health standards that are at least as effective as those promulgated by federal OSHA. A state's interpretation of its standard must also be at least as effective as federal OSHA interpretations. If you would like to further information regarding California's occupational safety and health requirements, you may contact the state's Division of Occupational Safety and Health at:

Division of Occupational Safety and Health
1515 Clay Street, Suite 1901
Oakland, California, 94612
Phone: (510) 286-7000
Fax: (510) 286-7037

Thank you for your interest in occupational safety and health. I hope you find this information helpful. OSHA's requirements are set by statute, standards, and regulations. 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 https://www.osha.gov. If you have any questions feel free to contact the Office of Health Enforcement at (202) 693-2190.


Patrick J. Kapust, Acting Director

Directorate of Enforcement Programs

[1] "Footnote 4" is a referenced in Table 1. -Assigned Protection Factors of 29 CFR § 1910.134 which states, "The employer must have evidence provided by the respirator manufacturer that testing of these respirators demonstrates performance at a level of protection of 1,000 or greater to receive an APF of 1,000. This level of performance can best be demonstrated by performing a WPF or SWPF study or equivalent testing. Absent such testing, all other PAPRs and SARs with helmets/hoods are to be treated as loose-fitting facepiece respirators, and receive and APF of 25."

[2] Code of Federal Regulations, 71 (2006): 50121-50192, at https://www.osha.gov/laws-regs/federalregister/2006-08-24

[3] NIOSH, NPPTL, Certified Equipment List, www.cdc.gov/niosh/npptl/topics/respirators/cel/default.html.