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Standard Interpretations - Table of Contents
• Standard Number: 1910.107(d)(9)

September 17, 2001

Robert Trinkl, Corporate Safety Manager
Harley-Davidson Motor Company
3700 West Juneau Avenue
P.O. Box 653
Milwaukee, WI 53201

Dear Mr. Trinkl:

Thank you for your July 11 letter to Ann Williams, the Occupational Safety and Health Administration's (OSHA's) Assistant Regional Administrator for Region V. Your letter has been referred to the Directorate of Compliance Programs for a response. This letter constitutes OSHA's interpretation only of the requirements discussed and may not be applicable to any situation not delineated within your original correspondence. You had a question about whether you could comply with National Fire Protection Association (NFPA) 33-1995 instead of 29 CFR 1910.107(d)(9). Our response to your paraphrased scenario and question is provided below.

Scenario:  We are considering installing recirculated air systems in spray booths in a new plant. The systems would be designed to comply with NFPA 33-1995 requirements and would use approximately 80% recirculated air and 20% fresh air. Employees would wear appropriate protective clothing including positive-pressure, air-supplied hoods.

We have found four letters of interpretation on OSHA's website which seem to pertain to this type of situation (October 16, 1987, Branstutter; November 3, 1989, Slavin; August 27, 1991, Ellis; and July 28, 1997, Karandikar). All four of these letters either allow the use of recirculated air (under specific conditions) or say that its use, in compliance with NFPA 33, would be considered a de minimis violation and would not be cited.

Question:  Would the use of recirculated air as described above be considered a "de minimis" violation of 29 CFR 1910.107(d)(9)?

Response:  As you may know, NFPA 33, Standard for Spray Application Using Flammable or Combustible Materials, was updated in 2000. According to subsection 5.5.1 of NFPA 33-2000, "air exhausted from spray areas shall not be recirculated." However, the standard does provide an exception if the recirculated air is, "make-up air for an unmanned spray operation or cascaded to subsequent unmanned spray operations, provided all of the following conditions have been met:
(a)   Solid particulates have been removed from the recirculated air.

(b)   The concentration of vapors in the exhaust airstream does not exceed 25 percent of the lower flammable limit.

(c)   Listed equipment is used to monitor the concentration of vapors in all exhaust airstreams.

(d)   An alarm will sound and the spray operation will automatically shut down if the concentration of any vapor in the exhaust airstream exceeds 25 percent of the lower flammable limit.

(e)   Equipment installed to process and remove contaminants from the air exhausted from spray operations is approved by the authority having jurisdiction."
Also, subsection 5.5.2 allows, "recirculated air to occupied spaces," including spray areas, spray booths, spray rooms, and other process areas, but states that, "other requirements addressing the toxicity and the permissible exposure limits," such as ANSI Z9.7, Recirculation of Air from Industrial Process Exhaust Systems, will also apply. According to ANSI Z9.7, "the potential for return of toxic contaminants to the facility through recirculation of industrial process air requires that this process be thoroughly analyzed and well-designed." This ANSI standard also lists several other standards and information which you may wish to review.

De minimis violations are violations of existing OSHA standards which have no direct or immediate relationship to safety or health and result in no citation or penalty; they do not have to be abated. Under the current OSHA policy on de minimis violations, employers are allowed to comply with the most current consensus standards applicable to their operations, rather than with the OSHA standard in effect at the time of inspection, when the employer's action provides equal or greater employee protection. Therefore, pursuant to the policy for de minimis violations, employers that fully comply with NFPA 33-2000, Section 5.5, Recirculation of Exhaust, (including subsections 5.5.1 through 5.5.2), would not be cited under 1910.107(d)(9). Also, please note that the referenced letters of interpretation will be reviewed and updated or removed to reflect the current information.

Thank you for your interest in occupational safety and health. We hope you find this information helpful. 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 appraised of such developments, you can consult OSHA's website at http://www.osha.gov. If you have any further questions, please feel free to contact the [Office of General Industry Enforcement] at (202) 693-1850.


Richard E. Fairfax, Director
Directorate of Compliance Programs

cc: Regional Administrator, Region V

[Corrected 04/21/2009]

Standard Interpretations - Table of Contents

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