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 8, 1997

Ms. Elsie L. Munsell
Deputy Assistant Secretary of the Navy
(Environment and Safety)
Department of the Navy
1000 Navy Pentagon
Washington, D.C. 20350-1000

Dear Ms. Munsell:

This is in response to your letter of March 14 requesting an interpretation of the Occupational Safety and Health Administration (OSHA) standard for the airflow rate required for a spray painting area.

29 CFR 1910.94(c) and 29 CFR 1910.107 both apply to spray areas. These sections are currently under revision and will be combined into one area of 29 CFR 1910.107. There is no specific flow rate mentioned in either standard for spray areas, OSHA uses National Fire Protection Association Publication, NFPA 33, 1995 edition, (copy enclosed) Spray Application Using Flammable or Combustible Materials, paragraph 5-2, which requires that "each spray area be provided with mechanical ventilation that is capable of confining and removing vapors and mists to a safe location and is capable of confining and controlling combustible residues, dusts, and deposits. The concentration of vapors and mists in the exhaust stream of the ventilation system shall not exceed 25% of the lower flammable limit." This means that the airflow may be variable depending on the job being performed. This also means that under the circumstances that you have described, OSHA considers these corrosion-control hangars to be spray areas as opposed to spray booths. The determining factor in this decision is that other work is also performed in the area and painting is incidental to the specific area that is being treated (wing, rudder, etc.), and not the entire aircraft on a repetitive basis.

The employees must also be fully trained in the hazards to which they are exposed and in the emergency action and fire protection plans required by 29 CFR 1910.38 [and 1910.39], in personal protective equipment as required in 29 CFR 1910 Subpart I and also in the health requirements listed in 29 CFR 1910 Subpart Z.

Should you have further questions, please contact [the Office of General Industry Enforcement at (202) 693-1850].

Thank you for your continued interest in occupational safety and health.


John E. Plummer, Director
Office of Federal Agency Programs




March 14, 1997





This is to request an interpretation of the Occupational Safety and Health Administration (OSHA) standard for the airflow rate required in a spray painting area. We are building several new aircraft corrosion-control hangars throughout the United States and need a standard design criteria for the ventilation systems.

Our questions are: (1) What OSHA standard applies for spray painting in a corrosion control hangar, 29 CFR 1910.94 or 29 CFR 1910.107? (2) What is the minimum required maintained ventilation velocity?

Spray painting performed in the hangars will be primarily spot maintenance, but large areas of the aircraft could occasionally be painted. We consider the painting area a spray area rather than a spray room or booth. Spray areas appear to be covered under 29 CFR 1910.107, which does not specify a minimum design airflow rate.

In Industrial Ventilation, A Manual of Recommended Practice, 22nd edition the American Conference of Governmental Industrial Hygienists (ACGIH) allows the designer to use a design flow rate of 75 cfm/ft(2) for very large, deep booths, see VS-75-01. Additionally, VS-75-04 allows the designer to further reduce the airflow rate to 50 cfm/ft(2) when the cross-sectional area in a drive-through booth is greater than 150 ft(2). The ACGIH guidelines and consensus standards criteria are typically recommended when there is no OSHA criteria addressing a particular problem.

The hangar designers will perform the necessary calculations to ensure the airflow rate will keep the hangar atmosphere below 25% of the lower explosive limit.

My point of contact for further information on this matter is Commander Carol Pickerel, USN, Special Assistant for Occupational Health at (703) 614-1276.

Deputy Assistant Secretary of the Navy
(Environment & Safety)