Ventilation and vapor-area limits for dip tanks

September 10, 2002

Mr. Darwin M. Irish

Manager, Safety & Environmental

FLEXcon Company, Inc.

[Recipient address omitted]

Dear Mr. Irish:

Thank you for your January 29 letter to Mr. Frank Gravitt, the Occupational Safety and Health Administration's (OSHA's) Acting Regional Administrator in Boston, Massachusetts. Your letter has been referred to the [Directorate of Enforcement Programs] for an answer to your question regarding the scope of a "vapor area," as applied in 29 CFR 1910.124. 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. We have summarized your inquiry as follows:

Question: Does 29 CFR 1910.124(b)(1) require an employer to maintain the airborne concentration of vapors at levels below 25 percent of their lower flammable limits (LFL) within the "vapor area"?

Reply: No. A "vapor area" is defined in 29 CFR 1910.123(d) as "any space containing a dip tank, including its drain boards, associated drying or conveying equipment, and any surrounding area where the vapor concentration exceeds 25% of the LFL of the liquid in the tank." This definition includes the vapor source, such as a dipped object, even though OSHA does not define the term "vapor source."

While OSHA attempted to clarify the requirements associated with dipping and coating operations when it developed 1910.124, the Agency did not intend to create additional or more stringent obligations for employers.[1] Thus, an employer complies with 1910.124(b)(1) when the employer limits the vapor area to the greatest extent feasible and provides ventilation sufficient to ensure that airborne concentrations of substances beyond the vapor area remain below 25 percent of the substances' lower flammable limits.

Further, by referencing NFPA 34-1995 in 1910.124(b)(4)(ii), the Agency provided additional guidance regarding the permissible scope of the vapor area in situations in which mechanical ventilation is used. Both the OSHA standard and the NFPA standard are designed to limit the size of the vapor area and to prevent dangerous vapor concentrations from migrating into areas where they may create hazards for persons working in the facility. Compliance with NFPA 34-1995 enables an employer to limit the vapor area and provide mechanical ventilation in a manner consistent with the requirements of 1910.124.

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 apprised 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.

Sincerely,

Richard E. Fairfax, Director

Directorate of Enforcement Programs

[Corrected 8/2/06]

[1] The now superceded 1910.94(d) and 1910.108 were the basis for 1910.124. The intent of 1910.108 was to limit the vapor area to as small an area as feasible. Thus, 1910.108(b)(1) stated that "[v]apor areas, as defined in paragraph (a)(2) of this section, shall be limited to the smallest practicable space by maintaining a properly designed system of mechanical ventilation arranged to move air from all directions towards the vapor area origin and thence to a safe outside location." [ back to text ]