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Standard Interpretations - Table of Contents
• Standard Number: 1910.146(c)(5)(i); 1910.146(c)(5)(ii)(E)

This letter constitutes OSHA's interpretation only of the requirements discussed and may not be applicable to any situation not delineated within the original correspondence.

November 17, 2005

Mr. Dewai Wong
Chief, Project Management Branch-Okinawa
Department of the Army
U.S. Army Engineer District, Japan
APO AP 96338-5010

Dear Mr. Wong:

Thank you for your July 11, 2005, letter to the Occupational Safety and Health Administration (OSHA). Your letter has been referred to the Directorate of Enforcement Program's (DEP) Office of General Industry Enforcement for an answer to your questions regarding compliance with OSHA's Permit-required Confined Spaces Standard, 29 CFR 1910.146. Your questions have been restated below for clarity.

Question 1: What constitutes "continuous forced air ventilation" as found in 29 CFR 1910.146(c)(5)(ii)(E)?

Reply: "Continuous forced air ventilation" means a delivery system or device that provides positive pressure for the space where the employees are working. When continuous forced air ventilation is used during the entries that follow the alternative procedures and authorized under 29 CFR1910.146(c)(5)(i)(A) through (F), the following conditions must be met: First, no employee may enter the permit space until the forced air ventilation has eliminated any hazardous atmosphere found within the space. Second, the ventilation must be directed to ventilate the immediate areas where an employee is or will be present within the space and must continue until all employees have left the space. Third, the air supply for the ventilation must be from a clean source and must not increase the hazards in the space. These provisions ensure that the atmosphere within the permit space remains safe during the entire entry operation.

Question 2: Does the use of a portable blower fan to clear the air during maintenance periods satisfy the OSHA requirement?

Reply: A portable blower fan could be used as the continuous forced air ventilation, provided that it does remove any hazardous atmosphere. This depends on several factors such as but not limited to the size and configuration of the permit space including the number of and distance between openings such as access doors or vents and the blower capacity, such as cubic feet per meter (CFM) of the fan itself. In addition, the fan must be approved for use in the particular hazardous location.

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 interpretations letters explain the 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. In addition, 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
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 Enforcement Programs

Standard Interpretations - Table of Contents

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