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.

July 10, 2006

John E. Williams III
Pasadena Tank Corporation
15915 Jacintoport Boulevard
Houston, TX 77015

Dear Mr. Williams:

This is in response to the January 18, 2006, letter you sent to the Occupational Safety and Health Administration, inquiring about the applicability of confined space requirements to aboveground storage tank construction. We apologize for the delay in our response.

We have paraphrased your questions as follows:

Question (1)(a): Aboveground storage tank (AST) construction proceeds in several stages. The first three stages are as follows:

Stage 1: a concrete base is constructed upon which the tank ring walls will sit. The first tank ring is erected, normally between 8 and 10 feet high. The only means of entry/exit is a manhole cut into one of the steel plates (a "sheet") that comprises the ring.

Stage 2: a second ring is erected on top of the first ring and welded into place. With this ring in place, the tank walls are 16 to 20 feet high. A "door sheet" is then cut out, creating an opening approximately 8 feet wide by 10 feet high. This opening provides access for personnel, equipment and material. Airflow is typically not a problem at this stage.

Stage 3: The top is erected and forced air ventilation is used to assist in air flow.

Once the door sheet is cut out in Stage 2, is the space considered a "confined space" for purposes of OSHA's confined space requirements?

Answer: On-site construction of the AST you describe would be considered a construction activity, and therefore the construction confined space standard, 29 CFR 1926.21(b)(6), would apply. Section 1926.21(b)(6)(ii) defines a confined space as follows:

For purposes of paragraph (b)(6)(i) of this section, confined or enclosed space means any space having a limited means of egress, which is subject to the accumulation of toxic or flammable contaminants or has an oxygen deficient atmosphere. Confined or enclosed spaces include, but are not limited to, storage tanks, process vessels, bins, boilers, ventilation or exhaust ducts, sewers, underground utility vaults, tunnels, pipelines, and open top spaces more than 4 feet in depth such as pits, tubs, vaults, and vessels.

Pursuant to this provision, for a space to be considered a "confined space" under this standard, it must have two characteristics: (1) limited means of egress, and (2) the potential for the accumulation of toxic or flammable contaminants or for an oxygen-deficient atmosphere to develop. The part of the provision specifying that "open top spaces more than 4 feet in depth such . . . as vessels," are considered confined spaces indicates that the Agency found that such vessels have the two listed characteristics. Unless it were clear that the 8' x 10' opening eliminated one of these characteristics, the space would be considered a confined space.

Based on the information you submitted, we cannot say that the 8' x 10' opening in the AST during Stage 2 would necessarily eliminate either of these characteristics. The potential for air contamination or low oxygen levels inside the AST at Stage 2 would depend on several factors, such as the diameter of the tank, the amount and nature of the activities conducted inside the tank, and the proximity of the activities to each other and to the 8' x 10' opening. Representative air quality monitoring data would typically be needed before determining that the potential for contamination and low oxygen levels was absent.

While the 8' x 10' opening may eliminate the characteristic of limited means of egress, we cannot say that that would always be the case. For example, the space would nonetheless have a restricted means of egress if there were restrictions within the space hindering an employee's access to that opening.

Question (1)(b): Would the space be considered a "confined space" for purposes of OSHA"s confined space requirements during Stage 3?

Answer: Your description of Stage 3 includes a reference to the use of forced-air ventilation. However, the determination of whether there is a potential for a dangerous atmosphere must be made assuming the absence of mechanical ventilation. Section 1926.21(b)(6)(ii) covers spaces with restricted egress that are "subject to" the accumulation of toxic or flammable contaminants or have an oxygen deficient atmosphere. If a space is "subject to" the development of such conditions in the absence of mechanical ventilation, it will continue to be subject to such developments with mechanical ventilation. That is because there is always a possibility that the mechanical ventilation will fail or otherwise become insufficient to control an atmospheric hazard. Therefore, for purposes of §1926.21(b)(6)(ii), the space remains "subject to" the development of a dangerous atmosphere even when mechanical ventilation is being used.

Consequently, the determination that must be made is whether, in the absence of mechanical ventilation, there would be a potential for the accumulation of toxic or flammable contaminants or for an oxygen-deficient atmosphere to develop. During Stage 3, the probability that the space would potentially develop air contamination or low oxygen levels is significantly enhanced because the top at that point is closed. Even with an 8' x 10' opening, such spaces would typically meet the definition of a confined space.

Question (2): At the stages of construction when the AST is considered a confined space under §1926.21(b)(6), we use mechanical ventilation to ensure a safe atmosphere. By doing so, and because there are no physical hazards in the space, we believe that, if §1910.146 were applicable, it would be considered a non-permit space under §1910.146(c)(5). If we followed §1910.146(c)(5), would we be in violation of either §1926.21(b)(6) or section 5(a)(1)("General Duty Clause") of the OSH Act?

Answer: Where a space meets the definition of a confined space set forth in §1926.21(b)(6)(ii), the employer is required to instruct employees about the hazards of working in a confined space, as stated in 29 CFR 1926.21(b)(6)(i):

All employees required to enter into confined or enclosed spaces shall be instructed as to the nature of the hazards involved, the necessary precautions to be taken, and in the use of protective and emergency equipment required. The employer shall comply with any specific regulations that apply to work in dangerous or potentially dangerous areas.

This requirement must be adhered to irrespective of whether an employer followed §1910.146(c)(5) for its entry operations in a confined space.

Section 5(a)(1) of the Occupational Safety and Health (OSH) Act states:

(a) Each employer —
(1) shall furnish to each of his employees employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to his employees.

Entering confined spaces is a recognized hazard in the construction industry. Under the General Duty Clause, employers are required to institute feasible means of protecting employees from confined space hazards. While the scope of OSHA's general industry standard for confined spaces excludes construction, one of the ways an employer can meet its General Duty Clause obligations for protecting against confined space hazards in construction is use procedures that accord with the general industry confined space standard at 29 CFR 1910.146.1

One of those general industry provisions is §1910.146(c)(5). It establishes alternative procedures for entering a permit-required confined space where the employer can demonstrate that the only hazard posed by the permit space is an actual or atmospheric hazard, and that continuous forced air ventilation alone is sufficient to maintain that permit space safe for entry is not applicable to construction. If an employer engaged in construction followed the terms of this provision, it would meet its General Duty Clause obligations for protecting against confined space atmospheric hazards.

In sum, where an employer in the circumstance you describe meets the requirement to instruct employees in accordance with §1926.21(b)(6)(i), complies with specific OSHA standards applicable to construction regarding work in dangerous or potentially dangerous areas, and follows procedures similar to §1910.146(c)(5), the employer would be in compliance with OSHA confined space requirements applicable to construction.

If you need additional information, please contact us by fax at: U.S. Department of Labor, OSHA, Directorate of Construction, Office of Construction Standards and Guidance, fax # 202-693-1689. You can also contact us by mail at the above office, Room N3468, 200 Constitution Avenue, N.W., Washington, D.C. 20210, although there will be a delay in our receiving correspondence by mail.



Noah Connell, Acting Director
Directorate of Construction

1 OSHA has been developing a new proposed rule for confined spaces in construction, which is anticipated to be published this year for public comment. [ back to text ]