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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

November 15, 1990

Mr. Kirk E. Osgood
CDC Inc.
10450 Brockwood Road
Dallas, Texas 75238

Dear Mr. Osgood:

In response to your inquiry of April 25, the Occupational Safety and Health Administration (OSHA) sent you, on July 10, a letter of interpretation of the OSHA standard 29 CFR 1910.66(e)(2)(iii)(A)(5) that pertains to intermittent stabilization system building anchors and components for powered platforms for exterior building maintenance. OSHA interpreted that "..each anchor or component associated with the intermittent stabilization system (described in the OSHA standard for exterior building maintenance), shall be capable of sustaining a minimum wind load of 300 pounds. The components must sustain at least four times the anticipated wind load of 300 pounds. Therefore, the minimum ultimate design load for these components is 1200 pounds." Several inquiries have been made since then, by various consulting groups questioning the accuracy of that interpretation.

The above design load (1200 pounds) was estimated based on adverse weather conditions, with a wind speed of 100 miles per hour (mph) and with a safety factor of four included in the design load calculation.

Based on the fact that employees are not allowed to use powered platforms during such adverse conditions (any wind velocity over 25 mph), and on the fact that OSHA has previously issued instruction on this subject, OSHA Instruction STD 1-3.3, dated November 1, 1982 (copy enclosed), OSHA has reevaluated the above interpretation in light of both the facts mentioned earlier, and of information submitted by various consulting engineers questioning OSHA's interpretation.

The design load for intermittent stabilization system or its components need not consider such an adverse condition (i.e 100 mph wind speed). However, at wind velocity of approximately 75 mph, which is a velocity that was considered in the development of the OSHA Instruction STD 1-3.3, and which is also an adverse condition with a wind velocity three times the limit for allowable working conditions, the load from this wind would be approximately 150 pounds. When a safety factor of four is applied, as required under the OSHA standard at 1910.66(e)(2)(ii)(A)(5), the minimum ultimate design load for these components is 600 pounds. If two anchors share the wind loading, the ultimate design load for each anchor is 300 pounds. However, if the loading is not shared, the ultimate design load for each anchor is 600 pounds.

We apologize for any inconvenience caused to you by our earlier interpretation. Thank you for your interest in safety and health.


Patricia K. Clark, Director
Directorate of Compliance Programs