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.

December 3, 1991

MEMORANDUM FOR:     JOHN B. MILES, JR.
                   REGIONAL ADMINISTRATOR

THROUGH:            LEO CAREY, Director 
                   Office of Field Programs

FROM:               PATRICIA K. CLARK, DIRECTOR
                   DIRECTORATE OF COMPLIANCE PROGRAMS

SUBJECT:            Mechanical Power Equipment/Distance to Overhead Power
                   Lines

After review of your memorandum of August 8 and our response to Mr. Paul N. Gibavic's letter of March 21 concerning operating a crane in close proximity to overhead power lines, we believe additional clarification may be helpful.

In regard to what is acceptable as insulating barriers to prevent physical contact of equipment or machinery with electric distribution and transmission lines when the equipment or machinery is operating within 10 feet of the power lines, please be advised as follows: Rubber insulating equipment meeting the requirements of 29 CFR 1910.137 is normally intended as protection from "brushing" type contact for employees working on the lines. Although 1910.137 is not applicable to construction work, it may be used as a compliance guide for barriers required under the exception to 1926.550(a)(15), under certain conditions. If hard direct contact with the line is not likely, rubber insulating equipment can provide protection from brush contact with the power line. However, if direct impact with the lines is reasonably likely or expected, this equipment will not provide the necessary protection. In such cases, other types of barriers would be required, such as those listed in the National Safety Council Data Sheet No. 1-743 New90 and the types of plastic guard equipment covered in ASTM F968, Specification for Electrically Insulating Plastic Guard Equipment for Protection of Workers. Although guards of a type consisting of ABS plastic, 1/8 inch thick, (approximate puncture strength 50,000 volts) are often successfully used on 15KV and 34.5KV systems, none are totally impact proof to the extent that strong direct blows would leave the air gap integrity unchanged or not cause sliding or other adverse movement along the line.

While the "goal post" type of guarding approach to overhead line safety probably provides the most durable means of withstanding barrier impact, it should be remembered that no practical barrier can absolutely prevent contact of a crane (or similar material handling device), simply because the capabilities of such heavy operating devices normally overwhelm any obstruction that may be installed.

If we can be of any further assistance please contact Roy Gurnham or Dale Cavanaugh of my staff in the Office of Construction and Maritime Compliance Assistance at (202) 523-8124.