Standard Interpretations - Table of Contents|
| Standard Number:||1926.451(f)(17)|
December 10, 1998
R.E. Dick Peterson, Supervisor
Safety and Health
ABB C-E Services, Inc.
Post Office Box 568
Windsor, CT 06095-0568
Dear Mr. Peterson:
This responds to your letter dated February 16, 1998 in which you ask that we revise part of the OSHA scaffold standard (29 CFR 1926 subpart L). We apologize for the lateness of our reply.
Your letter raises the issue of whether a suspended scaffold should be grounded while arc welding in industrial and utility boilers. You state that grounding the scaffold, which is required by the OSHA standard, is more hazardous than not using a ground, and that grounding the scaffold defeats the purpose of requiring that suspension cables be insulated. You also ask us to consider developing guidelines for different types of scaffolds.
Two provisions -- §1926.451(f)(17)(i) and (ii) -- require that suspension cable, or any additional independent lines from the ground, be insulated. Cable lengths of 100 feet or more must be insulated at least 4 feet from the hoist. If there is a cable below the hoist, it also must be insulated. Insulating the cable reduces the hazard of electrocution by preventing arcing due to welding operations.
Section 1926.451(f)(17)(iv) requires a grounding conductor to be connected to the structure from the scaffold when employees are welding. In your letter, you state that if the insulation requirement is fully met -- and all physical connections between the scaffold and the structure to which the scaffold is suspended (as well as lines in contact with the earth) are insulated, then there is no danger of arcing. Your point is that if the scaffold is then grounded, the arcing danger is re-introduced by the use of a ground.
The purpose of the grounding requirement is that, in the event of a fault, where there is an accompanying failure -- including a failure in insulating material -- the electrical energy would go to ground rather than through an employee on the scaffold. While a perfectly insulated scaffold would prevent an electrical arc to a scaffold component, the standard addresses the possibility that problems may arise in the planning and installation of insulators, as well as with the insulating devices and the welding equipment itself. For example, a fault in the welding equipment could create an electrical potential from one part of the welder through a portion of the scaffold platform to another part of the equipment. If the scaffold were not grounded, that area of the platform could become energized and pose an electrocution hazard to an employee standing in that area.
The electrical potential created by connecting the grounding conductor to the structure conducts any fault current that might be created when welding from suspended scaffold platforms away from the employees. Grounding the scaffold limits the voltage on the scaffold frame, supplementing the protection provided by insulating the cables. Grounding the scaffold therefore provides additional shock protection for employees welding from the scaffold.
You also assert that if another welder is working 100 or so feet above the scaffold, and accidentally comes in contact with the cable suspending the scaffold, there could be an arc to the cable if the scaffold is grounded. Such an arc, you suggest, could sever the suspension cable.
We disagree with your conclusion. The presence of another potential source of arcing to a cable does not justify eliminating the safety feature of grounding the scaffold. Instead, it requires the employer to take other steps to protect against that hazard. If welding was being performed on adjacent scaffolds, the employer would be required to provide additional insulation on the suspension cable or provide other means for protecting it from contact by the other welders.
We are considering including the issues that you have in OSHA's upcoming Advance Notice of Proposed Rulemaking on the scaffold standard. A final determination on what issues will be included has not yet been made.
Thank you for your letter. Send future inquiries to: The Directorate of Construction -- OSHA Office of Construction Standards and Compliance Assistance, Room N3421, 200 Constitution Avenue, N. W., Washington, D. C. 20210.
Office of Construction Standards and
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