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 Post subject: OSHA MAD vs NFPA Shock Hazard Boundaries
PostPosted: Wed May 20, 2015 10:18 am 

Joined: Wed May 20, 2015 10:07 am
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I was reading recently both OSHA and NFPA 70E standards and I wasn't able to distinguish the difference between the NFPA 70E shock hazard boundaries (Limited, Restricted and Prohibited) and the minimum approach distance (MDA) from OSHA 29 CFR. I would like to know the purpose of each one and where do they apply. I know for instance that the shock hazard boundaries are meant to prevent shock and electrocution. If I want to design a warning label, would I print both boundaries on the stickers or each one is more appropriate for certain specifics cases?


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 Post subject: Re: OSHA MAD vs NFPA Shock Hazard Boundaries
PostPosted: Fri May 22, 2015 8:04 am 
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NamFlash wrote:
I was reading recently both OSHA and NFPA 70E standards and I wasn't able to distinguish the difference between the NFPA 70E shock hazard boundaries (Limited, Restricted and Prohibited) and the minimum approach distance (MDA) from OSHA 29 CFR. I would like to know the purpose of each one and where do they apply. I know for instance that the shock hazard boundaries are meant to prevent shock and electrocution. If I want to design a warning label, would I print both boundaries on the stickers or each one is more appropriate for certain specifics cases?


The source for both that is clearly referenced is IEEE 516. This is the standard for overhead line work. In that standard, the minimum approach distance is the minimum distance at which a shock could occur plus an additional distance added considering potential inadvertent movement. In other words even though the flsahover distance at 480 V is less than 1", the approach distance is 7" to account for inadvertent movement.

Second, OSHA 1910.269 is for "generation, transmission, and distribution". OSHA 1910.3xx (Subchapter S) is for utilization equipment. The term "minimum approach distance" and the tables are used verbatim in 1910.269 as well as the National Electrical Safety Code (NESC, IEEE Standard C2). NESC is not quite 100% identical to OSHA 1910.269 but it is otherwise the consensus safety code for utilities and anyone else that has typical "utility equipment" (cogen, overhead lines, pole mounted equipment). OSHA 1910.3xx (Subchapter S) is based on an early/stripped down version of the NEC as well as an early version of NFPA 70E. Unlike utilities, the code for installations (NEC) is seperate and distinct from the code for work practices (NFPA 70E). With regards to IEEE 516, the restricted approach boundary is identical to the minimum approach distance.

Forget about the prohibited approach distance. This is essentially the MAD without the inadvertent movement adder. It was deleted in the 2015 edition of NFPA 70E.

The one thing not mentioned is the third boundary, the limited approach boundary. There is no specific TERM for this boundary under OSHA 1910.269 but it still exists. It starts at 10 feet up to 50 kV and then grows larger above that limit. Under 30 CFR 56/57/77 (MSHA), the limit is only 10 feet and there is no distance adder. Under OSHA 1926 there is still a distance adder.

If you do not have generation/transmission/distribution systems (typical industrial or commercial operation), forget about 1910.269 and the NESC. Just stick with NFPA 70E and NFPA 70 (NEC). If you do have to consider those things, you have to use BOTH rule sets depending on whether or not it is utilization. See 1910.269 Appendix A. Personally for my site I used the NFPA 70E terms across the board and only make room for the utility areas where it is apppropriate to do so. For instance utility equipment is designed for energized work and there is no "EEWP rule" so I drop that requirement over 10 kV, although I still require everything else but the EEWP form. Even though it is above and beyond, we follow the Subchapter S lockout procedure instead of 1910.269. And since it is a mining facility, abandoned power cables have to be physically removed and can't just be left derelict. This is not required by either set of regulations/codes but we require it here for uniformity. Another strange one to consider is 1926 vs. 1910 lockouts. Locks (but not tags) are required under 1910 but tags (and not locks) are required under 1926, and 1910.269 allows for either one depending on some other requirements.


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