Here is one that is discussed quite a bit with clients and in training. What's you're view?

OSHA 1910.269(I)(8)(ii) States: For each employee exposed to hazards from electric arcs, the employer shall make a reasonable estimate of the incident heat energy to which the employee would be exposed.

Note 1 states: (paraphrased) Appendix E provides guidance for estimating available heat energy......OSHA will deem employers following the guidance in Appendix E to be in compliance.... ......Employer may choose a method not in Appendix E if it reasonably predicts incident energy...

NESC Table 410-1 Clothing and clothing systems for voltages 50V to 1000V provides recommendations for minimum arc ratings based on specific equipment, voltage and other conditions defined in footnotes. This table is based on substantial testing and calculations such as IEEE 1584.

Here is the debate: not NESC Table 410-1 is NOT referenced in Appendix E as one of the acceptable methods, however "the employer may choose a method not in Appendix E..."

This week's Question:

Do you believe it is still appropriate to use NESC Table 410-1 (when it is applicable) even though it is not referenced in OSHA 1910.269?

Yes
No
Doesn't apply to me

If the clearing time for low side faults is based on high side transformer protection, methods suggested in OSHA Appendix E Table 3 often result in very high incident energy.

Table 410-1 is based on recent test data that takes into account that arcs are not sustained for a long period of time. I think this is a more accurate and appropriate approach.

I voted "Yes" but I know of a few that will vote no. Why? For some reason there are those that if they don't see something specifically spelled out in a standard, they are afraid to use their own judgement. Even if the standard permits alternatives such OSHA 1910.269 Appendix E.

Actual testing trumps calculations every time, but as usual, you have to look carefully at the fine print. Unfortunately though NESC (and for that matter, NFPA 70E) have a very bad habit of NOT attributing information to some sources. So vague references to "industry testing" fail to satisfy and the best we can do as an affirmitive defense is to cite a "consensus safety standard", with no backing as to the source. This impacts both NESC's tables (especially Table 410-2 for instance) as well as NFPA 70E's equipment table.

Personally I've found and read the EPRI reports. For <250 V equipment, it is actually better than IEEE 1584 which is based on a single test @ 208 V. Thus it is a better reference for incident energy than say IEEE 1584 or the tables in NFPA 70E from the point of view of estimating incident energy for <250 V.

From the utility standpoint, for the past half-dozen years or so (since NFPA 70E became the prevalent safety standard for commercial/industrial electrical workers) we knew something was wrong! We would be happily work on the outside of a cinder-block wall, say at an integral meter base, and eight inches away, on the other side of the wall, the electrician was in his bee-keeper suit.

While one could spend all day arguing which standard (NFPA 70E or NESC) was correct, one cannot deny both cannot be correct.

Based on reading the original 1500+ page document on development of the revised 1910.269, the NESC table 410-1 came out towards the end of development of the revised 1910.269, so it may not have been available at the time that the revisions were being done. As usual, OSHA is dealing with the fact that development and revision of regulations is glacially slow and the fact that by the time they write a regulation, it might be already outdated. So they gave references to what was available at the time and made it a performance-based requirement (do X. Here is one way to do it but as long as you do X, we're satisfied).

So 410-1 in its current form may not have existed when the revisions were going on.