Q: We understand that OSHA 1910.269 recommends and NFPA 70E requires Arc Rated shirts to be tucked in.

We are an electric utility cooperative. If an AR (Flame Resistant, Arc Rated) t-shirt is worn that matches the hazard and the AR t-shirt is tucked in and an outer AR shirt is also worn, primarily for warmth, does the outer AR shirt have to be tucked in?  Can this cause a “chimney effect” and cause arc facial burns to be worse from the arc coming up through the shirt to the face? A consultant trained our workers about this dangerous “chimney effect”, but it doesn’t make sense to us or to our management.

A: We typically recommend tucking in an AR shirt…

…for added protection and to lower the risk of direct skin burns (if no AR t-shirt is worn), and to lower the risk of undershirt ignition (if the undershirt is made of ignitable material, like cotton).

In the case that a non-AR cotton undergarment is worn and ignites, there can be a substantial “chimney effect”. This is when the outer AR shirt, left open and untucked, acts as a “chimney” allowing air to feed the fire from the bottom of the untucked shirt and cause the non-AR undershirt to burn more quickly by feeding the fire with oxygen from below.

There is NO “chimney effect” if the undershirt is an AR shirt and doesn’t ignite. You indicated a “consultant” had informed you this was some function of the arc under untucked shirts.  I can assure you that is not the case.

Tucking in the outer AR shirt when wearing an AR undershirt could increase protection levels in some instances. If one layer is matched to the rating, leaving an additional AR shirt on top untucked, this will not increase risk of injury from an arc exposure. But the total protection of some areas under the untucked shirt could have only the one layer of AR for protection. If this layer is matched to the hazard, the company should be in compliance with the OSHA standard 1910.269.

While this is an unusual question, it is important to accurately portray the facts.  Scaring workers into compliance with something that doesn’t make sense undermines our other facts in the future.  I prefer workers to “tuck, button and roll” the shirt properly. Your scenario adds no risk, but it just doesn’t take full advantage of an added layer of protection.

Here is my video to explain this a little better.

e-Hazard Training Video

Our lineman’s training covers this and many other topics in our video.

Live instruction is available as well, and we also offer a Train the Trainer to allow the training materials to be licensed to the utility.

Find out more about renting, purchasing, or licensing the video here.

More info about our Arc Flash Safety for Utilities (1910.269) Train the Trainer class.

Have a question about electrical safety and standards? Ask us here!