ECN Forum Forums Safety Discussion and News Occupational Safety Discussion Energized Work NFPA 70E

Don,
The result of the calculation, if you considered that the breakers didn't open, would surely be much higher than the highest rated PPE (following 70E, 40 cal/cm^2). You wouldn't be able to do any energized work, such as taking IR scans.
In many locations that I calculate using IEEE 1584 formula, and considering that the breakers or fuses operate, I get values in excess of achievable PPE.

An FD to the south of us had a LODD (Line Of Duty Death) of a Deputy Chief investigating an alarm at a shopping mall. Turns out the mall went into alarm because of a "brownout" D/T a dropped phase... unknown cause. After returning the engines, the Chief went into the panel room with the site electrician and an "engineer" for the property. They were discussing the situation when a) either the faulted UG line re-energized after OCP reset or b) the contractor digging 1 1/2 miles away struck the other phase and caused the short to fault at the point of least resistance - the panel for the mall. The arc flash and molten metal nailed him and the engineer.

IIRC, 2 & 3rd degree burns over something like 80-90% of his body surface. He was concious after the incident, and directed the crews responding to take care of the other victim before him. They knocked him out at the hospital - he lived for about a week after the incident. He wasn't wearing turnouts (Nomex FR) because he'd determined that there wasn't a fire on location, and was only 'investigating'.

Admittedly, a rare situation, but I noticed a lot less joking about my "other" job at the FD after the incident...

oh my. I think I remember this... at a mall that is near county borders not far from a tollway. Incedents like this always give me a bit of a wake up call, in that I find myself stopping and reviewing and thinking more about the 'unforseen' but 'still remotely possible' things that could happen while in similar situations - somewhat of a reminder to guard myself against getting complacent about safety and safe working methods.

I know of a couple of instances around these parts where arc flash has took it's toll as well. I don't think that the majority of EC's & even large corporations are paying attention to this. They are still thinking shock protection.

Having done arc flash assessments for a large industrial facility, the upper management did allow us at that time to make some changes to easily done things such as relay settings, but balked when it came time to pony up to such things as mandating Nomex clothing and changing long-time practices. The problem is that protective device setting is a lot of times it's a compromise to begin with, particularly with the setting of relays, and focuses on protecting equipment and maintaining electrical continuity, not protecting more fragile human beings.

Having been able to listen to Lanny Floyd in person once and doing some reading on the issue, basically in the worse case, one strives to make the event at least surviveable, not necessarily walk away with no injury whatsoever. The values that it takes to hurt a person is very small compared to the energy capable of being produced if a fault is allowed to linger.
The path to progress is paved in blood unfortunately.

I continue to have a fundamental problem with accepting the use of breaker settings and trip times to reduce the level of PPE that is required.
Don

resqcapt19,
I don't think that is realistic, as you are aware time to the point that the arc is extinguished plays a role in the energy equation. I agree that all the things you talked about can happen, but it's better to have protection based on what will most likely occur and more defensible from an economic standpoint. We all know hot work is going to be done, at the very least particularly of the testing nature (how else can you verify the de-energized state)

Don,
I must say that I agree with you, I don't really like the idea of reducing your level of PPE, based upon a certain Circuit Breaker rating, anymore than what you do.
To my way of thinking, a CB has an Inverse Time-Current characteristic under fault conditions and therefore, even if it does trip near instantly, it's going to be carrying a fair amount of current.
Elderly CB's have a habit of failing catastrophically, especially where a Dead Short has occured down-stream.