Arc flash hazards and the 2 second rule ? 3

[bdn2004]

There’s a part of the arc flash calculation method that bothers me some: the 2-second rule. We rely on this sometimes to lower the reported Incident energy by saying the max time of exposure is 2 seconds: that your natural reaction time getting away from a flash is maximum 2 seconds. It does not seem very scientific. It also discourages finding a real mitigation method.

Anyone else have any thoughts on this ?

 

[bdn2004]

We refer to it as the 2-second rule as that is what our Client sets in their standard as the maximum time with some extra verbiage that if the worker can't retreat - increase the time. But to what ? Doesn't say.

I'm aware of an arc flash incident where a guy was hurt very bad, lucky to be alive - even though he did something very stupid to initially cause the fault. But automatically they are asking what did the arc flash study say ? Why wasn't he wearing more PPE? Can the excuse be "I thought he could get out of the way in 2 seconds" ?

In the case I'm showing above it's occurred to me this is a good place to recommend a maintenance mode on their relays - although those things are so old they would have to be changed out. Also the big old slow oil circuit breaker that feeds this line they've been changing them out slowly over the years to vacuum breakers - this might give them more impetus to get that job done. Sometimes bad news sparks capital upgrades.

What I'm afraid of in this situation and some others that I've seen - is downplaying the potential risk, so that they don't have to change procedures or so that guys don't have to put on the monkey suits cause they don't like working in them.