Arc Flash and Arc Blast

There is no correlation between the arc flash incident energy at a bus and the arc blast risk. The current equation for arc flash incident energy, published in IEEE 1584-2018 is:

Its has grown in complexity since 2002, and if your interested in how to apply this by hand, Allumiax has an in depth Arc Flash Calculations Using Mathcad post where they compare the results using ETAP.

For arc blast the Crawford-Clark-Doughty model is much simpler and has been verified with testing (within shorter time periods):

What does all this mean?

Starting with what it doesn't mean, it doesn't mean that any PPE over 40cal/cm2 is just a body bag.

As I mention i a reply, I can't disagree more with this. Almost 4 years AFTER a paper was presented at ESW with actual measured results, trainers are still promoting this myth.

From the conclusions from the paper I referenced above:

The theory that copper vaporization is a substantial component of arc blast is not supported by these experiments but it could be a small component.

While there is metal vaporized in the arc, this reaches an equilibrium quite quickly and can no longer contribute to the pressure making its overall contribution quite small an unmeasurable in our experiment** and so inconsequential to be useless in equipment design of a macro scale like electrical equipment

What this tells me, is that arc blast is an issue, but not necessarily correlated with the arc flash incident energy. There can be an arc blast where the door of the switchgear comes off, but relatively low incident energy because the protection trips quickly.

More likely though is the arc fault is in the 5-10kA range for an extended period causing a large incident energy. You can have a 65cal/cm2 arc flash with minimal arc blast as a result.

No body bag needed.

Closing

What do you think? Is an arc blast a significant risk that we need to look at better? Do we, as an industry need more research on the results?