Dr. Ralph H. Lee was the man I consider to be the Godfather of the arc flash study and the arc flash protection industry.
His paper “The Other Electrical Hazard: Electric Arc Blast Burns,” published in 1982, is quoted in all the of the arc flash literature today. This short paper became the foundation for arc flash study work, probably because it is easy to read and explains the arc blast in understandable terms.
There are 3 main parts to Dr. Lee’s paper:
1. Model an arc blast as an expanding sphere with terrible energy
2. Determine whether the arc blast causes “curable” or “incurable” skin burns
3. Recommend ways to protect workers
1. The arc blast model
Dr. Lee models the worst case arc a worker might be exposed to by showing the arc as an expanding sphere of energy. Then, he models a worker caught somewhere in the sphere.
Depending on the energy of the arc blast, and the workers location, they will be exposed to a certain amount of energy.
This energy causes the skin temperature to rise a certain amount, and leads us to step #2.
2. Skin burns from the arc flash
The crux of the study looks at the rise in skin temperature from the arc blast, and whether or not the arc flash energy will cause a burn.
If it causes a burn, is it a “curable” burn, or an “incurable” burn? That is the question.
By using heat transfer basics, you can find the skin temperature rise. Then, you can figure out whether a burn will be caused, and what kind. Dr. Lee did this using skin temperature versus time curves.
3. Protecting personnel from arc flashes
Dr. Lee’s entire objective with this paper was to reduce injuries and deaths by making more people aware of the hazards in an arc flash.
When people are told “why” in addition to “what,” they tend to listen and absorb the information better. The human mind wants to understand why, and if it does, it will typically remember information.
Dr. Lee objectively presented the arc blast as an expanding sphere of energy, but he also described in terrible details the arc flash energy.
He recommends at least the use of additional clothing, eye protection, and hard hats to guard against the arc flash. He also describes the molten metal droplets and the projectiles produces during a blast.
The industry of arc flash PPE had a start with this paper.
Conclusion
Dr. Ralph Lee’s paper has helped to save lives and prevent injuries for many workers over the years.
Download, read, print out a hard copy, and refer back to it if you have anything to do with worker safety!
I carry around a hard copy of this paper in my professional paperwork. It’s only 6 pages long, has graphics and graphs that really explain all the basics of what an arc flash is, the terrible energy involved, and basic ways to protect workers. It is very easy to read.
In life and in engineering, we are lucky to “stand on the shoulders of giants.” Dr. Ralph Lee was a giant in the field of arc flash study.
Another of Dr. Lee’s papers in the field, “Pressures Developed by Arcs.”
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