What is so hard to believe about an engineer not relying on 921 to do engineering work? These are the people that by law must be competent in their craft - the law in every state. Engineers routinely see O&C reports in which the author has drifted into engineering work, violating the laws of nature - fires being created in situations where there is not enough energy, as an example.

What is funnier is some O&C trying to tell an engineer how to do his / her work. You don't have the math background. You don't have the experience. You never took the board exams. You don't have the schooling.

Last time I checked, the IEEE had well over 1100 standards, plus well over 51 journals. Hundreds of thousands of articles. Here is one way this works out...

Ground resistance can be important in a fire causation, particularly with surges. The NEC says 25ohms or less, and if not, add another grounding method. What is not said by NFPA?

Ground resistance changes during a lightning event. The way to know this is to check the IEEE article written by Alan Christman in 1979 on surge impedance and vertical antennas, 1979, Transactions on Broadcasting. You will find no such data in 921 or the NEC. A rare citation, but the data is there.

If an engineer was attempting to do O&C work, yes - 921 applies. And yes - engineers really ought to stay out of doing O&C