Jim,
This section (18.6.2) has always been problematical throughout the history of 921. It has been modified many times.
There are currently multiple proposals on this section to be considered week after next at the committee meeting in Kansas City.
Watch this space for continuing news.
Pat Kennedy, CFEI, CFPS, MIFireE
Fire and Explosion Analyst
Sarasota, Florida
[
www.kennedy-fire.com]