We have some information that warning line in a commercial flat roof is only allowed in maintenance jobs that is not frequently (once a month) and works less than 2-4 hours. Is it true?
I don't believe so. I believe a warning line does require a full-time person to be safety monitor and they are not supposed to do any other work.
Also, the state may have regulations that are more restrictive than federal OSHA rules.
So, in our solar roof construction phase, if there are not other requirements in Maine, a warning line with safety monitor could be suitable?