What country do you live? I have worked on water heaters still going strong that were installed in the 1920’s and I must say EVERY SINGLE one either had a indivual shut off valve going to a standing pilot OR the Fuel controller had a means of shuting of the fuel supply.
I think you had better contact a Master Gas fitter OR master Plumber to show you what is the proper way to service this potencial bomb. Also try to get the manufacturers name and send them a letter requesting an instruction book for SERVICE. Good luck sounds like your going to need it.
SylvanLMP