As my experience with fire investigations developed, my challenging mentor, Professor Rogers, decided that I should also learn something about explosives. He may have had an ulterior motive because one of the activities that kept him busy, often at night, was dealing with nitroglycerine (NG), remaining after it had been used to blow, or attempt to blow, a safe. During the depression years and into the 1970s, when cash was king and credit cards were rare, there were often substantial amounts of cash stored in the safes that were a common element of the furnishings of most retail businesses.