My tuppennyworth is to research the types of fuze you are likely to find, by diagrams and by how they were designed to function. Then when you find them you know what a complete, unexpended, version will look like. Be wary even of fuzes found on their own, not fitted to a shell - a French B & B I stayed at a couple of years ago had a number of recovered items in their front yard, including three expended German fuzes. With them was a fourth of the same type but it was complete. I brought this to their attention, told them it was probably live and advised them to contact the authorities. If in any doubt, leave them alone and inform the police. My favourite beach has versions of the 117 and 119 HE fuzes and the majority of what I find is obviously expended. As to whether they are inert, the biggest clue is whether they are still attached to a shell, although I found a fuze fitted to a shell where the steel safety cap had not been removed by the gunners before the shell was fired. In that state the fuze is probably in its most dangerous condition, fully armed and requiring a knock on the nose to make it function. Don't forget that other fuzes are designed to work on the graze principle, meaning that a large vibration to the shell could make them function. I have found other fuzes separate from shell that led me to think the shell had been found and destroyed by demolition years after they were fired, as there was little distortion to the fuze body but the magazine was empty and the external threads were stripped. I also find 25 Pr Smoke BE shell fitted with the 221 time combustion fuze (aka a powder train time fuze). The clue there is whether the base plate is still attached to the shell. You can also check whether a 221 Fuze is expended by looking at the base of the fuze to see whether the star shaped crimp has been opened up by exiting gas. Also each time ring was fitted with a blow-out plug so that slag and excess pressure could leave the fuze without speeding up the burning time. The WW1 fuze shown in this post is typical of other expended British WW1 HE fuzes I have found and I would be happy to have that as an ornament. The 100 and 101 fuzes I have seen were not much distorted by detonation but the clues with those are the stripped external threads and the rending of the metal around the area of the magazine.
