Strategy Page discusses one of the problems of wars long-gone, but still dangerous today:
These are the many bombs, shells, grenades, and other explosive devices that did not go off when they were supposed to. In the first half of the 20th century, over a billion fuzed devices were used in combat, and five to ten percent of them were duds. In Europe, the site of heavy fighting in two world wars, dozens of people are still killed or injured each year by duds.
In the last few decades of the 20th century it got worse, and the reason was submunitions. These were smaller bombs carried inside a container. The idea was that when the shell or bomb carrying submunitions was used, it would spread these smaller bombs over a larger area and do more damage than one large explosion. It worked, but it also created more duds. Not just more but smaller duds. Small enough for children to pick up and start playing with. Kids are more adventurous and less well informed than adults. A dud submunition looked like a new toy.
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In actual use submunitions turned out to have a higher dud rate than any previous weapon. New artillery shells have a dud rate of about two percent. Israel went so far as to fire 10,000 new shells to confirm that dud rate. But many nations stockpile shells and as these grow older, their dud rate increases. Shells actually have an expiration date, reflecting the fact that the chemicals in the explosives and the fuzes grow more unstable as they age. The Third World and communist nations often had poor quality control to begin with and were more prone to keep old ammunition. During the Afghanistan war of the 1980s, Russian shells appeared to have a dud rate of some thirty percent. And even the United States would sometimes use submunitions that had exceeded their recommended shelf life.
Submunitions were originally designed to have a dud rate similar to that of artillery shells. But in practice it was much higher, closer to five percent. Part of reason for this is the lighter weight of submunitions. Shell fuzes detonate a shell when the shell hits the ground. The impact sends a pretty strong message to the fuze that now is the time to do it, and go bang. But submunitions, weighing from a few ounces to a few pounds, can make a soft landing and not generate enough force to activate the fuze. These make even deadlier duds, for the fuze is not defective, just deceived. When enough force is applied to activate the fuze, you have an explosion. The dud rate got higher depending on where the submunitions landed. When there is a lot of snow or mud on the ground, the dud rate was as high as fifteen percent.
