On September 18th, 1980, Americans came very close to nuclear disaster. During maintenance on a Titan II missile in an Arkansas silo, an airman dropped a wrench, which plummeted 70 feet and punctured the missile, spraying rocket fuel everywhere. The incident was quickly covered up, but had the bomb exploded, millions would have been killed or irradiated. Source
Nuclear bombs don’t just explode. They have a bunch of failsafes to ensure they only detonate when you want them to. They don’t chainfire like other munitions.
The rocket exploded as some soldiers re-entered the complex to ascertain the severity of the situation. The blast door was flung high into the air and landed nearby. The warhead was also blown out and it landed a bit further away. All of its safety mechanisms operated correctly, so it landed intact and sealed.
The people who went back in were killed in the blast of the rocket, unfortunately. The base was then dismantled to prevent further incidents there.
https://en.wikipedia.org/wiki/1980_Damascus_Titan_missile_explosion