There was an A level chemistry experiment where I was heating sodium metal in an glass tube and allowing it to melt into an unknown chemical. We were then going to test what kind of organic compound it was by dropping the hot molten sodium into cold water. Unfortunately, the unknown chemical I used was an inorganic compund, and the reaction was very violent. I panicked and dropped the hot chemical sinto the cold water and it went off with a big bang. Lots of white smoke and many nerves shattered. I had picked up the chemical the teacher was going to demonstrate to us rather than the organic compund. That was over 25 years ago and I still remember the shock of the explosion.
Fortunately, since then, there have been plenty of things that have gone wrong in experiments but nothing so explosive.
I also had an experiment where I had to collect crayfish from the side of a pond in Lichfield so we could study them back in the aquarium. In the summer, the crayfish come onto the land overnight because there is more oxygen in the air than they can get across their gills in the water when its really warm. So we had to go and collect them at night, in mid summer. Its only really dark enough by midnight so we would creep around the poind looking in the wet grass. Every so often, there would be a loud “cracking” sound followed by a rude word and then “sorry” as another crayfish managed to find itself under another researchers Wellington boot!
I now work with umbilical cords and the only problems we have is when they burst as we wash them. Lots of blood and gore but all contained in a safety cabinet.