I mostly want to destroy the man working in the lab, although the lab can go too.
Your mention of the multiverse makes me think of experiments involving subatomic particles. If your lab does experiments involving fast-moving particles, there are plenty of things that can go wrong with that equipment. For example, bubble chambers (not used so much anymore, sadly) are filled with liquid hydrogen, which can explode satisfactorily if it leaks and mixes with oxygen. Newer equipment like wire chambers may use other kinds of flammable or explosive materials.
Then there are huge facilities like the Large Hadron Collider, which can have serious accidents if something goes wrong with the massive magnets that are used in the system. If you want to delve into weird particle collision scenarios, there is the possibility of accidentally creating black holes or strangelets... but at that point we're talking about accidents with the potential to swallow up Planet Earth (which may be overkill in your case).