If you know the contents of your fathers safe then maybe it should stay closed. in 20 or so years you'll opne it having forgotten whats in it. Or maybe your children will open it in 50 years and find stuff in it.
That would be a lovely surprise for them.
I say this because my family found a huge fireproof chest in one of my deceased relatives house, inscribed with the family name. Its victorian, and when we opened it we found family siver, relics, full dining sets and the cherry on top - 75 sovereigns.