As long as you are keeping an eye on your equipment and have a fire extinguisher nearby just in case, you should be just fine running Antminer S1's 24/7.
Ya, but that's a bit of a problem. When I'm at work (for example) the best fire extinguisher will be useless

There's no way around, you have to make the decision if you take the
risk and leave them alone without being able to intervene at all..