Hospitals, powerplants, chemical plant, generally any large installation have been dealing with critical issues during off-hours for centuries. The solution is an on-call rota. Labour law knows about this, and so do the unions.

Actually, the on-call rota is one of the things I ask about in interviews. If the interviewer doesn't know what to say or says they don't have one it's a showstopper. Operations are going to be a horrible mess, and it's not a place anyone would like to work at.