Easy solution: Use a PLC (programmable logic controller) as they are cheap and dead easy to program. I fail to understand why someone would bother to lash up a 8051 with relays and write the program in assembler to do such a job. A suitable PLC is less than $100 USD and has a bucket load of protection and is built for industrial control.

Failing this advice, get a PLC and figure out the circuitry so you can built it into your device.