Use high quality relays purchased from Digikey or another distributor (should be $10-30 in single quantities for AC mains) and put thermal fuses on the mains side of the relay (I generally put several, each going to different parts that are at risk of shorting). Slather everything but the heatsinks (add some if necessary) with fire retardant epoxy, carefully pushing the thermal fuse into the epoxy until it makes contact and pushes out most of the epoxy under the fuse.
Burning down the house isn’t even an issue for me. USB relay throws 24VDC from a UL-approved power supply that opens the valve. The noise from the air compressor OTOH....
There are probably a few kinks to work out that will come up in practice!