Timed Shut-Off Valves for Gases

simple solinoid valves ASCO, Whitey et al. I'll bet you could get one that works like the auto flush toilets.

A simple normally closed solenoid will do the trick when combined with a timer of some sort as suggested above but, re-instating the supplies need a little bit of thought. What would happen if the solenoid closed, then someone opened a manual valve downstream and effectively vented the system in the room down to atmospheric pressure. If the timer energised the solenoid valve the next morning and turned the supplies back on you could create either a highly oxidising atmosphere (O²) or one which could suffocate anyone entering the room (CO²).

At the very least some manual intervention must be provided, preferably a keyswitch to reinstate the supplies and better still, a "proof of closure system" to ensure that all downstream valves are closed. A simple pressure switch set to normal line pressure less say 10% and some basic relay logic would do the trick.

A packaged version is used in the UK for Natural Gas fired commercial kitchens to provide an interlock between the extract system and the gas supply.

Response #2 got a GA vote from me, but I would prefer to look at this as an education issue. Enforce a policy of shutting off the gas valves when not in use. There must be a reward for compliance and a penalty for failure.