Most of this discussion has used the term “lock out” however many of the suggestions have been means of cutting off the gas flow that may be useful at times but do not meet the requirements of a lock out process.  For example, installing a plug in place of the hose barb seems like a good thing for some extended maintenance operations, but is not something where the “key” can be under the control of the person working on the system.

There are purpose-designed lock out devices that are plastic clam-shells sized to fit over valves that work by twisting, like a faucet, or over  electrical plugs,.  A lock can be used to keep the cover closed, and when closed the valves cannot be turned, or the plug cannot be plugged in.  That meets the requirements of a lock out device.

I suspect devices of this kind can be found that will fit over the gas valve. I am not suggesting they are inexpensive, but they are there and comply with lock out requirements.

Peter Zavon
Penfield, NY

PZAVON**At_Symbol_Here**Rochester.rr.com

Our potential client is a contractor who has it in his bid specs but no particular mechanism is specified.  No idea what the rationale behind the specification is.  While it would certainly be interesting to know and something to discuss with the project manager who authored the bid, this gets beyond the original question which is can it be done on individual valves and, if so, how.