12/3/2016 5:12 AM
I came up with a solution to this problem. Fabricate a keyed lock for all diesel caps. The key(s) is then tethered to the diesel nozzle. The operators must have the diesel nozzle in their hand appx 1 foot from the cap (the length of the tether) to open the cap (with the key). This ensures no one can put gas in a diesel, which is the concern.
For some machines a locking fuel cap is available. For others, I fabricated the locks which consisted of a bracket, pin, and padlock, all of which "hovered" over the cap and had to be removed to unscrew the cap. I did a couple machines to prove the concept but never finished the project. Finishing that project (the rest of the machines) would have required a fair amount of time and funds and would have resulting in some bellyaching from the childre... er I mean operators. At the time I was working for a super who wasn't interested in it so I dropped it. But I do think I proved the concept.
The system Andrew described also sounds like a good option.