Bob
I can see the logic with conduit but not necessarily with tray.
If you had a pneumatic Thermostat line run in a conduit with a fault in it,it could melt a hole in the air line and you would loose temperture control of those units or unit.
Why take that chance?
What is it going to fault to? If poly air tubing they are insulators.
If the pipe they are run in is metallic it is either grounded and the overcurrent device trips or it is not grounded and the pipe becomes energized. The latter can be a dangerous situation but is of little threat to the air lines.
My suggestion of running an electric cable in same tubing, tray, or whatever does not mean run an EMT or RMC from a junction box at the ceiling that is part of electrical system down to a control panel with air soleniods in it and run both power and pneumatic lines down that raceway.
An example of what I am referring to would be a machine with several air actuated devices on it as well as proximity sensors, limit switches, etc. to sense presence of material before an air actuator makes its move. There would be nothing wrong with routing cables for sensors as well as air lines through a leg of the machine that happens to be hollow inside - as long as the cables are not required to be installed in raceways otherwise.
Single conductors of type MTW would not be allowed to be installed this way, they would have to be installed in a Ch 3 wiring method and the raceway would need to be complete from junction/device/pull box to the next junction/device/pull box.