[Mr V]

Using a system with a pressure switch that will control a relay whether it is a spike or simple 12v relay with a properly calibrated blow off valve would be safe in general, despite not being legal for use at an event.

The safety concern I would have is that if people are working on the rest of the robot while the pneumatics are pressurized there are potential safety issues. Power may inadvertently be applied to a solenoid causing an actuation that could harm someone who's hand or head was in or near a robot. A tool that slips or is dropped could potentially cause one of the plastic tanks to explode ect. It is for that reason that it is highly recommended that work only occurs on the robot when the power is off and the pressure has been relived from the pneumatics.