Final answer:
High pressure appliances can be evacuated to atmospheric pressure (0 psig) by removing air or gas from the appliance until the pressure is equalized with the surrounding atmosphere.
Step-by-step explanation:
When high pressure appliances are evacuated to atmospheric pressure (0 psig), it means that the pressure inside the appliance is reduced to match the pressure of the surrounding atmosphere. This can be done by removing air or gas from the appliance until the pressure is equalized. For example, if you have a high-pressure tank with air inside, and you open a valve to release the air, the pressure inside the tank will decrease until it reaches atmospheric pressure.