Final answer:
A cascade system is a method of piping air tanks together to provide air to the SCBA fill station using tanks with increasing pressure levels.
Step-by-step explanation:
The method of piping air tanks together to allow air to be supplied to the SCBA fill station using a progressive selection of tanks, each with a higher pressure level is referred to as a cascade system. In a cascade system, high-pressure air is transferred progressively from one tank to another, ensuring a continuous supply of air at the required pressure for the fill station.