Isolated means / Tip the car upside down after a hit of between 2 and 20 G's and NOT have any fuel leakage into the drivers compartment.
The "fuel cells" most folks are running are nothing more than cheap blow molded plastic tanks.
A REAL fuel cell is a ballistic bladder contained in a well designed composite or metallic container. I have used both ATL and Fuel Safe brand cells with confidence.
Car racing at Bonneville is expensive. Dying is not.
Living for six months in a burn center at U of M certainly is.
SCTA wording sometimes seems ambiguous, but the rules are meant as requirements. not words to tell you how to build a car. Back in the day, I helped John write the ECTA rule book, and the same approach was taken. There are too many types and styles of cars running in LSR to give specific rules for each car type. We DO NOT want a rule book as thick as NASCRAP or NHRA.
Sorry for the rant, but fire safety is really one of my buttons.