The 60 minute SCBA tanks are indeed 550 CI = 9 litres internal volume.... and the 45 minute tanks are 416 CI = 6.8 litres.... Although Boyle's Law for ideal gasses would predict that a 550 CI tank would hold 97 CF of air, once you surpass about 3000 psi, air no longer acts as a ideal gas, but a "real gas", and calculations must use VanDerWaal's formula, not Boyle's.... In fact that 550 CI tank only holds 88 CF of air (at STP) when filled to 4500 psi, not the 97 CF you sometimes see advertised.... The same holds true for the 416 CI (45 minute / 6.8 litre) tanks, they only hold 66 CF of air at 4500 psi, not 74 CF....

Bob