Scott 5500 used at 5500 psi
There are a number of things in the above forum entrys that give me cause for concern. While the Grade D & E air specifications DO NOT specify minimum dew points, there is a general consensus and specification that states: (Copied from Liberty Mutual Ins. Co.) "The dew point is the temperature at which H2O vapor will start to condense from air. This value depends upon the air's H2O vapor content and pressure. The H2O vapor content of intake air ranges from saturated to very dry. Saturation levels are in the low % range. For example, at 20°C (68°F) air can hold 2.3% H2O vapor (23,100 ppm v/v = 34 mg/L). At 40°C (104°F) this value is 6.8% (68,400 ppm v/v = 51 mg/L). The amount of H2O vapor that gets into SCBA air depends on the intake air level and filter efficiency. SCBA air is required to be dry enough to prevent malfunctions (e.g. air flow blockage) due to internal condensation or icing caused by expansion cooling past regulators. High H2O levels can also inhibit catalysts that convert CO into CO2. CGA G-7.1 does not list an H2O limit for Grade D or E air. However, SCBA air must either have a maximum H2O content of 63 ppm (0.05 mg/l), which corresponds to a -50°F dew point, or an H2O vapor maximum (ppm) resulting in a dew point that is 10°F lower than the coldest temperature expected for SCBA use. Therefore, H2O vapor limits for SCBA air are essentially dependent on the geographic region. CGA dew point limits are not pressure values but refer to "dew point over ice at 1 atm."
Notice that the spec is at one atmosphere, however, when air is compressed the dew point rises. From dew point calculators available on the internet, it is easy to determine that pressure dew points for any amount of moisture in a breathing cylinder at any pressure. The numbers that I am familiar with suggest that a minus 65 deg. F dewpoint, when compressed to 5,500 psi. will then have a dew point around 42 deg. F. This means that if you wear your pack in the cold weather and the cylinder temperature drops below 43 degrees, there will be some liquid water condensing inside the bottle. Not a problem unless that moisture begins to condense in the high pressure regulator stage causing ice to be formed in the regulator. Second problem (long term) could be rusting of the inside of steel cylinders. This might result in contamination (rust dust) entering high pressure regulators and filters as well as rejection of cylinders at the hydro-test inspection.
Another possible problem is with the design of the "Blast Containment" which will need to be able to contain the force of a 5500 psi bottle failure. I have asked our Scott representative about these concerns, but the factory has not given me a formal answer.