What is the nominal charge of the crew oxygen cylinder?

• A. 1800 psi
• B. 1850 psi
• C. 1900 psi
• D. 2000 psi

Answer: (B)

The concept here is understanding what “nominal charge” means for a crew oxygen cylinder. The nominal charge is the standard fill pressure used as a reference to define the cylinder’s contents and ensure a predictable oxygen supply during use. For crew oxygen cylinders in aviation, this standard fill is 1850 psi. This value is chosen to sit safely below the cylinder’s maximum service pressure (around 2000 psi for many oxygen cylinders) while maximizing the usable gas volume and accommodating pressure changes with temperature. At the reference temperature (typically 70°F), filling to 1850 psi gives the intended capacity and reliable regulator performance for the expected duration of use. Filling to a higher pressure would eat into the safety margin, while a lower pressure would reduce available oxygen.