Filling Ratio — FRCA Primary MCQ
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Correct answer: E — 0.67
The filling ratio is defined as the weight of gas in the cylinder divided by the weight of water the cylinder could hold. In the UK (temperate climate), the filling ratio for nitrous oxide is 0.67. In tropical climates it is 0.75 (lower to allow for thermal expansion of the liquid phase). Overfilling is dangerous as liquid expansion with temperature rise can cause cylinder rupture.
Reference: Al-Shaikh Stacey 2019 Essentials of Anaesthetic Equipment