Propellant filling apparatus

A propellant filling apparatus (10) comprising

• a filling booth (11) for receiving within it one or more containers for filling with a propellant;
• a propellant inlet (12) to the filling booth (11) that is capable of supplying propellant, for filing into one or more containers within the filling booth (11), from a propellant supply;
• an inert gas inlet (13) supplying inert gas from an inert gas supply (14) into the filling booth (11);
• a discharge outlet (16) from the filling booth (11);
• an extraction fan (17) that is capable of adjusting its fan speed to maintain the pressure of gas in the filling booth (11) to be lower than atmospheric pressure outside the filling booth (11);
• and
• an oxygen detector (27) that is capable of detecting levels of oxygen in the filling booth (11) and triggering circulation of inert gas in the filling booth (11) when the level of oxygen in the filling booth attains or exceeds an oxygen threshold level that is proportional to the maximum oxygen concentration of the propellant.