All of the following are safety measures to prevent the delivery of hypoxic gas mixture to the patient except –
Pin index system is to prevent incorrect cylinder attachment (not to prevent delivery of hypoxic gas mixture).
Location of important parts :-


Flow control valve and flow meter (rotameter) of oxygen should be in downstream position (most distal).
Fail-valve is located downstream from N2O and other non-oxygen gas supply source, but not downstream from O2 supply source.
Location of oxygen valve after the N2O valve
Presence of a PIN index system to prevent wrong attachment of the N2O and oxygen cylinders
Location of a fail-safe valve downstream from the nitrous oxide supply source
All of the above