According to the JAR OPS, when a commercial transport passenger airplane is equipped with a door in the flight crew compartment area, this door must include:
a locking system to prevent any unauthorized access.
a device preventing the flight crew from being locked in the cockpit.
distinctive red or yellow coloured markings indicating the access area (in case of a blocked door).
a sealing system allowing the maintenance for as long as possible of the pressure in the cockpit in case of a depressurization in the compartment area.