Airlines in the US have been told that they have to put emergency oxygen devices back into aircraft toilets having been told to remove them in February last year. The Federal Aviation Administration ordered the removal because it feared that terrorists might use the chemical system to start a fire on board an airliner.

The reversal of that decision comes because of fears that not having emergency oxygen in toilets could endanger passengers in the event that the cabin loses pressure.

However, the FAA said that new systems will have to be designed in a way which makes them tamper proof. A design is still to be settled on, but it is likely that the new oxygen provider will be positioned in a part of the cabin which is visible rather than behind the closed door of a toilet.

It is estimated that some 5,500 planes will have to be refitted at a cost to airlines of $44.2 million. The removal of the emergency systems cost around $935,000 according to the FAA. The body explained that installing oxygen systems would cost $6,000 in parts and take 12 times the labour that disabling or removing them did.

The FAA originally gave airlines 24 months to comply with the refitting order. However, because a new design has still not been decided on, carriers including Delta, United, Southwest and American, and aircraft manufactures Airbus and Boeing, have asked for more time. The FAA has revised the time limit to 37 months.