In order to take account of the increased risks in the event of a disaster, buildings where the lowest floor of the top level is more than eight metres above the outside ground must have a fire-stable structure with a fire rating of one hour and fire-stop floors of the same rating.
They are isolated from any building or premises occupied by third parties by at least one-hour fire-stop walls or by airlocks with half-hour fire doors fitted with door closers and opening towards the inside of the airlock.