A defect that is quite common throughout most fire door installations is incorrect margins where the door is hanging in the frame. The required gap in most instances (depending on the manufacturer’s certification) should be between 2 to 4mm, while at the threshold a fire smoke door should be no more than 3mm.
In a fire situation a timber door shrinks and distorts towards the fire. This reflection is mitigated by the engagement of the intumescent seals in the door frame which seal the door in place. If the margins around the doors are too excessive or indeed too little the fire door will fail