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Fire door upper and lower gaps

According to the EN1363-1: 2012 standard, the formula for calculating the clearances that a fire door must have for optimal operation is X = (a + b) / 2 + 2 mm, where "a" is the maximum clearance and "b "the average slack.

It is not necessary to insulate the bottom of the door to prevent the passage of flames and smoke into the protected area, as you might think.

Due to the very nature of the fire, it produces fire pressure on the upper two-thirds of the door so that air enters the fire through the lower hole in the door, instead of the fire entering the hole.

Therefore, the installation of fire doors with a small gap in their lower part between the floor and the door leaf is valid. This gap is necessary so that the leaf does not hit the ground, preventing the correct operation of the door closer.

Despite this, it is not advisable for the lower gap to exceed the maximum allowed since then the contribution of oxidizer (oxygen) to the fire would be favored, which helps it to grow and create even more unsafe conditions during the fire.