There are few parts in fire construction which are of so much importance, and generally so little understood, as fire doors.  Instances of the faulty construction of these, even by good builders and architects, may daily be seen.  Iron doors over wooden sills, with the flooring boards extending through from one building to the other, are common occurrences.  We frequently find otherwise good doors hung on wooden jambs by ordinary screws.  Sliding doors are frequently hung on to woodwork, and all attachments are frequently so arranged that they would be in a very short time destroyed by fire, and cause the door to fall.  In case of fire, a solid iron door offers no resistance to warping.  In an iron lined door, on the contrary, the tendency of the sheet iron to warp is resisted by the interior wood, and when this burns into charcoal, it still resists all warping tendencies.  I have seen heavily braced solid iron doors warped and turned after a fire, having proved themselves utterly worthless.  It is needless to say that when wooden doors are lined, they should be lined on both sides; but frequently we find so-called fireproof doors lined on one side only.

Good doors are frequently blocked up with stock and other material, so that in case of fire they could not be closed without great exertion; or they have been allowed to get out of order, so that in case of fire they are useless.  This has been so common that it has given rise to the jocular expression of insurance men, when they are told that a fire door exists between the two buildings, “Warranted to be open in case of fire.”  The strictest regulations should exist in regard to closing the fire doors nightly.  Frequently we find that although the fire door, and its different parts, are correctly made, there are openings in the wall which would allow the fire to travel from one building to the other, such as unprotected belt and shaft holes.  That a fire door may be effective, it must be hung to the only opening in the wall.

The greatest care must be exercised to keep joists from extending too far into the wall, so as not to touch the joists of the adjacent building, which would transmit the flames from one building to the other in case of fire.  A good stone sill should be placed under the door, and the floor thereby entirely cut.  Sills should be raised about one and a half inches above the level of the floor, in order to accomplish the necessary flooding of the same.  If stock must be wheeled from one building to the other, the sill can be readily beveled on both sides of the wall, allowing the wheels to pass readily over it.  Lintels should consist of good brick arches.  When swing doors are used, they should be hung on good iron staples, well walled into the masonry, and the staples so arranged that the door will have a tendency to close by its own weight.  The door should consist of two layers of good one and a quarter inch boards, nailed crosswise, well nailed together and braced, and then covered with sheet iron nailed on, or if of sheet tin, flanged, soldered, and nailed.  Particular care should be taken to insert plenty of nails, not only along the edge of the door, but crosswise in all directions.  I have seen cases, where the entire covering had been ripped off through the warping tendencies of the sheet iron.