The primary criterion for the acceptability of fire doors is that the fire door:

The primary criterion for the acceptability of fire doors is that the fire door:

• A. Closer is adjustable.
• B. Window is in a metal frame.
• C. Has a label from the testing laboratory.
• D. Has more than three hinges.

Answer: (D)

The key factor is structural support that keeps the door properly aligned under fire conditions. More than three hinges distribute the door’s weight and the load from heat more evenly along the frame, reducing sagging or warping that could create gaps and allow fire or smoke to bypass the seal. This helps the door stay closed and maintain the fire-resisting seal throughout the rated period. Other features matter in practice—closers ensure automatic closing, windows in frames affect visibility and rating, and a testing-lab label confirms approval—but they don’t by themselves guarantee the door will perform as intended under fire exposure like an adequate hinge system does.

The key factor is structural support that keeps the door properly aligned under fire conditions. More than three hinges distribute the door’s weight and the load from heat more evenly along the frame, reducing sagging or warping that could create gaps and allow fire or smoke to bypass the seal. This helps the door stay closed and maintain the fire-resisting seal throughout the rated period. Other features matter in practice—closers ensure automatic closing, windows in frames affect visibility and rating, and a testing-lab label confirms approval—but they don’t by themselves guarantee the door will perform as intended under fire exposure like an adequate hinge system does.