The space between the back of an elevator’s swing door and the cab gate is very dangerous. The American Society of Mechanical Engineers has created rules related to the design of elevators in an attempt to prevent injuries.
The ASME adopted A-17, the first safety code for private residential elevators, in 1955 to respond to safety concerns. It said that the distance from the door or gate to the sill could not exceed two inches and the distance from the hoistway face of the landing door or gate to the car door or gate could not exceed four inches. The requirements were relaxed over the years, which led to more safety concerns and the eventual adoption of the 3-5 Rule.
The current elevator code requires that the distance from the back of the swing door to the edge of the hoistway not be more than 3 inches. In addition, the distance from the back of the swing door to the cab gate may not exceed 5 inches.
Elevator contractors must be careful to comply with the 3-5 Rule. The contractor who builds the hoistway is responsible for meeting the requirement. Framing the hoistway with 2x4s helps meet the rule. Using 2×6 construction makes it more difficult to adhere to the 3-5 requirement. Contractors must use door jambs specifically designed to be used on residential elevators, and hoistways need to be perfectly plumb and square. Any variation can create a non-compliance issue.
Newer types of doors and gates comply with the 3-5 Rule. One is a specially manufactured swing door frame with a 1-inch maximum distance between the hoistway door and the edge of the landing sill. An automatic accordion gate operator is another good option because it will come in contact with any obstruction, fail to close, and prevent the elevator from moving and trapping a person. Power side slide doors and gates have tolerances well below the 3-5 requirement.