Section 7.253. Carriages

(a) Specifications. The carriage or chair shall have a foot platform with a seat or seats and an outer arm rest and a back so arranged as to provide safe support for passengers, provided they are of the self-locking type. Swivel-type seats are permitted.

(b) Truck and guides. The carriage shall be securely anchored to a truck which supports it. The truck shall be retained in a track or guide rail assembly. Supporting guide rails shall be securely anchored to the stairs or sidewall.

(c) Factor of safety. The factor of safety used in the design of the carriage, truck, guide rails, sprockets and sheaves shall be not less than five, based on the rated load.

(d) Safety devices. The carriage shall be provided with a safety of the instantaneous type operating on failure or slackening of the hoisting rope or chain. A slack-rope or chain switch shall be provided which removes power from the motor and brake if the hoisting rope or chain fails or slackens. An exception exists where self-locking drives utilizing a lead screw or other positive gearing will stop and hold the carriage with rated load within less than four inches of down travel after power is removed.