Phase I Emergency Recall Operation for elevators is primarily initiated by smoke detectors located in elevator lobbies, machine rooms, and hoistways. However, NFPA 72 explicitly permits the use of other automatic fire detectors, such as heat detectors, in these locations when ambient conditions could cause nuisance alarms if smoke detectors were used. For example, dusty, dirty, or high-humidity environments like some hoistways or machine rooms might be unsuitable for smoke detectors. In such cases, a heat detector is the specified and permitted alternative to ensure reliable initiation of the elevator recall function.

A. Smoke detector: The question specifically asks for a detection method besides smoke detection, which is the primary method.

C. Bean detector: Assuming this is a typo for "beam detector," it is a type of smoke detector and therefore not an alternative to smoke detection.

D. Carbon monoxide defector: Carbon monoxide detectors are for life safety from CO poisoning and are not recognized by NFPA 72 as a standard initiating device for elevator recall.

1. NFPA 72, National Fire Alarm and Signaling Code, 2022 Edition.

Section 21.3.6: "When ambient conditions prohibit the installation of smoke detectors, other approved automatic fire detectors (e.g., heat detectors) shall be permitted to be installed." This section directly supports the use of heat detectors as an alternative.

Section 21.3.5: This section establishes the primary requirement for smoke detectors in elevator lobbies, machine rooms, and hoistways, setting the context for the alternative mentioned in 21.3.6.

2. SFPE, Handbook of Fire Protection Engineering, 5th Edition.

Chapter 53, "Emergency Movement of Elevators," Section 53.4.2, "Initiating Devices": This section discusses the initiation of Phase I recall, stating, "The initiating devices for Phase I Emergency Recall Operation are required in each elevator lobby... and in the elevator machine room... The code requires smoke detectors to be used as the initiating devices, but it permits other types of automatic fire detectors to be used where smoke detectors are not suitable for the environment." (p. 1938).