Recall in Shaft for Machine Room-Less Elevators?

We have a machine room-less elevator where the motor is located on top of the elevator cab and the elevator equipment is located within the elevator shaft.

NFPA 13 (2016) 8.15.5.3(2) allows sprinklers to be omitted from the hoistway of "traction elevators" where the hoistway is "protected by smoke detectors, or other automatic fire detection installed in accordance with NFPA 72", and several other requirements.

NFPA 72 (2016) 21.3.3 states that only the elevator hoistway and elevator lobby smoke detectors or other automatic fire detection (as permitted by 21.3.9) shall be used to initiate Phase I Emergency Recall Operation. 

NFPA 72 (2016) 21.3.9 states that if "ambient conditions prohibit installation of automatic smoke detection" that other automatic fire detection initiating devices shall be permitted.

What type of ambient condition in an elevator shaft would qualify as prohibiting smoke detection? 

I understand smoke detectors in elevator hoistways can cause nuisance alarms (NFPA 72 2016 A.21.3.9) and are very difficult to test and replace within elevator shafts, so in my opinion a heat detector would be better for elevator recall in the shaft if it's allowed by code.

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