I have a situation where I have a mechanical chase that is approximately 10 to 12 feet wide. It is open from floor to deck with an overall height of 21feet tall. We have plumbing services starting at 10 feet with exhaust ducts between 14 to 18 feet above the floor. We were going to put smoke detectors on the ceiling, but they would be in a location where they would not be able to be tested and/or serviced. Is there an acceptation in NFPA 72 that would allow the smoke detectors to be placed lower so that they could be serviced and tested on a regular basis and still meet code?