I have no idea how or why someone would mount 12 coat hooks on one door. They would have to be thru-bolted because of the mineral core – you couldn’t put enough blocking into the door to support all 12 hooks. I can’t imagine in what application a 90-minute door would have coats hung on it (the most common use of a 90-minute door is in a stairwell), or how you would even fit 12 coats on the door.
But, being the people-pleasing problem-solver I am, I tried to find an answer. I spoke to a couple of manufacturers and there was nothing in their UL/WHI procedures that said they could or couldn’t do it. I checked NFPA 80 and the only section that sort of applied was regarding signage – section 18.104.22.168 says that signs have to be attached with adhesive, not screws or nails. So you can’t install signage with screws, but you can install protection plates or plant-ons with screws, so someone could argue either side in regard to coat hooks.
This is one of those cases where you have to let common sense prevail. The codes don’t address every possible scenario, and just because the codes don’t say you can’t do something, doesn’t mean that you can.
The thing to think about here is not so much the hooks themselves, but the additional fuel load created by the coats. The required rating for a door is based on the assumption that there will be clear floor space on both sides of the door, so minimal fuel loading. With coats hung on a door, or furniture pushed against it, the fuel load is much greater than planned.
I have a feeling that if the hooks were successfully mounted on the door, twelve coats somehow fit on the hooks (maybe they’re coats for preschoolers), and the fire marshal showed up, he would have a problem with the application. If he required the removal of the 12 hooks, now there are at least 12 holes that are supposed to be filled with the same material as the door.
Get a coat rack.