When the Fire Inspector, whether the local Engine boys or a full-time inspector, comes to to the annual routine inspection, they are to introduce themselves, state the purpose of their visit (routine fire inspection) and ask permission to conduct that inspection.
Mostly this technicality gets a little garbled. Most business owners think they are required to allow admittance. Many fire guys feel they don't have to ask permission to enter and can just come in and wander about. The training I received, as an inspector was quite specific. I was required to ask permission to enter and conduct an inspection and the property owner could deny me permission to enter.
There are times when it is just absolutely inconvenient for the property owner to drop what he is doing and cater to the wishes of the fire guys. It is absolutely reasonable to ask them to come back another time.
With regard to keys. It is reasonable for the fire guys to ask for a guide, with keys, to accompany them on their inspection. It is unreasonable for them to ask the owner for a pass key and they have no particular right to wander about the premises unescorted.
Residential premises (apartments) are somewhat different. California law prohibits the owner from entering individual apartments except by appointment or in emergencies. The fire guys will want to randomly inspect the operation of required smoke detectors, usually a random 10% of the units per year. In some complexes there will be a number of vacancies. That plus just knocking on some doors and asking if they might check the smoke detectors will usually do the trick.
The routine fire inspections should never deterioriate into an adversarial situation between the fire dept and the property owner/manager. Each must understand the rights and responsibilities of the other. The fire dept has the responsiblity, by the fire code, to conduct inspections. The property owner can insist on them getting a warrant (not really a good idea) or at least coming at a mutually convenient time ( a much better idea).
PH