The frequency of inspection is linked to the following data gathered during an audit:
The audit compliance score if an audit has been done
History of fires
Unwanted fire signals
Known fire setting in the area
Building features that may assist fire spread
Fire loading
Access for fire fighting
Water supplies
Maximum number of people in the premises
Size of the building
Vulnerability of occupants
Monitored automatic fire alarm
Area of building
Positive pressure smoke control
Sprinkler system
All of these give a relative risk level, that is then compared to the use of the building, i.e. Hospital. Then something somewhere does some maths, possibly taking into account the area that the building is situated in also, and comes up with an inspection frequency.
The very high risk buildings will get inspected yearly. For low risk the longest inspection period I have seen is 35 years. (100% life safety sprinklered small shop unit, very good compliance level etc)
In line with the Regulators Complaince Code we should all be following this type of approach.