According to all the guidance I can find, Internal fire doors require intumescent strips to be fitted. As you all probably know this strip expands during a fire due to heat and seals any gap between the doors.

In regard to the requirement to fit cold smoke seals (brushes) as well, I cannot seem to find a definitive answer. They don't seem to be required in all circumstances. In my opinion it would make sense to fit cold smoke seals in all cases as well as intumescent strips.

How does one make the decision as to wheter a cold smoke seals would be required? (and please dont say based on your risk assessment)

In most situations fire-resisting doors (FD30/60) should be fitted with smoke seals, as these restrict the passage of smoke into the escape route from the room where the fire is situated. The exception to this is where fire doors are fitted to rooms in premises where the fire detection system is restricted to the escape route. This will often be the case in three-storey shared houses. In these cases smoke seals should not be fitted, as their benefit will be outweighed by the fact that the smoke detectors in the escape route will only activate when the fire is at an advanced stage and beginning to breach the fire door. The resulting alarm may be so late sounding that the fire and smoke is already affecting the escape route.

There is some guidance documents out there stating that sleeping accommodation (care homes for example) have to have cold smoke seals fitted to fire doors, and the fire and rescue services use this guidance to enforce the requirements. This is of course taking into account that care homes should have L1 systems fitted.

http://www.gov.scot/resource/0044/00444923.pdf

See point 157. Hope this is helpful.