A B747-400 Captain reported spurious main cargo compartment fire warnings. The spurious signals appeared to be chronic maintenance items. A precautionary emergency was declared on landing and a CFR inspection proved negative.

Narrative

I was summoned to the cockpit because of an intermittent main deck cargo fire indication. The event consisted of the warbler; the master warning; and a light in the overhead 'arm' switch. No EICAS message illuminated. We referred to the QRH; however; this item had been previously written up on several legs before this flight. Also of note; several smoke detectors were on deferral. An inspection of the main deck revealed no sign of smoke; heat; or flames. There was no declared HAZMAT on board the aircraft. An inspection of the cargo documents revealed no additional items of interest. I contacted Dispatch.The conference included Dispatch and Maintenance. All involved in the discussion concurred that the problem was a spurious signal. Main deck inspections occurred at close intervals for the remainder of the flight. No smoke or fire was ever reported. No EICAS message illuminated. Also during this time period; several items in the aft bulk cargo failed: heat valve; fans; etc. Continuing to our destination; we declared an emergency and upon landing requested an exterior inspection by CFR. No anomalies were found. Again we inspected the main deck and found no trace of smoke or fire. We continued to the gate without further issues.