At least four times in my flying career I have had to "roll the trucks." Two of these times there was actual smoke in the cockpit (once closing down runway 18 in FRA much to the delight of the gents behind us...)
So Fritz did not shut down FRA, just one runway? THAT was a smart decision. LHR have shut down several times, even when one or both runways were available.
In this day and age we can fly into two runway airports without using an alternate. When you shut down a major airport you risk getting several fuel emergencies.
Who decides to shut down LHR, the operational management, or fire and rescue?