That's horrible. There's a board on Pinterest I follow that is nothing but pins about heat lamp fires. I just used the Mama heating pad method on my most recent batch of chicks and was super pleased. Will probably be retiring my old heat lamps.
Agree. I was cleaning thick layers of dust off my heat lamps almost daily last time I brooded. Heat lamps are more dangerous than a lot of people would think, so always be careful, use the smallest wattage bulb possible, or go with another brooding alternative such as a heating pad or a heat panel.
I don't think you'd be able to tell at only a week old. But you are right, RIR males feathers do come in quite a bit more sparse, and the feathers on their shoulders are a darker red. By 3 weeks you should be able to tell.