I hate heat lamps. I removed the clamps from them early on and secured them with non-flammable carabiners to an eye hook. I do not use them in the close quarters of the coops, but do hang them in the run during below freezing weather. Despite all my precautions, I had a hen burn her head on the bulb because I had misjudged the height. The hen had stretched her neck to its full length while standing under the lamp. Luckily, she just burned her head feathers, creating quite a stench. It's how I noticed it.
Even when people have been aware not to trust a heat lamp clamp, if a flammable material is used to secure the lamp such as twine, if it contacts the reflector or bulb, it can catch fire and the lamp can then fall, setting bedding on fire or the entire coop. I've been on BYC so long, I've seen several of these tragedies, not to mention my own close call.