Minecraft wiki entry for Spawner_traps, associated text: In the Nether, blaze spawners can be generated in nether fortresses, and can be trapped to collect blaze rods and mass amounts of experience. Blaze spawners are the most dangerous to trap because of the height of the structure and the additional danger of lava. One must be well-prepared to contain this type of spawner, lest they might die from heights, lava, the blazes, or even external mobs.