American Society of Mechanical Engineers (ASME) Practice Exam

In the context of furnace operations, the conditions that typically lead to an explosion are related to the improper management of fuel and air mixtures, as these can create an environment conducive to combustion. Normalized temperature, on the other hand, refers to the operational temperature being within normal, safe limits. When temperatures are within these ranges, they do not inherently contribute to the risk of explosion, as controlled surroundings usually prevent hazardous situations.

In contrast, improper purge, excess fuel, and an improper fuel/air ratio are all critical factors that can lead to dangerous situations. An improper purge means that the system may not be adequately cleared of previous combustibles or flammable gases before operation, while excess fuel ensures that there is a surplus of flammable material available, which can ignite uncontrollably. An improper fuel/air ratio can lead to conditions that either ignite spontaneously or result in severe combustion instability, both of which can culminate in an explosion.

Therefore, since a normalized temperature is a safe condition in the context of furnace operation, it is not a condition necessary for a furnace explosion to occur.