[homegroan]

is that when they change the fuel from a liquid to a gas? or vice versa?

[LOC1]

A Fluid Catalytic Cracking Unit converts feedstock that looks like lubricating oil into gasoline and diesel fuel. The unit operates at low pressure, but at relatively high temperatures, in the range of 1000-1100 deg F. The process involves circulating the powdered catalyst between two vessels. Sometimes mechanical failure or operating error can lead to release of the circulating catylst. It is a serious refinery accident, but not uncommon.