Being the philosophical sort that I am, I felt the need to define and distinguish this concept. First of all it refers to the end state of a dirty diaper. If one is refering to the ongoing process of dirtying a diaper, then one is probably talking about a poopathon, that is an ongoing or prolonged... well, you get it.
An ordinary diapering occurs when only the diaper needs to be changed. There may be some light secondary cleaning, but nothing dramatic.
So I figure that there are classes of pooptastrophe:
Class 1: The diaper and at least one other thing needs to be changed or cleaned. For example the diaper and the babies clothing need to be changed, or the diaper needs to be changed and an appendage (hand or foot) needs to be cleaned.
Class 2: The diaper and at least two or more other things need to be changed or cleaned. For example: in addition to the examples given in a class 1 pooptastrophe the diaper pad may need a good cleaning.
Class 3: After all is said and done the baby needs an immediate bath. When you've experienced a Class 3 pooptastrophe, you know it. Ther is, afterall only so much that you can do with little wipes. A class 3 requires serious cleaning - usually because the baby has squirmed so much and covered so much surface area that a weapon of mass cleaning is required to restore order.