Malfunction
Malfunction means any sudden, infrequent, and not reasonably preventable failure of air pollution control equipment, process equipment, or a process to operate in a normal or usual manner. Failures that are caused in part by poor maintenance or careless operation are not malfunctions.
Source
40 CFR § 60.2
Scoping language
The terms used in this part are defined in the Act or in this section as follows: