NFPA flammability ratings, such as those in NFPA 704, are standard safety classifications defined by specific flash point thresholds and other physical property criteria; no citation is needed for this established definitional fact.
The claim states that NFPA flammability ratings are defined by specific flash point thresholds. This is a matter of standard safety definitions and codes (such as NFPA 704), making it common knowledge by definition and everyday professional observation in fire safety and chemistry. Therefore, following the instructions for STEP 0, the verdict is COMMON_KNOWLEDGE and no citation indices are attached.