Final answer:
The MSDS label that indicates the greatest severity for harm is the National Fire Protection Agency (NFPA) 704 Hazard Identification System label. The blue diamond on the label represents the level of health hazard.
Step-by-step explanation:
The MSDS label that indicates the greatest severity for harm is the National Fire Protection Agency (NFPA) 704 Hazard Identification System label. This label provides safety information about certain substances and details flammability, reactivity, health, and other hazards. The blue diamond on the NFPA 704 label indicates the level of health hazard, with a rating of 4 indicating extreme hazard.