Moderate hazard: requires significant precautions or limited exposure.
Minimal hazard: poses no health, fire, or reactivity risk.
Serious hazard: high risk requiring specialized protective equipment.
Severe hazard: extreme risk of death or permanent injury.
Slight hazard: may cause irritation or require only minor safety precautions.
Numerical ratings (0-4) used in the NFPA 704 "fire diamond" for health, flammability, and instability.