Which characteristic describes a major hazard of Class 3 flammable liquids?

The characteristic that describes a major hazard of Class 3 flammable liquids is that they may be toxic, corrosive, or thermally unstable. This classification indicates that while these liquids are flammable and pose a significant fire hazard, they also have additional risks due to their chemical properties.

Many Class 3 flammable liquids can produce harmful vapors that may be toxic if inhaled, absorbed through the skin, or ingested. Furthermore, some of these substances can cause corrosion to materials and living tissues, leading to safety concerns for individuals handling them and for the environment. Additionally, thermally unstable liquids can change their properties under heat, leading to increased volatility and the potential for increased hazards. The understanding of these characteristics is crucial for safely managing and responding to incidents involving Class 3 flammable liquids.

The other choices suggest characteristics that do not accurately reflect the potential dangers associated with these substances. Flammable liquids typically do not fall under non-flammable designations or the inability to combust, nor are they limited solely to causing minor irritations.