Which of the following is NOT a major classification of hazardous materials?

The classification of hazardous materials typically encompasses categories that pose significant risks to health, safety, and the environment. Major classifications include explosives, flammable liquids, and compressed gases, as these substances can cause severe damage or pose serious health hazards in various situations.

Non-toxic substances, while they may not pose an immediate danger, do not fit into the same critical classifications that hazardous materials are known for. Instead, non-toxic substances are generally considered safe for handling and do not require the same stringent regulations or precautions associated with hazardous materials. Therefore, identifying non-toxic substances as a category of hazardous materials is inaccurate, distinguishing it from the other options which are indeed major classifications of hazardous materials.