Which hazard class includes substances that emit flammable gases on contact with water?

• A. Class 3 Hazards
• B. Class 6 Hazards
• C. Class 4 Hazards
• D. Class 8 Hazards

Answer: (C)

Understanding hazard classifications starts with recognizing that they group the type of hazard a material presents. Substances that release a flammable gas when they come into contact with water fall into Class 4, specifically the subset for water-reactive materials. This classification exists because contact with water can generate a flammable gas, creating a risk distinct from flammable liquids (Class 3), toxic substances (Class 6), or corrosives (Class 8). So the material described would be labeled as Class 4 hazards. For example, calcium carbide reacts with water to form acetylene, a flammable gas, illustrating why this category covers water-reactive flammable gas producers.