All of the following are hazardous gas materials except:

• A. Chlorine
• B. Hydrogen
• C. Diesel Fuel
• D. Anhydrous ammonia

Answer: (D)

Hazardous gas materials are substances that exist as gases under normal conditions and pose risks through inhalation, rapid dispersion, flammability in the gas phase, or corrosive/toxic effects. Among the options, chlorine is a toxic gas, hydrogen is a flammable gas, and anhydrous ammonia is a toxic, irritating gas—each presents gas-phase hazards. Diesel fuel, however, is a liquid hydrocarbon at room temperature; while its vapors can ignite, the material itself is not a gas hazard—its primary hazard is as a liquid fuel and potential spill or fire on a liquid surface. So diesel fuel is the exception.