Class 4.3: Dangerous When Wet Hazardous Substances

General Information:

Class 4.3 Dangerous When Wet are materials that react dangerously with water, releasing flammable or toxic gases, often at a rate or temperature high enough to ignite the gas or cause explosions. This reaction can occur with water or even just with the moisture in the air, making strict handling and storage procedures of upmost importance to prevent fire and explosion risks.

Main Hazards:

• Gas emitted may ignite spontaneously.
• Will emit flammable gases when in contact with water.
• May react with atmospheric moisture.

Examples:

• Calcium Carbide - Used in welding and cutting. When mixed with water, it produces acetylene gas, which creates and extremely high temperature flame ideal for cutting thick steel.
• Aluminium Phosphide - Used for fumigation commonly in grain silos, warehouse and shipping containers to kill insects and rodents. Solid tablets or pellets are placed in airtight enclosures, as they are exposed to air humidity, they react and converting to a gas that penetrates commodities to kill insect, larvae and rodents.