What hazardous condition is likely to occur when you fill a tank with water during the preparation for disposal?

Filling a tank with water during preparation for disposal can lead to the expulsion of flammable vapors through the vent and fill openings. This occurs because many tanks previously used for storing fuels or other hazardous materials can retain volatile vapors, which are both flammable and can create hazardous conditions. When water is introduced into the tank, it can displace these vapors, causing them to escape through any openings.

Proper procedures need to be followed during tank disposal to ensure that these vapors are managed safely, which often includes purging or venting the tank before filling it with water. If this step is neglected, the risk of fire or explosion increases due to the presence of these volatile substances. This highlights the importance of understanding the nature of materials stored in USTs and the potential hazards during the disposal process.