What is the procedure for safely inerting a tank that previously contained a Class 3 Flammable Liquid?

Safely inerting a tank that previously contained a Class 3 flammable liquid involves displacing the flammable vapors with an inert gas, typically nitrogen or carbon dioxide, to create an atmosphere that is incapable of supporting combustion. The procedure begins by ensuring the tank is properly isolated from all sources of flammable liquid and that all connections, except those needed for the inerting process, are closed and sealed. A thorough risk assessment must be conducted before commencing the inerting process, identifying potential hazards and implementing appropriate safety measures. The inert gas is then introduced into the tank at a controlled rate, typically through a dedicated inlet nozzle at the bottom of the tank, while the flammable vapors are vented from the top of the tank through a separate outlet. The inert gas displaces the flammable vapors, gradually reducing the oxygen concentration within the tank. Continuous monitoring of the oxygen concentration is essential throughout the process, using calibrated oxygen analyzers. Inerting continues until the oxygen concentration is reduced to a level below the lower explosive limit (LEL) of the flammable liquid, typically below 5% by volume. Once the desired oxygen concentration is achieved, the tank is considered inerted and can be safely entered for cleaning or maintenance. Maintaining a positive pressure of inert gas within the tank is crucial to prevent air from entering and compromising the inert atmosphere. Before any hot work or entry into the tank, the inert atmosphere must be continuously monitored and maintained. Proper grounding and bonding are essential to prevent static electricity buildup during the inerting process. Personnel involved in inerting operations must be properly trained and equipped with appropriate personal protective equipment (PPE), including respiratory protection. Therefore, careful planning, execution, and monitoring are essential to safely inert a tank that previously contained a Class 3 flammable liquid.