Which are the two standard methods of gas freeing a tank?

The two standard methods of gas freeing a tank are purging and ventilation.

Purging involves displacing the flammable or harmful vapors in the tank with an inert gas, typically nitrogen. This method is effective in reducing the concentration of hazardous vapors to a safe level, making it suitable for subsequent operations that require a vapors-free environment. Purging is particularly important in scenarios where the tank must be prepared for maintenance or inspection, ensuring safety for personnel and equipment.

Ventilation, on the other hand, is the process of using forced air to circulate inside the tank. This method helps to dilute and disperse any remaining vapors by introducing fresh air into the space. Effective ventilation minimizes the risk of explosive atmospheres, making it a crucial step in ensuring safety during tank cleaning or repairs.

Both methods are commonly used in tandem to efficiently reduce the risks associated with gas in cargo tanks and achieve a safe work environment. Other options like flushing, vacuuming, heating, and cooling do not directly pertain to the standard procedures recognized for gas freeing, which is why they do not relate to this question.