What method eliminates static electric build-up when transferring flammable liquids?

When transferring flammable liquids, a grounding system is essential to eliminate static electric build-up. Static electricity can accumulate during the movement of these liquids, especially when they flow through pipes or containers. This accumulation poses a significant risk as it can lead to sparks and potential ignition of the flammable vapors present, resulting in fires or explosions.

A grounding system functions by providing a conductive path that allows static charges to dissipate safely into the ground. This minimizes the risk of static discharge that could ignite the flammable liquid during transfer operations. Therefore, using a grounding system is a critical safety measure in environments where flammable liquids are handled.

The other options do not specifically address the issue of static electricity build-up in the same effective way. While non-sparking tools can help prevent sparks from igniting flammable vapors during maintenance or transfer, they do not directly manage static charge. Drum bung caps serve to close containers securely but do not serve the purpose of mitigating static electricity. Thus, the grounding system is recognized as the correct and most effective method to manage static electricity during the transfer of flammable liquids.