Which extinguishing agent is least likely to leave a residue after use?

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When evaluating extinguishing agents, considering whether they leave residue is important for cleanup and equipment safety. Carbon dioxide is the least likely to leave any residue because it is a gas that blankets the fire and then quickly dissipates, leaving no liquid film or solid material behind. Foam, on the other hand, leaves a surface film that can be slippery and difficult to remove from surfaces and equipment. Sodium bicarbonate and other dry chemical powders leave a fine residue that can cling to crevices, contaminate gear, and, if moisture is present, can become messy or even corrosive. So, carbon dioxide best fits the goal of leaving little to no residue after use.