Which of the following is NOT an element involved in producing firefighting foam?

Firefighting foam is a specialized agent used to extinguish fires, particularly those involving flammable liquids. The production and application of firefighting foam involve three primary elements: a water solution, foam concentrate, and a foam proportioner.

The water solution acts as the carrier for the foam, while the foam concentrate contains the necessary substances that create the foam itself. A foam proportioner is the mechanism or device that mixes the correct amounts of foam concentrate and water to generate an effective foam solution for firefighting purposes.

In contrast, fire retardants are chemicals designed to reduce the flammability of materials or surfaces but are not specifically involved in the production of foam. While fire retardants can be part of some fire suppression strategies, they are distinct from the components needed to create firefighting foam. Therefore, the correct distinction for what is NOT an element in producing firefighting foam is fire retardant, as it does not participate in the foam generation process.