Twin-Agent Fire Protection means the “twin-attack” capabilities of dry chemicals and foam firefighting agents. Whenever a hazardous area requires rapid disassembly and securement, two-agent systems are often recommended.
The basic principle of the Twin-Agent concept is the combined advantages of the Purple-K dry chemical agent and the AFFF agent. Purple K is a dry chemical based on potassium bicarbonate that ensures a quick extinction of the flames. It is especially effective on pressure, operation and discharge fires, making it a primary extinguishing agent for flammable liquid fires. Purple-K supports AFFF foam, and can be used regardless of application sequence.
AFFF, an aqueous synthetic foam forming a film, is used to cover the fuel with a thin film preventing the evacuation of flammable vapors. It also provides a certain level of cooling.
The main advantage of the double agent concept is that the dry chemical agent can quickly extinguish the fire while the AFFF agent ensures the safety of the hazard zone. When used in combination, most three-dimensional, running and pressurized fires can be extinguished by a single trained operator. The dual agent attack provides the most efficient extinguishing and securing capability known in many flammable liquid fires.
Reference: https://t3safety.com/product/twin-agent-fire-extinguisher-units/
