A twin-agent fire extinguishing system (TAFES), also commonly referred to as a twin-agent unit (TAU), incorporates the benefits of dry chemical and foam (AFFF or CAFS) fire extinguishing agents.
[1] The dry chemical, usually Purple-K (and in some applications ABC Dry Chemical), knocks down the fire rapidly, while the foam secures the hazard by laying a vapor-suppressing blanket on the fuel and helping to cool the fuel in skin fires.
Application is from twin hose lines connected together at the nozzle, one flows the dry chemical agent and the other foam.
See Airport crash tender Dry chemical tank capacities range from 450 to 3,000 pounds (200 to 1,360 kg).
Dry chemical flow rates vary from 5 to 8 pounds (2.3 to 3.6 kg) per second and 35 to 60 US gallons (130 to 230 L) per minute for the foam for handline application[citation needed].