Extinguisher Agent Behavior in a Ventilated Small Aircraft.

Hand-held Halon 1211 fire extinguishers were evaluated in a four-place Cessna Model 210C aircraft. The aircraft was operated in an airflow facility under simulated flight conditions. Extinguishers of 2.5 pound capacity were discharged to determine the dissipation rate and toxicity levels of Halon 1211 extinguishing agents. Agent concentrations dissipated rapidly. Analysis of dose calculations demonstrated that 2.5 pound Halon 1211 extinguishers were safe in the four-passenger test aircraft. Dose calculations for the pilot were only 25 percent of the limit for Halon 1211. Ventilation airflow produced air changes in the cabin of 1.16 minutes at 120 miles per hour airspeed and 1 minute at 140 miles per hour. The high cabin ventilation rates together with the effects of agent stratification resulted in safe conditions. The effective air change time found in analysis was of the order of one-third of a minute. This quantity used in the procedures outlined in Advisory Circular AC-20-42B leads to the conclusion that discharge of Halon 1211 weights of 6 pounds can be safely withstood in the C120 under flight conditions. Discharge of a 2.5 pound chemical powder extinguisher adversely affected visibility for over 22 seconds.