FAA Office of Aerospace Medicine
Civil Aerospace Medical Institute

Report No: DOT/FAA/AM-15/15

Title and Subtitle: A Study of Protection Provided by General Aviation Oxygen Masks With Open Ambient Ports in Toxic Environments

Report Date: August 2015

Authors: Paskoff LN, Mandella JG, Self DA

Abstract: Air transport of medical specimens aboard general aviation aircraft frequently utilizes dry ice for preservation. The sublimation of carbon dioxide (CO₂) within the confined space of the aircraft cabin, without sufficient outside air turnover presents a potential hazard. Aircraft equipped with oxygen systems utilizing modified clinical masks that allow oxygen to be diluted with air drawn in through side ports may not offer adequate protection from CO₂ contamination.

Methods.Experiment 1. A simulated aircraft cockpit and cabin area was constructed. Total volume was approximately 3.956 m³. Ten insulated biological specimen bags (12 x 17 x 20 in) that conformed to Department of Transportation regulations were filled with 5 lb of dry ice chips. This ratio of specimen bags to cabin volume reflected common industry practices. Air flow through the mock-up was set at a turnover rate of 9.73. CO₂ levels were monitored with mass spectrometry.

Experiment 2. A face mask with re-breather bag delivered aviator's oxygen at a flow rate of 3 Lpm and was fitted to a test mannequin head connected to two breathing machines that produced alternately an inhalation of mask contents, and then an exhalation of either ground level alveolar air (78.5% N₂, 16% O₂, 5.5 % CO₂), or alveolar air resulting from breathing 100 % O₂ (N₂ removed). The breathing machines delivered a physiological breath pattern with a tidal volume of 0.92 L at a rate of 20 breaths per minute (bpm). The head was inside a 0.76 m³ partially sealed box. CO₂ content in the box was gradually increased and the inhaled and end tidal gas compositions were measured.

Results.Experiment 1. Carbon dioxide levels reached a mean average of 2.02% after 12 min, and then stabilized.

Experiment 2. Inhaled partial pressures of CO₂ inside the mask were 5.496 mm Hg (ambient= 0.1%); 20.93 mm Hg (ambient = 2.44%); and 34.36 mm Hg (ambient= 4.75%).

Discussion. These results suggest that general aviation carriers may be creating levels of CO₂ in small airframe general aviation cabins with high densities of biological specimen bags that exceed the Occupational Safety and Health Administration and Federal Aviation Administration standards (0.5%). Further, commercially available general aviation oxygen equipment may not provide aircrews with adequate protection in environments with high CO₂ content.

Key Words: Oxygen Mask, Carbon Dioxide, General Aviation

No. of Pages: 13