The air inside an aircraft cabin usually consists of 40 to 60 percent recirculated air and 60 to 40 percent outside air, which is tapped from the jet engine and is therefore also known as bleed air. The exception is the Boeing 787, where fresh air is provided by electrically driven compressors. The cabin air volume is exchanged approximately 20 to 30 times per hour. The circulating air is cleaned by High Efficiency Particulate Arrestance (HEPA) filters, which even remove microorganisms (bacteria, viruses) as small as 0.1 µm from the circulating air. Optionally, the filters can contain a layer of activated carbon, which traps volatile organic compounds. Average CO2 concentrations are slightly higher in the aircraft cabin than in other indoor environments but are well below cabin air limits.
Under very rare and unfavorable circumstances, operating fluids (e.g. engine oil, hydraulic oil or deicing fluid) can get into the air supply and pollute the cabin air. This can lead to unusual odors and, in exceptional cases, to the development of visible smoke in the cabin. This is known as a fume event, or better as a fume and smell event. In rare cases, flight attendants and pilots have reported that they developed health complaints as a result of such incidents.
The question of whether cabin air contaminated by fume events affects the health of the flight crew and passengers and how this can be prevented or at least detected in time are among the key topics of our research.
As yet, all cabin air quality analyses during flight have failed to detect any of these extremely rare fume events directly on board with sensitive measuring equipment. Therefore, such events are now being artificially recreated on the ground. We are also conducting research on the thermal degradation products of potential bleed air contaminants with our Bleed Air Contamination Simulator BACS. Pyrolyzed engine oil is the main focus of interest. Under unfavorable circumstances, this can get into the bleed air and ultimately into the cabin air supply via damaged seals in the engine, thus impairing the air quality.
Using BACS, pressure and temperature conditions in the Environmental Control System (ECS) - the air supply in the aircraft - can be simulated. In addition, the air can be contaminated in a defined way and contamination products specifically analyzed. To this end, our accredited laboratory is equipped with numerous on-line analyzers as well as sampling points for off-line analysis. BACS provides a flexible test environment that can also be used to evaluate the efficiency of systems for purifying cabin air as well as sensors for monitoring cabin air quality.
Here you can take a look inside our Bleed Air Contamination Simulator BACS.
Fraunhofer Institute for Building Physics IBP