Wednesday, March 23, 2011

Jet engines, bleed air, and the phase changes of radioactive elements

Two recent news articles have caught my eye. First, reports of radioactive contaminated air filtration systems on aircraft

Second, reports of flight attendants carrying dosimeters

The first thing one must realize is that not all radiation is the same. There is a difference between passing through a field of radiation and eating the source of that radiation. If you eat, ingest, or inhale radioactive materials they stay with you and keep irradiating you from the inside. It is unlikely that the flight attendant's dosimeters will give them any true indication of the risk they face,unless they can distinguish between the shower of cosmic rays one gets when flying, versus the Fukushima radioactive fallout particles actually entering their bodies through their mouths and lungs. It is the difference between getting a CAT scan and eating the CAT scan machine.

So how much fallout is entering a modern jet aircraft flying through an atmosphere of ionizing radioactive dust and gas? It is an interesting question, one likely not studied in any detail with commercial aircraft. It’s also a question for the health and safety departments of the airlines. It’s a question that every passenger, crew member, maintenance, ground, and overhaul crew should be asking.

Consider that jet engines ingest large quantities of air which are then compressed/heated and passed into the aircraft cabin via engine bleed-air. Radioactive particles like Iodine and Cesium are relatively heavy and have low melting/vaporization temperatures at standard pressures. Depending on where the bleed air is drawn from the engine, the engine is likely to act like a large centrifuge concentrating these heavier radioactive particles into the bleed-air and into the cabin ventilation system. Even more worrisome is the high temperature and pressures these radioactive particles will experience in the jet engine.

The melting and boiling points of Iodine are 113.7°C and 184.4°C respectively, for Cesium the values are 28.4°C and 671°C. Without phase change charts and detail engine data, it is difficult to ascertain with certainty which states these materials are in inside the aircraft. But given that radioactive elements have been found in aircraft ventilation systems, it is an analysis that someone in the industry should be doing.

The questions for such an analysis would be how much molten radioactive Cesium (and molten/gaseous Iodine) is coating and building up inside the engine, air-conditioning and ventilation systems during each aircraft cycle? How much is making it through to the passengers? What’s the exposure to the maintenance and ground crews? Who is going to ensure the safety of the heavy maintenance and overhaul facilities? How may trips can an aircraft make through a fallout zone before the contamination becomes a health issue? If the aircraft is contaminated who is going to decontaminate it and where?

These are all valid questions worthy of analysis, but they are also question no one wants to answer because of the potential impact of a negative finding on air traffic. If the passengers, flight crew, and maintenance teams don’t demand answers, expect the same result as the firefighters and policeman who were told the air was safe to breath at the World Trade Center site after the 9-11 attack.

No comments:

Post a Comment