Health Concerns
The bleed air comes from the engines but is "bled" from the engine upstream of the combustor. Air cannot flow backwards though the engine except during a compressor stall (essentially a jet engine backfire), thus the bleed air should be free of combustion contaminants from the normal running of the aircraft's own engines.
However, on occasions components (carbon seals) can leak oil (containing highly toxic additives) into the bleed air, in what is known in the industry as a "fume event". This is generally dealt with quickly since failed oil seals will reduce the engine life.
Nevertheless, oil contamination from this and other sources within the engine bay is leading to serious health concerns, and has triggered research by a number of academic institutions.
Read more about this topic: Environmental Control System (aircraft)
Famous quotes containing the words health and/or concerns:
“Criticism is often not a science; it is a craft, requiring more good health than wit, more hard work than talent, more habit than native genius. In the hands of a man who has read widely but lacks judgment, applied to certain subjects it can corrupt both its readers and the writer himself.”
—Jean De La Bruyère (1645–1696)
“Mr. Christian, it is about time for many people to begin to come to the White House to discuss different phases of the coal strike. When anybody comes, if his special problem concerns the state, refer him to the governor of Pennsylvania. If his problem has a national phase, refer him to the United States Coal Commission. In no event bring him to me.”
—Calvin Coolidge (1872–1933)