The Recirculated Air Myth

Airplanes don’t recirculate air any more than most environments you spend time in. Despite this, people frequently claim various versions of this urban legend. Some say the air when they close the door stays in the cabin until they open it on landing. Others say it’s actually coming from air canisters stored on the aircraft. It is not true.

The air is really a 50/50 blend of recirculated air and new air bled through the engine air compressors (before combustion). The NY Times has a nice little writeup on cabin air:

Cabin air, he said, is refreshed about 15 times an hour, compared with less than 12 an hour in an office building. On most full-size jets, the air is also circulated through hospital-grade HEPA filters, which are supposed to remove 99.97 percent of bacteria and the minuscule particles that carry viruses. The cabin air is also divided into separate ventilation systems covering every seven rows or so, limiting the ability of germs to travel from one end of the plane to the other.

The reason most people feel the air quality is so low is because the humidity is about 10% to prevent corrosion of the aircraft, which is almost always metal. Newer aircraft are now being made using composites allowing for more natural humidity. The other factor is pressurizing to approx. 8,000 ft, which is higher than you’re used to.

Those HEPA filters employed are also more than adequate to filter air leaving it cleaner than most homes [pdf].

Presumably the confusion is aided by the emergency oxygen system on board modern airliners.

So next time someone claims that the air is literally unchanged through a 9 hour flight, you should call their bluff and ask for documentation. This has been a pet peeve of mine.

Decrypting The Internet

Bruce Schneier on the new wiretapping proposal:

Any surveillance system invites both criminal appropriation and government abuse. Function creep is the most obvious abuse: New police powers, enacted to fight terrorism, are already used in situations of conventional nonterrorist crime. Internet surveillance and control will be no different.

Official misuses are bad enough, but the unofficial uses are far more worrisome. An infrastructure conducive to surveillance and control invites surveillance and control, both by the people you expect and the people you don’t. Any surveillance and control system must itself be secured, and we’re not very good at that. Why does anyone think that only authorized law enforcement will mine collected internet data or eavesdrop on Skype and IM conversations?

I 100% agree here. A security vulnerability, intentional or not is a vulnerability. Even systems with no known security holes are eventually broken. Look at the recent reverse engineering of HDCP, which was theorized as vulnerable in 2001 but not broken for several years, a pretty good run. Eventually all security mechanisms will be broken. Starting with something broken just increases the window of opportunity for abuse and misuse.

In theory this proposal could (I’m no lawyer, I don’t even play one on TV) even impact things like Firefox Sync (Formerly Weave) which employs the best security mechanism I’ve seen in a service. To summarize, it works by encrypting your data before transmission to the server. However the key is never sent. That means even if the Gestapo took the servers with your data, they would still need to get the key from you, or do battle with the encryption which isn’t easy. Even Mozilla can’t read your data, unless a flaw were found in the encryption algorithm. The question is if sync were considered to fall under “services that enable communications”. That seems broad enough to leave room to argue that sync facilitates communication since the browser is the ultimate communication client. The browser is also valuable since it potentially has passwords, bookmarks, and history giving a good motivator to make that argument. Argue that to a 75-year-old judge who never used a computer and it might work.

Meanwhile just weeks ago UAE ironically gets criticized by the US for proposing a Blackberry ban for the same reasons.