3-1-1 liquids rule

TSA Response:

To answer your question, I'm going to tell you as much as I can about why the 3-1-1 liquids rule is necessary without getting into classified information.

The challenge with liquids and the vulnerability that terrorists tried to exploit in August 2006 is that liquid explosives don't look any different than regular liquids on the X-ray monitor. There is no way to tell one from the other without removing every liquid from every passenger's bag and testing it. I'm sure you could imagine the gridlock that would ensue if our officers had to test every liquid that came through the checkpoint. This led to an immediate ban on all liquids on August 10, 2006 because of the threat that was uncovered. Extensive testing started immediately to determine if there was a way liquids could be brought on board without posing a risk, because the total ban wasn't sustainable in the long term. These tests were conducted by multiple government agencies, national laboratories and other nations, and the end result was the 3-1-1 formulation: 3.4 ounce (100ml) containers, inside a 1-quart clear, plastic zip-top bag, 1 bag per passenger.
The sealed baggie limits the total volume of liquid per passenger and keeps all the liquids in one place so officers can get a good look at them.

Liquid explosives are extremely volatile and it was the general consensus of top explosives experts that it would be nearly impossible to create a successful explosive combining a small amount of liquids in a larger container on an airplane.

TSA is getting closer to finalizing upgraded software for X-rays that will allow liquids to be screened. Until this happens, we will continue with 3-1-1 to keep you safe when you fly.