Earlier today, British and Pakistani authorities busted a major terrorist plot to simultaneously detonate explosives aboard multiple airplanes traveling from Britain to the United States. According to news reports
, the terrorists were planning to carry bottles of a "British version of Gatorade", mix them with a gel-like substance and detonate them with an MP3 player.
As a trained chemist myself, I am surprised they have ever allowed passengers to bring liquids onto airplanes at all, especially since 9/11.
Many of the terrorist threats around airplanes that have come to light prior to this one have involved terrorists bringing premanufactured explosives onto an airplane. However, it is quite feasible for a terrorist to actually make the explosive compound on the plane itself. Essentially a plot like this would work as follows:
- The terrorist would bring two chemicals with him onto the plane: Compound A and Compound B. Both Compound A and Compound B are chemically stable. Compound A would likely be a strong acid (which would almost always a liquid), while Compound B may be a liquid, solid pellets, or a powder.
- While on the plane, the terrorist would mix Compound A with Compound B and shake the container. The strong acid (Compound A) would then react with Compound B to produce Compound C - a chemically unstable molecule capable of detonation.
- Depending on what Compound C is, it may spontaneously detonate on its own, or the terrorist may have to detonate it with a spark, by heating it, or by passing an electric current through it.
This same method could also be used to produce a poison gas that would kill most/all of the passengers on the plane. For example, in gas-chamber executions in the United States, a solid (sodium cyanide) is dropped into a liquid (sulphuric acid) to produce a poison gas (hydrogen cyanide).
There are many chemical combinations that could be used to wreak mayhem onboard an airplane, but most of them involve a bottle of a rather nasty liquid (such as a strong acid) being combined with some other chemical. If the terrorist cannot bring the liquid component on the plane, the rest of the plot will fail.
The major problem with liquids is that many of them look alike. Sulphuric acid and nitric acid look just like water, and if you put some sort of dye in them, they could be made to look like any beverage someone might want to bring on the plane: bottled water, Coca Cola, Gatorade, etc.
If we know that terrorists are plotting against us, and we know this type of attack is possible, there is a compelling reason not to allow passengers to bring liquids aboard the plane. In addition, there are very few reasons that someone actually needs to bring liquids on a plane. They serve drinks on the plane, and a mother who is formula-feeding her baby can bring powdered feed, and mix it with water on the plane. Yes, passengers may want to bring bottles of alcohol from exotic destinations, or things like this, but those items can be stored in checked luggage. Travelers regularly bring colognes, travel-sized shampoo bottles, and the like, which are are too small to store enough liquid chemical to cause real damage - perhaps these in small quantities could be allowed, but I would suggest the majority of liquids should be prohibited from being carried onboard an aircraft by a passenger.
Given the risks of allowing liquids on planes, and the plot that came to light today, I would not be surprised if the current ban on passengers carrying liquids is continued for a long time.