If you've ever went through the pain of dumping your favourite bottle of perfume or that expensive moisturizer at the airport because its quantity exceeded the limit, you might have either gotten into an argument with the screener or silently cursed the law which puts this limit on carry-on liquids. The procedure, called the "3-1-1 for carry-ons", allows only 100 ml liquids, gels, and aerosols to be carried inside the aircraft, apart from the checked luggage. This rule hasn't always been around, and in fact was introduced 10 years ago, in 2006.
But do you know the reason why only 100 ml (or 3.4 ounces) of liquids and gels are allowed to pass through the airport security?
The regulation was introduced in 2006 after the British Police uncovered a terrorist plot to detonate liquid explosives carried on board seven airliners travelling from the United Kingdom to the United States and Canada. Popularly known as the '2006 transatlantic aircraft plot', it was foiled by the British police well in advance, but led to the implementation of tight security measures at airports everywhere.
It is believed that a British man from Birmingham, Ahmed Ali, mediated the connection between the plotters and Al-Qaeda. When police opened his baggage, they found a powdered soft drink, Tang, and a large number of batteries, which raised alarm among the authorities. It was later discovered that the culprits were constructing bomb-devices using drink bottles, which they planned to detonate on the plane.
With immediate effect, the security at all British airports was increased and no luggage, including books, newspapers, and glass cases, was allowed inside the aircraft. Soon after, a liquid restriction on the hand luggage was also placed, with few exceptions like baby food, which had to be tasted by the passengers first, before it was allowed inside.
While initially, for a few days, there was a blanket ban on bringing liquids on board, later on a restriction of 100 ml was placed on the amount of liquid allowed inside. It also requires putting small liquids, gel, and aerosol containers into a clear, zip-top, one-quart-sized bag.
The restriction was introduced for the very reason that it's a challenging task to screen liquids and determine whether it's a threat or not. However, there are a large number of exceptions to this limit, which include prescription drug, life support and life sustaining liquids, baby formula, and so on. Security at airports in India was also tightened following this operation.