The in-flight liquid limit was introduced in 2006 after British police foiled an Islamist terror plot to detonate explosives on transatlantic flights. They planned to smuggle liquid explosives disguised as soft drinks in their hand luggage, in what would have been the deadliest terror attack since 9/11.

The 100ml (3.4 oz) restriction for liquids in carry-on luggage was implemented globally following a foiled 2006 terrorist plot in the UK involving liquid explosives. Security experts determined that 100ml was a high-value "limit of safety"—it is a small enough volume that, even if an individual managed to bring multiple containers, it would be extremely difficult to chemically stabilize a significant explosive device within a pressurized cabin during flight. While the rule has been a point of friction for decades, it remains the standard because it balances security with passenger convenience. However, in 2026, this rule is finally beginning to disappear at premier "Smart Airports" that have installed advanced CT (Computed Tomography) scanners. These high-tech machines create 3D images that can accurately identify the molecular structure of liquids, allowing passengers to keep larger volumes in their bags. Until these scanners are universal, the "3-1-1" rule remains the "gold standard" for aviation security to prevent a potential "liquid-based" catastrophic event at 35,000 feet.