Air travel has become a daily routine for many people, but every time you dig up your computer, power bank and travel-sized skincare products at the security checkpoint, have you ever wondered: why limit the amount of liquid you carry to 100ml?
As you may have already thought, the requirement to limit liquids is essentially a matter of flight safety: an airplane can carry hundreds of tons of fuel, for example, a Boeing 747-400 can carry 172 tons of jet fuel at a time, which is equivalent to a small and medium-sized gas station [1]. Although most of the materials used in the interior of the aircraft are non-combustible materials [2], once a human ignition source intervenes, the consequences are unimaginable.
Jet fuel has a higher ignition point and flash point than ordinary household fuel, and although it is stable under normal conditions, there is still a risk of fire once it is close to the fire source / Diagram Worm Idea
However, the limit on liquids is not set at 100 ml at the beginning.
In 1996, domestic passengers were also allowed to carry 500ml of perfume, 350ml of air freshener, 2 catties of well-packaged liquor, and even less than 5 boxes of safety matches and lighters [3].
However, in a flight accident in Dalian in 2002, a passenger carrying gasoline and setting it on fire killed all 103 passengers and nine crew members on board.
On February 5, 2003, the Civil Aviation Administration of China (CAAC) issued the Announcement on Strengthening the Management of Liquids Carried by Passengers on Civil Aviation Aircraft, requiring each passenger to carry a maximum of two bottles of liquid beverages of no more than 500 ml at a time, and to open the bottle to confirm that there is no doubt before carrying it on the plane [4].
At this time, foreign restrictions on liquids and even alcohol are also relatively relaxed: for example, in the 2005 ICAO Regulations for the Safe Transport of Dangerous Goods by Air, flammable liquids/solids, such as rubbing alcohol and alcohol swabs, can carry up to 500 ml or 500 grams [5].
Before a series of terrorist attacks, the airport did not strictly control liquids, and you could also bring alcohol and drinks on the plane
What made the global aviation industry truly aware of the potential dangers of carrying liquids was an attempted terrorist attack in the United Kingdom in 2006 [6].
On 10 August 2006, at Heathrow Airport in London, the capital of the United Kingdom, terrorists hid liquid bombs in 500-milliliter cans in an attempt to blow up at least seven transatlantic flights. They were convinced that a 500ml liquid bomb would be enough to blow up an aircraft [6].
The terrorist attack was unsuccessful, but it still caused great concern and panic around the world: the United States and Great Britain immediately banned passengers from carrying any liquids with them, except for milk powder. It wasn't until November of that year that the ban was relaxed, allowing passengers to carry liquids, gels or creams of 100 ml or less on board, but they needed to be placed in a clear plastic bag and taken out for inspection separately at the security check [6].
Other countries followed suit. At the time, the rule was widely criticized as an "overreaction" – not only increasing the workload of security personnel, but also delaying passengers from boarding.
The 100ml liquid limit, which is now taken for granted, was once under fire / Picture Worm Creativity
However, in 2007, the Council of the International Civil Aviation Organization (ICAO) issued the "Interim Security Control Guidelines" to 189 States Parties, requiring passengers to carry no more than 100ml of liquids, aerosols and gels (LAGs), including beverages, perfumes, cosmetics, glues, sauces, etc. [7].
At that time, the Civil Aviation Administration of China (CAAC) had the same requirements for international flights as ICAO, but the requirements for passengers on domestic flights were relatively more relaxed, requiring only one litre of liquids per person to carry on their carry-on baggage [8].
However, on March 7, 2008, during a flight from Urumqi to Beijing, a terrorist attempted to set fire to the plane's toilet by pouring gasoline into a can and sealing it to disguise it as a normal drink, but was fortunately stopped [9].
Within a week of the attack, the Civil Aviation Administration of China (CAAC) issued the Announcement on Prohibiting Passengers from Carrying Liquids on Domestic Flights, which prohibits all passengers on domestic flights from carrying any liquids on their bodies, except for a small number of cosmetics with a container volume of no more than 100 ml, which are placed in transparent plastic bags of no more than 1 liter and subject to bottle opening [10].
That's why now when you go to the airport, the bottle of cosmetics cannot exceed 100 ml, and all liquids including drinks and water must be drunk, thrown away or checked in. According to the information provided by Daxing Airport, as long as it is sealed water, it can theoretically be checked in no matter how much it is, as long as you want to bring it. However, if the quantity is particularly large, the staff will need you to explain the specific reason for bringing so much water.
Flammable or toxic dangerous goods, such as alcohol, gasoline and diesel, paint, hydrogen peroxide, 84 disinfectant, chlorine-containing disinfectant/effervescent tablets, etc., cannot be carried on board or checked in.
Such strict restrictions are mainly due to the fact that everyone is too good at hiding. The principle used in the security screening equipment of most airports is X-ray, which is relatively efficient, but X-ray will miss or misdetect containers with uneven thickness, and manual identification is required later [11].
In X-ray screening machines, organic matter is orange, inorganic matter is blue, and mixtures and light metals are green / [16]
Security screening requires not only the shape of the objects in the baggage, but also the identification of the materials of the objects in the baggage. Complex metal objects, such as computers and umbrellas, can interfere with X-ray imaging [12]. In addition, the detection of hazardous liquids was difficult to accurately and quickly distinguish in a short period of time due to the different compositions of containers and liquids, which required different methods of detection [13].
The 2006 transatlantic flight terrorist attack plan was a plan made by terrorists who found liquid explosives difficult to detect after examining airport security technology [14].
However, many specialized equipment has been developed for the detection of dangerous liquids, such as the dangerous liquid detector that we commonly use during subway security checks, whether you use plastic, glass, or metal cups, which can detect whether you are loading flammable or explosive liquids in a matter of seconds [15].
With the iterative update of security technology, security regulations will also become more relaxed.
Domestic airports such as Guangzhou Baiyun Airport have adopted advanced millimeter-wave security detectors to help airport security checks be faster and safer
The UK, for example, is planning to ease restrictions on carry-on liquids: from 1 June 2024, the 100ml liquid limit will be lifted to a maximum of 2 litres per person and the requirement to remove electronics and liquids from baggage checks will be lifted[6].
The reason for the UK's support is that they will be fitted with a new scanner that can use X-rays to scan passengers' luggage with computed tomography to produce high-resolution 3D images, speeding up baggage checks and reducing false positives [6].
After the application of this technology, cosmetics do not need to be thrown away, drinks do not need to be drunk in a hurry, computer power banks do not need to be paid one by one, and at the same time, we are too friendly to those who can only afford low-cost airlines, but cannot afford low-cost airline bottled water.