Airports' Fluid Detection: Advanced Screening Methods And Technologies

Airports have strict rules about the amount of liquid that can be taken on board a plane. In 2006, security services in the UK, US and Pakistan foiled a plot by al-Qaeda to set off bombs on planes using liquid explosives. Since then, the amount of liquid passengers can bring onto planes has been restricted. The 3-1-1 rule limits passengers to 3.4oz (100ml) containers of liquid, which must fit into a clear one-quart bag. Liquids that don't meet these rules may be thrown out or confiscated. Exemptions include duty-free liquids, breast milk, infant formula, toddler drinks and pureed baby food. These liquids are usually screened by X-ray, but may be tested for explosives.

X-ray screening

X-ray scanners emit X-rays that pass through luggage and are absorbed at varying rates by different materials inside. These X-rays can penetrate many materials due to their high energy, and the level of penetration is measured in kilovolt peak (KVP). The higher the KVP, the greater the X-ray penetration. As a result, dense substances like lead absorb the most radiation, blocking the X-rays, while less dense materials allow X-rays to pass through.

The X-rays that pass through the scanned items are then detected and measured, with the data used to generate images. These images are colour-coded based on the density and atomic number of the materials, allowing for differentiation between organic, inorganic, and metallic substances. Organic materials, such as food, liquids, and clothing, are typically represented by shades of orange as most explosives fall under this category. Security personnel are trained to identify suspicious items, including potential components of improvised explosive devices (IEDs).

While X-ray scanners provide valuable insights into the contents of luggage, they have limitations. They cannot determine the exact chemical composition of liquids or solids inside bottles. If the contents are unclear or suspicious, additional screening methods may be employed, such as manual inspection or chemical testing using detection kits. Furthermore, metal bottles or containers can be challenging for X-ray scanners to penetrate, often requiring further inspection.

X-ray technology has also been applied to full-body scanners, which are becoming more common in airports worldwide. These scanners utilise backscatter X-ray or millimeter-wave technology to generate images of a person's body, enabling the detection of concealed items without physical contact. This technology can even detect drugs swallowed by passengers, whether in pill or liquid form, and can identify the smallest amounts of metal, paper, or money.

3-1-1 rule

The 3-1-1 rule is a regulation by the Transportation Security Administration (TSA) that dictates how much liquid travellers are allowed in their carry-on bags. The rule was introduced in 2006 after security services in the UK, the US, and Pakistan foiled an al-Qaeda plot to set off bombs on airplanes using liquid explosives.

The "3" in the 3-1-1 rule refers to the 3.4-ounce (100ml) limit on the size of liquid containers. The first "1" refers to the fact that all 3.4-ounce containers must fit into a clear, quart-sized, resealable plastic bag. The final "1" means that only one such bag is permitted per passenger.

The 3-1-1 rule applies to liquids, gels, aerosols, creams, and pastes. This includes items like toothpaste, hair spray, shampoo, mascara, and mouthwash. Medication is exempt from the rule, including both prescription and over-the-counter medicines.

To comply with the rule, travellers should ensure they are only carrying liquids in 3.4-ounce or smaller containers, and that these are placed inside a clear, quart-sized bag. This bag should be packed last, on top of clothing and other items, so it can be easily removed at the security checkpoint.

Exemptions

The 3-1-1 rule, which limits the amount of liquid carried on board to 3.4 ounces (100ml) per container, has some exemptions. Medically necessary liquids, including prescription medication, breast milk, baby formula, toddler drinks, and pureed baby food, are typically exempt from the rule. Passengers are advised to inform TSA officers of any liquids that are exceptions to the rule and to have them clearly labelled to facilitate the screening process. Medication may be screened visually, via X-ray, or tested for traces of explosives.

Duty-free liquids purchased internationally and transported in a secure, tamper-evident bag are also exempt from the 3-1-1 rule. However, the bag must not show signs of tampering when presented for TSA screening. Additionally, some airports may allow containers of liquid up to 100ml to pass through security in hand luggage.

Passengers with infants under two years of age are allowed to bring baby food, milk, liquid formula, water, and juice in quantities exceeding 100ml. Essential non-prescription medicines, such as homeopathic products, pain relievers, cough syrup, decongestant spray, gel-based nutritional supplements, saline solution, and eye care products, are also exempt from the liquid restrictions. COVID-19 test kits are permitted without restrictions in both carry-on and checked baggage.

It is important to note that while these items are generally exempt, the final decision on whether an item is allowed rests with the TSA officer at the checkpoint.

International regulations

Some exemptions are allowed for specific items. Medically necessary liquids, including breast milk, infant formula, toddler drinks, and pureed baby food, are generally allowed in larger quantities but may require additional screening, such as X-ray or separate testing. Similarly, travellers with young infants (0-24 months) can carry baby food, milk, liquid formula, water, and juice in quantities exceeding 100 ml.

Duty-free liquids purchased internationally and transported in a secure, tamper-evident bag are also exempt from the size restrictions. However, these liquids must not show any signs of tampering when presented for TSA screening. Additionally, liquids purchased at an airport or on a plane, such as duty-free items, are permitted if sealed inside a security bag with the receipt visible. These items may be screened at the security point and must remain sealed until the final destination.

It is important to note that prohibited liquids, such as flammable substances, are not allowed in either checked or carry-on baggage. Furthermore, each country and airline may have its own specific restrictions. For instance, in Japan, security screening is conducted by individual airlines under the Civil Aeronautics Act, and the UK has reinstated liquid restrictions due to technological limitations. Therefore, it is crucial for travellers to check the rules and regulations of their departure, arrival, and connecting airports to ensure compliance with international standards.

Tamper-evident bags

STEBs are used for duty-free liquids purchased post-TSA security in the secure area of US airports. These liquids must be packed in transparent, secure, tamper-evident bags by the retailer and must not show signs of tampering when presented to the TSA for screening. This aligns with European Union security protocols and reduces the number of passengers surrendering duty-free liquids when transferring to international airports.

The use of STEBs is an additional security measure, particularly relevant after the 2006 foiled plot by al-Qaeda operatives to set off bombs on airplanes using liquid explosives. The TSA fluid limit for carry-on luggage was implemented as a result, restricting passengers to containers of 3.4 ounces (100 milliliters) or less, which must fit into a clear one-quart bag.

Prescription medication is exempt from the TSA fluid limit, while non-prescription medications fall under the 3-1-1 rule, which allows for containers of 3.4 ounces or less in a clear one-quart bag. Passengers are responsible for displaying and repacking these liquids and are advised to keep them easily accessible during screening.

Frequently asked questions