Airport Swab Detectors: How Do They Work?

Airport security is a necessary inconvenience to keep travellers safe. The swab detectors, or explosive trace detection (ETD), are used to check for traces of explosives, such as bombs or explosive material, on luggage, clothes and hands. The swab is a textured piece of cloth that picks up or scratches off a sample of the chemicals on your hands or luggage. The swab is then inserted into a machine and the sample is heated to separate the compounds. The machine then checks for certain explosive compounds, and if they are present, the machine alarms.

Swabbing is a secondary form of explosive detection

The swabbing process typically involves collecting samples from the hands, luggage, or clothing of individuals passing through security checkpoints. These swabs are then analysed for traces of explosives, including chemicals such as nitroglycerin, nitrates, and glycerin. While swabbing can also be used to screen items such as baggage, packages, and automobiles, it is most often employed as a secondary measure to complement full-body scanners.

The use of swabbing as a secondary detection method offers several advantages. Firstly, it helps to identify explosive devices that may have been missed by other screening methods. This includes improvised explosive devices (IEDs) or homemade explosives, which can be challenging to detect due to the use of commonly available materials. By collecting and analysing trace residue, swabbing provides a sensitive method for detecting explosive compounds that may be present in minute quantities.

Additionally, swabbing can help to reduce the number of false positives that may occur with other screening technologies. For instance, certain chemicals detected on an individual's hands or luggage, such as glycerin or nitrates, may be indicative of the presence of explosives, but they are also commonly found in personal care products like soap, shampoo, and hair products. By employing swabbing as a secondary measure, security personnel can conduct further investigations to confirm or rule out the presence of explosives.

The process of swabbing involves using specially treated swabs that can collect and preserve trace residue for analysis. For example, the Lincoln Laboratory swab, developed by MIT Lincoln Laboratory, is coated with an acidic polymer. When exposed to humidity, this coating increases the vapour pressure of collected particles, making it easier for analysers to detect their presence. This technology has been successfully tested at airports, demonstrating its effectiveness in detecting trace amounts of explosives with low false-alarm rates.

The swab picks up chemicals on your hands

The swab used in airport security is a piece of textured cloth woven to pick up, or scratch off, a sample of the chemicals on your hands. The swab is then inserted into a machine and the sample is mixed with hot air (up to 400°F) and a reacting gas, which is then ionized. The swab picks up chemicals on your hands, which are then analysed for nitroglycerin, nitrates, glycerin, or other chemicals. These include explosives such as toluene, pentaerythritol tetranitrate, nitroglycerine, cyclotrimethylene-trinitramine, and cyclotetramethylene-tetranitramine.

The swab test is used to detect explosive material and is not testing passengers' DNA, testing for viruses or illnesses, or testing for narcotics. The swab test is minimally invasive and is considered a good form of security that doesn't invade privacy. It is also not a test for DNA, which would be cost-prohibitive and unnecessary for airport security.

The swab test is a secondary form of explosive detection alongside full-body scanners. It is used to check if your luggage has come into contact with a bomb or explosive material. While it is usually luggage that is swabbed, travellers' clothes and hands may also be swabbed.

The swab test is also used in correctional facilities to detect narcotics. The IONSCAN 600, for example, can detect a wide range of narcotics, including opioids, and can distinguish between different varieties of the same drug, such as heroin and fentanyl analogues.

The swab is heated to evaporate volatile compounds

Gas chromatography is a process that separates the compounds based on their interaction with a solid or liquid phase. The time it takes for the compounds to pass through the chromatography instrument can provide some insight into the composition of the sample. However, this information is not always definitive, as different compounds may have similar retention times.

To address this challenge, other techniques such as optical spectroscopy, nuclear magnetic resonance, and chemical analysis can be employed. These techniques provide additional data to help identify the compounds more accurately.

The swabbing process is an effective secondary form of explosive detection alongside full-body scanners. It is minimally invasive and helps ensure the safety of air travel by identifying potential threats.

Explosives and drugs can be distinguished

Swab detectors at airports are used to detect threatening items and contraband such as weapons, explosives, and drugs. The swab is a textured piece of cloth designed to pick up or scratch off chemical samples from passengers' hands. The swab is then inserted into a machine and mixed with hot air and a reacting gas, which is then ionized. If the machine detects certain compounds, it will alarm.

The swab test is primarily used to detect explosive compounds such as toluene, pentaerythritol tetranitrate, nitroglycerine, cyclotrimethylene-trinitramine, and cyclotetramethylene-tetranitramine. It is also used to detect drugs. While the swab test cannot distinguish between explosives and drugs, it can detect the presence of either, which may then prompt further investigation by security personnel.

The Transportation Security Administration (TSA) randomly swabs passengers' hands at security checkpoints and airport gates to test for traces of explosives. The swab is analyzed for chemicals such as nitroglycerin, nitrates, glycerin, or other chemicals. This method of explosive detection has been praised by the American Civil Liberties Union as "a good form of security that doesn't really invade privacy."

In addition to hand swabbing, TSA officers may also swab a piece of carry-on or checked baggage and then place the swab inside a detection unit to analyze it for potential explosive residue. This process, known as explosive trace detection, is used to check if luggage has come into contact with a bomb or explosive material.

False positives are common

In addition, some people may be more likely to trigger a false positive due to their profession or hobbies. For example, hunters, firefighters, police officers, and military personnel are routinely exposed to various accelerants and munitions, which may cause them to test positive even though they are not carrying an explosive device.

It's important to note that a positive swab test does not automatically mean that someone is trying to carry an explosive onto a plane. If a swab test comes back positive, TSA personnel may ask additional questions and conduct a more extensive search of the person's baggage. However, as the detectors are fallible, a non-invasive body scanner may be used to double-check the results.

Frequently asked questions