Airport Tests: False Positives And Their Causes Explained

Airport security screenings are designed to ensure the safety of passengers and staff, but sometimes false positives occur. These false positives can be caused by a variety of factors, including the presence of certain chemicals, the amount of urine provided for a drug test, and even behaviours such as arriving late or appearing confused. While the technology used in airport screenings is advanced, with X-ray imaging capable of detecting items like cigarettes, it is not perfect and false positives can occur. To address this, organizations like the National Research Council (NRC) have conducted studies to examine the causes of false positives and make recommendations for improvement. Understanding the root causes of false positives is critical for effective risk management and process improvement in aviation security.

Everyday products like soap and lotion can cause false positives

Everyday products such as soap, lotion, and even flour can cause false positives at airport security. This is because certain ingredients in these products, such as glycerine, are also found in explosives. Explosive trace detectors (ETDs) at airports are designed to screen for microscopic traces of explosives, and the presence of these ingredients in personal care products can trigger a false positive.

In one instance, a woman named Linda was chosen for a random hand swab at an airport in Columbus, Ohio, and tested positive for explosives. The likely cause was the lotion she had used that morning, which she had slathered on her hands and up to her elbows. She was eventually cleared by TSA agents after a pat-down in a private room, but the experience left her shocked and rattled.

Instances of false positives due to everyday products are considered rare but have been reported at larger airports in the US, such as Dallas-Fort Worth International Airport. These occurrences highlight the challenge of balancing security with convenience and the potential impact on travellers' safety and liberty.

The use of immunoassay tests, which are quick and cheap, has been criticised for their high rate of false positives. Experts argue for more accurate testing methods and higher cut-off thresholds to reduce erroneous results. These tests identify compounds with similar structures to drugs, leading to false positives from various legal and common substances.

As a result, travellers may experience delays, miss flights, and suffer financial and emotional damage due to false positives. While airports strive to balance security and convenience, the impact on travellers underscores the need for continuous improvement in testing technology and protocols.

Technology used for testing

The Transportation Security Administration (TSA) uses a variety of technologies to test for explosives at airports. One method is the use of millimeter-wave advanced imaging technology, which can detect metallic and non-metallic objects, including weapons and explosives, concealed under clothing without physical contact. TSA also employs computed tomography systems and advanced technology X-ray machines to screen carry-on baggage for explosives and prohibited items. These systems provide enhanced detection capabilities and convenience for passengers by eliminating the need to remove electronics and liquids from bags.

Another technology used by TSA is explosives trace detection, which involves swabbing passengers' hands, carry-on, or checked baggage and then analyzing the swab for explosive residue. Bottled liquid scanners are also used at checkpoints to differentiate liquid explosives from common liquids, especially for medically necessary liquids in larger quantities. Credential Authentication Technology enhances the passenger screening process by improving the inspection of identification documents and confirming passengers' vetting status.

In addition, TSA has deployed Electronic Baggage Screening Programs (EBSP) at commercial airports, utilizing technologies such as EDS (explosive detection systems) and ETD (explosive trace detection) machines. These systems employ computed tomography imaging to capture images of bags and detect potential threats. TSA also explores new technologies, such as 3D scanners and portable X-ray backscattering imaging systems, to enhance baggage screening capabilities.

To further improve security, TSA has collaborated with organizations like Micro-X and Karsa Oy, adopting their technologies. Karsa Oy, for example, presented an automated explosives vapor detector capable of screening all vapors emitted by an object. Additionally, TSA has invested in the development of mass spectrometers, aiming to mimic the capabilities of canine units in detecting trace amounts of explosives. This technology has been tested at the University of Rhode Island and is supported by the Department of Homeland Security's (DHS) Detection Canine Program.

While the use of canine units has been effective, the development of mechanical methods that can replicate their abilities remains a challenge. TSA and research institutions like MIT Lincoln Laboratory are working to enhance the speed and safety of airport security screening by leveraging machine learning and advanced technologies. The NextGen ETD program, for instance, focuses on developing technologies that can detect tiny amounts of explosive residue or vapors, addressing emerging security needs at airports and other entry points.

Human error

One example of human error contributing to false positives is the use of subjective criteria in behavioural profiling. Security personnel may use behavioural indicators to identify potentially high-risk individuals for additional screening. However, this approach can be prone to error, as innocent behaviours can sometimes be misinterpreted as suspicious. For instance, arriving late, whistling, repetitive grooming gestures, tightly gripping a bag, or appearing confused or disoriented are all behaviours that can earn passengers additional screening points, increasing the likelihood of a false positive.

In addition, the interpretation of screening results can also be subject to human error. Even with advanced technology, such as computed tomography-based screening, the analysis and resolution of false positives require human input. The National Research Council (NRC) has studied false positives produced by aviation security equipment and made recommendations to improve the process. Their work has involved observing security measures, engaging with experts, and evaluating the impact of false positives on resource allocation.

Furthermore, the pressure and time constraints faced by security personnel can influence the likelihood of human error. Airports are fast-paced environments, and security staff must make quick decisions while processing a high volume of passengers. This can increase the risk of errors, particularly if staff are fatigued or lack adequate training and support.

To mitigate human error, it is essential to have robust standard operating procedures, regular training, and a culture of continuous improvement. By recognising the potential for human error, airports and security organisations can implement measures to reduce its impact and enhance the overall effectiveness of security screening.

Contamination causing faint readings

The use of immunoassay test kits at airports is a contentious issue, with many experts challenging their suitability for border security. These tests are quick and cheap, but they are also prone to false positives. The tests do not directly detect drugs; instead, they identify compounds with similar structures. This means that many everyday, legal substances can trigger false positives. For example, in Perth, a resident named David tested positive for cocaine at the airport, despite never having used the drug.

Instances of contamination often cause faint readings, leading to false positives. This is a significant issue, as these erroneous results can have severe financial and emotional repercussions for those involved. For example, in 2008, Lynn Faulkner had a life-changing false positive for marijuana at an airport in St. Louis. The experience led her to advocate for policy reform, and the airport now uses more accurate testing methods.

Everyday products can also cause false positives. In 2013, a woman in Ohio tested positive for explosives after using hand lotion. The lotion contained glycerin, which is also an ingredient in explosives. Similarly, substances as common as flour or soap can trigger positive results for cocaine.

Critics argue that the arbitrary cut-off thresholds for positive results should be raised, as contamination often causes faint readings. They contend that clearer evidence should be required to accuse travelers of a crime.

Testing for compounds with similar structures to drugs

False positives can occur when a test detects a substance that isn't actually present. This can be caused by byproducts of prescription or over-the-counter medications, nutritional supplements, or certain foods. For example, cannabidiol (CBD) products made from hemp can contain small amounts of THC, the psychoactive ingredient in marijuana, which may lead to a false positive.

When testing for compounds with similar structures to drugs, it is important to employ a rigorous methodology to avoid false positives. One approach is to use computational methods that leverage chemical structure information to predict compound bioactivity. This can be done through chemical similarity searches, which involve using unique chemical information, such as molecular formulas or chemical descriptors, to identify similar molecules in databases like the PDB archive. SMILES (Simplified Molecular Input Line Entry Specification) and InChI (International Chemical Identifier) are two commonly used chemical notations that allow for the representation and comparison of chemical structures.

The Chemical Sketch tool, for instance, can be used to draw and edit the 2D structure of a ligand, which can then be converted into SMILES or InChI chemical descriptors. These descriptors can be used to search for exact matches or similar molecules in the PDB. Additionally, graph matching searches can be performed to identify ligands with similar substructures by comparing atom type, formal charge, bond order, and aromaticity.

By utilizing these chemical similarity search tools and computational methods, researchers can improve the accuracy of compound testing and reduce the likelihood of false positives. This approach can be particularly useful in drug discovery, where small variations in chemical structures can have significant impacts on compound activity and safety.

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