Airport security

Explosives trace detection and CT cabin bag scanners

Explosives trace detection (ETD) tests a swab for tiny residues of explosives. Officers wipe hands, clothing, shoes, bags or laptops and put the swab in a detector ¹. Passengers are picked at random or when other checks cannot clear them, for example with medical devices or casts ^1,2. CT cabin bag scanners are a separate tool. In Europe they are tested under ECAC's Common Evaluation Process and graded C1, C2 or C3 ^6,8.

Last checked: 19 October 202612 sources

How a swab test works

Most explosives give off very little vapour. A 2010 statement to the US Congress by the National Institute of Standards and Technology (NIST) says that for this reason most deployed trace detectors sample particle residues, not vapour. Samples are collected by wiping a surface, by blowing air over a person in so-called puffer systems, or by sniffing vapour directly ⁴.

NIST said the main limit on detecting traces in real conditions was collecting the sample well. It has worked with ASTM International on standard test materials and on ASTM E2520-07, a standard practice for checking the minimum performance of trace explosive detectors ⁴. A NIST research paper on aviation checkpoint trace detection is indexed under keywords that include the ion mobility spectrometer ⁵.

What gets swabbed

CATSA says its officers may swab carry-on bags, clothing, shoes or laptops. When a person needs a trace test, the officer swabs the hands, waist area and feet or footwear, then tests the swab for explosives ¹.

In Australia, the officer may place the equipment directly on areas of the body selected for further screening, or ask the passenger to run their hands over those areas and then test the hands. The officer must explain the process first ².

When passengers are selected

Selection follows set rules and random choice. CATSA lists passengers who must undergo ETD: those randomly selected, those wearing medical casts or large bandages, those with prosthetic or orthotic devices or implanted medical devices, and those travelling with live animals, including service animals ¹. CATSA says random additional screening is a legal requirement at all major Canadian airports ¹.

Australia uses ETD for passengers who cannot be screened by body scanner or metal detector, and for passengers chosen at random after the first screening ². In the UK, the government announced on 5 January 2010, after the failed attack on a Detroit-bound flight on Christmas Day 2009, that it would increase the use of explosive trace detection and plan more random searches of passengers ³.

Country	When ETD is used	Passenger options	Source
Canada	At random, or for passengers with casts, large bandages, prosthetics, implanted medical devices or live animals. Bags, clothing, shoes and laptops may be swabbed ¹	A private search room on request ¹	CATSA ¹
Australia	When a passenger cannot be screened by body scanner or metal detector, or after random selection ²	The officer must explain the process. A passenger who needs a frisk search can ask for a private room and an officer of the same gender ²	Department of Home Affairs ²
United Kingdom	More use of ETD and random searches announced on 5 January 2010 ³	Not stated in the source ³	Department for Transport ³

CT scanners for cabin bags

Computed tomography (CT) scanners build three-dimensional images of a bag that officers can rotate on screen. CATSA says this makes it easier to find explosives and other threats than with its older two-dimensional images ¹⁰. Dublin Airport says its new C3 scanners use technology similar to hospital CT scanners ¹¹.

CT changes what passengers must unpack, but rules differ. At CATSA's CT lanes, passengers can leave laptops, medical devices and liquids of 100 ml or less in the bag, but permitted liquids over 100 ml must still go in a bin ¹⁰. At Dublin, liquids of up to 2 litres and electronics now stay in the bag ¹¹.

ECAC standards C1, C2 and C3

The European Civil Aviation Conference (ECAC) runs the Common Evaluation Process (CEP), a laboratory testing programme for security equipment. Its categories include Explosive Detection Systems for Cabin Baggage (EDSCB), Liquid Explosive Detection Systems (LEDS), Explosive Detection Systems (EDS), security scanners, Explosive Trace Detection equipment, walk-through metal detectors and explosive vapour detection equipment. Since January 2020 the European Commission has made a CEP result a precondition for EU approval. ECAC says approval itself remains the job of each state's aviation security authority ⁶.

EU law grades cabin bag scanners by what they can screen inside the bag. Regulation (EU) 2015/187 set three levels, according to an analysis of the text by Aertec Solutions. C1 is the minimum for any cabin bag scanner. C2 covers bags that hold laptops and other large electronic devices. C3 covers bags that hold both those devices and liquids ⁸.

Commission Implementing Regulation (EU) 2024/2108 of 29 July 2024 restated the C3 rule. All EDS for cabin bags holding laptops, other large electrical items and liquids must meet at least C3. C3 equipment counts as equal to LEDS standard 2 for screening liquids. C3 equipment approved before 1 August 2024 may screen liquids only up to a 100 ml container limit ⁷. The Commission said the change applied from 1 September 2024 ⁹.

Who tests and approves the machines

ECAC's contributing authorities in the CEP are France, Germany, the Netherlands, Spain, Switzerland and the United Kingdom. The US Transportation Security Administration joined as an Associated Authority on 9 June 2025, after signing a memorandum of understanding. Australia and Canada run their own test programmes and take part in ECAC technical meetings ⁶.

ECAC publishes lists of equipment configurations that meet a current ECAC and EU standard, usually updated each quarter. It says the listing is not an approval or certification by ECAC ⁶. The 2024 EU regulation shows how approval can change. It told manufacturers to verify their C3 configurations and resubmit them for CEP testing, and said the 100 ml cap could be lifted once test reports showed the verified configurations met the standards ⁷.

Trace detection is one part of a wider system. TSA's 2016 rule on body scanners describes a layered approach that includes screening technology, trained staff, intelligence sharing, behaviour detection and explosives detection dog teams ¹².

Common questions

Why was my hand swabbed at airport security?

You may have been picked at random, or another check could not clear you. In Canada random additional screening is a legal requirement at major airports ¹.

Can I ask for a private room for a swab test?

In Canada, yes. CATSA says you can ask to be screened in a private search room ¹.

Do medical devices mean a swab test?

In Canada, passengers with implanted medical devices, prosthetics, casts or large bandages must undergo ETD ¹. In Australia, ETD is used when a passenger cannot go through a body scanner or metal detector ².

What does C3 mean on a cabin bag scanner?

It is the EU standard for scanners that can screen bags with laptops and liquids left inside ^7,8.

Who certifies airport scanners in Europe?

ECAC laboratories test them under the CEP. Each state's aviation security authority approves them, and the European Commission requires a CEP result for EU approval ⁶.

Sources

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