ETD: Explosives
trace detector
Explosives trace detectors (ETD) are security equipment able
to detect explosives of small magnitude. The detection can be done by sniffing
vapors as in an explosive vapor detector or by sampling traces of particulates
or by utilizing both methods depending on the scenario. Most explosive
detectors in the market today can detect both vapors and particles of
explosives. Devices similar to ETDs are also used to detect narcotics. The
equipment is used mainly in airports and other vulnerable areas considered
susceptible to acts of unlawful interference.
Current State of Passenger
Explosives Trace Detection - Explosives detection for aviation security has been an area
of federal concern for many years. Much effort has been focused on direct detection
of explosive materials in carry-on and checked luggage, but techniques have
also been developed to detect and identify residual traces that may indicate a
passenger’s recent contact with explosive materials. These techniques use
separation and detection technologies, such as mass spectrometry, gas
chromatography, chemical luminescence, or ion mobility spectrometry, to measure
the chemical properties of vapor or particulate matter collected from passengers
or their carry-on luggage. Several technologies have been developed and deployed
on a test or pilot basis. Parallel efforts in explosives vapor detection have employed
specially trained animals, usually dogs. The effectiveness of chemical trace analysis is highly
dependent on three distinct steps:
(1) sample collection
(2) sample analysis, and
(3) Comparison of results with known
standards.
(4) If any of these steps is suboptimal, the test
may fail to detect explosives that are present.
When trace analysis is used for
passenger screening, additional goals may include nonintrusive or minimally intrusive
sample collection, fast sample analysis and identification, and low cost. While
no universal solution has yet been achieved, ion mobility spectrometry is most
often used in currently deployed equipment. In 2004, TSA began pilot projects
to deploy portal trace detection equipment for operational testing and
evaluation. In the portal approach, passengers pass through a device like a
large doorframe that can collect, analyze, and identify explosive residues on the
person’s body or clothing. The portal may rely on the passenger’s own body heat
to volatilize traces of explosive material for detection as a vapor, or it may
use puffs of air that can dislodge
small particles as an aerosol. Portal deployment is ongoing.3 one alternative
to portals is to collect the chemical sample using a handheld vacuum “wand”.
Another is to test an object handled by the passenger, such as a boarding pass,
for residues transferred from the passenger’s hands. In this case, the
secondary object is used as the carrier between the passenger and the analyzing
equipment.4 the olfactory ability of dogs is sensitive enough to detect trace
amounts of many compounds, but several factors have inhibited the regular use
of canines for passenger screening. Dogs trained in explosives detection can
generally only work for brief periods, have significant upkeep costs, are
unable to communicate the identity of the detected explosives residue, and
require a human handler when performing their detection role.
5. In addition, direct contact
between dogs and airline passengers raises liability concerns.
Detection of Bulk Explosives. - Direct detection of explosives concealed on passengers in
bulk quantities has been another area of federal interest. Technology development
efforts in this area include portal systems based on techniques such as x-ray backscatter
imaging, millimeter wave energy analysis, and terahertz imaging.6 As such systems
detect only bulk quantities of explosives, they would not raise “nuisance
alarms” on passengers who have recently handled explosives for innocuous
reasons. Some versions could simultaneously detect other threats, such as
nonmetallic weapons. On the other hand, trace detection techniques are also
likely to detect bulk quantities of explosives and may alert screening
personnel to security concerns about a passenger who has had contact with
explosives but is not actually carrying an explosive device when screened.
Current deployments for passenger screening are focused on trace detection, and
the remainder of this report does not discuss bulk detection. However, many of
the policy issues discussed below would apply similarly to bulk detection
equipment.
Policy Issues-Any
strategy for deploying and operating passenger explosives detection portals
must consider a number of challenges. Organizational challenges include
deciding where and how detectors are used, projecting costs, and developing
technical and regulatory standards. Operational challenges include maximizing passenger
throughput, responding to erroneous and innocuous detections, ensuring passenger
acceptance of new procedures.
Equipment Location and Use.
-An
important component of a deployment strategy is identifying where and how
passenger explosives detection equipment will be used. Portals could be
deployed widely, so that all locations benefit from them, or they could be used
only at selected locations, where they can most effectively address and mitigate
risk. In any given location, portals could be used as a primary screening technology
for all passengers, or as a secondary screening technology for selected passengers
only. Widespread deployment and use for primary screening might provide more
uniform risk reduction, but would require many more portals and thus increase costs.
Cost of Operation.- The total cost
of deploying explosives detection equipment for passenger screening is unknown.
According to TSA, the portal systems currently being deployed in U.S. airports
cost more than $160,000 each.7 Document scanning systems are somewhat less expensive;
according to a 2002 GAO study, similar tabletop systems used for screening
carry-on baggage can cost from $20,000 to $65,000.8 It is possible that
technology improvements or bulk purchasing could lower costs. The number of
devices required would depend on throughput rates, device reliability and lifetime,
and deployment strategy. The United States has more than 400 commercial passenger
airports; if equally distributed, several thousand devices might be required, corresponding
to a total capital cost for equipment of up to hundreds of millions of dollars.
Installation and maintenance costs would be additional. Operating the equipment
would require additional screening procedures and might lead to costs for
additional screening personnel, or else create indirect costs by increasing
passenger wait times. It is unknown whether the personnel limit for TSA
screeners, currently set at 45,000 full time equivalent screeners nationwide
(P.L. 108-90), could accommodate the potential additional staffing
requirements.
Impact on Screening Time. -When multiplied
by the large number of airline passengers each day, even small increases in
screening times may be logistically prohibitive. The TSA goal for passenger
wait time at airports is less than 10 minutes, and screening systems reportedly
operate at a rate between 7 to 10 passengers per minute;10 additional screening
that slows passenger throughput and increases passenger wait time may add to
airport congestion and have a detrimental economic impact. A 1996 GAO study
stated that throughput goals for portal technologies at that time were
equivalent to 6 passengers per minute.11 According to the same study,
non-portal technologies, such as secondary object analysis, had slightly higher
throughput goals. The TSA’s pilot deployment of passenger explosives trace
detection equipment will likely provide useful information on passenger
throughput. If no appreciable increase in screening times occurs, then
passenger explosives screening may involve few additional direct economic costs
beyond those of procuring, deploying, operating, and maintaining the equipment.
If passenger throughput is drastically decreased, then alternatives for passenger
screening may need to be considered. In between these extremes, it may be possible
to moderate the economic impact by adding screening lanes or by using explosives
detection equipment only on those passengers who are selected for secondary screening,
as recommended by the 9/11 Commission as a possible initial step.
Erroneous and Innocuous
Detection.
A potential
complication of explosives trace detection is the accuracy of detector
performance. False positives, false negatives, and innocuous true positives are
all challenges. If the detection system often detects the presence of an
explosive when there actually is none (a false positive) then there will be a
high burden in verifying results through additional procedures. Because of the
large volume of air passengers, even small false positive rates may be
unacceptable.
Conversely, if
the system fails to detect the presence of an explosive (a false negative) then
the potential consequences may be serious. Assuming the system has adequate sensitivity
to detect explosives traces in an operational environment, the detection threshold
or criteria required for an alarm can generally be adjusted, enabling a
tradeoff between false positives and false negatives, but neither can be
eliminated entirely; the appropriate balance may be a matter of debate. Innocuous
true positives occur when a passenger has been in contact with explosives, but
for legitimate reasons. Examples include individuals who take nitroglycerin for
medical purposes or individuals in the mining or construction industry who use
explosives in their work. Such passengers would be regularly subject to
additional security scrutiny. Similar issues arise from the current use of
trace detection equipment on some airline passenger carry-on baggage, and innocuous
true positives in such cases are generally handled without incident. The impact
of innocuous true positives will likely depend on their frequency and on the
proportion of passengers subject to explosives trace detection.
Passenger Acceptance.
Some passengers may have personal
concerns about the addition of passenger explosives trace detection to the
screening process. Issues of privacy may be raised by the connection between
innocuous true positives and passenger medical status or field of employment.
Also, equipment that uses a vacuum “wand” or puffs of air for sample collection
may offend some passengers’ sense of propriety or modesty. Passenger reluctance
could then increase screening times. Allowing alternative forms of screening,
such as within privacy enclosures or through different imaging technology,
might mitigate passenger concerns in some cases.
Potential for Intentional
Disruption.
Another concern is the possibility that
a passenger screening regimen that includes explosives trace detection could be
exploited to intentionally disrupt the operation of an airport. The dissemination
of trace quantities of an explosive material on commonly touched objects within
the airport might lead to many positive detections on passengers. This would
make trace detection less effective or ineffective for security screening, and
might disrupt airport operations generally until alternative screening
procedures, such as enhanced baggage screening by TSA personnel, could be put
in place or the contamination source could be identified and eliminated.
Research and Development.
The DHS and its
predecessor agencies have historically been the main funders of research on
explosives detection for airport use. (Most of this research has focused on
detecting explosives in baggage rather than on passengers.) Several other
federal agencies, however, also fund research related to trace explosives
detection. These include the Departments of Energy and Justice, the National Institute
for Standards and Technology, and the interagency Technical Support Working Group.
Much of this research has been dedicated to overcoming technical challenges, such
as increasing sensitivity and reducing the time required for sample analysis. A
different research challenge is the detection of novel explosives. Detectors
are generally designed to look for specific explosives, both to limit the
number of false or innocuous positives and to allow a determination of which
explosive has been detected. As a result, novel explosives are unlikely to be
detected until identifying characteristics and reference standards have been
developed and incorporated into equipment designs. Unlike imaging techniques
for detecting bulk quantities of explosives, trace analysis provides no
opportunity for a human operator to identify a suspicious material based on
Experience or
intuition. Liquid explosives are a novel threat that has been of particular
interest since August 2006, when British police disrupted a plot to bomb aircraft
using liquids. The DHS is evaluating technologies to detect liquid explosives.12
Its efforts are mainly focused on bulk detection, such as scanners to test the
contents of bottles. Like solid explosives, however, liquids might be found
through trace detection, if the trace detection system is designed to look for
them.
Characteristics: 1. Sensitivity-
it is defined as the lowest amount of
explosive matter a detector can detect reliably. It is expressed in terms of
nano grams (ng), pico-grams (pg) or femto-grams (fg) with fg being better than
pg better than ng. It can also be expressed in terms of parts per billion
(ppb), parts per trillion (ppt) or parts per quadrillion (ppq). Sensitivity is important because most
explosives have a very low vapor pressure and give out very little vapor. The
detector with the highest sensitivity will be the best in detecting vapors of
explosives reliably.
2. Light weight- Portable explosive detectors need to
be as light weight as possible to allow users to not fatigue when holding them.
Also, light weight detectors can easily be placed on top of robots.
3. Size-Portable explosive detectors need to
be as small as possible to allow for sensing of explosives in hard to reach
places like under a car or an inside a trash bin.
4. Cold start up time
and analysis time - The
startup time should not be a parameter for evaluation of an explosive detector.
Startup time only indicates the time required by the detector to reach the
optimized temperature for detection of contraband substances.
Technologies used in various explosive detectors
Ion mobility spectrometry: Explosive detection using Ion mobility spectrometry (IMS) is
based on velocities of ions in a uniform electric field. There are some variant
to IMS such as Ion trap mobility spectrometry (ITMS) or Non-linear dependence on
Ion Mobility (NLDM) which are based on IMS principle. The sensitivity of
devices using this technology is limited to pg levels. The technology also
requires the ionization of sample explosives which is accomplished by a
radioactive source such as Nickel-63 or Americium-241. This technology is found
in most commercially available explosive detectors like the GE Vapor Tracer,
Smith Sabre 4000 and Russian built MO-2M and MO-8. The
presence of radioactive materials in these equipment’s cause regulatory hassles
and requires special permissions at customs ports. These detectors cannot be
field serviced and may pose radiation hazard to the operator if the casing of
the detector cracks due to mishandling. Bi-yearly checks are mandatory on such
equipment in most countries by regulating agencies to ensure that there are no
radiation leaks. Disposal of these equipments is also controlled owing to the
high half-life of the radioactive material used. Currently there are companies
entering the market with non-radioactive ionization methods for IMS for the ETD
application –to overcome the limitations mentioned above. The Bruker
"DE-tector" and the Implant Sciences "QS-B220" are examples
of these next generation instruments. Electrospray Ionization, Mobility
Analysis (DMA) and Tandem Mass Spectrometry (MS/MS) is used by SEDET (Societal Europe
de Detection) for the “Air Cargo Explosive Screener (ACES)”, targeted to
aviation cargo containers currently under development in Spain.
"SEDET" is a Joint Venture
created by SEADM, Morpho and CARTIF in order to develop a new generation of
explosive trace detection systems.
Thermo redox-This technology is based on
decomposition of explosive substance followed by the reduction of the NO2
groups. Most military grade explosives have an abundance of NO2 groups on them.
Explosive vapors are pulled into an adsorber at a high rate and then pyrolized.
The presence of NO2 groups in the pyrolized products is then detected. This technology
has significantly more false alarms because many other harmless compounds also
have an abundance of NO2 groups. For example most fertilizers have NO2 groups
which are falsely identified as explosives, and the sensitivity of this technology
is also fairly low. A popular detector using this technology is Scientrex EVD
3000.
Chemiluminescence- This technology is based on the
luminescence of certain compounds when they attach to explosive particles. This
is mostly used in non-electronic equipment such as sprays and test papers. The
sensitivity is pretty low in the order of ng.
Amplifying fluorescent
polymer - Amplifying
fluorescent polymer (AFP) is a promising new technology and is based on synthesized
polymers which bind to explosive molecules and give an amplified signal upon
detection. The sensitivity is in the order of fg. Explosive trace detectors based
on AFP technology are produced by FLIR Systems. The current generation, Fido X3
provides broad-band trace explosive detection and weighs less than 3 lbs.
Mass Spectrometry Recently- Mass Spectrometry (MS) has emerged
as another ETD technology, in products such as the Griffin 824 by FLIR Systems.
Adoption of Mass Spectrometry should lower false alarms rates often associated
with ETD due to the higher resolution of the core technology. Primarily used in
desktop ETD systems, Mass Spectrometry can be miniaturized for handheld ETD but
at the cost of compromising much of the performance that defines the
technology.
Thanks.
.jpg)
