An Automatic Trace Detection System for the Detection of Explosives ...

An Automatic Trace Detection System for the Detection of Explosives’
Vapours and Particles in Luggage
L. Fricano, M. Goledzinowski, R. Jackson, F. Kuja, L. May, S. Nacson
Barringer Research Limited, 1730 Aimco Blvd., Mississauga, Ontario, L4W 1V1
Abstract
Barringer has designed and engineered an Automatic Trace Detector (ATD) to sample
luggage for explosive particles and vapours, using advanced high volume pre-concentration
and detection systems. The ATD has been designed and developed under funding from the
US Federal Aviation Administration (FAA). Barringer’s design provides speed, sensitivity,
robustness and ease of servicing, while minimizing chemical interferences.
The ATD screens checked luggage for explosives by collecting both particles and vapours.
The item being checked enters the first of two chambers, where sampling tubes scrape,
dislodge and collect any surface particulates, and transport them to a 2-stage preconcentrator,
and then to an IMS detector. The bag then enters the second chamber,
where it is mechanically burped to expel explosive vapours, which are transported to an
identical 2-stage pre-concentrator, and then analysed by its’ associated IMS. The system
utilizes two separate IMS detectors, one optimized for particles and the other for vapours.
This dual IMS arrangement offers increased speed of analysis for each item, as the system
has the capability to screen over 700 bags per hour. The novel engineering features of the
ATD will be presented.
Introduction
Detection of explosives concealed in luggage is a continuous challenge to airport security
personnel. Presently, checked luggage is x-rayed, and any suspicious pieces are pulled
from the conveyor and tested separately. The US Federal Aviation Administration, FAA,
funded Barringer Instruments to develop an Automatic Trace Detector, ATD, screening
system to enable them to rapidly screen baggage for traces of explosives. Barringer was
chosen to engineer a commercial, reliable system using their well-proven IONSCAN
technology, in concert with a novel pre-concentration technique, which was developed by
Sandia National Laboratories, and licensed to Barringer.
Details
The complete system is shown schematically in Figure 1. It consists of two discrete
contiguous sampling “tunnels”, mounted over a branch conveyor belt, the 1 st is for collection
of particles present on exterior surfaces of luggage, and the 2 nd is for sampling luggage
interiors for vapours.
As luggage enters the ATD, a series of mechanical and optical sensors relay information on
its length, width, height and shape to position the sampling manifolds correctly over the
luggage for optimum collection of particles.
The particle unit consists of 3 sampling manifolds, or banks, containing a total of 225 flexible
tubes that “pick up” and transport the particles to the primary pre-concentrator. Just after
the luggage enters the sampling tunnel, a hinged mechanical “pusher” positions the luggage
horizontally against the stationary left side sampling bank, while the top and right side banks
are positioned by the CPU logic/mechanical links. When positioned correctly, the sampling
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tubes contact the luggage surfaces, and flex slightly. The 2 moveable banks are agitated
lightly over the luggage, using a lateral motion to “brush” the surfaces, and dislodge any
particles. Concurrently, a high-suction airflow of 4,500 l/min (20 l/min/tube) is initiated,
which transfers the particles to the primary pre-concentrator, a tortuous-path stainless steel
screen mesh, which efficiently traps and absorbs particles.
Feeder Belt
SYSTEM OPERATION CONCEPT DIAGRAM
Jam Detector
Main Belt
Oversize Detector
Luggage Size/Position
Sensors (insidde tunnel)
Sampling Tunnels
Particles
Sandia preconcentrator
Heat
Vapors
Coated mesh
Vapor Concentrator
Heat
Vapors
Logic
Controller
IONSCAN ®
IMS
Vapors
Sandia preconcentrator
Vapors
Coated mesh
Vapor Concentrator
Vapors
IONSCAN ®
IMS
Reject Belt/Shute
Alarms
Main Belt
Figure 1:
ATD Schematic
After sample collection, the pre-concentrator housing is sealed, and a cross-flow of clean air
initiated, while simultaneously the mesh is resistively heated for 1.5 seconds using a
transformer. All traces of explosive particles absorbed on the mesh are flash-vaporized into
the clean, cross-flow air stream, then absorbed in a proprietary secondary concentrator,
mounted in a rotating table. The cross-flow air stops, and the table rotates and positions the
cartridge directly underneath the IONSCAN inlet. The cartridge is then sealed in the inlet,
and heated to vapourise the absorbed analyte directly into the IMS (Figure 2). This
secondary concentration/ vapourization cycle transfers a much cleaner sample into the
IONSCAN, minimising interference, and reducing the amount of background matrix entering
the IMS and contaminating it.
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A similar technique is employed for sampling for vapours. Immediately after particle
sampling, the luggage enters the vapour tunnel. A high suction airflow is turned on, and a
mechanical inclined 3-pronged bar descends, pressing down physically on the luggage and
“burping” it to release any explosive vapours that are present in the interior. All the air in the
tunnel is effectively sampled by the powerful suction flow.
The suctioned air stream passes through the primary pre-concentrator, where the vapours
are absorbed. The next steps are identical to the particle system, i.e. cross-flow air, rapid
mesh heating, absorption into the secondary concentrator, and from there, thermal
desorption into the IONSCAN for analysis (Figure 3).
The complete system is capable of processing approximately 700 pieces of luggage per
hour. A timing diagram (Figure 4) shows the sequence of events.
Figure 2: Particle collection, 2-stage concentration and IMS analysis
PARTICLE SAMPLING SYSTEM
AC Heater Power
AC Heater Power
Sandia Preconcentrator
Primary Pre-concentrator
Cartridge
Particles
Vapors Vapors
IONSCAN ®
IMS Detector
Moveable Moveable Sampling Sampling
Tube Tube Manifolds Manifold
Secondary
Vapor Coated Concentrator Mesh
Vapor Concentrator
Rotary
Table
P1
P2
Luggage
Sampling Tubes
Suction Tubes
Figure 3: Vapour collection, 2-stage concentration and IMS analysis
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100
cm
Bag
1
150
cm
Bag
2
Bag
3
Bag
4
Bag
5
Bag
6
2 s
3 s 2 s 3 s 2 s 3 s 2 s 3 s
S
D & RT
PDA
20 sec
Figure 4:
Timing sequence
Summary of Events Timing
Sampling (S)
7 sec
Desorption and Maximum bag size 75 x 75 x 100 cm
Rotation of Table (D & RT) 3 sec Bag throughput rate 720/hour or 1/5 sec
Particle Desorption Conveyor belt speed 50 cm/sec
and Analysis (PDA) 10 sec IMS rate 6 samples/min
Total Cycle
20 sec
The IONSCAN operating parameters for particles and vapours were:
Particles Vapours
IMS drift tube temperature ( o 115 60
C)
Inlet temperature ( o C) 245 110
VAPOR SAMPLING SYSTEM
AC Heater Power
AC Heater Power
Vapors
Sandia
Sandia
Preconcentrator
Preconcentrator
Cartridge
Cartridge
Vapors Vapors
IONSCAN ®
IMS Detector
Moveable Tube
Manifold Moveable ”Burper”
Manifold
Coated Mesh
Vapor Coated Concentrator Mesh
Vapor Concentrator
Mechanical “burper” bar
Rotary
Table
Luggage
P1
P2
Suction exit
Suction Tubes
Sampling Plenum
Drift gas flow rate (ml/min) 350 350
Sample gas flow rate (ml/min) 300 300
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Conclusions
Barringer has developed and built a novel, effective Automatic Trace Detector for the rapid
screening of luggage for traces of explosives' vapours and particles.
Future developments will focus on further optimization of the primary pre-concentrator for
vapour analysis, and overall improvements to the flow dynamics of the system. A final
assessment for false alarm rates in a real-world, busy airport environment is planned when
the complete system is optimized.
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