Abstract: Critics contend that investments in sensors for biological
weapons are a “dead-end” [Brown, 2004]. However, over two decades of incidents
involving explosives offer compelling evidence that terrorists are deterred if
they perceive sufficient risk of failure. Therefore even imperfect WMD sensor
systems can form the foundation of a highly effective deterrent.
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Sensors deployed
strategically throughout an area, fixed or mobile, can be used as an early
warning system to remotely detect the presence of biological agents, chemicals,
explosives, and nuclear radiation. As recently discussed in Science [Brown,
2004], some critics question the wisdom of funding research in sensor systems that
detect biological weapons of mass destruction (WMD),
1.
Can sensors systems
ever be accurate enough to encompass the wide range of possible threats?
2.
Can sensor
systems ever be cost effective?
These questions about
biological sensors apply as well to sensors for conventional explosives,
nuclear, and chemical materials. Even a single attack that evades detection
might seem to render investment in a sensor system moot. Acknowledging that
sensor systems can never be perfect, a more relevant question is whether the
deployment of these systems increases terrorists’ risk of failure. In its
report, the 9/11 Commission points out that,
“Just
increasing the attacker’s odds of failure may make the difference between a
plan attempted, or a plan discarded. The enemy also may have to develop more
elaborate plans, thereby increasing the danger of exposure or defeat.” [p. 383,
Kean, 2004].
Sensors, which
are imperfect detectors, can serve as a disproportionately stronger deterrent
to the would-be attacker, i.e. as a nonlinear deterrent. On one hand, it is hard to predict exactly how
effective a WMD sensor system would be in deterring WMD terrorism [see U.S.
Congress, Office of Technology Assessment, 1993] simply because attacks using
them have been historically rare, calling into question the value of
investments in WMD sensor research. However, historical data involving use of conventional
explosives in terrorism can be used to gauge the expected deterrent effect of
sensors: we examine the role that screening of passengers and luggage for
conventional explosives has played in deterring terrorist use of explosives
within airports and airplanes. Critiques of airport screening measures have
also focused primarily on less than perfect detection probability, i.e. whether
or not a weapon or explosive will pass through the screening process at the
airport. For instance, [p. 52, Szyliowicz, 2004] remarks on the “porousness” of airport
screening by citing the United States GAO finding (July 2002) that fake weapons
and explosives had passed through airport screeners a quarter of the time at 32
major airports [p. 2, Dillingham, 2002]. As we shall see below, the deterrence
effect of screening has turned out to be far greater than would have been
predicted simply by a linear extrapolation of the detection probability.
Here, we employ data
from the RAND-MIPT database ([MIPT, 2002], [
1.
ALL: all
terrorist incidents
2.
EXPLOSIVES:
explosives were used or detonated
3.
AIRPORT/PLANE:
explosives in an airport or onboard an airplane
4.
AIRPLANE:
explosives onboard an airplane.
From
1989 onwards, ALL fatalities and fatalities from EXPLOSIVES not only increase,
but so does their rate as shown by the increasing steepness of the slope (the
apparent discontinuity on the ALL graph represents the deaths of nearly 3000
victims on
Figure 1
Upon
a closer examination of the data for categories AIRPORT/PLANE and AIRPLANE, we
find two extended periods of comparatively low fatalities preceded by periods
of much greater intensity. In Table 2 below, we show these periods along with
the fatalities for each category. Periods II and IV have much smaller
fatalities for AIRPORT/PLANE and AIRPLANE when compared to the corresponding
statistics during periods I and III. However, during all periods, including I
and II, the number of fatalities in EXPLOSIVES or ALL showed no signs of
slowing down. We conclude that during periods II and IV, there was a
“displacement[1]”
from airplanes as terrorist bombing targets onto other environments.
|
Period |
Dates |
Length (years) |
ALL |
EXPLOSIVES |
AIRPORT/PLANE |
AIRPLANE |
|
I |
|
2.5 |
593 |
391 |
296 |
283 |
|
II |
|
7.5 |
2027 |
1250 |
51 |
7 |
|
III |
|
4.5 |
2050 |
1520 |
708 |
700 |
|
IV |
to |
14 |
12302 |
4492 |
26 |
14 |
Table 1: Fatalities for each category and time period
Despite continuous
increase in fatalities for ALL and EXPLOSIVES, the presence of two periods of
accelerated fatalities followed by extremely low fatalities for AIRPORT/PLANE
and AIRPORT is telling. We believe that the
underlying reason for this trend is that during these periods airport screening
programs were greatly expanded:
·
First,
following frequent hijackings beginning in the late 1960s, a variety of
security measures including metal-detectors and X-Ray machines to screen
carry-on baggage were introduced in the United States as part of the Air
Transportation Security Act of 1974 [Malotky, 1998].
Indeed, a reduction in skyjackings in the
·
Second,
following an intense wave of fatalities during period III primarily due to use
of explosives in airports/airplanes culminating in the Pan Am airliner
explosion over Scotland[2],
increased vigilance and better procedures to sniff and screen for explosives in
airports appears to be directly responsible for the period of low fatalities
beginning in 1989 and continuing on into the present era. The end of this
period was also marked by the United States Aviation Security Improvement Act of
1990 [Bush, 1990].
·
Finally, over
the 1990s, increasingly better detection techniques and a greater degree of
automation to screen for explosives were introduced at airports worldwide [Malotky, 1998] thereby continuing to raise the bar for
terrorists who sought to employ explosives aboard airplanes.
Also shown in Figure 1, during periods II and IV, there was
also a significant reduction, but not elimination, in terrorist incidents
(attempts) to deploy explosives in airports and airplanes, even though overall
terrorist incidents using explosives continued to rise at an accelerated pace. These
trends suggest two important conclusions: 1) airport screening of explosives,
although imperfect, has successfully prevented fatalities despite a significant
number of continued attempted attacks at airports. 2) The screening measures
have been successful in deterring a much greater number of attempts that would
have taken place had the screening not been present, serving as a nonlinear
deterrent.
Detection systems for
explosives employed in today’s airports could not be extended more broadly in
populated areas since these systems are based on technology that requires
physical contact (swabbing) to wipe off traces of explosive which can then be
analyzed by techniques such as ion mobility spectrometry within specialized
machines [Malotky, 1998 and p. 114 Committee on
Science and Technology for Countering Terrorism, 2002]. But recent advances in
remote sensor techniques open up the possibility of extending explosive screening
to more spread-out areas without relying on checkpoints. They enable miniature
trace-detection sensors for conventional explosives such as TNT [for instance,
see Pinnaduwage, 2003] which sniff for explosive
particulate matter in the air and recognize specific explosives from a
distance, analogous to how a dog would. Similarly, the development of remote
non-intrusive sensors for chemical, biological, nuclear, and radiological
(dirty) bombs would be needed to defend against these threats.
Taking into account the
experience in deterring terrorism in commercial aviation, research in sensors
and systems to detect WMD is not a “dead-end” as critics contend, but would be
a decision based on a successful proof of concept. The nonlinear deterrence that
could be achieved through detection of WMD offers what may be the last line of
defense for otherwise vulnerable metropolitan areas.
1.
Brown, K.
2004. “Up In The Air,” Science. 305:
1228-29,
2.
Kean, T. H., et. al. 2004. The 9/11
Commission Report,
3.
Bush, G. 1990.
“Statement on Signing the Aviation Security Improvement Act of 1990,” 16
November. <http://bushlibrary.tamu.edu/papers/1990/90111605.html>
4.
Committee on
Science and Technology for Countering Terrorism. 2002. Making the Nation Safer,
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Devabhaktuni,
Srikrishna. 2004. “Could a citywide network of sensors prevent terrorist use of
bombs?,” 14 September. < http://www.devabhaktuni.us/research/sensors.htm
>
6.
Dillingham, G.
L. 2002. “AVIATION SECURITY: Transportation Security Administration Faces
Immediate and Long- Term Challenges,” United
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9.
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and Response,” Congressional Research Service, Order Code RS21293, 13 August.
< http://www.fas.org/irp/crs/RS21293.pdf
>
10.
MIPT. 2002.
“MIPT Terrorism Database System,” 27 August. <http://db.mipt.org>
11.
O’Hanlon, M.
E., et. al. 2002. Protecting the American
Homeland: A Preliminary Analysis,
12.
Szyliowicz, J.
2004. “Aviation Security: Promise or Reality?” Studies in Conflict and Terrorism, 27:47-63.
13.
Pinnaduwage, L. A., et. al. 2003. “Explosives: A microsensor
for trinitrotoluene vapour,” Nature. 425: 474,
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15.