Marcela Najarro and Greg Gillen 

Forensics @ NIST

November 29, 2012 - Gaithersburg, MD 
Who is a target?

C-4: Blast effects from Bali, Indonesia nightclub 

bombing

C-4: Damaged hull of U.S.S.

Cole in Yemeni port

Semtex: Pan Am Flight 103

ANFO (4K lbs): Oklahoma City Murrah Building TNT: U.S. embassy in Nairobi, Kenya TNT: U.S. embassy in Tanzania
Detection Technology

 Explosive Trace Detectors (ETDs) are widely 

deployed to rapidly screen vehicles, people, and 

their belongings for trace contraband residue

 Locard’s Exchange Principle: “Every contact 

leaves a trace....”

 the perpetrator of a crime will bring something into the 

crime scene and leave with something of it

 What are we looking for? 

 Microscopic evidence or indication of the past presence 

 or existence of contraband
Trace Detection

Chemical Analyzer/

Detection

Sample Collection

Sample Analysis

Trace

Residue

Operational User
Law Enforcement Needs 

 Need: To protect federal 

agencies/infrastructure from potential terrorist 

threats 

 How do we know if our detector is

 working?

 What should my detection 

 requirements be?

 SOPs and best practices for screeners

 Considerations for setting operational parameters

○ false alarm rate, contamination issues, the effect of 

environmental conditions, sample throughput etc
What is the Test Bed? 

 A unique partnership between law enforcement 

(end-users) and researchers

 Physical location: NIST campus entry-points

 ETDs complement canine detection team

 Benefits: 

 Researchers: Evaluate NIST laboratory findings in realworld field conditions

 End-users: Explosives trace materials (no cost) and 

specialized screener training
Operator Training 

 Characterization of the threat 

○visual, chemical, thermal characteristics

○particle size distribution

○contamination: how much to expect, where 

to look (“hot spots”), fingerprints, dirt, etc. 
Operator Training 

 Sample collection

○ Wipes and particle collection

 efficiency (PCE)

 “sweet spot”

○ Best practices for swiping

 Direction

 Force

○ Wands 

 Design and optimization 
 Instrument operation

○ How does the instrument work?

○ Optimization of parameters

○ Verifying instrument performance

 Test materials 

Operator Training 
Test Materials (TMs) 

 Explosives test materials are standards with a 

known amount of explosive

 Test materials applications:

 Daily instrument performance check 

 Evaluate screener performance 

 Support “red team” operations

 Evaluate instrument variability

○ False alarms

○ Limit of detection

 Lab vs field instrument response comparison

 Monitor instrument drift (environment)

 Define detection requirements

 Define limit of detection (LOD)

 Assess return from service 
Inkjet Printing Technology

o Mass production

o Large dynamic range

o Wide range of threats

o Repeatable, traceable

o Flexibility

o Low cost and easy to use

1. Verkouteren et al., Anal. Chem., 2009, 81 (20), 

pp 8577-8584 

2. Windsor et al., Anal. Chem., 2010, 82 (20), pp 

8519-8524

3. Verkouteren et al., Langmuir., 2011, 27 (15), 

pp 9644-9653

Fluid at

Ambient

pressure 

Transducer

(Piezo or 

heater)

Orifice

Substrate

Driver

Character

Data 
Laboratory vs Field Response 

August November

•Test materials were stable during testing period 

•Showed subtle changes in instrument performance

•All samples produced a 100 % alarm rate 

•Good sample shelf-life (+85 days)

n = 5

~10 % RSD
Instrument Drift 

•The average field temperature during this testing period was 16 oC 

and 41 % relative humidity

•High TM variability alerted of a need for preventative maintenance: 

bakeout cycles and replacing the O-ring of the sample flange

58 % RSD
Instrument Response Comparison 

•Uncertainty is the standard deviation of the 10 measurement data set

•There was no operational indication or warning that “C” was performing 

with lower sensitivity than the other instruments

Explosive X Explosive Y
Operational Improvement 

Recommendation (OIRs) 

 

a b

Optimizing sampling 

Optimizing instrument design Optimizing operational conditions 
Conclusions 

 Test Bed was developed to bridge the gap 

between the laboratory and the field 

 Assess value of research findings to the end-user 

in the field

 Address the needs and requirements of the trace 

detection community 

 Operator training is critical to ensure the 

reliability of the trace detection analysis chain

 Fundamental research in the lab and field 

studies at the NIST explosives test bed 

confirm the critical need for measurements 

and standards for the trace detection 

community
Future Goals 

 Develop an inter-agency program with federal, 

state, and local law enforcement agencies 

interested in using test materials

 Provide scientific documentation to support 

educational/training programs for screeners

 Develop test materials for the narcotics 

detection community (dual mode ETDs)

NIST Law Enforcement 

Contraband Test Bed

RDX

cocaine
Acknowledgments 

 The Science and Technology Directorate of the U.S. 

Department of Homeland Security sponsored the production 

of this material under Interagency Agreement IAA HSHQDC10-X-00297 with the National Institute of Standards and 

Technology (NIST)

Questions?

Thank you for your time and attention! 

Contact information: Marcela Najarro

 marcela.najarro@nist.gov

 (301) 975-5395

*Certain commercial equipment, instruments or materials are identified in this paper to specify adequately

the experimental procedure. Such identification does not imply recommendation or endorsement by the

National Institute of Standards and Technology, nor does it imply that the materials or equipment identified

are necessarily the best available for the purpose.