Olfactory discrimination of oxygen
based explosives and propellants by
rats
Kimberly Kirkpatrick and Marina Vilardo
Kansas State University
Acknowledgments
Marina Vilardo
 Dr. John Tomich
 Ben Katz
 Kansas State University

HERO Rats (APOPO)
Background

Liquid explosives such as acetone peroxide have been
used in recent terrorist attacks:
◦ London Underground bombing
◦ The Christmas Day bomber
◦ The Shoe-Bomber
Liquid explosives have been used extensively in IED
devices which have been responsible for countless
deaths and injuries of American soldiers in
Afghanistan and Iraq
 Non-nitrogen based explosives are difficult to detect
through currently available electronic screening
devices
 However, these explosives have characteristic odors
that could be detected by trained animals

Previous research
Rats can readily detect nitrogenbased explosive odors (Marshall et
al., 1981; Nolan et al., 1978;
Weinstein et al., 1992)
 Rats can be trained to search and
alert for odors associated with
contraband items (Otto, Brown, and
Long, 2002)

Method: Apparatus
Acid Group
Butyric acid (BUT; 10%)
Propionic acid (PRO; 10%)
Acetic acid (AA; 10%)
Ketone/Peroxide Group
..
..
Methyl ethyl ketone (MEK; 10%)
Acetone (ACE; 20%)
Hydrogen peroxide (H2O2; 20%)
General Method

8 Sprague-Dawley rats
◦ Acid group (n = 4)
◦ Ketone/Peroxide group (n = 4)
Initial acclimation to apparatus
 Shaped to rear for sucrose+Nutella
 Reinforced for rearing to target

Methods: Phase 1
Phase
Description
Baseline
Target odor alone; 6 sessions x 6 trials
[BUT or MEK]
Target + one distracter odor; 8 sessions x 6 trials
[Distracters from within group]
Target + 2 distracter odors; 8 sessions x 6 trials
[Distracters from within group]
Target + 5 distracter odors; 8 sessions x 6 trials
[Distracters from both groups]
SOD1a/SOD1b
SOD2
SOD5
Results: Phase 1 Baseline
Percentage of "Hits"
100
80
60
40
BUT-EMPTY
MEK-EMPTY
20
0
0
2
4
Session
6
Subsequent visits to empty cups < 1%
Results: Phase 1 SOD1a
Percentage of "Hits"
100
80
60
40
BUT-AA
MEK-ACE
20
0
0
2
4
6
Session
8
Results: Phase 1 SOD1b
Percentage of "Hits"
100
80
60
40
20
BUT-PRO
MEK-H202
0
0
2
4
6
Session
8
Results: Phase 1 SOD 2
Perentage of "Hits"
100
80
60
40
BA-AA,PA
20
MEK-ACE,H2O2
0
0
2
4
6
Session
8
Results: Phase 1 SOD 5
Percentage of "Hits"
100
80
60
40
20
BUT-ALL
MEK-ALL
0
0
2
4
6
Session
8
Acid Group
Percentage of "Hits" or "FA"
100
80
60
40
BUT
PRO
AA
20
MEK
ACE
H2O2
0
0
2
4
Sessions
6
8
Percentage of "Hits" or "FA"
Results: Phase 1 SOD 5
Ketone/Peroxide Group
100
80
60
40
MEK
ACE
H2O2
BUT
PRO
AA
20
0
0
2
4
6
Sessions
8
Methods: Phase 2
Phase
Description
Baseline
Target odor alone; 6 sessions x 6 trials
[AA or ACE]
Target + one distracter odor; 8 sessions x 6 trials
[Distracters from within group]
Target + 2 distracter odors; 8 sessions x 6 trials
[Distracters from within group]
Target + 5 distracter odors; 8 sessions x 6 trials
[Distracters from both groups]
Target odor alone; 6 sessions x 6 trials
[PRO or H2O2]
Target + one distracter odor; 8 sessions x 6 trials
[Distracters from within group]
Target + 2 distracter odors; 8 sessions x 6 trials
[Distracters from within group]
Target + 5 distracter odors; 8 sessions x 6 trials
[Distracters from both groups]
SOD1a/SOD1b
SOD2
SOD5
Baseline
SOD1a/SOD1b
SOD2
SOD5
Results: SOD 1a/1b
Percentage of "Hits"
100
Acid Group
*
AA
80
PRO
60
40
BUT
20
0
AA-PRO
BUT-AA
BUT-PRO
Target-Distracter Pair
AA
PRO
BUT
Results: SOD 1a/1b
Ketone/Peroxide Group
Percentage of "Hits"
*
*
MEK
..
..
100
80
ACE
60
40
H2O2
20
0
MEK-ACE ACE-H2O2 MEK-H202
Target-Distracter Pair
..
..
MEK
H2O2
ACE
Methods: Phase 3

During the previous phases, the rats
experienced:
◦ Reinforcement in the arena
◦ Self-correction contingency

Phase 3 tested the impact on performance
◦ Baseline – 2 days on SOD 3 [PRO or H2O2]
◦ Testing – 8 days on SOD 3
 Rats were removed following first rearing response
 Reinforced if target, not reinforced if FA
Results: Phase 3
Percentage of "Hits"
100
80
60
Baseline
Test
40
20
0
PRO-ALL
H2O2-ALL
Summary and Conclusions

Rats were able to learn to search and
alert to specific targets
◦ Accurate discrimination performance:
 Emerged quickly
 Transferred readily to new distracters

Rats were able to learn to search and
alert to new targets that had been
previously trained as distracters
Summary and Conclusions

Rats discriminated all target-distracter
pairs to a high degree
◦ Acid group generalized most between AAPRO and AA-BUT
◦ Ketone/peroxide group generalized most
between the two ketones

While self-correction and/or
reinforcement in the arena may have
aided learning, they were not necessary
for accurate performance
Future directions

Detection of oxidation
◦ H2O2 oxidizes rapidly
◦ Can rats detect oxidation?
◦ Relevant to detecting peroxide-based
explosives (acetone peroxide)
What is the threshold for detection?
 Addition of “rejection response”
