Vapor Signatures from Military Explosives
Part 1. Vapor Transport from Buried Military-Grade TNT
THOMAS F. JENKINS, DANIEL C. LEGGETT, AND THOMAS. A. RANNEY
INTRODUCTION
In a more detailed study, Leggett et al. (1977)
Background
reported results for 8 domestic and 14 foreign
In the early 1970s, CRREL personnel conducted
military-grade TNT samples. Except for two
a series of experiments for which the ultimate
unknown compounds that responded on the GC-
goal was to define the vapor signatures of buried
ECD, the results confirmed that the major portion
landmines. The strategy employed was to initially
of the vapor composition was ascribable to the
define the signature of military-grade explosives
various isomers of DNT and TNT. The largest
and then try to understand the attenuation and
component of the vapor was 2,4-DNT for all eight
modification of these signatures attributable to
domestic TNTs, and all but four of the foreign
the mine casings and soil barriers. The intent was
TNTs. In most cases, the concentration of 2,4-
to provide this information to those groups that
DNT in the vapor exceeded that for 2,4,6-TNT by
were developing chemical sensors to detect the
an order of magnitude or more.
presence of landmines by sensing their associated
A preliminary study was also conducted to
vapor signature in near-real time.
assess how quickly vapors of military-grade TNT
Initially, the vapor signature of military-grade
could penetrate soil barriers (Jenkins et al. 1974).
TNT was investigated. Using gas chromatogra-
In this study, 1 g of military-grade TNT was
phy with an electron capture detector (GC-ECD),
placed on top of portions of two moist test soils (a
Murrmann et al. (1971) found that while 2,4,6-
sand and a clay) and was then covered with 2.5
trinitrotoluene accounted for 99.8% of the solid
cm of the appropriate soil in enclosed septum
military-grade TNT sample they studied, it pro-
vials. The vials were stored at room temperature
vided only 58% of the equilibrium vapor in the
for 25 days and the headspace above the soil was
headspace above the solid TNT. The manufactur-
sampled periodically. The results indicated that
ing impurity, 2,4-dinitrotoluene (2,4-DNT), while
2,4-DNT had penetrated through the soil to the
accounting for only 0.08% of the solid explosive,
headspace within 4 days, while vapors of 2,4,6-
accounted for 35% of the vapor composition
TNT were not detectable in the headspace until
owing to its much higher vapor pressure. The
day 12 (Table 1). From these results, the authors
remainder of the vapor composition was other
concluded that DNT and TNT vapors can diffuse
isomers of DNT and TNT. The authors concluded
through soil barriers in a relatively short period,
that 2,4-DNT could be as important as 2,4,6-TNT
and during the diffusion process, vapors are
for purposes of land mine detection. Despite a
largely retained within the soil barrier (Table 2).
special effort to detect vapor components other
Therefore, the surface soil directly above a buried
than isomers of TNT and DNT using GC-ECD
mine should have considerably larger amounts of
and GC-flame ionization detection (GC-FID), no
DNT and TNT than the headspace above.
other vapor components were identified.
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