1. Journal of Loss Prevention in the Process Industries 20 (2007) 1–6
A closed pressure vessel test (CPVT) screen for explosive properties of
energetic organic compounds
A. Knorra
, H. Kosekib
, X.-R. Lib
, M. Tamurac
, K.D. Wehrstedta
, M.W. Whitmored,Ã
a
Bundesanstalt fu¨r Materialforschung und –pru¨fung (BAM), Division II. 2 ‘‘Reactive Substances and Systems’’, Unter den Eichen 87, Berlin 12205, Germany
b
National Research Institute of Fire and Disaster (NRIFD), 14-1Nakahara, 3-Chome Mitaka-Shi, Tokyo 181-8633, Japan
c
Yokohama National University, 79-1, Tokiwadai, Hodagayu-ku, Yokohama 240-8501, Japan
d
41 Long Lane, Willingham, Cambridge CB4 5LD, England, UK
Abstract
Results of a round-robin test on a mini-autoclave are reported and previously proposed criteria reviewed. Criteria based upon the
results for three standard materials are now put forward. These standards-based criteria, in contrast to numerical criteria, theoretically
allow any laboratory to utilize the data accumulated to date, irrespective of the equipment used. The practical requirement is that
adequate discrimination can be achieved. Data to assess this are given.
r 2006 Elsevier Ltd. All rights reserved.
Keywords: Closed pressure vessel test; Mini-autoclave; MCPVT; Explosive properties
1. Introduction
Data were presented at an International Workshop
(IWS) in Tokyo that indicated that a closed pressure vessel
test (in this case Adolf Ku¨ hner’s mini-autoclave) could
provide a more efficient screen for explosive properties
than decomposition energy (Baker & Whitmore, 1998).
Mini-autoclave results were correlated with an explosive
rank as defined in Table 1.
Screening criteria were proposed based on maximum
rate of pressure rise (MPR) and a measure of event-
temperature (Tp), defined as the baseline temperature when
the sample temperature was maximum. (Tp was chosen
rather than onset temperature because it can be determined
more reproducibly.) The criteria were
if MPR exceeds 124 MPa sÀ1
, assume rank A;
if MPR is equal to or less than 124 MPa sÀ1
, but greater
than or equal to 15;
MPa sÀ1
and Tp is less than 167 1C, assume rank B;
if MPR is equal to or less than 124, but greater than or
equal to 15 MPa sÀ1
and Tp greater than or equal to
167 1C, assume rank C;
if MPR less than 15 MPa sÀ1
, assume rank D;
As made clear in the IWS paper and subsequently, the
inclusion of Tp in the criteria does not mean that the
explosive potential of rank B and C materials having
similar MPR is different under extreme conditions, merely
that under the conditions of transport, the potential of
rank C materials is less likely to be realized by virtue of
high Tp. Another way of looking at this is that since in the
UN tests the initial temperature of the test material is
ambient, the results are only applicable to material at or
near ambient temperature.
In a follow-up paper (Whitmore Baker, 2001), the
above criteria were tested. In respect of ranks A and B, the
criteria were validated. However, at least partly due to
the poor agreement between UN tests for deflagration and
thermal explosion (Brown, Mak, Whitmore, 2000), the
application of ranks C and D could not be sustained. Two
further points emerged from this work. First, that the
criteria should not be applied to water-wetted materials.
ARTICLE IN PRESS
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0950-4230/$ - see front matter r 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jlp.2006.08.002
ÃCorresponding author. Tel.: +44 1954 201177.
E-mail address: martynwhitmore@hotmail.com (M.W. Whitmore).

2. Second, rupture of the bursting disc (35 MPa at 450 1C),
should lead to the assumption of Rank A. Subsequently,
re-examination of the data showed that the lower MPR
limit for rank B could be increased to 38 MPa sÀ1
.
Between-laboratory comparisons (round-robin test) of
mini-autoclave measurements are reported and the screen-
ing criteria reassessed.
2. Round-robin test
Adolf Ku¨ hner’s mini-autoclave system is essentially a g-
scale DTA system which enables the measurement of
pressure as well as temperature (Adolf Ku¨ hner, undated;
Baker Whitmore, 1998). Japanese workers have modified
the autoclave by replacing the thermo well with a directly
inserted thermocouple. Also, the original Ku¨ hner heating
block/oven, which accommodates up to three autoclaves,
was been replaced with an electrically heated oven to
contain a single autoclave.
Organisations participating in the round-robin test were
Bundesanstalt fu¨ r Materialforschung und -pru¨ fung
(BAM), Berlin, Germany.
National Research Institute of Fire and Disaster
(NRIFD), Tokyo, Japan.
Marine Surveyors and Sworn Measures Association
(NKKK), Yokohama, Japan.
Kayatech Co. Ltd, Yamaguchi, Japan.
BAM used the Ku¨ hner hardware, whilst other partici-
pants used the Japanese modification.
Test conditions:
sample mass 1.00 g;
uniform heating rate 2.5 K minÀ1
(BAM 2.4);
pressure data acquisition 1 kHz.
ARTICLE IN PRESS
Table 1
Explosive rank
Explosive rank Severest property according to UN Class 1 tests (UN, 1995) Correspondence to UN transport
classification
A Detonatesà Potentially class 1
B Deflagrates rapidlyÃÃ and/or gives violent effect upon heating under
confinementÃÃÃ
Potentially class 1, but not detonable
C Deflagrates slowly and/or medium or low effect of heating under
confinement
Not class 1
D Does not deflagrate and shows no effect of heating under confinement No explosive properties
ÃBAM 50/60 steel tube test.
ÃÃTime-pressure test.
ÃÃÃKoenen test.
Table 2
Summary of round-robin and IWS results, giving means, number of replications and standard deviations
Material IWS BAM NRIFD NKKK Kayatech
Tp MP MPR Log
MPR
Tp MP MPR Log
MPR
Tp MP MPR Log
MPR
Tp MP MPR Log
MPR
Tp MP MPR Log
MPR
Bronopol Mean 172 17.5 410 2.610 183 23.9 868 2.935 180 27.0 2209 3.339 185 26.1 1300 3.061 180 23.5 1464 3.142
Rep. 2 2 2 2 3 3 3 3 3 3 3 3 2 3 3 3 4 4 4 4
Std dev 2.83 0.71 70.7 0.075 0.58 1.82 133.4 0.064 3.21 1.95 437.6 0.083 4.95 5.51 813.1 0.255 2.63 3.39 562.2 0.164
BPO75 Mean 86 8.8 335 2.523 103 7.1 657 2.817 101 7.8 883 2.945 106 7.0 809 2.895 101 7.2 916 2.954
Rep. 2 2 2 2 3 3 3 3 3 3 3 3 2 8 8 8 2 7 7 7
Std dev 0 1.06 49.5 0.064 0.58 0.25 42.0 0.028 0.58 0.27 88.2 0.042 0.71 0.83 217.6 0.107 1.41 0.90 183.7 0.093
AIBN Mean 96 10 120 2.079 97 8.3 333 2.521 99 8.1 349 2.532 99 6.5 272 2.433 74 5.9 305 2.478
Rep. 1 1 1 1 4 4 4 4 3 3 3 3 2 5 5 5 2 4 4 4
Std dev — — — — 1.50 0.10 31.1 0.040 3.60 0.90 93.6 0.123 2.12 1.79 33.1 0.050 3.54 0.42 57.7 0.081
BPB Mean 108 8.3 55 1.74 116 9.1 110 2.039 115 5.4 108 2.024 115 8.4 137 2.116 122 6.2 99 1.981
Rep. 2 2 2 2 3 4 4 4 3 3 3 3 2 5 5 5 1 7 7 7
Std dev 0 0.354 7.1 0.056 1.15 0.47 12.9 0.049 3.79 0.47 26.4 0.1032 4.24 1.07 48.3 0.156 — 0.50 26.1 0.122
MN Mean 222 2.9 35 1.542 242 3.4 37.5 1.572 235 2.5 52 1.701 — 2.4 79 1.898 223 2.4 84 1.899
Rep. 2 2 2 2 4 4 4 4 1 3 3 3 0 1 1 1 1 3 3 3
Std dev 25.5 0.141 4.2 0.053 6.98 0.21 4.1 0.048 — 0.53 17.2 0.1542 — — — — — 1.16 35.8 0.172
A. Knorr et al. / Journal of Loss Prevention in the Process Industries 20 (2007) 1–62

3. Measurements:
maximum pressure (MP);
maximum rate of pressure rise (MPR);
base-line temperature when sample temperature is
maximum (Tp).
Test materials, obtained from Aldrich Chemical Company:
2-Bromo-2-nitropropane-1,3-diol (Bronopol, BR), 98%.
Dibenzoyl peroxide 75% with water (BPO75).
2,20
-Azobis(2-methylpropanenitrile) (AIBN), 97%.
tert-Butyl peroxybenzoate (BPB), technically pure.
Malononitrile (MN), 99%.
3. Results of round-robin test
The round-robin results are summarized in Table 2,
together with the corresponding results reported at the
IWS in Tokyo (Baker Whitmore, 1998). Mean results are
ARTICLE IN PRESS
MP
1.0
MN BPB AIBN BPO BR
MN BPB AIBN BPO BR
MN BPB AIBN BPO BR
10.0
100.0
Pmax/MPa
IWS
BAM
NRIFD
NKKK
Kayatech
MPR
10
100
1000
10000
MPR/MPa/s
IWS
BAM
NRIFD
NKKK
Kayatech
Tp
0
50
100
150
200
250
300
Tp/°C
IWS
BAM
NRIFD
NKKK
Kayatech
Fig. 1. Comparison of round-robin and IWS results.
MP
1
10
100
100101
IWS MP/MPa
OtherLaboratoriesMP/MPa
BAM
NRIFD
NKKK
Kayatech
Power (BAM)
Power (NRIFD)
Power (NKKK)
Power (Kayatech)
MPR
10
100
1000
10000
10 100 1000
IWS MPR/MPa/s
OtherLaboratoriesMPR/MPa/s
BAM
NRIFD
NKKK
Kayatech
Power (BAM)
Power (NRIFD)
Power (NKKK)
Power (Kayatech)
Tp
0
50
100
150
200
250
300
50 100 150 200 250
IWS Tp/°C
OtherlaboratoriesTp/°C
BAM
NRIFD
NKKK
Kayatech
Linear (BAM)
Linear (NRIFD)
Linear (NKKK)
Linear (Kayatech)
Fig. 2. Correlation of round-robin and IWS results.
A. Knorr et al. / Journal of Loss Prevention in the Process Industries 20 (2007) 1–6 3

4. compared in Fig. 1 and their correlations with IWS results
are shown in Fig. 2.
Fig. 1. shows there are considerable differences between
laboratories. A good deal of work would be necessary to
elucidate the origin of these differences (details of equip-
ment and procedures, data capture, data handling etc.) and
eliminate them to arrive at useful numerical criteria.
Indeed, such a goal might not be achievable. On the other
hand, Fig. 2 shows that the correlations between the
laboratories for all three measurements are good. It ought
to be possible, therefore, instead of having numerical
criteria, to have criteria based upon the results obtained in
each laboratory for specified reference materials. Such an
approach may require little further work. Moreover, with
this kind of approach any equipment offering similar
discrimination to the mini-autoclave could be employed.
Preliminary work using the accelerating rate calorimeter
has been reported (Bodman Chervin, 2004).
4. Discussion
The current criteria are illustrated in Fig. 3. So far these
criteria have proved valid in respect of Class 1 properties,
but the data suggest that the boundaries might slope
upwards from left to right. If this is so, then at lower Tp
values these criteria will be unsafe, whilst at high Tp values
they will be overly conservative. It may be appropriate
therefore to consider criteria such as shown in Fig. 4.
This approach has a precedent. Japanese workers
examined the relationship between DSC decomposition
energy (Qdsc) and onset temperature (To) and explosive
properties (Yoshida et al., 1987; Yoshida, 1987). They
found that the boundary between explosive and non-
explosive materials was an upward sloping straight line on
a plot of log Qdsc against To-25. Although not discussed in
the paper, the use of To-25 instead of To, suggests that the
Japanese workers thought that the energy required to raise
the temperature of the test material in the explosive tests to
the decomposition temperature, and the energy lost in the
time this took, was the origin of the upward sloping
boundary.
This reasoning can account for the relationship of the
boundaries in Fig. 4. The rank A boundary has a lower
slope than the rank B lower boundary. In general, rank A
materials, as well as being more powerful, are more
energetic than rank B materials. So, for a given event
temperature, the energy used and lost in raising the
temperature from ambient to the decomposition tempera-
ture, will be a greater proportion of the energy available for
rank B than rank A materials. Hence, the lower boundary
for rank B materials will be steeper than the boundary for
rank A materials.
Fig. 5 shows that the criteria proposed in Fig. 4, can be
conservatively approximated as follows. A rectangle is
constructed by drawing horizontal lines through the BPO
and MN points and vertical lines through the AIBN and
MN points. Drawing a line between the lower left corner
ARTICLE IN PRESS
1
10
100
1000
10000
0 100 200 300 400
Tp/°C
MPR/MPa/s
A
B
C
D
124 MPa/s
38 MPa/s
Fig. 3. Previously proposed criteria. The data shown are from Baker and
Whitmore (1998) and Whitmore and Baker (2001).
1
10
100
1000
10000
0 100 200 300 400
Tp/°C
MPR/MPa/s
A
B
C
D
Fig. 4. Alternative criteria. The dashed lines are the criteria shown in
Fig. 3.
1
10
100
1000
10000
0 100 200 300 400
Tp/°C
MPR/MPa/s
A
B
C
D
MN
BPO75
AIBN
Fig. 5. Construction of boundaries. Solid lines are the sloping boundaries
from Fig. 4. Dash-dot lines are boundaries constructed from BPO75,
AIBN and MN points.
A. Knorr et al. / Journal of Loss Prevention in the Process Industries 20 (2007) 1–64

5. and upper right corner of this rectangle gives the lower
rank B boundary. By connecting the AIBN point and the
upper right corner of the rectangle the rank A boundary is
obtained.
In Fig. 6, the criteria constructed in this way for each
laboratory, except NKKK due to missing Tp data, are
shown. Overall, the impression is that all the sets of criteria
offer similar discrimination.
A partial test of the BAM criteria was possible using
published data from the BAM on a number of organic
peroxides (Wehrstedt, Knorr, Schuurman, 2003). These
data are compared with the BAM rank B lower boundary
of Fig. 6 in Fig. 7. It is seen that these data confirm the
slope of the boundary. The position of the boundary
appears unsafe, but the MPR data in Fig. 7 were low
compared to the round-robin data from the BAM by at
least a factor of 1.5.
Fig. 8 is a modified version of Fig. 4 with (Tp-20) as
abscissa. A potential attraction of using temperature
difference as abscissa is that it could be used to directly
ARTICLE IN PRESS
IWS
10
100
1000
10000
0 50 100 150 200 250 300 350 400 0 50 100 150 200 250 300 350 400
Tp/°C Tp/°C
0 50 100 150 200 250 300 350 400 0 50 100 150 200 250 300 350 400
Tp/°C Tp/°C
MPR/MPa/s
BAM
10
100
1000
10000
MPR/MPa/s
10
100
1000
10000
MPR/MPa/s
10
100
1000
10000
MPR/MPa/s
NRIFD
Kayatech
Fig. 6. Constructed criteria for each laboratory.
1
10
100
1000
0 50 100 150 200 250
Tp/°C
MPR/MPa/s
B
C
Fig. 7. Test of BAM criteria. The boundary shown is from Fig. 6 (BAM).
1
10
100
1000
10000
0 100 200 300 400
(Tp-20)/°C
MPR/MPa/s
A
B
C
D
Fig. 8. Alternative presentation of criteria. The sloping boundaries from
Fig. 4 are plotted with (Tp-20) as abscissa.
A. Knorr et al. / Journal of Loss Prevention in the Process Industries 20 (2007) 1–6 5

6. assess situations other than transport. As mentioned in the
Introduction, the explosive potential of materials having
similar MPR, but different ranks by virtue of different Tp is
not different. It is only that the lower ranked material, by
virtue of its high Tp, is less likely to exhibit its potential
under the low temperature conditions of transport. When
handled at higher temperature, it will likely exhibit more
severe properties if initiated. Consider, for example, a
material having MPR 220 MPa sÀ1
and Tp 250 1C. Its rank
from Fig. 8 will be C. However, if it is to be handled at
150 1C, what properties might it exhibit? Regarding the
abscissa scale as (Tp-operating temperature), we can read
off at 100 1C (250–150) that an MPR of 220 MPa sÀ1
lies in
the detonable or rank A range.
By basing the CPVT criteria on the results obtained with
three reference materials (BPO75, AIBN and MN), in
principle any laboratory can utilize the data accumulated
so far, irrespective of the equipment they use. The
constraint is that they must achieve similar discrimination
to that observed by the five laboratories that have provided
data.
From the way the boundaries were constructed in Fig. 7,
it is evident that the potential discrimination depends upon
the separations on the MPR scale between AIBN and MN
and between BPO75 and AIBN, and the separation on the
Tp scale between MN and AIBN. Because the MPR scale is
logarithmic, the separation can be represented by ratios.
The actual discrimination achieved for a given level of
replication will depend on the reproducibility of log MPR
and Tp.
The data to assist laboratories in their assessments are
shown in Table 3.
In setting up a closed vessel test replication will be
essential, but the degree cannot be prescribed here as it will
depend upon the separation and reproducibility seen in
individual laboratories. Evidently the guiding principle
must be to do sufficient replication to establish satisfactory
criteria and to ensure statistically valid assignments of test
substances.
The test is not applicable to water-wetted materials,
liquids in the cavitated state or materials diluted with
relatively volatile inert materials.
5. Conclusion
The concept of basing CPVT screening criteria on
standard materials rather than numerical values allows
any laboratory potentially to utilize the data so far
collected, provided satisfactory discrimination is achieved.
Data are given on the separation and reproducibility from
the five participating laboratories to provide a basis for
assessing the suitability of a particular laboratory’s
methodology.
References
Adolf Ku¨ hner, A. G. (undated). Mini-autoclave instruction manual.
Switzerland: Basle.
Baker, G. P., Whitmore, M. W. (1998). Investigation of the use of a
closed pressure vessel test for estimating condensed phase explosive
properties of organic materials. In Proceedings of international
workshop (IWS) on safety in the transport, storage and use of
hazardous materials, I-3-1–I3-15 and addendum, NRIFD, Tokyo.
Published in slightly modified form in Journal of Loss Prevention in the
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from HSE Language Services, Magdalene House, Bootle, Merseyside,
L20 3QZ, UK. Email: languageservices@gsi.gov.uk.).
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Table 3
MPR ratios, Tp differences and reproducibility standard deviations
MPR ratio BPO75: AIBN MPR ratio AIBN:MN Std dev log MPR Tp MN–Tp AIBN Std dev Tp
IWS 2.79 3.43 0.0985Ã 126 2.64Ã
BAM 1.97 8.89 0.0467 145 1.05
NRIFD 2.53 6.68 0.108 136 1.09
NKKK 2.97 3.45 0.137 No data 3.45
Kayatech 3.01 3.64 0.123 124 2.69
ÃFrom Baker and Whitmore (1998) and Whitmore and Baker (2001).
A. Knorr et al. / Journal of Loss Prevention in the Process Industries 20 (2007) 1–66