S2S
A GATEWAY FOR PLANT AND PROCESS SAFETY
Proposal N°: CTC1 – 2001 – 43061
Contract N°: G1RT – CT – 2002 – 0594
Document Title: technical report on measurement methods of physicochemical properties
Author(s): Dr. Pablo Lerena, Swiss Safety Institute
Document number: D_WP2&3_T0_SWISSI02(1)
Synopsis of contents
This technical report discusses the classification of a substance as “explosive” based on
physicochemical properties according to different regulations.
Table of contents
1 Introduction and keywords ............................................................................................. 3
2 State-of-the-art ................................................................................................................. 3
2.1
Directive 67/548/EEC .............................................................................................. 3
2.2
UN Recommendations for the transport of dangerous goods .......................... 3
3 Methodologies used ........................................................................................................ 3
3.1
Methodology 1 .......................................................................................................... 3
3.2
Methodology 2 .......................................................................................................... 7
3.2.1
Screening procedure ....................................................................................... 7
3.3
Complete acceptance procedure .......................................................................... 8
3.3.1
Un gap test for determining propagation of detonation ............................. 8
3.3.2
Koenen test for determining the effect of heating under confinement .. 10
3.3.3
Time/pressure test ......................................................................................... 10
3.3.4
Internal ignition test ....................................................................................... 11
4 Needs for future development ..................................................................................... 13
5 Listing of well-known institutes, organisations and consultancy firms in the area
(To the best of author’s knowledge) ................................................................................... 13
5.1
TNO ......................................................................................................................... 13
5.2
BAM ......................................................................................................................... 13
5.3
Swiss Safety Institute ............................................................................................ 13
6 Related literature ........................................................................................................... 13
1
Introduction and keywords
This technical report discusses the classification of a substance as “explosive” based on
physicochemical properties according to different regulations.
Keywords:
2
2.1
State-of-the-art
Directive 67/548/EEC
The tests methods for physicochemical properties are described and compiled in the annex V
of the directive 67/548/EEC. The European Chemicals Bureau (ECB) is in charge of the
follow-up of the progress of the state-of-the art of these methods (Adaptation to Technical
Progress, ATP).
This is the list of the tests for physicochemical properties:
A.1 Melting/freezing temperature
A.2 Boiling temperature
A.3 Relative density
A.4 Vapour pressure
A.5 Surface tension
A.6 Water solubility
A.8 Partition Coefficient
A.9 Flash-point
A.10 Flammability (solids)
A.11 Flammability (gases)
A.12 Flammability (contact with water)
A.13 Pyrophoric properties of solids and liquids
A.14 Explosive properties
A.15 Auto-ignition temperature (liquids and gases)
A.16 Relative self-ignition temperature for solids
A.17 Oxidizing properties (solids)
A.18 Number - average molecular weight and molecular weight distribution of polymers
A.19 Low molecular weight content of polymers
A.20 Solution / extraction behaviour of polymers in water
A.21 Oxidising Properties (liquids)
The annex VI describes the classification of dangerous products based on the
physicochemical properties determined by the tests described in annex V.
2.2
UN Recommendations for the transport of dangerous goods
The tests methods to classify products as dangerous goods for transport are described in the
Manual of tests and criteria, 14th Edition and the criteria of classification based on the results
of the tests in the Model Regulations, 14th revised edition.
3
3.1
Methodologies used
Methodology 1
The methodology proposed by the directive European Directive 67/548/EEC to classify
products as “explosives” is described as follows in the Annex VI of the directive:
2.2.1. Explosive
Substances and preparations shall be classified as explosive and assigned the symbol “E”
and the indication of danger “explosive” in accordance with the results of the tests given in
Annex V and in so far as the substances and preparations are explosive as placed on the
market. One risk phrase is obligatory, it is to be specified on the basis of the following:
R2
Risk of explosion by shock, friction, fire or other sources of ignition
-
Substances and preparations except those set out below.
R3
Extreme risk of explosion by shock, friction, fire or other source of ignition
-
Substances and preparations which are particularly sensitive such as picric acid salts
or PETN.
The risk of explosion by the action of fire is determined using the apparatus described in the
figure below (Koenen test). The principle consists on heavily heating a sample of 9 cm 3 of the
product contained in a steel tube. The tube is closed with a pressure resistant orifice plate
(allowing a hole of different diameters).
It may be important for the safety of experimenters that certain preliminary tests, using
small amounts of material, be conducted first before proceeding to experiment with
larger quantities.
The results of the test are judged according to the deformation of the tube after the test as
shown in the figure below.
The risk of explosion by mechanical action (shock or friction) is determined by using the
falling hammer test and the friction test. The first method involves subjecting substances to
the shock of a specified mass from a specified distance. The friction test involves subjecting
solid or pasty substances to friction between standard surfaces under specified conditions of
load and relative motion.
The introduction of the presentation of the methods states:
The method is appropriate for determining whether a substance will present a danger of
explosion (thermal and mechanical sensitivity) under the particular conditions specified in the
directive. It is based on a number of types of apparatus which are widely used internationally
and which usually give meaningful results. It is recognised that the method is not definitive.
Alternative apparatus to that specified may be used provided that it is internationally
recognised and the results can be adequately correlated with those from the specified
apparatus.
The tests need not be performed when available thermodynamic information (e.g. heat of
formation, heat of decomposition) and/ or absence of certain reactive groups in the
structural formula establishes beyond reasonable doubt that the substance is incapable of
rapid decomposition with evolution of gases or release of heat (i.e. the material does not
present any risk of explosion). A test of mechanical sensitivity with respect to friction is not
required for liquids.
These statements indicate the limitations of the method, it is thus useful to provide more
information about alternative apparatus and a closer understanding of the thermodynamic
information that should be needed to decide if a substance may show explosive properties or
not. A more complete approach is given by the United Nations Recommendations on the
Transport of Dangerous Goods.
3.2
Methodology 2
The methodology of classifying products as explosive based on thermodynamic properties
according to the UN recommendations consists on a screening and a complete acceptance
procedure.
3.2.1 Screening procedure
The screening procedure is described in the Appendix 6 of the Manual of Test and Criteria. It
allows to exclude the possibility of a product being explosive based on the following
properties and assuming that the substances are not manufactured with the intention of
producing an explosive or pyrotechnical effect:

If the substance doesn’t contain certain chemical groups which may show explosive
properties as e.g.,
o C-C unsaturation: Acetylenes, acetylides, 1,2-dienes
o C-Metal, N-Metal: Grignard reagents, organo-lithium compounds
o Contiguous nitrogen atoms: Azides, aliphatic azo compounds, diazonium salts,
hydrazines, sulphonylhydrazides
o Contiguous oxygen atoms: Peroxides, ozonides
o N-O: Hydroxylamines, nitrates, nitro compounds, nitroso compounds, Noxides, 1,2-oxazoles
o N-halogen: Chloramines, fluoroamines



o O-halogen: Chlorates, perchlorates, iodosyl compounds
When the substance contains chemical groups associated with explosive properties
which include oxygen and the calculated oxygen balance is less than -200.
When the organic substance or a homogenous mixture of organic substances contain
chemical groups associated with explosive properties but the exothermic
decomposition energy measured e.g., in a Differential Scanning Calorimeter is less
than 500 J/g and the onset of exothermic decomposition is below 500 ºC. (If the
decomposition energy of a product is lower than 800 kJ/kg it is assumed that it is not
able to propagate a detonation or to be sensitive to shock.)
For mixtures of inorganic oxidizing substances of Division 5.1 with organic
material(s), the concentration of the inorganic oxidizing substance is below certain
limits.
It could be inferred that these criteria could be used to discard the performance of
thermodynamic tests according to the EC 67/548/EEC. However, it cannot be excluded that
substances complying with the conditions of the UN screening procedure may show a positive
Koenen test: it is the case of substances with a decomposition energy lower than 500 KJ/kg
but releasing important quantities of gas during the decomposition. The resulting overpressure
may damage the test tube leading to a positive result.
3.3
Complete acceptance procedure
The procedure is rather complex and the approach is different form the Methodology 1
because the purpose of the classification is to avoid accidents during the transport. That means
for example that a potentially explosive substance that is sensitive to shock or friction
(determined with similar tests as for Methodology 1), the substance is too dangerous for
transport and should be modified for its purpose (e.g., flegmatization).
It may be important for the safety of experimenters that certain preliminary tests, using
small amounts of material, be conducted first before proceeding to experiment with
larger quantities.
If the substance was not manufactured to produce an explosive or pyrotechnical effect and if it
is not a ammonium nitrate or gel intermediate for blasting explosive, the explosive character
of a substance is determined on the basis of 4 tests:
o Test 1(a):
o Test 1(b):
o Test 1(c)(i):
o Test 1(c)(i):
UN gap test for determining propagation of detonation
Koenen test for determining the effect of heating under confinement
Time/pressure test for determining the effect of ignition under
confinement (deflagration)
Internal ignition test determining the effect of ignition under
confinement (transition from deflagration to detonation)
3.3.1 Un gap test for determining propagation of detonation
This test is used to measure the ability of a substance, under confinement in a steel tube, to
propagate a detonation by subjecting it to the detonation from a booster charge. It may be
applied for solids or liquids.
The test sample is contained in a 400 mm long and 48 mm diameter vertical steel tube
together with a booster and a detonator. On the upper end there is a mild steel witness plate as
shown in the figure below.
The test is considered positive if the tube is fragmented completely or a hole is punched
through the witness plate.
3.3.2 Koenen test for determining the effect of heating under confinement
The test is the same as described before.
3.3.3 Time/pressure test
This test is used to determine the effects of igniting the substance under confinement in order
to determine if ignition leads to a deflagration with explosive violence at pressures which can
be attained with substances in normal commercial packages.
5g of sample (or 0.5 g if screening tests indicates that a rapid reaction is likely to occur) are
introduced in a cylindrical steel pressure vessel 89 mm in length and 60 mm in external
diameter equipped with an ignition system and a pressure transducer as shown in the figure
below.
The test results (ability to deflagrate) are interpreted in terms of whether a gauge pressure of
2070 kPa is reached and, if so, the time taken for the pressure to rise from 690 kPa to 2070
kPa gauge.
3.3.4 Internal ignition test
This test is used to determine the tendency of a substance to undergo transition from
deflagration to detonation.
The sample of substance to be tested is contained in a 45.7 cm length steel pipe with inside
diameter 74 mm, wall thickness 7.6 mm, capped at both ends with a forged steel pipe cap. An
igniter consisting of 20 g of black powder is located at the centre of the sample vessel as
shown in the figure below.
The test result is considered "+" if either the pipe or at least one of the end caps is fragmented
into at least two distinct pieces. Results in which the pipe is merely split or laid open, or in
which the pipe or caps are distorted to the point at which the caps are blown off, are
considered "—".
4
Needs for future development
As it was shown in the previous paragraphs, the physicochemical properties taken into
account into the directive 67/548/EEC are only a part of those considered by the UN
Recommendations for transport of dangerous goods. It is clear that the risks related to
transport imposes some limits as for example the avoidance of substances with explosives
properties sensitive to mechanical impact or friction. However, the concept of “explosive” in
the EEC directive is limited to the ability of the substance to have an explosive effect when
heated under confinement or to the sensitivity to shock or friction.
All the tests proposed are empirical, involve relatively large amounts of material and
installations were explosions in a small scale can be performed safely. Very few attention is
paid to the measurement of the energy that can be liberated by the substances and the amount
of gas produced in the chemical reactions that are at the origin of the explosive behaviour. An
interesting field of further development and research is to find a correlation between the large
scale tests and other properties of the materials that could be measured using experiments
involving a significant lower sample size or risk as e.g., energy and amount of gas released,
crystalline state and apparent density. The ultimate goal would be to replace the actual
empirical tests with small-scale laboratory tests with less empirical basis.
5
Listing of well-known institutes, organisations and consultancy firms in the area (To
the best of author’s knowledge)
5.1 TNO
5.2 BAM
5.3 Swiss Safety Institute
6
Related literature
Directive 67/548/EEC, (1992)
UN Recommendations for the transportation of dangerous goods, 14th. Edition, (2005)
Louis Medard, “Les explosifs occasionnels”, Editions Tec&Doc, (1999)
T.Yoshida, “Safety of reactive chemicals”, Elsevier, (1987)