Energetic materials encompass a wide range of chemical compounds all associated with a
significant risk of fire and explosion. They include explosives, fireworks, pyrotechnics, powders,
propellants and other unsteady chemicals. These materials store a high level of chemical
energy and are able to release it rapidly without external contribution of oxygen or any other
oxidizer. The behaviour of these materials in case of explosive detonations is relatively wellknown
from empirical and practical points of view. However, fundamental scientific questions
remain unanswered related to the mechanisms of heat release. The current understanding of
these mechanisms lacks appropriate thermochemical characterisation. The aim of the study is
the analysis of thermal and chemical characteristics of energetic materials under conditions
that exclude detonations. Detonation is excluded in order to better isolate the thermal and
chemical mechanisms involved in the burning process. The experimental work has been
conducted using the FM Global Fire Propagation Apparatus (FPA) [ASTM E2058‐03]. One of the
benefits of using this experimental apparatus rather than the Cone Calorimeter is that it allows
controlling the feed of heat and oxidizer to the reaction zone.
The material chosen to conduct experiments on is a ternary smoke powder based on a mixture
of starch and lactose as fuel components and potassium nitrate as oxidizer. This product is
currently used by fire brigades to assess smoke venting systems efficiency of buildings. The
kinetics associated with the combustion of the material was assessed slow enough to allow
measuring instruments to capture the thermal and chemical evolution during combustion
reaction. Thermal analysis has first been carried out by means of DSC, TGA, DTA, MS and FTIR
data in order to understand the decomposition of the material and its energetic evolution
when undergoing heating. However, if the latter methods help defining the decomposing path
of the material, they do not provide an integral view of its combustion behaviour, in particular,
the emissions of toxics which are kinetic path dependent. Subsequently, combustion tests
have been carried out using the FPA. Its ability to capture the evolution of gases emissions
formed during the reaction has been proved. The influence of two configuration parameters
on the combustion behaviour and on the gaseous emissions of the material has been
investigated. The proportion fuel/oxidizer has been varied as well as the composition of the
reacting atmosphere. Results shows that the quantity of oxidizer in the material affects the kinetics of the reactions taking place in the condense phase. Increasing the concentration of
potassium nitrate in the mixture enhanced the reaction rate of the smouldering combustion.
Higher quantity of volatiles is released which favoured the initiation of a diffusion flame
regime in the gaseous phase, above the sample. While the kinetics of the condense phase is
governed by the oxidizer concentration, experiments show that the flaming regime is
influenced by the concentration of oxygen (O2) in the reacting atmosphere. A transition from
diffusion to premixed flame is found when the concentration of O2 surrounding the sample is
reduced below 18%. An analytical model has been used to explain the existence of a transition
for a critical O2 concentration. Finally, thermal and combustion analyses have allowed to
characterise the behaviour of the material under critical conditions, in terms of decomposition
taking place in the condense phase but also potential toxic emissions that can be released.
Toxicity, kinetics, temperature evolution do not provide a complete view of the combustion
phenomenon. Beside these elements that characterise the behaviour of a material for given
conditions as well as also the degree of fire hazard encountered, the energetic issue holds as
an essential feature that cannot be neglected. The heat release rate (HRR) is a critical
parameter that defines a fire. It does not constitute an intrinsic material property but it
describes the energetic response of the couple formed by the material and its environment.
Oxygen Consumption calorimetry (OC) and Carbon Dioxide Generation calorimetry (CDG) are
widespread methods to calculate the HRR resulting from a combustion reaction. Apparatuses
such as the FPA or the cone calorimeter have already proved their potential to qualify the
burning behaviour of common fuels in addition to polymers when their data are combined
with an adapted calorimetric procedure.
The same approach has been applied to energetic materials. However, prior to using these
techniques, it is fundamental to have identified their restrictions. These techniques provide
approximate estimations of the HRR. Results are affected by the propagation of uncertainties.
Several sources of uncertainties can be found. One can cite:
1. Uncertainties associated with the sample material;
2. Uncertainties associated with the test conditions;
3. Uncertainties associated with the measurements;
4. Uncertainties associated with calculation assumptions.
If uncertainties cannot always be estimated, the three first sources cited have received
attention in the past from the scientific community, alike the last one. The restrictions
associated with the assumptions developed for using the OC and CDG principles have to be
clarified. The limits of validity of the hypotheses have to be clearly defined. In particular, the
present dissertation questions the relevance of the energy constants that have been specified
for OC and CDG as well as their related uncertainties. One of the purposes of the research
deals with the ability to estimate accurate error bars for the calculation of the HRR. Once
uncertainties related to the calorimetric methods are assessed, a method adapted from the
basic OC and CDG principles is introduced that allows estimating the HRR of energetic
materials. The approach is based on considering the chemical decomposition of the burning
compound and defining a fictitious molecule for which energy coefficients can be calculated.
Nevertheless, it requires the material to be known. Finally, the question of the advantage
brought by these techniques over others, in terms of accuracy, is discussed within the
framework of unconventional products, such as energetic materials or compounds whose
composition is ignored. The results from this work will contribute to the development of fireanalysis
methodologies and validate their use with energetic materials