Chemistry Reference
In-Depth Information
86.05
100
90
80
70
60
50
40
147.31
30
124.34
20
99.06
222.31
193.30
10
75.27
240.71
292.41
320.38
345.08
370.69
414.49
0
50
100
150
200
250
m/z
300
350
400
450
Figure 8.23
Mass spectrum for the peak at 15.9 min.
• Energy, as some means of ignition (e.g., heat), must be applied.
• he fuel and oxidiser must interact in a self-sustaining chain reaction.
8.4.1 Combustion
Combustion is an oxidative decomposition in which an oxidant (usually oxy-
gen) oxidises a fuel. Combustion is an exothermic (heat-releasing) reaction
in which the reactants are converted to products that are predominantly gas-
eous in nature. The product gases heat up and expand and, during a fire, this
expansion generates plumes with predictable behaviours that leave distinc-
tive markings at the scene of the fire. These markings are typically referred
to as postfire indicators and will be used to help a fire investigator establish
what may have happened.
Fire is essentially a chemical reaction producing physical effects. It is
important to understand what a chemical reaction is and how it is involved
in a fire since there are many chemical reactions taking place at the same
time. The main reactions that take place during a fire are known as oxidative
reactions. These reactions occurring during a fire are the atoms in the fuel
being oxidised by the oxygen in the air.
Most of the important fuels involved in structure (buildings) and forest
fires are organic compounds. Organic compounds are many and varied but
will always contain carbon (C) and hydrogen (H) and sometimes oxygen (O),
nitrogen (N), sulphur (S) and phosphorus (P). The most basic of the organic
compounds are hydrocarbon compounds and are composed solely of carbon
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