Fire and explosion hazards
Fires and explosions are reactions or conversions of solids, liquids or gases involving a high release of energy and they are triggered by an ignition or by self-ignition of the substance system. The result is a rapid rise in temperature.
In the case of fires under atmospheric conditions, an ignition is followed by oxidation with (atmospheric) oxygen of combustible substances with the formation of flames or smouldering.
Fires can also take place under non-atmospheric conditions with another oxidation source than oxygen. These processes play more of a secondary role in the context of fire protection and can be considered as being the consequence of oxidative self-ignition, thermal decomposition and other exothermic chemical reactions – as described in chapter 3.4 Other health hazards – chemical reactions.
The preconditions for the onset of explosions include, among others, the presence of:
- explosive atmospheres (that means substance-(atmospheric)oxygen mixtures in concentrations within certain explosion limits,
- explosive substance mixtures (systems) or
- explosive substances and
- the triggering of processes in the substance system.
Alongside the rapid rise in temperature, there also occurs a major pressure increase with explosions: with a deflagration at subsonic speed and a detonation at supersonic speed with the build-up of a blast wave.
With the exception of physical explosions, a strongly exothermic chemical reaction takes place in explosions. If this reaction is oxidation within the combustible substance-(atmospheric) oxygen mixture under atmospheric pressure-temperature conditions, one speaks of an atmospheric explosion. In the case of physical explosions, on the other hand, an extremely strong heat transfer for the mixture of fragments of hot and colds liquids leads to the formation of vapour and the build-up of pressure.
You will find a comparison between chemical and physical explosions in Table 5-1.
A fire can act as an ignition source in triggering an explosion. In reverse an explosion can set light to combustible substances which are, however, not an explosive substance system, and hence lead to the subsequent fire.
In this chapter a description is given of hazards due to
- atmospheric fires, see chapter 5.1 Combustible solids, liquids, gases,
- atmospheric explosions (explosions caused by ignition due to an explosive atmosphere), see chapter 5.2 Explosive atmosphere,
- explosive substances and pyrotechnic objects, see chapter 5.3 Explosive substances and
- physical explosions, see chapter 5.4 Physical explosions.
Hazards due to non-atmospheric fires and explosions as a result of exothermic chemical reactions, i.e. without atmospheric) oxygen, are not dealt with in this chapter, however. These reactions can in general only lead to a fire or explosion if this takes place in an uncontrolled form or without the adequate extraction of head and gas. In chapter 3.4 Other health hazards – chemical reactions an explanation is given as to how undesirable chemical reactions can be avoided and other exothermic chemical reactions can proceed in a controlled fashion.
Further information is only available in German.