Explosions – what causes them?


As a rule, for an explosion to happen, three factors must be present at the same time:

  • Flammable substance
  • Oxygen (air)
  • Source of ignition

 

Flammable substances

Flammable gas - may be an element such as hydrogen which can be made to react with oxygen with very little additional energy. Flammable gases are often compounds of carbon and hydrogen. These flammable gases and vapours require only small amounts of energy to react with atmospheric oxygen.

Flammable liquids – are often hydrocarbon compounds such as ether, acetone or petroleum spirit. Even at room temperature, sufficient quantities of these can change into the vapour phase so that an explosive atmosphere forms near their surface.

Flammable solids – in the form of dust or flyings can react with atmospheric oxygen and produce disastrous explosions.

Oxygen

When the quantity of the flammable material and the available atmospheric oxygen are near to the correct ratio, the effect of the explosion – temperature and pressure increase – is most violent.

Sources of ignition

  • Hot surfaces
  • Flames and hot gases
  • Mechanically generated sparks
  • Electrical apparatus
  • Lightning
  • Radio frequency (RF electromagnetic waves

 

Take note

  • An explosion is defined as a sudden reaction involving a rapid physical or chemical oxidation reaction or decay generating an increase in temperature or pressure or both simultaneously.
  • In production and workplaces, hazardous areas can develop wherever there are flammable substances and oxygen present – not an uncommon situation.
  • Flameproof equipment prevents ignition sources or the coming together of such sources with potentially explosive atmospheres thus effectively preventing explosions.

 

Published as: Explosion protection: Parts 1 and 2,  By H Kühl, BARTEC

Electricity+Control, December 2011 (pgs 28 – 31) and March 2012 (pgs 44 – 46)