What is explosive atmosphere?

According to the new directives, dust is now considered an explosive atmosphere
An explosive atmosphere is an atmosphere that develops explosively because an uncontrolable combustion  Explosive atmosphere consists of air and some sort of combustible material such as gas, vapours, mists or dust in which the explosion spreads after ignition  Typical exam- ples of productions where combustible dust is of major concern, is the handling of cereals, animal feed, paper, wood, chemicals, plastics and coal
Examples of sources of ignition that can cause the atmosphere to explode:

• Electrical sparks
• Flames
• Hot surfaces/ spots
• Static electricity
• Electromagnetic radiation
• Chemical reaction
• Mechanical forces
• Mechanical friction
• Compression ignition
• Acoustic energy
• Ionising radiation

An explosion is an uncontrolled combustion wave that produces a rapid increase in temperature and pressure  For an explosion to take place, three elements have to be present at the same time: fuel, (such as explosive gas) an oxidiser, (such as the oxygen in the air) and a source of ignition, (such as electrical sparks)  The combination of these three elements is generally referred to as the Fire Triangle 

To generate a potentially explosive atmosphere, the mixture of fuel and oxidiser has to have a cer- tain concentration  This concentration depends on the ambient pressure and the content of oxygen in the air, and is referred to as the explosion limits  Outside these limits, the mixture of fuel and oxi- diser will not ignite, but has the potential to do so if the proportions change  For an explosive atmosphere to form, a certain concentration of combustible material must be present