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Basics of Hazardous Areas

The risk of explosion

In petroleum, chemical but also food industries, many dangerous substances such as gases, fumes, liquids, powders or dusts are used or released during the manufacture, processing or storage of everyday products such as gas, hydrocarbons, plastics, varnishes, paints , medicines, powders, cereals, cosmetics, adhesives …

Conditions for an explosion to occur

An explosion can occur when three elements are present :

When these flammable substances are mixed with oxygen from the ambient air in certain proportions, just a source of ignition to cause an explosion. The ignition source can be: an open flame, spark or electrical mechanical, static electricity, or even a simple hot surface.

To avoid explosions while using electric power, it is essential to use ATEX electrical appliances that have been specifically designed to ensure the safety of such hazardous environments.

Flammable Materials

The classification of flammable materials includes several key characteristics including:
Relative Density: This is the density of the gas, vapour or dust relative to the density of air.
Flash Point: This is the minimum temperature at which a vapour, air mixture forms over the surface of the liquid, that can be ignited by a seperate source.
Flammable Limit: This is the upper and lower explosive limits at which a substance will ignite (mixture percentage of gas / dust to air), i.e. methane LEL 4.4%, UEL 17%.

Minimum Ignition Energy (MIE)

This is the lowest energy which is suffi cient to effect ignition of the most easily ignitable explosive atmosphere under specified test conditions.

Sources of Ignition

There are many sources of ignition which can cause an
explosion these include:

  • hot surfaces
  • flames and hot gases
  • mechanically generated sparks
  • electrical installations
  • electrical equalizing currents, cathodic corrosion protection
  • static electricity
  • lightning
  • electromagnetic waves (high frequency)
  • optical radiation
  • ionizing radiation
  • ultrasound
  • adiabatic compression and shock waves
  • exothermic reactions

Hazardous Substances

They are separated into two main categories: gases, vapors and flammable liquids on the one hand, the dust layers or other clouds part.

The table below provides a non-exhaustive overview of the most common substances: