Definition of explosion risks in Hazardous Areas
In the chemical, oil and food industries, many dangerous substances in the form of gas, fumes, liquids, powders or dust are used or released during the manufacture, processing or storage of common products such as: gas, hydrocarbons, plastics, varnishes, paints, drugs, powders, cereals, cosmetics, glues …
Conditions for an explosion to occur
An explosion can occur when 3 elements come together:
When these flammable substances are mixed with the oxygen in the ambient air in certain proportions, all it takes is an ignition source to trigger an explosion. This ignition source can be: an open flame, a mechanical or electrical spark, static electricity, or even a simple hot surface.
To avoid explosions while using electrical energy, it is therefore essential to use ATEX electrical devices which have been specially designed to ensure the safety of this type of hazardous environment.
The classification of flammable materials includes several key characteristics, including:
• Relative density: This is the density of gas, vapor or dust relative to the density of air.
• Flash point: This is the minimum temperature at which a vapor forms an air mixture on the surface of the liquid, which can be ignited by an independent source.
• Flammability limit: These are the upper and lower explosion limits at which a substance ignites (percentage of gas / dust mixture in air), namely methane LEL 4.4%, UEL 17% .
Minimum Ignition Energy (MIE)
This is the lowest energy required to initiate ignition of the most easily flammable explosive atmosphere under specified test conditions.
Source of ignition
There are many sources of ignition that can cause
- hot surfaces
- flames and hot gases
- mechanically generated sparks
- electrical installations
- of the compensation electric current
- static electricity
- electromagnetic waves (high frequency)
- cathodic protection against corrosion
- static electricity
- optical radiation
- shock waves
- exothermic reactions …
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