An atmosphere is explosive when the proportion of gas, vapor or dust in the air is such that a spark from an electrical circuit or the heating of an appliance causes an explosion. What conditions must be met for an explosion to occur? To produce an explosion, three elements are needed:
Fuel + Air Oxygen + Spark = Explosion
Since the oxygen in the air is always present, the two other elements need to be brought together to produce an explosion. A spark or flame is not always necessary for an explosion to occur. An equipment can, by increasing the temperature on its surface, reach the flash point of the gas and cause the explosion.
What types of products can produce an explosion?
Risk products are classified into 4 groups: I, IIA, IIB and IIC.
These products are generally:
• Heating gas.
• Solvent for glue and adhesives.
• Solvent and thinners for paints.
• Varnish and resins.
• Additives manufacturing pharmaceutical products, dyes, artificial flavors and perfumes.
• Plastic materials, rubber, artificial fabrics and cleaning chemicals.
• Elements for the treatment and manufacture of alcohols and derivatives.
Where can an explosive atmosphere form?
All locations where the above-mentioned products are manufactured, stored and processed are pre-arranged to contain an explosive atmosphere and are subject to regulation of areas at risk of explosion.
What is a risk zone?
International regulations distinguish the following categories of hazardous areas: zone “O”, zone “1” and zone “2”. These areas are geographical, but the boundaries between each of them are never defined. An area can move for several reasons: heating products, ventilation failure in place and (or) handling error.
The explosive atmosphere is always present – Zone “O”.
Zone where an explosive mixture of gas, steam or dust is permanently present (the gaseous state within a container or reservoir constitutes an “O” zone).
The explosive atmosphere is often present – Zone “1”.
Zone where an explosive mixture of gas, vapors and dust may eventually form in normal installation service.
The explosive atmosphere may be accidentally present – Zone “2”.
Zone where an explosive mixture may only appear in case of abnormal operation of the installation (loss or negligent use).
Equipment for use in Hazardous Areas must be ATEX certified compatible with the requirements of the areas of use.