Hazardous locations were discovered in the early coal mines, where there was a double hazard (gas and dust). The first method of protection in this mining industry was to ventilate the mines with fresh air to keep the explosive gas below lower explosion limits (LEL). First this was arranged by furnaces and later by steam driven ventilation systems.
When will an explosion occur?
As a rule, three basic requirements must be met for an explosion to take place in atmospheric air. The following three elements must exist simultaneously:
- Explosive material: this can be a gas, vapour or dust in sufficient quantities.
- Source of ignition: can be any source of energy, e.g. a heat source or spark etc. (a spark or high temperature)
- Oxygen: usually present
The basic principle for explosion proof protection is to eliminate one or more legs of the explosion triangle.
In the case of gases, the ratio of concentration determines whether an explosion is possible. The mixture can only be ignited if the concentration of the material in air is within the lower (LEL) and upper explosive limits (UEL).
Examples of ignition sources which can cause an explosion under the right circumstances are:
- Short circuit, switching operations;
- Mechanically created sparks, e.g. caused by friction, impact etc;
- Hot surfaces, for example a heater or metal cutting;
- Electrostatic sparks;
- And much more…
Basically we can divide these sparks into 3 groups:
- Hot surfaces;
- Electrical sparks;
- Friction and impact sparks (mechanical).
To ‘protect’ these ignition sources and to avoid them becoming effective, we have various protection methods (standards) which we can use. These have been laid down in the EN IEC 60079 standard range.
- Flameproof enclosures, Ex d in compliance with EN IEC 60079-1;
- Increased safety, Ex e in compliance with EN IEC 60079-7;
- Pressurisation, Ex px in compliance with;
- EN IEC 60079-2;
- Intrinsically safe, Ex ia in compliance with EN IEC 60079-11.
Besides electrical equipment being a possible ignition source for hazardous areas, we can also have non-electrical, mechanical ignition sources. For example: brake units, gear boxes, fans etc. Anywhere we are dealing with moving parts, we can have potential ignition sources. For these applications, there are standards to show conformity with the ATEX.
The IECEx Scheme facilitates the international exchange and acceptance of product safety test results among participating laboratories for national approval or certification in one or more countries, normally without the need for additional testing. This is a universal goal among suppliers, consumers, and interested parties stated as “one standard, one test, accepted everywhere.”
The objective of the IECEx Scheme is to facilitate international trade in electrical equipment intended for use in explosive atmospheres.
The ultimate goal of the IECEx Scheme is to remove any trade barriers between countries and have a single unifed stamp, single test procedure and reciprocal agreements among countries and test labs for implementation.
- IECEx 01: Basic Rules
- IECEx 02: Certi ed Equipment Scheme covering equipment for use in explosive atmospheres – Rules of Procedure
- IECEx 03: Certi ed Service Facilities Scheme covering repair and overhaul of Ex equipment – Rules of Procedure
- IECEx 04: Conformity Mark Licensing System – Regulations
- IECEx 05: Scheme for Certi cation of Personnel Competencies for Explosive Atmospheres
Labeling for Explosion Proof Equipment
All the explosion proof equipment and protective systems must be marked legibly and indelibly with the following minimum information as shown on the following label with additional explanation.
- Name and address of the manufacturer
- CE Mark
- Designation of series of type
- Serial number
- Year of construction
- The ATEX Ex mark