TECHNICAL DEVELOPMENT OF EXPLOSION PROTECTION
In the 19th century, electrical equipment was introduced into industry and households. Immediately afterwards, the occurrence of methane and coal dust in hard coal mining prompted the development of the basics of electrical explosion protection. The advantages of electricity were so convincing that intensive work was carried out to find a way to reliably prevent contact between an explosive atmosphere and ignition sources - originating from the use of electrical equipment - and thus prevent explosions.
These days, the construction of explosion proof equipment goes far beyond the field of electrical engineering. As will be demonstrated in the further descriptions, non-electrical equipment will also require testing or at least assessment. Here the knowledge gained by manufacturers over the decades on the explosion proof electrical equipment is particularly important and it now also benefits the manufacturers of non-electrical equipment.
Internationally, the standpoints on the explosion protection of electrical and non-electrical equipment are co-ordinated by specialized IEC and ISO working groups. In the area of electrical engineering, internationally harmonized design agreements were formulated in IEC standards at a very early stage. For the most part, this was done in conformance with the CENELEC standards. A visible sign of the harmonisation is that the relevant IEC/ISO (global), EN (Europe) documents on standards agree in content and in the registration number (60079 series). Harmonization is being worked on intensively at present. This reorganization involves continuous amendments but will also make future international work easier. ISO/IEC working groups work in an identical way and use (80079 series) for application to non-electrical equipment.
Under the IECEx System, Ex equipment is developed, tested and certified with a Certificate of Conformity (IECEx CoC) in accordance with the internationally uniform requirements (IEC/ISO standards) and is in the meantime applicable to Ex equipment assemblies consisting of electrical and non-electrical equipment too.
Explosion
Explosions are suddenly, with huge speed, occurring oxide reactions which generate a temperature and pressure increasement. Most well-known are reactions of flammable gases, vapours or dusts together with oxygen out of the air.
Basis for an explosion
As a rule, for explosions to happen in atmospheric air, three factors have to be present at the same time (see Figure 2):
- flammable substance
- oxygen (air)
- source of ignition
In production and work places, hazardous areas can develop wherever the first two preconditions for an explosion are fulfilled. Typical hazardous areas form in chemical factories, refineries, enamelling plants, paint workshops, cleaning equipment, mills and stores for milled products and other combustible dusts, in tank facilities and loading areas for flammable gases, liquids and solids.
The first two preconditions - the flammable material and air - must be present in justified quantities between LFL and UFL (Lower Flammable Limit and Upper Flammable Limit) to form an explosive atmosphere. The statutory definitions of explosion protection - derived from the health and safety at work regulations - are in relation to workplaces. For this reason, explosion protection is generally limited to description of reactions with oxygen in the air. Oxidation reactions normally involve increasements in heat and pressure and therefore fulfil the criteria of an explosion.
