Unwanted ignitions are older than mankind. Atmospheric discharges – lightning – triggered fires long before humans walked the earth. In 1753 the first lightning conductor was invented, enabling electrostatic discharges as the sources of ignition for fires to be significantly reduced. Lamps in mining also constituted another high fire risk for many years, because mine air mixed with methane – so-called firedamp – was able to cause explosions when sufficiently strong ignition sources were present. In 1815 Sir Humphry Davy introduced the first mine safety lamp, a non-electrical item of equipment for mining. Two wire glass screens arranged on top of each other separated the flame - which was to be kept as small as possible inside the screen - from the flammable mixture present, while allowing combustion inside the screen. When used correctly, the screens prevented an external ignition.
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.
After bitter experiences in the beginning, the occurrence of firedamp explosions was greatly reduced and well-monitored electrical equipment was utilised with very high safety standards.
Today, fortunately, the number of accidents caused by electrical ignition sources is low. The expenditure on development and manufacturing and the statutory regulations have proven to be successful and the frequently posed question as to “whether such expenditures are justified“ must be answered with yes. Any neglection is comparable to culpable carelessness. Unfortunately there are still numerous examples of explosions that demonstrate the devastating effects on humans, environment and plants.
Priority is given to what is regarded as primary explosion protection, for example the focussing of attention on the use of non-flammable substances that are not capable of forming an explosive atmosphere.
However, it is not always possible to exclude flammable substances such as methane or coal dust in mines, or petrol and in future perhaps hydrogen in vehicles. In such cases protection and safety are provided by equipment which is reliably explosion proof. Such solution, by providing type(s) of protection is referred to as secondary explosion protection.
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.
There are many applications which require explosion proof equipment. During the over 100 years of electrical explosion protection, principles and techniques have been developed which allow the use of electrical measuring technology, even where, for example in reaction vessels, an explosive atmosphere is permanently present.
The applications in the mining area were the beginning. The utilisation and processing of mineral oil and natural gas offer a wide scope for using explosion proof equipment. Organic chemistry, the paint industry and the pharmaceutical industry all process flammable liquids and gases. Because of the production and utilisation of biogas and the ecological utilisation of waste dumps, new applications are constantly developing. The utilisation of hydrogen is being discussed in depth, practised in experimental installations and will be in our lives as renewable energy.