Test & measurement
Explosion protEction in prEssurE mEasurEmEnt tEchnology
ThE EffEcTs of ExpLosions On 21 September 2001, 300 tonnes of artificial fertiliser exploded at a factory belonging to the company TotalFinaElf. Twenty two employees and seven residents died in the explosion, and 2,500 people were injured. As has been the case in previous industrial disasters, the risks were known about beforehand and yet the precise causes remained unclear after the accident. On 8 June 1999, there was an explosion and
then a fire at the factory premises of Bayer AG in Wuppertal. This disaster led to over 100 injuries and damages payouts in the millions, as well as leaving behind a landscape of rubble around the boiler house. Luckily, no lives were lost in the accident but the chemicals and soot released caused long-term breathing difficulties, headaches, nausea and eye and skin irritation in countless people.
WhAT cAusEs ExpLosions? An explosion is a sudden chemical reaction involving an inflammable substance in the form of gas, dust, vapour or mist combining with oxygen and releasing large amounts of energy. This leads to an explosive atmosphere if the mixture achieves a very specific concentration ratio. If the concentration is too high (rich mixture) or too low (lean mixture), then a steady combustion reaction will occur, but no explosion. The mixture will only behave explosively on ignition if it is between the upper and lower explosive limit. The environmental pressure and the proportion of oxygen in the air influence the limits of the explosive atmosphere.
pRoTEcTion fRom iGniTion As much as a century ago, the necessity and importance of all-encompassing provisions for explosion protection had been demonstrated by the many devastating accidents of the past. It was
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then that the first national regulations and laws were enacted, and these remained in force until 1994. Since 1994, explosion protection has been regulated in European Directives:
ATEX 95 or 94/9/EC (Equipment Directive)
ATEX 137 or 1999/92/EC (Workplace Directive) Businesses operating in potentially explosive
environments are required to ensure that at least two measures are in place to prevent explosions. The primary measure requires the operating company to prevent an explosive atmosphere from coming about to begin with. The concentration ratio can be changed and rendered non-hazardous using the following measures:
replacing inflammable substances with non- hazardous alternatives.
adding nitrogen, carbon dioxide, etc., which neutralises inflammable substances.
using natural or mechanical ventilation so as to limit the concentration.
If it is not possible to create an explosion-proof
environment, then as a secondary measure the risk potential needs to be divided into three danger zones according to the probability of a source of ignition occurring. These three zones state whether an explosive atmosphere could occur at all times, intermittently or for brief moments. This way, devices designed to be used in these zones can be chosen accordingly.
ExpLosion-pRoof pRoDucTs Products used in a potentially explosive environment need to be designed to offer the
November 2021 Instrumentation Monthly
Explosions can be violent and tend to leave behind a great deal of damage. With this in mind, the ultimate aim when building electronic devices for use in potentially explosive environments is to completely prevent explosions. KELLER AG für Druckmesstechnik has been producing products for use in explosive environments since 1988. These certified products ensure safe operation in the most diverse range of use cases.
protection necessary for the class of hazard present. Explosion-proof products are subject to various directives and standards such that the necessary protection is ensured at all times. There are different licensing bodies and sets of standards depending on geographical location. Explosion-proof products for the European
market are tested and certified according to the European Directive 2014/34/ EU (which supersedes the original Directive 94/9/EC). All products for this market must be designed according to the EN 60079 set of standards. These standards cover areas at risk of gas and dust explosions, and classify the products according to types of ignition. These define how operating equipment needs to be built so that it cannot trigger any kind of ignition in a potentially explosive environment.
inTRinsicALLy sAfE pREssuRE mEAsuREmEnT TEchnoLoGy by KELLER In addition to type d (flameproof enclosure) and type ec (increased safety) ignition protection products, KELLER AG für Druckmesstechnik mainly produces pressure transmitters, level probes and digital gauges of the ignition protection type i (intrinsic safety). Products certified to be intrinsically safe limit the energy so that ignition of an explosive atmosphere cannot be triggered either by sparks or thermal effects. KELLER is an international company and as such
is not only limited to the European market. For this reason, the manufacturer of pressure measurement technology offers a wide range of
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