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Air jacket and spark trap

Air at pressure above atmospheric can prevent ignition hazards for electrical equipment operated in potentially explosive atmosphere

19.05.2000

[es]Are the safety precautions in explosion hazardous areas severe enough? This question, which has been on everyone's lips since the Enschede accident, constantly occupies the minds of the experts at the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig - but not in connection with solid matter as in the Dutch fireworks factory. PTB is involved when easily ignitable liquids or gases are concerned. It checks, among other things, whether electrical equipment meets the strict explosion protection requirements before it is marketed. One of the types of protection that may be applied is the so-called pressurization. The aspects which must be taken into account when this type of protection is submitted to a test are currently explained by PTB at the ACHEMA, the international fair for chemical technology, environmental protection and biotechnology held in Frankfurt/Main.

Dangerous neighbourhood: electrical equipment in a room or area in which flammable gases may occur. There is only one thing one can do: The ignition source (spark or hot components) must be separated from the gas source - by an air buffer, for example. In the case of the pressurization type of protection, this is achieved in a simple way: The equipment is rinsed with air and pressurized so that no explosive ambient air can penetrate. The so-called gauge pressure must be constantly controlled. It is the PTB's task to check whether this mechanism functions properly.

PTB thus renders a service to the manufacturers who, under European regulations, are bound to prove that the severe explosion protection regulations are observed by them. And yet another service: The PTB certifies that the manufacturers have taken explosion protection into account in production and in their quality management systems. In both cases a certificate is issued to the manufacturers.

Whoever wants to obtain more detailed information about the PTB's test work can contact its experts at the ACHEMA in Frankfurt/Main between May 21 and 27, 2000 (Hall 9.1, Stand K21/22, telephone at the fair: ++49 (0)69 7 44 12 55).

Additional information can be obtained from:
Dr. U. Johannsmeyer, tel. ++49 (0)531-592-3420; e-mail:ulrich.johannsmeyer(at)ptb.de
W. Ellwardt, tel. ++49 (0)592-3523; e-mail: wolfgang.ellwardt(at)ptb.de
Intrinsic Safety and Safety of Systems section,
Physikalisch-Technische Bundesanstalt (PTB)