Explosion Protection Basic Guidelines to achieve reliable Explosion Protection

Author / Editor: Ulrich Stolz / Marcel Dröttboom

Apart from using approved system components, operators have to fulfill a number of obligations to meet the strict requirements of today's explosion protection directives. If this is not sufficient, there is a number of constructive measures available to reach this goal.

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Fig. 1: There is a number of contructive measures avilable for de-dusting systems to meet the safety requirements.
Fig. 1: There is a number of contructive measures avilable for de-dusting systems to meet the safety requirements.
(Picture: Keller Lufttechnik)

An explosion risk exists not only at the treatment of chemicals, varnish or oil. But also dusts are able to explode. The Atex-guidelines 94/9/EC (Atex95) and 99/92/EC (Atex137) prescribe Europe-wide standard requirements for safety at work and unit safety in such a surrounding. Via the German VDI 2263-6, requirements at the fire prevention and explosion protection at de-dusting systems are specified.

General Guidelines

Guideline 99/92/EC deals with the operator's explosion protection and imposes the employer the following obligations:

  • Identification of the explosion based on the technological dust characteristics (ignition point, glow temperature, minimum ignition energy, self-ignition behaviour, electrostatical behaviour, etc.).
  • Division of the company into Ex-zones according to the explosion risk. Marking of the zones of explosion risk.
  • Determination of protection measures.
  • Operating instruction for employees.
  • Creation of an explosion protection document which contains all acquired data and accomplished measurements.

The manufacturer guideline affects all devices, protective systems and components which are located in an explosive atmosphere. Besides, non-electrical devices with an own source of ignition also belong to this guideline.

Gallery

The guideline comprises safety, control and regulation devices which are positioned outside the danger area if they are necessary regarding the explosion risk and the safe operation of devices and protective systems.

The manufacturer has the following obligations with the Atex 95:

  • Performance of a hazard analysis for the product.
  • Determination of the conventional utilization and the service conditions.

Changes by the VDI 2263-6

The VDI 2263-6 'Ignition and explosion protection at dedusting systems' was published in September 2007. Some aspects of explosion protection at de-dusting systems which often lead to insecurities and different interpretations are now more precisely.

This includes, for example, the division into different areas within the crude gas piping and within the clean gas zone of filtering separators, the definition of hybrid mixtures and protective measures that result from this definition, as well as the geometric design of filtering separators regarding the optimal ignition and explosion protection.

Practical Experience

Based on characteristics given by the operator and the division into zones, a hazard analysis has to be conducted and corresponding protective measures for each dedusting system have to be taken. The basis for each explosion protection concept is the avoidance of ignition sources within the de-dusting system. This includes the following measures:

  • Grounding of conductive components which are located in zones.
  • Conductive filter material for extremely explosive dusts (minimum ignition energy < 10 mJ).
  • Utilization of ATEX-approved devices (solenoid valves, motors, etc.) according to the zone division.

Important for the determination of further protective measures is the evaluation if there exists the danger of collection and extraction of effective ignition sources. The operator has to...

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