TECHNICAL INFORMATION

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Type of Signs

Section

Regulations & Information on Explosion-Protection

 Definitions “as per the NEC”:

 Explosion Proof Apparatus:

Apparatus enclosed in a case that is capable of withstanding an explosion of a specified gas or vapor that may occur within it and of preventing the ignition of a specified gas of vapor surrounding the enclosure by sparks, flashes or explosion of the gas or vapor within, and that operates at such an external temperature that a surrounding flammable atmosphere will not be ignited thereby.

 Applications:

In manufacturing plants, refineries, chemical, petrochemical and other industrial process facilities, waste or sewage treatment facilities, offshore, dockside and harbor installations and other heavy industrial applications.

 Zone 0 covers areas in which an explosive atmosphere caused by a mixture of air and gases, vapours or mists is present continuously, for long periods or frequently. Zone 0 mainly encompasses the areas inside closed containers, pipelines and apparatus that contain inflammable liquids. The respective operating temperature lies above the flash point. The hazardous area is above the liquid level and not within the liquid.

With apparatus in the category 1 G (for Zone 0), in order to avoid ignition hazards resulting from electrical circuits of the apparatus, it is necessary to guarantee the specified degree of safety:

·                      in the event of two independent faults when only one protection measure is applied, or

·                      in the event of the failure one protection measure, by means of a second, independent protective measure.

These conditions are deemed fulfilled if, for example, the apparatus:

·                      is designed in the type of protection “ia” to EN 50020, or

·                      intrinsically safe apparatus  to “ib” is also potted according to EN 50028.

The requirements on apparatus with regard to electrostatic charges are considerably higher than those for Zone 1 or Zone 2.

Zone 1 covers areas in which the occasional occurrence of an explosive atmosphere due to the presence of gases, vapours or mists is likely.

Inflammable or explosive substances are made, processed or stored in Zone 1. This includes the area surrounding charging doors, the immediate vicinity of filling and emptying devices, the immediate vicinity of fragile equipment and lines, as well as around cable glands on pumps and slides that do not seal adequately. The occurrence of an explosive atmosphere is likely during normal operation.

With apparatus of the category 2 G (for Zone 1), it is either necessary to ensure that the occurrence of an ignition source is excluded, or the ignition source must be encapsulated by a recognized type of protection in such a way that the ignition of an explosive atmosphere surrounding the apparatus is prevented. This applies in Zone 1 for both normal, trouble-free operation and for the operating faults that commonly occur. The constructional and test regulations for the permissible types of protection are laid down in EN 50014 ff. The table on page 0/6 is a comparison of these types of protection for Zone 1 apparatus.

Zone 2 covers areas in which the occurrence of an explosive atmosphere due to the presence of gases, vapours and mists is not likely, but if one should occur, then only rarely and only for a short period.

Zone 2 encompasses areas around Zones 0 and 1 and areas around flanged joints of pipelines in closed rooms. Furthermore, it includes areas in which, due to natural or forced ventilation, the lower explosion limit is reached in exceptional cases only, e.g. the surroundings of outdoor installations.

Inflammable or potentially explosive materials are made and stored in Zone 2. In such a way that the probability of the occurrence of an explosive atmosphere is rare, and then only for a short time.

Zone 20 covers areas in which an explosive atmosphere due to dust/air mixtures is present continuously, for long periods or frequently.

If these conditions occur, they are usually found in closed containers, pipelines, apparatus, etc.

Zone 21 covers areas in which the occurrence of an explosive atmosphere due to dust/air mixtures is to be expected occasionally.

This can, for example, include areas in the immediate vicinity of dust extraction or filling stations and areas where dust deposits can occur and can form a potentially explosive concentration of inflammable dust mixed with air under normal operating conditions.

Zone 22 covers areas in which the occurrence of an explosive atmosphere due to whirled-up dust is not likely, but, if it occurs, then in all probability only rarely and only for a short period.