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'New' ATEX advice: still confused by the 'new' ATEX directives of 2006? David Almond, head of sales and marketing at Pressure Vacuum Level Ltd offers some advice.

Suppliers of components for industrial systems frequently get telephone calls from customers who are having difficulty interpreting the rules laid down by the ATEX 95 equipment directive 94/9/EC and the ATEX 137 workplace directive 99/92/EC, both of July 2006, stipulating stringent requirements for the electrical and mechanical components of instruments used in hazardous areas, where even the slightest spark could cause a devastating explosion. This not particularly surprising, since the ATEX Directives could be described, in a context less sensitive about the use of language, as a minefield.

Is ATEX changing the engineering world?

The key point about the influence of ATEX regulations on engineering practice that many people fail to realise is that, although ATEX regulations have not themselves changed since the summer of 2006, the detail of definitions within the Directive are constantly changing as new research into potential causes of explosions reveals new risks.

It is important to understand that the ATEX Directive (94/9/EC), defines an explosive atmosphere as 'a mixture with air, under atmospheric conditions, of flammable substances in the form of gases, vapours, mists or dusts, which, after ignition has occurred, combustion spreads to the entire unburned mixture.

The Directive only applies where there is equipment which introduces energy into the hazardous area, such as electrical equipment, which introduces electrical energy, or mechanisms introducing mechanical energy. It is not intended to apply to locations where there is no equipment. Therefore, the interior of storage tanks or vessels would not be covered unless there was equipment present.

Equipment and protective systems used outside the hazardous area, but which contribute to the safety of the hazardous area, are covered. This provision includes barriers for intrinsically safe circuits, explosion suppression control systems and inerting or decoupling systems.

The Directive uses the concept of three zones based on the period of time that a flammable atmosphere is present:

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Zone 0 means that flammable gas is present continuously, or for long periods of time (often quantified as >1000hrs/yr);

Zone 1 means that flammable gas is likely to occur during normal operation (often quantified as between >10 and <1000hrs/yr);

Zone 2 means that flammable gas is not likely to occur in normal operation and, if it occurs, will exist for only a short time (often quantified as <10hrs/yr).

Similar definitions for dust are referred to as Zones 20, 21 and 22.

Although the Directive has not changed, the standards are in a state of flux with many modifications recently completed or underway. The latest to be affected by changes is the standard for zone 2 equipment (EN60079-15) which has been modified recently at IEC level to make ATEX more consistent across zones.

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These IEC changes will carry forward directly into the EN version when it is published. Specific clauses which are relevant for zone 0 or 1 have been removed from IEC60079-15 and placed in the corresponding zone 0/1 standards. This has the effect of making compliance for zone 2 potentially harder.

For example the technique of energy limitation (Ex nL)--where the maximum temperature and energy in a spark are limited--is no longer allowed in IEC60079-15, and equipment for all zones must use a potentially more restrictive intrinsic safety approach (Ex ic) using IEC60079-11.

With the changes in this standard applying to the lowest categories--and therefore the largest number of ATEX products--engineers designing systems for hazardous or potentially hazardous environments should review the specifications of the products they specify to make sure that they meet the new requirements.

But, of course, there is a lot more to it than that.

The ATEX 137 directive 99/92/EC is the key set of rules for defining which electrical components or instruments are appropriate to specific hazardous areas. It details the requirements that suppliers and manufacturers of such products must meet if they are to achieve the ATEX accreditation that they need.

Enforcement of these standards in the UK is the responsibility of the Department of Trade and Industry and of the Health and Safety Executive. The table that forms part of this article sets out how ATEX product marking is derived and how it should be interpreted.

Note that the temperature class for a component or instrument does not represent the operating temperature of the component but the maximum permissible surface temperature of the material making up the component, which has to remain below the corresponding ignition temperature when operating normally.

Gases and vapours are sub-divided into temperature classes depending on their ignition temperature, with increasing specifications from T1 to T6:

T1 < 450[degrees]C T2 < 300[degrees]C T3 < 200[degrees]C T4 <135[degrees]C T5 < 100[degrees]C T6 < 85[degrees]C

So what types of products are available in ATEX-approved form?

Virtually any class of switch used in fluid processing--whether gases or liquids--in the process industries, in mining, in the manufacture of powders, or in the industrial woodworking and furniture industries, will be needed by some or all industries in an ATEX-approved form. Explosions can happen where wood dust is extracted from furniture factories, where sugar is pneumatically conveyed, cocoa powder is manufactured or wheat flour is packed. ATEX is not only about petrochemical and gas processing.

So all sorts of industries need ATEX pressure or vacuum switches, flow switches, level switches, proximity switches and other process controls.

In the area of mechanical engineering, manufacturers need couplings, clutches, brakes and friction devices which cannot create sparks so cannot cause explosions. In mining, extraction machinery has to be incapable of causing explosions, as do transportation equipment, both for workers and mined ore. The fact is, ATEX is just about everywhere in industry.

Where can you get advice?

No one organisation can advise upon and supply every kind of equipment that is required in ATEX form and a little internet research can provide a range of sources, whatever your needs. Whoever you approach, be sure that you are being advised by qualified engineers who are accustomed to explaining the ATEX requirements and identifying products that meet both the ATEX rules and your particular needs. You need engineers, not just salesmen, to provide workable solutions.

For further information please visit: www.pvl.co.uk
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Title Annotation:Health & Safety: Focus on: ATEX
Author:Almond, David
Publication:Plant & Works Engineering
Date:Aug 1, 2011
Words:1038
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