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Understanding the 'X-Factor'

01 October 2008

Ever wondered about the significance of the ‘X’ at the end of a hazardous area certificate number? Graham Doran offers some enlightenment but warns that there may be subtle technical differences between electrical products from different manufacturers

When it comes to the acquisition of electrical equipment for hazardous areas, end users and contractors have to ensure that apparatus not only meets the appropriate Health & Safety standards. They also have to make the correct purchasing decisions, based on the cost of ownership of a product, not simply based on initial purchase price. This may include the cost of installation, maintenance, service and repair. The cost of an unscheduled shut down in a hazardous area to repair faulty equipment, must also be taken into consideration.

For hazardous area applications, these types of purchasing decisions are further complicated by European and International Health & Safety Standards, which allow electrical equipment to be marked with an ‘X’ at the end of the certificate number. This ‘X’ denotes that the equipment is subject to ‘specific conditions for safe use’, which is specified in the schedule to the certificate. ‘X’ may denote enhancements but can also denote limitations. The owner of the equipment must thus be aware of the meaning of the ‘X’ on the equipment in use as it could mean that he must carry out a risk assessment on that particular equipment.

It is crucial that engineers understand the subtle technical differences between electrical products from different manufacturers. While different products may carry the same ‘ATEX classification’, the customer must consider the possible ‘hidden’ costs of the ‘X’.

Take explosion-protected control stations or overhead fluorescent lighting for hazardous areas as an example. As long as the lighting unit carries the required ‘ATEX classification’ and test certification, the end user may not be duly concerned with any ‘X’ marks on the certificate. However, the ‘X’ in this particular example could denote that the control station or light fitting can only be installed where there is a low risk of mechanical damage.

‘Low risk of mechanical damage’ is open to the customer’s own interpretation, but may mean that the unit cannot be installed in certain production areas, handling or lifting bays. The ‘X’ on a control station or light fitting then denotes that the housing is rated below the 7N impact test required as standard for equipment used in hazardous areas. This is rather like buying a car without airbags and being told by the seller that you can only have low speed impacts!

Another example could be a limitation in the ambient temperature. Instead of the standard range (-20°C up to +40°C) the equipment may be limited for use in an ambient range between 0°C up to +40°C. This means that the equipment is restricted to indoor use only. On the other hand, the same ‘X’ could also refer to an increased ambient temperature range.

The ‘X’ may also have other special conditions that increase the cost of ownership for the end user. For example, special installation instructions and maintenance procedures may be necessary. This might mean that self-tapping screws are supplied with the lighting to lock the diffuser clamps. These must be fitted to maintain the certification. If the customer is installing hundreds of lights throughout a plant, the subsequent additional time and cost of installation can be significant.

Apart from the possible restrictions created by an ‘X’ in the certificate, inspection and maintenance are also key considerations when purchasing light fittings for hazardous environments. Some light fitting manufacturers have moved from being suppliers of lighting for general industrial use to ‘explosion-protected’ versions. Often, these suppliers have to include special maintenance conditions. You might find yourself having to inspect a light fitting every 12 months to meet the terms of the certificate, and this could cost you dear in terms of maintenance.


Graham Doran is with Cooper Crouse-Hinds. He is a specialist in the field of explosion-protection, including implementation of the latest standards relating to explosion-protected apparatus, according to the new ATEX regulations


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