Fans fall foul of expanded ATEX directives

With the introduction of the ATEX Directives on 1st July 2003, mechanical equipment in hazardous areas will be subject to similar certification as has applied to electrical equipment for many years.

With the introduction of the ATEX Directives on 1st July 2003, mechanical equipment for use in hazardous areas will be subject to similar certification as has applied to electrical equipment for many years.

As fans are used over a wide range of industries, and are often seen as a major "ignition source", CEN TC 305 has commissioned a specific standard "Design of fans working in potentially explosive atmospheres".

This standard forms the basis of this article, but the principles are equally applicable to other areas of manufacturing.

Currently, electrical equipment is covered by current hazardous area certification (Exn, Exd, Eexde etc), but no such certification exists for non electrical machinery, including fans.

Whereas manufacturers may offer spark reducing features that vary from brass rubbing strips, to more sophisticated levels of security, the degrees of protection vary widely.

Often, in more demanding applications, the final specification is arrived at by consultation between manufacturer and end user and others in the supply chain.

Nonetheless, the manufacturer will require additional information for equipment to be used in hazardous areas.

The familiar Zones 0, 1 and 2 are retained for gases and vapours and 20, 21 and 22 for dusts.

The categories 1, 2 or 3 are introduced to give an indication as to the level of security.

The category is a function of the zone - the likelihood of the presence of an explosive mixture - and the consequence of an explosion.

As with existing electrical equipment, the manufacturer must be informed of the nature of the explosive component.

This could include gas group, auto ignition temperature and dust type.

In order for the equipment manufacturer to carry out a full risk assessment, all normal and anticipated operating conditions must be considered.

Consider the case of a centrifugal fan operating a solvent extract system.

At a specific duty point, the design temperature rise across a fan may be known and acceptable.

If, for instance, a number of extract legs were shut down, the fan characteristics would change with a corresponding rise in temperature.

So although the fan standard covers some deviation from the normal operating point, major changes from design duty point could cause increased heating within the fan.

With the increase in use of inverter drives, another potential hazard is increased temperature generation within a motor.

It is a common misconception that all fans follow a variable square torque characteristic with varying speed.

Although this is true for a fixed system, such as an extract fan, for other duties this is not the case.

An induced draught fan on an incinerator may be used to give a constant negative pressure in the combustion chamber at varying flow rates and flue gas temperatures.

Often the motor may be required to run at 50% speed and produce well in excess of 25% full load torque.

The manufacturer would therefore need to ensure that the motor is capable of providing the required torque over the design speed range.

In the event that the motor was outside the scope of supply the relevant information would need to be passed to the motor supplier.

Risk assessment is required to identify significant hazards and possible hazardous events that may occur.

In the standard for industrial fans, this has been carried out as part of the standard.

It is however, the manufacturer's responsibility to ensure that all significant risks have been covered for the particular machine in question.

The risk assessment also includes measures to prevent an ignition source from becoming effective.

It may be that some industrial equipment will require very little in the way of design changes.

However, in the case of industrial fans this is not the case.

In order to certify units ATEX compliant, and dependant on the category supplied, previous industry standards will not be applicable.

Some of the more far reaching changes could include: gas tight fan cases; impellers capable of overspeed testing; preferred materials for rotating - nonrotating parts; bearing design; drive arrangement; and impeller attachment.

The final execution of the design lies with the manufacturer.

Where, as is the case of fans, a specific standard exists, this can be used as basis for the design.

For more specialised machinery, the design features are left to the manufacturer who would need to work within the relevant general European standards.

Increased testing is also a requirement of the new regulations.

Where testing requirements are clearly defined it is the manufacturer's responsibility to ensure these are carried out.

In the absence of a specific standard, it is the responsibility of the manufacturer to ensure that suitable testing is carried out, to show that ignition sources are prevented from becoming effective during normal operating malfunction and rare malfunction.

In some cases, typically Category 1 fans, a degree of third party certification is required.

This should be carried out by the relevant notified body.

There are also specific documentation requirements, dependent on the degree of protection.

Clear labelling is required, giving full information on the manufacturer, CE marking, ID of the machine, rating data, conditions of use and safety standards among others.

Additionally, for Category 1 and 2 fans, the rating information shall also be on the nameplate.

The manufacturer also has a responsibility to consider activities that may cause additional risks once the equipment has left the place of manufacture and testing.

This could be damage in transit, erection, handling or incorrect installation, therefore the manufacturer also has a duty to provide full installation instructions.

Along with shipping and storing instructions, and manuals covering erection, commissioning, operation and maintenance.

Cost escalates dramatically with the increasing safety category.

A Cat 1 ATEX fan will cost up to seven times that of a standard fan.

At present Halifax is one of fewer than half a dozen manufacturers in Europe than can produce a Cat 1 fan, which type probably represents less than 0.5% of total fan applications.

With Zone 0 and Zone 20 defined as areas with the permanent presence of explosive mixture, possibly pushing many thousands of dust handling fans or extract fans into Category 1, then the demands of fans and other equipment for compliance must increase.

Take the example of a fan handling air from a dryer.

The air stream could contain both flammable gases and/or dust.

Historically the fan would have been supplied with spark minimising features.

If now ATEX is applied, and the view taken that in its normal operation the fan handles an explosive mixture, might this demand a Category 1 fan?.

From a manufacturer's view point no clear guidance exists.

There may be a tendency to adopt a "better safe than sorry" attitude, but, even removing commercial considerations, there is probably not enough capacity in test houses alone to certify all the units that could fall in this category.

To conclude, in order to satisfy the new ATEX directives manufacturers will require full instruction from the user with regard to zone classification, equipment category operating conditions and any other details that may affect operation of the equipment and its ability to prevent it becoming a possible source of ignition.

They will then be required to carry out a risk assessment regarding ignition sources and effective preventative measures, carry out best practice design and suitable testing.

They will be required to archive necessary design information for future inspection and provide detailed instructions for the installation, commissioning and use of equipment within their scope of supply.

Taking industrial fans only as an example, the new ATEX Directive will call for manufacturers to take extra responsibility for their products.

The end user in turn will suffer additional expense, complexity and longer lead times.

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