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Graham Doran, sales and marketing director at Cooper Crouse-Hinds (UK), discusses how companies can reduce the risk of dust explosions.

Dust explosions are more of a risk than some people may think.

A dust explosion requires only air, combustible dust and a source of ignition such as an electrical spark or hot surface.

Combustible dusts are present in many process manufacturing environments.

These dusts include wood shavings, carbon dust, flour, custard powder, sugar, coffee, tea and aluminium dust.

When these combustible dusts are left to gather on hot surfaces such as on an overheated electric motor or fan, they can cause smouldering fires or an explosion when the dust is kicked up, for example by a person opening a nearby window.

Dust explosions can kick up even more dust, which triggers a chain reaction through the plant, often resulting in mass destruction of equipment and buildings, as well as causing possible death or injury.

Therefore, all electrical equipment installed in these areas, including mixers, filling hoppers, conveyor systems, mills, silos, dust extraction plants, kilns and drying systems, must be protected and designed to operate under these conditions.

Anyone responsible for the health and safety of employees, or for sourcing electrical equipment for hazardous areas, must be aware of the risks of dust explosions, the European directives and standards relating to electrical equipment installed in hazardous areas and the measures that can be taken to eliminate the risk of dust explosions.

Owners of equipment are governed by the compulsory European directive 1999/92/EC, implemented in the UK as the ‘Dangerous Substances and Explosive Atmospheres Regulations 2002’ (DSEAR).

From 2006, this directive included old and new equipment.

Owners must identify the risks of explosion; implement explosion protection measures such as avoiding sources of ignition (secondary explosion protection); define zones in areas at risk from dust explosions; create an explosion protection document; use suitable production equipment; and create a test plan.

For electrical equipment in areas at risk from dust explosions, a new standard, EN61241, was introduced.

This stricter standard came into effect from 1 October 2008 and supersedes the existing standard EN 50 281.

Within this new standard, one of the main protection types for production equipment at risk from dust explosions in accordance with ATEX Directive 94/9/EC, is the protection by enclosures type tD.

This protection type is where the electrical production equipment is equipped with an enclosure to prevent dust penetration and where measures have been taken to limit the surface temperature.

The main changes to this standard concern: impact energy – high demand on impact energy as in Zone 1; electrostatics – electrostatic conductance of the enclosure; and ageing resistance – high demand on the ageing resistance of the plastic enclosure.

Owners need to be aware of these changes when sourcing or upgrading electrical equipment for hazardous dust areas.

Hazardous areas for explosive dust atmospheres are classified into three zones.

Zone 20 is an area in which an explosive atmosphere, in the form of a cloud of combustible dust, is present continuously, for long periods or frequently.

Zone 21 is an area in which an explosive atmosphere, in the form of a cloud of combustible dust, is likely to occasionally occur in normal operation.

Zone 22 is an area in which an explosive atmosphere, in the form of a cloud of combustible dust, is not likely to occur in normal operation but, if it does occur, will persist for a short period.

On 6 April 2008, the Corporate Manslaughter and Corporate Homicide Act 2007 came into force in the UK, which means companies could face severe fines or even imprisonment should a dust explosion occur.

About 2,000 dust explosions occur in Europe every year.

Cooper Crouse-Hinds provides explosion-protected electrical equipment, including fluorescent light fittings, emergency lighting, switches, terminal boxes, control stations and portable lamps.

For a free copy of Cooper Crouse-Hinds’ ‘Catalogue Dust-Ex 712: Dust Explosion-Protected Luminaries and Apparatus’, contact the company’s UK sales office.

Cooper Crouse-Hinds

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