Feature Dust & fume extraction Dust in the factory – an explosive subject
Gordon Low, marketing segment manager at COOPER Crouse-Hinds, discusses how factories can reduce the risk of dust explosions occurring in the workplace and the latest standards relating to explosion-proof electrical equipment installed in these areas
T
he risk of a dust explosion occur- ring in a factory is not as remote a possibility as people might think. A dust explosion requires only
three things: air, combustible dust and a source of ignition such as an electri- cal spark or hot surface.
Indeed, many companies are poten- tially at risk here. Why? Because com- bustible dusts are present in many manufacturing environments. Wood shavings, carbon dust, flour, grain, custard powder, sugar, coffee, tea, animal feed, plastic and aluminium dust are just some examples of highly combustible dusts. The problem is when these combustible dusts are left to gather on hot surfaces in a work- place, such as on an overheated elec- tric motor or fan. This can cause smouldering fires to occur, or can cause an explosion when the dust is kicked up, for example, by a person opening a nearby window.
Dust explosions can have cata- strophic consequences because the ini- tial shock wave resulting from the explosion kicks up more dust, which triggers a chain reaction through the plant, often resulting in mass destruc- tion of equipment and buildings, as well as causing possible death or injury to employees.
Therefore, as potential sources of ignition, all electrical equipment installed in these areas, including mixers, filling hoppers, conveyor sys- tems, mills, silos, dust extraction plant, kilns and drying systems, need to be adequately protected and designed to operate under these condi- tions. Anyone who is responsible for the health and safety of employees or for sourcing electrical equipment for hazardous areas – needs to be fully 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 elimi- nate the risk of dust explosions occur- ring. Therefore, the European Directive for hazardous equipment 94/9/EC pointed out that this was valid in the same way for dust explo- sion-protected equipment as well as for gas hazardous areas.
Owners of new equipment are gov- Factory Equipment MARCH 2012 25
erned 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 also includes ‘old’ as well as ‘new’ equipment. In sum- mary, owners are required to identify the risks of explosion; implement explosion protection measures such as avoiding sources of ignition (sec- ondary explosion protection); define zones in areas at risk from dust explo- sions; create an explosion protection document; use suitable production equipment; and to create a test plan. The standards for electrical equip- ment in areas at risk from dust explo- sions have seen a few changes in the last few years. EN61241-0 came into effect from 1st July 2007 and came into force on the 1st October 2008. This stricter standard superceded the old standard EN 50 281.
On 16th April 2010, the new version of the standard EN 60079-0:2009 came into effect. In this standard, the requirement for explosive dust atmos- pheres now includes significant changes with respect to the previous edition. There are a number of changes to the current and future standards, which you should be aware of. There are increased requirements, from the old 50281 series to the 61241 series and now to the 60079 series such as: impact energy – high demand on impact energy as in Zone 1; electrosta-
Combustible dusts can vary from wood shavings to carbon dust to plastic and aluminium dust among others
tics – electrostatic conductance of the enclosure; and ageing resistance – high demand on the ageing resistance of the plastic enclosure associated with an ingress protection test after ageing. Customers need to be aware of these changes when sourcing or upgrading electrical equipment for hazardous dust areas, so that they can purchase equipment that fully com- plies with the new requirements.
When can dust explode? A dust explosion requires three ingre- dients: air, combustible dust and a source of ignition. Combustible dust- air mixtures have different ignition temperatures. The surface temperature of the equipment in areas where there is a risk of dust explosions is allowed to reach two-thirds of the minimum ignition temperature of the surround- ing dust-air mixture. With a 5mm thick layer of dust, this surface temperature must be at least 75°K below the mini- mum ignition temperature of the dust (glow temperature).
It is therefore the equipment
Equipment owners must ensure that no dust layers are thicker than 5mm
owner’s responsibility to ensure the cleaning and maintenance intervals of installed equipment with a dust explo- sion risk are scheduled so that no dust layers thicker than 5mm are allowed to form. At higher dust deposits, the min- imum ignition (glow) temperature of the dust is reduced significantly. The goal of the current European Directives is to protect operating plants from dust explosions and to prevent damage or personal injury. The explo- sion protection measures are divided into ‘Owner’ and ‘Manufacturer’ Directives. Again, the objective is to implement all necessary measures to ensure explosion-protected products can only be operated if they do not pose any danger to health and safety and provided that they are correctly assembled, installed, maintained and used for their intended purpose.
Cooper Crouse-Hinds T: 024 7630 8930
www.coopercrouse-hinds.eu Enter 325
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56