Combustible and explosive dusts occur more often than you think.
For example during the processing of:
– wood and fibre materials
– foods, beverages, tobacco and fodder
– metals and metal alloys
But technical chemical products of plastic, resin and rubber can create combustible dusts and explosive atmospheres.
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If you store combustible dusts on hot surfaces such as overheated electric motors, smoldering fires may occur which can cause an explosion when the dust is kicked up, for example by opening a window.
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Dust explosion are particularly dangerous because the shock wave can kick up more dust and trigger a chain reaction.
The result is often destruction on a dramatic scale and danger to human life.
Dust is almost everywhere - air too! But you can prevent sources of ignition!
In connection with building and organizational measures and by choosing suitable equipment certifi ed for use in dust Ex-areas the risk of an explosion can be minimized. Cooper Crouse- Hinds UK Ltd offers you a wide selection of electrical equipment for safe use in dust Ex-areas.
The following three conditions must be satisfied for a dust explosion:
- The LEL for many food dusts, for example is between 30 and 60 g/m3, the UEL is 2 to 6 kg/m3.
- A suffi cient amount of air oxygen.
- A suitable ignition source, e.g. an electrical spark which may occur when pulling a plug out of a socket or a hot surface (e.g. 300°C to 600°C).
Always the right equipment:
According to their potential risk, dust explosion areas are classified in different zones in the European Union to which equipment categories 1D to 3D are assigned. This zone classification can be demonstrated particularly well by the example of a sack emptying station without dust suction.
Zone 20: Filling hopper of a sack emptying station
Zone 21: Close vicinity of the feed opening (e. g. radius 1 m)
Zone 22: Area with dust deposits outside zone 21
One spark may be enough!
The new standard EN 61241... supersedes the previously valid dust standard EN 50 281 from July 1, 2007.
This new standard EN 61241... must be observed because a high risk potential in dust explosion areas is involved in which peoples' lives are in danger.
The standard takes into account that the demands on the electrical equipment in areas with a risk of dust explosion are increased in comparison with the industrial standard and the previous standard EN 50281.
This obliges the owner to use products which correspond to and conform with the EN 61241 standard exclusively for new installations.
Which individual demands have changed exactly?
Impact strength of the housings
Electrostatic discharge capability of the housings
Aging resistance of the plastics used
In order to always be on the safe side in future, the dust Ex equipment of the brand comply with the new EN 61241-0 and EN 61241-1 + A1 standards for the dust ignition protection type "protection by housing" (tD) and are approved accordingly.
Dust explosion-protected equipment of the CEAG brand are of course subject to extensive quality assurance measures. We naturally have a quality management certifi ed by DIN EN ISO 9001: 2000 with additional regular auditing by an independent test body (ATEX Audit).
Our dust explosion-protected light fi ttings and electrical equipment comply with the latest standards and have all the important national and international approvals. For instance, our products are subjected to a conformity evaluation process for use in dust Ex-areas in which a named independent body tests their technical suitability for use in Ex-areas of zones 20, 21 and 22 (device category 1/2/3D). With the EC type test certifi cate or type test certifi cate / declaration of conformity, the test body certifi es the appropriate suitability and grants approval.
Dust explosion are more dangerous - and more common than you think!
Approximately 2,000 dust expplosions occur every year in the EU with average damages s of about €25,000 per accident. In an explosion at the Rolandmühle in Bremen alone, 14 people died, 17 were injureed and damages of 50 million Euro were caused!
An analysis of almost 600 dammage cases in Germany revealed that 31 % were caused by wood dust, 25 % by fodder and food dusts, 13% by plastic dust and 9% by coal dust. Silos, dedusting and connveyor systems, mills, drying kilns, heatings, saws, carpenttry shops and mixing systems are particularly affected.
To make your dust Ex-area safe
Mills, mixers or conveyors in areas where there is a risk of dust explosion require electrical energy – reliable, safe and explosion-protected. We provide the safe power supply for your drives with dust explosion-protected switches, motor intermediate terminal boxes and plug devices. And that's not all: Your drives can clearly and visibly be disconnected from the mains supply by our range of plug and sockets. This also makes maintenance of your machines very safe and convenient.
Shining examples of explosion protection
Risks can only be recognized and accidents avoided under good visibility conditions. Therefore good lighting is a must, especially in areas where operations favor the development of dust.
Our dust explosion-protected light fittings and downlights provide reliable light here whilst emergency exit luminaires safely show the way in case of a power failure.
All from one provider
Our extensive product portfolio of the CEAG brand offers you products for almost all areas of application:
Portable light fittings, fluorescent light fittings and downlights
Emergency exit luminaires
Plug devices and branching sockets
Switchgear and terminal boxes
Command and indicator devices
Safety switch with emergency stop functionas well as customer-specifically configured switching systems and controls.
You are responsible
You the owner are responsible for the protection of the work force and safety of your plant according to the new European ATEX directive 1999/92/EC (ATEX 137).
This work force protection directive also covers electrical installations in areas where there is a risk of dust explosion. This EC directive has become valid in all member states by national laws and regulations and supplements the product- related (technical) work protection as it is governed by the ATEX directive 94/9/EC among other things (characteristic requirements). The work protection directive 1999/92/EC also governs the carrying out of a risk assessment and division of Ex-areas into zones.
In accordance with this directive, only appropriately certified electrical equipment may be used in areas with a risk of dust explosion.
(name of the solid)
|Minimum ignition temperature of a dust layer (glow temperature) in acc. with IEC 61241-2-1 proc. A||Minimum ignition temperature of a dust cloud in acc. with IEC 61241-2-1 proc. B|
|Milk powder (full, spray)||330||520|
|Chemical-technical products (examples)|
|Laminate (grinding dust)||330||510|
Source: BIA - Report (excerpt) Combustion and Explosion Variables
Issued by: HVBG
When can dust explode?
Combustible dust-air mixtures have different ignition temperatures.
The surface temperature of the equipment in areas with a risk of dust explosion may reach 2/3rd of the minimum ignition temperature of the surrounding dust-air mixture at the maximum and with a 5 mm thick layer of dust must be at least 75°K below the minimum ignition temperature of the dust (glow temperature). It is therefore the owner's job to ensure that the cleaning and maintenance intervals of installations with a dust explosion risk are scheduled so that no dust layers thicker than 5 mm are allowed to form. At higher dust deposits the minimum ignition temperature (glow temperature) of the dusts are reduced drastically. Examples for the ignition and glow temperatures can be taken from the table right.