Introduction to ATEX
Past legislation to control explosive atmospheres has only been concerned with electrical equipment. The current ATEX directives now include hazards from mechanical sources, such as mills. A seized bearing or mechanical failure causing excessive heat generation is as likely a cause of explosion as an electrical fault and is now considered of equal importance in the design and use of size reduction equipment for powder processing.
ATEX Standards
There are currently two European directives in existence, 94/9/EC which is principally for manufacturers and another for operators of the equipment 99/92/EC. 94/9 EC is implemented in the UK by the Equipment and Protective Systems intended for use in Potentially Explosive Atmospheres Regulations 1996 (EPS Regulations). 99/92/EC is implemented in the UK by the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR).
Both EU directives have been in place for several years, 94/9/EC since 1st July 2003 and the provisions of 99/92/EC extended to 1st July 2006.
Complying with ATEX
To comply with these standards a number of precautions must be taken to eliminate any risk potential. The first step is to carry out a risk analysis (Ignition Hazard Assessment) on the product to be milled and the environment in which the size reduction process will take place. This assessment will determine type of hazardous zoning inside and outside the mill and should be carried out by the user of the equipment.
Using the information provided, the mill supplier can then design the equipment to meet the appropriate ATEX Directive measures. The mill supplier is also responsible to advise the user of any precautions necessary to operate the mill safely.
ATEX Categorisation
In addition to the consideration of mechanical machine features, further categorisation is divided between gas and dust risks. The levels of risk fall into various zones; 0, 1 or 2 for gas, 20, 21 and 22 for dust. There are also individual equipment categories; 1, 2 and 3 (see table).
| Zone (Gas) | Zone (Dust) | Zone Definition | Equipment Category | Protection Method |
|
0 |
20 |
Explosive atmosphere is present continuously, for long periods or frequently. |
1 |
Equipment must be safe under normal operation, expected and rare malfunction. |
|
1 |
21 |
Explosive atmosphere is likely to occur occasionally under normal operation. |
2 |
Equipment must be safe under normal operation, expected malfunction. |
|
2 |
22 |
Explosive atmosphere may occur under abnormal operation and only persists for a short period. |
3 |
Equipment must be safe under normal operation. |
Source: RS Components
To comply with each level of risk various accessories may be fitted to the machine such as temperature sensors, nitrogen purging systems, earth-bonding and anti-static castors. ATEX rated electrical equipment and accessories are also used including motors, safety switches and control panels.
Equipment Location
It is important to ensure that when positioning equipment that either contains an explosive atmosphere, or is situated in an ATEX zoned environment that the location is matched with the equipment in use. If the equipment is situated in an ATEX zoned area then the external features of the mill must comply with the ATEX provisions according to the zone. Special care should be taken relating to the effect on the surrounding area and also affects resulting from the surrounding area.
Manufacturer’s Responsibilities
The mill manufacturer has a responsibility to the customer to provide correctly designed equipment and the user or purchaser has a legal right to expect an acceptable level of safety from the equipment supplier. It is therefore of paramount importance to ensure the user has adequate information on the limitations of use and operating parameters. Adequate instructions of the limitations of use and operation must be supplied along with training where required to ensure equipment is used safely and as intended.
The ATEX Compliant Hanningfield Mill
With many years experience of designing and supplying explosion category milling equipment, the Hanningfield Uni-Mill provides the ideal solution to meet ATEX legislation directives.
Hanningfield holds ATEX/Ex-Proof accreditation which enables us to self-certify the Uni-Mill (conical mill) and Kwik-Sift (centrifugal screening) models for use in ATEX zone 0/20.
Special features such as continuous earth design, temperature monitoring and nitrogen purging ensure appropriate compliance measures are in place for every machine supplied to meet the level of hazard specified.
Click here for more information on the Hanningfield Uni-Mill.
By Colin Ellis (Managing Director, Hanningfield)
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