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Certification of equipment in hazardous areas

 

 

Hazardous Area Classification/ Certification of equipment in hazardous areas

 

 

 

R&B Industrial has recently passed the 10th Anniversary of our first order for a DSEAR (the Dangerous Substances and Explosive Atmospheres Regulations) report. Since then we’ve completed around 150 DSEAR risk Assessments and Hazardous Area Classifications, aiming to improve the quality, depth and clarity of our advice every time.

The reports generally focus on Regulations 5 (Risk assessment) and 7 (Hazardous Area Classification), however unlike most consultancies we are also in a strong position to practically assist clients in reducing risk (Regulation 6). Our reports also advise on correct identification of containers and pipes containing hazardous substances (Regulation 10) and comment on whether current emergency procedures and training (Regulations 8 and 9) are adequate.

 

How to Reduce Extents of Zone

 

One problem which our clients frequently face is over-classification of hazardous areas. This can make compliance extremely expensive, or in some cases impossible – if the equipment is simply not available as an ATEX version. The principal codes and standards used (BS EN60079-10 parts 1&2, EI15, various LPG and gas codes, etc.) tend to be over-conservative and there is no statutory requirement to follow these rigidly. In many cases reducing extents of hazardous areas is possible as follows:

Pressurised gases and Liquids: The main failing of the standards is that they do not account for the turbulence of the release, which tends to ensure that a flammable gas is rapidly diluted to safe levels within a short distance, except in enclosed spaces. The HSL’s QUADVENT model can be used to make more realistic predictions and can eliminate or reduce zoned regions around pressurised gas transport or storage in many cases. The QUADVENT 2 software tool is also able to make predictions for pressurised liquid releases. Practical measures may also be taken, for example reducing the compressed air pressure of a spray gun or installing ventilated enclosures.

Liquid pool releases (leaks and spills): The standards are often more realistic in this case as there may be little atmospheric turbulence and vapour concentrations can build up. Nevertheless, material safety data sheets do not always give accurate information regarding relevant substance properties. For example, the flash point and vapour pressures are often based on the properties of the worst-case component. By calculating the true flash point of the mixture it can sometimes be shown that it is more than 10C higher than the highest anticipated temperature, which will generally allow the hazardous area to be removed, provided that there is no potential for mist formation. More accurate calculation of the mixture vapour pressure can also reduce extents of zone, especially if temperature is also controlled, as the release rate will be reduced. Use of bunding can also limit the release area and hence the release rate.atex sign

Dust Releases: there is very little guidance on the extents of dust zones in BS EN60079-10-2:2015, other than tentative notes suggesting that 1m and 3m are often sufficient for zones 21 and 22 respectively. In practice, a better knowledge of the process and the dust properties can often be used to justify much smaller extents of zone. For example, terminal velocities of the dust particles can be calculated and compared with air flow distributions, which can be assessed based on our expertise in LEV systems. In some cases, the amount of dust released may be used to justify a smaller extent of zone based on the minimum explosive concentration. If a dust or powder is sufficiently cohesive, it may be possible to justify removing the hazardous area altogether.

In all cases, sufficient ventilation – either general or local -will allow reducing the area classification, e.g. from zone 1/21 to zone 2/22. By taking measures to ensure the ventilation is reliable and robust, it may be possible to effectively eliminate the hazardous area altogether.

 

Non-Electrical Ignition Risk Assessment

 

Where a hazardous area classification cannot be reduced, either by a more detailed analysis or by changes to equipment or procedures, it is often possible to carry out a non-electrical ignition risk assessment (NEIRA). This often means that minor changes may be made to the equipment to make it safe for use under the appropriate ATEX area classification, for example by replacing non-ATEX electrical components, installing current limiting barriers on sensors, installing thermocouples to detect emerging hot spots, or selective use of non-sparking components. We have carried out NEIRAs on equipment which has not been formally ATEX marked and made the modifications necessary for it to be safe in a hazardous area