AEMT - Association of Electrical and Mechanical Trades

Understanding the basics of Ex

There are major differences between “d” and the capital “D” when looking at the labels of ATEX equipment – What is the difference?

There is a critical difference between the lower case letter d, as in Ex d, or Ex de, and the capital D, as in Ex tD or GD. They have two very different meanings, and knowing which one is which will determine the way the equipment is repaired and what standards are required.

Ex d

The lower-case “d” after an “Ex” indicates a flameproof machine. The equipment is designed specifically to operate where volatile gases and vapours could be present. This protection concept relies upon:

  • The enclosure containing an explosion should the surrounding gas enter the enclosure and become ignited, and
  • Ensuring that the exhaust gases are sufficiently cooled before entering the surrounding atmosphere through flamepaths to prevent further ignition.

Ex tD, Ex pD, GD or Group III equipment:

The capital “D” stands for “Dust”, where the protection concept Ex tD uses high Ingress Protection (IP) enclosures (as per the table below) and controlled surface temperatures as the means of protection.

Understanding Zones in ATEX hazardous areas.

If it is known that gases, vapours, and dusts of a hazardous nature are present at various locations in a particular plant, it would be very convenient to make the complete plant one hazardous zoned area.

All of the electrical equipment being situated in that area would be required to be of special construction (ATEX Certified in Europe) to ensure that ignition of the hazardous gas/vapour/dust could not take place. The cost of this special equipment is high so the total cost of equipment in the installation could be much higher than necessary to ensure a safe plant.

It is likely that there would be areas in the plant where hazardous gas would never appear. Economics would suggest that the plant should be divided into areas with degrees of probability of the explosive gas/dust being present, and then to select electrical equipment suitably built to those areas and the type of hazard as in the table below.

A risk assessment must be carried out to assess the degree of risk, then actions are taken to minimise the risk of using electrical equipment in such areas. These areas are known to contain “ATmosphere EXplosif” in French, conveniently shortened to ATEX.

The European ATEX Directives require all areas to be risk assessed for the amount of time that a hazardous atmosphere may exist. These areas are categorised into Zones.

The table below relates to Group I for mining equipment, Group II non-mining equipment, and Group III equipment for dust.

Equipment Category Likelihood of Gas or Dust cloud presence Gas Zone (G) Group I Group II Dust Zone (D) Group III
1

Continuous
No Power Equipment Allowed

Zone 0 Zone 20
2 Likely to occur in normal operation
10-1000 Hours per year
Zone 1 Zone 21
IP 6X
3

Not usually present, only during malfunction
Up to 10 Hours per year

Zone 2 Zone 22
IP 6X Conductive Dust
IP 5X Non-conductive Dust
- None Safe Zone Safe Zone

Best workshop practices of working with Ex equipment.

  • When handling ATEX apparatus, there can be no room to deviate from the statutory safety requirements.
  • A Quality Management System should be in operation, to cover all aspects of repair and overhaul of Ex electrical and mechanical equipment.
  • All aspects of the repair and overhaul must be clearly recorded on the relevant forms.
  • All communications with customers should be either in writing or confirmed with agreed written statements.
  • All personnel must have been trained, assessed, and competent to work on Ex equipment.
  • Refresher courses and reassessment are required every three years to ensure competence and maintain an up to date Ex Repair Certificate.
  • Repairs and overhauls must be carried out to comply with the most recent repair standard IEC BS EN 60079-19 (Explosive atmospheres. Equipment repair, overhaul and reclamation), and other relevant Standards shown on the equipment’s certificate, applicable during the year of certification.
  • A calibrated set of tools, suitable for the size of equipment repaired, shall be available to inspect and complete any maintenance or repair of the equipment.
  • Appropriate containers or pallets shall be provided for holding assemblies or components at all stages from receipt through to final despatch.
  • A ‘bonded’ store area shall be provided where Ex equipment rejected after inspection can be held awaiting scrap or recovery. Rejected equipment shall be clearly marked with reject labels.
  • ‘Best Practice’ workshop general principles relating to machine & pump repair may be found by reference to:

    ‘The Effect of Repair/Rewinding on Motor Efficiency’, AEMT/EASA

Which standards to use when repairing Ex equipment.

Always make sure your standards library is up to date with THE MOST RECENT REPAIR STANDARD, IEC BS EN 60079-19.

Always check the certification documentation for the correct standards. If you don’t have the certificate, refer to the table and flow diagram in 60079-19, Annex C and use it to determine the maximum safe gap to reclaim parts to.

In order to find out which standards to repair to, make sure you can read and understand the equipment’s nameplate.

The key pieces of information you need to be able to find are:

  1. The year the equipment was certified, which are usually the first two digits of the certificate number for ATEX equipment.
  2. What the protection concept(s) of the equipment are.

Once you know the year the equipment was certified and what the protection concepts of the equipment are, look up which standards were available to the manufacturers when the equipment was certified.

For ATEX equipment (with CE marking) refer to European Standards bodies or the IEC. For America refer to the equivalent UL or FM organisations. The AEMT labels booklet lists all relevant ex standards and can also be referred to.

For example:

 

Certificate number = INERIS 01ATEX0001XATEX

Protection concept = EEx d

Date = INERIS 01 ATEX, “01” are the last two letters of the date “2001”.

Standards required from the certificate (and available in 2001):

  1. BS EN 50018:2000 - Ex d protection by flameproof.
    1. The latest Ex d standard can also be used, but only by following what Annex C of the latest repair standard (60079-19) recommends.
  2. BS EN IEC 60079-19’s most recent repair standard.