Selecting ATEX Equipment
When conducting DSEAR risk assessments we often find that ATEX equipment isn’t suitably rated. The aim of this article is to allow you to correctly determine the specification of ATEX equipment required for your process and provide a summary of the ongoing actions required once you have selected the correct equipment.
In the UK, if an electrical or mechanical item of equipment is placed in a potentially explosive atmosphere, it needs to be suitably ATEX rated and comply with The Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres Regulations 2016 (known as EPS). This article is for people who have already conducted a Hazardous Area Classification (HAC) to identify the hazardous areas – also known as hazardous zones – where an explosive atmosphere could occur. If you need any support with HAC or specifying ATEX equipment, please get in touch and we’ll be happy to help.
What Information Do I Need?
It is a somewhat common misconception that equipment is simply either ATEX rated or isn’t – however, there are a number of parameters that determine the required minimum specification for ATEX equipment. These are:
1. What hazardous zone has been classified?
2. The material properties of the substances present, namely:
a. Gas/vapour or dust group and subdivision
b. Autoignition Temperature (AIT) of gases/vapours;
c. Minimum Ignition Temperature (MIT) and Layer Ignition Temperature (LIT) of dusts
All of the relevant parameters above will be included in some form on the ATEX marking, which should be found in the equipment documentation (certificate and manual) and also legibly and indelibly marked on the nameplate of the equipment (if possible). It’s probably useful at this stage to look at the minimum requirements of marking as defined by the EPS legislation relating to equipment selection. There are other marking requirements, but this article is focused purely on selecting the correct equipment.
Equipment Marking
The EPS requires the specific marking of explosion protection, followed by the Equipment Group (for non-mining equipment, this is equipment group II), the Equipment Category, and the letter “G” or “D” for gases/vapours/mists or dusts respectively. The minimum required Equipment Category is based upon the hazardous zone which has been classified.
An example of the minimum ATEX marking required in line with the EPS legislation for an item of non-mining equipment suitable for used in an area classified as Zone 1 or Zone 2 is as shown.
This is the minimum basic requirement for equipment marking in line with the EPS legislation. It is very common for equipment to be declared or certified in line with a specific Harmonised European Standard – these have their own nomenclature and marking requirements that are acceptable under the EPS. Instead of an Equipment Category, you may see an Equipment Protection level (EPL). The table below shows how these correlate.
Using our example from before, the minimum ATEX marking required in line with the Harmonised European Standard for an item of non-mining equipment suitable for used in an area classified as Zone 1 or Zone 2 is as shown. Here, we have introduced a couple of additional terms – Type of Protection and Temperature Class.
Type of Protection
The Type of Protection denotes the specific measures that have been applied to the equipment to avoid ignition of an explosive atmosphere. Some examples of these include intrinsically safe (i), increased safety (e), encapsulation (m), and flameproof enclosure (d). This is not usually important for the selection of equipment and is used by the manufacturer to achieve a desired Equipment Protection Level – hence the corresponding “a”, “b” or “c” suffix.
Temperature Class (Gases/Vapours)
The Temperature Class is used for Group II equipment (suitable for gas, vapour or mists) and Maximum Surface Temperature is used for Group III equipment (suitable for dusts). Temperature Class is the maximum surface temperature the equipment can reach and is defined in BS EN IEC 60079-0 (electrical equipment) and ISO 80079-36 (non-electrical equipment) as shown below.
EN 1127-1 states that the maximum surface temperature of Category 1 or 2 equipment should not exceed 80% of the AIT of the material forming an explosive atmosphere.
Maximum Surface Temperature (Dusts)
The Maximum Surface Temperature is used for Group III equipment (i.e. suitable for dusts) and is not marked in line with a Temperature Class, but rather with an actual maximum surface temperature (e.g. T125, T200, T315) in degC.
For the user to determine what Temperature Class or Maximum Surface Temperature is required, they need to know the material properties of the combustible materials. For fluids, the Autoignition Temperature (AIT) must be known. A Temperature Class is then selected accordingly (e.g. a material with an AIT of 185 degC would require a Temperature Class of T3, T4, T5 or T6).
For dusts, it is slightly more complicated due to the variable nature of dust properties. The end user often has to conduct the testing on combustible dusts to determine the properties required to specify ATEX equipment due to poor information on supplier safety data sheets. Both the Minimum Ignition Temperature (MIT) and Layer Ignition Temperature (LIT) must be known, and the user must apply a safety margin defined in BS EN 60079-14.
The Maximum Surface Temperature must not exceed the lower of either 2/3 MIT or LIT – 75 degC. The LIT is typically based on a dust layer of 5 mm. If the dust layers in the facility exceed this, then a lower Maximum Surface Temperature should be selected (i.e. a greater safety margin than 75 degC) to account for the increased insulation provided by the dust layer. As the dust layer depth increases, the Maximum Surface Temperature decreases.
Special Conditions for Use
One further consideration to bear in mind when selecting ATEX equipment are any Specific Conditions of Use specified by the manufacturer. These are indicated by an “X” on the equipment marking (typically at the end of the certificate number), with the conditions detailed in Section 17 of the ATEX Certificate. It is worth checking what these are prior to purchasing ATEX equipment to ensure they can be complied with, and relevant conditions should also be included in any ATEX equipment register or inspection schedule.
Summary and Next Steps
This article should now allow you to select the appropriate ATEX equipment for your process. However, there are also requirements for the installation and inspection of ATEX equipment. These are vital in ensuring that they continue to provide the required level of protection. The list below is a summary of the actions required to correctly specify, inspect and maintain ATEX equipment:
Obtain the properties of the materials handled.
Conduct a Hazardous Area Classification to determine the hazardous areas.
Select equipment based on the hazardous zone AND the material properties.
Install the equipment using competent personnel (e.g. CompEx).
Create a register of ATEX equipment which will facilitate proper inspection and maintenance in line with the manufacturer’s instructions.
Conduct an Initial Inspection of ATEX equipment in line with BS EN 60079-14.
Conduct Periodic Inspections in line with BS EN 60079-17.
If you have any questions or would like to discuss any of the points raised in the article, or any area of DSEAR compliance, please get in touch and we’ll be happy to help!