The ATEX directives are a European set of directives aimed at the management of explosive atmospheres to ensure they are classified, and that the appropriate equipment is installed in potentially explosive atmospheres. Mostly associated with the petrochemical world, ATEX is relevant for any substance which is potentially explosive in a dust, gas, vapour or mist form, noting that some fluids with given flash points also fall under ATEX.
ATEX is actually the name of a group of two European directives which are:
• Directive 99/92/EC (also known as ‘ATEX 137’ or the ‘ATEX Workplace Directive’) which covers workplaces and the responsibility of employers who have a relevant substance. This typically covers the hazardous area classification (HAC), and other organisational methods.
• Directive 94/9/EC (also known as ‘ATEX 95’ or ‘the ATEX Equipment Directive’) which relates to equipment that is installed within a potentially hazardous area (zone) and the associated protective systems.
For the majority of companies, ATEX 137 is more relevant and will be the main focus of this article; however, when lighting is discussed in more detail, the equipment directive will also be discussed.
Both these ATEX Directives aim to reduce and control the risk to as low as reasonably practical (ALARP), through a risk assessment (which the hazardous area classification is part of) and associated controls (such as the equipment within the zone).
“ATEX is for any substance which is potentially explosive in a dust, gas or mist form”
Do I need to consider ATEX?
This question crops up a lot. In most industries it is obvious when ATEX is required as they deal with potentially flammable substances, such as fuels, starches or other organic dusts. Within the directive the official definition of an explosive atmosphere is:
“a mixture with air, under atmospheric conditions, of flammable substances in the form of gases, vapours, mists or dusts in which, after ignition has occurred, combustion spreads to the entire unburned mixture”
So practically, what does this mean? It means that if we look at the Material Safety Data Sheet (MSDS) for the substance, we should be able to find this information out. Within the MSDS there are two important sections that show whether the equipment falls under ATEX, namely Section 2 and Section 9.
Section 2 covers the Hazards identification. Within this section, if the substance falls under any of the categories of flammability – and it can be in a gas, vapour, mist, or dust – it will be covered under the requirements of the directive. In this case, a dust generally must have a particle size of less than 500 microns (0.5mm) to be considered as part of the standard, as if it is larger the combustion is likely to stop before being spread to the entire unburnt mixture. However, there is a classification for larger size particles, referred to as ‘flyings’, which needs to be considered for certain substances.
A typical example (for methane in this case) of section 2 from an MSDS is shown opposite.
As can be seen in Figure 1, methane is an extremely flammable gas, and hence would fall under the ATEX directive.
As previously mentioned, one important area to be aware of is that when the particle size is larger than 500 microns, section 2.3 mentions that the substance may be explosive when in a dust form. These are referred to as ‘flying’, which are common in, for example, polyethylene beads used in various plastic processes. If, in that case, it is possible that dust could be created (which it frequently is at the bottom of silos or within the process) then ATEX would need to be considered.
Section 9 of the MSDS covers the physical properties of the material, which is important in regard to ATEX as it helps specify the equipment that will be installed in the zone. An example of a Section 9 is included in Figure 2 below (again for methane).
This should provide important information:
1. Flash Point: The point at which a fluid starts to turn to vapour. This is important as any fluid with a flash point under 85ºC must be considered, but if the flash point is much higher than operating conditions within the process, anything above 85ºC would not need to be zoned under the ATEX directive (controls to prevent the temperature being approached would be required).
2. Flammability: The type of flammable substance.
3. Lower Explosion Limit (LEL): The lowest concentration of the substance with air that will create a potentially explosive mixture. This is usually measured as percentage volume for gases, but g/m3 for dusts.
4. Upper Explosion Limit (UEL): The highest concentration of the substance with air that will create a potentially explosive mixture. This is usually measured as percentage volume, but g/m3 for dusts.
5. Auto-ignition Temperature/ *Minimum ignition Temperature: The temperature that the substance will self-ignite when in a cloud mixture with air, potentially causing an explosion.
6. *Layer Ignition Temperature (LIT): The temperature at which a layer of 5mm dust will ignite, which is important for the maximum surface temperature of equipment.
7. Minimum Ignition Energy (MIE): The minimum energy required to ignite a cloud of gas, vapour, or dust.
8. *Dust Explosion Class (St0 – 3): The strength of any potential explosion ranging from 0 (no explosion) to 3 (very strong explosion), which is based on how rapidly the pressure increases over time.
*Specifically for dusts
In our experience, the MSDS for vapours and gases are much more informative with many of the items being complete, while for dusts these items are either missing or listed as “Information not available”. In either case, it is the responsibility of the organisation to ensure that the correct equipment is installed within any zones identified, which means that this information is required. In most cases, a sample of dust must be sent to a test house who will carry out tests to gather this information for you.
Hierarchy of Control
ATEX, as with all hazards, has a hierarchy of control used for risk reduction. Where possible, an organisation should attempt these controls, starting with the first and finishing with the last:
1. Elimination or Substitution – Do you need to use the substance, or can you remove it from site? Can an alternative substance that does not create a potentially explosive atmosphere be used? A typical example of this is hydraulic oil, which can be replaced with mineral oils that are not flammable.
2. Reduce Amounts – Can you reduce the amount stored, or that is used in the process, which will reduce the potential consequences of an incident?
Typically, these first two steps are easy to answer because the substance is required as part of the process. This is rarely documented however, and it is important to be able to prove that no alternative or reduction is possible.
3. Reduce Releases – Design the system so that any release of mist, gas, vapour, or dust are minimised. This can be in volume, duration or even the amount of release sources. If, for example, you only have one release source, it is easier to control than the entire room having a release source
4. Control Ignition Sources – If a release, and hence potentially explosive atmosphere, is possible, then you need to control the ignition sources within that area. This applies to normal operation, equipment failure, and maintenance work – this is where lighting will come in later. Another method of controlling ignition sources, which falls partly in control and partly in mitigation, is spark detection and suppression. This is a system that will detect a spark and douse it rapidly (typically with CO2 or N2) before ignition of the explosive atmosphere can occur.
5. Mitigate Explosion – If there was to be an ignition, it is also possible, through engineering means, to mitigate an explosion through explosion vents and explosion suppression. These need to be properly specified to be able to handle the energy and speed of any potential explosion.
6. PPE and Information – Finally, at the bottom is the provision of PPE information and training for people working within or in the vicinity of the area. This is key for anyone carrying out maintenance or installing ATEX rated equipment.
Hazardous Area Classification
Hazardous Area Classification is also called Zoning when it comes to ATEX, and it is the process of defining the likelihood of an explosive atmosphere being present. There are various standards available that provide guidance on this, but the zones are split into three categories.
Zone 0/20 are typically easy to identify, but where possible equipment in those areas should be avoided. This is usually within pipework, vessels, hoppers/silos, and areas where equipment is limited.
For the remaining zones, the word “likely” must be interpreted. In the oil and gas world, the IGEM and Energy Institute standards provide guidance on when these zones occur, such as on a creep relief or condensate drain.
Depending on the application, there is guidance, but in our experience there are some common areas that are frequently missed. These are items such as flexible connections, which are a common failure point as over time they can crack and provide small leakage points, and through breathers when the filter fails, etc.
One of the common items where zoning is missed is a manually loaded hopper with Local Exhaust Ventilation (LEV). In normal operation the LEV would remove any potentially explosive atmosphere, however, if the hopper can be loaded when the LEV is not running (or is broken) then a Zone 22 would still be present. A similar principle is required with mechanical ventilation and any item which could foreseeably fail.
It is important to mention that for gases there is also a Zone 2 Negligible Extent (NE), which is a situation where, due to the ventilation and leakage rates, a potentially explosive atmosphere of no larger than 0.5m3 can be created. In this case, ATEX equipment is not required in that area, however, other controls for maintenance such as hot works are still required.
Control Ignition Sources
ATEX instructs that any designated potentially hazardous area requires that the electrical, instrumentation, and mechanical equipment (since 2013) should be appropriately ATEX rated. The best place to start is knowing how you can tell if equipment is ATEX rated. Well, the answer is the markings on the nameplate, which may look something like this:
I have highlighted the key items to check on the label in red, which mean:
• Category – ATEX equipment comes in category 1, 2 and 3, where a category 1 piece of equipment can be used in Zones 0 or 20, category 2 in Zones 1 or 21, and a category 3 piece of equipment can only be used in zone 2 or 22.
• Type of protection – Such as flameproof or intrinsically safe. These are covered in the IEC 60079 group of standards for electrical equipment and EN 80079 for non-electrical equipment.
• Temperature/Temperature Class –This is the maximum temperature the equipment will reach. For dusts, this is a temperature in degrees Celsius, whereas for gases this is a Temperature Class which are as per the table below:
There are other elements to check, such as the equipment class (for mining, combustible flyings etc.), however, there are plenty of other articles and reference materials that go into that detail.
The key thing to identify and understand, is to ensure that the equipment is correct for the substance (i.e., Gas or Dust), and that the surface temperature is correct. The surface temperature must be appropriate for the substance, for a gas/vapour this is easy as the temperature class must be lower than the auto ignition temperature.
For dusts, the maximum equipment temperature must be less than the Layer Ignition Temperature minus 75ºC and 2/3rds of the Minimum Ignition Temperature.
“while lighting is available for zones 1/21 and 2/22, at the moment there is only “portable” lighting available for zone 0/20”
So now that we know what the zones are, and what equipment is in it, lets discuss lighting. One of the most commonly missed items with regards to ATEX is lighting. While the process which creates the potentially explosive atmosphere and the equipment installed are considered, the lighting that goes within the area is frequently missed.
Whether this is outside in a gas terminal, or inside next to a hopper for dusts, the flood lights, light fittings, torches, and headlamps all need to be appropriately rated for the zone that they are located in or are taken into.
While lighting is available for zones 1/21 and 2/22, at the moment there is only “portable” lighting available for zone 0/20, which has led to some ingenious solutions with flood banks of portable lights. As you can imagine, the main struggle with lighting is the temperature that they achieve and before LEDs became mainstream, it was very difficult to achieve an ATEX rating at all, apart from in dust zones where ingress protection (IP) could be applied.
For lighting there are normally two options, which are to purchase the appropriate ATEX rated equipment, or to move the equipment outside of the zone. Frequently moving the lighting outside of the zone is more cost effective, as long as the lighting levels can still be maintained.
“consideration must be given to the process that is creating the explosive atmosphere but also any external equipment ”
One of the more common issues can be maintenance or inspection staff members with torches (and other electrical equipment such as tablets and phones) bringing a non-ATEX rated piece of equipment into a potentially hazardous area. For this reason, it should be made obvious, that only ATEX rated equipment is allowed within the area, and that staff must have the appropriate training to be able to identify that.
So, once you have identified the potentially hazardous areas (Zones), make sure that you not only consider the process that is creating the potentially explosive atmosphere but also any external equipment to that process such as the lighting. You also need to consider any equipment introduced into the area, such as a vacuum cleaner or torches. Once you have defined the zones, you will need to identify that the equipment within the zone is appropriate. To do this you will need to know what the explosive substance is and its explosive properties, as well as the ratings on the equipment.