Non-electrical equipment and own potential source of ignition
14 April 2020
As a process, safety and equipment consultant I have been involved in several projects where a client (the end-user) has integrated a number of items of powder handling equipment to form an assembly. These assemblies have included electrical equipment and non-electrical equipment.
(Click here to view article in digital edition)
With the exception of “simple apparatus”, it is generally recognised that electrical equipment has its own potential source of ignition. However, this is not so clear cut with non-electrical equipment and this article explores the issues associated with non-electrical equipment.
ATEX Equipment Directive 2014/34/EU includes the following in its definition of equipment covered by the directive: “which are capable of causing an explosion through their own potential sources of ignition.”
Potential ignition sources are equipment related ignition sources which are a sub-set of the possible ignition sources defined in EN 1127-1 and include electric sparks, electrostatic discharges, hot surfaces, flames, mechanically generated sparks etc.
EU guidance “ATEX 2014/34/EU Guidance” states, “equipment can be said to have its own potential source of ignition, if, when operated as intended … in a potentially explosive atmosphere, it is capable of igniting the latter unless specific safety measures are taken. Therefore, equipment must ensure the required level of protection.”
The guidance also states, “If the only source of electrostatic charging comes from the process, such items are not considered to have their own source of ignition, and they are not in scope of Directive 2014/34/EU. In these cases, they should not be ex or CE marked according to Directive 2014/34/EU.”
On the other hand, the guidance states, “could become charged … by the intended use of the equipment … if they are placed on the market specifically for this intended use.”
From this guidance, it is clear that non-electrical equipment, which has its own potential source of ignition, such as a mechanical spark or hot surfaces or that can generate static electricity from moving non-conductive parts, must be in compliance with the ATEX Equipment Directive and as a result must be ex and CE marked.
On the other hand, it also indicates that there is some equipment that is on the borderline between requiring certification under the ATEX Equipment Directive and not requiring it because it does not have its own potential source of ignition. This is particularly true for equipment placed on the market with a specific use where the process can generate static electricity. The following examples examine two borderline cases in more detail.
Borderline Example 1 – Hand Operated Valves
Hand operated valves move slowly, with no possibility of forming hot surfaces or mechanical sparks. Some valve designs incorporate polymeric parts, which could become electrostatically charged, but the EU guidance specifically states that these are not covered by the directive.
However, it is clear (see calculation 1) that if a valve is included in a process system that could generate a large electro-static charge, for example a pneumatic conveying system or an isolated metal part, such as the ball in a ball valve, could become sufficiently charged to ignite the powder being conveyed. Since the pneumatic conveying system, as a whole, could be placed on the market specifically for a use where it has its own potential source of ignition, it seems logical that such a system would need to be ATEX certified (one certificate for the whole system) including any manual valves that are part of the system.
Borderline Example 2 – IBC Blender
BS EN ISO 80079-36 “Non-electrical equipment for explosive atmospheres - Basic method and requirements” states that, “Static autonomous process equipment includes items such as tanks, vessels, fixed pipework and hand operated valves which do not have their own source of energy that could create a potential ignition source during operation.” This indicates, as would be expected, that a static metal intermediate bulk container (IBC) is not covered by BS EN ISO 80079-36 (which is a standard harmonised to the ATEX Directive) and hence it is not covered by the ATEX Directive since it would not have its own potential source of ignition.
However, this would not be the case for an IBC that contains powder and is being used for powder blending. It is to be expected that filling the IBC and tumbling powder in the IBC could generate static electricity. If this is the case, and the IBC is not earthed via the blender machinery, the IBC could generate an electro-static spark powerful enough to ignite a dust cloud inside the IBC. Calculations 2, 3 and 4 provide estimates of the potential spark energies.
Calculation 2 shows the estimated spark energy for an unearthed IBC that becomes electro-statically charged during filling. Calculation 3 provides an estimate of an electro-static cone discharge from the powder itself. In both cases, the electro-static discharge could ignite a powder with a low minimum ignition energy. Calculation 4 shows that tumbling the powder in an unearthed IBC could lead to a powerful spark that could ignite many powders.
Since an IBC Blender would be specifically placed on the market for an application that could have an effective source of ignition, unless protection measures are taken it is reasonable to suggest that the IBC Blender as a system should be ATEX certified.
DSEAR and the EU ATEX Workplace Directive
These two borderline cases indicate that it is difficult to decide if a complete process system should be ATEX certified. Powders that can form an explosive atmosphere are dangerous substances as defined by the Dangerous Substances and Explosive Atmospheres Regulations (DSEAR) and therefore employers must comply with the following regulation:
“Elimination or reduction of risks from dangerous substances
6.—(1) Every employer shall ensure that risk is either eliminated or reduced so far as is reasonably practicable.”
The EU ATEX Workplace Directive 1999/92/EC states:
Prevention of and protection against explosions
With a view to preventing, within the meaning of Article 6(2) of Directive 89/391/EEC, and providing protection against explosions, the employer shall take technical and/or organisational measures appropriate to the nature of the operation, in order of priority and in accordance with the following basic principles:
— the prevention of the formation of explosive atmospheres, or where the nature of the activity does not allow that,
— the avoidance of the ignition of explosive atmospheres, and…”
It is clear from this that to comply with these regulatory requirements, it is necessary to minimise the sources of ignition no matter whether it is the equipment or the process that is the potential source of ignition.
To comply with DSEAR and the ATEX Workplace Directive, my recommendation is that a full global ignition hazard assessment is carried out using the method presented in BS EN ISO 80079-36 Explosive atmospheres Part 36: Non-electrical equipment for explosive atmospheres — Basic method and requirements.
Once this global ignition hazard assessment has been carried out, it is possible to go the whole way to ATEX certifying the complete process system. To achieve this, a conformity assessment covering the essential safety requirements of the ATEX Equipment Directive, the compilation of a Technical File and the drawing up of an EU Declaration of Conformity are required.
This task is not too onerous and in the case of the Zone 21 (non-electrical equipment) and Zone 22 (all equipment), this certification process can be carried out by the company that created the integrated process system including the case where this is the end-user. The final step is that the Technical File must be lodged with a notified body who need to acknowledge receipt and hold the file for a minimum of 10 years. There is no requirement for the notified body to read or comment on the Technical File.
Since going to full ATEX certification does not add significantly to the cost, my recommendation is that this certification is carried out so that the doubt that surrounds borderline cases can be eliminated.
The BPE team have the experience and detailed knowledge to guide our clients through this process and ensure the required certification can be carried out by the manufacturer/integrator/end-user of the process system.
About the Author:
Keith Plumb Eur Ing, CEng, CSci, FIChemE, is a process and equipment consultant at chemical and biochemical engineering design company BPE. Keith has more than 40 years’ experience covering the pharmaceutical, biopharmaceutical, fine chemical industries and food/beverages. His MBA, continued involvement with MBS and work with the media has given him a much wider prospective than most engineers. Keith has been involved with all stages of the manufacturing process. He is familiar with process safety, notably HAZOPs and risk assessments, Hazardous Area Classification, and the requirements for ATEX, Pressure Equipment Directive, Machinery Directive and for CE Marking.
Contact Details and Archive...