The brave new world of mechanical explosion protection

Thursday, 8 October 2015

Introduction

The processes of developing mechanical explosion-protection techniques and standards started within ATEX [ATmospherique EXplosive] with a generalised EU Directive (1993) requiring the management of ignition risks in hazardous areas. There was no distinction made between electrical, mechanical, chemical or natural ignition sources

The Directive imposes requirements on the entirety of the supply chain including designers, manufacturers, importers/agents, end-users.

The Directive applies to all equipment brought into the EU, including second hand equipment from overseas countries.

The Directive needed a series of standards to guide stakeholders as they attempted to meet the Directive requirements. These were produced as EN (European Normative) Standards. In 2005 the decision was taken to internationalise the standards and ISO/IEC SC31M was established as a joint IEC & ISO committee to produce a suite of mechanical Ex Standards. This work is ongoing. The chart (following) outlines the activity in the development of the new standards.

New Standards

The development of the standards required to satisfactorily address mechanical Ex techniques, EPLs (Equipment Protection Levels),

ignition hazard assessments and ignition sources is ongoing.

It may be many years before a suite of standards similar to the AS/NZS(IEC)60079 series is available for the management of Ex

mechanical issues.

The development of these new standards has been undertaken in a “parallel universe” to the similar Ex electrical standards.

The Ex mechanical standards are so closely aligned that they share common elements and even common standards with electrical Ex standards and requirements.

AS/NZS(IEC)60079.0 – 1 – 2 – 31 & 34

AS/NZS(IEC)60079.0 – 1 – 2 – 31 & 34 apply to both to Ex mechanical and Ex electrical devices and

systems. The chart (preceding) illustrates the interaction and applicably of current “electrical” standards to

both electrical and mechanical Ex.

We are able to use three of the “electrical” techniques from the AS/NZS(IEC)60079 series of Standards and

apply the techniques equally to either “electrical” or “mechanical” devices or systems.

The techniques are;

  • Exd - Flameproof – AS/NZS(IEC)60079-1
  • Exp - Pressurisation (gas) - AS/NZS(IEC)60079-2
  • Ext - Enclosure (dust) – AS/NZS(IEC)60079-31

AS/NZS(ISO)80079.34 : Explosive Atmospheres – Application of quality systems for equipment manufacture.

This standard adds detail to AS/NZS(ISO)9001 and provides Quality Management System guidance to the manufacturers of Ex equipment. It does not differentiate between Ex Electrical and Ex mechanical.

 

ISO80079.36 : Non-electrical equipment for explosive atmospheres – Basic method and requirements

ISO80079.36 is the “core” standard for Ex mechanical devices and systems but it also relies on many of the provisions of AS/NZS(IEC)60079.0. This standard should be published early in 2016 and be available for use. It may be applied to couplings, pumps, gearboxes, brakes, hydraulic and pneumatic motors and any combination of devices to realise a machine, fan, engine, compressor, assemblies, etc.

Part 36 applies to Group I (methane), Group IIA, IIB & IIC (typically; propane, ethylene and hydrogen) and Group IIIA, IIIB & IIIC (dusts & flyings).

Part 36 applies ignition hazard assessments to mechanical devices and systems and identifies;

  • Possible ignition sources (any type of ignition source, hot surfaces, flames & hot gasses, mechanically generated sparks etc)
  • Equipment related ignition sources (by the equipment – regardless of its ignition capacity)
  • Potential ignition sources (by the equipment with the capability to ignite an explosive atmosphere)
  • Effective ignition sources [a potential ignition source, able to ignite an explosive atmosphere with consideration of when? Normal operation, expected malfunction or rare malfunction. (This determines the EPL)]

While EPLs and Zones overlap – they are different. Equipment Protection Levels (EPLs) consider not just likelihood, but also consequence – that is RISK.

ISO 80079.36 provides good guidance and some worked examples as to how ignition hazards are assessed and what the (EPLs) really mean in mechanical explosion protection

  • We need to decide what is tolerable in a given situation? Do we need to provide effective controls for malfunctions in normal operation, expected malfunctions and rare malfunctions? – If so, then we must aim for the top – for Group I that is EPL Ma and for Group II that is EPL Ga …. Or Da for dust & flyings.
  • Or can we provide a sufficient assurance of operational safety if we do not cater for rare malfunctions and just deal with malfunctions in normal operation and expected malfunctions? - for Group I that is EPL Mb and for Group II that is EPL Gb …. Or Db for dust & flyings.
  • Perhaps the consequence of an ignition is low enough that we can live with providing controls for malfunctions in normal operation? - for Group II that is EPL Gc …. Or Dc for dust & flyings.

 

ISO80079.37 : Non-electrical equipment for explosive atmospheres – Non electrical type of protection constructional safety ”c”, control of ignition source ”b”, liquid immersion ”k”

We then move to the mechanical (only) explosion-protection techniques that are available in order to achieve the pre-determined EPL.

ISO 800079.37 introduces and applies three specific, new, mechanical techniques.

  • Ex h(c) - Constructional safety
  • Ex h(b) - Control of ignition source
  • Ex h(k) - Liquid immersion

 

ISO80079.38 Equipment and components in explosive atmospheres in underground mines

This part of ISO/IEC 80079 specifies requirements for the constructional features of equipment and components that may be an individual item or form an assembly, to enable them to be used in mines, or parts of mines, susceptible to explosive atmospheres of firedamp and/or combustible dust.

Both non-electrical equipment and the interconnection of electrical/non-electrical equipment require an ignition hazard assessment.

This standard should be published early in 2016 and be available for use.

 

ISO80079.41 : Non-electrical equipment for explosive atmospheres – Ex Reciprocating internal combustion engines

This International Standard covers the technical requirements necessary to avoid or minimize the significant hazards identified, which could occur during normal operation, maintenance or foreseeable malfunction of reciprocating internal combustion engines intended for use in explosive atmospheres including

 

  • Group I EPL Mb for use in underground workings susceptible to firedamp and/or combustible dust,
  • Group II EPL Gb and Gc for use in potentially explosive atmospheres of flammable gas and vapour and
  • Group III EPL Db and Dc for use in potentially explosive atmospheres of combustible dust.

 

This standard is intended to cover all reciprocating internal combustion engines regardless of the fuel used and the means of ignition. (i.e. “spark” and “compression” engines are included)

This standard is in the early stages of preparation and it may be 3-4 years before publication.

AS/NZS3584.1:2015 Diesel Engine Systems for Underground Coal Mines

The Australian & New Zealand Standard, Diesel Engine Systems for Underground Coal Mines is well advanced – it should be out for “Public comment” soon. This new revision adopts and adapts the new mechanical Ex standards by;

  • Requiring an ignition hazard assessment from ISO 80079.36
  • Adopting and adapting the new Ex Techniques – Ex c, Ex k, Ex b, Ex d from ISO 80079.37
  • Using the Equipment Protection Level concept for EPL Mb (+ consideration of rare malfunctions)
  • Requiring a QMS – AS/NZS9001 + AS/NZS80079.34
  • Using functional safety analysis (SIL 2 min) for control systems where the control system is the prime oronly barrier preventing an effective ignition source
  • Going from simple regulatory concentrations for emissions to gravimetric determinations (g/kW/Hr) toEU Directives (EU Stage III min)
  • Making certification possible under the ANZEx Scheme

This standard should be published early in 2016 and be available for use.

Certification

General

It is not a requirement that any of the standards listed mandate certification under the provisions of the ATEX, IECEx or ANZEx Schemes. Generally standards provide reference to certification schemes as being one of the means of demonstrating compliance.

Many manufacturers may choose to test their device/equipment to the requirements of relevant standard(s) within a Testing Laboratory (TL) and have a Certificate of Conformity (CoC) issued by a Certifying Body (CB) under one or more of the Schemes. They may do this to demonstrate that the device/equipment is “fit-forpurpose” and that they are managing all inherent risks in an appropriate manner.

“Regulators” in some jurisdictions may mandate certification under one of the Schemes in Acts, Regulations or legal instrument. (e.g. a Gazette Notice.)

ANZEx Scheme

Work is progressing to include provisions for the testing and certification of mechanical Ex devices and equipment under the provisions of MP087.1.

Similarly, the probability is that the “Recognised Service Facility” program in MP087.2 will be extended to include both electrical and mechanical workshops. This may be particularly important when workshops wish to expand their scope to include both disciplines?

Under the ANZEx Scheme mechanical Ex devices and equipment may be certified to relevant AS standards, AS/NZS standards, IEC standards or ISO standards.

IECEx Scheme

Work is progressing to include provisions for the testing and certification of mechanical Ex devices and equipment under the provisions of the IECEx Scheme.

ExMC Working Group WG15 was formed to develop the necessary IECEx Scheme documents to enable inclusion of the IEC/ISO SC31M series of Standards covering non-electrical items to be included in the IECEx 02 Certified Equipment Scheme.

WG15 led by the Convener, Mr Jim Munro has held various meetings to consider the necessary documents, one being the Draft “Guide to certification of non-electrical equipment”, which was finalised during the recent May 2015 Toronto meeting of WG15.

This Draft document is now submitted for consideration by the IECEx Management Committee (ExMC) during its September 2015 annual meeting in Christchurch, NZ. It is reasonable to anticipate that these provisions will be adopted.

Disclaimer

The foregoing very brief summary of the current status, progress and interaction of standards and schemes as they relate to mechanical explosion-protection was written by Phil Berriman to better inform stakeholders and interested persons and at the request of some interested groups.

Any persons or organisations requiring more detailed or definitive information should contact the relevant organisations or bodies.

The views expressed are those of the author only. They do not purport to represent the views of Standards Australia (SA), Standards New Zealand (SNZ), International Electrotechnical Commission (IEC), International Electrotechnical Commission System for Certification (IECEx), International Standards Organisation (ISO) or any other organisation.

 

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