Covering all bases

Safety of electrical and non-electrical equipment in Ex areas

By Claire Marchand

Miners had learnt the hard way that their jobs were fraught with risks – fire damp, methane accumulation or suspended coal dust – when electric power was introduced. All it took to ignite methane for instance was a spark emitted by a lighting fixture or a motor. And the rapid growth of the oil and gas industry in the 20th century and the numerous accidents and explosions that occurred in oil drilling operations and refineries raised awareness of the dangers facing those working in this sector.

ABC mine ventilation fan Underground mines are equipped with ventilation fans (Photo: ABC Ventilation Systems)

Early involvement of the IEC

The need to develop specific techniques to reduce or eliminate the risk of explosion for electrical equipment used in hazardous areas involving gases, vapours and mists led the IEC to establish Technical Committee (TC) 31: Equipment for explosive atmospheres. That was in July 1948. 

For close to 70 years, the TC and its Subcommittees (SCs) have published International Standards – the IEC 60079 series – covering the life-cycle of electrical equipment from design and manufacture to installation, maintenance and repair. Area classification and inspection are also addressed in TC 31 publications. 

Extended scope

To meet industry needs, the mining sector in particular, decision was made in 2007 to initiate standardization work addressing non-electrical equipment used in explosive atmospheres. 

In 2007, a joint decision made by the IEC and the International Organization for Standardization (ISO), through the IEC Standardization Management Board (SMB) and the ISO Technical Management Board (TMB), led to the establishment of SC 31M: Non-electrical equipment and protective systems for explosive atmospheres. 

Non-electrical equipment is defined as "equipment which can achieve its intended function mechanically". Protective system is defined as “devices other than components of the equipment which are intended to halt incipient explosions immediately and/or to limit the effective range of an explosion". 

SC 31M is authorized to produce both ISO and ISO/IEC International Standards within IEC and IEC TC 31. The development process occurs according to IEC procedures but voting on Committee Draft for Vote (CDV) and Final Draft International Standard (FDIS) documents is conducted in parallel, with each organization following its own rules for voting. 

While all International Standards developed by IEC TC 31 and its SCs follow the IEC numbering, i.e. IEC 60079-x, SC 31M publications are in the ISO/IEC 80079-x series. The first Standard issued by SC 31M was ISO/IEC 80079-34, Explosive atmospheres – Part 34: Application of quality systems for equipment manufacture, in 2011. 

Electrical and non-electrical equipment for the mining sector

Most of the electrical equipment used on mining machinery is certified as an individual item of equipment, e.g. the motor or the switchgear, and meets its own marking requirements. This certification, however, does not deal with the interconnection of these items of equipment by cables or with the machine electrical power system as an entity. The equipment and components, including their interconnections, should be assessed, from an ignition point of view, by the manufacturer. Both non-electrical equipment and the interconnection of electrical/non-electrical equipment require an ignition hazard assessment. 

New publications

New International Standards were added to the series in February 2016. Two were dual logo: 

The first, ISO/IEC 80079-20-2, Explosive atmospheres - Part 20-2: Material characteristics - Combustible dusts test methods, describes the test methods for the identification of combustible dust and combustible dust layers to permit classification of areas where such materials exist. This in turn allows the proper selection and installation of electrical and mechanical equipment in the presence of combustible dust. This first edition cancels and replaces the first edition of IEC 61241-2-1 published in 1994, the first edition of IEC 61241-2-2 published in 1993 and the first edition of IEC 61241-2-3 published in 1994, combining the requirements into a single document. 

The second, ISO/IEC 80079-38, Explosive atmospheres - Part 38: Equipment and components in explosive atmospheres in underground mines, specifies the explosion protection requirements for the design, construction, assessment and information for use (maintenance, repair, marking) of equipment that may be an individual item or form an assembly. This includes machinery and components for use in mines susceptible to explosive atmospheres of firedamp and/or combustible dust. It also deals with the prevention of ignitions of explosive atmospheres caused by burning (or smoldering) of combustible material such as fabric fibres, plastic "O"-rings, rubber seals, lubricating oils or greases used in the construction of the equipment if such items could be an ignition source. 

Two others were published under the ISO logo: 

  • ISO 80079-36, Explosive atmospheres - Part 36: Non-electrical equipment for explosive atmospheres - Basic method and requirements
  • ISO 80079-37, Explosive atmospheres - Part 37: Non-electrical equipment for explosive atmospheres - Non electrical type of protection constructional safety "c", control of ignition source "b", liquid immersion "k"

More information on IECEx:

ABC mine ventilation fan Underground mines are equipped with ventilation fans (Photo: ABC Ventilation Systems)
A worker operating a mine machinery with remote control Operating machinery via remote control in a mine (Photo: imgur_blog_goodyoda13)
A worker drilling mine in India Drilling blast holes to reach the high grade zinc ore in the Rampura Agucha mine in India (Photo: Mining & Construction)