Standards Update

25 August 2011

How important are international standards in the Ex world? How widely are they adopted? Who produces and revises them? How much influence can my country have on the content? How can I get involved? What is Committee TC 31 and why do there seem to be several TC 31s? What standards does TC 31 develop? How can I get my Ex equipment certified to the TC 31 standards?

Jim Munro

I get these and many other questions as Chairman of International Electrotechnical Commission (IEC) Committee TC 31 Equipment for Explosive Atmospheres. In this article and subsequent articles I hope to unravel some of the mysteries.

First let’s just cover a couple of basics. When I talk about explosive atmospheres, I am addressing flammable substances in the form of gas, vapour, dust, fibres, or flyings mixed with air. Equipment covers both electrical and non-electrical equipment. The colloquial term Ex Equipment is now often used for such equipment when it is designed for explosive atmospheres.

So looking first at standards, I recently attended a session in Geneva of the United Nations Economic Commission for Europe (UNECE) Committee on Trade. This was particularly focused on developing countries covering all types of trade potential. I was fascinated to hear how often the use of standards, preferably international standards, together with the need for appropriate certification, was mentioned. This was relevant to both importing and exporting. Of course in the Ex field they are also critical for safety. Effective international standards have become a need in everything we do in recent times.

However, the need for international standards in the Ex field was recognised back in 1948 when the International Electrotechnical Commission founded Committee TC 31. The initial standards were simplistic by today’s standards. The first standard on pressurisation published in 1962 was only a few pages. Since then the number of standards has grown significantly and the size of standards has also grown. For the example above, the pressurisation standard is now 111 pages and to this needs to be added the requirements in general requirements standard.

But the most significant achievement in recent years is that the adoption of the IEC TC 31 standards at national and regional level has been widespread. They also form the basis for certification of Ex equipment, in particular in the international IECEx System.

So this takes us into the first two questions; how important are international standards in the Ex world; how widely are they adopted?

If you check the electrical Ex standards being used throughout the world now, you will find most countries are using them with few or no changes. Often the differences are not technical. For example, in Europe the marking requirements have to be modified to bring them into the line with the ATEX Directive 94/9/EC. The IECEx Bulletin provides a good source of information on differences between countries’ standards and the IEC standards. If we take a couple of standards, out of 30 countries, 24 accept the latest Ex d standard, IEC 60079-1, without change and 25 accept the Ex p standard, IEC 60079-2, without change.

One of the key reasons that the standards are getting such acceptance is the active involvement of so many countries in TC 31. This gives them the opportunity to have input into getting the content of international standards to meet their needs and to improve their confidence in the standards. IEC TC 31 has 34 participating countries, called P-members, and 12 observer countries. Most countries have suspended their direct development of standards that are covered by TC 31 in favour of working under the TC 31 umbrella. 27 of the 30 member countries of IECEx are P-members of IEC TC 31 and the other 3 are O-members. Within TC 31 there are large numbers of active participants working on many projects helping us produce standards that are relevant and acceptable.

Before moving on, let’s clear up the TC 31 question. In IEC, ‘TC’ is short for ‘Technical Committee’ it would have been the 31st technical committee formed by IEC, hence the ‘31’. However, throughout the world probably in most, if not all, the member countries there are mirror committees of TC 31. These are normally numbered according to a system of the local standards body. However, there are instances where the mirror committee adopts essentially the same numbering to reflect its relationship to IEC TC 31. The most well known of these is the CENELEC mirror committee of IEC TC 31 which is designated as CENELEC CLC/TC 31 Electrical apparatus for potentially explosive atmospheres.

Sometimes the link is not quite so direct. In China, while their mirror committee is SAC/TC9, they do have a China Office of IEC/TC31. There is also an ISO committee TC 31. But this is ISO/TC 31 Tyres, Rims and Valves and so has no relevance to explosive atmospheres. So ‘TC 31’ can appear in a variety of places. In this article, unless otherwise indicated, I will be talking about the TC 31 committee located within IEC.

The process of adoption of the TC 31 standards in other countries varies. In Europe in recent years most of the IEC TC 31 standards have been submitted for what is called parallel voting, as prEN within CENELEC. This occurs at the committee draft for voting (CDV) and Final Draft International Standard (FDIS) stage. It occurs in line with an agreement signed in 1996 between IEC and CENELEC, call the Dresden Agreement. Other countries may go through a similar process or may wait until a standard is published before seeking acceptance in their own countries. Hence the period for adoption of standards can be quite variable.

IEC Technical Committee TC31 Equipment for explosive atmospheres
So let’s look a bit closer at what IEC Technical Committee TC 31 does. The scope of TC 31 is to prepare and maintain international standards relating to equipment for use where there is a hazard due to the possible presence of explosive atmospheres of gases, vapours, mists or combustible dusts. A few years back the name and scope of the committee were changed to remove reference to electrical equipment to open up the option of covering non-electrical equipment.

TC 31 has 3 sub-committees, 7 working groups, 2 joint working groups, one project team, 11 maintenance teams and 2 ad-hoc working groups. It has 34 participating countries, called P-Members, and 12 observer countries, called O-Members. The subcommittees also have working groups, project teams and maintenance teams. The total committee is responsible for over 40 standards associated with hazardous areas.

The secretariat of TC 31 is held by the UK, with Mick Maghar being the current secretary.
The three subcommittees of TC 31 are:

• SC 31G Intrinsically-safe apparatus - the secretariat for this subcommittee is also in the UK.

• SC 31J Classification of hazardous areas and installation requirements - the secretariat for this subcommittee is Croatia.

• SC 31M Non-electrical equipment and protective systems for explosive atmospheres - the secretariat for this subcommittee is in Germany.

Contact Details and Archive...

• International Electrotechnical Commission (IEC)

Print this page | E-mail this page

E-mail this page

Your name :
Recipient name :
Recipient e-mail :
Enter the code shown :