Don't Let It Happen to You
Published: 10th Apr 2003
The new European Union 'ATEX1' legislation provides a timely reminder of the dangers that lurk wherever flammable substances are present. There are too many grim pictures of the devastation that can be caused if the proper precautions are not taken.
From the early days of coal mining when ignition of the naturally-occurring firedamp caused disastrous explosions to the modern petro-chemical plant where lack of care leads to loss of life and livelihood the hazards of potentially explosive atmospheres have been recognised.
The new legislation comes from two strands of the EU's process of achieving convergence of the laws of the member states. One strand involves improving the conditions for workers so as to protect their health and safety. Directive 1999/92/EC 2 requires employers to minimise the risk from potentially explosive atmospheres by adopting appropriate safety measures. Amongst these is the use of equipment complying with a directive from the other strand of legislation which is primarily about allowing products to circulate freely within the EU. Directive 94/9/EC 3 sets the requirements which must be met before products within the scope of the directive can be placed on the market or put into service within the EU.
But why is this legislation necessary, what is the underlying philosophy and what effect is it likely to have?
Need for legislation
The two areas of legislation relate to safety of workers and removal of trade barriers. There is already extensive legislation in both fields but the regulators are caught between two groups:
those who believe that there is already too much and those who are more comfortable if they have more detailed requirements with which to comply. The skill of those drafting the directives is to spell out the duties of those affected while leaving them to decide on how they will carry out those duties.
The legislation sets out the minimum standards expected of employers and the standards expected of products for use at work. As a result, the working conditions throughout the EU must reach a level regarded by the member states as being the minimum that is acceptable. This outcome ensures that workers are protected from harm and also that employers cannot compete on a basis of lower costs from unsafe working practices. At the same time, the safety of workplaces can be assured through the supply of suitable products while, once again, suppliers cannot compete on the basis of making products to inferior standards.
Explosion hazard area philosophy
When looking at the philosophy for protection against explosion hazards, the place to start is the ATEX worker protection directive 1999/92/EC. Here the usual documented risk assessment and control process is defined. The aim is to reduce the likelihood of harm to people to an acceptably low level. Fig 1 illustrates the measures that need to be considered.
The explosion safety hierarchy follows the steps:
The first step is obvious but often impossible to achieve, since the substances are either naturally occurring, as in the case of firedamp in coal mines, or inherent in the process, such as the occurrence of sawdust in a timber sawmill. However if substitution is not possible, consideration must be given to keeping people as far away from endangered areas as possible. For the purposes of the ATEX legislation, a flammable substance is taken to mean a gas, vapour, mist or dust which, when mixed with air, is capable of being ignited under normal atmospheric conditions.
Looking at Step 2 it is necessary to consider what we mean by an explosive atmosphere and the subtle difference between that and a potentially explosive atmosphere. Fig 2 illustrates the idea that a mixture of a flammable substance with air can be ignited when the concentration is right. The limits of explosibility are known as the lower explosion limit (LEL) and the upper explosion limit (UEL). Outside the explosible range, the mixture forms a potentially explosive atmosphere, in that a change in concentration can take the mixture to within the explosion limits. Such a change might happen through a build up of the flammable substance for a mixture below the LEL or a dilution with air if the mixture is above the UEL.
To conform to the requirements for Step 2 it is necessary to prevent the flammable substance from leaking into the air or to prevent air from leaking into the containment system for the flammable substance. If releases of the flammable substance are unavoidable, for example at loading or draw-off points, then measures are required to disperse and dilute them to keep them below the LEL. Particular care is needed at start up and shut down of process plants, and during maintenance operations.
If Step 2 is insufficient to reduce the risk of fire and explosion to an acceptably low level, we enter the area where most of the explosion safety technology has been concentrated over the past 100 years, the prevention of ignition of explosive atmospheres. Through the work of the International Electrotechnical Commission there is now a classification system accepted in most parts of the World which defines three zones of risk that an explosive atmosphere will occur. For gas atmospheres the following system is used:
Zone 0: explosive atmosphere present continuously or for long periods of time.
Zone 1: explosive atmosphere likely to occur occasionally in normal operation.
Zone 2: explosive atmosphere not likely to occur in normal operation and then only infrequently and for short periods of time.
A similar system is used for combustible dust atmospheres with a "2" prefix to give Zones 20, 21, 22.
In addition, reference is made to the misleadingly named "nonhazardous area", meaning an area where it is safe to place ignition sources, not where a person would be safe if an explosion were to occur in one of the hazardous zones. The zone system is incorporated in the ATEX directives, explicitly in 1999/92/EC and implicitly in 94/9/EC.
Having defined the zones of hazard, attention turns to Step 3, the control of potential ignition sources. This is where Directive 94/9/EC comes into the picture. Once again, the first priority is to avoid any ignition sources within the hazard zones. And once again this is not easy to achieve, because of the many items which, under worst case circumstances, could ignite an explosive atmosphere. Ignition sources can be categorised broadly into those producing arcs and sparks such as electrical switch contacts, mechanically rubbing surfaces and electrostatic discharges, and those arising from hot surfaces, whether from electrical, mechanical or chemical processes.
Directive 94/9/EC follows the risk-based approach by defining three categories of product according to the level of protection against an ignition source becoming active. Category 1 products provide a very high level of protection of ignition sources, Category 2 products provide a high level of protection while Category 3 products provide a normal level. These levels are not defined in the Directive other than by reference to the intended use of products in areas meeting the definitions of Zones 0, 1 and 2 respectively.
Explosive atmospheres formed by some flammable substances are more easily ignited than others and behave differently with the different types of ignition sources. Fig 3 shows the classification for gases and vapours, while for combustible dusts a different system is used.
The control of potential ignition sources has been the subject of extensive research in many parts of the World over the past 100 years. A range of different types of ignition protection was identified, based on removing one of the three essential ingredients for ignition as indicated in Fig 4. Standards were developed first at national then at international levels for electrically powered equipment as shown in Fig 4.
Directive 94/9/EC raised the need for a similar system to be developed for the non-electrical sources of ignition. CEN, one of the European standardisation organisations, is developing a range of standards that will define similar measures to those adopted for electrical equipment.
The last defence against explosions is found at Step 4 in the hierarchy, where Directive 94/9/EC again focuses attention on an area that has had little attention from a standardisation point of view. The idea here is that an explosion that cannot be prevented can be controlled in such a way as to remove the danger to people. There are four basic methods as shown in Fig 5. Directive 94/9/EC refers to the products through which these methods are applied under the collective term of "protective systems". CEN is developing a further range of standards for these products.
Directive 1999/92/EC requires employers to select the appropriate products as defined in Directive 94/9/EC when implementing their risk control system. Other key measures are proper training for people, co-ordination of the activities of different employers on the site, and marking of hazardous zones with the sign shown in Fig 6.
Impact of ATEX legislation
So what effect is the new legislation going to have on those involved in the operation of plants where explosion hazards might exist and on those supplying products for use in those areas?
As usual, the phrase "it all depends" comes to mind. For those who have kept abreast of technological developments in the field of explosion protection there should be little impact on the practical level. The most obvious effect is the requirement for the risk control measures to be demonstrably adequate and for the documentation to be sufficiently explicit. The requirement in Directive 1999/92/EC for an explosion protection document to be drawn up should be met by current risk assessments of hazardous operations provided that they have been kept up to date.
Employers who have not given sufficient attention to explosion risk control will find that they will have a lot of work on their hands. The hazards need to be identified, the risks assessed and the necessary control measures introduced. This situation is likely to occur in small and medium enterprises where the level of expert knowledge might be limited. It could also prevail in older process plants where the original risk assessments such as hazardous area classification have not been re-evaluated as changes have been introduced and where the people with the detailed knowledge of the safety risks have moved on.
For employers with existing plants where flammable substances may be present, the explosion protection document and all risk control measures must be in place by 30 June 2006. Any new or modified plant brought into operation after 30 June 2003 must comply from the date of commissioning. There is no need to replace existing equipment not in compliance with Directive 94/9/EC, provided that the risk assessment shows that an acceptable risk level is being achieved.
Manufacturers of products for use in potentially explosive atmospheres have a greater task to accomplish. All products placed on the market after 30 June 2003 for use in the EU must comply with the Directive. Electrical products need to be re-certified to the ATEX requirements, including an additional marking code (See Fig 7). Directive 94/9/EC applies also to non-electrical products which could constitute ignition sources and to protective systems. Manufacturers of these last two groups of products have a greater change to contend with. Firstly, there will be new standards to be applied, and secondly they will not previously have been involved with the conformity assessment procedures required by ATEX. Although the Directive does not require the use of standards, it is the method most commonly applied because it reduces the uncertainty as to what constitutes a compliant product.
The Directive specifies essential health and safety requirements for all products coming within its scope. The European standardisation bodies CEN and CENELEC have developed standards which add substance to the essential requirements such that designers, manufacturers and certifiers have a more precise specification to work to. The European Commission, which has mandated the bodies to produce the standards, publishes a list of the standards in the Official Journal of the European Communities.
Once the list is published, the standards are regarded as "harmonised" under the terms of Directive 94/9/EC . The Directive requires manufacturers to work to the current state of technological knowledge, so when standards are amended it will be necessary to make changes to products that are affected by the changes. The list of harmonised standards gives the date of withdrawal of the previous versions of the standards, as advised by the standardisation bodies.
The other aspect of Directive 94/9/EC relates to the conformity assessment procedures that are required. Manufacturers are responsible for ensuring that the correct procedures are used but in many cases they will need to use the services of a "notified body". Notified bodies are certification bodies which have been appointed by their member states to carry out certain of the conformity assessment procedures. The member states notify the European Commission of the bodies they have appointed, hence the term "notified".
The legislators who drafted the Directive selected the conformity assessment procedures according to the risks involved in the use of the products. Category 1 products require the design and production to be assessed by a notified body. Electrical products and internal combustion engines coming within Category 2 also require notified body assessment, while non-electrical Category 2 products together with Category 3 products are subject to the manufacturer's self-declaration of compliance.
The new ATEX legislation is intended to align the worker safety and product safety laws in the member states. For those who maintain a high standard and keep abreast of technological developments in the safety field there will be little technical change and a relatively small amount of procedural change to contend with. For those who have let standards slip or are not well informed on the control of explosion risks, the legislation is a wake up call. Let us hope that they heed it before disaster strikes. _
Useful sources of information
Worker safety directive 1999/92/EC: http://europa.eu.int/eur-lex/en/search/search_lif.html
Year: 1999, Document Number: 92, Type of document: Directive http://www.hse.gov.uk/spd/frameset/dsear.htm B, http://europa.eu.int/comm/enterprise/atex/index.ht m www.dti.gov.uk/strd/atex.htm
Ian Cleare is an independent adviser on conformity assurance and explosion safety. He is the Managing Director of Buxton Technology Ltd, a provider of independent technical advice to manufacturers, users, certification bodies, industry associations, standardisation bodies and regulatory authorities in the fields of ATEX and conformity assessment. He was director of the Health and Safety Executive's Electrical Equipment Certification Service at Buxton from 1987 to 2002. During that time he played a leading role in the setting up of the worldwide IECEx certification scheme and was involved in the negotiations leading to the ATEX 94/9/EC directive. Before joining HSE, Ian had held senior management roles in manufacturing industry after qualifying as a professional engineer.
Tel/Fax: +44 (0) 1298 85200.
Published: 10th Apr 2003 in Health and Safety International