ATEX and fuel burning equipment.

Some confusion has arisen with the ATEX directive and its application to fuel burning equipment.

Apart from domestic gas appliances which are specifically excluded from the scope of the directive, there are no specific exclusions in the directive itself for other gas and oil burning equipment but the guidelines interpret them to be outside the scope of the directive.

Explosive atmospheres in the combustion chamber arising from fuel released at the nozzle but not burned immediately are excluded from the ATEX directive by an interpretation in guideline 4.1.2 and the EC's ATEX directive standing committee decision of 6&7 Feb 2003.

This risk must still be assessed according to Machinery Directive EHSR 1.5.7. This would normally be protected with a flame failure and lockout system of adequate reliability.

Further details on the requirements for fuel handling systems for equipment within the scope of the machinery directive may be found in the appropriate harmonised standards, e.g. EN 746-2 Industrial thermoprocessing equipment. Safety requirements for combustion and fuel handling systems.

Although these flame failure and lockout systems may appear to be safety accessories in the terms of the ATEX directive, they are not within the scope of the directive because protective equipment is only defined as equipment which controls sources of ignition not the formation of explosive atmospheres.

The zoning standard EN 60079-10 classifies the following areas as secondary sources of release:

• seals of pumps, compressors and valves

• flanges connections and pipe fittings

• relief valves, vents and other openings where releases are not expected as part of normal operation.

In layman’s terms this means that these appliances are prone to leaks from fuel pipework and valves. Clearly ignition sources such as hot surfaces and flames are unavoidable.

The European Commission's ATEX directive standing committee and other National committees have discussed the issue and agreed that "as a general rule, such types of equipment are excluded from the Directive". The ATEX directive standing committee's decision of 6&7 Feb 2003 is explained rather ambiguously.

This is not a firm exclusion from the ATEX directive, and is not backed up with a reasoned technical justification. It seems they are implying that fuel burning equipment in general is excluded. Unfortunately the standing committee cannot say this directly because they are only meant to interpret the directive not change or add to it.

The Notified Body view is that they would not expect a fuel burning appliance to be certified for ATEX unless it was intended for use in an explosive atmosphere arising from a separate source of release. As far as the Notified Bodies are concerned, it is the manufacturer’s responsibility to determine whether the directive applies by assessing whether explosive atmospheres can occur and, if they can, whether the equipment has its own ignition sources which can become active.

The way manufacturers usually justify that an explosive atmosphere cannot occur is as follows:

• Minimise the risk of leaks by making the fuel line adequately robust with minimal joints.

• For oil fired equipment, prevent leaking fuel from being raised above its flashpoint by routing the fuel line away from hot surfaces.

• Ensure that there is adequate ventilation in the installed location. This will ensure that small leaks are diluted below their lower explosion limit before they form a hazardous explosive atmosphere. In many places, including the UK, only approved fitters are allowed to install gas appliances and ventilation is one of the things their codes of practice require them to consider.

• Recommend the user to isolate the gas supply and ventilate the area if they smell gas. Alternatively gas detection monitors can be installed.

• Recommend the user to test for leaks as part of regular servicing

If sources of release are still considered likely to cause an explosive atmosphere in spite of these measures, then it will be necessary to carry out an explosion risk assessment and demonstrate that sources of ignition have been adequately protected.

This same issue of sources of release and unavoidable ignition sources is much worse with gas turbines because they are hotter and have much more pipework and fuel around. The ATEX standing committee have decided that these are within the scope of the directive and explained how explosions are avoided.

There is no need to certify fuel burning equipment in case the user installs it in an explosive atmosphere without the manufacturer’s permission. Under the ATEX worker directive 1999/92/EC (The Dangerous Substances and Explosive Atmospheres Regulations 2003 in the UK) employers are required to ensure that equipment for explosive atmospheres is suitable. If it is not supplied with the Ex logo and a declaration of conformity to the ATEX equipment directive, the user cannot install it in an explosive atmosphere. For extra clarity, some manufacturers include a warning in the installation instructions "Not for use in explosive atmospheres".