§35 異なる爆発の可能性のある雰囲気とのインタフェース

This point seeks to provide guidance on the application of the ATEX Directive 2014/34/EU to equipment intended to operate with interfaces to different potentially explosive atmospheres.

At this point it is necessary to note that equipment that contains a potentially explosive atmosphere but is neither connected to, nor intended for use in, an external or process related potentially explosive atmosphere does not fall under the scope of Directive 2014/34/EU. However, any equipment inside this "container" will, so long as it fulfils the criteria for inclusion in scope, need to comply with the relevant provisions.

The categorisation of equipment is to be determined based on the ignition risk assessment by the manufacturer or his authorised representative and the equipment's relationship with respect to its interface with its process atmosphere and any external atmosphere.

The following diagram illustrates this point:

For example, the inside or process side of a pump for flammable liquid which normally runs full but occasionally contains an explosive atmosphere may, depending on the actual situation, be considered zone 1 if no other measures have been taken to prevent the pump running dry. If it has been decided that the surroundings or external explosive atmosphere is zone 2 then a pump conforming to category 2 inside and category 3 outside must be used to meet the essential health and safety requirements of the Directive.

Note: the process atmosphere zone (and the respective category) needs not necessarily to be the same for the two connections to the process atmosphere.

The following guidelines may help in the selection of an appropriate category:

The ATEX category (or categories) assigned to equipment shall be determined for each part of the equipment which comes into contact with, or is connected to, a zone with a potentially explosive atmosphere (see Directive 1999/92/EC).

The category assigned to a piece of equipment intended to contain a potentially explosive atmosphere not connected to the outside of that equipment is determined by the ignition risk associated with the outside parts of the equipment, not by its internal atmosphere i.e. only the part of the equipment which is intended to come into contact with a zone is relevant for the assignment of the appropriate category.

The category (or categories) assigned to the process connecting points of equipment containing an explosive atmosphere cannot be higher than that appropriate to the ignition risk.

For example, consider the case of a fan conveying an explosive gas atmosphere over its rotating blades, or a powder mill producing an explosive dust atmosphere inside the mill. Each having an outlet connected to an external potentially explosive atmosphere. The ignition risk assessment for both these items of equipment has shown for these specific examples that an effective ignition source (for the explosive atmosphere connected to them) is not present in normal operation but may be present in the case of an expected malfunction. If such equipment/assembly is placed on the market without additional ignition protection or a protective system, it can only be classified as category 3 (see section § 44 on combined equipment (assemblies)).

Such equipment can only be used when it is connected to an explosive atmosphere which is present continuously (i.e. zone 0/20) if additional ignition protection or a protective system is fitted (see Directive 1999/92/EC).

Where a piece of equipment is fitted with an autonomous protective system such as flame arresters, or a suppression system which is already compliant to Directive

2014/34/EU, additional testing and conformity assessment of the resulting assembly, i.e. equipment together with the protective system, is not required provided the protective system is used within its intended design capabilities covering the specific case, is installed in accordance with the manufacturer's instructions and no new ignition hazards are introduced. However, an ignition risk assessment will be required and relevant action taken if additional hazards are identified.

Similarly, Directive 2014/34/EU does not require that the pressure resistance of a vessel or container protected against the effects of an explosion by an autonomous protective system be tested, if it has been demonstrated that the autonomous protective system successfully detects and suppresses an explosion and if the vessel can withstand the residual pressure peak of the suppressed explosion.

Example

Note: The following is one of many examples that can be used to illustrate the above points. The assumptions made in this example should not be taken as the only possible situation. The categorisation of a particular piece of equipment will depend on the specific ignition hazard assessment that is made of the equipment and its intended use together with any ignition protection measures applied. The example only considers the inside and connecting explosive atmospheres, i.e. the process side. A separate ignition hazard assessment and categorisation must be made of the outside if the equipment is to be used in potentially explosive atmosphere.

Consider a powder mill as shown in the following scheme:

The ignition hazard assessment carried out by the manufacturer has identified that in this case:

there is no ignition source inside the mill which can become effective in normal operation;

there is an ignition source inside the mill which can become effective during expected malfunctions.

The highest category that can be assigned to the mill is therefore category 3 when it is placed on the market as shown. The outlet from the mill in this case produces fine dust in the form of a potentially explosive dust cloud which is continuously present in normal operation, i.e. category 1 is required. In cases when category 1 cannot be provided, the manufacturer has to take additional measures that the mill can used safely, e.g. to provide an explosion-resistant design of the mill. If the explosion safety can be reached through additional explosion prevention or protection measures of the end-user, the manufacturer's instructions must therefore make clear that the mill can only be used with these additional measures.

Analysis

Directive 2014/34/EU defines equipment as follows: - intended for use in potentially explosive atmospheres; - and/or for the processing of material; - capable of causing an explosion through their own potential sources of ignition.

This definition applies to the grinding assembly of a mill for combustible materials of the food and fodder industry. Therefore, these are within the scope of Directive 2014/34/EU.

The intended purpose of a grinding assembly in a mill is the grinding of combustible materials whereby the content of fine particles is increased considerably.

According to the risk assessment the grinding installation should fulfil the requirements for category 1, but in the best case it will meet category 3. Despite all construction measures to prevent ignition sources, the occurrence of dust explosions cannot be excluded definitely. Therefore, the mill when fully installed must be provided with additional protection measures, which reduce the effect of a dust explosion for people and goods to below a dangerous level.

These measures are essential for the grinding system to fulfil the requirements of Directive 2014/34/EU.

Consequently:

all requirements on the construction of the grinding assembly (e.g. suitable selection of material and bearings, minimum distances between rotating and fixed parts), on certain equipment of the mill (e.g. foreign particles separator, overload protection, temperature detector at the bearings) and

all construction measures of the mill (explosion pressure resistant design for the maximum explosion pressure, or explosion pressure resistant design for the reduced explosion pressure in combination with explosion pressure relief or explosion suppression, and in most cases additional explosion decoupling for connected installations) are necessary to make the grinding operation safe.