Explosion-proof motors - ATEX Grundfos

Explosion-proof motors - ATEX

What is ATEX?
ATEX (ATmosphère EXplosible) refers to two new EU directives about danger of explosion within different areas. The first ATEX directive (94/9/EC) deals with requirements put on equipment for use in areas with danger of explosion. The manufacturer has to fulfil the requirements and mark his products with categories.
The second ATEX directive (99/92/EC) deals with the minimum safety and health requirements that the owner of the equipment has to fulfil, when working in areas with danger of explosion.

What is explosive atmosphere?
According to the new directives, dust is now considered an explosive atmosphere. An explosive atmosphere is an atmosphere that develops explosively because an uncontrolable combustion.
Explosive atmosphere consists of air and some sort of combustible material such as gas, vapours, mists or dust in which the explosion spreads after ignition.
Typical examples of productions where combustible dust is of major concern, is the handling of cereals, animal feed, paper, wood, chemicals, plastics and coal.

Examples of sources of ignition that can cause the
atmosphere to explode:
• Electrical sparks
• Flames
• Hot surfaces/ spots
• Static electricity
• Electromagnetic radiation
• Chemical reaction
• Mechanical forces
• Mechanical friction
• Compression ignition
• Acoustic energy
• Ionising radiation

What is an explosive atmosphere?

An explosion is an uncontrolled combustion wave that produces a rapid increase in temperature and pressure. For an explosion to take place, three elements have to be present at the same time: fuel, (such as explosive gas) an oxidiser, (such as the oxygen in the
air) and a source of ignition, (such as electrical sparks).
The combination of these three elements is generally referred to as the Fire Triangle.

To generate a potentially explosive atmosphere, the mixture of fuel and oxidiser has to have a certain concentration. This concentration depends on the ambient pressure and the content of oxygen in the air, and is referred to as the explosion limits.
Outside these limits, the mixture of fuel and oxidiser will not ignite, but has the potential to do so if the proportions change. For an explosive atmosphere to form, a certain concentration of combustible material must be present.

Explosion-proof motors - ATEX

For an explosive atmosphere to ignite, a certain quantity of energy has to be present. Minimum ignition energy is defined as the smallest possible amount of energy that is converted during the discharge of a capacitor. It is the amount of energy that is just enough to ignite the most ignitable mixture of fuel and oxidiser. The minimum ignition energy is around 5 - 10 joules for hydrogen and a few joules for certain types of dust.

What kind of equipment does the ATEX directive 94/9/EC cover?
• Safety equipment and safety systems exposed to explosive gasses or dust.
• Safety, control and adjustment devices, which ensure a safe operation of production material and control equipment.
• Electrical, mechanical, hydraulic and pneumatic equipment including pumps and electric motors.


Which obligations do the ATEX directive
99/92/EC imply for the equipment owner?
 
To prevent explosion, the user of the equipment must:
• Take the necessary technical and organisational
precautions.
• Make a complete estimate of the risk of explosion
• Divide potential explosive risk areas, into zones.
• Indicate the danger zones clearly.

How is an explosive atmosphere
divided into zones?
 
The ATEX directive 99/92/EC distinguishes between two types of explosive atmospheres: gas and dust. Areas subjected to these two kinds of explosive atmospheres are each divided into three zones. The zone’s characteristics are identical for gas and dust, but
their numbering is different. Zones 0, 1, 2 refer to gas and zones 20, 21, 22 refer to dust.
Zone 0 / 20: Constant danger
Permanent presence of explosive gasses or combustible
dust. Minimum category 1 equipment.
Zone 1 / 21: Potential danger
Occasional presence of explosive gasses or combustible
dust during normal duty. Minimum category 2 equipment.
Zone 2 / 22: Minor danger
Presence of explosive gasses or combustible dust not
likely to occur or only for a shorter period of time.
Minimum category 3 equipment.
Grundfos manufactures pumps, with motors in both category 2 and category 3. The illustration on your right shows the division of an area into zones with different levels of danger of explosion. For each of the three zones it is only a certain category of equipment – in this case motors – that can be used due to danger of explosion.
The owner of the equipment is responsible for defining whether an area is to be considered hazardous within the regulations stated in the ATEX directive. However, if the user has any doubts about the definition of hazardous areas, he has to contact the proper authorities for advice.

How to ensure compliance with the
ATEX directives?

Equipment and zones have to comply with the ATEX directive. The CE marking is the proof that the equipment is manufactured according to all the basic requirements and assessment procedures that apply for every EU member state.

Who is responsible for meeting the
requirements in the ATEX directive?
Depending on whether you are the equipment manufacturer,
owner or service engineer there are certain
safety requirements that you have to fulfil.
The manufacturer
As manufacturer Grundfos is exclusively responsible
for producing equipment that meets the requirements
stated in the EU directive.
The user
The equipment owner has to inform Grundfos of what
kind of equipment he needs, as to:
- Category, e.g. 2G
- Temperature, e.g. 125°C
- Type of motor protection, e.g. EExe II T3
In addition, the equipment owner has to use the product according to the defined zones and thereby take any possible risks into account. Likewise, the equipment owner is responsible for ensuring that the equipment runs safely through continuous maintenance.
As per 1 July 2003, new installations must meet the requirements stated in the ATEX directive. If the equipment owner is also the manufacturer, the owner has to fulfil the requirements for both. Already existing installations have to comply with the requirements in the ATEX directive 99/92/EC by the latest on the 30rd june 2006.