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    The reasons why you need ATEX protection

Relevant news for plant engineers and operators

An explosion is the sudden release of mechanical and thermal energies. In simple terms, an explosion suddenly releases motion energy, heat and pressure into the environment in an abrupt manner.

Three things are needed for an explosion: air, more exactly oxygen, a certain ignition energy as ignition source and some combustible material. In this case, the oxygen as well as the combustible material feed the flames that have ignited through sufficient ignition energy. If these three components are in a certain proportion to each other, an explosion may occur. In the opposite case, should any of these factors be missing, there will be no explosion.

graphic Explosion triangle

The relation of the three factors can be described with the help of limits. There is a so-called lower explosion limit and an upper explosion limit. These limits refer to the ratio between combustible material and oxygen. The limits describe an extremely low concentration or an over-concentration of the combustible substance, as a result of which a flame cannot propagate independently when being ignited.

The range within these limits is known as explosive atmosphere.

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Combustible materials are substances that in the event of ignition produce an exothermal reaction with oxygen. An exothermal reaction releases heat to the environment. This describes the sudden release of thermal energy as mentioned earlier. If enough heat is released to ignite nearby substances, a chain reaction takes place. More and more particles ignite each other. If this happens in an abrupt manner, we speak of an explosion. Even solid substances such as flour, coal, starch etc. may become explosive. Especially fine dust has particles smaller than 0,5 mm and forms large surfaces that absorb the heat easily. Then the individual particles ignite rapidly and oxidise quickly. For comparison, a compact solid body such as a metal plate or a piece of coal would not even be combustible.

Accordingly, combustible materials may be gaseous or solid, or they consist of steam or a mixture thereof.

It is getting delicate.

In closed rooms of more than ≥ 100 m³, already 10 litres of coherent explosive atmosphere are considered dangerous. If the room volume is less, a smaller amount is sufficient to be regarded as explosive.

In this context, a coherent atmosphere describes the mixture of combustible materials with air-borne oxygen.

Be wise! Always remember this!

The following rule of thumb can be used as a rough estimate: A danger exists in enclosed spaces with a coherent, explosive atmosphere of ≥ 1/10,000.

Some nice checklists for you!

Rules & laws…

  • ATEX Operational Directive 1999/92/EG
  • ATEX Product Directive 2014/34/EU
    for ex. DIN EN ISO 80079-36, EN 1127-1 (harmonised standard)
  • As well as the respective nationally applicable regulations derived from the mentioned directives.

Do you use self-acting industrial valves? Notice…

These ignition sources must be taken into account according to EN 1127-1 for the use of automatic control valves.

  • Hot surfaces
  • Flames and hot gases incl. hot particles 
  • Mechanically generated sparks
  • Electrical Installations
  • Electrical transient currents, cathodic corrosion protection
  • Static electricity: Electrostatic discharge as a result of separation processes in which at least one rechargeable substance is involved
  • Stroke of lightning
  • Electromagnetic waves in the frequency range from 104 Hz to 3 x 1011 Hz
  • Electromagnetic waves in the frequency range from 3 x 1011 Hz to 3 x 1015 Hz
  • Ionising radiation
  • Ultrasound
  • Adiabatic compression and shock waves 
  • Exothermic reaction including spontaneous ignition of dusts

The maximum surface temperature…

The maximum surface temperature of the device must be determined, corrected by the indicated safety margins. This information is essential for all device parts that come into contact with the potentially explosive area or on which a dust layer may form, in order to assess the ignition hazard and the ignition source and to define the hazard-free use via the temperature class.

If the surface temperature does not depend on the device itself but mainly on the operating conditions, the pertinent information must be included in the operating instructions and the device must be suitably marked.

The max. surface temperature of the device must not exceed the limits of the temperature class specified in the table.

Temperature class Max. permitted surface temperature of the equipment Ignition temperature of the combustible matter Examples
T1 450 °C > 450 °C acetone (540 °C), propane (470 °C)
T2 300 °C > 300 °C ... ≤ 450 °C n-butane (365 °C), ethylene (425 °C)
T3 200 °C > 200 °C ... ≤ 300 °C petrol (220 - 330 °C)
T4 135 °C > 135 °C ... ≤ 200 °C ethyl ether (180 °C)
T5 100 °C > 100 °C ... ≤ 135 °C
T6 85 °C > 85 °C ... ≤ 100 °C carbon disulphide (95 °C)

To select the suitable valve for the customers‘ applications, the groups I or II are relevant (I Mining, II Industry (gases and dusts)).

As additional information, the explosion group (gas type, dust type) should be defined. Gas type IIA IIB IIC, dust type IIIA, IIIB, IIIC. Here the groups marked with C are substances with low required ignition energy.

In addition, the device category is necessary in order to maintain the required safety level. Category M1 and M2 for group I (mining), categories 1, 2, 3 for II and III (gases and dusts). The smaller the category number, the higher the protection level as well as the pertaining design and inspection efforts.

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