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ACADEMY

Understanding ATEX & NFPA Regulations

ATEX ATmosphere EXplosible means a mixture of combustible substances in the form of gas, vapor, mist, or combustible dust with air under atmospheric conditions. The combustion after ignition spreads throughout the unburned mixture.

According to European directives, the working environment has to be minimum safe enough for the workers from the explosion risk. And this risk assessment has to be taken care from the owner of the facility. That’s why zone criteria have to be pointed at the ATEX 137 Article with directive 1999/92/EC of the European Parliament. Machine producers have to give appropriate products to these zones, and this is also given in the ATEX 2014/34/EU Guideline.

NFPA regulations and calculations are similar but have to be recalculated according to dust/gas criteria, explosivity, etc. values and the design has to be rechecked.

A fire naturally occurs when the elements are present and combined in the right mixture.

We call it The Fire Triangle that fire needs to ignite: Heat, Fuel, and an Oxidizing Agent usually oxygen. If oxygen is missing then the fire will extinguish itself and we call LOC – Limiting Oxygen Concentration.

The fire triangle directly affects Explosion Pentagon while there are 2 other essential elements that affect the Explosion Pentagon Confinement and Mixture. For example, confinement and mixture increase will increase the Kst value.

On the other hand, if there will be missing concentration then there will be a lack of fuel and there will be no explosion, we call LEL – Lower Explosion Limit depending on the characteristics of the dust or gas.

If there will be too much concentration also there will be no explosion due to the lack of oxidizer and we call UEL – Upper Explosion Limit.

MIE – Minimum Ignition Energy is the lowest value of the electrical energy stored in a capacitor which ignites the most readily ignitable mixture at room temperature and atmospheric pressure. Pmax – Maximum Explosion Pressure that the maximum explosion pressure and the rate of pressure rise describe the violence of reaction in case of ignition. Pred – Reduced Explosion Pressure with venting device maximum explosion pressure is reduced to this pressure or overpressure from the vented explosion.

KSt maximum value of the pressure rise per unit time for dust in 1m3 vessel. KG maximum value of the pressure rise per unit time for gas in a 1m3 vessel.

ATEX Zone Classification & ATEX Category

Zones

ATmosphere – EXplosive

Equipment

Applications

Gases

Dusts

Group

Category

0

 

Continuously / Long Periods / Frequently

II

1G

Other Areas – Gas

 

20

(over 1000 hours per year or >10% of the time)

II

1D

Other Areas – Dust

1

 

Occasionally

II

2G

Other Areas – Gas

 

21

(10 – 1000 hours per year or 0.1 to 10% of the time)

II

2D

Other Areas – Dust

2

 

For a Short Period Only

II

3G

Other Areas – Gas

 

22

(under 10 hours per year or 0 to 0.1% of the time)

II

3D

Other Areas – Dust

ATEX 137 99/92/CE

I

M1

Mines

I

M2

Mines

ATEX 2014/34/EU

 

  1. ATEX 2014/34/EU Guideline
  2. ATEX 137 99/92/CE Directive
  3. NFPA 68, 484, 652
  4. EN 1127-1 – Non-electrical equipment for use in potentially explosive atmospheres – Part 1: Basic method and requirements
  5. EN 14460 – Explosion resistant equipment
  6. EN 14491 Dust explosion venting protective systems.
  7. EN 14994 Gas explosion venting protective systems.
  8. IEC 60079-0 – Explosive atmospheres – Part 0: Equipment – General requirements
  9. IEC 60079-7 – Explosive atmospheres – Part 7: Equipment protection by increased safety “e”
  10. IEC 60079-10-1 Explosive atmospheres – Part 10-1: Classification of areas – Explosive gas atmospheres
  11. IEC 60079-10-2 Explosive atmospheres – Part 10-2: Classification of areas – Explosive dust atmospheres
  12. ISO/IEC 80079-20-2 Explosive atmospheres – Part 36: Non-electrical equipment for explosive atmospheres – Basic method and requirements
  13. ISO/IEC 80079-34 Explosive atmospheres Application of quality systems for equipment manufacture