Explosion protection and potentially explosive zones

Even a small spark or hot surface is often enough to cause extremely serious industrial accidents in potentially explosive working environments, in other words wherever the handling of flammable substances is part of everyday work, for example in the chemical industry or the oil and gas sector. But even in some areas of the processing industry such as the textile, wood or food industries, explosions caused by flour dust for example can also have devastating effects, endangering human lives and causing high financial costs. Occupational health and safety is the top priority here and electric motors must ensure this high level of safety by means of a special design and the appropriate certification to prevent accidents at work and protect human lives.

When do potentially explosive atmospheres exist?

A potentially explosive working environment can exist if the following factors occur simultaneously:

  1. a flammable substance (gas or dust) and oxygen O2 (air)
  2. a source of ignition (spark, hot surface, smoldering nests etc.)
  3. a specific ratio of oxygen to flammable substance

The risk of an explosion must be evaluated in a risk assessment. Various aspects must be considered when determining the potential hazard:

  • Are potentially flammable solid, gaseous, liquid or dust-like substances present in a plant or a facility, or can they occur in the work process and, if so, where they can arise (inside equipment, for example)?
  • What quantities of explosive atmosphere can be present or can arise?
  • Are the expected quantities of an explosive atmosphere hazardous due to local and operational conditions and can they be prevented from forming?

How are hazardous zones classified?

Hazardous areas are divided into the following zones according to the frequency and duration of occurrence of a potentially explosive atmosphere:
Explosion hazard 
Continuous, over prolonged periods or frequently
Occasional
Not normally likely or only for short periods
Gases, vapors, mist

Zone 0

An area in which a dangerous potentially explosive atmosphere consisting of a mixture of air and flammable gases, vapors, or mist is present continuously, frequently or for long periods. 

Zone 1

An area in which a potentially explosive atmosphere consisting of a mixture of air and flammable gases, vapors, or mist occasionally occurs during normal operations. 

Zone 2

An area in which a dangerous potentially explosive atmosphere consisting of a mixture of air and flammable gases, vapors, or mist never, rarely or only briefly occurs during normal operations.

Dusts

Zone 20

An area in which a dangerous potentially explosive atmosphere in the form of a cloud of combustible dust in the air is present continuously or for extended periods or frequently.

Zone 21

An area in which a potentially explosive atmosphere in the form of a cloud of combustible dust in the air is likely to occur occasionally during normal operations. 

Zone 22

An area in which a dangerous potentially explosive atmosphere in the form of a cloud of combustible dust in the air is not likely to occur, or only for short periods, during normal operations.

Key Visual SIMOTICS XP

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You'll be safer than ever with SIMOTICS XP explosion-proof motors from Siemens. This is because our rugged explosion-proof motors run for a very long time and are absolutely fail-safe, even under the most extreme conditions – for line as well as converter operation. These motors have proven themselves hundreds of thousands of times worldwide. 

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