Zoning in on Explosive Atmospheres

Everybody wants to wake up in the morning and know they’re going to a safe workplace. A major safety concern among certain industries is the occurrence of fires and explosions. This makes for some of the most expansive safety codes and standards. This article is aimed at explaining hazardous area classification in simple terms for easy comprehension. Before we begin to classify hazardous areas, it is crucial to define what they are.

What is a hazardous area?

A hazardous area is a place in which an explosive atmosphere may occur in quantities requiring the implementation of special precautions to protect the health and safety of workers. Hazardous areas are classified into two major categories: gases/vapors and dusts.

Classification of hazardous areas

Both categories are further divided into three ATEX Zones, as directed by the European Union for protection against explosive atmospheres. Each zone indicates the frequency and duration an explosive atmosphere may be present. Hazardous areas involving gases/vapors are classified as follows:

    • Zone 0 is an area where an explosive atmosphere consisting of a mixture of air with flammable substances in the form of gas, vapor, or mist is present continuously for long periods or frequently (continuous hazard)
    • Zone 1 is an area where an explosive atmosphere is likely to occur in normal operation occasionally (intermittent hazard)
    • Zone 2 is an area where an explosive atmosphere is unlikely to occur in normal operating conditions, and if it does occur, it is likely to do so for a short period only (possible hazard)

Similarly, dusts classify into three different zones: Zones 20,  21, and  22, each representing identical meanings as their gas/vapor code counterparts, respectively. The gas station example below offers a real-world picture of these hazardous zones.

Gas station hazard zonesThe vessels containing the fuel underground and on the truck are classified as Zone 0 because these areas are continuously holding flammable substances. The gas pumps and any valve or opening into the gas containers are classified as Zone 1 because gas will be passing through intermittently — when a customer uses the pump or an employee fills the tanks. Zone 2 is the natural space or the natural environment. While fuel should not be exposed to the natural environment under normal operating conditions, it is possible. Spills, for example, can create a possible hazard for a short duration.

It’s important to note the European Union ATEX directive is not compliant with OSHA standards in the United States. While similar, the U.S. has its own classification system for identifying hazardous zones called the NEC Zone Classification System. See how the two systems compare here.

Safety

The more frequent an explosive gas or dust cloud is present, the more dangerous the zone. Therefore, companies practice ATEX zone reduction by implementing safety measures.

In areas with risk of explosion, accurate and reliable position detection is often relied on to complete tasks. Examples include monitoring hydraulic and pneumatic cylinders, checking hydraulically and pneumatically controlled valves, and level detection.

Certification of Equipment in Hazardous Areas

This post was originally published on Innovating-automation.blog.

Industrial processes often need to be carried out in a hazardous atmosphere or when hazardous materials such as explosive gases, dust or flammable liquids are present. Such substances can be ignited by sufficient energy coming from sources like electrical sparks, open flames, and hot surfaces. The equipment installed in these areas must therefore be planned such that it does not represent an ignition source. In most countries around the world, national and/or local governments enact electrical construction standards intended to prevent accidents and enhance the safety of people and property. To ensure that installed components have been designed and tested according to regulations and offer sufficient protection, testing agencies are used. They certify that a particular device meets the specifications of the special standards for hazardous locations.

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Country Certification

There are many types and categories of possible hazards in explosion hazard areas. How these areas are classified depends on in which country or region the equipment is being installed:

  • In the USA the NEC (National Electrical Code) uses two methods for classifying hazardous locations: these are based on both the class/division and the zone. Categorization into class/division is a long proven procedure in the USA. Division into zones is a newer alternate concept which is becoming more and more established. As soon as the decision is made as to which method will be used for certification, that method is consistently applied.
  • Canada is similar to the US but follows the Canadian Standards Association (CSA) electrical codes.
  • In the European Union a harmonization scheme is used to eliminate technical trade barriers. The ATEX Directive 2014/34/EU is applied to devices and protection systems for proper use in explosion hazard areas. As part of a hazard assessment the operator divides the areas into zones and selects devices for the corresponding category.
  • For the rest of the world various local regulations and standards apply. But more and more countries are turning to the uniform global standard IECEx (International Electrotechnical Commission Explosive). It is however possible that a country specifies IECEx as the basic standard while requiring additional national certifications to meet country-specific regulations.

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For a comprehensive overview about the protection classes for electrical devices you may refer to following poster and brochure (including Balluff products for hazardous areas) that can be downloaded from the Balluff Homepage – or ask your Balluff sales representative for a printed version.