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.

NFPA 79 for AWM Cables in 2011

Share

Since my first post on NFPA79  in relation to sensor cables was published, there have been more and more customers asking me for a statement of compliance.  So after much review, we decided to ask the professionals.  As a member of the NFPA you can call and talk to a document specialist to help you clarify the wording and how it applies to your exact situation.

During my conversations with them, I learned that a new revision of NFPA79 that will be released in 2011.   This version I hope will help clarify the concerns people have with the original wording “12.2.7.3 Single conductor or multi-conductor Type AWM shall not be permitted.”  Most, if not all, sensor cables are built-in the Type AWM.

Continue reading “NFPA 79 for AWM Cables in 2011”

Sensor Cables and the National Fire Protection Agency

If you aren’t familiar with the NFPA, here is a brief summary from their website:
“The mission of the international nonprofit NFPA, established in 1896, is to reduce the worldwide burden of fire and other hazards on the quality of life by providing and advocating consensus codes and standards, research,training, and education.”  http://www.nfpa.org/

Continue reading “Sensor Cables and the National Fire Protection Agency”