When trying to choose the right intrinsic safety device for your business, you will have to weight in many factors, both technical (compatibility, functional performance) and non-technical (such as price). However, the starting point (and the factor on which your decision must hinge) is safety.
Choosing the right intrinsic safety device for your business is, fundamentally, a problem of matching the risks present in your hazardous areas with the device that efficiently mitigates them.
The framework for this decision is not arbitrary, but dictated by a set of national and international regulations. Unfortunately, since intrinsic safety, as an engineering approach, predates many of the international efforts of regulatory harmonization, the regulatory framework varies from one geographical region to another. However, the engineering basis is similar all over the world, so a rough correspondence between standards does exist.
Regulatory Framework
Broadly speaking, there are 2 major regulatory frameworks that you need to be aware of.
The National Electric Code (NEC) sets the intrinsic safety requirements in North America, primarily through 2 documents: NEC 500 and NEC 505. NEC standards are used as a basis for other regulatory documents all over the world, such as CEC (in Canada) and NFPA (global).
In Europe, the regulatory framework is primarily based on EU Directive 1999/92/EC, commonly called ATEX (from "ATmosphères EXplosibles"). This directive has been further expanded in ATEX 2014/34/EU. Like its NEC counterpart, derivatives of ATEX are being adopted by many Countries, outside Europe as well.
The standards organisations, that elaborated and maintained NEC and ATEX, do not directly test or provide ratings for devices. This is handled by notified bodies or testing laboratories, such as Factory Mutual (FM), the Canadian Standards Association (CSA), ZELM or KEMA (in the Netherlands and, respectively, Germany).
Choosing the Right Device
The criteria you need to follow when choosing the right device vary depending on location – and, therefore, depending on the regulatory framework that applies.
The NEC framework classifies areas (and rates devices) based on 3 parameters:
- Class, which defines what explosive or ignitable substances (vapors, gasses, dust, fibers etc.) may be present in a given area. NEC, CEC and NFPA define 3 classes - I (flammable vapors and gases), II (combustible dust) and III (fibers or flyings).
- Division, which defines how likely it is for the substance in a class to be present in a potentially dangerous concentration. NEC, CEC and NFPA recognize 2 divisions - Division 1 (ignitable concentrations of hazardous materials exist under normal operation conditions) and Division 2 (ignitable concentrations of hazardous materials are normally handled only in closed containers, from which they can escape only in case of malfunction).
- Group, which classifies materials in classes I and II based on their ignition parameters. There are 4 recognized groups for group I - A, B, C and D - and 3 groups for group II - E, F, G.
The ATEX framework classifies areas based on hazard source and the likelihood of its presence. ATEX 2014/34/EU recognizes 6 zone ratings:
- Zone 0, 1 and 2, for hazardous areas where the explosive atmosphere consists of a mixture of air with gas, vapor or mist. The likelihood of this mixture being present in dangerous concentration ranges from permanent, for zone 0, to unlikely and only for short periods of time, for zone 2.
- Zone 20, 21 and 22, for hazardous areas where the explosive atmosphere consists of a cloud of combustible dust. The likelihood of this mixture being present in dangerous concentration ranges from permanent, for zone 20, to unlikely and only for short periods of time, for zone 22.
Devices are classified, according to Directive 2014/34/EU, in 2 groups:
- Group I, comprised of products used in underground mines, contains 2 categories, M1 and M2.
- Group II, comprised of products used in all other surface industries, contains 3 categories, labelled Cat. 1, 2 and 3.
Device Ratings
A device can be rated for operations under multiple conditions, based on definitions from multiple regulatory frameworks.
It is worth remembering, though, that this is a design property, not a general rule. For example, while Zones 0 and 1 (ATEX) roughly correspond to Division 1 (NEC), they are not, strictly speaking, equivalent. A device that is rated for input from Zone 0 / Division 1 has been tested against both; a device that is only rated for input from Zone 0 may not be appropriate for input from division 1.
Conclusions
Choosing the right intrinsic safety device for your business can be challenging, but the good news is that the framework for this decision is not arbitrary.
Once you have narrowed down potential options, based on national legislation and standards, you can make a final choice based on functional and price constraints and on requirements from external partners, such as insurance companies.
But remember: the decision you make will be fundamental to the effectiveness of your policy. In this field, quality matters.
