Terminology



This glossary is offered as a guide to some of the terminology associated with hazardous areas and explosion prevention. It is not a substitute for recognised codes and standards and is subject to revision as these develop and are substituted. Always consult currently applicable standards, codes and governing bodies before initiating loop design and installation of hazardous area equipment.


Approval, approved, third-party approval, NRTL

North American terminology relating to the examination, testing and qualification of devices intended to meet codes and standards governing their use in hazardous (classified) locations. Equivalent to the term "certified" used in Europe and other parts of the world. Approval of a given device is gained through submission to a nationally recognised testing laboratory (NRTL). An approved device will be labelled with the mark of the approving NRTL together with information governing its use.

Associated apparatus

A device which serves to limit the energy available to an intrinsically safe circuit or system and which maintains the intrinsic safety of such a circuit or system under prescribed conditions. Typically a "zener barrier" or intrinsically safe power supply, and usually required to be installed in a non-hazardous (unclassified) location.

ATEX Directive

Abbreviation from the French "ATmospheres EXplosible". Specifically, Directive 94/9/EC of the European Commission, which provides the technical requirements to be applied to equipment intended for use in potentially explosive atmospheres. The Directive has been in effect within the European Community since July 1st, 2003. Manufacturers who comply with its provisions and affix the prescribed CE marking are able to sell their equipment anywhere in Europe without further localised testing or certification with respect to the risks covered. However, note that the CE mark is not exclusive to Directive 94/9/EC and may denote compliance to multiple directives relating to matters of health and safety. Also note that a given directive is not a standard in itself, but requires adherence to relevant standards.
Also see: CE mark ; CENELEC

Barrier, IS barrier, galvanically isolated barrier, isolating barrier, safety barrier, shunt-diode safety barrier, Zener barrier

Any one of a number of alternative electrical devices designed to limit the energy available to an intrinsically safe circuit under specified conditions. Such devices range in design from simple resistor/fuse/Zener diode combinations, often referred to as "Zener barriers" or "shunt-diode safety barriers", to more complex galvanically isolated interfaces. The latter are often loosely referred to as "isolating barriers" or simply "isolators". However, it should be understood that all barrier devices are required to be built and approved/certified to the relevant standards for intrinsically safe energy limiting devices.
Also see: associated apparatus

CE mark

A mark of compliance authorised by the European Community and applied to products meeting a wide ranging group of "directives" primarily concerned with health and safety. Products that meet the applicable directives and bear the mark may be sold freely within the EC without the need for further testing or certification. Note that the directives do not constitute standards in themselves, but give the manufacturer a number of options for attestation ranging from self-declaration to type-approval by a notified body against recognised standards. The directive specifically applying to products for use in potentially explosive atmospheres is ATEX Directive 94/9/EC.
Also see: ATEX Directive; certified; certification

CENELEC

From Comité Européen de Normalisation Electrotechnique (European Committee for Electrotechnical Standardisation). The body within the European Community responsible for writing electrical standards to be used by the member countries. Most electrical products certified under ATEX Directive 94/9/EC are certified to CENELEC standards even though the directive gives manufacturers a number of options, including self-declaration.

Certified, certification

Terminology used principally outside North America relating to the examination, testing and qualification of devices intended to meet codes and standards governing their use in hazardous areas. Equivalent to the term "approved" as used in North America. Certification of a given device is typically gained through submission to a "notified body" (recognised testing laboratory). A certified device will bear the mark of the notified body, the CE mark, plus information governing its use.
Also see: notified body

Control drawing

Generally associated with product approvals in North America, a technical drawing containing schematics and engineering data which describe the correct use and application of an approved device. As such, it is an integral part of the approval documentation.

Countable fault

Considered in the analysis of protective devices, countable faults are faults to components of the equipment being tested which affect the integrity of the protection being provided, not faults to the field wiring components.

Entity concept

A concept for matching intrinsically safe devices (intrinsically safe apparatus) with the safety parameters of a given energy limiting barrier (associated apparatus) and the interconnecting wiring. Use of the entity concept enables construction of intrinsically safe circuits and systems with maximum flexibility in the choice of suitable devices and cable types, and has largely replaced the earlier practice of approving or certifying specific combinations or systems.

Entity parameters

Terminology used in North America for the electrical parameters established by design, and confirmed by testing, which describe the contribution or burden that a given device will add to an intrinsically safe circuit. Similar to the "safety description" used in Europe and elsewhere. The entity parameters for an energy-limiting "barrier" (associated apparatus) will describe how much power it can safely deliver to the circuit, and how much capacitance and inductance it can safely support, under fault conditions. Conversely, the entity parameters for a field device (intrinsically safe apparatus) will describe how much power it can safely absorb under fault conditions, and how much capacitance and inductance it will add to the circuit. By also taking into account the distributed inductance and capacitance of the circuit cabling a simple analysis can be made to establish that a given combination of devices and cabling is safe. Note that the entity parameters for a given device are quite different from its normal operating parameters.
Also see: safety description

explosionproof

North American terminology describing a device enclosed in a housing that is capable of withstanding an explosion of a specified gas or vapour that may occur within it and of preventing the ignition of a specified gas or vapour surrounding the enclosure by sparks, flashes or explosion of the gas or vapour within, and that operates at such an external temperature that a surrounding flammable atmosphere will not be ignited thereby. Roughly equivalent to, but not interchangeable with, the term "flameproof" as used in the U.K. and elsewhere.
Also see: EExd; flameproof

Ex d

Code used to identify "flameproof" to IEC 60079-1. Similarly, EEx d to EN50 018 and AEx d to FM 3600 (also to ISA 12.22.01 & 12.00.01).

Originally a British term describing a device enclosed in a housing that is capable of withstanding an explosion of a specified gas or vapour that may occur within it while preventing the propagation of flame to a surrounding flammable atmosphere, and operating at such an external temperature that a surrounding flammable atmosphere will not be ignited thereby. The design of such a device includes consideration of pressure wave propagation and pressure piling within the enclosure. May be used in Zone 1 and Zone 2. Roughly equivalent to, but not interchangeable with, "explosionproof" as used in North America.

Ex e

Code used to identify "increased safety" to IEC 60079-7. Similarly, EEx e to EN50 019 (until July 2006) or EN 60079-7, and AEx e to FM 3600 (also to ISA 12.16.01 & 12.00.01).
A fault tolerant protection concept applied to electrical apparatus that does not produce arcs or sparks in normal operation, and to which additional measures are applied to provide increased security against the possibility of excessive temperature or incidence of arcs or sparks. It is based primarily upon mechanical isolation and typically used for rotating machines, lighting, junction and terminal boxes. May be used in Zone 1 and Zone 2.

Ex ia

Code used to identify "intrinsic safety" to IEC 60079-11 when capable of remaining safe with two countable faults applied. Similarly, EEx ia to EN50 020/39, and AEx ia to FM 3610 (based on ISA 12.02.01). Intrinsic safety to category "ia" is the only method of protection permitted in Zone 0 (plus Zones 1 & 2 by default).
Also see: intrinsic safety; countable faults

Ex ib

Code used to identify "intrinsic safety" to IEC 60079-11 when capable of remaining safe with one countable fault applied. Similarly, EEx ib to EN50 020/39, and AEx ib to FM 3610 (based on ISA 12.02.01). Intrinsic safety to category "ib" is only permitted in Zones 1 & 2.
Also see: intrinsic safety; countable faults

Ex m

Code used to identify "encapsulation" to IEC 60079-18. Similarly, EEx m to EN50 028, and AEx m to FM 3600 (also to ISA 12.23.01 & 12.00.01).
A protection method primarily based upon the mechanical encapsulation of electrical components using resin compounds to insulate and isolate sources of electrical energy from a flammable atmosphere. Mostly used for small inexpensive devices where economical repair is not a priority. May be used in both Zone 1 and 2.

Ex nA

Code used to identify "non-sparking apparatus" to IEC 60079-15. Similarly, EEx nA to EN50 021, and AEx nA to FM 3600 (ISA 12.12.02).
Describes devices that have no normally arcing parts or inherent thermal effects capable of ignition of a flammable atmosphere under prescribed conditions. Limited to Zone 2.

Ex nC

Code used to identify several similar concepts including "enclosed break device", "non-incendive component", "sealed device", "hermetically sealed device", "encapsulated device", and "otherwise protected sparking apparatus" to IEC 60079-15. Similarly, EEx nC to EN50 021, and AEx nC to FM 3600 (ISA 12.12.02).
Protection typically applied to arcing contacts and based variously upon containing ignition and preventing propagation to a surrounding flammable atmosphere, or by sealing off the arcing contact from a surrounding flammable atmosphere - often by the use of elastomers, soldering, welding, glass-to-metal fusion, etc. Note that the criteria for meeting this classification is less onerous that for Ex m "Encapsulation" and may only be used in Zone 2 only.

Ex nL

Code used to identify "limited energy apparatus" to IEC 60079-15. Similarly, EEx nL to EN50 021.
Closely resembles the concept of intrinsic safety except that a lower safety factor applies and only normal working conditions are considered. Limited to Zone 2 applications.

Ex nR

Code used to identify "restricted breathing enclosure" to IEC 60079-15. Similarly, EEx nR to EN50 021, and AEx nR to FM 3600 (ISA 12.12.02).
An enclosure designed to restrict the ingress of a flammable atmosphere with special emphasis on the method of sealing - typically by gaskets. Only permitted in Zone 2 areas.

Ex nZ

Code used to identify "simplified pressurized enclosures" to IEC 60079-15.
An attempt to simplify pressurisation requirements for Zone 2 applications only.

Ex o

Code used to identify "oil immersion" to IEC 60079-6. Similarly, EEx o to EN50 015, and AEx o to FM 3600 (also to ISA 12.16.01 & 12.00.01).
A protection method based upon immersing electrical apparatus in oil, such that arcing is quenched before it can ignite a surrounding flammable atmosphere. The oil also serves to dissipate heat and prevent hot spots that might otherwise be a source of ignition. Typically used for transformers and switchgear. May be used in both Zone 1 and Zone 2.

Ex px, Ex py, Ex pz, EEx p

Codes used to identify "pressurization" as follows:

Ex px reducing a Zone 1 classification to general purpose to IEC 60079-2;
similarly, USA X-purge to FM 3620

Ex py reducing a Zone 1 classification to Zone 2 to IEC 60079-2;
similarly, USA Y-purge to FM 3620

Ex pz reducing a Zone 2 classification to general purpose to IEC 60079-2;
similarly, USA Z-purge to FM 3620

EEx p pressurisation to EN 50 016
Also see: pressurisation

Ex q

Code used to identify "powder filled apparatus" to IEC 60079-5. Similarly, EEx q to EN50 017, and AEx q to FM 3600 (also to ISA 12.25.01 & 12.00.01).
A protection method which relies upon inert powder or sand to surround electrical apparatus so that any arcing or hot surfaces which occur under the surface of the media cannot cause ignition of a surrounding flammable atmosphere. Typically used for power supplies, and often combined with intrinsic safety for special applications. May be used in both Zone 1 and Zone 2.

FISCO

An abbreviation for Fieldbus Intrinsically Safe Concept - a specific approach to the use of intrinsic safety protection in Fieldbus systems without the need for a detailed safety analysis, and permitting the installation of additional devices without having to reconsider such analysis. The concept relies in part upon the findings from new research into the incendive capabilities of cable coupled with the fact that Fieldbus systems require well defined cable parameters for functionality, plus new designs of constant current power supplies.

Flameproof

Originally a British term describing an Exd device - i.e. enclosed in a housing that is capable of withstanding an explosion of a specified gas or vapour that may occur within it, whilst preventing the propagation of flame to a surrounding flammable atmosphere. May be used in Zone 1 and Zone 2. Roughly equivalent to, but not interchangeable with, "explosionproof" as used in North America.
Also see: Exd; explosionproof

FNICO

An abbreviation for Fieldbus Non-Incendive Concept - a specific approach to the use of non-incendive protection in Fieldbus systems without the need for a detailed safety analysis, and permitting the installation of additional devices without having to reconsider such analysis. The concept relies in part upon the findings from new research into the incendive capabilities of cable coupled with the fact that Fieldbus systems require well defined cable parameters for functionality, plus new designs of constant current power supplies.

Hazardous area

Primarily a British term for a physical location subject to the presence of potentially explosive gas or dust atmospheres. Such an area is categorised according to the nature of the risk and the relative risk level.

Hazardous (classified) location

North American term for a physical location where fire or explosion hazards may exist due to the presence of flammable gases or vapours, flammable liquids, combustible dust, ignitable fibres or ‘flyings′. Such an area is categorised according to the nature of the risk and the relative risk level.

IEC

The International Electrotechnical Commission (IEC) is the leading global organisation that prepares and publishes international standards for all electrical, electronic and related technologies. These serve as a basis for national standardisation and as references when drafting international tenders and contracts.
Through its members, the IEC promotes international co-operation on all questions of electrotechnical standardisation and related matters, such as the assessment of conformity to standards, in the fields of electricity, electronics and related technologies.

IECEx

International certification directly referenced to IEC standards for equipment to be used in hazardous (classified) locations and increasingly accepted by a number of countries including Australia and New Zealand.

Intrinsic safety; I.S.

A fault tolerant protection concept based upon energy limiting and useful for creating electrical circuits in hazardous (classified) locations where there is risk of sparks and excessive surface temperatures causing ignition of coincident flammable atmospheres. Typically used for low voltage, low current instrumentation and process control loops. There are two sub-categories of intrinsic safety based upon consideration of countable faults.
Also see: Ex ia; Ex ib

Intrinsically safe circuit

A circuit in which any spark or thermal effect is incapable of causing ignition of a specified mixture of flammable or combustible material in air under prescribed conditions.

Intrinsically safe system

An assembly of interconnected intrinsically safe apparatus, associated apparatus, and interconnecting cables in that those parts of the system that may be used in hazardous (classified) locations are intrinsically safe circuits.

IP rating

A European system of two-digit codes for defining the level of ingress protection for electrical enclosures. The first digit defines the degree of dust impregnability, the second offering the same for water - specifically IEC Standard 60529. Similar in concept to the alpha-numeric NEMA 250 standard used in North America.

NEMA

National Electrical Manufacturers Association (in the U.S.A.). A trade association for electrical equipment manufacturer′s, historically responsible for developing U.S. standards and now contributing to global standards and harmonisation. Author of the NEMA 250 standard - an alpha-numeric coding system defining the level of ingress protection for electrical enclosures and which is similar in concept to the two-digit "IP" code used in Europe.

NFPA

National Fire Protection Association (in the U.S.A.). A not-for-profit organisation devoted to fire prevention and public safety, historically responsible for developing U.S. standards and now contributing to global standards and harmonisation. Author of NFPA 496 - a standard for purge control systems in North America.

Non-incendive; N.I.

A North American protection method based variously upon the sealing or encapsulation of arcing devices, or energy limiting in the case of low voltage, low current electrical circuits. The latter is similar in concept to type nL and also intrinsic safety, except that a lower safety factor is permitted. Consequently, non-incendive techniques may only be used in Division 2 or Zone 2 hazardous locations where flammable atmospheres are not expected to be encountered on a routine basis.

Non-incendive circuit

An electrical circuit in which any arc or thermal effect produced under intended operating conditions of the equipment, or due to opening, shorting, or grounding of field wiring, is not capable under specified conditions of igniting a coincident flammable gas, vapour, or dust-air mixture. Limited to Division 2 or Zone 2 hazardous locations.

Notified body

A European third-party certification agency providing examination, testing, and qualification of devices to EC directives (for example, the ATEX Directive). Such bodies have gone through a nomination process by their member country and been "notified" of their acceptance by the European Commission. Notified bodies are largely replacing the traditional government-run certification agencies in Europe.
Also see: certified; certification

N-type

A European term for a broad class of protection based upon devices which are non-sparking in normal operation and limited to use in Zone 2 areas. Recently superseded by a series of more closely defined sub-categories:
Also see: ExnA; ExnC ; ExnL; ExnR; ExnZ

Pressurization

A protection technique which enables the hazardous area classification of an enclosed space to be reduced by purging the enclosure with clean air or an inert gas, and then by maintaining a minimum prescribed positive pressure to prevent the ingress of a flammable atmosphere. Depending upon the original area classification and the type of purge controller employed, the reduction may either be to a lower hazard classification or to a general-purpose classification. Special dilution provisions apply to enclosures containing apparatus with an internal source of released gas, such as a gas analyser. Pressurised enclosures may be operated on the basis of "leakage compensation" to economise on purge media, or "continuous flow" where interior cooling or dilution of internally released gas is required.
Also see: X-purge

Purge controller

A system for controlling and monitoring the pressurisation of an enclosed space for the purpose of reducing the hazard classification within the enclosure. Depending upon the pressurisation category, the system may include automatic interlocks to control the power supplied to apparatus installed within the enclosure. It may also include a pressure release vent to alternatively facilitate fast purging then minimise the loss of pressure during normal pressurised operation.

Purging

A term often used interchangeably with "pressurisation" but more correctly describing the preparatory stage in using a pressurised enclosure - purging the interior of the enclosure of a potentially flammable atmosphere before applying electrical power. Standards governing the use of pressurised enclosures mandate minimum purge times relative to enclosure volume and flow rate.

Safety description

Terminology used in Europe and elsewhere for the combination of electrical parameters established by design, and confirmed by testing, which describe the contribution or burden that a given device will add to an intrinsically safe circuit. Similar to the "entity parameters" used in North America, the safety description for an energy-limiting "barrier" (associated apparatus) will describe how much power it can safely deliver to the circuit under fault conditions. Conversely, the description for a field device (intrinsically safe apparatus) will describe how much power it can safely absorb under fault conditions. Data for inductance and capacitance are also provided to enable a safety analysis to be made which includes the effects of energy storage and release. Note that the safety description for a given device does not replicate its normal operating parameters.
Also see: entity parameters

Simple apparatus

A device which cannot inherently generate or store significant amounts of energy as defined in standards for intrinsic safety. Such a device may be added to an intrinsically safe circuit without further analysis of its′ affect on the integrity of such a circuit.

Temperature classification; T-rating

A system of codes to classify devices for use in hazardous (classified) locations according to the maximum surface temperature that can be developed (as a potential source of ignition).

X-purge

Type X purging systems reduce the classification of an enclosed space from Division 1 (or Zone 1) to unclassified. Since an enclosure with Type X protection may house devices which could ordinarily cause ignition of a flammable atmosphere, the system is required to automatically interrupt power to the interior of the enclosure and to provide remote alarm annunciation upon loss of positive pressure. There is an exception to the requirement for immediate power interruption where the consequences of interruption are judged to be more dire than the risk of a flammable atmosphere entering the enclosure (for example where the enclosure houses a process controller).

Y-purge

Type Y purging systems reduce the classification of an enclosed space from Division 1 (or Zone 1) to Division 2 (or Zone 2). As such, apparatus contained within the enclosure must be approved/certified for use in a Division 2 (or Zone 2) hazardous (classified) location.

Z-purge

Type Z purging systems reduce the classification of an enclosed space from Division 2 (or Zone 2) to unclassified.


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