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 circuit or system under prescribed conditions. Typically a "safety barrier" or intrinsically safe power supply, and usually required to be installed in a non-hazardous (unclassified) location.

ATEX Directive
Abbreviation for the French "ATmosphere 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 localized 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 carrier, 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 authorized by the European Community and applied to products meeting a wide ranging group of "directives" primarily concerned with health and safety. Products which 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 recognized 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 Standardization). 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" used in North America. Certification of a given device is typically gained through submission to a "notified body" (recognized testing laboratory). A certified device will bear the mark of the notified body, the CE mark, plus information governing it's 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.

dBi
The relative gain of an antenna with respect to an equivalent isotropic antenna (an imaginary point that radiates a signal equally in all directions, a theoretical situation), expressed on the decibel logarithmic scale. Normally used to describe the gain for antennas operating at 1GHz or above.

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 flexibilty 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 it's 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 vapor that may occur within it and of preventing the ignition of a specified gas or vapor surrounding the enclosure by sparks, flashes or explosion of the gas or vapor 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.

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 vapor 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 propogation and pressure piling within the enclosure. May be used in Zone 1 and Zone 2. Roughly equivalent to, but not interchangeable with, the term "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.

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 pressurization 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 by the oil before it can ignite a surrounding flammable atmosphere. The oil also serves to dissipate heat and prevent hot spots which 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 X-purge to FM 3620
EEx p pressurization to EN 50 016
Also see: pressurization

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
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.

FNICO
Fieldbus Non-Incendive COncept: a specific approach tp 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.

galvanic isolator
A form of signal conditioner which employs transfomer coupling to prevent direct (galvanic) current flow between input and output. Often used to create a "floating" signal loop which is isolated from ground potential.
Also see: galvanically isolated barrier

hazardous area
Primarily a British term for a physical location subject to the presence of potentially explosive atmospheres. Such an area is categorized 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 vapors, flammable liquids, combustible dust, ignitible fibers or flyings. Such an area is categorized according to the nature of the risk and the relative risk level.

IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes international standards for all electrical, electronic and related technologies. These serve as a basis for national standardization and as references when drafting international tenders and contracts.
Through its members, the IEC promotes international cooperation on all questions of electrotechnical standardization 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. 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. Specifically, IEC Standard 60529. Similar in concept to the alpha-numeric NEMA 250 standard used in North America.

ISA12
A U.S. standards committee sponsored by the Instrumentation, Systems, and Automation Society (ISA). It is charged with the formulation of standards, recommended practices, and technical reports for safe and practical use of electrical equipment in hazardous (classified) locations, and for equipment used for the detection of combustible gases. It is currently active in the the reduction in national differences in the U.S. adoption of the I.E.C. standards used for U.S. certification, and in the adoption of the IECEx Scheme.

LAN
Local Area Network: a data communications network covering a small area, usually within the confines of a building or manufacturing plant; a relatively high-speed computer communications network for local data transfer and applications. Common LAN protocols are Ethernet and Token Ring.

MESH, mesh network
A wireless network designed such that multiple radio nodes are connected to each other and thereby have alternative redundant transmission routes in the event of equipment failures or transmission interference. A mesh network is said to be self-healing.

MSHA
Mine Safety & Health Administration: the U.S. Federal agency that regulates safety and health issues in the mining industry. Responsible for approving electrical and other equipment for mine use.

NAT
Network Address Translation: a networking protocol that enables multiple computers to dynamically share a single internet or local area network IP address. It creates multiple new IP addresses for the client computers from a single access IP address. Typically part of the functionality of a network router and employed in firewall security.

NEMA
For the National Electrical Manufacturers Association (in the U.S.A.). A trade association for electrical equipment manufacturers. Historically responsible for developing U.S. standards, and now contributing to global standards and harmonization. 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
For the National Fire Protection Association (in the U.S.A.). A not-for-profit organization devoted to fire prevention and public safety. Historically responsible for developing U.S. standards, and now contributing to global standards and harmonization. Author of NFPA 496, a standard for purge control systems, also NFPA77 a recommended practice for static electricity control.

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 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 eqipment, or due to opening, shorting, or grounding of field wiring, is not capable under specified conditions of igniting a coincident flammable gas, vapor, 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

NRTL
Nationally recognized testing laboratory in the U.S.A. accredited for conducting third-party approvals of products intended to meet national standards. An approved device will be labelled with the mark of the approving NRTL together with information governing it's controlled use.
Also see: approval; approved; third-party approval

N-type
A European term for a broad class of protection methods based upon devices which are non-sparking in normal operation and limited to use in Zone 2 areas. Recently superceded by a series of more closely defined sub-categories:
Ex nA ; Ex nC ; Ex nL ; Ex nR ; Ex nZ .

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 analyzer. Pressurized enclosures may be operated on the basis of "leakage compensation" to economize on purge media, or "continuous flow" where interior cooling or dilution of internally released gas is required.
Also see: X-purge ; Y-purge ; Z-purge

purge controller
A system for controlling and monitoring the pressurization of an enclosed space for the purpose of reducing the hazard classification within the enclosure. Depending upon the pressurization 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 minimize the loss of pressure during normal pressurized operation.

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

QoS
Quality of Service, in respect of digital data transmission networks, a collective measure of the level of service delivered to a network user. QoS can be characterized by several basic performance criteria including availability (low downtime), error performance, response time and throughput, lost transmissions due to network congestion, connection set-up time, and speed of fault detection and correction.

RFID
Radio Frequency IDentification: radio frequency data exchange between electronic tags and reader devices; a more capable alternative to barcode identification in that RFID enables dynamic data modification and real-time asset tracking.

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 it's 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 it's affect on the integrity of such 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).

WAP
Wireless Access Protocol: An open, global standard for bringing Internet content to mobile devices. WAP works on most wireless networks and delivers content via a markup language called WML.

WEP
Wired Equivalency Privacy: a set of encryption algorithms designed to protect data transmitted wirelessly. Now considered obsolete and replaced by WPA, WPA2.

WLAN
Wireless Local Area Network: a data communications network using high frequency radio transmission instead of wiring, usually covering a small area within the confines of a building or manufacturing plant. A relatively high-speed computer communications network for local data transfer and applications. Typical WLANs use 2.4 GHz and 5.8 GHz radio frequency bands and operate within the IEEE 802.11 standard.

WPA, WPA2
WiFi Protected Access: a protocol for wireless transmission security defined by IEEE 802.11i. It replaces WEP, and the latest version is WPA2.

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 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.

Zener barrier
A resistor, fuse, Zener diode combination, alternatively referred to as a "shunt-diode safety barrier", designed and certified to limit electrical energy to an intrinisically safe circuit in a hazardous (classified) location under prescribed conditions.
Also see: associated apparatus barrier