Intrinsic safety (IS) is a protection technique for safe operation of electrical equipment in hazardous areas by limiting the energy, electrical and thermal, available for ignition. In signal and control circuits that can operate with low currents and voltages, the intrinsic safety approach simplifies circuits and reduces installation cost over other protection methods. Areas with dangerous concentrations of flammable gases or dust are found in applications such as petrochemical refineries and mines. As a discipline, it is an application of

inherent safety In the chemical industry, chemical and process industries, a process has inherent safety if it has a low level of danger even if things go wrong. Inherent safety contrasts with other processes where a high degree of hazard is controlled by protect ...

in instrumentation. High-power circuits such as

electric motor An electric motor is an Electric machine, electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a Electromagneti ...

s or lighting cannot use intrinsic safety methods for protection.

Operating and design principles

In normal use, electrical equipment often creates tiny

electric arc An electric arc, or arc discharge, is an electrical breakdown of a gas that produces a prolonged electrical discharge. The electric current, current through a normally Electrical conductance, nonconductive medium such as air produces a plasma (p ...

s (internal sparks) in switches, motor brushes, connectors, and in other places. Compact electrical equipment generates heat as well, which under some circumstances can become an ignition source. There are multiple ways to make equipment safe for use in explosive-hazardous areas. Intrinsic safety (denoted by "i" in the ATEX and IECEx Explosion Classifications) is one of several available methods for electrical equipment. Others include explosion proof (NEC 500) or flameproof enclosures ("d" in IEC, ATEX and NEC 505), increased safety ("e"), encapsulation ("m"), enclosed-break device ("nC"), sealed device ("nC"), hermetically-sealed device ("nC"), restricted-breathing enclosure ("nR"), oil immersion ("o"), protection of optical radiation ("op"), venting ("p"), powder or sand filling ("q"), special protection ("s") and dust ignition protection by enclosure ("t"). For handheld electronics, intrinsic safety is the only realistic method that allows a functional device to be explosion protected. A device which is termed "intrinsically safe" has been designed to be incapable of producing heat or spark sufficient to ignite an explosive atmosphere, even if the device has experienced deterioration or has been damaged. There are several considerations in designing intrinsically safe electronics devices: reducing or eliminating internal sparking, controlling component temperatures, and eliminating component spacing that would allow dust to short a circuit. Elimination of spark potential within components is accomplished by limiting the available energy in any given circuit and the system as a whole. Temperature, under certain fault conditions such as an internal short in a semiconductor device, becomes an issue as the temperature of a component can rise to a level that can ignite some explosive gasses, even in normal use. Safeguards, such as current limiting by resistors and fuses, must be employed to ensure that in no circumstance can a component reach a temperature that could cause

autoignition The autoignition temperature or kindling point of a substance is the lowest temperature in which it spontaneously ignites in a normal atmosphere without an external source of ignition, such as a flame or spark. This temperature is required to su ...

of a combustible atmosphere. In the highly compact electronic devices used today PCBs often have component spacing that create the possibility of an arc between components if dust or other particulate matter works into the circuitry, thus component spacing, siting and isolation become important to the design. The primary concept behind intrinsic safety is the restriction of available

electrical Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by ...

and thermal energy in the system so that

ignition Ignition may refer to: Science and technology * Firelighting, the human act of creating a fire for warmth, cooking and other uses * Combustion, an exothermic chemical reaction between a fuel and an oxidant * Fusion ignition, the point at which a ...

of a hazardous atmosphere (explosive gas or dust) cannot occur. This is achieved by ensuring that only low voltages and currents enter the hazardous area, and that no significant energy storage is possible. One of the most common methods for protection is to limit electric current by using series resistors (using types of resistors that always fail open); and limit the voltage with multiple zener diodes. In zener barriers dangerous incoming potentials are grounded, with

galvanic isolation Galvanic isolation is a principle of isolating functional sections of electrical systems to prevent current flow; no direct conduction path is permitted.John Huntington ''Show Networks and Control Systems: Formerly Control Systems for Live ...

barriers there is no direct connection between the safe- and hazardous-area circuits by interposing a layer of insulation between the two. Certification standards for intrinsic safety designs (mainly

IEC The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and r ...

60079-11 but since 2015 also IEC TS 60079-39) generally require that the barrier do not exceed approved levels of voltage and current with specified damage to limiting components. Equipment or instrumentation for use in a hazardous area will be designed to operate with low voltage and current, and will be designed without any large capacitors or inductors that could discharge in a spark. The instrument will be connected, using approved wiring methods, back to a control panel in a non-hazardous area that contains safety barriers. The safety barriers ensure that, in normal operation, and with the application of faults according to the Equipment Protection Level, EPL, also if accidental contact occurs between the instrument circuit and other power sources, no more than the approved voltage and current enters the hazardous area. For example, during

marine transfer operations Marine Transfer Operations are conducted at many ports around the world between tanker ships, barges, and marine terminals. Specifically, once the marine vessel is secure at the dock a loading arm or transfer hose is connected between a valve hea ...

when flammable products are transferred between the marine terminal and tanker ships or barges, two-way radio communication needs to be constantly maintained in case the transfer needs to stop for unforeseen reasons such as a spill. The

United States Coast Guard The United States Coast Guard (USCG) is the maritime security, search and rescue, and law enforcement service branch of the United States Armed Forces and one of the country's eight uniformed services. The service is a maritime, military, mult ...

requires that the

two way radio A two-way radio is a radio that can both transmit and receive radio waves (a transceiver), unlike a broadcast receiver which only receives content. It is an audio (sound) transceiver, a transmitter and receiver in one unit, used for bidirec ...

must be certified as intrinsically safe. Another example is intrinsically safe or explosion-proof mobile phones used in explosive atmospheres, such as refineries. Intrinsically safe mobile phones must meet special battery design criteria in order to achieve UL,

ATEX directive The ATEX directives are two EU directives describing the minimum safety requirements for workplaces and equipment used in explosive atmospheres. The name is an initialization of the French term ''Appareils destinés à être utilisés en ATmos ...

, or IECEx certification for use in explosive atmospheres. Only properly designed

battery Battery most often refers to: * Electric battery, a device that provides electrical power * Battery (crime), a crime involving unlawful physical contact Battery may also refer to: Energy source *Automotive battery, a device to provide power t ...

-operated, self-contained devices can be intrinsically safe by themselves. Other field devices and wiring are intrinsically safe only when employed in a properly designed IS system. Such systems shall be designed and documented according to the standard IEC 60079-25 ''Intrinsically safe electrical systems'', installed according to IEC 60079-14 and inspected and maintained according to IEC 60079-17.

Certifying agencies

Standards for intrinsic protection are mainly developed by

br>International Electrotechnical Commission
but different agencies also develop standards for intrinsic safety. Agencies may be run by governments or may be composed of members from insurance companies, manufacturers, and industries with an interest in safety standards. Certifying agencies allow manufacturers to affix a label or mark to identify that the equipment has been designed to the relevant product safety standards. Examples of such agencies in North America are the

Factory Mutual FM Global is an American mutual insurance company based in Johnston, Rhode Island, United States, with offices worldwide, that specializes in loss prevention services primarily to large corporations throughout the world in the ''Highly Protecte ...

Research Corporation, which certifies radios,

Underwriters Laboratories The UL enterprise is a global safety science company headquartered in Northbrook, Illinois, composed of three organizations, UL Research Institutes, UL Standards & Engagement and UL Solutions. Established in 1894, the UL enterprise was founded a ...

(UL) that certifies mobile phones, and in Canada the

Canadian Standards Association The CSA Group (formerly the Canadian Standards Association; CSA) is a standards organization which develops standards in 57 areas. CSA publishes standards in print and electronic form, and provides training and advisory services. CSA is composed ...

. In the EU the standard for intrinsic safety certification is th
CENELEC
standard EN 60079-11 and shall be certified according to the

, while in other countries around the world the IEC standards are followed. To facilitate world trade, standards agencies around the world engage in harmonization activity so that intrinsically safe equipment manufactured in one country eventually might be approved for use in another without redundant, expensive testing and documentation.

References

Intrinsic safety on-line assessment tool

Operating and design principles

Certifying agencies

See also

References

Further reading