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 instrumentation. High-power circuits such as

electric motor An electric motor is a 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 electromagnetic coil, wire winding to gene ...

s or lighting cannot use intrinsic safety methods for protection. Intrinsic safety devices, can be subdivided in to: * Intrinsically safe apparatus * Associated apparatus

Intrinsically safe apparatus

Intrinsically safe apparatuses are electrical devices that have connected circuits that are intrinsically safe circuits whilst in the hazardous area.

Associated apparatus

Associated apparatuses are electrical devices that have both intrinsically safe and non-intrinsically safe circuits and is designed in a way that the non-intrinsically safe circuits cannot negatively affect the intrinsically safe circuits.

Intrinsically safe circuit

An intrinsically safe circuit is designed to not be capable of causing ignition of a given explosive atmosphere, by any spark or any thermal effect under normal operation and specified fault conditions.

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 ( ...

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. see Types of protection for more info. 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. * 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 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 possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwel ...

and thermal energy in the system so that ignition 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 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 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), even 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 Admiralty law, law enforcement military branch, service branch of the armed forces of the United States. It is one of the country's eight Uniformed services ...

requires that the

two way radio A two-way radio is a radio transceiver (a radio that can both transmit and receive radio waves), which is used for bidirectional person-to-person voice communication with other users with similar radios, in contrast to a broadcast receiver, whi ...

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, or IECEx certification for use in explosive atmospheres. Only properly designed battery-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. Requirements for intrinsically safe electrical systems are given in the IEC 60079 series of standards.

Certifying agencies

Standards for intrinsic protection are mainly developed by

International Electrotechnical Commission The International Electrotechnical Commission (IEC; ) is an international standards organization that prepares and publishes international standards for all electrical, electronics, electronic and related technologies. IEC standards cover a va ...

(IEC), 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 Research Corporation, which certifies radios,

Underwriters Laboratories The UL enterprise is a global private safety 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. In the EU the standard for intrinsic safety certification is the

CENELEC CENELEC (; ) is responsible for European standardization in the area of electrical engineering. Together with ETSI (telecommunications) and CEN (other technical areas), it forms the European system for technical standardization. Standards harmon ...

standard EN 60079-11 and shall be certified according to the ATEX directive, 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 toolIEC 60079-11:2023