Intrinsic safety
Encyclopedia
Intrinsic safety is a protection technique for safe operation of electronic
equipment in explosive atmospheres and under irregular operating conditions. The concept was developed for safe operation of process control instrumentation
in hazardous areas, particularly North Sea gas platforms. As a discipline, it is an application of inherent safety
in instrumentation.
The theory behind intrinsic safety is to ensure that the available electrical
and thermal energy in the system is always low enough that ignition
of the hazardous atmosphere cannot occur. This is achieved by ensuring that only low voltages and currents enter the hazardous area, and that all electric supply and signal wires are protected by Zener
safety barriers. Sometimes an alternative type of barrier known as a galvanic isolation
barrier may be used.
In normal uses, electrical equipment often creates internal tiny sparks in switches, motor brushes, connectors, and in other places. Such sparks can ignite flammable substances present in air. A device termed intrinsically safe is designed to not contain any components that produce sparks or which can hold enough energy to produce a spark of sufficient energy to cause an ignition. For example, during marine transfer operations
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 requires that the two way radio must be certified as intrinsically safe.
Another aspect of intrinsic safety is controlling abnormal small component temperatures. Under certain fault conditions (such as an internal short inside a semiconductor device), the temperature of a component case can rise to a much higher level than 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.
No single field device or wiring is intrinsically safe by itself (except for properly designed battery
-operated, self contained devices), but is intrinsically safe only when employed in a properly designed IS system. Such systems are usually provided with detailed instructions to ensure safe use.
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
equipment in explosive atmospheres and under irregular operating conditions. The concept was developed for safe operation of process control instrumentation
Instrumentation
Instrumentation is defined as the art and science of measurement and control of process variables within a production, or manufacturing area....
in hazardous areas, particularly North Sea gas platforms. As a discipline, it is an application of inherent safety
Inherent safety
Inherent safety is a concept particularly used in the chemical and process industries. An inherently safe process has a low level of danger even if things go wrong. It is used in contrast to safe systems where a high degree of hazard is controlled by protective systems...
in instrumentation.
The theory behind intrinsic safety is to ensure that the available electrical
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
and thermal energy in the system is always low enough that ignition
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...
of the hazardous atmosphere cannot occur. This is achieved by ensuring that only low voltages and currents enter the hazardous area, and that all electric supply and signal wires are protected by Zener
Zener diode
A Zener diode is a special kind of diode which allows current to flow in the forward direction in the same manner as an ideal diode, but will also permit it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage, "Zener knee voltage" or "Zener...
safety barriers. Sometimes an alternative type of barrier known as a galvanic isolation
Galvanic isolation
Galvanic isolation is a principle of isolating functional sections of electrical systems, thus preventing the movement of charge-carrying particles from one section to another, i.e. no direct current flows between the sections. Energy or information can still be exchanged between the sections by...
barrier may be used.
In normal uses, electrical equipment often creates internal tiny sparks in switches, motor brushes, connectors, and in other places. Such sparks can ignite flammable substances present in air. A device termed intrinsically safe is designed to not contain any components that produce sparks or which can hold enough energy to produce a spark of sufficient energy to cause an ignition. For example, during marine transfer operations
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 header on the dock and the manifold header on the vessel...
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 requires that the two way radio must be certified as intrinsically safe.
Another aspect of intrinsic safety is controlling abnormal small component temperatures. Under certain fault conditions (such as an internal short inside a semiconductor device), the temperature of a component case can rise to a much higher level than 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.
No single field device or wiring is intrinsically safe by itself (except for properly designed battery
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
-operated, self contained devices), but is intrinsically safe only when employed in a properly designed IS system. Such systems are usually provided with detailed instructions to ensure safe use.
Further reading
- Redding, R.J., Intrinsic Safety: Safe Use of Electronics in Hazardous Locations. McGraw-Hill European technical and industrial programme. 1971. ISBN 978-0070942240
- Paul, V., '"The earthing of intrinsically safe barriers on offshore transportable equipment". IMarEST. Proceedings of IMarEST - Part A - Journal of Marine Engineering and Technology, Volume 2009, Number 14, April 2009 , pp. 3-17(15)