Types of Protection for Equipment
There are many different explosion protection techniques that ExTC are accredited to test and certify.
Some of them listed in IEC 60079-0 include:
- Flameproof enclosures “d”
- Oil filled enclosures “o”
- Intrinsic safety “i”
- Pressurized enclosures “p”
- Increased safety “e”
- Sand filled enclosures “q”
- Protection by Enclosure “t” (used to be DIP or tD)
- Encapsulation “m”
- Non-sparking (Non-incendive/ restricted breathing) “n”
- Optical radiation “op”
- Non-electrical “h”
- Special protection “s”
Flameproof Enclosures “d” (IEC 60079-1)
Equipment which is constructed so that it can withstand an internal explosion and provide relief of the external pressure by a flamepath. A flamepath may be a flange, thread, labyrinth, cylindrical and several other constructions. The escaping gases must be sufficiently cooled so that by the time they exit the flamepath and reach the outside of the enclosure the gas temperature is not a source of ignition.
Oil filled enclosures “o” (IEC 60079-6)
This type of protection is not commonly used for most equipment but when used is typically for transformers and other large electrical apparatus. The equipment is protected by using a liquid (or oil) in which the electrical equipment or parts of the electrical equipment are immersed so that an explosive gas atmosphere which may be above the liquid or outside the enclosure cannot access the electrical source of energy and be ignited.
Intrinsic safety “i” (IEC 60079-11)
This is the ‘limitation of energy by electronic circuit design’ when all parts of the electrical circuits have been designed to have spark and thermal energy lesser than that required for ignition of the explosive atmosphere, with up to two faults applied for “ia”, or one fault for “ib” or no fault but subjected to the most onerous conditions for “ic”. This includes protection provided by “associated apparatus” located in the non-explosive atmosphere but connected to circuits that enter the explosive area. The energy in the circuit after application of the faults is tested by connecting to a Spark Test Apparatus that causes greater than 1600 make-and-break contacts of the circuit using tungsten wires and a cadmium disc inside a chamber filled with the most sensitive gas mixture expected in the explosive atmosphere.
Pressurised enclosures “p” (IEC 60079-2)
Protection by pressurisation uses the principle of gas exclusion so that there’s no explosive atmosphere in the enclosure. There’s a number of ways this can be achieved such as a system of purging potentially explosive with clean air or inert gas. A system might be statically pressurised by creating a hermetic enclosure. Typically, these systems will rely on pressure sensing devices and other protection devices to ensure that the explosive gas has been purged, the pressure is maintained, and the temperatures of surfaces exposed to explosive atmosphere are not exceeded.
Any parts of the equipment that are to be energised prior to protection using the pressurised enclosure are required to be protected using another type such as increased safety “e” or intrinsic safety “i”.
Increased safety “e” (IEC 60079-7)
This is the ‘robustness of design’ concept where all possible places where a spark or high temperature could occur is negated by special designs such as special non-slip anti-rotational terminals that prevent spark or high temperature to occur and using larger distances of suitable non-conductive materials between conductive parts. All surfaces internal and external are considered when assessing the surface temperature of the equipment.
Protection by Enclosure “t” (IEC 60079-31)
This design is useful for Group III explosive atmospheres where explosive dusts and fibres may be present. The entry of dust inside enclosures where electrical energy may be released is prevented by specially designed enclosures that prevent entry of dust and fibres. The inside of the enclosure is typically considered a non-explosive area but the configuration of equipment inside it is controlled to ensure that the external surface temperature does not exceed the temperature rating.
Encapsulation “m” (IEC 60079-18)
This type of protection is another ‘exclusion of gas’ design where the electrical circuits are covered by a casting compound. The equipment is also protected from overheating since it might cause the encapsulation to degrade or cause excessive surface temperatures. Often thermal fuses are installed to ensure that the supply is isolated when there’s an internal fault. Equipment protected using this method is typically not repairable and are changed out in the field with new devices.
Optical radiation “op” (IEC 60079-28)
This protection type addresses the ignition hazard caused by the optical energy. The energy from light might cause ignition in a number of different ways. This standard describes precautions, tests and requirements to be taken when using optical radiation transmitting equipment in explosive gas or dust atmospheres.
Non-electrical “h” (ISO 80079-36)
This protection type addresses the ignition hazard caused by non-electrical equipment in explosive atmospheres. Equipment such as bearings, gears, hydraulics and pneumatics, equipment that has an energy source that it transfers, or stores without the use of electricity.
For additional and specific details of manufacturing documentation required for Protection Types see IECEx Operation Documentation 017 (OD017)