Classification of International Protection marking (IP) and Safety Integrity Level (SIL)
Gas detection equipment is often used in harsh environments: water jets, dust, and so on.
For that reason, classifications have been drawn up so that users can identify the degree of protection provided by enclosures and casing as clearly as possible:
- International Protection marking, known as the IP code, is an international standard published by the International Electrotechnical Commission on the degrees of protection against ingress of water and dust, etc., published for the first time in 1989. It was transposed into European Standard EN 60529. This marking indicates the degree of protection provided by a material against intrusion by solid and liquid foreign objects.
- Safety Integrity Level (SIL) is defined as a relative level of risk reduction provided by a safety function, or to specify a target level of risk reduction. In simple terms, SIL is a measurement of performance required for a safety instrumented function (SIF).
Classification of International Protection marking (IP code)
The use of classification codes to indicate the degree of protection provided by enclosures and casing against ingress of water and solid matter is now commonplace. These classifications also cover the protection of persons in the event of contact with energised parts or parts in motion inside the enclosure.
The rating system used to indicate the degree of protection is formed by the letters IP followed by two figures (characteristic numerals) that give the degree of protection:
- The first characteristic numeral gives the degree of protection of persons in case of contact with energised parts or parts in motion inside the enclosure.
- The second characteristic numeral gives the degree of protection of the enclosure or casing against ingress of water, dust, etc.
- An enclosure classified as IP65 offers full protection of energised parts and parts in motion against ingress of dust or water.
- An enclosure classified as IP67 indicates that the equipment is protected against dust and the effects produced by immersion.
Note: this type of classification is suitable for gas detection equipment, such as control units, but the cooling of the electronic system needs to be monitored.
IP codes (IEC/EN 60529)
Safety Integrity Level (SIL) classification
There are four Safety Integrity Levels. The higher the SIL, the lower the PFD (probability of failure on demand). Many gas and fire detection products were designed before the introduction of SILs and may therefore be assigned a low SIL, or even declared not eligible for a SIL, when assessed individually. There are several ways of getting around this problem, such as more frequent testing, or combining the systems with different technologies (which eradicate the most common failures) in order to increase the SIL assigned.
In order to determine the SIL of a given safety system, the sum total of all the probabilities of failure on demand (PFD) must be taken into account.
For example, for SIL2: PFD (sensor) + PFD (resolver) + PFD (trigger) < 1x10-2
The choice of SIL required for the system must be made based on the level of safety management in the process itself. E/E/PES (Electrical/Electronic/Programmable Electronic Safety-related Systems) should not be considered to be the main safety system. Regardless of the industrial process, design, use and maintenance are the most important parameters in terms of safety.
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