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What is SIL?

SIL fire systems use equipment that performs instrumented safety functions (RIS) as part of a functional safety management structure (FSM). This safety mechanism is measured to give a SIL (Safety Integrity Level) which indicates the quantified objective to be achieved by the safety control.

Who is SIL for?

Although the reliability of a fire safety product is crucial in any type of environment, some applications require additional proof of reliability. These are applications such as marine, rail, hazardous areas and power stations for which shutting down the site or closing an area represents a very high cost.

Many of these types of sites require all safety devices to be SIL approved. This ensures that the safety equipment is robust and unlikely to stop working. However, even the most reliable products will crash at some point or require maintenance. The SIL assessment gives an estimated failure rate of a product, which then allows applications like these to estimate the costs of downtime/loss of revenue over a period of time.

What are the standards?

Standard EN61508

This standard specific to control systems incorporates safety rules, technical specifications and personnel training, taking into account the life cycle applied to safety.

It replaces the EN954 standard since the end of November 2009.

Standard EN62061

This standard from EN61508 specifies the requirements and gives the recommendations for the design, integration and validation of electrical, electronic and programmable electronic control systems relating to the safety of machinery. it shall take into account, for the field of use of the machines, the entire life cycle, from the design phase to decommissioning.

Note: This standard complements EN/ISO 13849-1, which deals with the electrical safety of simple non-electrical and electrical control systems (hydraulic, pneumatic, mechanical).

Particularity: it encourages to make a functional analysis of the architecture, to cut into subfunctions, to analyze the interactions before assigning them a hardware solution. This approach is one of the originalities of this standard, it did not exist in the specifications of the old EN 954 standard.

Sil

From the previous standard is derived the notion of SIL (Safety Integrity Level) which describes the performance capacity of the control relating to safety:

Note a SIL quantifies while the notion of category (1, 2, 3 and 4) from the old EN954 safety standard qualified.

How to estimate the level of SIL?

Four parameters allow the risk assessment and are to be determined by:

  • Severity of risksSe – value from 1 (not serious) to 4 (very serious) – in example: 4
  • Frequency of dangerous exposureFr– value from 2 > (one year) to 5 < (one hour) – in example: 3
  • Probability of occurrence of dangerous movementPr – value from 1 (negligible) to 5 (very strong) – in the example: 5
  • Probability of avoiding or limiting damageAv – value from 1 (probable) to 5 – in example: 3

Add the last 3 parameters: CI = Fr + Pr + Av; in the example: 12

Position these two parameters: CI on the abscissa and Se on the ordinates in the sils estimation table.

The intersection will indicate the SIL level to be reached by the electrical control system relating to the safety of the machines: SRECS (Safety Related Electrical Control Systems).

 

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