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Pre-purge (SIL 2, PL d)

The combustion chamber, the connected spaces and the flue gas system must generally be purged as described in EN 746-2:2010 subclause to ensure that no flammable gas mixture remains in these areas.

Requirement as per EN 746-2


Ignitable mixture in the combustion chamber → explosion

Determining the required SIL pursuant to IEC 62061

Frequency & exposure duration Fr: < 1 per h to ≥ 1 per day; > 10 min → 5 points

Probability Pr: as the two shut-off valves (SIL 3, PL e) shut off the gas supply safely, the probability that a hazardous event occurs is rather low. → 2 points (Above 1200 kW, EN 746-2 also prescribes a tightness control.)

Avoidance Av: the hazard can be avoided by regular maintenance and the use of a tightness control. → 3 points

Effects: death, loss of an eye or arm

Determining the required PL pursuant to ISO 13849-1

Severity of injury S: severe (usually irreversible injury including death) → S2

Frequency and/or duration of hazard exposure F: frequent to continuous and/or long exposure to hazard → F2

Possibility of avoiding hazard or limiting harm P: possible under certain conditions → P1

Enter details


Enter the calculated values in the adjacent “app” to determine the required safety level.



Select products






The required SIL and PL can be achieved with these products. The calculation (see below) provides verification of this.

Sensor: pressure switch for gas DG

Logic: protective system control FCU

Actuator: solenoid valves for gas VAS











The flowchart shows how the products are integrated into the application to achieve the required safely level.

Calculating the SIL, PL

Select products in the adjacent “app”. Depending on the product click on whether the function should have one or two channels and enter the demand rate per hour or per year.


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