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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.

App: Determining the required SIL, PL




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.


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