About Calculations in LOPA

Unmitigated Consequence Frequency = Frequency of Initiating Event x Probability of occurrence of Enabling Event x Probability of occurrence of Conditional Modifier

Where,

• Frequency of Initiating Event is the value in the Frequency of Initiating Event field in LOPA.
• Probability of occurrence of Enabling Event is the value in the Enabling Event/Conditional Probability field in LOPA.
• Probability of occurrence of Conditional Modifier is the product of value in Probability field of all the Conditional Modifiers associated with the LOPA.

If Enabling Event/Condition Probability field is blank, a default value of 1 will be used in the calculation.

Total IPL PFD = Product of value in PFD field of all the Safeguards associated with the LOPA

Mitigated Consequence Frequency = Unmitigated Consequence Frequency x Total IPL PFD

Where,

• Unmitigated Consequence Frequency is the value in the Unmitigated Consequence Frequency field in LOPA
• Total IPL PFD is the product of value in the PFD fields of all the Safeguards associated with the LOPA

If there are no IPLs associated with the LOPA, then Mitigated Consequence Frequency is equal to the Unmitigated Consequence Frequency.

Required PIF PFD = Required Mitigated Consequence Frequency / Mitigated Consequence Frequency

Where,

• Required Mitigated Consequence Frequency is the value in Required Mitigated Consequence Frequency in LOPA.
• Mitigated Consequence Frequency is the value in the Mitigated Consequence Frequency field in LOPA.

Required PIF Risk Reduction Factor = 1/ Required PIF PFD

Where,

• Required PIF PFD is the value in Required PIF PFD field in LOPA.

This value is derived based on the industry standard for SIL values.

The following table contains the data used in the example and only lists fields that are required and contain a value.