PDS Method
The PDS method is used to quantify the safety unavailability and loss of production for safety instrumented systems (SIS). The method accounts for all relevant failure categories; technical, software, human, etc. The PDS method is documented trough a PDS method handbook and a PDS data handbook.

The PDS method handbook presents simple calculation formulas for calculating Probability of Failure on Demand (PFD), and provides unavailability formulas for continuously (high demand mode) operating systems, i.e., Probability of Failure per Hour (PFH) formulas. The PDS data handbook comprises recommended failure data on various SIS components, both topside and subsea. Both the handbooks are updated approximately every 3rd year.

The PDS method is in line with the main principles advocated in the IEC 61508 / 61511 standards, and is a very useful tool when implementing and verifying quantitative (SIL) requirements as described in these standards. The PDS method is continuously updated, and new method and data handbooks were issued in August 2013. The data handbook is based on extensive experience with operation of instrumented safety systems in the Norwegian petroleum industry and presents data applicable for performing SIL analyses according to IEC 61508 / 61511.


The PDS handbooks can be purchased here.

Published January 1, 2017



Norwegian centre of force for developing Safety Instrumented Systems (SIS) in the petroleum industry