What is the PDS method
PDS is a method used to quantify the safety unavailability and loss of production for safety instrumented systems (SIS). The method is widely used in the offshore industry, but is also applicable to other business sectors.

The PDS method has, through the PDS forum, been developed in close co-operation with oil companies as well as vendors and researchers of control and safety systems.

Even though the model is considered realistic, it is still relatively simple. The method is primary a tool for non-experts in reliability, and should thus contribute to enhance the use of reliability in the engineering disciplines and to bridge the gap between reliability theory and application.

The PDS method is function orientated, which gives an integrated approach to hardware, software and human factors. Thus, the model accounts for all typical failure causes, e.g.:

  • Normal aging
  • Software faults
  • Design related failures
  • Installation errors
  • Stress and environmental conditions
  • Operational failures

The PDS method is considered to be realistic as it accounts for all major factors affecting reliability during system operation, such as:

  • All major failure categories/causes
  • Common cause failures
  • Automatic self-tests
  • Functional (manual) testing
  • Systematic failures
  • Complete safety function
  • Redundancies and voting logic

Through a research project sponsored by the Norwegian Research Council and the PDS members, the PDS method has recently been updated, including activities such as:

  • Updating the PDS data and method handbook (new versions issued in January 2013)
  • Using the method for practical SIL implementation and SIL follow-up in the operational phase
  • Developing a computerised calculation program (“PDS tool”) which includes the PDS formulas and generic data (members only)
  • Developing an example collection on how to use the method on practical projects 

Failure classification used in PDS

Failure classification used in PDS


Published January 1, 2017



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