Safety Lifecycle

Lets take a look at each stage of the safety lifecycle.


Risk Analysis


Once a concept has been developed and documented, the equipment under control (EUC) has been defined a hazard analysis needs to be done to determine the risk level of every safety function. Then, determine the safety integrity level (SIL) for each function.


The standard provides quantitative and qualitative methods to determine risk levels. Once risk level is determined they are compared to the tolerable risk criteria that have been decided by person responsible. If the risks calculated are higher than the criteria measures have to be taken to lower the risk factor. The measures taken can either be process changes or safety procedures.


The standard allows for other means of risk reduction-other technology safety-related systems and external risk reduction facilities. But, does not consider them within the scope.


Performance Criteria


Here it is important to figure out the type of safety system required. The standards provide performance criteria in the form of safety integrity levels (SIL). These values are derived from the probability of failure on demand (PFD). The safety system must satisfy the integrity requirements. A performance verification is needed in order to know if the system meets the requirements.


Performance Verification


Manufacturers need third party verification. There are third party organizations like TUV that provide certification on safety systems. End users and engineering companies will generally not accept a system unless it has been third party certified.


Planning


While evaluating the risk factor, a major planning effort is required for:

• Installation & commissioning
• Validation
• Operation and maintenance

This is when the importance of documentation really stand out. If the planning is not properly documented potential hazards could be implemented into the safety system. If the detailed specifications, procedures and tests are not performed by competent people there is very high probability that system failure will be prominent during the system life.

Installation & Commissioning/Verification Testing

Both should be carried out in strict accordance with the plans. Documented evidence that all of safety related sytems, other technology and external risk reduction facilities are ready for installation.

Operation & Maintenance

Should be carried out in strict accordance with the plan. Need records of all modification made that have an impact on the hazards recorded in the assessment. All modifications must still meet functional safety requirements. The modifications will need justification documentation an impact analysis study and full reports covering everything.

Decommissioning

During decommissioning all the functional safety requirements must still be meet. An impact analysis must be carried out and include adjacent EUC's and the impact on there study.

IEC 61508 Overall Lifecycle