Why do control systems go wrong?
The safety life-cycle, sometimes spelled lifecycle, was conceived after the Health and Safety Executive (HSE - a UK government agency) found that accidents involving control systems could be attributed to various different root causes.
The highest root cause of accidents was found to be poor specification of the system (44% of cases), followed by modification after commissioning (20%), and then poor operation or maintenance (15%).
4 out of 5 of the root causes of accidents involving control systems are typically under the full control of the hazard owner.
In practice, despite the hazard owner (end user) being responsible as duty holder, many control and safety system automation projects are sub-contracted to one or more third parties. Engineering contractors and system integrators are typically providing much of the input to detailed specifications, and they are often involved with almost every aspect up to final validation and hand-over of the system.
In the view of this author, this is one of the key challenges of applying the safety life-cycle approach in practice. The key to reducing risk in all parts of the life-cycle is effective management of the companies involved in delivering products and services. "Management" in this context means policies, planning, people, procedures and paperwork. If any of these elements is lacking, it can lead to project problems.
Unfortunately, many functional safety consulting companies have focused on providing technical calculations for probability of failure as being the main activity required for risk reduction during the safety life-cycle. The standards IEC 61508 (applicable to equipment vendors), IEC 61511 (process industry) and IEC 62061 (machinery safety) do require these calculations. However, the focus is somewhat over-emphasized. As ever, engineers tend to like technical calculations - but they often fail to tackle the huge issues of poor management!
If we're going to see reduced risk over the long term, then functional safety management must be improved.