The publication of the international functional safety standards IEC 61508 (1999), IEC 61511 / ISA-84 (2004) and IEC 62061 (2005) were significant milestones in the effort to increase equipment and process safety. 1,2,3  Unfortunately, the release of safety standards does not by itself make the world a safer place.

Analysis of past process safety incidents underscores the role that people can play in preventing these accidents. A study by the UK’s Health and Safety Executive (HSE) showed that most safety incidents could have been prevented.  It found that the number one cause of accidents was incorrect and incomplete design specification (44%). Another 15% was from improper design & implementation. The study also found that a significant percentage of incidents were caused by changes made after commissioning (21%), as well as errors during operation and maintenance (15%). 4  A subsequent study on accidents in the chemical sector found that three most common causes of failure were errors in operating procedures (37%), in plant design (32%), and in hazard analysis (26%). 5

Figure 1 – Results of HSE Study 4

Exhaustive analysis of process plant disasters by Trevor Kletz concludes that all accidents are traceable to human error in some form.6

Personnel Functional Safety Certification programs are designed to address these shortcomings by improving the safety design knowledge and practices of individuals who are involved with the design and operation of critical equipment and processes.

NOTE: The full Personnel Functional Safety Certification Programs Whitepaper by Todd Stauffer can be found here.


  1. ANSI/ISA-84.00.01-2004 (IEC 61511 Mod) Part 1 Functional Safety: Safety Instrumented Systems for the Process Industry Sector – Part 1: Framework, Definitions, System, Hardware and Software Requirements [S84]
  2.   IEC 61508 Ed.1.0 b 2005, “Functional Safety of Electrical/Electronic/Programmable Electronic Safety-Related Systems”
  3.   IEC/ISO 62061 Ed. 1.0 b:2005 , “Safety of machinery - Functional safety of safety-related electrical, electronic and programmable electronic control systems”
  4.   “Out of Control: Why control systems go wrong and how to prevent failure”, U.K. Health & Safety Executive, 1995
  5.   “Findings From Voluntary Reporting of Loss of Containment Incidents 2004/05”, U.K. Health & Safety Executive, 2005.
  6.   Kletz, Trevor A., “What Went Wrong: Case Histories of Process Plant Disasters Fourth Edition, Gulf Publishing Co., 1999.


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