Systems theory causation

Analysis, that can assist with the identihcation of causal factors. The concepts of incident causation encompassed in these tools are fundamental to the majority of investigation methodologies. (See Chapter 3 for information about the Domino Theory, System Theory, and HBT Theory.) The simplest approach involves reviewing each unplanned, unintended, or adverse item (negative event or undesirable condition) on the timeline and asking, Would the incident have been prevented or mitigated if the item had not existed If the answer is yes, then the item is a causal factor. Generally, process safety incidents involve multiple causal factors. 

The STAMP (Systems-Theoretic Accident Model and Process) model of accident causation is built on these three basic concepts—safety constraints, a hierarchical safety control structure, and process models—along with basic systems theory concepts. All the pieces for a new causation model have been presented. It is now simply a matter of putting them together. 

Accident causation theories include the human factors theory, the domino theory, the systems theory, the combination theory, the epidemiological theory, and the accident/inddent theory [1,2]. The first two of these theories are described below. 

Both the integrative model by Smillie Ayoub (1975) and the deviation concept by Kjellen (1984a) connect the general systems theory to the sequencing and energy models of accident causation. They encompass technical, organizational and human components of the system. Various methods of system safety analysis (e.g. fault tree analysis, incidental factor analysis) support the identification of technical and human deviations as well as the analysis of the conditions and consequences of these deviations. From the discussion of near misses and conflicts it became clear that frameworks of accident causation should cover all kinds of incidents, thus becoming frameworks of incidents. 

The book begins with a discussion of the theories of error causation and then goes on to describe the various ways in which data can be collected, analyzed, and used to reduce the potential for error. Case studies are used to teach the methodology of error reduction in specific industry operations. Finally, the book concludes with a plan for a plant error reduction program and a discussion of how human factors principles impact on the process safety management system. 

One of the origins of this view of error and accident causation is the theory of accident proneness, which tried to show that a small number of individuals were responsible for the majority of accidents. Despite a number of studies that have shown that there is little statistical evidence for this idea (see, e.g., Shaw and Sichel, 1971) the belief remains, particularly in traditional industries, that a relatively small number of individuals accoimt for the majority of accidents. Another element in the emphasis on individual responsibility has been the legal dimension in many major accident investigations, which has often been concerned with attributing blame to individuals from the point of view of determining compensation, rather than in identifying the possible system causes of error. 

The design of most process plants relies on redundant safety features or layers of protection, such that multiple layers must fail before a serious incident occurs. Barrier analysis ) (also called Hazard-Barrier-Target Analysis, HBTA) can assist the identification of causal factors by identifying which safety feature(s) failed to function as desired and allowed the sequence of events to occur. These safety features or barriers are anything that is used to protect a system or person from a hazard including both physical and administrative layers of protection. The concepts of the hazard-barrier-target theory of incident causation are encompassed in this tool. (See Chapter 3.)... 

One of the most suitable forms for mapping the causation for chemical reaction systems are the so-called flow graphs. In this case the flow graph displays a sequence of conversions, representing a combination of intercormected steps, as the precursor-product . We suppose that the reader has a minimum knowledge on the graph theory, the main principles of which may be found in the books [49-55]. 

Manuele (1997a) believes the domino theories are too simplistic. He proposes the term unsrrfe act also be eliminated. He suggests the chief culprits in accident causation are less-than-adequate safety policies, standards, and procedures and inadequate implementation accountability systems. Manuele attempts to pull different causation theories together into one working theory. His approach also incorporates some of the following ideas. 

Figure 12-8 The domino theory loss causation accident sequence model. Cox. Sue. Tom Cox, Safety Systems and People, Figure 3.2 (adapted from Bird and Loftus, 1931), p. 52, Butterworth-Heinemann, 1996. Modified with permission.

In fact, the basis of an audit is the assumption that its designer does indeed understand the process and has created an instrument to ensure that the process performs properly. Audits then, derive their content from the theory of accidents held by the author(s) of the audit. For example, depending on the author s point of view, the audit might emphasize unsafe conditions, unsafe acts, deficiencies in the safety-management system, or any number of other personally held accident-causation philosophies. 

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