The Nimrod Review - Official Documents

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Chapter 18 – Accident Theory and High-Risk Technologies
in the defences. A large proportion of accidents, however, require the timely concatenation of both active
and latent failures to achieve a complete trajectory of accident opportunity. This was true of a number of
disasters including The Herald of Free Enterprise and the Dryden crash. 51
‘Defences, barriers and safeguards’ stand between hazards and damaging losses. In some instances, these
defences are undermined from within the system via the active failure pathway. In other cases, the gradual
accretion of latent failures reaches a point where the hazard can invade the system from the outside. 52
‘Latent’ errors pose just as great a threat to the safety of complex systems as ‘active’ errors. ‘Latent’ errors
are those whose adverse consequences may lie dormant within the system for a long time. ‘Active’ errors
are associated with ‘front line’ operators of a complex system, such as pilots, whose effects are felt almost
immediately. Operators tend to be the inheritors of system defects created by poor design, incorrect
installation, faulty maintenance and bad management decisions. These are all examples of ‘latent’ errors
spawned by those whose activities are removed in both time and space from the direct control interface. In
James Reasons’ colourful description: “[the operator’s] part is usually that of adding the final garnish to the
lethal brew whose ingredients have been long in the cooking.” 53
The ‘organisational theory’ analytical framework has been adopted by the International Civil Aviation
Organisation (‘ICAO’), the International Air Transport Association (‘IATA’), the International Federation of
Air Traffic Controllers Associations (IFATCA), the National Transportation Safety Board (‘NTSB’) of the United
States, the Bureau of Air Safety Investigations (BASI) of Australia, the Transportation Safety Board (TSB) of
Canada, and British Airways. 54 It is a valuable aid to the pro-active analysis of safety in high-technology
systems.
The age of the organisational accident
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In the words of James Reason, we are in the age of the organisational accident. The operation of complex
technologies such as aviation necessarily involves organisational processes and cultures which affect human
behaviour. In my view it is increasingly important to focus on those organisational processes and cultures in
order to raise standards of safety in an increasingly technological world.
Trend Analysis - Heinrich’s Triangle
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55 As Professor John McDermid has pointed out, there are many ‘low-level’ errors which are precursors of, and
hence warnings of, impending accidents. He emphasises, “Good safety management identifies these lowlevel
issues and feeds them back to reduce risk”. Analysis of 1920s industrial accidents led to the development
of “Heinrich’s Triangle” showing the relationship between low-level deviations and accidents. Ratios of 600:1
are often reported. The example below illustrates data reported from air traffic management about the
number of low level Operational Errors (OE) and Operational Deviations (OD). Whatever the precise ratio in
any given field, the key point is to capture and understand these low level errors and deviations before they
conspire to cause an incident or accident.
51 See Daniel E Maurino, James Reason, Neil Johnston and Rob B Lee, Beyond Aviation Human Factors, 1995, pages 26-27.
52 Ibid.
53 See James Reason, Human Error, 1990, page 173.
54 Daniel E Maurino, James Reason, Neil Johnston and Rob B Lee, Beyond Aviation Human Factors, 1995, page xi.
55 JA McDermid, PHD, FREng, University of York, Through Life Safety Management: Some Concepts and Issues, 2007.
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