A short explanation of “practical drift”

The theory of practical drift emerged from Snook’s root cause analysis of a 1994 friendly fire accident in which two U.S. Air Force F15 fighter jets patrolling the No-Fly-Zone over northern Iraq shot down two U.S. Army Black Hawk UH-60 helicopters. Twenty-six peacekeepers lost their lives.  It is critical for anyone trying to manage safety and reliability.

broken glass

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Organizations rely on plans and procedures.  Personnel will always seek to find a easier, cheaper, faster or better way of achieving the task. This leads to “the slow steady uncoupling of practice from written procedure” (p.194). Over time, “behavior that is locally efficient” and “acquired in practice” becomes “legitimized through unremarkable repetition” (p. 182)

The seductive allure of pragmatism

As Snook points out, “when the rules do not match the situation, pragmatic individuals adjust their behavior accordingly; they act in ways that better align with their perceptions of current demands. In short, they break the rules” (p. 193).  As time passes, “the seductive persistence of pragmatic practice loosens the grip of even the most rational and well-designed procedures” (p. 193).It is the “perverse combination of practical drift and tight coupling [which] set the conditions for randomly triggered disaster” (p.200).  Snook reminds us “the tighter the rules, the greater the potential for sizable practical drift to occur as the inevitable influence of local tasks takes hold” (p.201).


  • Practical drift is inevitable – it is rooted in human nature.
  • Adding or lengthening procedures increases the potential for practical drift.
  • Ideally the right way to do accomplish a task should also be the easiest.
  • Spend time watching how operators do their work.
  • Start with how tasks are being done than how you think they should be done.
  • Give operators the opportunity to help you design the procedure.
  • Religiously update procedures in line with current practice.

Essential reading

Snook’s book helps managers to consider to “critical design features of a organisation” that will enable willl “increase the likelihood of accomplishing the “total task” consistently?” (p. 235).  The book is a must read for anyone working in process safety and accident prevention. It is linked to the theories of high reliability organization and resilience engineering and will also appeal to managers in general.

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2 thoughts on “A short explanation of “practical drift”

  1. I believe it is worth noting that the drift is like a crack in a windscreen it will go in all directions pulling the process apart until it breaks. It is at that point that incidents occur. Depending on the significance of the process depend on the seriousness of the incident. So quite easily this can and does cause serious HSE issues.