I first came across James Reason’s (1990) Defence in Depth accident trajectory model, or as it is more commonly known the ‘Swiss Cheese model’, 12 years ago and it surprised me that this approach had not been adopted more widely in the area of occupational health.
Put simply, the Defence in Depth model (refer Figure 1) when used in an occupational health setting allows any organisation to build in layers of defence to safeguard against failure. Failure in this context can mean notifiable injuries, a loss in productivity due to ill health or post-employment claims.
What Reason proposes is that risk has a trajectory, which passes through corresponding holes in the layers of defence, barriers and safeguards and if it achieves a ‘direct flow through’, will result in a failure. Reason indicates that a defence in depth approach acknowledges that all systems are fallible and that by lining up layers of defence in depth, organisations are presented with the opportunity of catching, retarding or retiring risk prior to failure.
Figure 1 Defence in Depth Model (Reason, 1990)
Human risk factors essentially follow a similar trajectory in that there are both active failures and latent conditions (over a period of time combined with degenerative conditions) that coexist within the workplace and when these factors come together they often lead to poor health and result in poor productivity outcomes.
To apply the Defence in Depth theory in an occupational health setting, we will explore four critical health defence layers that can improve the ability to control health risks:
Pre-Employment health screening
Health Management (including health surveillance & assessments, wellbeing & absenteeism)
Injury Management / Rehabilitation (Workers Compensation )
Each of these four key defence layers has the ability to “catch, retard or retire risk” so that an error trajectory is not achieved and more importantly, the likelihood of a failure is reduced significantly.