"Those who ignore history are bound to repeat it", so the saying goes. Every month, #*IT Happens offers lessons from the misfortune of others with the hope that more examples of these accidents can be prevented.This month, however, we provide a useful model which explains why accidents happen, in order to allow you to identify those accidents waiting to happen and to help investigate those that have. The ‘Swiss Cheese' Model of Defences

The 'Swiss Cheese' model of defences is a useful way of explaining what causes accidents and injury.

The model, presented by Professor James Reason, suggests that any potential accident will be caused by a failure of at least one and up to four layers of control (defensive layers). They are organisational influences, management system failures, preconditions for unsafe acts, and the unsafe acts themselves. He argues that most defences will have certain conditions upon which they will fail. When failures of defensive layers coincide, an accident will occur.

In a public venue there are numerous levels of control (or defences) that exist to prevent accidents from occurring. From the training of staff to minimise unsafe acts and monitor hazards; to the well designed and maintained spectator thoroughfares; to building management systems that monitor plant and maintenance; to the budgeting process that ensures adequate funds are available to manage risk. All these layers help prevent accidents from occurring.

The model presented is dynamic in that changing conditions dictate the effectiveness of each layer. Layers can become deliberately or accidentally ineffective; however a failure in one defence layer alone is not necessarily sufficient to cause an injury.

Ineffective defensive layers can be the result of active failures (through people's actions) or latent conditions relating to physical conditions, management systems or even the organisation's culture.

The Reason Model

Active Failures

Active failures result from human error that are either deliberate (violations) or by mistake. The failure could also be by mismatch of the competency of a person and their task, or that the person lost attention at a crucial time when undertaking an activity. Errors, violations, mismatches or slip ups represent unsafe acts.

Latent Conditions

Latent conditions are management system failures which relate to elements such as the physical design of venue layout, or organisational factors such as failures in training effectiveness, breakdowns in supervision or poor procedures.

Preconditions for unsafe acts include fatigued staff or volunteers working on a long event or inadequate communications practices between shifts. Unsafe supervision encompasses such things as contractors undertaking high risk construction work in public areas without supervision. Unsafe management system might involve a poorly designed staff schedule that dictates excessive work hours resulting in fatigue.

They are latent in that they may lay dormant for some time, before combining with local circumstances and active failures, to break through the various levels of defence.

Such latent conditions can be derived from failures by the organisation's key decision-makers at the strategic or policy level. These might result from a lack of resource allocation, inadequate knowledge and skills on the part of key decision-makers, or as a result of poor strategic planning.

Key difference between active failures and latent conditions

The key difference between active failures and latent conditions is that active failures usually have an immediate impact. They affect the people involved directly with the accident causing injury.

Latent conditions relate to the actions of key decision-makers. In the case of a venue operators or event organisers, these decision-makers may be made well in advance of an incident by senior management who are not involved in the day-to-day operations of events.