So if we see the active failures as outcomes of some underlying cause, then we can start to say, well what are these underlying causes. And these underlying causes are generally called Latent Conditions, which may result from a faulty design or management decision that may lie dormant for a long time, until such time as a correct mix of circumstances lines up and we have an accident.
Latent Conditions are present in all systems NOW, and are inevitable part of organisational life. They are there waiting for the correct circumstances to line up. It could be because resources are rarely distributed equitably in relation to risk and clearly managers, purely because they are human, can’t foresee all of the outcomes or potential outcomes of their decisions.
Whereas particular active failures tend to be unique to a specific event, the same latent conditions – if undiscovered and uncorrected – can contribute to a number of different accidents.
For example, a case study of the Nakina, Ontario Derailment in Canada 1930, where a rail bed was built on a portion of a beaver dam. Apparently the design rules at the time said you could do this.
While the beavers were there, they kept that area in good condition, so the rail bed was able to support the train and the beavers themselves acted as the repair people.
So the bed was quite functional and worked well. Over time the railroad decided that they wanted to get rid of the beavers because of the potential problems the beavers could cause to the sleepers. So they got rid of the beavers.
The problem was when you got rid of the beavers, who looked after the dam? Nobody. So the dam weakened. They had a decent rain downpour, which washed away the dam, and there was nothing left underneath the rails. So the train came around the corner and saw the rails one metre above the ground and two people died.
The people themselves did nothing wrong, there was no Active Failure on the part of the train driver. The Latent Condition was one way back in 1916 when someone made a decision to go this way and failed to understand that the beaver dam was there.
The necessary conditions for an accident is the rare conjunction of a set of holes in successive defences, allowing hazards to come into contact with people and assets.
It’s rare because of the multiplicity of defences and the mobility of holes.
So we concentrate on correcting latent conditions, which will reduce accidents in the long run. The important point is that you cannot change the human condition, but we can change the conditions under which people work.