Failures don't all matter in the same way

RCM developed in the civilian aviation industry, where there was a common assumption that all failures could impact in some way on operational availability. As a result, there was considerable pressure to prevent all failures. But as we know, the failures themselves are not what drive maintenance policy. It is what happens as a result of the failure, the failure consequences, that are important.

RCM prioritises maintenance according to the consequences of failure, and recognises that maintenance is only worth doing if it achieves our targets for operational availability, safety and environmental risk.

The process of selecting a maintenance task to manage each failure mode begins by assigning it to a consequence category.

Why does the consequence category matter? Because there is no point in carrying out a maintenance task if it doesn't deal with the failure consequences. Any proposed task must achieve the target for that category before it can be selected.

Consequence Category What it Means Target
Safety One or more individuals could be injured or killed Maintenance must reduce the risk of a safety incident to a tolerable level
Environmental An environmental regulation that applies to the process could be breached Maintenance must reduce the risk of an environmental breach to a tolerable level
Operational The failure would stop production, including effects on product quality Maintenance is only worth doing if the cost of maintenance is less than the cost of lost production and any secondary damage
Non-operational The failure has no effect on safety, the environment or on production Maintenance is only worth doing if it costs less than the cost of repairing any secondary damage
Hidden The failure on its own has no effects at all in normal circumstances. The failure only has effects during abnormal circumstances, typically when a second failure has occurred Maintenance reduce the risk of a multiple failure to a tolerable level