Types of Failure Consequences in Maintenance

Failure consequence refers to the impact of a certain failure mode, primarily used in evaluating assets when using reliability centered maintenance (RCM).

Overview

The development of RCM introduced a type of maintenance strategy that accounts for the effects of failures to the plant and its stakeholders. While RCM also requires rigorous analysis on the causes of failure, as would other types of maintenance, it further looks into the repercussions of identified failure events. RCM aims to manage the consequences of failure events by avoiding or reducing their effects.

With the additional analysis required to perform RCM, arises a need to qualify and classify failure effects into different types. The society of automotive engineers (SAE), through SAE JA1011, formally categorizes possible consequences of failure modes. Simplifying the points from SAE JA1011, failure consequences can be categorized according to how they impact the organization’s objectives – hidden, safety/environmental, operational, and non-operational.

Types of failure consequences

Each failure mode can cause one of the following types of failure consequences:

1. Hidden

There are consequences to every failure mode – even failure modes that have not been identified yet. Failure consequences that are hidden would be due to the source of the consequence being hidden as well. These consequences are from failures that are not evident to the workers in charge or even their respective teams. Due to the failure event being hidden and basically unknown to the team, failure consequences could be safety, environmental, operational, or non-operational in nature.

Most of these failures are due to protective devices that do not work as intended. Risks associated with installed protective devices that are not fail-safe under certain conditions should be identified and considered.

2. Safety/Environmental

Safety and environmental concerns go hand in hand. Failure events that affect the safety of the organization’s workers or any of the stakeholders fall into this category. In the same manner, adverse failure events that endanger the environment are also included in this category. Catastrophic incidents that might result in physical injuries, or the degradation of protected landforms are some general examples of this type of consequence.

The next two categories only have economic consequences to the organization:

3. Operational

Failure effects with operational consequences directly impact the production of the plant. Typical examples that fall under this category are when failure events negatively affect the plant’s production output, raw material security, product quality and production capacity, etc. These types of consequences could incur monetary losses to the organization as a result of reduced production capability.

4. Non-operational

Non-operational consequences are caused by failure events that might not directly affect the plant’s production, but still impact the organization’s expenses. These consequences are usually in the form of costs from the repair and replacement of equipment, when these costs outweigh the value of any incurred production losses.

Deciding which failure consequence category is most appropriate

Due to the multiple types of failure consequences, and the seemingly overlapping characteristics of the categories, deciding on the most appropriate type can be a challenging task. If it gets too confusing, it might help to take a step back to remember the purpose of this exercise – that is to identify a category that would help the evaluation of performing RCM. The goal is to choose the type that would best describe the consequence of failure, to guide the strategies around how to carry out RCM activities.

The order by which the types are enumerated above can be used as a guide in identifying which failure consequence is most appropriate:

First, determine whether any failure event is associated with hidden causes (e.g. due to a protective device). If yes, consider using hidden failure consequence.

Next, assess whether workers or stakeholders are exposed to physical or psychological danger. Alternatively, check if the failure event will cause environmental damages or violate environmental laws. For any of these, consider using safety/environmental failure consequence.

If the failure event is still uncategorized at this point, evaluate its economic impact to the company, with particular detail on the source of the incurred costs. If the majority of the costs are due to losses in operations or production, categorize the consequence as operational. For costs primarily due to repairs, or any other cause, categorize the failure consequence as non-operational.