Page 625 - Marine Structural Design

Chapter 34 Risk Centered Maintenance 60 1

The work packages are implemented in systems that ensure the work is done.
34.3.3 Risk-Centered Maintenance (Risk-CM)
Risk-Centered Maintenance (Risk-CM)
RCM began in US. commercial aviation industry for maintenance for highly redundant
aircraft. Criticality class in a RCM is categorized with respect to safety, operatiodproduction,
economics and hidden failure. The difference between Risk-CM and RCM is that the
criticality class in RCM is replaced with a direct evaluation of risks in Rick-CM (Jones, 1995).
The direct risk evaluation gives a more complete description of the hazards than the coarser
assessment (criticality class). This Risk-CM involves independent estimation of frequency and
consequence for each failure mode, providing the ranking mechanism based on risk concept.
When risks are calculated for individual failure modes, it is possible to rank priority for
maintenance tasks based on the risks. Qualitative risk assessment may be fairly adequate for
Rick-CM as comparative risks are sufficient for priority ranking. It is not require to accurately
estimate absolute risks. Consistency between the risk evaluations is rather important. There are
however, two difficulties in applying Risk-CM (1) risk concept is still not llly accepted by
the industry in some areas (2) there is indeed a lack of data for the adequate evaluation of risks,
in particular for some new applications on which little industry experience exists.
Operational Risk Assessment
Operational risk assessment is performed on process critical equipment and facilities. Its
objective is to focus maintenance resources (money and manpower) in the plants that have
highest risk. Operational risk assessment starts with data gathering and evaluation. The data
used for operation risk assessment are usually collected during the equipmentlfacility
operations. There are three major contributors to the operational risk, namely:
Equipment: It is no doubt that the equipment is a major contributor to operational risk.
Equipment is operated by human to produce products. Maintenance activities are
performed on equipment.
Production: Loss production (including scheduled maintenance and turnaround) and
product quality below standards are an operational risk. Production loss may be due to
equipment failure, lack of raw material supplies, shortage in packaging, shipping and
storage.
Human: Humans are the key contributors to operational risk. People often cause system
failure and make up costs when equipment fails and production reduced, e.g. in terms of
labor costs.
Human Contribution to Risk
People are an integral part of plant operation and maintenance, and take the main liabilities.
There are two types of human errors (Jones, 1995):
Active errors: result in instantly observable effects.
Latent errors: Have consequences that are not realized for relatively long period of time
until they combine with other factors that result in accidents.
Machine operation used to be more hands on activities. As computer promoted people to
higher level, the information people receive is computer displays in control room. Latent
failures are generally major players in these situations.