After being created by the commercial aviation industry, RCM was adopted by the U.S. military (beginning in the mid-1970s) and by the U.S. commercial nuclear power industry (in the 1980s). It began to enter other commercial industries and fields in the early 1990s.
Reliability-Centred Maintenance, often known as RCM, is an industrial improvement approach focused on identifying and establishing the operational, maintenance, and capital improvement policies that will manage the risks of equipment failure most effectively. It is defined by the technical standard SAE JA1011, Evaluation Criteria for RCM Processes.
Reliability centred maintenance is an engineering framework that enables the definition of a complete maintenance regime. It regards maintenance as the means to maintain the functions a user may require of machinery in a defined operating context.
As a discipline it enables machinery stakeholders to monitor, assess, predict and generally understand the working of their physical assets. This is embodied in the initial part of the RCM process which is to identify the operating context of the machinery, and write a Failure Mode Effects and Criticality Analysis, or FMECA. The second part of the analysis is to apply the "RCM logic", which helps determine the appropriate maintenance tasks for the identified failure modes in the FMECA. Once the logic is complete for all elements in the FMECA, the resulting list of maintenance is "packaged", so that the periodicities of the tasks are rationalised to be called up in work packages; it is important not to destroy the applicability of maintenance in this phase. Lastly, RCM is kept live throughout the 'in-service' life of machinery, where the effectiveness of the maintenance is kept under constant review and adjusted in light of the experience gained.
Reliability Centred Maintenance can be used to create a cost-effective maintenance strategy to address dominant causes of equipment failure. It is a systematic approach to defining a routine maintenance program composed of cost-effective tasks that preserve important functions.
The important functions (of a piece of equipment) to preserve with routine maintenance are identified, their dominant failure modes and causes determined and the consequences of failure ascertained. Levels of criticality are assigned to the consequences of failure. Some functions are not critical and are left to "run to failure" while other functions must be preserved at all cost. Maintenance tasks are selected that address the dominant failure causes. This process can only address maintenance preventable failures, i.e. it cannot defend against unlikely events, non-predictable acts of nature, etc.
The result is a maintenance program that focuses scarce economic resources on those items that would cause the most disruption if they were to fail. RCM emphasizes the use of Predictive maintenance (PdM) techniques in addition to traditional preventive measures.
This is a method which can be used to determine the most effective approach to use of resources for medical devices maintenance. RCM involves identifying actions that, when taken, will reduce the probability of failure and that are the most cost effective. It seeks the optimal mix of Condition-Based actions, other Time- or Cycle-Based actions, or a Run-to-Failure approach. RCM is an ongoing process that gathers data on performance and uses this data to improve planning for future maintenance. These maintenance strategies, rather than being applied independently, are integrated to take advantage of their respective strengths to optimise departmental / equipment operation and efficiency within the given resource constraints.
The RCM method employs Planned Preventive Maintenance (PPM), Predictive Testing and Inspection (PT&I), repair (also called reactive maintenance) and Proactive Maintenance techniques in an integrated manner to increase the probability that a medical device or component will function in the required manner over its design life-cycle. The goal of the method is to provide the required reliability and availability at the lowest cost. RCM requires that maintenance decisions be based on maintenance requirements supported by sound technical and economic justification. As with any method, there are many paths, or processes, which lead to a final goal. This is especially true for RCM where the consequences of failure can vary dramatically.
EBME has adopted a simplified approach to the traditional RCM processes practiced in some NHS Hospitals. Underlying EBME's RCM approach is the concept that maintenance actions should result in real benefits in terms of improved safety, required operational capability, and reduced life-cycle cost. It recognizes that unnecessary maintenance is counterproductive and costly and can lead to an increased chance of failure.
Reliability Centred Maintenance Principles
The primary principles upon which RCM is based are the following:
- Function oriented. It seeks to preserve system or equipment function.
- Device group focused. It is concerned with maintaining the overall functionality of a group of devices rather than an individual device
- Reliability centred. It uses failure statistics in an actuarial manner to look at the relationship between operating age and the failures. RCM is not overly concerned with simple failure rate; it seeks to know the probability of failure at specific ages.
- Acknowledges design limitations. Its objective is to maintain the inherent reliability of the equipment design, recognizing that changes in reliability are the province of design rather than maintenance. Maintenance can only achieve and maintain the level provided for by design.
- Driven by safety and economics. Safety must be ensured at any cost; thereafter, cost-effectiveness becomes the criterion.
- Defines failure as any unsatisfactory condition. Therefore, failure may be either a loss of function (operation ceases) or a loss of acceptable quality (operation continues).
- Uses a logic tree to screen maintenance tasks. This provides a consistent approach to the maintenance of all kinds of equipment.
- Tasks must be applicable. The tasks must address the failure mode and consider the failure mode characteristics.
- Tasks must be effective. The tasks must reduce the probability of failure and be cost effective.
- Acknowledges two types of Maintenance tasks and Run-to- failure. The tasks are Interval (Time- or Cycle-)-Based and Condition-Based. In RCM, Run-to-Failure is a conscious decision and is acceptable for some equipment.
- A living system. It gathers data from the results achieved and feeds this data back to improve future maintenance. This feedback is an important part of the Proactive Maintenance element of the RCM program.
Using RCM develops maintenance standards for ensuring that a system or device meets its designed reliability or availability (even in the procurement and installation phases).
RCM determines maintenance requirements by considering the following questions:
- What does the device/system do?
- What is its function?
- What failures are likely to occur?
- What are the likely consequences of failure?
- What can be done to reduce the probability of the failure, identify the onset of failure, or reduce the consequences of the failure?
RCM analysis determines the type of maintenance appropriate for a given equipment item. It results in a decision of whether a particular piece of equipment should be reactively maintained ("Accept Risk" and "Install Redundant Units"), PM'ed ("Define PM Task and Schedule") or predicatively maintained ("Define PT&I Task and Schedule").
Failure is the cessation of proper function or performance. RCM can examine failure at device group level, system level, component level, and sometimes even the parts level. The maintenance approach must be based on a clear understanding of the consequences of failure at each level. For example, a failed lamp on a device may have little effect on overall performance; However, several combined, minor components in degraded conditions, could collectively cause a failure of the entire device.
1. Identify the Functions.
This step involves examining the capability or purpose of the device/system. Some items, such as a dyalysis pump, perform an on-line function (constantly circulating a fluid); their operational state can be determined immediately. Other items, such as a compressor sump pump, perform an off-line function (intermittently evacuating a fluid when its level rises); their condition can be ascertained only through an operational test or check. Functions may be active, such as pumping a fluid, or passive, such as containing a fluid. Also, functions may be hidden, in which case there is no immediate indication of a failure. This typically applies to an emergency or protective component such as a circuit breaker that operates only in case of a short circuit.
2. Identify Failures.
The proactive approach to maintenance analysis identifies potential system failures and ways to prevent them. It, along with human observations during normal operations or maintenance tasks, also identifies pre-failure conditions that indicate when a failure is imminent. (The latter is a basis for selecting PT&I applications.). The Database Maintenance Management System and work order form should include fields for failure codes in order to maintain historical data.
3. Identify the Consequences of Failure.
The most important consequence of failure is a threat to safety. Next is a threat to the environment or operating capability. The RCM analysis should pay close attention to the consequences of the failure of infrequently used, off-line equipment and hidden function failures (e.g. over-pressure sensors, over-temperature sensors). Also, it should consider the benefit (reduced consequences of a failure) of redundant systems.
4. Identify the Failure Process.
Determining the methods and root causes of failures provides insight into ways to detect or avoid failures. The examination, which investigates the cause of the problem and not just its effect, should consider factors such as wear, overload, fatigue, or other processes.
Verify the Device group/System.
Before efforts are expended on a system, it is important to verify that the system was installed or is being used correctly as originally intended by the design. This review of the Maintenance Support Information (MSI) may reveal the root cause of a past or anticipated problem. Although the existing design may have been correct, the installation, while functional, may have been improper or there may have been latent manufacturing defects. These deficiencies should be discovered and corrected during the acceptance process, before the equipment is given to the user. Changes in the intended use of equipment can also create problems leading to excessive wear and premature failure.
Define the Maintenance Task.
The following factors should be considered when defining the maintenance task: Once it has been determined that the failure of an equipment item will have a direct effect on the safety or operation, then a PT&I, PM, or PGM task or combination of tasks should be identified that will lessen the chances or consequences of a failure. Where applicable, predictive technologies should be used to monitor the condition of the equipment. If the technology or local expertise is not available, a preventive maintenance program is normally applicable.
Maintenance tasks can be time directed (e.g., every 12 weeks), condition directed (e.g., when pH is greater than 7.3), or inspection directed (e.g., if a component is found worn). A particular cooling fan on a patient monitor can be monitored for vibration and cleanliness (PTI), routinely cleaned and checked (PM), or replaced prior to its expected failure point.
Evaluation should be undertaken to ensure that all the individual tasks maintain the system at the same degree of reliability. The tasks should also be grouped to ensure that they can be executed in the most economical manner. This may be by multiple tasks on an individual equipment item or like tasks on numerous items of equipment in a given facility.
Install Redundant Unit(s).
Situations exist where, despite all effective maintenance efforts, the risk of a potential failure is still unacceptable. Very critical care areas may require uninterrupted equipment to maintain services. The criticality may prelude even shutdown for maintenance purposes. In these situations, redundancy is justified and recommended. The problem may be corrected through additional devices being made available (e.g. Equipment library). The need for a redundant device should be determined before the situation becomes critical. This will preclude premature failure resulting from a lack of maintenance on a system/device that cannot be shut down. Often the loss to services would be of much greater cost than the redundant system. This need requires close coordination and communication with the user.
Accept the Risk.
It may be that further safety or environmental precautions are not possible or that the economic or operational cost of a failure is insignificant or substantially less than the cost of any effective maintenance procedure. In the former case, the accepted risk should be identified and quantified, and all parties concerned should be made aware of the risk and appropriate recovery procedures.
- High risk devices: Life support, key resuscitation, critical monitoring and other devices whose failure or misuse is reasonably likely to seriously injure patients or staff. (Ventilators, defibs, anaesthetic machines)
- Medium risk devices: Device, including diagnostic instruments, whose misuse, failure or absence (e.g. out of service with no replacement available) would have a significant impact on patient care, but would not be likely to cause direct serious injury. (Clinical lab equip, Ultrasound scanners, ECG)
- Low risk: Devices whose failure or misuse in unlikely to result in serious consequences. (opthalmoscopes, Electronic thermometers, cast cutters).
In the latter situation, it does not make business sense to implement a PM or PGM task. This method is known as "run-to-failure."
RCM Program Benefits.
EBME Policy should be to avoid loss of life, personal injury or illness, property loss or damage, or environmental harm from any of its activities and ensure safe conditions for patients and staff alike. By its very features, including analysis, monitoring, taking decisive action on systems or devices before they become problematic, and thorough documentation, RCM is highly supportive of and an integral maintenance process.
RCM places great emphasis on improving equipment reliability, principally through the feedback of maintenance experience and equipment condition data to maintenance managers, technicians, and manufacturers. This information is instrumental in continually upgrading the specifications for equipment to provide increased reliability. The increased reliability that comes from RCM leads to fewer equipment failures and, therefore, greater availability for patients and lower maintenance costs.
Due to the initial investment required in obtaining the technological tools, training and equipment condition baselines, a new RCM program typically results in a short-term increase in maintenance costs. This increase is relatively short lived. The cost of repair decreases as failures are prevented and preventive maintenance tasks are replaced by condition monitoring. The net effect is a reduction of both repair and a reduction in total maintenance cost.
The ability of a condition-monitoring program to forecast maintenance provides management time for planning, obtaining replacement parts and arranging environmental and operating conditions before the maintenance is done. PTI eliminates unnecessary maintenance performed by a time-scheduled maintenance program which tends to be driven by the minimum "safe" intervals between maintenance tasks. Additionally, a principal advantage of RCM is that it obtains the maximum use from equipment. With RCM, equipment replacement is based on equipment condition - not on the calendar. This condition-based approach to maintenance thereby extends the operating life of the properly maintained facility and its equipment.
Safety is the primary concern of RCM. The second most important concern is cost-effectiveness. Cost-effectiveness takes into consideration the priority or care service necessity and then matches a level of cost appropriate to that priority. The flexibility of the RCM approach to maintenance ensures that the proper type of maintenance is performed on equipment when it is needed. Maintenance that is not cost effective or not required is identified and not performed.
Impact of RCM on the Life Cycle.
The life cycle is often divided into two broad stages, acquisition and operation. RCM affects all phases of the acquisition and operations stages to some degree. Decisions made early in the acquisition cycle profoundly affect the life-cycle cost. (e.g. consumable costs over the life of a device can sometimes make the purchase price of the device seem insignificant). Even though expenditure for equipment may occur later during the acquisition process, their cost is committed at an early stage. Planning affects the overall life-cycle costs.
The decision to include a device group in the RCM program, including PTI, is best made during the planning phase. As RCM decisions are made later in the life-cycle, it becomes more difficult to achieve the maximum possible benefit from the RCM program.
Even though maintenance is a relatively small portion of the overall life-cycle cost, 3 to 5 percent of operating cost, RCM is still capable of introducing significant savings during the Operations and Maintenance (OM) phase. Savings of 30 to 50 percent in the annual maintenance budget are often obtained overtime through the implementation of a balanced RCM program.
RCM Program Components.
An RCM program includes reactive, preventive, predictive and proactive maintenance.
Reactive Maintenance also is referred to as breakdown, repair, fix-when-fail, or Run-to-Failure (RTF) maintenance. When applying this technique, maintenance, equipment repair or replacement occur only when the deterioration in an equipment's condition causes a functional failure. This type of maintenance assumes that failure is equally likely to occur in any part, component or system. Thus, this assumption precludes identifying a specific group of repair parts as being more necessary or desirable than others. If an item fails and repair parts are not available, delays ensue while parts are obtained. If certain parts are urgently needed to restore a critical medical device or system to operation, a premium for expedited delivery must be paid.
Stages of Life-Cycle Cost Commitment.
Also, there is no ability to influence when the failures occur because no (or minimal) action is taken to control or prevent them. When this is the sole type of maintenance practiced, a high percentage of unplanned maintenance activities, high replacement part inventories, and inefficient use of the maintenance effort typify this strategy. A purely reactive maintenance program ignores the many opportunities to influence equipment survivability. On the other hand, reactive maintenance can be used effectively when it is performed as a conscious decision based on the results of an RCM analysis that compares the risk and cost of failure with the cost of the maintenance required to mitigate that risk and the cost of failure. For example, periodic maintenance on a standard, inexpensive bathroom fan could not be cost-effective. Typically this type of fan would be run-to-failure and simply replaced at that time, since the cost of maintenance or repair would probably exceed the cost of a replacement fan.
Preventive Maintenance (PM).
PM consists of regularly scheduled inspection, adjustments, cleaning, lubrication, parts replacement, calibration, and repair of components and equipment. It is performed without regard to equipment condition. PM schedules periodic inspection and maintenance at predefined intervals in an attempt to reduce equipment failures for susceptible equipment. As equipment ages the frequency and number of checkpoints may need to be re-evaluated. This is a process that uses PTI and other methods to extend the period between PM tasks while maintaining equipment condition.
Consequences of Equipment/System Failure
- Emergency - Safety of life or property threatened. Immediate serious impact on mission.
- Urgent - Continuous facility operation threatened. Impending serious impact on mission.
- Priority - Degrades quality of mission support. Significant and adverse effect on project.
- Routine - Redundancy available. Impact on services insignificant.
Reactive Maintenance Priorities.
This process can result in substantial maintenance savings. These savings are dependent on the PM intervals set, which can result in a significant decrease in inspection and routine maintenance; however, it should also reduce the frequency and seriousness of unplanned medical device failures for components with defined, age-related wear patterns.
Traditional PM is keyed to failure rates and times between failures. It assumes that these variables can be determined statistically, and therefore one can replace a part due for failure before it fails. PM assumes that the overhaul of medical devices by disassembly and replacement of worn parts restores the medical device to like-new condition with no harmful side effects and that the new components are less likely to fail than the old components of the same design.
Failure rate, or its reciprocal, mean-time-between-failures, is often used as a guide to establishing the interval at which maintenance tasks should be performed. The major weakness in the application is that failure rate data determines only the average failure rate. In reality, failures are equally likely to occur at random times and with a frequency unrelated to the average failure rate. For some items, failure is not related to age, and consequently, timed maintenance can often result in unnecessary maintenance. PM can be costly and ineffective when it is the sole type of maintenance practiced.
Predictive Testing and Inspection (PTI)
PTI, also known as predictive maintenance or condition monitoring, uses primarily non-intrusive testing techniques, visual inspection, and performance data to assess medical device condition. It replaces arbitrarily timed maintenance tasks with maintenance that is scheduled only when warranted by equipment condition. Continuing analysis of equipment condition-monitoring data allows for the planning and scheduling of maintenance or repairs in advance of catastrophic and functional failure. Collected PTI data is used for trend analysis, pattern recognition, data comparison, tests against limits and ranges, correlation of multiple technologies and statistical process analysis to determine the condition of the equipment and to identify the precursors of failure. PTI does not lend itself to all types of equipment or possible failure modes and therefore should not be the sole type of maintenance practiced.
Proactive maintenance improves maintenance through better installation, maintenance procedures, workmanship and scheduling.
The characteristics of proactive maintenance are the following:
- It uses feedback and communications to ensure that changes in procedures are promptly made available to managers. list item
- It employs a life-cycle view of maintenance and supporting functions.
- It ensures that nothing affecting maintenance occurs in isolation.
- It employs a continuous process of improvement.
- It optimises and tailors maintenance techniques and technologies to each application.
- It integrates functions that support maintenance into maintenance program planning.
- It uses root-cause failure analysis and predictive analysis to maximize maintenance effectiveness.
- It periodically evaluates the technical content and performance interval of maintenance tasks (PM and PTI)
A successful maintainability program will have the following attributes:
- Corporate commitment
- Program support
- Maintainability planning
- Maintainability implementation
- Program updating
The maintainability process has six major milestones:
- Management commitment to maintainability. Demonstrated through commitment of resources, development policies, and designating a maintainability champion.
- Establishing a maintainability program. Demonstrated through development of a maintainability staff, procedures and a database.
- Obtaining maintainability capabilities. Demonstrated by establishing project level maintainability responsibility and developing resources for project maintainability reviews.
- Planning Maintainability implementation. Demonstrated by forming a cross-functional medical devices group, defining maintenance strategies and maintainability goals and integrating appropriate RCM technology
- Implementing maintainability. Demonstrated by conducting maintainability meetings, providing documentation and conducting maintenance training.
- Updating the maintainability program. Demonstrated by evaluating program effectiveness and updating the process in the database.
RCM is a common sense evidence based approach to maintenance. This system is becoming the industry standard and has been adopted by many large organisations.
Compiled and Edited by John Sandham IEng MIET MIHEEM