We can identify how significant each failure mode is by examining the system effects. In this case, failure to start can eventually cause loss of life. However, if we have another power source, say a bank of batteries, the failure to start of the engine will not really matter. There may be some inconvenience, but there is no safety implication. The failure is the same; that is, the engine does not start, but the consequences are different.
The purpose of maintenance is to ensure that the system continues to function. How we maintain each sub-system will depend on the consequences, as described by the system effects. For example, if the failure of an item does not cause immediate loss of function, we can limit the maintenance to repairing it after failure. In each situation, the outcome is dependent on the configuration of the facility. The operating context may differ in seemingly identical facilities. The FBD and FMEA will help identify these differences and take the guesswork out of decision making.
The elegance of the functional approach will now be clear. For every business, we can define its objectives at the top level, or its overall functions. We can break these down to identify the related systems and sub-systems. Next, we identify the functions of each system and sub-system, and carry out an FMEA. The analysis is applicable to an operating plant or to one that is still on the drawing board. As a result of this top-down approach, we can concentrate the planning effort on what really matters to the organization.
Individuals and organizations can fall into the trap of rewarding activity instead of the results achieved. Movement and activity are often associated with hard work. Sometimes this is of no avail, so activity by itself has no merit. We have to plan the work properly so as to achieve meaningful results.
The functional analysis concentrates on the results obtained, and the quality standards required. We have discussed its use in the context of maintenance work, but we can apply the method in any situation where we can specify the results clearly. For example, Knotts1 discusses their use in the context of business process re-engineering.
2.5 PREVENTION OF FAILURES OR MITIGATION OF CONSEQUENCES?
Once we identify the functional failures, the question arises as to how best to minimize their impact. Two solutions are possible:
1.We can try to eliminate or minimize the frequency of failures or
2.Take action to mitigate the consequences.
If we can determine the root cause of the failure, we may be able to address the issue of frequency of events. Usually, this will mean elimination of the root cause. Historically, human failures have accounted for nearly three quarters of the total. Hence, merely designing stronger widgets will not always do the trick. Not doing the correct maintenance on time to the right quality standards can be the root cause, and this is best rectified by re-training or addressing a drop in employee motivation. Similarly, changes in work practices and procedures may eliminate the root cause. All of these steps, including physical design changes, are considered a form of redesign. In using these methods,we are attempting to improve the intrinsic or operational reliability of the equipment, sub-system, or system. As a result,we expect to see a reduction in the failure rate or frequency of occurrence.
An alternative approach is to accept the failure rates as they are, and devise a method to reduce their consequences. The aim is to do the applicable and effective maintenance tasks at the right time, so that the consequences are minimal. We will discuss both of these risk reduction methods, and the tools we can use, in Chapter 10.
Once we identify the tasks, we schedule the tasks, arranging the required resources, materials, and support services. Thereafter, we execute the work to the correct quality standards. Last, we record and analyze the performance data, to learn how to plan and execute the work more effectively and efficiently in the future.
When there are safety consequences, the first effort must be to reduce the exposure, by limiting the number of people at risk. Only those people who need to be there to carry out the work safely and to the right quality standards should be present. Maintaining protective devices so that they operate when required is also important. Should a major incident take place in spite of all efforts, we must have damage limitation procedures,equipment designed to cope with such incidents, and people trained in emergency response.
At the time of this writing, the details of the Fukushima Dai-ichi power station disaster in Japan in March 2011, following the severe earthquake and tsunami, are not very clear. However, the management of damage limitation seems very poor. Apart from the physical damage occurring to the soil around the plant with conflicting radiation levels being reported in the produce, seawater, and sea life, the release of information seems very poorly managed. As we will see in Chapter 7, people feel a great sense of dread and uncertainty when there is a lack of full and timely disclosure of information.
Some years ago, we saw an example showing the usefulness of such damage limitation preparedness. In September 1997, an express train traveling from Swansea to London crashed into a freight train, at Southall, just a few miles before reaching London-Paddington station. The freight train was crossing the path of the passenger train, which was traveling at full speed, so one can visualize the seriousness of the accident. The response of the rescue and emergency services was excellent. The prompt and efficient rescue services should be given full credit as the death toll could have been considerably worse than the seven fatalities that occurred.
The functional approach is aligned closely with the objectives of a business. The IDEF methodology is an effective way to understand and communicate this approach. We used this tool to understand the functions of a range of applications, from pencils and pizza business to gas compression systems in process plants. A clear definition of the functions enables us to identify and understand functional failure. Thereafter, we use the FMEA to analyze functional failures. We make a distinction between the use of the functional and equipment level FMEAs. Using a top-down approach, we identify functional failures and establish their importance.
In managing risks, we can try to reduce the frequency of failures or mitigate their consequences. Both methods are applicable,and the applicability, effectiveness, and cost of doing one or the other will determine the selection. Lastly, we touched on the importance of damage limitation measures.
REFERENCES
1.Knotts, Rob. 1997. “Asset Maintenance Business Management:A Need and An Approach.” Exeter: Proceedings, 7th International M.I.R.C.E. Symposium on System Operational Effectiveness, pp. 129-133.
2.Mayer, R.J. 1994. “IDEFO Functional Modeling: A Reconstruction of the Original.” Air Force Wright Aeronautical Laboratory Technical Report. Knowledge Based Systems Inc. AFWAL-TR-81-4023.
3.Jones, R.B. 1995. Risk-Based Management: A Reliability-Centered Approach. Gulf Professional Publishing Company. ISBN: 0884157857.
4.Davidson J. 1994. The Reliability of Mechanical Systems. Mechanical Engineering Publications, Ltd. ISBN: 0852988818. pp. 78-82.
Further Reading
1.Anderson R.T., and L.Neri. 1990. Reliability Centered Maintenance:Management and Engineering. Springer. ISBN: 9781851664702.
2.Moubray J. 2001. Reliability-Centred Maintenance. Industrial Press, Inc. ISBN: 978-0831131463
3.Smith