Software Fmea Techniques
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Failure mode and effects analysis (FMEA; often written with \"failure modes\" in plural) is the process of reviewing as many components, assemblies, and subsystems as possible to identify potential failure modes in a system and their causes and effects. For each component, the failure modes and their resulting effects on the rest of the system are recorded in a specific FMEA worksheet. There are numerous variations of such worksheets. An FMEA can be a qualitative analysis, but may be put on a quantitative basis when mathematical failure rate models are combined with a statistical failure mode ratio database. It was one of the first highly structured, systematic techniques for failure analysis. It was developed by reliability engineers in the late 1950s to study problems that might arise from malfunctions of military systems. An FMEA is often the first step of a system reliability study.
The analysis should always be started by listing the functions that the design needs to fulfill. Functions are the starting point of a well done FMEA, and using functions as baseline provides the best yield of an FMEA. After all, a design is only one possible solution to perform functions that need to be fulfilled. This way an FMEA can be done on concept designs as well as detail designs, on hardware as well as software, and no matter how complex the design.
When performing an FMECA, interfacing hardware (or software) is first considered to be operating within specification. After that it can be extended by consequently using one of the 5 possible failure modes of one function of the interfacing hardware as a cause of failure for the design element under review. This gives the opportunity to make the design robust for function failure elsewhere in the system.
During the 1970s, use of FMEA and related techniques spread to other industries. In 1971 NASA prepared a report for the U.S. Geological Survey recommending the use of FMEA in assessment of offshore petroleum exploration. A 1973 U.S. Environmental Protection Agency report described the application of FMEA to wastewater treatment plants. FMEA as application for HACCP on the Apollo Space Program moved into the food industry in general.
Although initially developed by the military, FMEA methodology is now extensively used in a variety of industries including semiconductor processing, food service, plastics, software, and healthcare. Toyota has taken this one step further with its design review based on failure mode (DRBFM) approach. The method is now supported by the American Society for Quality which provides detailed guides on applying the method. The standard failure modes and effects analysis (FMEA) and failure modes, effects and criticality analysis (FMECA) procedures identify the product failure mechanisms, but may not model them without specialized software. This limits their applicability to provide a meaningful input to critical procedures such as virtual qualification, root cause analysis, accelerated test programs, and to remaining life assessment. To overcome the shortcomings of FMEA and FMECA a failure modes, mechanisms and effect analysis (FMMEA) has often been used.
The FMEA worksheet is hard to produce, hard to understand and read, as well as hard to maintain. The use of neural network techniques to cluster and visualise failure modes were suggested starting from 2010. An alternative approach is to combine the traditional FMEA table with set of bow-tie diagrams. The diagrams provide a visualisation of the chains of cause and effect, while the FMEA table provides the detailed information about specific events.
An empirical study of introducing the Failure Mode and Effect Analysis technique to Norwegian business critical software developers Department of computer and information Science, Norwegian University of Science and Technology Torgrim Lauritsen, Tor StålhaneAbstractThis article describes an experiment with three Norwegian IT companies, who develop business critical software. The goal of the experiment was to evaluate if it is beneficial to use safety analysis techniques when developing business critical software. The participants in the experiment tried to identify possible failure modes from a class diagram. Half of the participants used the Failure Mode and Effect Analysis (FMEA) method that is widely used in the development of safety critical systems, while the other participants used ad hoc brainstorming. The number of failure modes is used as an indicator for the effectiveness of each technique. Our experiment showed that the participants that used ad hoc brainstorming wanted a method that could help them to reveal more problems. The participants who used the FMEA method found the method useful because it was easy to understand and helped them to identify failure modes in a structured way.
Unfortunately, meeting safety requirements is not a simple matter such as meeting a set of written specifications . The design effort needed to make a system safe is one of a series of coordinated activities needed to assure that the final product will be safe. We believe that developers who develop business critical software must, in addition to satisfying the functional requirements, also add safety requirements to their solution, [9, 10], or else, the software will undermine the prospects for creating value and delivering profits to businesses . The rest of this paper is organized as follows: First we give a short description of the FMEA technique. Thereafter we describe the experiment and the results from the experiment. Finally we conclude the paper and discuss some further work.
The Failure Mode and Effect Analysis (FMEA) is a method that is widely used for reliability analysis of systems, subsystems, and individual system components . FMEA was introduced in 1954, and formalized in 1968. FMEA has been used with success for many years in safety-critical systems like avionics, trains, and nuclear plants and for the process industry. FMEA allows a systematic analysis of possible hazards and failures, and also allows us to assess the effects of these hazards and failures on the components of a system. In object oriented software development this can, for instance, be classes and their methods . A method is formally a part of the object structure and as long as all methods of an object are executing in accordance with their specification, the object has not failed. Conversely, when a method does not execute in accordance with its specification, the object has failed. The failure effect will depend on the conditions under which the method failed. For example, look at the class diagram shown in figure 1, where objects are uniquely characterized by their methods. Analysing and searching for failure modes in a class diagram using FMEA is done by filling out the FMEA table shown in table 1.
We wanted to evaluate the effect FMEA could have in a business critical software development environment. Our experiment was designed as an exploratory and qualitative study. The goal of the experiment was to see if the participants would
We coded the results from the experiment, and the failure mode categories found by each group are shown in table 2. The failure modes can, if used as a basis for additional safety requirements, help to reduce the hazard of using the software.
Table 2. Failure modes We use a paired t-test because we wanted to determine whether the two techniques are likely to have the same mean of the two samples. The paired t-test (p-value one tail = 0.27) shows no evidence that the FMEA group identified more failure modes than the ad hoc brainstorming group. The conclusion from our first research question (RQ1) is therefore that there is no difference between the FMEA technique and the ad hoc method when it comes to the number of failure modes identified.
Table 3. How do you analyze and reduce failures in your software systems We see that the participants do some preventive work, e.g. analysis and continuous considerations of failure situations, but their main focus is on testing. 19 of 36 answers consider testing when they want to analyze and reduce failures in their software systems. It is, in our opinion too late to consider safety when the implementation is finished. We asked the participants if they were familiar with any safety analysis techniques such as Hazard and Operability analysis (HazOp) or FMEA, but got only two positive answers, and only one of them said he uses safety analysis techniques actively in his work but without specifying which safety analysis techniques he uses. After the experiment, we gave the two groups (A and B) tailored questionnaires. The answers from the ad hoc group are presented in section 4.3, while the results from the FMEA group are presented in section 4.4. In section 4.5 we discuss possible threats to the validity of our conclusions.
Three participants were sure that they had found more problems and failure modes with the FMEA method than without it. The other three participants, however, were not totally sure that they had found more problems and failure modes with the FMEA method. When we asked them if they found the FMEA technique helpful, we got the answers summed up in table 6. All participants felt that the FMEA method helped them to structure the failure identification process. The FMEA method was easy to understand based on the problem we showed them during the experiment. The answer to our second research question (RQ2) is thus yes, the software developers found the FMEA method useful.
Application of FMEA to software design anticipates defects before they occur, thus allowing quality to be built into software products. Software FMEA assesses the ability of the system design, as expressed through its software component, to react in a predictable manner to ensure system safety. Thus, Software FMEA is a form of Design FMEA. 781b155fdc