Traceability examples

Traceability Example Measur ement of Cadmium in Soil... 

FIGURE 33.3 Traceability Example All of the Functional Specifications and Design Specifications in This Table are Derived from the User Requirement Labeled URS-1. 

The general purpose of an audit may be to determine if the toller has management systems and documented procedures in place to ensure process safety, environmental responsibility, product quality and traceability of materials. The need to audit could be to evaluate compliance with regulations or accordance with client requirements related to specific performance elements. A subjective rating system for ranking management systems audit results is often used. An example of one that might be appropriate is shown below ... 

The reason for an Exposition is so that there is a description of the system showing how it works and how it controls the achievement of quality. This is different from the policies and procedures. The policies are a guide to action and decision and as such are prescriptive. The procedures are the methods to be used to carry out certain tasks and as such are task related. They need to be relatively simple and concise. A car maintenance manual, for example, tells you how to maintain the car but not how the car works. Some requirements, such as those on traceability and identification, cannot be implemented by specific procedures although you can have specific policies covering such topics. There is no sequence of tasks you can perform to achieve traceability and identification. These requirements tend to be implemented as elements of many procedures which when taken as a whole achieve the traceability and identification requirements. In order that you can demonstrate achievement of such requirements and educate your staff, a description of the system rather than a separate procedure would be an advantage. The Exposition can be structured around the requirements of ISO/TS 16949 and other governing standards. It is a guide or reference document and not auditable. 

Traceability is achieved by coding items and their records such that you can trace an item back to the records at any time in its life. The chain can be easily lost if an item goes outside your control. If, for example, you provide an item on loan to a development organization and it is returned some time later, without a certified record of what was done to it, you have no confidence that the item is in fact the same one, unless it has some distinguishing features the inspection history is now invalidated because the operations conducted on the item were not certified. Traceability is only helpful when the chain remains unbroken. It can also be costly to maintain. The system of traceability that you maintain should be carefully thought out so that it is economic. There is little point in maintaining an elaborate traceability system for the once in a lifetime event when you need it, unless your very survival, or society s survival, depends upon it. 

The standard of cleanliness which must be achieved has been stated to be that which will allow the subsequent process to be carried out satisfactorily . As an example, the degree of cleanliness required to satisfactorily zinc plate from an acid solution is somewhat higher than that required prior to zinc plate from a high-cyanide alkali zinc solution. This should never be taken as a licence to skimp on surface preparation. However, the arguments over surface-tolerant paint coatings abound and will probably continue. It is to a very large extent true that problems of early failure in metal finishing are traceable to incorrect or insufficient surface preparation. 

Very specific forms of low pH localized corrosion may develop in large high heat-flux WT boilers. Where subsequent analysis work is undertaken, the results usually provide the basis for a traceable chain of cause and effect. An example of such a chain of cause and effect is detailed in an interesting corrosion case history provided by Maringer, Saavedra, Selby, and Haberman, and published by Tall Oaks Publishing, Inc. A synopsis is provided below (with kind permission of Tall Oaks Publishing). 

The third approach is also known as a collaborative study or a collaborative trial. Both names underpin the joint effort of the coordinator and participants to characterize the reference material. In any case, the measurement methods used in the characterization should be traceable to what is called stated references , and preferably to SI. The aspect of traceability of measurement results goes well beyond the actual measurements it also includes the transformation of the sample from the state of the reference material to the state in which it can be measured. An example of such a transformation is the destruction of the sample. 

It should be recognized that, in some cases, it is not difficult to set up a traceable measurement system. The best examples of this are in physical metrology where traceability is often based on direct measurements of the SI units. There is also general agreement that a similar SI fink is highly desirable in the case of chemical measurements, but, for a variety of reasons, direct chemical traceability is difficult to achieve in most of the analytical chemistry applications. Only a very few analytical chemistry procedures exhibit a direct measurement capability that allows the set-up of a traceable measurement pathway such as in physical metrology measurements most of these procedures have been accepted as primary methods if carried out under certain constraints (CCQM 1998). 

In a different example, traceability in the amount-of-substance analysis of natural potassium, thorium, and uranium by the method of passive gamma-ray spectrometry was demonstrated by Nir-El (1997). For an absolute quantitative determination, accurate values of two parameters were required (i) the emission probability of a gamma-ray in the decay of the respective indicator radionuclides, and (2) the detection efficiency of that gamma-ray. This work employed a number of CRMs in the critical calibration of the detection efficiency of the gamma-ray spectrometer and the establishment of precise emission probabilities. The latter results compared well with literature values and provided smaller uncertainties for several gamma-rays that were critical for the traceabUity claim. The amount-of-substance analytical results of the long lived naturally occurring radionucHdes K, Th, and... 

Operationally, a procedure may be based on measuring the yield of a reaction traceable to ionization, usually giving a lower limit to the ionization yield. Thus, in the radiation chemistry of hydrocarbon liquids, the product of an electron scavenging reaction (for example, C2H3- radical from the scavenger C2H5Br)... 

In addition, a system for making sure staff are appropriately qualified and trained for the work that they are doing must be in place. This will enable an auditor to see clearly the demonstrated competence of the staff and how this has been checked. The requirements for all major items of equipment must be listed, to ensure that the equipment in use is suitable for the task, is in working condition and, where necessary, is calibrated. For all of the instrumentation there needs to be a documented schedule for maintenance. Measurements must be traceable, that is, the laboratory must be able to show how the calibration of measurement instruments is traceable to National or International Standards. Where this presents practical problems, as in some chemical measurements for example, interlaboratory comparison and the use of reference materials (and preferably Certified Reference Materials) will be required. 

Decoupling tends to introduce much more separation between concepts than is typically found in an analysis. For example, any aspect of an object s behavior that could conceivably be varied tends to get delegated to a separate plug-in module. Thus, we end up with many more types of objects than were mentioned in the specification. Nevertheless, our refinement techniques (see Chapter 6, Abstraction, Refinement, and Testing) enable us to keep the traceability between the two models. 

Are they traceable For example, to CRM, a reference method, interlaboratory comparison, or other. 

The highest quality reference materials are certified for the concentration values of the constituent(s) of interest, reflecting high confidence in the value s accuracy and the thorough investigation of all known or suspected sources of bias. Used appropriately (e.g., Roper et al., 2001 Zschunke, 2000), these certified values provide an effective means to ensure comparability (both among laboratories and over time). It is not always practical, however, to undertake the work required to produce a certified value in many such cases, a value can be carefully determined, but insufficient information exists to assess the associated uncertainty. This information value is nevertheless of substantial interest to other users of the reference material. It can, for example, allow laboratories to compare results even though full traceability is impractical. 

Where traceability of measurements to SI units is not possible and/or not relevant, the same requirements for traceability to, for example, certified reference materials, agreed methods and/or consensus standards, are required as for calibration laboratories. 

Part of this chain is formed by the analyst in his/her laboratory (the "end user"), while part of it may be formed between NIST and the vendors. For example, a laboratory analyst can purchase a primary standard acid (which a vendor can certify as traceable to an SRM) for solution standardization and then base a number of secondary standardizations, such as acids and bases, on that one primary standard. Similarly, an analyst can purchase an atomic absorption reference standard (which a vendor can again certify as being traceable to an SRM) and then make one or more dilutions of this reference standard before creating the final series for the standard curve. 

Sabe and Rauret [33] and Drolc et al. [34], however based upon the Eurachem/ CITAC guide on traceability [3]. In their examples, all authors take into account specific steps or influences in the analytical procedure which can lead to a broken chain of comparisons, such as sampling and sample treatment or preparation steps. Some authors have reported on uncertainties associated with sampling in particular [35,36]. 

Each of these principles will arise in some guise or other in this book. For example, principle 5 relates to metrological traceability (chapter 7) and measurement uncertainty (chapter 6). These principles will be revisited in the final chapter. 

In this chapter I use the term metrological traceability to refer to the property of a measurement result that relates the result to a metrological reference. The word metrological is used to distinguish the concept from other kinds of traceability, such as the paper trail of documentation, or the physical trail of the chain of custody of a forensic sample. When the term traceable standard is used to refer to a calibration material, for example, the provenance of the material is not at issue, but the quantity value embodied in the standard. 

From the definitions and examples above, it should be clear that metrological traceability is established by a series of comparisons back to a reference value of a quantity. In the mass example it is easy to picture a number of scientists with ever more sophisticated balances comparing one mass with another down the chain of masses from the international prototype of the kilogram to bathroom scales. This is known as a calibration hierarchy. A mass farther up the chain is used to calibrate the next mass down the chain, which in turn can be used to calibrate another mass, and so on, until the final measurement of the mass is made. 

The metrological traceability of a measurement result is rarely as straightforward as the chain of comparisons shown in the example of mass in fig-... 

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