What to look for in test reports

Reviewing the essential elements of SATRA test reports and how to understand them.

SATRA issues thousands of test reports every year. Some show compliance with a specification or requirements – often with respect to legislation, whereas others provide information on how a fault occurred and, in many cases, how it can be resolved. Some outline how a new design or product may perform.

Every test report must be understandable and fulfil the customers’ needs. All reports contain essential elements to give the customer confidence in the results while explaining the information contained within.

Accreditation

SATRA is accredited by the United Kingdom Accreditation Service (UKAS) to the ISO 17025 international standard. It has a quality system in place that covers every aspect of work – from staff training to customer communication. Documented procedures ensure that SATRA services are consistent, and that all work is done by trained, competent staff. This is overseen and audited regularly by UKAS. All tests within the UKAS scope of SATRA’s activities are reported under the UKAS logo, and include the company number. SATRA’s schedule of accreditation (those tests covered by UKAS accreditation) is displayed on the UKAS schedule.

Test methods

Test reports should always provide reference to the method used, and be clear about what has been tested (and what has not).

Most geographical areas will have standards, such as ISO (international), EN (Europe) and ASTM (US), while some standards may be developed by individual country standard makers – for example, British Standards. Other standards may be industry led, such as SATRA’s own TM standards for footwear.

In some cases, a test method may not exist, and the work may have been developed specifically for the client’s needs. If so, a full description of the procedure followed should be given, along with the results.

Careful testing is essential to produce valuable reports

Numerical results and detection limits

Usually, test results are shown by a numerical value, which allows comparison with previous testing. This would be included within the SATRA test report, whether a simple test or more complicated analysis has been conducted. If the work has been carried out to satisfy a requirement, the numerical value will show how well the product has performed. A borderline pass may cause concern about bulk production.

Results may also be expressed as below a numerical value, usually written ‘<x’. Generally, this is because the actual value is below the point at which the equipment or method used to carry out the test is deemed to be accurate. This point (the ‘detection limit’) varies between tests, as well as between the equipment used. It may also differ between laboratories, even if they have nominally used the same procedure.

Units

Results within SATRA reports are likely to be detailed as having a numerical value and a set of units. The units used govern the meaning of the numerical value. Knowing the units is important, as comparing results can be difficult (if not impossible) if they are unknown. For instance, a specification for leather might require a maximum level of a certain fungicide of 0.25 per cent. If specimens are sent to two separate laboratories, the results could be given in two ways – ‘laboratory A: 0.13 per cent’ or ‘laboratory B: 1,300ppm’.

The specimen from laboratory A has clearly met with the requirement. However, laboratory B’s result is expressed in ‘parts per million’ (ppm). A result in parts per million is a factor of ten thousand times larger than a percentage (1 per cent = 10,000ppm). Hence, the results are the same. If laboratory B had not presented the units as well as the result, we would not have known this, and so might have thought the specimen had failed.

Understanding the detail

This article is not comprehensive, but does serve as a guide to what to look for. All reports are different. If you are unsure whether the test report is suitable for your needs, we advise you to contact SATRA, as we can help to interpret the results. However, for reasons of confidentially we cannot discuss reports with third parties without written permission from our clients.

Basis

The ‘basis’ is most important for analysis carried out on leather and other materials that can gain and lose moisture. Leather can do this, depending on storage conditions. Under very dry conditions, leather can have a moisture content as low as 8 per cent. By contrast, it may be up to 20 per cent in very humid conditions. When a specimen is weighed for analysis, the moisture level will change the amount of leather actually being tested, thus affecting results.

Therefore, results may consider both moisture content and grease content. This is referred to as the ‘basis’, and should be reported along with the result. Using a different basis can lead to a different numerical value being obtained.

Generally the different types of basis used in analysis of leather are:

as received, with no correction for moisture or grease
dry weight, in which the result is calculated as if the leather contained no moisture. To do this, the moisture content at the time of analysis is also determined
14 per cent moisture. Here, the moisture content is determined and the results are calculated as if the leather contained 14 per cent moisture rather than the actual amount
dry fat-free weight has a result that is calculated as if the leather contained no moisture or grease. To do this, the moisture and grease content of the leather at the time of analysis are determined
14 per cent fat-free – The result is calculated with the moisture being 14 per cent and the grease content zero. This is also known as ‘86 parts fat-free’.

How old is the report?

Generally, the older the report, the less it should be relied upon to represent current production processes. SATRA reports will where possible clearly state the material or product that has been tested, as unclear references will make it difficult to tie the report to a specific product or material at a later date, and may make it unacceptable to some organisations.

How can we help?

Please email footwear@satra.com for assistance with the commissioning of test reports and correct interpretation of results.

Publishing Data

This article was originally published on page 8 of the January 2018 issue of SATRA Bulletin.