by Robert Holcombe

In 1998, ASTM Committee D13 on Textiles launched a Proficiency Testing Program. Designed to measure the proficiency of labs testing to various D13 standards for fabrics, the program has been successful in its mission and has resulted in the publication of a new D13 standard.

ASTM Committee D13 on Textiles initiated the development of the Proficiency Test Program (PTP) for Textiles after the publication of an article by Dean Flinchbaugh in the June 1995 issue of SN. This article described the formation of an ASTM-sponsored system of proficiency tests for laboratories with a specific field of interest.

Proficiency testing is a procedure for examining one aspect of a laboratory’s performance. It is accomplished by comparing test results generated between laboratories, otherwise known as “interlaboratory comparisons.” A comparison of actual test results from a proficiency study is one indication of the competence of the laboratory. Proficiency testing is similar to, but does not have the same purpose as, interlaboratory studies conducted to validate individual ASTM tests.

Why a PTP?

Having an internationally recognized PTP for the field of textile testing provides the participating laboratories with a strong tool not only for accreditation, but also for establishing customer confidence in their competence and test results. Prior to the inauguration of the ASTM PTP for textiles in 1998, each lab in the textile industry operated independently either with customers or other ad hoc groups involved with demonstrating proficiency. These efforts often resulted in several disjointed activities with mediocre programs that were questioned during the accreditation process. The comparisons of data had been inconsistent. The ASTM PTP was designed to provide participating laboratories with a statistical quality assurance tool that would enable them to compare their performance in conducting test methods within their laboratories and against other laboratories worldwide.

The initial concept for establishing an ASTM-sponsored proficiency testing program was presented to the D13 Executive Committee in October 1995. The Subcommittee on Inflatable Restraints, D13.20, was instructed to champion the program. Most of the interested laboratories were International Organization for Standardization (ISO)/ International Electrotechnical Commission (IEC) Guide 25-accredited and they were familiar with the requirements of a PTP. As a result, these labs were eager to be part of a recognized proficiency testing program. The program advisory group has since been assigned to the jurisdiction of D13.93, the subcommittee on Statistics, as well as the ASTM PTP staff.

The Startup

A survey, outlining the design of the proposed proficiency program, was mailed to ASTM D13 members in April 1997. The initial response indicated that at least 20 laboratories had participated in some type of ad hoc proficiency or interlaboratory testing study in the past. These same ASTM D13 member company labs were very interested in joining an ASTM-sponsored program that involved the internationally famous standard tests that they developed and used routinely in their laboratories. Some of the remarks made in response to the market survey were: “[a program like] this gives management confidence in the test results”; “too many labs are reporting invalid results and don’t know it”; “if we are to participate in the U.S. and international market, we must be able to prove proficiency and competence”; and “it is important to be accurate and have test results that are reliable and able to be correlated to other laboratory data involving the evaluation of textile products.”

The focus of the program is to use the ASTM methods that are commonly used to test and certify textile products. Using the critical end use of the fabric as a starting point in designing the ASTM PTP, the task group selected the fabric variables of construction, air permeability, tear resistance by tongue method, strength/elongation by the grab method, and strength/elongation by the strip method. Yarn and sewing thread methods may be added when enough interest is generated.

Based on requests from participants, the methods for tear resistance by falling pendulum and fabric mass/unit area have been added to the program’s scope of testing. A proficiency testing program on the flammability testing of textiles has been proposed, however, samples are not available at the present time.

In the beginning, it was hoped that 12 to 15 laboratories would participate. The first test cycle of the PTP was conducted in October 1998. Thirty-four laboratories participated. To date, the program currently has 70 participants of which 36 are international. The PTP has been presented, described, and discussed during a series of lectures in the Peoples’ Republic of China and it was well received (see International Scene). Those companies who participate in the PTP program represent domestic and foreign commercial textile testing laboratories of which many have plant or company support facilities.

Most of the participating laboratories are accredited. Some non-accredited laboratories participate in PTPs in order to satisfy particular customer demands, use results as an internal quality assurance tool and as a marketing tool. As a laboratory evolves into a position for accreditation, participation in a proficiency test program is typically mandatory by the accreditation body.

The Process

The ASTM documents that were used as guides in designing the program were:

• ASTM E 1301, Standard Guide for Proficiency Testing by Interlaboratory Comparison, and
• ASTM E 691, Standard Practice for conducting Interlaboratory Studies to Determine Precision of Test Methods.

The test materials used in the PTP are supplied in-kind from ASTM D13 member companies. The test specimens are prepared and distributed by an accredited host laboratory. Subcommittee D13.93 decides what fabrics will be used in the program. Representative fabric samples are selected from a homogeneous batch roll and identified. Homogeneous materials are considered to be those laboratory samples that are cut from the same batch (lot) sample and selected at random for use by the participants.

The PTP Data Report Package (DRP) containing the text instructions, cover letter and report forms are sent to the participants with the fabric samples for each test cycle. The PTP is conducted using three different test samples: a light, medium, and heavy fabric. A different sample set is distributed in February and August, which is the test cycle schedule for this PTP.

The laboratory reports the average and standard deviation of five determinations for each test method. All test results are submitted directly to ASTM’s proficiency testing service. A strict code of confidentiality is maintained by ASTM. Each participating lab is notified of their individual lab identification code number that applies to their test results in the final statistical summary report distributed to those participants who provided data.

All final report data appears in individual data tables by reporting parameter. The data is also presented in graphic output for easy, visual comparison of results. The final statistical summary report shows the position of each laboratory’s data plotted against the others.

The test results are reported using two statistical procedures. The fabric counts of construction are reported against an assigned value or correct response. The sample preparation company determines this assigned value. This value is determined by averaging several counts through the batch rolls. The other test method results are reported using the statistical technique of Z scores. The criteria for the Z score is:

• [Z] < 2 = satisfactory,
• 2 <[Z] < 3 = questionable, and
• [Z] > 3 = unsatisfactory.

The data, as generated and statistically treated, shows those participating laboratories that are capable of getting the same answer on the batch material as well as how each laboratory’s result compares to the data generated by all participants.

Feedback from the participants is welcomed and encouraged. Procedures for considering suggestions on program improvement are in place within Subcommittee D13.93.

One of a Kind

At the current time, the ASTM Proficiency Testing Program for Textiles is the only program of its kind that exists in the world. It has proven to be more comprehensive than first thought, and it has profound international recognition and participation.

The data generated from each PTP test cycle are made available to the individual D13 subcommittees for their information and use in revising or improving their ASTM standard test methods. The data is real-world, marketplace feedback on the ASTM program tests. The results of the PTP also aid the ASTM textile subcommittees in their effort to validate the PTP program tests by allowing for the development of sound precision and bias statements. As new methods are developed for particular and specific fabric variables, the PTP for textiles will provide valuable information and data that can be used to support technically credible statements on the reproducibility of the new method. The data generated from the broad-based international participation in the PTP will help produce credible international standard tests with known precision for the industry worldwide.

More Concrete Results

After the PTP was established and functioning, D 6674, Standard Guide for Proficiency Test Program for Fabrics, was written. Guidance on planning a proficiency test program, selecting the sample fabrics to be used, the testing protocol, and the calculations for the data to be reported are included should other ASTM D13 subcommittees endeavor to establish another PTP for fabric testing.

The guide is designed to meet the quality systems proficiency and competence requirements of participating laboratories. The guide follows the logic of full scale laboratory tests as described in D 2904, Practice for Interlaboratory Testing of a Textile Test Method that Produces Normally Distributed Data, and E 1301, Guide for Proficiency Testing by Interlaboratory Comparisons, except its emphasis is on proficiency testing. The methods described in the guide are applicable to methods based on the measurement of discrete measurement data and grades or scores.

ASTM D 6674 stands as a true testimony to the success and benefits derived by all parties associated with the ASTM Proficiency Testing Program for Textiles.

For more information and/or registration details on the PTP for textiles, visit the ASTM PTP Web page or contact Helen Mahy. //

Copyright 2002, ASTM