Putting Gloves to the Test
Material testing: a manufacturer's strong point
By Lisa Arnseth
Whether a procedure is being performed in the OR or in an exam room, gloves are a crucial part of the job. Evaluating the durability of the glove under a variety of situations is not something to be done on the floor, but by the manufacturer through a variety of research and development applications.
Several manufacturers and industry professionals have developed a set of standards to determine the amount of strain a glove can handle before it will compromise its protection abilities. The American Society for Testing and Materials (ASTM) has formulated voluntary consensus standards for several industries, including the medical materials arena. Manufacturers follow the ASTM prescribed testing methods and classifications. Timothy Brooke is a manager in the Technical Committee Operations division and a spokesman for the ASTM's Committee D11 on Rubber. According to Brooke, the committee is made up from manufacturing representatives, academia and healthcare workers as well as FDA representatives. The FDA is the governing body that oversees whether or not certain gloves are acceptable to be sold in the US. "We (ASTM) essentially manage the process whereby the standards are developed," says Brooke.
Several of the top glove manufacturers refer to ASTM standards when preparing gloves for market release. Richard McManuis a product manager at Instron Corporation, a materials testing equipment provider, based in canton, MA answered some common questions as to what happens to a glove before it reaches the healthcare worker.
How has glove testing technology changed over the last decade?
McManuis: Modern glove materials stretch more before failure. This requires testing instruments to have a larger test area and more crosshead travel if standard specimens are used. More suppliers are using software today to automate data collection, result calculations and reporting.
More manufacturers are also using a strain measuring instrument called an extensometer in place of having the test operator hold a ruler beside the specimen to "eyeball" extension during the test. Since the rubber is very thin, new video extensometers that do not physically contact the specimen are beneficial.
What are the common testing methods used by manufacturers today to test gloves prior to hospital utilization?
McManuis: Mechanical testing is limited to measuring tension and strain, and then calculating stress at various points. Typical tension test results are tensile strength, ultimate elongation, and stress at 500% strain.
How are physical factors, such as flexure, friction and tension, tested by manufacturers?
McManuis: Flex and peel tests are not done on glove materials. There is some tear and some coefficient of friction testing done but tension is by far the most common mechanical test. ASTM D3577 specification for rubber surgical gloves, ASTM D3578 specification for rubber examination gloves and ASTM D6319 specification for nitrile examination gloves for medical application all recommend ASTM Method D412 for tension testing. Some suppliers have changed from using the ASTM D412 die C specimen to the shorter die D specimen to reduce the absolute crosshead travel required to produce failure. Peel tests are often done on glove packaging.
How can the aforementioned tests fail?
McManuis: The mechanical tests are a reliable measure of glove performance. Correlation between test results and in-use failure is straightforward.
In regards to quantity of actual gloves tested, do manufacturers tend to do spot-testing?
McManuis: QC testing protocols vary but are usually either spot tests or some fraction of production quantity. The mechanical tests are destructive so it is not possible to do 100% testing. Some testing is for research and development purposes as well. Gloves are normally tested as they come off the production line and after accelerated aging as specified by ASTM Method D573.
How are tests performed differently for different types of gloves?
McManuis: I am not aware of different test methods as a function of end-use. Most glove materials exhibit 700% to 1000% strain to failure. Pulling a glove onto the hand requires no more than 200 to 300% strain, so there is a good safety factor.
Are there any new testing methods on the horizon, especially when it comes to new glove materials now on the market, such as nitrile?
McManuis: There has been a notable increase in latex sensitivity problems driving suppliers to provide nitrile rubber gloves in addition to natural rubber. ASTM Specification D6319 for nitrile gloves was adopted just last year (2000), but it recommends the same tension test method since the end-use has not changed.
As more and more materials come into use, I do not expect to see any significant change in the mechanical test methods.
For more information on the ASTM and information on ordering the Annual Book of ASTM Standards, visit www.astm.org.
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