Impact penetration tests measure the resistance of fabrics to the penetration of water by impact. The test was developed to predict the probable rain penetration resistance of a fabric and most methods still include this language in the scope. The test has also been adopted by the medical industry as a measure of liquid barrier performance for protective apparel and drapes.
A test specimen is mounted tautly, face-up on an angled surface. A pre-weighed sheet of blotter paper is mounted behind the specimen. A volume of water is sprayed against the face of the specimen. The blotter paper is then re-weighed to determine water penetration. The increase in mass of the blotter paper indicates the mass of water that passed through the test specimen. Lower test results indicate less penetration and better water repellency or resistance of the fabric.
There are several versions of this test, all based on the AATCC test method originally published in 1945. Perhaps most importantly for the current environment, the impact penetration test is one of several used to evaluate Level 1-3 barrier materials for medical personnel personal protective equipment. Anyone developing, producing, or testing surgical gowns, isolation gowns, other protective apparel, surgical drapes, or drape accessories must understand how to select the correct test method.
ANSI/AAMI PB70, Liquid barrier performance and classification of protective apparel and drapes intended for use in health care facilities, outlines the requirements for protective apparel and drapes.
AATCC TM42, Test Method for Water Resistance: Impact Penetration, is a required test for materials classified as Level 1-3; however, it must be performed with an alternate blotter paper. The blotter paper specifications are included in the AAMI PB70 standard.
The most recent version of AAMI PB70 also allows WSP (Worldwide Strategic Partners) 80.3 as a substitute for AATCC TM42. WSP 80.3 has since been superseded by NWSP (Nonwovens Standard Procedure) 80.3. The blotter paper specified in these methods is close but not quite the same as that described in AAMI PB70. Different versions of NWSP 80.3 specify different mass per unit area, while the AAMI standard lists no value for this property. Since no year is cited, one can assume that the most recent version of NWSP 80.3 should be used.
Although the AAMI standard indicates that the methods are equivalent, there are small differences that could impact results for some materials. All reports should indicate which impact penetration test was performed. A complete comparison of the AATCC and NWSP methods is included below.
The blotter has been a source of confusion and frustration. The blotter paper traditionally used for AATCC TM42 should NOT be used for testing and classification of barrier performance according to AAMI PB70. As noted above, the blotter paper described in the AAMI and NWSP standards are not exactly the same. A complete explanation of the differences is included below.
For practical purposes, EDANA (the publisher of NWSP 80.3) recommends Ahlstrom grade 989 blotter paper, while indicating that other papers may also be suitable. Note that not all properties specified in AAMI PB70 or NWSP 80.3 are listed on data sheets provided by the blotter paper manufacturer and not all properties listed match the specifications exactly. For example, one data sheet indicates a target absorbent capacity of 512.0%, with a minimum of 434.0% and a maximum of 590.0%; AAMI PB70 requires an absorbent capacity of 480% ±30% (450% – 510%); NWSP 80.3 requires an absorbent capacity of ≥ 480%.
For AAMI PB70 Level 1-3, perform AATCC TM42-2017e as written, with the exception of the blotter paper. Use blotter paper meeting the specifications listed in AAMI PB70, section 5.2.1.2. For borderline results on nonwoven fabrics, it may be helpful to use a Type II tester to reduce vibrations during testing.
As an alternative, perform NWSP 80.3.R1 (19) as written. Use blotter paper meeting the specifications listed in NWSP 80.3.R1. Be sure to indicate the version of the method used as there are significant differences in the blotter paper specified in previous versions.
Perform AATCC TM42 or NWSP 80.3 to meet AAMI PB70 requirements; do not perform both tests.
Use the sampling plan indicated in AAMI PB70 whether testing with AATCC TM42 or NWSP 80.3. This will typically require more specimens than called for in the test methods. In most cases, 15-20 specimens per component is appropriate. If fewer specimens are tested due to limited sample size or agreement among all parties, this should be noted in the test report.
While AATCC TM42 and NWSP 80.3 are intended for testing unsewn fabric, AAMI PB70 also requires testing of seams and attachment points as these are the most likely point of failure for water resistance. Test each relevant component (base material, seam, attachment, etc.) of the protective apparel or drape separately.
Center seams widthwise so they run along the length the specimen. Center points of attachments on the specimen (see Fig. 1). Test multi-layer products as they are used in the final product—include all layers in the correct order, outermost layer on top (facing the water spray). Specific guidance on critical zones for testing is included in AAMI PB70.
Perform additional tests (AATCC TM127, ASTM F1671, ASTM F1670) as needed, depending on intended AAMI PB70 classification level.
Fig. 1 Center seams widthwise so they run along the length the specimen (left). Center points of attachments on the specimen (right).
Summary
For AAMI PB70 Level 1-3, perform AATCC TM42-2017e as written, with the exception of the blotter paper. Use blotter paper meeting the specifications listed in AAMI PB70, section 5.2.1.2.
As an alternative, perform NWSP 80.3.R1 (19) as written. Use blotter paper meeting the specifications listed in NWSP 80.3.R1.
In most cases, 15-20 specimens per component is appropriate.
Test each relevant component (base material, seam, attachment, etc.) of the protective apparel or drape separately.
Perform additional tests (AATCC TM127, ASTM F1671, ASTM F1670) as needed, depending on intended AAMI PB70 classification level.
