Big changes were made when EN13795, the European consensus standard for surgical gowns, surgical drapes, and clean air suits, published a new revision this year. The standard was split into two parts. Part one deals with requirements and test methods for surgical drapes and gowns, while part two addresses clean air suits.
Performance requirements are largely unchanged, but now require a statistical representation of the data rather than just providing all the testing data points. There has long been question whether to use individual results or the average of all results for approval of products. With the introduction of a “Treatment of Results” section in the Annex of the standard, manufacturers no longer need to guess how to determine compliance with the requirements. Built into the test statistic is an allowance for outlying results. There is now potential for products to comply with the standard requirements, which may have previously failed the testing when examining individual results. The introduction of upper and lower quartile test statistics gives an easy to follow guideline for determining compliance. This new treatment of results applies to all test methods except for the evaluation of wet microbial penetration (ISO 22610:2006).
For tests with maximum performance requirements, such as dry microbial penetration, microbial cleanliness, and particle release the upper quartile statistic, which is the medium, upper half of the data set, is used. Test sets in which the upper quartile result meets the performance requirement are considered compliant with the standard, whether all individual results meet the criteria or not. Take for example, the dry microbial penetration testing. The requirement for the less critical product area of either a standard performance or a high performance gown is ≤300 colony forming units (CFU) of the challenge organism detected after testing and incubation. Previously, if a sample set gave results per table 1 below, it would have been difficult to determine whether the sample was in compliance with the requirements of the standard.
Table 1. Example dry microbial penetration test results
|Sample #||Result (CFU)||Sample #||Result (CFU)|
The average of these results is 94 CFU, which meets the requirements of the standard, but an individual result is above 300 CFU. With the previous revision, there may have been some question about whether this product met the requirements of the standard. Using the new direction given in section A.3 of EN13795-1:2019, we can easily determine whether the product meets the requirement. First, order the values in the data set from smallest to largest:
0, 8, 20, 32, 40, 84, 106, 118, 222, 310
Next, multiply k percent (k = 0.75 for the upper quartile) by the number of values, n (10 in this case) to determine the index value. This gives us an index value of 7.5. Since this value is not a whole number, following the rounding instructions in the standard, we round the number up to 8, the nearest whole number. Next, look in the index at the ordered values and find the value corresponding to the index number (8 in this case).
0, 8, 20, 32, 40, 84, 106, 118, 222, 310
Compare this value (in red and bold) with the performance requirements to determine compliance with the standard. In this case, as the standard requirement is ≤300 CFU, the product would meet the performance requirements; in spite of the individual value, which is above the performance requirement.
Let’s look at another example using the lower quartile statistic which is the medium of the lower half of the data set. This is used for tests with a minimum performance requirement, such as liquid penetration, bursting strength, and tensile strength. The above exercise would be similar for a test that requires the lower quartile. Dry bursting strength of a high performance product, for example, requires a result of ≥40 kilopascals (kPa) for the critical product area. Let’s examine a test set with results (in kPa) of 133, 38, 128, 111, and 97. The 38 kPa result could be of concern, as this individual result is below the requirement of 40 kPa. Again, following the new test statistic instructions, we order the results from lowest to highest:
38, 97, 111, 128, 133
In this case, to calculate the index for the lower quartile calculation, k = 0.25, and n = 5 (as only 5 results are required). Multiplying 0.25 x 5 gives an index value of 1.25. According to the standard, this should be rounded up to 2.
Counting the values to reach the index number gives a value of 97 kPa.
38, 97, 111, 128, 133
Since this value is above the minimum requirement set by the standard, the test set passes the criteria. If the sample which gave the 97 kPa result had performed worse, for example a 39 kPa, this test set would have failed to meet the criteria, as the Lq would have been the result of 39 kPa.
The test method standards have remained unchanged in this revision of EN 13795; in spite of a new revision of BS EN ISO 22610 Surgical drapes, gowns and clean air suits, used as medical devices, for patients, clinical staff and equipment. Test method to determine the resistance to wet bacterial penetration, published in 2018, EN13795-1:2019 continues to require testing to the 2006 version of this standard. Since ISO 22610 already has a test statistic built into the calculations (Index Barrier, IB), this test was not included in the treatment of results quartile calculations and the IB should be compared to the performance requirements table for compliance.
There is another big change that could potentially impact manufacturers sampling plans for testing. Annex A indicates, “Testing shall include potential weak spots.” This statement was also in the previous revision but this new revision adds a note, which states, “In particular, all types of joints in critical areas, such as seams in sleeves of surgical gowns, are regarded as potential weak spots.” This new note makes it clear that manufacturers should test any seams or points of attachment within the critical area of the gown or drape as defined by the manufacturer. AAMI PB70, Liquid barrier performance and classification of protective apparel and drapes intended for use in health care facilities, is one US analog of EN13795. This document has long included requirements to test potential weak spots such as seams and tie attachments, and gives specific requirements to the number to test for each area. The requirements for compliance with PB70 contain a full set of testing on each potential weak area in addition to testing the base material alone. While EN13795 does not define specific requirements about how testing of potential weak spots should be approached, the requirements in PB70 can be used to give guidance. Joint and seam areas in critical areas of products should be considered weak spots, and should be subjected to testing to ensure full protection for health care workers and their patients.
Fire risk in relation to the use of products tested under EN13795 should be evaluated and included in information about the products. The standard recommends that you make a clinical evaluation of products prior to their end use to test characteristics that may not be adequately captured in the testing required by the standard. This will help ensure suitability and comfort during end use of the products.
The changes to this requirement make the document easier to follow, and introduce a simplified approach to determining compliance with the performance requirements. Clearer instructions about how to treat the testing results will lead to fewer questions about compliance. Instructions for manufacturers and processors aid in their determination of an appropriate sampling plan.