Finding the right test for PPE
Many firefighters take for granted that their clothing and equipment go through a number of rigorous tests. Firefighters expect that the certification of the various PPE products on which they depend takes care of all the little details, whether it is how the clothing is designed or more importantly how it performs.
They realize that a number of different tests go into how clothing is evaluated for its acceptability but rely on the label indicating conformity to the standard and the mark of the certification organization to know that it is appropriate to wear.
However, what many firefighters do not know is how the committees that write standards come up with the tests that establish the safety of their gear. In this article, we would like to pass on our knowledge for what goes into finding the right test.
The testing of bunker gear and all the elements that make up the protective ensemble that firefighters wear is a critical business. These tests and the criteria written for the tests determine what materials will be used, how those materials interact, and how the various materials, components, subassemblies, and overall product function for your protection.
It would be nice if we could say that a very systematic and comprehensive scientific process governs how everything comes together. But the fact is the process is more piecemeal, with more starts and stops in the development of tests than we would care to report.
This is a little unnerving because there is essentially a network of tests, the result of which is the product that you wear. Furthermore, the tests are not independent of one another. Setting a requirement too high in one area may make it impossible to achieve an appropriate level in a different area.
The latter situation creates tradeoffs. For example, it would seem only natural to increase the insulative qualities of bunker clothing to their maximum. But in doing so, breathability, flexibility, and comfort would be sacrificed. So there must be a balance and this is only one consideration in choosing a test.
So how does a committee that writes standards on firefighter protective clothing choose the right test? The answer, if the process is followed correctly, is through a series of well considered steps.
Determining the need
The first part of the process is to determine the need. As standards are written by committee and public input is a key part of the process, ideas for changing an existing standard can arise from a multitude of sources.
One such source may be a firefighter who wants to prevent exposure to a certain type of hazard where injuries occur. Another possible source may be a manufacturer or material supplier who believes that some new product or fabric technology can benefit the fire service.
The need must come first and that need should be based on solving a genuine problem. The solution to the problem can be a change in the design for a product, but preferably it should be a performance-based answer. Performance based criteria becomes something that can be measured and hence establishes the need for a test.
Test methods that are able to measure the specific area of concern should be selected . Further, any procedures that are used should be repeatable so that any laboratory can run the test and get the same results.
Finally, and most importantly, the test should discriminate the performance of the firefighter protective clothing consistent with field observations. The last part is absolutely the most essential step because there can be tests that make what seem to be relevant measurements and can provide reproducible results, but then fail to relate those results in a meaningful way to field performance. A good test is one that ranks or rates products the same way that firefighters experience those products.
The best way to illustrate this process is by going over some examples, some positive and others perhaps less so.
Heat loss testing
As a first example, consider total heat loss testing for garments. The total heat loss test was implemented in the 2000 edition of NFPA 1971 for structural firefighting protective clothing using a very systematic process. The problem or need was heat stress.
Fire departments could specify any level of thermal insulation they wanted, usually by requesting high thermal protective performance ratings for the clothing systems they purchased.
While providing more insulation from heat, these same systems prevent heat escaping from firefighters' bodies and led to high incidences of heat stress. In fact, stress-related causes still lead firefighter fatalities.
The total heat loss test was proposed as a solution, but even though the test could show differences between fabric systems and had a certain level of repeatability, there were concerns as to whether it provided a relevant discrimination of firefighter clothing.
After all, like most tests applied to clothing, only pieces of the material are tested, not the full clothing system. In 1998, the International Association of Fire Fighters put together an extensive field study to evaluate a number of different firefighter clothing using material systems with a range of total heat loss, including some clothing systems that would be considered extremes in the test method measurements (e.g., no moisture barrier on one end and totally impervious systems on the other).
The study was able to show a significant correlation for the measurements of total heat loss on material systems with the impact of the clothing made of the same material systems on firefighter physiological responses.
Consequently, the total heat loss test was included in the standard for garments and eventually the IAFF requirement was adopted. This example shows a case where a test method was properly identified and validated through a field study.
Over many years, there has been a concern that firefighters get burned under ordinary fireground exposure conditions. The specific issue is that the clothing exterior layers get hot and absorb heat and then when compressed against the body by kneeling, leaning, or even bending a limb, the energy stored in the material layers transfers to the skin and causes burn injuries.
The phenomenon, known as "stored energy," led to an effort that lasted more than 15 years to find the right test. Eventually, through some independent research and public funding, a test method was developed and work was carried out to determine the repeatability of the test method.
Unfortunately, none of the effort focused on establishing the link between the test method results and the incidence of firefighter burn injuries. While there was some evidence to suggest that the test could be applied to areas of the garment that were reinforced with exterior impermeable and relatively dense materials, there was equal information that showed that these same areas could sometimes result in greater protection than the surrounding parts of the garments.
The stored energy test and related performance criteria will be introduced into the next (2012) edition of NFPA 1971, but it is unknown what benefit or effect the new test will have on firefighter protection until its impact is analyzed some time after clothing is introduced with modifications needed to accommodate this test.
This example shows how a test can be selected and positioned for attempting to address problem, yet the uncertainty in its implementation shows why it is important to relate field observations for setting the acceptance criteria.
One final example relates to gloves. As gloves have evolved to address the increasing demand for improvements in hand function and dexterity, some design changes have come at the expense of thermal insulation to the firefighter's hands.
During the revision process for the 2007 edition of NFPA 1971, a conductive heat resistance test was added to the back of the gloves. This was a curious change because there was already a conductive heat resistance test for the palm side of the gloves where firefighters could more likely expect to come in contact with hot surfaces.
Another interesting part of this change was that the pressure applied to the back of the gloves was four times that of pressure applied to the palm, making the back of the glove tested to a more rigorous requirement.
This requirement turned out to be one of the more limiting tests of gloves in the standard and manufacturers complained that the test marginalized many of the glove products already in the industry.
This led to attempts for finding a more appropriate test based on a radiant heat exposure, the type of field exposure that generally occurs when the back of a firefighter's hands were burned.
A number of different tests were proposed and considered, but it was not until a major large metropolitan department experienced a series of back-of-the-hand burn injuries after changing gloves that it became clear which test was more appropriate.
All of the new tests failed to predict the department's burn injuries; however, the original high pressure conductive heat resistance test properly ranked the products in terms of the back-of-the-hand heat protection.
This situation demonstrates a key point in testing — a good test does not always have to simulate the event at hand to properly discriminate product performance. Instead, a good test is one that properly predicts field performance, as was the case for a seemingly wrong conductive heat resistance test. The upshot for all of these findings was that the committee decided to retain the old test in deference to other, more sophisticated tests.
Developing new tests to demonstrate product performance for protecting firefighters is not an easy process. The committees responsible for PPE standards are generally getting better at this process, but it is still a difficult challenge. The most successful processes occur when a clear need is identified, a test is selected that provides a solution to that need, and when it can be demonstrated that the test will produce results that can show field-performance based benefits.
Post note from Grace: Back in the 1980s, Jeff was heavily involved in the different NFPA committees and I can remember many days when Jeff would play with our daughter in the afternoon and then do "all nighters" for incorporating the comments and the revisions for the many standards he was involved in, as well as attend the meetings. Earlier this year, Jeff received a letter from the National Fire Protection Association acknowledging his contributions for over 25 year for technical committee service. I am proud of him for his participation to the fire service industry in the NFPA codes and standards process; it is a noteworthy achievement! Congratulations!Sponsored by Globe
Jeffrey O. and Grace G. Stull are president and vice president respectively of International Personnel Protection, Inc., which provides expertise on the design, evaluation, selection and use of personnel protective clothing, equipment and related products to end users and manufacturers. They are considered amongst the leading experts in the field of personal protective equipment. Send questions or feedback to Jeff or Grace at Jeffrey.O.Stull@FireRescue1.com. The views of the author do not necessarily reflect those of the sponsor.