By Jeffrey O. and Grace G. Stull
Of all the parts in the firefighter’s protective ensemble, perhaps the most challenging design and performance goals exist for gloves. Gloves are by far the cheapest of any part of bunker gear, and in some departments gloves are considered a commodity item subject to frequent replacement.
Gloves are also unique in the firefighter anatomy they must protect. The hands have one of the highest ratios of surface area to body volume (second only to the ears). This means that there is less body mass under the glove to store and dissipate the heat before the onset of a burn injury.
There has been a great deal of discussion on the firefighter gloves, their design, and the acceptable minimum protection that is needed in the fire service. We recently had an opportunity to visit North Carolina State University where they are involved in current research funded by the Department of Homeland Security to investigate new methods for understanding and evaluating whole hand protection for firefighters.
Gloves, like turnout gear, are subject to a large number of requirements for structural firefighting as specified in NFPA 1971. These requirements pertain to their design and the performance properties. Design criteria cover the length of the glove and the proportion of the hand that is protected by the glove relative to the interface that exists between the gloves and coat sleeves.
These requirements also focus on the number of minimum sizes that should be provided by the glove manufacturer. Right now, manufacturers are required by NFPA 1971 to provide their gloves in sizes ranging from extra-extra-small to extra-extra-large for a total of seven sizes. Nevertheless, the number of glove sizes that are available come nowhere near the number of sizes that must be provided for footwear or garments. This is important to realize because like any type of apparel, good fit is essential for proper protection, functionality and comfort.
Specific tests
Gloves and glove materials are subjected to a number of specific tests. These tests examine the performance of gloves in terms of several properties, including flame resistance, heat resistance, thermal insulation, barrier protection, physical hazard resistance, and functional performance.
In some cases, the whole glove is tested for a given property. For example, the entire glove is put into an oven at 500 F for five minutes and evaluated for heat degradation properties, such as melting, dripping, ignition, and separation; the glove is also measured for thermal shrinkage following the heat exposure.
In this test, the glove is filled with glass beads to simulate the mass of a human hand inside the glove. Additionally, the glove lining is separately tested as an individual material under the same conditions for the purpose of determining if the lining could potentially melt against the hand.
Flame resistance and thermal insulation tests are also done on materials representing the composite of layers used in the glove’s construction. Unlike bunker coats and pants, only the exterior of the gloves is exposed to flame and evaluated for flame resistance, though the full glove composite is included as part of the test sample.
Glove composite materials must meet the same thermal protective performance (TPP) requirements as garments. TPP tests simulate the extreme short-term exposure conditions the firefighter potentially faces during a flashover or backdraft. This is theoretically more difficult for gloves to achieve because the material layers must wrap around the fingers in a fashion that still allows adequate dexterity.
Unfortunately, many gloves have artificially high TPP ratings because the leather used as the outer shell radically shrinks and buckles during the test, trapping air between the layers and acting to enhance insulation.
However, this same phenomenon does not occur in actual use but is instead an artifact of the test method. Glove composite materials are also evaluated for conductive heat resistance where the times to a predicted second-degree burn and the sensation of pain are measured when the glove composite material is placed on a hot plate at temperature of 536 F.
Superheated objects
This test is intended to represent the circumstances when a firefighter places his or her hand on a superheated object, e.g., like a doorknob. These tests are applied to both the back and palm side of the gloves. Nevertheless, there is no current test in the NFPA 1971 standard that addresses radiant heat exposures that occur during ordinary fireground conditions. The committee responsible for NFPA 1971 is considering adding a new requirement.
There are also difficulties in assessing insulation for gloves because different combinations of material appear in different parts of the glove. For this reason, North Carolina State University has developed a device they call “Pyro-Hand,” which is an instrumented handform containing sensors for measuring the heat transfer that occurs through simulated flash fires for predicting which regions of the hand will sustain burn injury.
The device, which you can learn more about in the video within this article, also shows promise for measuring radiant protection of gloves on the back of hands where firefighters sometimes are burned when holding a nozzle or keeping their hands out in front of them for extended periods of time. Burns on the knuckles can occur because as the fingers clench an object, the glove materials are pulled tightly over the top of the fingers, effectively reducing insulation.
Over the last 15 years, gloves have been required to incorporate a moisture barrier, just as garments do. Barrier materials are required because firefighters can be exposed to hot water, fireground chemicals and blood or body fluids. The barrier material is intended to prevent the penetration of these hazardous liquids into the glove interior to contact the firefighter’s hand.
Gloves are tested for their ability to resist penetration by specific liquids; they are also evaluated for their overall integrity in preventing liquid penetration. Nevertheless, many firefighters still complain that their hands get wet from liquids entering through the top of the gloves.
This problem may be due as much to the interface between the coat sleeve and the glove as to the glove itself. The integration of the barrier material as part of the overall glove construction can be a challenge as most barrier materials require a film that does not have the same flexibility or stretch as shell and lining materials. However, barrier materials do contribute to the overall insulation provided by the gloves.
Physical hazard resistance
Surprisingly, the tests that probably have as much impact as anything else on the choice of materials used in glove construction are those used to demonstrate physical hazard resistance — primarily, cut and puncture resistance.
Criteria based on these tests affect how thick leather and other materials must be in order to prevent cutting or puncturing that may occur in physically challenging environments. The established levels of performance are being re-examined to determine if appropriate trade-offs between protection and the impact of glove construction of functionality have been made.
The most important trade-offs for glove material selection and design relate to how gloves impact hand function — dexterity, grip and tactility. The NFPA 1971 standard provides tests for both dexterity and grip. In both tests, human test subjects perform hand functions barehanded and then wearing gloves.
The change in hand function is thus based relative to how gloves interfere with basic manipulation capabilities. For example, in evaluating glove dexterity, test subjects have to pick up a number of smooth pins and place them individually in polls on a pegboard. This activity is timed and the wearing of gloves increases the test times significantly.
NFPA 1971 permits that test times can be up to 250 percent worse for glove trials relative to barehanded trials. This type of criteria may explain why firefighters have difficulties in operating radios and handling certain tools, which require fine dexterity and tactility. North Carolina State University is looking at a variety of hand function tests that have the potential for better assessing glove effects on the ability of firefighters to perform common tasks.
The above discussions also point out how difficult it is to balance all the different performance properties that are required for gloves to provide adequate protection and still allow sufficient hand function.
It is hoped that the research at North Carolina State University and by the glove manufacturing industry as a whole will be able to advance glove design and materials to a reasonable set of criteria that provides the maximum function without loss of protection.
As with any endeavor to increase firefighter protection, industry benefits from firefighter observations and input. We invite your comments and insight for how to bring new information and suggestions to the glove.
