The new NFPA 1970 standard – officially titled the Standard on Protective Ensembles for Structural and Proximity Firefighting, Work Apparel, Open-Circuit Self-Contained Breathing Apparatus (SCBA) for Emergency Services, and Personal Alert Safety Systems (PASS) – has been in effect since mid-September 2024. And with the new standard comes new requirements and information that are expected to impact decisions for how fire departments select their turnout gear.
While there has been a significant amount of focus related to restricted substances in primary gear materials, among other hot topics, there are additional forthcoming requirements that can affect the traditional ways in which departments choose their clothing. Moreover, it is important to realize that even with this new information, there are still many other factors that are not covered in the NFPA standard – factors that departments should account for.
With this in mind, here we’ll detail how to integrate NFPA 1970 changes in the turnout gear selection process and review the additional factors that should be considered.
Prior practices
Over the last couple of decades, fire departments have often focused some parts of their gear choices on the principal protective garment materials that include the outer shell, moisture barrier and thermal barrier. Collectively, these layers are referred to as the garment material “composite.” In general, a key consideration for choosing the composite has been the respective Thermal Protective Performance (TPP) and Total Heat Loss (THL) values.
- TPP has been and continues to be the key metric for judging the clothing composite overall thermal insulation for protection against heat. The minimum insulation number or TPP rating, at 35 calories per square centimeter, has remained unchanged since it was first introduced in the 1986 edition of the NFPA standard for structural firefighting protective garments. This rating was derived from the expectation for the “reasonable” firefighter survivability in an average flashover condition. It does not mean that gear at this level, or any level for that matter, will not result in burns or other serious thermal injuries. The protective capabilities of all gear can easily be overwhelmed under extreme high-heat conditions. Obviously, by increasing the TPP rating, greater protection is afforded to the individual firefighter. However, TPP considered by itself is not a good way to base the heat protection needs.
- THL also looks at insulation but from the perspective of the firefighter’s ability to lose heat through the clothing, particularly when wearing turnout gear in the initial stages of the response prior to entry. Instead of measuring the penetration of outside heat energy through the clothing composite toward the firefighter’s skin, this test measures the release of heat both from sweat moisture transfer from the skin to the outside environment and conduction of body heat from the inside of the garment to exterior layers. These forms of heat loss slow the rate of heat buildup in the firefighter’s body caused by wearing relatively heavy clothing under rigorous work conditions, which in turn lessen the likelihood for the onset of heat stress and other overheating injuries. The current minimum requirement of 205 watts per square meter was established based on physiological testing of firefighters that showed a correlation of composite test results with lower rates of heat buildup.
Ideally, fire departments have selected clothing that gave their members what was believed to be an optimum balance of thermal heat protection with lessened physiological stress from the gear. This is because increasing TPP usually comes at the expense of decreasing THL, and vice versa (i.e., choosing a composite with a high THL may lessen thermal protection).
Of course, fire departments have also factored in other information for selecting composites, which is not specifically set by the NFPA test requirements. Examples of these other factors include fabric layer durability, flexibility and comfort against the skin. While tests exist for these properties such as abrasion resistance, stiffness and coefficient of friction, these properties are often best assessed by wear trials. It is also important to point out that material properties affect the perception of product designs and vice versa. Relying exclusively on material properties alone does not tell the whole story.
The reality is that the specification of TPP and THL as the overall measures of heat protection and breathability can be misleading. The reported measurements and their requirements apply only to the three-layer principal garment composites. The tests for measuring these properties are performed on flat samples of material. Yet, all garments have trim, reinforcements, pockets, overlapping areas, lettering and emblems, and other possible features or layers, which add to these composites making the overall material layering thicker. These thicker parts of the garment provide increased TPP but decreased THL. Therefore, depending on how much of the garment has extra layering, the impact of small differences in TPP and THL value can be less significant.
Another measure where the TPP and THL tests fail to reflect reality is the inability to account for air gaps between layers and between the clothing and the firefighter’s skin. These air gaps contribute to increased insulation in the form of additional thermal protection. This principle is the same as is observed in double-pane windows where the interior trapped layer of air is the most significant overall factor in reducing heat transfer. Air gaps vary with the design of the clothing, how clothing fits the individual firefighter, and the position and movements of the firefighter. Like extra layers, air gaps benefit TPP but detract from THL.
In the area of heat protection, TPP for garment composites is supplemented by specific properties in specific areas of clothing. As part of the continuing development process for the NFPA standards over the years, it was recognized that certain parts of the garment require additional insulation accounting for how it is worn. Nearly two decades ago, the conductive and compressive heat resistance test (called CCHR) was added to mandate additional layers for the knee areas of the protective pants and shoulder areas of the protective coats. The premise of the test was that when clothing is compressed, such as when happens when a firefighter kneels on a hot surface, squishing the layers together removes many of the protective air gaps, allowing for faster direct conductive heat transfer through the material composite. Shoulder areas are important because the wearing of an SCBA and its weight on the firefighter’s back naturally compresses the top of the garment. Thus, the testing in the NFPA standard forces reinforcements in these areas.
Another kind of heat transfer is similar, but instead of direct conduction, it can occur from the buildup of heat on exterior layers from radiant heat exposure that transfers to the firefighter’s skin when the clothing is compressed against the body. This phenomenon is called stored heat energy. It is particularly consequential with extended exposure to dense materials placed on the outside of the clothing such as reflective trim. Stored heat energy burn injuries occur when a significant amount of heat is absorbed by the material on the exterior surface that transfers to the firefighter’s skin when the clothing is pulled taut against the firefighter’s body. The NFPA standard requires this testing for any exterior mounted material on the protective coat sleeves.
New NFPA 1970 metrics
In the new edition of NFPA 1970, some additional tests and reporting requirements have been introduced that will further address gear selection. Most notably among these is a new breathability test called “evaporative resistance.” For all practical purposes, the equipment and procedures for this test appear to be nearly identical to THL. However, the biggest differences are that the test only assesses heat loss by sweating, and the test conditions are hotter and drier. Moreover, the values reported by this test are much different than THL. Evaporative resistance, or “Ret” as it is often called, provides rather strange values in the form of pascals meters squared per watt. Instead of measuring heat loss, it is a resistance, where a smaller number is better for Ret while high THL values are indication of better performance.
The impact of Ret is a new factor in gear selection. The new requirement is considered somewhat liberal, yet the most significant difference that fire departments will notice is that there is no relationship between THL and Ret. A higher THL does not necessarily mean a lower Ret. Factoring in Ret as part of the composite selection process is therefore likely to create complications in the heat insulation versus heat loss tradeoff due to the newness of this requirement. It may also depend on how a department will choose to weigh THL versus Ret for making their composite decision. Many findings from prior applications of Ret in multilayer clothing suggest that the choice of the moisture barrier layer impacts the Ret value the most. Ultimately, like many other factors for truly understanding the specific safety benefits of tests, it may be best evaluated in field trials accounting for different seasonable environmental conditions for the specific geographical location of the fire department.
The tear resistance of outer shells is now being evaluated after a larger set of preconditions that include multiple laundering cycles, high-heat exposure and repeated flexing. The requirement for tear resistance has not changed, but this preconditioning does represent a greater challenge for outer shells than previously used in the earlier edition of NFPA 1971. The only way to use this information is to learn the ending tear resistance following the multi-conditioning procedures and compare that value to the tear resistance test without any preconditioning to see how much the tear resistance declines following the rigorous application of different conditions. Larger percentage drops in multi-conditioned samples would suggest less durable outer shell material.
Most of the other new tests in NFPA 1970 entail requirements for the manufacturer to provide data based on required tests where no specific criteria are provided. For these properties, judging the relative impact of the test data can now be part of the garment selection process, but understanding the value of the new test may take some time for their implementation in specifying new gear. Tests in this category include the following:
- Outer shell tear resistance is measured and must be reported following a standardized exposure to UV light. Like the multi-conditioning procedures described above, the relative tear resistance performance for the UV-light exposed samples versus unexposed samples should provide awareness for the degree to which the outer shell material is affected by UV light.
- Outer shell repellency, absorption and penetration to diesel fuel must now be measured. The test results to be reported include the percentage of diesel fuel volume that runs off the material versus the percentages that penetrate through the material and stay in (are absorbed) by the outer shell. This test is expected to show some moderate levels of absorption for current outer shell materials. For reporting purposes, the flame resistance of the diesel fuel-exposed outer shell material is also assessed both before and after one cycle of cleaning according to standardized washer/extractor procedures. These report-only procedures will yield information about the susceptibility of different outer shell materials to diesel fuel absorption and how cleaning removes residual diesel fuel to lower flame resistance risk.
- Cleaning effectiveness will further be assessed for all three garment layer materials based on reported efficiencies for removing both organic and inorganic (heavy metal) contaminants. These results to be reported by the manufacturer provide an additional factor for relating the ease of material layer cleaning to other attributes judged as influential in gear selection.
Applying new selection rules
A better understanding of data derived from material testing according to NFPA 1970 using legacy evaluation approaches, combined with newer performance and reporting requirements, can aid gear selection decisions. As firefighter PPE requirements become more comprehensive and involve multiple tradeoffs, standardized data – when interpreted with an understanding of its specific limitations – can support fire departments in making more informed gear selection decisions.
Note: The views of the author do not necessarily reflect those of the sponsor.
