Anthropometric Evaluation of NFPA 1977 Sizing System for U.S. Female Wildland Firefighters: A Contingency Table Analysis

Abstract

Ensuring proper sizing and fit for U.S. female firefighters’ personal protective clothing and equipment (PPE) is a crucial challenge for researchers and manufacturers. The National Fire Protection Association (NFPA) establishes design and performance standards in the U.S., with NFPA 1977 specifying sizing guidelines for wildland firefighting gear. However, the absence of an anthropometric database representing female firefighters limits the effectiveness of these standards. This research evaluates the effectiveness of NFPA 1977 sizing system by investigating whether correlated body measurements maintain internal consistency and provide data-driven recommendations for improvement. Anthropometric data from 187 U.S. female firefighters were analyzed to assess the 2016 and 2022 NFPA 1977 upper and lower torso sizing systems. Correlation analysis was performed between body measurements and corresponding sizes. Contingency tables presented proportion of participants accommodated. Results indicated significant correlations between chest and wrist measurements and sizes in the upper torso, though these were the only available measurements. In the lower torso, hip size strongly correlated with thigh and knee sizes. However, the system inadequately accommodates female firefighters with larger waist and hip measurements. Furthermore, rise sizes demonstrated inconsistent, weak relationships with hip circumference. Overall, the NFPA 1977 sizing requires revision to better serve U.S. female firefighters.

1. Introduction

Addressing the sizing and fit challenges of ill-fitting personal protective clothing and equipment (PPE) for female firefighters is a goal that many researchers and manufacturers are diligently working toward [1,2,3,4,5,6,7]. Firefighting PPE standards serve as crucial reference points for practitioners working to tackle these challenges, although such standards may not provide definitive solutions [5,8]. In the United States, the National Fire Protection Association (NFPA) establishes these standards for structural and wildland firefighting PPE. Leading PPE manufacturers then employ various methods to implement these standards. Some rely on physical measurements, custom fittings, and sample wear trials, while others provide online sizing charts and instructions [9].

For wildland firefighters, NFPA 1977 provides requirements for PPE to protect personnel engaged in wildland firefighting operations [10,11]. The latest revision of this standard has been incorporated into the new consolidated NFPA 1950 standard, published in 2025 [12]. While the 2025 version did not change the sizing content from the 2022 edition, it introduced slight modifications to the sizing guidelines for wildland firefighting pants compared to the 2016 version.

Historically, the absence of a U.S. female firefighter anthropometric database has led to extensive measurement and fit communications between manufacturers and wearers [3,5]. This gap has caused significant challenges for PPE technical design practitioners in addressing sizing and grading issues, highlighting an urgent need for robust anthropometric data to enable sustainable, evidence-based solutions, rather than relying on trial-and-error feedback. More critically, the long-term use of ill-fitting PPE that stem from these historical data gaps has been associated with increased risks of physical injury, heat exposure, and psychological stress among female firefighters. These risks are often attributed to reduced protective coverage due to garment gaps and higher rates of PPE noncompliance resulting from discomfort or poor fit [3,5,7]. Such challenges not only impact the job safety of female firefighters but may also contribute to decreased job satisfaction and higher turnover rates within the fire service.

This research aims to provide a systematic evaluation of the effectiveness of the NFPA 1977 sizing standard, particularly focusing on the consistency of relevant body measurements within the sizing system. By utilizing anthropometric data, this study seeks to suggest improvements to NFPA 1977 and similar standards, thereby helping PPE manufacturers better meet the sizing and fit needs of female firefighters in the U.S.

1.1. NFPA 1977 Wildland Firefighter Sizing Standard

The NFPA 1977 standard establishes essential requirements for protective clothing and equipment designed to protect personnel from adverse environmental effects encountered in wildland firefighting operations. The standard is released on a three-to-five-year circle. A critical aspect of this standard is its upper and lower torso garments sizing charts. The NFPA 1977 standard specifies the required minimum values for each size, with alpha sizes (XS–XXL) for upper torso garments and numerical sizes (e.g., 25, 27, 29) for lower torso garments. Unlike other commonly used sizing standards, such as the ASTM standards [13] or commercial apparel sizing charts based on body measurements, the NFPA 1977 standard provides sizing ranges in terms of garment measurements. This approach is also adopted in NFPA 1970 for sizing structural firefighting [14]. The sizing ranges for women are presented in

Table 1. NFPA 1977 sizing range (upper torso garment), 2016 and 2022.

Body Measurement (cm)	NFPA 1977 Range (Same for 2016 and 2022)
Collar Length	37.5–52.7
Collar Width	7.6
Front Length	62.9–78.1
Back Length	71.1–86.4
Sleeve Length	77.5–92.7
Sleeve Cuff Circumference	30.5–38.1
Chest Circumference	99.1–160.2
Waist Circumference	83.8–144.8
Bottom Circumference	96.5–157.5

and

Table 2. NFPA 1977 sizing range with difference (lower torso garment), 2016 and 2022.

Body Measurement (cm)	NFPA 1977 Range		Difference
	2016	2022	Lower	Upper
Waist Circumference	58.4–99.1	63.5–104.1	+5	+5
Seat Circumference	94–134.6	94–134.6	n/a	n/a
Thigh Circumference	63.5–83.8	63.5–83.8	n/a	n/a
Knee Circumference	44.5–59.7	45.1–60.3	+0.6	+0.6
Leg Cuff Circumference	39.4–49.5	38.1–48.3	−1.3	−1.3
Front Rise	25.1–32.1	22.5–29.5	−2.6	−2.6
Back Rise	39.1–45.4	37.8–44.8	−1.3	−1.3
Inseam Length	71.1–91.4	71.1–91.4	n/a	n/a

, with observed differences in lower body sizing detailed in Table 2.

In the upper torso chart, the lack of distinction between women’s and men’s sizes presents a fundamental issue, given the anatomical and anthropometric differences between sexes. Specifically, research indicates that men generally exhibit larger total muscle mass and muscle size than women, both absolutely and relatively to body size, attributable to inherent rather than acquired factors [15]. Consequently, even when height and weight are identical, women and men could exhibit dimensional variations in areas such as shoulders and chests [16]. The NFPA technical committee previously discussed splitting the sizing charts into women’s and men’s categories, based on a manufacturer representative’s suggestion to tailor the women’s upper torso garment to accommodate a shorter total length, shorter sleeves, and a smaller chest-minus-waist difference [17] (pp. 61–65). However, this change was not adopted, possibly due to the similarity in measurement ranges proposed for men and women. Nevertheless, the NFPA 1977 standard acknowledges sex-based variation in the lower torso, providing sizing requirements to accommodate the typically wider hips of females [18]. Table 2 shows that the newer version has removed the smallest size, a 23″ waist (approximately 58.4–63.5 cm) from the older version and introduced a 39″ waist size (approximately 99.1–104.1 cm) as the new largest option. Compared to the 2016 version, the 2022 sizes have been adjusted downwards in terms of measurements relevant to the crotch (front and back rise). This indicates that the newer charts for lower torso garments offer female firefighters a larger waist size option, and the remaining sizes are not as voluminous as those in the 2016 version. This demonstrates an attempt at sizing improvements for female firefighters in the 2022 version. However, analysis against actual female firefighter anthropometric data has never been performed. In addition, NFPA 1977 includes requirements for minimum ease (

Table 3. NFPA 1977 minimum garment ease requirements, 2016 and 2022.

Body Measurement (cm)	NFPA 1977 (2016 and 2022)
Upper Torso Garment
Neck Circumference	2.5
Chest Circumference	15.2
Hip Circumference	15.2
Bottom Circumference	15.2
Cuff Circumference	15.2
Amount of Front and Back Length Extending Below Top of Hip Line	15.2
Lower Torso Garment
Waist Circumference	2.5
Seat Circumference	17.8
Thigh Circumference	15.2
Knee Circumference	15.2
Bottom Circumference	27.9
Rise (Front and Back)	27.9

), which remained unchanged between the two versions.

1.2. Optimizing Sizing Charts by Integrating Anthropometric Data

Sizing charts are essential guidelines that assist clothing consumers in selecting appropriately fitting products and enable manufacturers to efficiently allocate resources in production. With advances in scanning technology, extensive body measurements can be collected useful for anchoring sizing systems in the anthropometric data of the served population [19]. However, many existing sizing charts are influenced by historical issues and are often not grounded in anthropometric data, which is especially true for the female firefighter population. Research and reports show that most firefighting PPE is developed based on male body measurement or unisex sizing systems, which forces female firefighters to wear ill-fitting gear that does not account for their body structure, regardless of whether they size up or down [20,21]. This mismatch causes additional weight and mobility challenges, contributing to a higher rate of injury among female firefighters compared to their male counterparts [4,22]. The lack of relevance and fit to the target population, along with a disconnect from grading practices, requires a thorough evaluation and improvement of current sizing charts [23,24].

A robust and appropriate sizing chart should fulfill its purpose of accommodating most of its target population and be grounded in solid statistical foundations. It should consider variations and relationships among different body measurements and feature primary measurements that are intuitive to both manufacturers and the targeted population [25,26]. Linear correlation was used as an initial approach to explore the strength and direction of association between body measurements. Identifying and utilizing primary body measurements with strong correlations to other measurements is crucial for developing and optimizing sizing systems in an anthropometric approach because these primary measurements can serve as predictors for related secondary measurements, to ensure the size system effectively captures the majority of the target population [25,27,28]. While body measurement relationships can be non-linear, linear correlation offers a practical and interpretable method for identifying predictive relationships in sizing system development, especially from a data-driven mass manufacturing perspective [29].

Principal Component Analysis (PCA) is a commonly used statistical method for determining primary body measurements by reducing the number of variables to principal components that capture most of the variations in body measurements. For instance, a study by Xia and Istook using a U.S. female data pool identified seven primary body measurements: height, chest circumference, waist circumference, hip circumference, neck circumference, shoulder length, and arm length [25]. Similarly, Kolose et al. applied PCA to identify primary body measurements for clustering within the New Zealand Defense Force (NZDF), finding that height and waist circumference were crucial for the upper body, and inseam length and hip circumference for the lower body among female participants, with some variations for male participants [28]. This highlights how sex influences the primary measurements identified for an appropriate sizing system.

Beyond body measurements, effective sizing charts should have consistent and proportional size changes, reflecting natural variations in body measurements. These variations are typically observed through mean and standard deviation analyses of targeted body measurements, which help form the lowest and highest values of the sizing interval to determine sizing increments that should be evaluated during production to ensure suitability to specific clothing patterns and fabrics [26,30].

1.3. Female Firefighter Anthropometric Characteristics

Due to the lack of U.S. female firefighter anthropometric data, their precise body characteristics remain unknown, despite established anthropometric differences between male and female groups [15,16]. Beyond sex, structural and wildland firefighters may also differ in body shape due to distinct tasks involving varying weights and repetition requirements, influencing muscle development over long-term training [31].

In a recent comparative analysis, U.S. female firefighters were compared to the general U.S. female population [32]. The study analyzed body measurements such as bust, height, waist, hip, and other circumferential dimensions and vertical lengths, finding that female firefighters are generally taller by 6.7 cm and have wider waists (by about 9 cm) and hips (by about 4 cm) [32]. Significant differences were also observed in secondary measures, such as leg inseam length and center back waist length. These results indicate that female firefighters possess unique anthropometric characteristics compared to the general population.

2. Methods

2.1. Participants and Data Collection

This study employed body measurements of active-duty structural and wildland female firefighters across the U.S. (Sample size n = 187), collected using a free iOS supported app known as MeThreeSixty 3.4.2 (Cary, NC, USA; Size Stream, LLC). This user-friendly app is an accessible alternative to a large 3D stationary body scanner, with its accuracy in capturing most body circumferences and lengths supported by past studies and comparable to professional methods [33,34]. The scanning scene is presented in Figure 1a showing the capture of front A-pose and side I-pose photos, where green lines indicate successful full-body capture, along with required participant inputs including height, weight, sex, and age. Figure 1b presents an example of the resulting 3D body model.

The study employed a convenience sampling method due to time constraints. To evaluate the representativeness of the sample, height and bust circumference were used as primary indicators, given their strong relevance to garment sizing. The height distribution of the participants approximated a normal distribution, with a mean of 170 cm and a standard deviation (SD) of 6.6 cm. Bust circumference had a mean of 106 cm and an SD of 11.3 cm. These SDs are comparable to those reported in previous research by Hsiao et al. [2] while the mean values have shifted upward by approximately 3.3 cm for height and 9.7 cm for bust circumference. This suggests that the sample retains sufficient variability, with mean values reflecting more contemporary body dimensions [35,36].

As reviewed in the previous section, structural and wildland female firefighters may have general body dimensional differences. However, a questionnaire accompanying the data collection indicated that 39% of participants (n = 2000+) performed both structural and wildland firefighting, while 61% were exclusively structural firefighters [7]. This reflects the status of the current database, where female firefighters have limited opportunities for task-specific training that would lead to distinctive body shape differences.

A standardized scanning protocol ensured uniform and consistent data collection at all site locations [33,34]. Participants provided pre-scanned photos, height, and weight measurements and wore form-fitting clothing as base layers. A portable tablet on a stationary tripod ensured proper participant placement within the scanning application. Each participant was scanned once. Data was collected in Spokane, WA, Orlando, FL, and Raleigh, NC. This research was approved by the Institutional Review Board. Informed consent was obtained from each participant prior to scanning.

2.2. Data Analysis

The NFPA 1977 standard provides breaks and increments between garment sizes. Since NFPA 1977 specifies garment measurements rather than body measurements, the correspondence between garment measurements and body measurements were confirmed, and then the garment ease (Table 3) was subtracted from the garment measurements to derive the body measurements [37]. Based on this approach, the analysis focused on chest circumference, wrist circumference, waist circumference (for lower torso measurements only), hip circumference, thigh circumference, knee circumference, front rise, and back rise. Specifically, for upper torso body measurements, only two body regions, chest and wrist (corresponding to sleeve cuff), have garment measurements and ease that align appropriately, making it possible to use this approach to calculate the corresponding body measurements. Each participant’s body measurements were matched to a corresponding size using the calculated size intervals derived as detailed in the appendix of [34].

Data analysis was conducted using JMP Pro 17 (version 17.0.0 622753). An initial correlation analysis was conducted to explore relationships between the values of these body measurements. This analysis aimed to identify primary measurements (or controlled variables), for both the upper torso (chest circumference, wrist circumference) and lower torso (waist circumference, hip circumference, thigh circumference, knee circumference, front rise, and back rise). Once identified, another correlation analysis assessed the effectiveness of the two versions (2016 and 2022) of the NFPA 1977 sizing system in enabling participants to choose garments that provide a comprehensive fit across different body areas. The results were presented in contingency tables, showing the count and percentages of participants fitting within the sizing system.

3. Results

3.1. Primary Measurements and Size Matching Results

For the upper torso body measurements, only chest circumference could serve as the primary measurement for correlation. The correlation fit results indicate that chest circumference has a significant correlation with wrist circumference within the participant sample (p < 0.0001). The correlation coefficient of 0.57 suggests that chest circumference has a moderate linear relationship with wrist circumference, making it a suitable primary measurement. The size matching outcomes for chest and wrist, referring to the mean and standard deviation of body measurements within each size category based on the participant sample according to the NFPA 1977 (2016 and 2022) size intervals, are presented in

Table 4. Means and standard deviations of upper torso body measurements by size (unit: cm).

	Beneath	XS	S	M	L	XL	2XL
Chest		91.1 ± 0.6	98.9 ± 0.3	109.5 ± 0.4	118.9 ± 0.8	129.7 ± 0.8	138.8 ± 1.6
Wrist	15.1 ± 0.2	16.0 ± 0.0	17.1 ± 0.0	18.1 ± 0.1	19.3 ± 0.2

.

For the lower torso body measurements, either hip or waist circumference could serve as the primary measurement for correlation. The correlation fit results indicate that both hip and waist circumference have significant linear relationships with the other measurements within the participant sample (p < 0.0001). However, hip circumference has a stronger linear relationship with all other measurements, as indicated by the correlation coefficients: 0.95 > 0.85 for thigh circumference, 0.89 > 0.78 for knee circumference, 0.44 > 0.33 for front rise, and 0.46 > 0.35 for back rise. This suggests that hip circumference is a more suitable primary measurement. The size matching results for the lower torso measurements are presented in

Table 5. Means and standard deviations of lower torso body measurements by size (2016) (unit: cm).

	Beneath	23	25	27	29	31	33	35	37	Over
Hip					97.0 ± 3.5	102.1 ± 1.1	106.8 ± 0.5	111.7 ± 0.5	116.5 ± 0.6	128.1 ± 0.6
Waist							84.3 ± 3.5	89.7 ± 1.9	94.0 ± 1.2	108.4 ± 0.7
Thigh				54.8 ± 1.1	57.3 ± 0.5	59.7 ± 0.3	62.2 ± 0.3	64.8 ± 0.3	67.0 ± 0.4	73.6 ± 0.3
Knee				34.7 ± 0.4	36.3 ± 0.2	37.9 ± 0.1	39.5 ± 0.1	41.3 ± 0.1	43.3 ± 0.2	46.6 ± 0.2
Front Rise							15.4 ± 2.1	16.5 ± 3.0	17.5 ± 1.3	25.3 ± 0.2
Back Rise	22.3 ± 0.1	25.5 ± 0.2	26.4 ± 0.3	27.1 ± 0.2	27.9 ± 0.2	28.6 ± 0.3	29.3 ± 0.4	30.1 ± 0.3	30.8 ± 0.4	32.3 ± 0.4

(2016 size version) and

Table 6. Means and Standard Deviations of Lower Torso Body Measurements by Size (2022) (Unit: cm).

	Beneath	25	27	29	31	33	35	37	39	Over
Hip					97.0 ± 3.5	102.1 ± 1.1	106.8 ± 0.5	111.7 ± 0.5	116.5 ± 0.6	128.1 ± 0.6
Waist							84.3 ± 3.5	89.7 ± 1.9	94.0 ± 1.2	108.4 ± 0.7
Thigh				54.8 ± 1.1	57.3 ± 0.5	59.7 ± 0.3	62.2 ± 0.3	64.8 ± 0.3	67.0 ± 0.4	73.6 ± 0.3
Knee				35.0 ± 0.4	36.9 ± 0.1	38.1 ± 0.1	39.9 ± 0.1	42.1 ± 0.2	43.8 ± 0.2	46.8 ± 0.2
Front Rise									15.4 ± 2.3	25.0 ± 0.2
Back Rise	21.5 ± 0.1	24.3 ± 0.3	25.0 ± 0.2	25.8 ± 0.2	26.7 ± 0.2	27.4 ± 0.2	28.2 ± 0.2	29.1 ± 0.2	30.3 ± 0.2	32.0 ± 0.2

(2022 size version).

3.2. Size Correlation Analysis of Upper Torso Measurements: Chest vs. Wrist

Correlation analysis revealed a significant association between chest and wrist circumference (p < 0.0001). Figure 2 presents the contingency table of participants’ wrist and chest sizes based on NFPA 1977 (2016 and 2022) standards, overlaid with a heatmap showing size consistency performance. In the figure, the absence of sizes in certain columns or rows indicates that no participants fell into these categories according to the standard sizing tables. Figure 2 highlights that no participants were categorized under the 2XL wrist size. In the heatmap visualization, deep blue indicates a perfect size match between the two sizes, while light blue represents a one-size difference, suggesting a reasonably good fit. Light orange and dark orange indicate two-size or greater mismatches, with dark orange representing severe size discrepancies or sizes falling outside the standard range. Figure 2 reveals that three participants did not fit into any available upper torso garments as their wrist circumference was below the smallest size (XS). Within the available wrist size range, a total of 38 participants (20.3%) could not find an appropriate, holistic fit, as their wrist circumferences were too small compared to the range provided for their corresponding chest size. Among them, 12 participants (6.4%) exhibited a severe mismatch between the two sizes. Overall, the sizing system accommodated 146 participants in terms of wrist and chest measurements (n = 187; 78.1%). However, due to a lack of clearly defined body measurements in the NFPA standards, only these two upper torso measurements could be analyzed out of the nine total measurement specifications.

3.3. Size Correlation Analysis of Lower Torso Measurements

3.3.1. Hip vs. Waist

The size correlation analysis results show that there is a significant association between the hip and waist sizes in both standard versions (p < 0.0001). Figure 3a shows that a significant portion of participants struggled with fitting into lower torso garments according to the 2016 version of the standard. Specifically, for 118 participants (63.1%), their waist circumferences were beyond the provided size range. Within this group, 38 participants (20.3%) had both waist and hip measurements outside the sizes offered. In Figure 3b, the 2022 version of the standard shows some improvement in this regard, reducing the number of participants facing the waist issue to 91 (48.7%), yet this still constitutes about half of the sample. From the 2016 to the 2022 standard version, the fit rate (indicated by blue cells) increased from 19.3% (36 participants) to 46.0% (86 participants), with the number of perfect matches rising from 1.6% (3 participants) to 19.3 (36 participants). However, both figures revealed that most mismatches (shown by orange cells) occurred where participants’ waist measurements were larger than those indicated by their base hip size, while these mismatches decreased from 80.7% (151 participants) in 2016 to 54% (101 participants) in 2022. Additionally, the analysis revealed that in the 2016 version, no participants had waist measurements that fell under the size 33, or hip measurements that were under the size 29 threshold. The updated 2022 version similarly showed no participants with waist measurements under size 33, but the threshold for hip measurements increased slightly, with no measurements under size 31. This indicates that a large number of individuals with larger hip and waist circumferences were not adequately accommodated by the sizing standards in both the 2016 and 2022 versions.

3.3.2. Hip vs. Thigh

Results demonstrate a significant association between the hip and thigh sizes in both versions as well (p < 0.0001). Figure 4a,b detail the sizing transitions from the 2016 version to the 2022 version, indicating that all participants experienced a shift upwards by one size in their thigh and hip circumference measurements, though the overall distribution pattern remained consistent. Specifically, 44 (23.5%) participants, represented by the deep blue shade, consistently matched their sizes across the two measurements. Another 86 (46.0%) participants found their sizes differing by one size, with the majority having a larger hip size relative to their thigh size. Additionally, 32 (17.1%) participants were unable to find suitable sizes in either version of the standard because their thigh and hip measurements exceeded the largest available sizes. No participants fell under the smallest thigh size in the 2016 (size 27) or 2022 (size 29) 2022 versions.

3.3.3. Hip vs. Knee

For hip and knee, the size correlation analysis results show a significant association in both versions (p < 0.0001). Figure 5a,b display a slight improvement in accommodating participants with larger measurements in the 2022 version, as the number of participants whose knee and hip circumferences exceed the largest available sizes decreased slightly from 15 (8.0%) in the 2016 version to 13 (6.9%) in the 2022 version. However, other findings suggest worse adjustments in the newer version: the number of participants who could find consistent sizes across knee and hip measurements dropped from 24 (12.8%) in the 2016 version to 16 (8.6%) in the 2022 version. The count of participants with only one size difference between their knee and hip measurements also decreased from 93 (49.7%) in the 2016 version to 77 (41.2%) in the 2022 version. These changes indicate that the 2022 version may have a poorer correlation between knee and hip sizes compared to the 2016 version, as the new version categorizes participants with larger hips—around size 37 in the 2016 version and size 39 in the 2022 version—into smaller knee sizes.

3.3.4. Hip vs. Front Rise

The size correlation results between the front rise and hip sizes found no significant association in either version of the standard (2016: p = 0.6631, 2022: p = 0.6378), suggesting that front rise and hip sizes do not align predictably across these standards. This is not appropriate for effective sizing. Figure 6a,b revealed that most participants could not find sizes that accommodated their front rise measurements, as they exceeded the largest size available. Notably, the number of participants facing this issue increased from 179 (95.7%) in the 2016 version to 185 (98.9%) in the 2022 version, indicating the problem has intensified rather than improved. Additionally, the 2016 standard appears to distribute sizes better amongst the remaining participants whose measurements fall within the available ranges, compared to the 2022 version. This observation suggests that the adjustments made in the 2022 version might not serve the needs of those with larger front rise measurements.

3.3.5. Hip vs. Back Rise

Unlike hip and front rise, the correlation analysis of the hip and back rise sizes across both standard versions indicates a significant association among participants (2016: p = 0.0012, 2022: p = 0.0004). As detailed in Figure 7a,b, both versions widely distribute participants’ measurements for hip and back rise. The overall distribution patterns are similar across the two versions, though there are some differences in size and the number of participants matching specific size categories: in the 2022 version, three additional participants exceeded the largest back rise size available compared to the 2016 version. The number of participants who could not find consistent sizes across the back rise and hip measurements increased slightly, by two participants, in the 2022 version. For the 2022 version, there was an increase in participants who found their sizes differed by only one size (from 5 (2.7%) in 2016 to 27 (14.4%) in 2022), suggesting a tighter clustering around more common measurements. Furthermore, the number of participants whose measurements were below the smallest available back rise size decreased from 50 (26.7%) in 2016 to 42 (22.5%) in 2022, indicating that the revised size ranges in 2022 better accommodate those with smaller back rise measurements. These findings highlight that, despite some increases in sizing mismatches, the updated 2022 size ranges generally offer better alignment with participants’ back rise measurements.

4. Discussion

4.1. Suitability of NFPA 1977 Upper Torso Sizing System

The upper torso chart provided in the NFPA 1977 standard exhibits two primary issues, which were not evident in the correlation analysis conducted in this paper. These issues hinder a comprehensive examination of the study. Firstly, the use of a unisex sizing chart lacks scientific anthropometric evidence, resulting in an inadequate fit for female firefighters [20]. Secondly, there is a lack of alignment between the garment measurement chart and the garment ease chart, making it difficult to determine which body dimensions each size is intended to accommodate. Essential measurements that could serve as primary indicators, such as height and waist circumference, are missing from this sizing system. Clearly, the upper torso sizing system fails to provide adequate information for both manufacturers and end users. Unfortunately, this issue persists in both the 2016 and 2022 versions of the standard.

Due to the absence of essential measurements and the lack of alignment between garment, ease, and body measurements in the standard, only chest and wrist circumferences were available for upper torso correlation analysis. The contingency table with heatmap (Figure 2) reveals that the upper body sizing system generally accommodates most participants with a rate of 78.1%. However, it also highlights specific fit issues for participants whose wrist circumferences are smaller than the smallest available size (XS) or disproportionately small relative to their chest measurements. This discrepancy suggests that the wrist circumference parameters in the sizing table may have been overestimated compared to actual body measurements. Therefore, adjustments to the sizing standards are necessary to better reflect the true distribution of wrist sizes within the population.

4.2. Suitability of NFPA 1977 Lower Torso Sizing System

Similar to the upper torso sizing system, the lower torso sizing system also lacks alignment between the garment measurement chart and the garment ease chart. However, it is not as problematic, allowing the six body measurements obtained, including hip measurement as the primary measurement, to generally depict the body dimensions each size is intended to accommodate. The contingency tables detailing the relationship between hip and waist measurements (Figure 3) demonstrate that the 2022 version improved the correlation between these two measurements, potentially aiding more participants in finding consistent sizes. However, the analysis revealed that in both versions, the smaller sizes available are too small. In the 2016 version, no participants had waist measurements below size 33 or hip measurements under size 29. The 2022 version had no participants with waist measurements under size 33 and no hip measurements under size 31. This could partially be due to the small sample size that does not include as many lean-waisted and narrow hip female firefighters. However, female firefighters of all statures from 151.4 to 198.0 cm (5′0″ to 6′5″) were included in the database sample. Expanding the data pool is necessary to validate this finding.

Moreover, a significant number of individuals with larger hip and waist circumferences were not adequately accommodated by the sizing standards in both the 2016 and 2022 versions. This indicates a need to expand the sizes at the larger end or to improve the correlation between waist and hip measurements to make them more consistent.

The correlations critical for consistent sizing between hip and other body areas did not demonstrate significant improvements in the 2022 version. A particularly notable issue is the excessive garment ease provided for front and back rise lengths, which appears to be unsuitable for female wearers. This excessive ease results in front and back rise lengths that are disproportionately short compared to hip sizes. According to both the 2016 and 2022 versions of NFPA 1977, the ease for women is stated as 27.9 cm (11″), whereas for men, it is only 15.2 cm (6″). This significant difference raises questions, as there is no clear evidence to support the idea that women require substantially more crotch length ease than men. Previous studies have highlighted the fit problem of the baggy crotch from female firefighters’ perspectives [3,38]. It can be reasoned that this amount of ease (27.9 cm) is inappropriate based on qualitative and quantitative fit, mobility, and comfort feedback from female firefighters, and a lack of justification by NFPA as to why women’s pants are required have almost double the amount of front and back rise ease. A re-evaluation of these ease measurements is necessary to better align with the actual needs and proportions of female firefighters.

4.3. General Suggestions for NFPA 1977 Sizing Improvements

The most inherent change to be suggested is the adoption of standardized body measurement sizing charts instead of garment measurement charts. The current garment measurement sizing charts resemble production specifications more than they reflect the perspective of the wearers’ bodies. However, body measurement standards are supposed to guide the fitting process of apparel products, providing reference for the identification of fit models and improving the structural design of clothing [39,40]. This is the aspect that should truly be standardized for fitting purposes for all members of the fire service, male and female. In addition, incorporating more body measurements into the standard is also essential, such as height, which can serve as a primary vertical measurement, and waist circumference for upper torso sizing, as well as other important measurements like neck circumference that reflect the diversity of body shapes and sizes. The addition of these measurements would make the standard sizing system more practical and persuasive. These proposed changes should be supported by more expansive anthropometric survey results from female firefighter participants, as well as male firefighters, and the involvement of personnel who have a deep understanding of anthropometric data to enhance the sizing system.

5. Conclusions

This study examined the effectiveness of the sizing system provided by the NFPA 1977 standard in both the 2016 and 2022 versions for female wildland firefighters. Using anthropometric data from 187 U.S. female firefighter participants and analyzing the structure and principles of the sizing systems for upper and lower torso garments, this study found that both editions play an ambiguous role in guiding sizing and fit for U.S. female firefighter PPE. Overall, the sizing standards lack clear size indicators for specific body measurements and demonstrate poor alignment between garment measurements and garment ease requirements.

Through correlation analysis of the available measurements, it was identified that the lower torso garment chart makes it challenging for both manufacturers and wearers to select the appropriate pant size. The chart fails to provide consistent size correlations between the lower torso body measurements for a significant number of individuals, with mismatch rates ranging from 30.5% to 99.5%, depending on the measurements examined. The most problematic aspect of the sizing standard is the front rise measurements, where no correlation exists within the standard.

Limitations of this research include the use of a small convenience sample size of 187 subjects, which may affect the generalizability of the findings. In addition, as independently validated in another study, compared to commercial stationary 3D body scanners, scanning apps may introduce inaccuracies in smaller circumference areas such as the ankle and wrist, and may also differ in how body landmarks and measurement levels are identified, due to variations in algorithms across scanner software [34]. As a result, the wrist circumference analysis in this study may be subject to bias, and the sizing classification of outcomes could vary depending on the body data extraction software used.

Further, this study uses the first and largest U.S. female firefighter anthropometric database to date, providing the first opportunity for an in-depth evaluation of standard sizes that was not feasible in earlier research. Unlike prior publications based on this dataset [32,34,37], this study integrates NFPA 1977 sizing standards at a more detailed level, evaluating sizing effectiveness through two-body-measurement correlation coverage rather than only one-dimensional range coverage. The present approach provides a more holistic snapshot of the current state of the NFPA 1977 sizing system and enables more specific suggestions for sizing improvement. Future research should include the expansion of the U.S. female firefighter database and the inclusion of male firefighters to improve the sizing and fit of firefighting PPE for all 1.1 million firefighters in the U.S. Similar analysis should also be conducted for structural firefighting turnout gear.