i

NIST Technical Note 1751

Accelerated Weathering of Firefighter 

Protective Clothing Containing 

Melamine Fiber Blends

Shonali Nazaré

Shaun Flynn

Rick Davis 

Joannie Chin

http://dx.doi.org/10.6028/NIST.TN.1751
ii

NIST Technical Note 1751

Accelerated Weathering of Firefighter 

Protective Clothing Containing 

Melamine Fiber Blends

Shonali Nazaré

Shaun Flynn

Rick Davis

Flammability Reduction Group

Fire Research Division

Engineering Laboratory

Joannie Chin

Polymeric Materials Group

Materials and Structural Systems Division

Engineering Laboratory

http://dx.doi.org/10.6028/NIST.TN.1751

August 2012

U.S. Department of Commerce

Rebecca M. Blank, Acting Secretary

National Institute of Standards and Technology

Patrick D. Gallagher, Under Secretary of Commerce for Standards and Technology and Director
iii

Certain commercial entities, equipment, or materials may be identified in this

document in order to describe an experimental procedure or concept adequately.

Such identification is not intended to imply recommendation or endorsement by the

National Institute of Standards and Technology, nor is it intended to imply that the

entities, materials, or equipment are necessarily the best available for the purpose.

National Institute of Standards and Technology Technical Note

Natl. Inst. Stand. Techn. Techn. Report XXX, 37 pages (August 2012)

CODEN: NTNUE2 
iv

Abstract

In this study, the mechanical properties critical to the protective performance of firefighter 

turnout gear were evaluated in environmentally stressed outer shell (OS) 

fabrics containing melamine fiber blends. Environmental stress factors that affect the 

durability of turnout gear include temperature, ultraviolet (UV) radiation, moisture, abrasion, 

and laundering. The effect of fiber blend, fabric construction, and finishing processes 

including water repellent coatings and pigmented melamine- containing OS fabrics were also 

studied. Melamine-containing OS fabrics show comparable thermal protective performance 

and have superior tear resistance when compared to the traditionally used polyaramid blends.

 

This study reveals that the thermal protective protection (TPP) rating of fabric assemblies 

incorporating environmentally stressed OS fabrics containing melamine fiber blends is well 

above the NFPA minimum TPP requirement of 35 Cal/cm2. However, the tear strength

(measured using ASTM D 5587 standard test method ) of all melamine-containing OS fabrics 

exposed to environmental stresses was observed to have significantly deteriorated, and most 

OS fabrics, depending on fiber blend and fabric structure, would fail to meet requirements of 

NFPA 1971 standard. The study thus suggests that environmental stressing has a more 

detrimental impact on the tear strength than the thermal protective performance of OS fabrics. 

Deterioration in tear strength of all UV exposed OS fabrics is largely due to photodegradation 

of constituent fibers. Changes in tear strength of OS fabrics subjected to thermal exposures 

and laundering is cumulative effect of loss in tensile strength of single yarns and dimensional 

stability of the fabric itself. Furthermore, finishing treatments affect performance properties of 

fabric by increasing fiber packing factor in yarn, changing yarn crimp and yarn spacing thereby 

making dimensional changes to the fabric. Surface coatings alter tear resistance of fabric by 

influencing yarn slippage and fabric rigidity. Fabrics dyed with black and dark blue dyes cause 

less UV degradation of fibers than bright yellow and brown dyes. 

Keywords

Accelerated weathering, UV irradiation, abrasion, laundering, heat exposures, fire fighter 

turnout gear, melamine fibers.
v

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vi

Contents

List of Tables............................................................................................................................... vii

List of Figures............................................................................................................................. viii

List of Acronyms.......................................................................................................................... ix

1. Introduction............................................................................................................................ 11

2. Experimental .......................................................................................................................... 12

2.1. Fabrics............................................................................................................................ 12

2.2. Environmental stressing................................................................................................. 13

2.2.1. UV aging................................................................................................................. 13

2.2.2. Laundering .............................................................................................................. 13

2.2.3. Abrasion and wear .................................................................................................. 13

2.2.4. Heat exposures........................................................................................................ 14

2.3. Mechanical testing ......................................................................................................... 14

2.3.1. Tear strength ........................................................................................................... 14

2.3.2. Tensile strength....................................................................................................... 15

2.4. Thermal protective performance testing ........................................................................ 15

3. Results and Discussion........................................................................................................... 17

3.1. Tear resistance ............................................................................................................... 17

3.2. Tensile strength of yarn ................................................................................................. 20

3.3. Thermal protective performance of fabric ensemble ..................................................... 21

4. Summary and Conclusions ................................................................................................... 24

5. References............................................................................................................................... 35
vii

List of Tables

Table 1. Description of outer shell fabrics................................................................................ 12

Table 2. Tear strength of OS fabrics containing melamine fiber blends. Uncertainties in 

measurement of tear strength are expressed as experimental standard deviations. ................... 18

Table 3. Tensile properties of yarns extracted from OS fabrics. Uncertainties in measurement 

of tensile strength are expressed as experimental standard deviations. ..................................... 20

Table 4. Protection time for OS fabrics containing melamine fiber blends. Uncertainties in 

measurement of time to second degree burn are expressed as experimental standard deviations.

.................................................................................................................................................... 22

Table 5. Percent reduction in TPP values: Individual and combined effects of environmental 

stressing on thermal protective performance of OS fabrics....................................................... 23

 

 
viii

List of Figures

Figure 1. Schematic of: (a) Martindale type abrader and (b) modified assembly of Martindale 

type abrader................................................................................................................................ 26

Figure 2. Schematic of TPP test apparatus. .............................................................................. 27

Figure 3. Single tear fabric configuration [26]. ........................................................................ 28

Figure 4. Deterioration in tear strength of OS fabrics exposed to simulated UV radiation. 

Error bars are ± experimental standard deviation. ..................................................................... 30

Figure 5. Percentage reduction in tear strength of environmentally stressed OS fabrics. ........ 30

Figure 6. Deterioration in tensile strength of OS fabrics exposed to simulated UV radiation. 

Error bars are ± experimental standard deviation. ..................................................................... 32

Figure 7. Percentage reduction in tensile strength of yarn unraveled from environmentally 

stressed OS fabrics..................................................................................................................... 33

Figure 8. Thermal protective performance of environmentally stressed OS fabrics. Error bars 

are ± experimental standard deviation. ...................................................................................... 34
ix

List of Acronyms

AATCC American Association of Textile Chemists and Colorist

ASTM ASTM International

LbL Layer-by-Layer

LOI Limiting Oxygen Index

MB Moisture Barrier

NC Natural Conditions exposure

NFPA National Fire Protection Association

NIST National Institute of Standards and Technology

OS Outer Shell

RH Relative Humidity

SPHERE Simulated Photodegradation via High Energy Radiant Exposure

TGC Turnout Gear Conditions

TiO2

TL

TPP

Titanium dioxide

Thermal Liner

Thermal protective performance

UPF Ultraviolet Protection Factor

UV Ultraviolet
x

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11

1. Introduction

Most turnout gear commonly used by firefighters in the United States is comprised of 

three layers, each performing a distinct function. The outer shell (OS) fabric provides 

flame protection and serves as a primary defense to mechanical injury, heat, and fire. The 

waterproof middle layer acts as a moisture barrier (MB), and the thermal liner (TL) 

which is next to the skin, provides thermal insulation and protects the wearer from burn 

injury. The outer shell fabric is predominantly made from fiber blends of poly(mphenylene isophthalamide) (PPI), poly(p-phenylene terephthalamide) (PPT),

polybenzimidazole (PBI), and polyphenylenebenzobisozazole (PBO). Selection of fiber 

type and blend ratios are often driven by cost. Very recently, melamine fibers are finding 

applications in high performance clothing. Heat resistance and thermal properties of 

these fibers are comparable to inherently fire resistant fibers traditionally used in OS 

fabrics. OS fabrics containing blends of aramid fibers have been studied in detail and 

extensively reported [1,2,3,4,5,6,7,8,9]. However, few studies have been carried out and 

reported in the literature on OS fabrics containing melamine fibers. 

The melamine fibers, more accurately termed melamine-formaldehyde fibers, are 

produced via a condensation reaction between melamine and formaldehyde in a molar 

ratio of 2:1. Hydroxyoxaalkylmelamines and other additives are also utilized in small 

amounts. Melamine fibers have excellent heat resistance (e.g., limiting oxygen index 

(LOI) of 32 %, no melting, and high temperature strength retention) and have tenacity of 

2.0 g/denier to 2.3 g/denier. High heat stability is primarily due to the cross-linked nature 

of the polymer. When exposed to heat/flame, the fibers char without shrinking. 

Melamine fibers are also known to be the most thermally-insulative fibers. Generally, 

thermal conductivity of inherently fire resistant fibers is high, however melamine fibers 

have the lowest thermal conductivity values (≈ 0.285 [W/ (m∙K)] ) amongst all inherently 

fire resistant fibers [10]. Because of their low tensile strength, melamine fibers are 

generally blended with stronger aramid fibers.

At National Institute of Standards and Technology (NIST), we have been studying effects 

of accelerated weathering on performance of OS fabrics [7, 11]. The main aim of this 

study is to improve guidelines for the retirement of firefighters turnout gear. In the first 

phase of this work, accelerated weathering of polyaramid and polybenzimidazole outer 

shell (OS) fabrics was studied and reported [7]. OS fabrics were exposed to simulated 

ultraviolet (UV) radiation at 50 °C and 50 % relative humidity. The aging performance 

profile (APP), which is the deterioration of properties as a function of time, suggested 

that 13 d continuous exposure (equating to 6.6 years of turnout gear exposure to UV 

radiation under natural conditions of usage) to the conditions mentioned above caused 

significant deterioration in the mechanical performance of OS fabrics [7]. Environmental 

stress factors that affect the durability of turnout gear include temperature, UV radiation, 

moisture, abrasion, and laundering. Reported here is a study of the individual 

environmental stress factors on the performance metrics of OS fabrics containing 

melamine fibers. Environmental stress factors were reproduced at a laboratory level, 

simulating environmental stressing experienced during actual end-use conditions. 
12

Environmentally stressed fabric samples were evaluated for thermal and mechanical 

properties that are critical to the protective performance of firefighter turnout gear. 

2. Experimental1

2.1. Fabrics

Four OS fabrics made from ring spun yarn consisting of 40 % melamine and 60 % paraaramid fibers were used in this study. Description of all four OS fabrics is given in Table 

1. Fabrics varied in their physical properties as well as chemical finishes applied. Three 

OS fabrics (BK-00, BK and BBK) had similar fabric construction with a rip stop weave

which is generally used to increase a fabric’s tear resistance and tensile properties. BKP 

has a basket weave with a rip stop yarn woven into the construction. BBK fabric having 

area density of 254 g/m

2 has a durable fluorocarbon water repellant finish and is dyed

black using acid dyes. BK is a slightly denser fabric with area density of 264 g/m2 and 

thickness of 0.66 mm. BKP is a blend of melamine (32 %), para-aramid (60 %) and uses 

proprietary core spun yarn (with polyphenylenebenzobisozazole (PBO) filament as core 

and poly(p-phenylene terephthalamide) in the sheath) as rip stop yarn. PBO fibers have 

superior tensile strength and high modulus, and are used as a reinforcing element. PBO 

also has a very high flame resistance and is self-extinguishing. LOI of PBO (68 %) is 

much higher than aramid fibres [ 12 ]. BK-00 has similar construction and fiber 

composition to BK except that BK-00 fabric is ‘gray’ fabric that has not been subjected 

to textile finishing processes. This selection of experimental fabrics allows us to study 

the effect of fiber blend, finishing processes including water repellent coating and 

pigmentation of melamine containing OS fabrics on protective performance of 

environmentally stressed OS fabrics. 

Table 1. Description of outer shell fabrics.

Fabric 

name

Fiber blend (%)

Thickness

, mm

Weight

g/m2 (oz/yd2

)

 

Fabric weave Water 

repellant 

finish

Melamine Poly(pphenylene 

terephthalamide)

Polyphenylenebenzobisozazole 

(PBO)

BK-00 40 60 - 0.66 264 (7.8) Plain/ Rip stop None

BK 40 60 - 0.66 264 (7.8) Plain/ Rip stop Hypel+B2

BKP 32 60 8 0.78 264 (7.8) Basket 

weave/Rip stop Hypel+B2

BBK 40 60 - 0.54 254 (7.5) Plain/ Rip stop

Durable water 

repellent 

finish

 1 Certain commercial equipment, instruments or materials are identified in this paper in order to specify the 

experimental procedure adequately. Such identification is not intended to imply recommendation or endorsement by 

the National Institute of Standards and Technology, nor is it intended to imply that the materials or equipment 

identified are necessarily the best available for this purpose.
13

2.2. Environmental stressing

2.2.1. UV aging 

UV irradiation experiments were conducted as previously described [7]. Fabric 

specimens having approximate dimensions of 10.2 cm × 7.6 cm (4 in × 3 in) were 

exposed to high UV irradiance in the NIST integrating sphere-based weathering device, 

referred to as SPHERE (Simulated Photodegradation via High Energy Radiant 

Exposure). Accelerated exposure of the fabrics to high UV irradiance was carried out 

using the mercury arc lamp system that produced a collimated and highly uniform UV 

flux in the environmental chambers of the SPHERE. A borosilicate glass window was 

placed between the lamp system and the integrating sphere to eliminate all UV 

wavelengths < 290 nm. The dichroic reflector in the lamps removed wavelengths > 450 

nm. Additional details on the construction and properties of the SPHERE have been 

published elsewhere [ 13]. The fabric samples were continuously exposed to a UV 

irradiance dosage of 15.9 kJ/m2 ± 0.02 kJ/m2 for prescribed periods of time. Based on the 

prescribed amount of UV exposure on the SPHERE, various parameters including 

continuous sun (CS) days (calculated number of days where sunlight is assumed for 24 h 

a day), natural conditions (NC) day calculated assuming 9 h of sunlight in a day and 

exposure period for turnout gear have been calculated and reported elsewhere [7]. 

2.2.2. Laundering

The OS fabrics having approximate dimensions of 380 mm x 380 mm (15 in x15 in) were 

subjected to 5 cycles of a washing and drying at Maryland Fire Equipment Corporation, 

Rockville, MD. To avoid fraying of the edges, Fray Check (Prime Consumer USA Inc.) 

glue was applied to the edges of the fabric pieces. Washing was carried out in an 

industrial washing machine at 40 oC using a wash cycle of approximately 1 h. Front 

loading automatic machines were used that do not utilize an agitator which is known to 

result in greater clothing “wear” during washing [14]. The 1993 AATCC Standard 

Reference Detergent which is specified in the NFPA 1971, Standard on Protective 

Ensembles for Structural Fire Fighting (2000 Edition) was used. The amount of 

detergent used was 5 g/L and the liquor (liquid containing water and detergent) ratio was 

1:5. No other chemicals were used during washing. Fabric samples were dried on drying 

racks.

2.2.3. Abrasion and wear

In order to simulate wear and tear during use, OS fabrics were abraded on a Martindale 

abrader (James and Heal Co. Ltd, UK) which simulates the damage due to rubbing 

against another. Such a method is generally used to assess the abrasion resistance of 

textile materials. A schematic of the test apparatus is shown in

Figure 1(a). In this study, the Martindale test method (DIN EN ISO 12947-3) [15] was 

modified to abrade a larger area of the fabric samples. A schematic of the modified test 

apparatus is shown in
14

Figure 1(b). Generally, according to the DIN EN ISO 12947-3 Martindale test method, 

circular fabric samples (38 mm diameter) are mounted in sample holders and are rubbed 

against a standard wool fabric. However, for this study, a 38 mm diameter specimen 

were not large enough to evaluate thermal protective performance and hence the position 

of the abrader (the standard wool fabric) and test sample were reversed (see 

Figure 1(b)). With the modified experimental set-up, it was possible to abrade larger 

areas of OS fabrics. The OS fabrics were abraded under a known pressure of 9 kPa and 

with the translational movement of the abrader tracing a Lissajous figure [ 16]. The 

rotational speed of the top moving plate was set at 47.5 revolutions per min with a 

maximum stroke length of 60.5 mm. With these operating parameters, an approximate 

area of 3660 mm2 was abraded. Each OS fabric specimen was subjected to 20, 000 rub 

cycles. None of the specimens showed signs of rupture following the test cycle. 

2.2.4. Heat exposure

OS fabrics were exposed to convective heating according to ISO 17493 [17]. Fabric 

specimens having approximate dimensions of 380 mm x 380 mm (15 in x 15 in) were

suspended in a convection oven by metal hooks such that the airflow was parallel to the 

plane of material. Two heat exposure conditions were chosen for this study: 260 o

C for 

5 min and 180 oC for 24 h. 

2.3. Mechanical testing 

2.3.1. Tear strength

NFPA 1971 Standard on Protective Ensembles for Structural Fire Fighting and Proximity

Fire Fighting [18] requires testing tear resistance of OS fabrics using the test procedure 

described in ASTM D 5587 [19]. The standard describes measurement of tear strength 

by the trapezoidal method (an in-the-plane tear propagation). In the textile industry, this 

method is not frequently used as the stress pattern measured by this method is largely 

determined by variables at the disposition of the operator and the tear strength values are 

high since the fabric yarn is pulled, not torn, apart. For these reasons, the fabric tear 

resistance for this study was determined using the single tear method described in ASTM 

D 2261[20]. Moreover, it has been shown that changes in tear strengths due to fabric 

construction, finishing treatments, washing and weathering could be best determined by a 

rip test [21]. The single tear test (also called the rip tear test) is an out-of-the-plane tear 

that propagates at relatively low loads and results lower tear strength values as compared 

to trapezoidal tear test values. Both the single tear and trapezoidal tests simulate the

tearing of fabric by hand [21].

The single tear tests were conducted on an Instron universal testing machine (model 

5582, Instron Corp., Northwood, MA) equipped with 2 kN load cell and custom grips for 

fabrics. The gauge length between grips was 25 mm, and crosshead speed was 50 

mm/sec. A single 25 mm (1.0 in) tear was introduced at one end of specimen having 
15

approximate dimensions of 68 mm × 25 mm (2.66 in × 1.0 in). Tests were performed on 

OS fabrics cut along the warp direction (longitudinal tearing direction). Four replicates 

of each fabric were tested per sampling interval. Uncertainties in measurement of tear 

strength are reported as Type A uncertainties [22, 23] with experimental standard 

deviations in Table 2.

2.3.2. Tensile strength

Due to specimen size limitations, the tensile strengths of fabrics were based on yarn 

tensile strength values. The tensile strength or breaking strength of a fabric is generally 

greater than its tear strength. In the single tear test described above, each cross-section of 

yarn is subjected to progressively increasing tension. The cross-yarn fails singly, doubly 

or even in multiples, depending on the type of weave, yarn strength and elongation 

properties. It is important to note that in a tear test, the yarn fails individually in tension 

and for this reason the fabric tear strength is much lower than its breaking strength where 

all yarns fail at the same time. Thus, for a more precise understanding of fabric 

deterioration, the individual yarns extracted from fabrics exposed to various conditions 

were tested for tensile strength and breaking elongation. 

The yarn strength is the stress at which the yarn fails or fractures. Elongation at break is 

the increase in length produced by the breaking force, expressed as a percentage of the 

original nominal length. Since the properties depend on the specimen dimensions and 

testing conditions (e.g., strain rate and gauge length) the values are best used for relative 

comparison and not as absolute values to compare with results reported elsewhere. Due 

to the complexities in calculation of cross-sectional area of ply-twisted yarns with fiber 

blends, the breaking force and breaking strain values of extracted yarns are considered in 

this study. 

Tensile properties of ply-twisted yarn from fabric specimens were measured using a TA 

Instruments RSA III Dynamic Mechanical-Thermal Analyzer operating in transient mode 

(DMTA, TA Instruments-Waters LLC, New Castle, DE). Gauge length was 10 mm and 

specimen extension rate was 0.005 mm/s. Since the instrument is not equipped with an 

extensometer, the strain was calculated by the change in grip spacing. Therefore, the data 

represent trends and not absolute values. A minimum of five individual ply-twisted yarns 

was analyzed per sampling interval. Uncertainties in measurement of tensile strength are 

reported as Type A uncertainties [22, 23] with experimental standard deviations in Table 

3.

2.4. Thermal protective performance testing

A thermal protective performance (TPP) tester developed by Measurement Technology 

Northwest was used in this study to measure the thermal protective performance of 

environmentally stressed OS fabrics. A schematic of the test apparatus is shown in

Figure 2. The instrument is based on the NFPA 1971 test standard and the test method 

uses data from Stoll and Chinta [24] to estimate the time it takes for second degree burn 

injury to the skin behind a fabric assembly when exposed to a given heat flux. 
16

The test apparatus consists of two Meeker burners and bank of quartz tubes calibrated to 

provide 50 % radiative and 50 % convective heat flux. The test sample is exposed to a 

total heat flux of 84 kW m-2 ± 5 kW m-2 (2 cal cm-2s

-1

± 0.1 cal cm-2s

-1

). This exposure 

condition typically represents military fire flash conditions that are similar to 

emergencies encountered by firefighters [9]. The total heat flux was calibrated every day 

prior to experimentation. The Meeker burners were kept at an angle of 45o to the 

horizontal so that the flames converge at a point immediately under the test specimen. 

Burner flames were carefully monitored for any turbulence.

The sample assembly consists of a frame for securing the fabric specimen and a heat 

sensor placed in direct contact with the back of the fabric assembly. The NFPA 1971 

standard [18] requires inclusion of a spacer between the heat sensor and the back of the 

fabric assembly. Inclusion of the spacer in the sample assembly represents an air gap 

between the skin and the fabric and typically increases TPP rating due to the presence of 

the insulating air gap [8]. However, in this study the spacer was not used as it was found 

to detrimentally distort the results with some materials more than others [25]. 

The heat sensor consists of a copper calorimeter embedded in an insulating board which 

is placed face down on the fabric assembly. The copper calorimeter consists of a 

blackened copper disc of 40 mm diameter and has thickness of 1.6 mm. Three 32-gauge 

chromel/alumel thermocouples are mounted in the disk at 120° intervals. The heat sensor 

with calibrated copper calorimeter is connected to a ThermDac data acquisition system 

which records the rate of temperature rise of the sensor. 

The water-cooled shutter is pneumatically actuated and automated for precise control of 

exposure timing. It covers the heating elements so as to allow time for the sample 

carriage to move into position above the heat source. At the start of the test, the heat 

sensors are kept approximately below body temperature. The rise in temperature after the 

exposure is calculated by subtracting the starting temperature and the recorded 

temperature. The rate of temperature rise versus the time is used in conjunction with 

calorimeter constants to calculate heat flux received. The heat flux behind the test 

sample is translated into protection time using the Stoll criterion based on time-to-second 

degree burn [24]. Once the time-to-second degree burn is reached, the shutter closes and 

the test ends. The TPP rating of the fabric assembly is determined by multiplying the 

recorded protection time by the heat flux exposure. The higher the TPP rating, the better 

the thermal protective performance of the fabric assembly. 

Upon completion of the test, the sensors were carefully examined for any sticky residue 

or char from degraded sample. Any accumulated residues were carefully cleaned from 

the sensor and sample holder surfaces as well. Three specimens were tested for each 

sample. Uncertainties in measurement of exposure time to second degree burn and TPP 

values are reported as Type A uncertainties [22, 23] with experimental standard 

deviations in Table 3 and Figure 8 respectively.
17

In order to evaluate the impact of environmental stressing of OS fabrics on thermal 

protective performance of protective ensemble, the moisture barrier

(polytetrafluoroethylene-based film laminated to woven aramid substrate) and thermal 

liner (composite fabric consisting of a woven face fabric quilted to a spunlaced nonwoven) were kept consistent in all test specimens. Fabric components tested were placed 

on the sample holder in the representative sequence encountered in turn-out gear, in that 

the OS is exposed to the heating elements and the thermal liner in contact with the sensor. 

This condition measures the barrier characteristic of the surface material and the 

insulation characteristics of the total assembly.

3. Results and Discussion

3.1. Tear resistance

The mechanism of tearing in woven structures generally includes four main stages: (1) 

the stretching and slippage of longitudinal yarns closest to the tip of the crack; (2), the 

crowding of these longitudinal yarns on the edges of a Del zone (see Figure 3) [26] and 

the transfer of the load to the transversal yarns held in tension in the so-formed Del zone; 

(3), the stretching and alignment/jamming of these transverse yarns; and (4) finally the 

rupture of the outer transverse yarn [27]. These stages proceed cyclically until the whole 

sample has failed.

A typical tear test load-extension plot has a saw-tooth shape. The peaks in the force–

displacement curve correspond to failure of each successive transverse yarn as the tearing 

progresses. The middle part of the load-extension curve represents 50 % of the entire tear 

distance. For a given sample, determining tear resistance by static single tear test method

(ASTM D2261) relies on determining the median of the five largest tear forces from the 

middle part of the load-extension curve. 

Tear strength values for experimental OS fabrics are provided in Table 2. Tear strength 

of untreated BK-00 fabric has the highest tear strength value of 175 N ± 10 N. The lower 

yarn density in BK-00 allows greater yarn mobility and therefore increased tear strength. 

Since BK-00 has not been subjected to textile finishing processes, which essentially

includes wetting and drying, the loose fabric structure with lower yarn density allows

greater yarn mobility as compared to BK fabric. The BK fabric that has been modified 

by finishing process and surface treatments has the lowest tear strength value of 88 N ± 5

N. Finishing treatments can affect tearing strength by altering single yarn strength, ease 

of slippage, fabric rigidity, and possibly by influencing structural properties as yarn 

spacing and yarn crimp [21]. Higher packing density of yarns in BK fabric as compared 

to BK-00 decreases longitudinal yarn mobility leading to a more rapid crowding of the 

yarns in the Del zone. The number of transverse yarns in the Del zone, which support the 

applied load, is thus reduced. However, this trend is not straightforward and 

discrepancies may arise due to differences in the failure mechanisms [28]. The slightly 

higher tear strength value for BKP (113 N ± 6 N) as compared to BK fabric can be 

attributed to the presence of PBO fibers in the fabric blend and the weave of the fabric. 

The basket weave in BKP fabric has longer yarn floats and is known to resist tearing
18

[21]. The pigmented BBK fabric has tear strength of 110 N ± 6 N which is slightly 

higher than BK fabric. The small difference in tear strength values despite similar fiber 

blend and fabric structures may be attributed to differences in coatings and the stiffness it 

imparts to the final finished fabric. 

Considering reduced tear strength values when tested using the single tear method, all OS 

fabrics containing melamine fiber blends would meet the tear strength requirement (tear 

strength >100 N) specified in NFPA 1971 standard [18]. 

Table 2. Tear strength of OS fabrics containing melamine fiber blends. Uncertainties in 

measurement of tear strength are expressed as experimental standard deviations. 

Exposure conditions Tear strength, N

BK-00 BK BKP BBK

Control 175±10 88±5 113±6 110±6

Heat exposure

At 240 oC for 5 min 

128±8

(-27%)

79±3

(-18%)

96±7

(-18%)

88±10

(-20%)

Heat exposure

At 180 oC for 24 hrs 

100±9

(-51%)

93±6

(-21%)

94±5

(-25%)

109±6

(-15%)

UV exposure, 13 days 13±1

(-93%)

12±2

(-88%)

26±2

(-80%)

42 ± 3

(-62%)

Laundering 112±7

(-36%)

92±9

(-5%)

120±11

( 3%)

109±9

(0 %)

Abraded - - - -

Note: Values in parentheses indicate % change in tear strength w.r.t. control sample. 

Negative values indicate decrease in tear strength w.r.t. control sample and positive values 

indicate enhanced tear strength.

3.1.1. Impact of environmental stressing on tear strength of OS fabrics

The ageing performance profiles (APP), which is the deterioration of property as a 

function of UV exposure time, for melamine containing OS fabrics are shown in Figure 

4. The tear strengths of all melamine containing OS fabrics were significantly 

deteriorated when exposed to UV irradiation for 13 d ± 1 d at 50 oC and 50 % RH and 

would certainly not meet requirements of the NFPA 1971 standard. UV irradiation for 

13 d ± 1 d typically corresponds to UV aging that a turnout gear would experience during 

a ≈ 6 years period of use. This time period also corresponds to maximum degradation 

noted on the aging performance profile of previously studied aramid OS fabrics [7]. BK00 fabric shows highest deterioration (93 %) in tear strength primarily because BK-00 

fabric is untreated (no water repellent coating) and therefore UV degradation of 

constituent fibers/yarns is much greater than those with water repellent coatings. The 

water repellant coating shields the underlying fibers from direct irradiation thereby 

causing less UV degradation. BBK fabric shows the least deterioration in tear resistance 
19

(62 %), possibly due to the greater UV resistance of dark shaded BBK fabric. Fabrics 

dyed with black and dark blue are known to disrupt ultraviolet radiation [29] thereby 

causing less UV degradation of fibers. Deterioration in tearing strength of all UV 

exposed OS fabrics is largely due to photodegradation of constituent fibers [7].

Heat exposures were observed to have a small detrimental effect on tear strength of OS 

fabrics tested in this study (Table 2). Heat exposure at 260 oC for 5 min reduced tear 

resistance of all OS fabrics by ≈ 10 %. Heat exposure at 260 o

C for 5 min has practically 

same effect as heat setting process on fabric. Prolonged exposures (24 h) to 180 oC had 

varied impact on all four OS fabrics. Tear strength of BK-00 fabric decreased by ≈ 30 %. 

This ‘gray’ fabric shrinks considerably to increase yarn density thereby reducing its tear 

strength. The very slight observed increase in tear strength of BK fabric exposed to 180 o

C for 24 h can be attributed to loss in stiffness of the fabric as a result of prolonged heat 

exposure. Water repellent coating imparts stiffness to the fabrics which restricts yarn 

mobility in the fabric structure. The water repellent coating is slightly degraded during 

prolonged heat exposures thereby relaxing the yarns and increasing their mobility. As 

discussed earlier, increased yarn mobility in the Del zone increases the tear strength of a 

fabric. BBK fabric which is similar to BK, except the pigmentation, shows very slight 

deterioration in tear strength but has significant discoloration due to prolonged heat 

exposure. 

In this study, the laundering and drying process has considerable impact on tear 

resistance of BK-00 fabric. Untreated BK-00 fabric lost ≈ 20% of its tear strength when 

subjected to 5 cycles of washing and drying. This damage is dominant in BK-00 fabric 

with no surface coating. On the contrary, BK and BKP fabrics show slight improvement 

in tear strength. Increased tear strength of these fabrics may be due to improved 

flexibility and relaxation of yarns in the fabric structure. This essentially increases yarn 

mobility and thereby the tear resistance of fabrics. Laundering may have caused damage 

to fibers and yarns in the fabric due to mechanical agitation and chemical action of the 

detergent. When subjected to routine and repetitive laundering drying cycles, a piece of 

fabric is subjected to complex physical and chemical actions resulting in physical and 

chemical degradation of fabric [30]. Changes in the tear strength of washed OS fabrics 

could be due to the combined effect of dimensional changes of a fabric, increased fiber 

packing factor in yarn, and fiber damage due to physical and chemical actions during 

washing. OS fabrics with a suitable surface coating tend to stabilize and gain 

dimensional stability after the first washing cycle, resulting in improved tear resistance. 

In addition to dimensional changes in the fabric, the effects of washing on tear strength 

may arise from removal of certain types of finish that have detrimental effect on tearing 

strength, or from lubrication of the fabric by residual detergent. The magnitude of the 

effect in any particular case will depend on the extent to which these factors are 

operative.

Percentage reduction in the tear strength of OS fabrics subjected to various environmental 

stresses is graphically shown in Figure 5. It is clear that UV exposure has the greatest 

impact on tear resistance of OS fabrics which is mainly due to photodegradation of 

constituent fibers [7]. Heat exposures have minimal impact on tear strength of OS 
20

fabrics. Changes in tear strength of heat exposed and laundered OS fabrics are largely 

due to dimensional changes in fabric properties (e.g., area density, thickness, flexibility).

Due to sample limitations, the impact of abrasive wear on tear strength of OS fabrics was 

not quantified in this study. 

3.2. Tensile strength of yarn

The tear strength of a fabric is largely governed by the single-yarn strength and slippage 

of yarn during the test. The slippage of yarn is dependent on spacing of yarn, weave and 

surface finish [21]. From the above discussion, it is clear that changes in tear strength of 

OS fabrics could be a combined effect of reduced yarn strength and dimensional changes 

in the fabric. To delineate the cause(s) of tear strength deterioration due to environmental 

stressing, changes in single-yarn strength are discussed in this section. Breaking force and 

breaking strain values for yarns extracted from OS fabrics are given in Table 3. 

Table 3. Tensile properties of yarns extracted from OS fabrics. Uncertainties in 

measurement of tensile strength are expressed as experimental standard deviations.

Note: Values in parentheses indicate % change in tensile properties w.r.t. control sample. 

Negative values indicate decrease in tensile properties w.r.t. control sample and positive values 

indicate enhanced tensile properties.

Exposure conditions BK-00 BK BKP

Breaking 

force, g

%-

Breaking 

strain

Breaking 

force, g

%-

Breaking 

strain

Breaking 

force, g

%-Breaking 

strain

Control 2930±250 13±4 2210±280 15±4 1520±190 11±1

Heat exposed at

260 oC for 5 min

2840±290

(-3%)

14±3

(+8%)

1920±280

(-13%)

15±2

(0%)

1250±130

(-18%)

12 ±2

(+9%)

Heat exposed at

180 oC for 24 h

2200±210

(-25%)

14±3

(+8%)

1990±210

(-10%)

14±1

(-7%)

1500±60

(-1%)

13±2

(+18%)

Laundering 2860±330

(-2%)

13±2

(0%)

2170±280

(-2%)

13±4

(-13%)

1630±260

(+7%)

7 ±1

(-36%)

UV exposure (d) 1±0.5 2110±290

(-28%)

10±1

(-23%)

2000±330

(- 9%)

15±4

(0%)

1590±110

(+5%)

11±0.3

(0%)

 4±0.5 530±50

(-82%)

8±2

(-38%)

730±30

(- 67%)

11±0.2

(-27%)

620±80

(- 59%)

8±2

(-27%)

 7±0.5 400±40

(-86%)

8±2

(-38%)

520±80

(- 77%)

14±2

(-7%)

430±60

(- 72%)

8±2

(-27%)

 13±0.5 200± 30

(-93%)

7±2

(-46%)

260±80

(-88%)

11±2

(-27%)

190±20

(-87%)

8±2

(-27%)

 28±0.5 150±30

(-95%)

8±2

(-38%)

170±20

(- 92%)

10±1

(-33%)

130±20

(- 91%)

7±1

(-36%)
21

Within the measurement uncertainty, single yarn strength of BK-00 in tensile test is 

similar to that of BK. Despite inclusion of high tenacity PBO fibers, the overall tensile 

strength of BKP yarns is lower than that of BK-00 and BK yarns. All the fibers displayed

somewhat brittle failure with average breaking strain of 15 % ± 4 %. Since para-aramid 

fibers constitute the majority (60 %) of BK-00, BK and BKP yarns, their tensile 

properties are mainly dominated by the highly oriented structure of poly(p-phenylene 

terephthalamide) [11]. 

Comparing the APP of yarns in Figure 6, it can be noted that all the yarns rapidly lose 

tensile strength upon UV exposure. BK-00 yarns lost more than 90 % of their initial 

tensile strength after 13 d of continuous exposure to UV radiation while BK and BKP lost 

> 85 % of initial strength. Similar to trends observed for tear strength, further exposure 

up to 28 d resulted in continued deterioration of tensile strength at a significantly slower 

rate. All the yarns retained less than 10 % of its original strength at the end of 28 d 

exposure to UV/50oC/50%RH. The UV exposure also changed tensile behavior of BK00 and BKP yarns from brittle failure (% breaking strain of 13 % ± 4 %) to very brittle 

failure (% breaking strain of 8 % ± 2 %). Yarns from BK OS fabric, however, did not 

show any change in their failure mechanism.

Tensile properties of yarns extracted from fabrics exposed to other environmental stresses

including heat exposures and laundering are given in Table 3 and percentage loss of 

tensile strength with respect to unexposed control specimens for BK-00, BK and BKP OS 

fabrics is plotted in Figure 7. It can be noted from Figure 7 that UV exposure has 

maximum impact on tensile properties of all yarns. Heat exposures have a small 

detrimental effect on tensile properties of all yarns. Laundering has a variable effect on 

tensile properties of yarns tested in this study. Yarns from BK-00 and BK OS fabrics 

show very small loss of tensile strength while yarns from BKP OS fabric show increase 

in tensile strength. This small increase in breaking force can be attributed to shrinkage of 

yarn and increased packing density of fibers in BKP yarn. 

Comparing percentage loss of tear strength and tensile strength in Figure 5 and Figure 7, 

it is clear that loss in tear strength of OS fabrics is slightly greater than the loss in tensile 

strength of single yarn extracted from OS fabrics. This suggests that changes in tear 

strength of OS fabrics are a cumulative effect of loss in tensile strength of single yarns 

and dimensional stability of the fabric itself.

3.3. Thermal protective performance of fabric ensemble 

Several researchers have studied the thermal protective performance of various fabric 

assemblies including single-layer OS fabrics as well as effects of instrumentation. King 

et al [31] measured the relative TPP of a wide range of flame-retardant (FR) fabrics, both 

in single and multiple layers. Their studies suggested that high density fabrics with FR 

fibers and FR finishes provide additional protection and that more protection is obtained 

by using two or more layers of fabrics as opposed to thicker fabrics. Moreover, two 

layers are effective only when both layers contain fabrics that do not melt and fuse 

together. They also classified fabrics on the basis of failure mechanism. The FR cotton 
22

typically failed due to embrittlement and shrinkage while most wool containing fabrics 

failed via melting and decomposition. Glass and aluminum containing fabrics failed due 

to discoloration and embrittlement. 

Barker et al [32] studied the influence of fiber composition and fabric construction on the 

thermal protective performance in high intensity tests. They measured insulation 

properties of fabrics via conductive heat transfer and found that in such type of tests, the 

temperature of the hot surface and the pressure applied during the exposure are 

controlling test variables. Above 300 o

C, the insulative performance of some fabrics 

deteriorates significantly due to heat degradation that causes changes in physical 

properties.

Day [ 33 ] studied effect of nature of heat sources (radiative and/or convective) on 

measurement of TPP of fabrics assemblies. The 50/50 or 70/30 convective/radiative heat 

fluxes have very little impact on determining the heat transfer properties of garment 

assemblies. However, the specimen mounting has significant impact on TPP ratings. The 

additional weights, restraining pins, and air gap affects thermal shrinkage, thereby 

affecting TPP ratings. The study also revealed that the NFPA values were always higher 

than those obtained with the ASTM techniques. This difference in TPP values was not 

due to the difference in radiative to convective heat ratio but due to greater sagging of 

specimen into the larger opening of the sample holder in the NFPA method.

The thermal protective performance of fabric assemblies including OS fabrics containing 

melamine fibers were measured in this study. The exposure times to second degree burn 

for all OS fabrics are given in Table 4 and their thermal protective performance ratings 

are plotted in Figure 8. Generally, thermal protective performance of melamine 

containing OS fabrics is comparable to that of OS fabrics traditionally made from aramid 

and PBI fibers or their blends and is well above the NFPA minimum TPP requirement of 

35 cal/cm2

. Within the experimental error, the TPP rating (55 cal/cm2 ± 0.9 cal/cm2) of 

BBK is highest amongst the melamine containing OS fabrics, providing the wearer the 

maximum protection time of 27 s ± 0.43 s. BKP has a lower TPP rating (48 cal/cm2 ± 0.9 

cal/cm2), giving a maximum protection time of 24 s ± 0.88 s. The lower thermal 

protective performance of BKP fabric could be due to the greater fabric thickness and/or 

to the presence of the highly conductive PBO fibers. Furthermore, compact construction 

with basket weave in BKP fabric may also increase heat transfer by conduction [8]. 

Table 4. Protection time for OS fabrics containing melamine fiber blends. Uncertainties 

in measurement of time to second degree burn are expressed as experimental standard 

deviations.

Exposure conditions Time to second degree burn, s 

BK-00 BK BKP BBK

Control 25.8 ± 0.3 24.5 ± 0.6 24.1 ± 0.9 27.6 ± 0.4
23

Heat exposure

At 240 oC for 5 min 

22.6 ± 0.4 22.7 ± 0.3 21.9 ± 0.2 24.1 ± 0.8

Heat exposure

At 180 oC for 24 hrs 

22.0 ± 0.1 23.0 ± 0.7 22.86 ± 0.5 24.8 ± 0.9

UV exposure, 13 d on 

SPHERE

23.4 ± 0.4 22.3 ± 0.4 22.5 ± 0.8 22.7 ± 0.7

Laundering 24.1± 0.9 24.7 ± 0.2 23.9 ± 0.5 24.8 ± 0.6

Abraded 22.3 ± 0.3 22.3 ± 0.7 22.24 ± 0.8 23.2 ± 0.3

Figure 8 shows a comparison of the thermal protective performance ratings of 

environmentally stressed OS fabrics. Generally, the TPP ratings of environmentally 

stressed fabrics are lower than their respective control OS fabrics. However, the TPP 

ratings of all environmentally stressed fabrics still meet the NFPA minimum requirement 

of 35 cal/cm2

. Amongst the environmental stressing factors, abrasion and UV exposure 

have the most detrimental effect on thermal protective performance of all OS fabrics 

tested in this study. All test assemblies with abraded and UV exposed OS fabrics had 

almost similar (45 cal/cm2± 1 cal/cm2) TPP ratings. This suggests that chemical and 

physical degradation of yarn and constituent fibers due to UV exposure and abrasion 

respectively have detrimental effects on thermal barrier properties of OS fabric. Heat 

exposure and washing seem to have very little effect on TPP rating of OS fabrics. 

Changes in the TPP ratings of washed and heat exposed fabrics could be due to the

combined effects of dimensional changes in fabrics as well as degradation of constituent 

fibers and surface properties. In conclusion, the detrimental effect of environmental 

stressing on thermal protective performance could be ranked as: washing < heat 

exposure < abrasion< UV exposure. 

Table 5. Percent reduction in TPP values: Individual and combined effects of 

environmental stressing on thermal protective performance of OS fabrics.

OS 

fabric

Laundering Abraded UV 

exposure, 

13 d on 

SPHERE

Heat 

exposure

At 240 

o

C for 5 

min

Heat 

exposure

At 180 

o

C for 

24 hrs

% 

Average 

reduction 

in TPP 

% 

Cumulative 

reduction 

in TPP 

Calculated TPP 

value of OS 

fabric subjected 

to all 

environmental 

stressing, cal/cm2

BK-00 8 13 13 12 15 12 62 20

BK -2 8 10 6 6 6 29 35

BKP 0 8 8 8 4 6 29 34

BBK 9 16 16 11 9 12 62 21

Presented in Table 5 are percent reductions in TPP values of various OS fabrics due to 

each individual environmental stressing factor. Based on this information, average and 

cumulative effects of environmental stressing on thermal protective performance of

various OS fabrics have been calculated and presented in Table 5. It can be noted from 

Table 5 that averaging the detrimental effects of all stressing factors, BK-00 and BBK 
24

shows highest percent reduction ( 12 % w.r.t. control fabrics) while BK and BKP has 

lowest percent reduction ( 6 % w.r.t. control fabrics) in TPP values. Furthermore, 

presuming OS fabrics to have experienced all types of environmental stressing, then the 

cumulative detrimental effect on thermal protective performance can be estimated by 

simple addition of percent reductions in TPP values due to individual stressing. From the 

calculated TPP value of OS fabric subjected to all environmental stressing in Table 5 it 

can be seen that fabric ensemble with BK and BKP ( considering given experimental 

uncertainties ) outer shell will still meet the NFPA minimum TPP requirement of 35 

Cal/cm2

. However, fabric ensembles with BK-00 and BBK outer shells would fail to 

meet the requirements of NFPA 1971 standard. 

4. Summary and Conclusions 

In this study, environmentally stressed OS fabrics containing melamine fiber blends were 

evaluated for thermal and mechanical properties that are critical to the protective 

performance of firefighter turnout gear. The effects of fiber blend, fabric construction, 

and finishing processes including water repellent coating and pigmentation of melaminecontaining OS fabrics were also studied. The melamine-containing OS fabrics showed

comparable thermal protective performance and superior tear resistance when compared 

to the traditionally used polyaramid blends. All the OS fabrics examined in this study 

performed well above the requirements of NFPA 1971 specifications. 

Results suggest that post-processing of ‘gray’ fabric which includes application of 

various finishes and coatings have significant impact on both, thermal protective 

performance and tear resistance of OS fabrics. Finishing treatments affected performance 

properties of fabric by increasing the fiber packing factor in yarn, changing yarn crimp 

and changing yarn spacing thereby making dimensional changes to the fabric. Surface 

coatings altered tear resistance of fabric by influencing yarn slippage and fabric rigidity. 

Fabrics dyed with black and dark blue dyes caused less UV degradation of fibers than 

bright yellow and brown dyes. 

Individual environmental stressing has varied impact on protective performance of OS 

fabrics. However, cumulative detrimental effect of all the stressing factors on thermal 

protective performance is maximum on BK-00 and BBK outer shell fabrics. UV exposure 

in particular causes more impairment of OS fabric as compared to other environmental 

stressing. Deterioration in tear strength of all UV exposed OS fabrics is largely due to 

photodegradation of constituent fibers. In cases where environmental stressing alters 

dimensional properties of a fabric including mass area density, thickness and flexibility, 

its effect on tear resistance of OS fabrics is a cumulative effect of loss in tensile strength 

of single yarns and dimensional stability of the fabric itself. The tear strength of all 

melamine containing OS fabrics exposed to environmental stressing has significantly 

deteriorated, and most OS fabrics, depending on fiber blend and fabric structure, would 

fail to meet requirements of NFPA 1971 standard. However, the TPP ratings of 

environmentally stressed OS fabrics containing melamine fiber blends are well above the 

NFPA minimum TPP requirement of 35 cal/cm2. The study thus suggests that 

environmental stressing has a more detrimental impact on tear strength than on the 

thermal protective performance of OS fabrics. 
25

To mitigate the detrimental effects of UV, we are currently investigating a novel coating 

method using a layer-by-layer (LbL) deposition to fabricate nanometer- to micrometerthick TiO2 coatings on the high performing fiber fabrics. The LbL coated fabrics will be 

evaluated for thermal and mechanical properties that are critical to the protective 

performance of firefighter turnout gear. The performance of LbL coated fabrics exposed 

to accelerated environmental stressing including UV exposure, laundering, wear and 

abrasion will also be evaluated. 
26

Figure 1. Schematic of: (a) Martindale type abrader and (b) modified assembly of Martindale type abrader.

Top moving plate

Top weight

Sample holder

Abrasive cloth holder Machine base

Top moving plate

Top weight

Abrasive cloth holder

Sample holder Machine base
27

Figure 2. Schematic of TPP test apparatus.

Radiant heater

Gas burners Gas burners

Shutter Shutter

Sample carriage

Sample holder

Thermocouple

Sample

Calorimeter assembly
28

Figure 3. Single tear fabric configuration [26].

Longitudinal warp yarns

Clamping jaws

Transverse weft yarns

Clamping jaws

Del zone
29

0

50

100

150

200

250

Control 1 day 4 days 7 days 13 days 28 days

Tear strength, N

BK-00

BK

BKP

BBK
30

Figure 4. Deterioration in tear strength of OS fabrics exposed to simulated UV radiation. Error bars are ± experimental standard 

deviation.

Note: Negative values indicate loss of tear strength.

Figure 5. Percentage reduction in tear strength of environmentally stressed OS fabrics.
31

0

500

1000

1500

2000

2500

3000

3500

Control 1 day 4 days 7 days 13 days 28 days

Breaking force, g

BK-00

BK

BKP
32

Figure 6. Deterioration in tensile strength of OS fabrics exposed to simulated UV radiation. Error bars are ± experimental standard 

deviation.
33

Note: Negative values indicate loss in tensile strength.

Figure 7. Percentage reduction in tensile strength of yarn unraveled from environmentally stressed OS fabrics.
34

Figure 8. Thermal protective performance of environmentally stressed OS fabrics. Error bars are ± experimental standard deviation.

0

10

20

30

40

50

60

Thermal Protective Performance (TPP), cal/cm2

Control

Laundered

Abraded

UV Exposed

Heat exposed, 240 °C for 5 min

Heat exposed, 180 °C for 24 h

35
35

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