*Effect of Fabric Features on SPP/TTTE*

Table 3 shows that the SPP of triple-layered fabric systems is much higher than for single- or double-layered fabric systems. This is because a triple-layered fabric system including a moisture barrier can trap higher amounts of dead air than single- or doublelayered fabric systems [36–40]. Consequently, triple-layered fabric systems prove to be more thermally insulated and can provide better protection against steam exposure [7]. In this context, it is necessary to mention that the SPP per unit thickness of a doublelayered fabric system incorporating a moisture barrier (e.g., AF or FA) is equivalent or sometimes even higher to triple-layered fabric systems; however, the SPP per unit thickness of a double-layered fabric system not comprising a moisture barrier (e.g., AC or AE) is much lower than triple-layered fabric systems (Table 3). This finding could help to establish that structural differences, such as the presence or absence of moisture barriers in fabric systems, are crucial to the SPP. In fact, only the presence of a moisture barrier in combination with a shell fabric (e.g., FA) could give better protection than a few high thickness triple-layered fabric systems (e.g., AFC, AFD, and AFE). Furthermore, it is evident from Table 3 that the TTTE through triple-layered fabric systems is lower than for single- or double-layered fabric systems. This is because triple-layered fabric systems have increased amounts of empty space (among their constituent shell fabrics (SF), moisture barriers (MB), and thermal liners (TL)), and these empty spaces can store steam within the fabric systems [21]. As the stored steam inside the triple-layered fabric system remains high, the transferred steam or the TTTE through the fabric system is low (Figure 3). *Textiles* **2022**, *2*, FOR PEER REVIEW 6 than triple-layered fabric systems (Table 3). This finding could help to establish that structural differences, such as the presence or absence of moisture barriers in fabric systems, are crucial to the SPP. In fact, only the presence of a moisture barrier in combination with a shell fabric (e.g., FA) could give better protection than a few high thickness triple-layered fabric systems (e.g., AFC, AFD, and AFE). Furthermore, it is evident from Table 3 that the TTTE through triple-layered fabric systems is lower than for single- or double-layered fabric systems. This is because triple-layered fabric systems have increased amounts of empty space (among their constituent shell fabrics (SF), moisture barriers (MB), and thermal liners (TL)), and these empty spaces can store steam within the fabric systems [21]. As the stored steam inside the triple-layered fabric system remains high, the transferred steam or the TTTE through the fabric system is low (Figure 3).

**Figure 3.** TTTE through (**a**) triple-layered and (**b**) double-layered fabric systems. **Figure 3.** TTTE through (**a**) triple-layered and (**b**) double-layered fabric systems.

Furthermore, the results of the *t*-test (T-stat and P-value) between normalized values of the fabric system properties (Table 2) and SPP/TTTE (Table 3) are shown in Table 5. In Table 5, the T-stat values of thickness, weight, and thermal resistance with SPP are positive, whereas the T-stat values of these properties with TTTE are negative. This indicates that these properties possess a positive and negative relationship with the SPP and TTTE, respectively. The relationship plots of these properties with SPP and TTTE, shown in Figures 4–6, suggest that a moderate relationship exists between each of them and the SPP/TTTE. These relationships can be further explained by the theory of heat transfer Furthermore, the results of the *t*-test (T-stat and P-value) between normalized values of the fabric system properties (Table 2) and SPP/TTTE (Table 3) are shown in Table 5. In Table 5, the T-stat values of thickness, weight, and thermal resistance with SPP are positive, whereas the T-stat values of these properties with TTTE are negative. This indicates that these properties possess a positive and negative relationship with the SPP and TTTE, respectively. The relationship plots of these properties with SPP and TTTE, shown in Figures 4–6, suggest that a moderate relationship exists between each of them

through fabric systems [14,18,20]. In a high-pressurized steam exposure, intimate contact occurs between fabric systems and the skin of the wearers (skin simulant sensor) (Figure

toward the skin. In this situation, a fabric with high weight and thickness can trap more insulative dead air, which can augment the thermal resistance of the fabric. This highly thermally insulated and resistive fabric can enhance the SPP by slowly transferring conductive thermal energy and generating slower burns on the bodies of wearers. Turning our attention to Figure 7, Equations (1) and (2) represent in analytical and mathematical terms the conservation of conductive thermal energy for a one-dimensional rectangular coordinate, X and Y coordinates-based fabric system [41]. Based on Equation (2), it can be inferred that the behavior of the TTTE through a fabric system is dependent upon the area of the fabric system (A in cm2), gradient of temperature along the x direction of the fabric system (*δT*/*δx* in °C/cm), rate of energy generation per unit volume of the fabric system (*qg* in W/cm3), density of the fabric system (*ρ* in g/cm3), thickness of the fabric system (*dx* in cm), specific heat of the fabric system (*Cp* in J/gm. °C), total steam exposure time (*t* in s),

and thermal conductivity of the fabric system (*kf*in W/m.K).

and the SPP/TTTE. These relationships can be further explained by the theory of heat transfer through fabric systems [14,18,20]. In a high-pressurized steam exposure, intimate contact occurs between fabric systems and the skin of the wearers (skin simulant sensor) (Figure 7). Consequently, a conductive thermal energy transfer proceeds from the fabric systems toward the skin. In this situation, a fabric with high weight and thickness can trap more insulative dead air, which can augment the thermal resistance of the fabric. This highly thermally insulated and resistive fabric can enhance the SPP by slowly transferring conductive thermal energy and generating slower burns on the bodies of wearers. Turning our attention to Figure 7, Equations (1) and (2) represent in analytical and mathematical terms the conservation of conductive thermal energy for a one-dimensional rectangular coordinate, X and Y coordinates-based fabric system [41]. Based on Equation (2), it can be inferred that the behavior of the TTTE through a fabric system is dependent upon the area of the fabric system (A in cm<sup>2</sup> ), gradient of temperature along the x direction of the fabric system (*δT*/*δx* in ◦C/cm), rate of energy generation per unit volume of the fabric system (*q<sup>g</sup>* in W/cm<sup>3</sup> ), density of the fabric system (*ρ* in g/cm<sup>3</sup> ), thickness of the fabric system (*dx* in cm), specific heat of the fabric system (*C<sup>p</sup>* in J/gm. ◦C), total steam exposure time (*t* in s), and thermal conductivity of the fabric system (*k<sup>f</sup>* in W/m.K). *Textiles* **2022**, *2*, FOR PEER REVIEW 7 Thermal energy conduction into the fabric system + Thermal energy generation inside the fabric system = Thermal energy conduction out of the fabric system + Thermal energy storage inside the fabric system (1)

Thermal energy conduction into the fabric system + Thermal energy generation inside the fabric system = Thermal energy conduction out of the fabric system + Thermal energy storage inside the fabric system (1) *<sup>T</sup> <sup>x</sup> dx <sup>t</sup> <sup>A</sup> dxC T q Adx k A <sup>T</sup> <sup>k</sup> <sup>A</sup> <sup>p</sup>* δ δ δ ( / 2, ) . . . . . . . . . . <sup>+</sup> <sup>−</sup> <sup>+</sup> <sup>=</sup> <sup>−</sup> <sup>+</sup>

$$-kA.\frac{\delta\Gamma}{\delta\mathbf{x}}\Big|\_{\mathbf{x}} + q\_{\text{\S}}A.d\mathbf{x} = -kA.\frac{\delta\Gamma}{\delta\mathbf{x}}\Big|\_{\mathbf{x} + \delta\mathbf{x}} + \rho A.d\mathbf{x}.\mathbf{C}\_{p}\frac{\delta\Gamma(\mathbf{x} + d\mathbf{x}/2\mathbf{t})}{\delta\mathbf{t}}\tag{2}$$

**Table 5.** Results of *t*-test. **Table 5.** Results of *t*-test.


SPP TTTE

0 100 200 300 400 500 600 700 800

Weight (g/m2)

TTTE (kJ/m2)

**Figure 4.** Relationship plot of thickness with SPP and TTTE. **Figure 4.** Relationship plot of thickness with SPP and TTTE.

**Figure 5.** Relationship plot of weight with SPP and TTTE.

0

5

10

15

SPP (Time to Second-degree Burn that is

measured in Seconds)

20

25

30

Thickness (mm)

*Textiles* **2022**, *2*, FOR PEER REVIEW 7

Thermal energy conduction into the fabric system + Thermal energy generation inside the fabric system = Thermal energy conduction out of the fabric system + Thermal energy storage inside the fabric system (1)

*q Adx k A*

*g*

**Table 5.** Results of *t*-test.

0

5

10

15

SPP (Time to Second-degree Burn that is

measured in Seconds)

20

25

30

*<sup>T</sup> <sup>k</sup> <sup>A</sup> <sup>p</sup>*

*x*

δ

δ

*x*

*x T*

( / 2, ) . . . . . . . . . . <sup>+</sup> <sup>−</sup> <sup>+</sup> <sup>=</sup> <sup>−</sup> <sup>+</sup>

δ

δ

*x x*

+

δ

ρ

**Fabric Properties SPP TTTE** 

**Thickness** 2.60 0.03 −1.95 0.08 **Weight** 2.71 0.02 −1.52 0.17

**Thermal Resistance** 1.90 0.09 −1.31 0.2 **Air Permeability** −2.65 0.001 3.56 0.007

SPP TTTE

*t*

**T-Stat** *p***-Value T-Stat** *p***-Value** 

TTTE (kJ/m2)

(2)

δ

*<sup>T</sup> <sup>x</sup> dx <sup>t</sup> <sup>A</sup> dxC*

δ

**Figure 5.** Relationship plot of weight with SPP and TTTE. **Figure 5.** Relationship plot of weight with SPP and TTTE.

**Figure 4.** Relationship plot of thickness with SPP and TTTE.

**Figure 6.** Relationship plot of thermal resistance with SPP and TTTE. **Figure 6.** Relationship plot of thermal resistance with SPP and TTTE.

Conductive Thermal Energy Transfer Area (A) Fabric System Human Skin/Sensor High-pressurized Steam Moreover, Table 5 shows that the T-stat value of air permeability is negative with respect to the SPP; however, the T-stat value of air permeability is positive with respect to the TTTE. This implies that air permeability has a negative and positive relationship with the SPP and TTTE, respectively (Figures 8 and 9). In addition, the *p*-values (0.001 and 0.007) of air permeability are least among all fabric properties and are below 0.05. This means that air permeability is the most important and significant property to understand the SPP of or the TTTE through fabric systems. This finding can be explained comprehensively by the theory of mass (steam) transfer through fabric systems [11–15]. In this context, it is notable that a regular fabric is a multiphase, porous media, which comprises both solid fiber and gaseous air phases (Figure 10); and Darcy's law states that the mass transfer through porous media depends upon the permeability of that media (Equation (3). According to this law, a fabric with high air permeability can quickly transfer thermal energy in the form of convective steam jets through its air phase; eventually, the SPP and TTTE become low and high, respectively. Here, steam that has entered the fabric system gradually condenses and produces a mixture of steam and hot water; this hot water mainly transfers

**Figure 7.** Conductive thermal energy transfer through a fabric system under steam exposure.

X

Moreover, Table 5 shows that the T-stat value of air permeability is negative with respect to the SPP; however, the T-stat value of air permeability is positive with respect to the TTTE. This implies that air permeability has a negative and positive relationship with the SPP and TTTE, respectively (Figures 8 and 9). In addition, the *p*-values (0.001 and 0.007) of air permeability are least among all fabric properties and are below 0.05. This means that air permeability is the most important and significant property to understand the SPP of or the TTTE through fabric systems. This finding can be explained comprehensively by the theory of mass (steam) transfer through fabric systems [11–15]. In this context, it is notable that a regular fabric is a multiphase, porous media, which comprises both solid fiber and gaseous air phases (Figure 10); and Darcy's law states that the mass transfer through porous media depends upon the permeability of that media (Equation (3). According to this law, a fabric with high air permeability can quickly transfer thermal energy

Y

through the fabric system toward the bodies of wearers and generates burns (Figure 10). In the steam condensation process, a considerable amount of thermal energy is released, which also causes burns on the bodies of wearers [34,37]. Through inference testing (hypothesis and a 95% confidence interval) of the dataset shown in Table 3, it has been found that a significant difference exists between the TTTE of air-impermeable and airpermeable fabrics (*p*-value < 0.05), and this difference always remains negative. This demonstrates that the TTTE through an air-impermeable fabric is much lower than an airpermeable fabric, because air-impermeable fabrics do not allow a steam transfer, lowering the TTTE [42,43]. In the case of multilayered, impermeable fabric systems (shown in Table 3), a fabric system including a moisture barrier in its outer layer has less TTTE (or high SPP) than a fabric system including a moisture barrier in its inner (middle) layer. This is because the presence of a polyurethane-coated (smooth surfaced) moisture barrier in its outer layer can immediately stop the steam transfer through the fabric system during exposure; as a result, the TTTE becomes lower, or the SPP enhances (Figure 11). This immediate stop of the steam transfer is less prominent in a fabric system with a moisture barrier in its inner layer. In this context, it is also notable that Fabric-B (in Table 3) is an air-impermeable, single-layered fabric (without any moisture barrier) that possesses a moderately acceptable SPP. This is because Fabric-B has encapsulated fiber finishing that did not allow a transfer of steam through its structure; as a consequence, the SPP enhances (Figure 12). *Textiles* **2022**, *2*, FOR PEER REVIEW 8 200 300 400 500 600 700 10 15 20 25 30 TTTE (kJ/m2) SPP (Time to Second-degree Burn that is measured in Seconds) SPP TTTE

$$Q = \frac{-KA(P\_b - P\_a)}{\mu L} \tag{3}$$

where *Q* = the total discharge of steam per unit time (m3/s), *K* = fabric permeability (m<sup>2</sup> ), *A* = cross sectional area of mass flow (m<sup>2</sup> ), *P<sup>a</sup>* = pressure of the steam jet (Pa), *P<sup>b</sup>* = pressure of steam jet after passing through the fabric system (Pa), *µ* = viscosity (Pa·s), and *L* = thickness of the fabric systems (m). **Figure 6.** Relationship plot of thermal resistance with SPP and TTTE. 0 0.05 0.1 0.15 0.2 Thermal Resistance (Km2/W)

0

5

**Figure 7.** Conductive thermal energy transfer through a fabric system under steam exposure. **Figure 7.** Conductive thermal energy transfer through a fabric system under steam exposure.

Moreover, Table 5 shows that the T-stat value of air permeability is negative with respect to the SPP; however, the T-stat value of air permeability is positive with respect to the TTTE. This implies that air permeability has a negative and positive relationship with the SPP and TTTE, respectively (Figures 8 and 9). In addition, the *p*-values (0.001 and 0.007) of air permeability are least among all fabric properties and are below 0.05. This

sively by the theory of mass (steam) transfer through fabric systems [11–15]. In this context, it is notable that a regular fabric is a multiphase, porous media, which comprises both solid fiber and gaseous air phases (Figure 10); and Darcy's law states that the mass transfer through porous media depends upon the permeability of that media (Equation (3). According to this law, a fabric with high air permeability can quickly transfer thermal energy

*Textiles* **2022**, *2*, FOR PEER REVIEW 10

*Textiles* **2022**, *2*, FOR PEER REVIEW 9

in the form of convective steam jets through its air phase; eventually, the SPP and TTTE become low and high, respectively. Here, steam that has entered the fabric system gradually condenses and produces a mixture of steam and hot water; this hot water mainly transfers through the fabric system toward the bodies of wearers and generates burns (Figure 10). In the steam condensation process, a considerable amount of thermal energy is released, which also causes burns on the bodies of wearers [34,37]. Through inference testing (hypothesis and a 95% confidence interval) of the dataset shown in Table 3, it has been found that a significant difference exists between the TTTE of air-impermeable and air-permeable fabrics (*p*-value < 0.05), and this difference always remains negative. This demonstrates that the TTTE through an air-impermeable fabric is much lower than an airpermeable fabric, because air-impermeable fabrics do not allow a steam transfer, lowering the TTTE [42,43]. In the case of multilayered, impermeable fabric systems (shown in Table 3), a fabric system including a moisture barrier in its outer layer has less TTTE (or high SPP) than a fabric system including a moisture barrier in its inner (middle) layer. This is because the presence of a polyurethane-coated (smooth surfaced) moisture barrier in its outer layer can immediately stop the steam transfer through the fabric system during exposure; as a result, the TTTE becomes lower, or the SPP enhances (Figure 11). This immediate stop of the steam transfer is less prominent in a fabric system with a moisture barrier in its inner layer. In this context, it is also notable that Fabric-B (in Table 3) is an air-impermeable, single-layered fabric (without any moisture barrier) that possesses a moderately acceptable SPP. This is because Fabric-B has encapsulated fiber finishing that did not allow a transfer of steam through its structure; as a consequence, the SPP enhances (Figure

> *L KA <sup>P</sup> <sup>P</sup> <sup>Q</sup> <sup>b</sup> <sup>a</sup>* μ

where *Q* = the total discharge of steam per unit time (m3/s), *K* = fabric permeability (m2), *A* = cross sectional area of mass flow (m2), *Pa* = pressure of the steam jet (Pa), *Pb* = pressure of steam jet after passing through the fabric system (Pa), *μ* = viscosity (Pa·s), and *L* = thick-

<sup>−</sup> ( <sup>−</sup> ) <sup>=</sup> (3)

**Figure 8.** Relationship plot of air permeability and SPP. **Figure 8.** Relationship plot of air permeability and SPP. *Textiles* **2022**, *2*, FOR PEER REVIEW 10

ness of the fabric systems (m).

12).

**Figure 9.** Relationship plot of air permeability and TTTE. **Figure 9.** Relationship plot of air permeability and TTTE. **Figure 9.** Relationship plot of air permeability and TTTE.

**Figure 10.** Steam transfer mechanisms through regular fabrics.

**Figure 10.** Steam transfer mechanisms through regular fabrics. **Figure 10.** Steam transfer mechanisms through regular fabrics.

*Textiles* **2022**, *2*, FOR PEER REVIEW 11

**Figure 11.** High-pressurized steam transfer through (**a**) a triple-layered fabric with SF in the outer layer, and (**b**) a triple-layered fabric with MB in the outer layer. **Figure 11.** High-pressurized steam transfer through (**a**) a triple-layered fabric with SF in the outer layer, and (**b**) a triple-layered fabric with MB in the outer layer. **Figure 11.** High-pressurized steam transfer through (**a**) a triple-layered fabric with SF in the outer layer, and (**b**) a triple-layered fabric with MB in the outer layer.

**Figure 12.** High-pressurized steam transfer through a single-layered encapsulated fiber finished fabric. **Figure 12.** High-pressurized steam transfer through a single-layered encapsulated fiber finished **Figure 12.** High-pressurized steam transfer through a single-layered encapsulated fiber finished fabric.

#### **4. Summary and Conclusions**  fabric. **4. Summary and Conclusions**

In this study, it has been found that a fabric system with a low total transmitted thermal energy (TTTE) generally possesses high steam protective performance (SPP). The SPP/TTTE are mainly dependent upon the constructional attributes and physical properties of fabric systems. Usually, multilayered fabric systems comprising a moisture barrier are highly thermally insulated due to higher amounts of dead air trapped in their structures, and they can store steam in the empty spaces present among their constituent layers. Consequently, multilayered fabric systems have a high SPP and a low TTTE. It can also be concluded from this study that moisture barriers present in fabric structures play a crucial role in achieving a high SPP and low TTTE, by minimizing mass transfer through **4. Summary and Conclusions**  In this study, it has been found that a fabric system with a low total transmitted thermal energy (TTTE) generally possesses high steam protective performance (SPP). The SPP/TTTE are mainly dependent upon the constructional attributes and physical properties of fabric systems. Usually, multilayered fabric systems comprising a moisture barrier are highly thermally insulated due to higher amounts of dead air trapped in their structures, and they can store steam in the empty spaces present among their constituent layers. Consequently, multilayered fabric systems have a high SPP and a low TTTE. It can also be concluded from this study that moisture barriers present in fabric structures play a crucial role in achieving a high SPP and low TTTE, by minimizing mass transfer through In this study, it has been found that a fabric system with a low total transmitted thermal energy (TTTE) generally possesses high steam protective performance (SPP). The SPP/TTTE are mainly dependent upon the constructional attributes and physical properties of fabric systems. Usually, multilayered fabric systems comprising a moisture barrier are highly thermally insulated due to higher amounts of dead air trapped in their structures, and they can store steam in the empty spaces present among their constituent layers. Consequently, multilayered fabric systems have a high SPP and a low TTTE. It can also be concluded from this study that moisture barriers present in fabric structures play a crucial role in achieving a high SPP and low TTTE, by minimizing mass transfer through fabric systems toward the bodies of wearers. Altogether, it can be suggested that designing a thermal protective fabric system comprising a moisture barrier and considerable empty space may be useful to provide adequate protection against steam.

Furthermore, it was found that intimate contact occurs between fabric systems and the bodies of wearers in high-pressurized steam exposure; as a result, conductive thermal energy transfers through fabric systems toward the bodies of wearers. In this case, a thick, weighty, and thermally resistive fabric system can reduce the conductive thermal energy transfer, lower the TTTE, and enhance the SPP. Along with the physical properties of fabrics (e.g., weight and thickness), thermal properties (thermal conductivity, specific heat, and density) also contribute equally to the TTTE/SPP. Sometimes, thermophysical properties (e.g., weight, thickness, thermal conductivity, specific heat, and density) of fabric systems may change due to the compression exerted on them by high-pressurized steam; this situation can lower the SPP. Thus, it is expected that anticompression-based fabric systems could provide better protection from steam by achieving a high SPP. Furthermore, it can be concluded that the air permeability of a fabric is the most important property that affects the SPP/TTTE. As fabric is a porous medium comprising both solid fibers and gaseous air phases, a highly air-permeable fabric can transfer steam quickly in its air phase, resulting in a lower SPP. Generally, an air-impermeable fabric system can be used effectively to achieve a high SPP or a low TTTE. In the case of multilayered, impermeable fabric systems, it is suggested to place a moisture barrier in their outer layers. This configuration can effectively reduce the overall air permeability of these fabric systems; eventually, their mass transfer may decline and result in a lower TTTE and a higher SPP.

Overall, the findings obtained from this study can be useful for textile/material engineers to develop high performance thermal protective fabrics that increase the occupational health and safety of firefighters and industrial workers. This study can be further extended by analyzing the heat flux profile through fabric systems in the steam exposure of a certain duration.

**Author Contributions:** S.M., conceptualization, designing and performing experiments, writing, and data analysis; G.S., conceptualization. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the University of Alberta, Canada, by an Izaak Walton Killam Memorial Scholarship to Sumit Mandal and Oklahoma State University, USA, by a start-up grant to Sumit Mandal.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors appreciate technical support from Mark Ackerman (Adjunct Professor, Department of Mechanical Engineering, University of Alberta, Canada) and Stephen Paskaluk (Research Engineer, Department of Human Ecology, University of Alberta, Canada).

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

