**1. Introduction**

Firefighters and industrial workers often incur burn injuries when they encounter hazardous thermal exposures while performing their job duties [1–3]. Contextually, it has been identified that water used by firefighters to put out a fire may convert into steam, which may reach the firefighters [4–8]. Additionally, upstream oil and gas industry workers are often exposed to steam while extracting bitumen from oil sands and producing heavy oil [9,10]. As the performance of thermal protective clothing worn by firefighters and industrial workers depends upon the various thermal exposures these workers face in their occupations [11–17], it can be inferred that steam has a significant impact on the thermal protective performance of clothing [4–8]. In steam exposure, a significant amount of thermal energy transfer occurs through clothing, which causes burns to workers in these occupations.

In considering thermal protection and steam exposure, many researchers studied the SPP of fabric materials used in thermal protective clothing [4–8,18–21]. Keiser et al. (2008), Keiser and Rossi (2008), Keiser et al. (2010), Mandal et al. (2013), and Shoda et al. (1998) suggested that imposed high-pressurized steam enters into the fabric structure and gradually condenses [4–8]. After the condensation phase, the steam converts into hot water. This hot water generates burn injuries when it comes into contact with the human body. These researchers identified that a permeable fabric allows more steam transfer toward wearers than an impermeable fabric. As a result, they suggested that thermal protective fabrics should be steam impermeable in nature to provide effective protection from steam exposure. Mandal et al. (2013) further found that the air permeability of the outer layer (shell fabric) is crucial for the SPP of a multilayered thermal protective fabric system (i.e., an assembly of shell fabric, moisture barrier, and/or thermal liner) [7]. They recommended that it

**Citation:** Mandal, S.; Song, G. Characterizing Steam Penetration through Thermal Protective Fabric Materials. *Textiles* **2022**, *2*, 16–28. https://doi.org/10.3390/ textiles2010002

Academic Editor: Laurent Dufossé

Received: 23 November 2021 Accepted: 26 December 2021 Published: 3 January 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

is essential to place a moisture barrier with zero air permeability in the outer layer of multilayered fabric systems in order to achieve a high SPP. This air-impermeable moisture barrier will immediately stop the steam penetration through the fabric system, which will considerably decrease the chances of burns on the bodies of wearers [7,18–24]. Along with air permeability, Desruelle et al. (2002) indicated that the thickness of the fabric systems has a considerable impact on its steam protective performance [25]. Recently, Su et al. (2018) found that fabric thickness insignificantly improves the steam protective performance in comparison to the air permeability of the fabrics [26].

Although previous researchers extensively studied steam penetration through fabrics by evaluating the SPP, only a few studies focused considerably on the TTTE through fabrics in steam exposure of a certain duration [4–10,18–26]. This paper studied experimentally both the SPP and TTTE and identified fabric features affecting both. The SPP is also compared with the flame and radiant heat protective performance of fabrics. Steam penetration through fabric systems was studied based on the theory of heat and mass transfer. This paper will contribute to understanding the mechanisms associated with the heat and mass transfer in fabric systems, and the results obtained could help textile/material engineers to develop fabrics for high performance thermal protective clothing.

#### **2. Materials and Methods**

In this study, multiple thermal protective fabrics (A–F) were selected for testing (Table 1). These fabrics are commercially available and commonly used in the clothing of firefighters and industrial workers. These fabrics were assembled to produce multilayered fabric systems; these configured fabric systems were A (Fabric-A), B (Fabric-B), AC (Fabric-A + Fabric-C), AE (Fabric-A + Fabric-E), AF (Fabric-A + Fabric-F), FA (Fabric-F + Fabric-A), AFC (Fabric-A + Fabric-F + Fabric-C), AFD (Fabric-A + Fabric-F + Fabric-D), AFE (Fabric-A + Fabric-F + Fabric-E), and FAD (Fabric-F + Fabric-A + Fabric-D). The constructional attributes and physical properties of these fabric systems were measured using the American Society for Testing and Materials (ASTM) standards (Table 2) [27–30]. In this context, it is notable that porosity (the ratio of pore volume to the total volume of the fabrics depending upon the open and closed porosity) is an important fabric property that could affect the steam penetration through fabrics. However, it is difficult to accurately characterize the pore volume because the pore system within a fabric typically forms a very complicated pore surface that is geometrically irregular; in fact, it is also not accurate to define the pore size in terms of the diameter considering the different structures of pores existing in the fabric [31–33]. Considering this situation, although porosity and air permeability are not the same thing, air permeability is measured as an indirect measurement of porosity and is used for explaining the SPP.

Three specimens (200 mm × 200 mm) of each fabric system were conditioned in a standard atmosphere (21 ◦C temp. and 65% relative humidity) for 24 h. To understand the steam penetration parameters of the fabric systems, these specimens were tested under steam exposure using the instrument shown in Figure 1. In this test, a specimen of the fabric system was placed on a Teflon-plated specimen holder embedded with a skin simulant sensor. Steam was generated at 150 ◦C using a 3 kW boiler, and the steam generated was administered at 200 kPa from 50 mm above the specimen through a 4.6 mm nozzle. The skin simulant sensor was used to measure the heat flux, and this heat flux was applied using burn prediction software (programmed according to Henrique's Burn Integral algorithm) to calculate the time required to generate second-degree skin burns [34]. The skin simulant sensor was developed by the University of Alberta in Canada using inorganic material called 'colorceron', which is a mixture of calcium, aluminum, silicate, asbestos fibers, and a binder; and this sensor was calibrated using the standardized Schmidt–Boelter watercooled sensor [34]. The predicted mean burn time obtained from the three specimens was interpreted as the SPP of the fabric system. The TTTE of the fabric system specimen during (30 s) and after (10 s) of steam exposure was also measured. Subsequently, the fabric properties, SPP, and TTTE values were normalized statistically, and a *t*-test was carried

out using STATCRUNCH software (developed by West of Texas A&M University, USA). The association among the fabric properties, SPP and/or TTTE was inferred based on the sign (+ or −) of the T-stat value obtained from the *t*-test. *p*-values obtained from the *t*-test for all fabric properties were also analyzed. If the *p*-value for any property was less than 0.05, this property was identified as the key property affecting the SPP/TTTE. Relationship plots were developed among the fabric properties, SPP, and/or TTTE; and the coefficient of determination (R<sup>2</sup> ) of the plots developed was calculated. A R<sup>2</sup> value with proximity to 1 was inferred as a strong association among the fabric properties, SPP, and/or TTTE. Inference tests (hypothesis test (*p*-value) and a 95% confidence interval (upper and lower limits)) were carried out to understand the differences in the SPP/TTTE of various sets of fabric systems.

#### **Table 1.** Thermal protective fabrics.


<sup>a</sup> Measured by the ASTM D 1777: 1996; <sup>b</sup> Measured by the ASTM D 3776: 2009 [27,28].

**Table 2.** Assembled fabric systems.


<sup>a</sup> Measured by the ASTM D 1777; <sup>b</sup> Measured by the ASTM D 1518: 2011; <sup>c</sup> Measured by the ASTM D 737: 2004 [27,29,30].

**Figure 1.** Steam exposure test.

**Steam Penetration Parameters** 

**SPP (Second-degree** 

**SPP/Thickness (Second-degree Burn Time in Seconds/mm)** 

#### **3. Results and Discussion**

The parameters for steam penetration (SPP and TTTE) through the selected fabric systems (obtained from the steam exposure test) are shown in Table 3. The SPP per unit thickness of each fabric system is also calculated and presented in Table 3. Based on the data shown in Table 3, a relationship plot between the SPP and TTTE is displayed in Figure 2. According to Figure 2, the trend line of the plot is negative, and the R<sup>2</sup> value is close to 1; hence, a strong negative relationship exists between the SPP and TTTE. From this, it can be inferred that the TTTE through a fabric system is generally low if the fabric system possesses a high SPP. Mandal et al. (2013) previously evaluated the flame and radiant heat protective performance of the same set of fabric systems mentioned in Table 3, which firefighters often encounter in flame and radiant heat exposures [7]. A comparison of these previous results (Table 4) with the SPP values of Table 3 clearly shows that the protective performances of air-permeable fabric systems are significantly lower in steam exposure. This is because flame and radiant heat exposures mainly involve a heat transfer through the fabric systems toward the bodies of wearers [35]; however, in steam exposure, a hot mass transfer mainly occurs through fabric systems. As the mode of thermal energy transfer differs in these exposures, the performance of the fabric systems lowers under steam exposure. In the following section, the effect of fabric features on the SPP/TTTE is established to characterize the steam penetration through the fabric system. *Textiles* **2022**, *2*, FOR PEER REVIEW 5 **Table 3.** Steam penetration parameters of fabric systems. **Fabric Systems Single-Layered Double-Layered Triple-Layered A B AC AE AF FA AFC AFD AFE FAD Burn Time in Seconds)** 0.34 2.26 0.59 0.71 7.95 10.35 11.44 19.27 22.2 25.55 **TTTE (kJ/m2)** 610.6 526.5 581.3 533.9 416.3 216.2 375.5 249.6 240.2 221.2

0.74 3.37 0.38 0.18 5.10 6.63 4.33 5.31 4.33 7.04

**Table 3.** Steam penetration parameters of fabric systems.


**Figure 2.** Relationship plot between SPP and TTTE. **Figure 2.** Relationship plot between SPP and TTTE.

*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 in-

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 double-layered 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


**Table 4.** Flame and radiant heat protective performance of selected fabric systems [adapted from Mandal, et al. (2013)] [7].
