Effect of Thermal Barrier on Thermal Protective Performance of Firefighter Garments

Transcription

1 Journal of Fiber Bioengineering & Informatics 4:3 (2011) doi: /jfbi Effect of Thermal Barrier on Thermal Protective Performance of Firefighter Garments Lu Jin a, Kyoung-A Hong a, Hyun Do Nam b, Kee Jong Yoon a, a Department of Fiber System Engineering, Dankook Univerisity, Yongin, , Korea b School of Electronics & Electrical engineering, Dankook Univerisity, Yongin, , Korea Abstract For firefighter protective clothing, thermal protective performance is of primary importance. In this regard, the effects of thermal barrier construction on the level of thermal protection were investigated. In this study, needle punched nonwovens of varying thicknesses for application as thermal barrier were prepared from 100% meta-aramid, 100% wool, and 90% meta-aramid/10% para-aramid fibers. The effect of the number of layers in multilayer thermal barriers prepared from these nonwovens and the effect of spacers on the thermal protective performance were examined. The possibility of incorporation of aerogels into the thermal barrier to enhance the protective performance was examined. The needle punched nonwovens were padded with 5 wt% aerogels dispersion in acetone. The differences in thermal protective performance of nonwovens were evaluated by heat transmission on exposure to flame, heat transmission on exposure to radiant heat and heat transmission on exposure to both flame and radiant heat methods. Multi layer constructions with spacers and nonwovens treated with aerogels exhibited higher thermal protective performance. Keywords: Aerogels; Thermal Protective Performance; Firefighter Clothing; Flash Fire Mannequin; Multi-thermal Barrier 1 Introduction Firefighters are exposed to many hazards associated with their work environment. Apart from many toxic substances in the ambient air, high radiant heat intensities and hot flames are common risks in fire extinguishing work. Firefighter s turnout equipment is designed to protect against environmental hazards. Especially for firefighter protective clothing, the thermal protective performance is of great importance to the lives of firefighters. Thermal protective performance is an important factor in the firefighter s protective clothing development. The firefighter s protective clothing must resist heat, flames and hot substances and international standards are available for testing such properties [1-2]. Corresponding author. address: [email protected] (Kee Jong Yoon) / Copyright 2011 Binary Information Press & Textile Bioengineering and Informatics Society September 2011

2 246 L. Jin et al. / Journal of Fiber Bioengineering & Informatics 4:3 (2011) Generally, firefighter protective clothing was composed of 3 layers such as outer shell, middle layer and inner layer or 2 layers such as outer shell and inner layer with a combination of a moisture barrier and a thermal barrier. The outer layer prevents body skin from the exposure of heat radiation or flame and middle layer provides both the performance of waterproof and heat insulation. Usually, the aramid fibers are used as the layer of insulation and PTFE membrane is used as the breathable waterproofing layer. As the thermal insulation is a layer of insulating material to retard heat flow through the garment, it is very important to develop this. Shin et al. [3] examined heat protective perfor mances of firefighter s protective clothing and heat-resistant clothing circulated in the domestic setting. Song et al. [5] studied the effects of air layers in the firefighter s protective clothing on the heat protective performances under the flash fire. Zhu et al. [6] investigated into firefighter protective clothing made of different material combinations, based on the demand for radiant protective perfor mance and heat-moisture transfer properties, which are closely associated with comfort performance. In this study, we aim to apply a new type of thermal layer with increasing thermal protective performance to firefighter s protective clothing. Aerogel represents what technology experts consider the best insulation material ever invented. Aerogels are synthesized using sol-gel processing followed by supercritical drying or ambient pressure, which leaves the original gel structure virtually intact. Aerogel has an extremely fine and highly porous structure, composed of individual features only a few nanometers in size. By mass, it is 99.8% air, making it the least dense man-made substance. Aerogels with very higher insulation are widely applied in construction, aerospace, defense and clothing [4]. In this paper, we studied the thermal protective performance of nonwovens treated with aerogel and used with spacers. Heat transmission on exposure to flame, heat transmission on exposure to radiant heat, and heat transmission on exposure to both flame and radiant heat methods were used to measure the thermal protective performance of nonwovens treated with aerogels and used with spacers. Finally we manufactured a firefighter s protective clothing by using aerogel composite material, and the flash fire mannequin test method (ISO 13506) was used to measure the thermal protective performance. 2 Experimental 2.1 Sample Needle punched nonwovens composed of 100% meta-aramid fibers, 100% wool fibers and 90% meta-aramid/10% para-aramid fibers changing thickness and area mass are compared. We Also prepared the thermal layer at different thicknesses and assemblies. D50 nanogels with particle size 7 11um, specific surface area m 2 /g and density kg/m 3 were purchased from Cabot Co. (Germ.) The details of the fabrics are illustrated in Table 1.

3 L. Jin et al. / Journal of Fiber Bioengineering & Informatics 4:3 (2011) Table 1: The characteristics of samples Sample code Type of fiber Thickness (mm) GSM (g/m 2 ) SC 100% meta-aramid M1 100% meta-aramid M2 100% meta-aramid M3 100% meta-aramid W 100% Wool M/P 90%meta/10%para w1 100% Wool w2 100% Wool w3 100% Wool w4 100% Wool m1 100% meta-aramid m2 100% meta-aramid m3 100% meta-aramid s spacer SC(SanCheong): Commercial material 2.2 Aerogels Treatment The needle punched nonwovens were padded with 5 wt% aerogel dispersion in acetone. After drying for 12 hours at room temperature, nonwovens treated with aerogels were dried under vacuum for 12 hours at 60 in oven. Both sides of samples were laminated by PTFE membrane because of nonwovens treated with aerogel produced dust. 2.3 Test Method The differences of thermal protective performance of nonwovens were evaluated by heat transmission on exposure to flame (ISO9151), heat transmission on exposure to radiant heat (ISO6942), heat transmission on exposure to both flame and radiant heat (ISO17492) methods. Flame retar- Fig. 1: Flash fire mannequin testing system

4 248 L. Jin et al. / Journal of Fiber Bioengineering & Informatics 4:3 (2011) dancy of samples was measure by LOI test. Three-layer assemblies of fabrics, namely, the outer layer, thermal layer and inner layer, were tested. The outer layer and inner layer were 100% meta-aramid fabrics (Sancheong Co.) and the thermal layers were used with various nonwovens treated with aerogels and used with spacers. Finally we manufactured the firefighter s protective clothing by using one of aerogel composite materials considering the thickness and weight, and the flash fire mannequin testing method (ISO 13506) was used to measure the thermal protective performance [8-11]. Fig. 1 is an image of flash fire mannequin testing system in dankook university. 3 Result and Discussion 3.1 Thermal Protective Performance In this study, we selected M1 sample to investigate the thermal protective performance by varying the amount of aerogels 0, 7.5wt%, 35.0wt% and 68.2wt%. Then the HTI(heat transmission index) values were measured by heat transmission on exposure to flame, heat transmission on exposure to radiant heat and heat transmission on exposure to both flame and radiant heat methods. The data is illustrated in Table 2. Table 2: The values of the HTI of needle-punched nonwoven after aerogel treated Sample code Aerogel add-on (%) ISO 6942 (HTI 24 ) ISO (HTI 24 ) ISO 9151 (HTI 24 ) M M1 a M1 b M1 c M M W M/P To investigate the thermal protective performance by changing the thickness of samples treated with aerogel, the M1, M2, M3 were prepared and then impregnated in an aqueous bath containing aerogel and padded through squeeze rollers. And the HTI value was measured by heat transmission on exposure to flame, heat transmission on exposure to radiant heat, heat transmission on exposure to both flame and radiant heat methods. From the results, M1 b presented higher HTI values than M2. It seemed that the thickness of sample affects the thermal protective performance. The thicker samples exhibit the higher thermal protective performance. The thickness is a principal factor in thermal protective performance. However, the sample s thickness is over a certain level (3 mm), and the thermal protective performance could be reduced due to the convection [5]. As can be seen from Fig. 2, the HTI values of the flame transmission was higher as the thickness increased. The HTI 24 values between the thermal barriers with spacers and without were only 1 5% different. It seemed that the thermal barrier prevented flame transmission because spacers made air layers to insulate while maintaining the thickness.

5 L. Jin et al. / Journal of Fiber Bioengineering & Informatics 4:3 (2011) Without spacer With spacer 25 HTI 24 (sec) SC m1 w2 m2 w3 m3 m4 m1/ m1 Sample m1/ w1 Fig. 2: Value of the HIT 24 of multi-thermal barrier with and without spacers For m1 and w2 with 1 spacer, the HTI values of the thicker w2 were higher than ones of m1. This is because w2 contained much air. For the same thickness (m2 and w3), the HTI values of m2 with great heat resistant property were higher. In the multi thermal barrier with 2 spacers, the HTI values of the m1/w1 were higher than ones of m1/m1. It was considered that m1/w1 contained much more air as the weight per unit area was lower. It seemed that air in the spacers of multi-layered thermal barrier is one of the major factors affecting heat transfer through multiple layers. 3.2 Flame Retardancy To investigate the effect of the amounts of aerogel on the flame retardancy, the samples were treated with the different concentrations of aerogel prepared and were measured by the LOI test. As can be seen from Fig. 3, the sample treated with aerogel had higher LOI values than the untreated sample. It relates that the inorganic aerogel particles which attaches on the surface 32 LOI (%) Aerogel add-on (%) Fig. 3: LOI of meta-aramid needle punched non woven impregnated with different amounts of aerogel

6 250 L. Jin et al. / Journal of Fiber Bioengineering & Informatics 4:3 (2011) of the samples could increase the flame retardant property. However, when the concentration of aerogle is over 7.5 wt%, there is no significant change in the sample treated with aerogels. 3.3 Flash Fire Mannequin Test Quantitative evaluation of thermal protective garments to fire exposure represents an important step in the design of clothing for hazardous environments. In this paper, an automated system for testing the garments under flash fire is presented. [7] The system uses a size 40 regular mannequin made from a flame resistant polyester resin reinforced with fiberglass. The mannequin is suspended from the ceiling of an 5 5 m fire-resistant burn chamber and surrounded by twelve industrial burners capable of producing a large volume, with simulated flash fire capable of fully engulfing the mannequin in flames. The mannequin is instrumented with 110 individual sensors distributed over the surface of the body. In addition to measuring the heat transfer of the mannequin with exposure of the test garment or protective clothing ensemble, these sensors also set the exposure level by directly exposing the mannequin to the flames in a test without the garment. The test specimen is placed on the mannequin at ambient atmospheric conditions and exposed to the flash fire simulation with controlled heat flux, duration, and flame distribution. The incident heat flux measured by the sensors, during and after exposure, is used to calculate the changing temperature of human tissue at two skin depths, one representing a second degree burn injury point and the other a third degree burn injury point. A computer system controls data acquisition, calculation of surface heat flux, calculates the skin temperature distribution histories, and predicts the skin burn damage for each sensor location. The computer produces a full report of the test including a contour mapping of burn locations. We manufactured firefighter garment using the thermal barrier treated with aerogel (sample M1, aerogel add-on 27 wt%). In order to evaluate the thermal protective performance, we compared it to the summary of second degree burn of both garments using the thermal barrier treated with aerogels and without. As can be seen from Figs. 4 and 5, the summary of second degree of the aerogel garment is 5.55%. This value is lower than commercial garments (Sanchoeng Co). Therefore, the garment using the thermal barrier treated with aerogels exhibited higher thermal protective performance than commercial garment and there is great potential to use it as flame or Fig. 4: Calculated location of skin burning on mannequin (Commercial garment, 84 kw/m 2, 8 second exposure)

7 L. Jin et al. / Journal of Fiber Bioengineering & Informatics 4:3 (2011) heat resistant garment. Fig. 6 shows the aerogel garments before and after flash fire mannequin test. Although the outer layer of garment made by meta-aramid fabric is destroyed extensively, the thermal barrier exhibits no damage. Fig. 5: Calculated location of skin burning on mannequin (Aerogel treated garment, 84 kw/m 2, 8 second exposure) Fig. 6: Images of aerogel garment before and after flash fire mannequin test 4 Conclusion Different thermal barriers were studied in this work. Thermal barriers employing aerogels and multilayer thermal barriers with or without spacers were studied to enhance the thermal protective performance of flame resistant garment. The thermal protective performance was measured by heat transmission on exposure to flame, heat transmission on exposure to radiant heat and heat transmission on exposure to both flame and radiant heat methods. We found that the HTI values increased with increasing amount of aerogel. For similar thicknesses, the values HTI of multi-layered thermal barrier with spacer are higher than those without spacers. This is because the spacers increase the total thickness of the constructions and the amount of air. The garment using the thermal layer treated with aerogel exhibited higher thermal protective performance than commercial firefighter s garment. The multilayer constructions and the incorporation of aerogels have significantly enhanced the thermal protective performance.

8 252 L. Jin et al. / Journal of Fiber Bioengineering & Informatics 4:3 (2011) References [1] Holmer, P., Protective clothing and heat stress, Ergonomics, 1995, 38(1), [2] Baitinger, W. F., Product engineering of safety apparel fabrics: insulation characteristics of fireretardant cottons, Textile res. J., 1979, 49(4), 221 [3] Dong Seung Shin, Youn-Hee Jeon, Seung-Kook An and Eui-so Lee Evaluation for Thermal Protecctive Performance of Protective Clothing Textile Science and Engineering, 2006, Vol. 43. No 1 [4] Soleimani Dorcheh., M. H. Abbasi, Silica aerogel; synthesis, properties and characterization journal of materials processing technology, 2008, 199, [5] Guowen Song, Clothing Air Gap Layers and Thermal Protective Performance in Single Layer Garment, JOURNAL OF INDUSTRIAL TEXTILES, Vol. 36, No. 3, [6] Zhu Fanglong, Zhang Weiyuan, Chen Minzhi, Investigation of Material Combinations for Firefighter s Protective Clothing on Radiant Protective and Heat-Moisture Transfer Performance FIBRES & TEXTILES, 2007, Vol. 15, No. 1 (60), [7] D. Juricic, B. Musizza, Evaluation of fire protective garments by using instrumented mannequin and model-based estimation of burn injuries IEEE, 2007 [8] Protective clothing-protection against heat and fire-method of test: Evaluation of materials and material assemblies when exposed to a source of radiant heat, ISO 6942, 2002, Third edition [9] Clothing for protection against heat and flame-determination of heat transmission on exprosure to both flame and radiant heat, ISO17492, 2003 [10] Protective clothing against heat and flame-determination of heat transmission on exposure to flame ISO 9151, 2007 [11] Protective clothing against heat and flame-test method for complete garments-prediction of burn injury using an instrumented manikin, ISO13506, 2008