effect of thermal barrier on thermal protective performance of firefighter garments

Journal of Fiber Bioengineering & Informatics 4:3 (2011) 245252http://www.jfbi.org | doi:10.3993/jfbi09201104

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,aDepartment of Fiber System Engineering, Dankook Univerisity, Yongin, 448-701, Korea

bSchool of Electronics & Electrical engineering, Dankook Univerisity, Yongin, 448-701, Korea

Abstract

For firefighter protective clothing, thermal protective performance is of primary importance. In thisregard, 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 wereprepared from 100% meta-aramid, 100% wool, and 90% meta-aramid/10% para-aramid fibers. Theeffect of the number of layers in multilayer thermal barriers prepared from these nonwovens and theeffect of spacers on the thermal protective performance were examined. The possibility of incorporationof aerogels into the thermal barrier to enhance the protective performance was examined. The needlepunched nonwovens were padded with 5 wt% aerogels dispersion in acetone. The differences in thermalprotective performance of nonwovens were evaluated by heat transmission on exposure to flame, heattransmission on exposure to radiant heat and heat transmission on exposure to both flame and radiantheat methods. Multi layer constructions with spacers and nonwovens treated with aerogels exhibitedhigher 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 frommany toxic substances in the ambient air, high radiant heat intensities and hot flames are commonrisks in fire extinguishing work. Firefighters turnout equipment is designed to protect againstenvironmental hazards. Especially for firefighter protective clothing, the thermal protective per-formance is of great importance to the lives of firefighters. Thermal protective performance is animportant factor in the firefighters protective clothing development. The firefighters protectiveclothing must resist heat, flames and hot substances and international standards are available fortesting such properties [1-2].

Corresponding author.Email address: [email protected] (Kee Jong Yoon).

19408676 / Copyright 2011 Binary Information Press & Textile Bioengineering and Informatics SocietySeptember 2011

246 L. Jin et al. / Journal of Fiber Bioengineering & Informatics 4:3 (2011) 245252

Generally, firefighter protective clothing was composed of 3 layers such as outer shell, middlelayer and inner layer or 2 layers such as outer shell and inner layer with a combination of amoisture barrier and a thermal barrier.

The outer layer prevents body skin from the exposure of heat radiation or flame and middlelayer provides both the performance of waterproof and heat insulation. Usually, the aramid fibersare used as the layer of insulation and PTFE membrane is used as the breathable waterproofinglayer.

As the thermal insulation is a layer of insulating material to retard heat flow through thegarment, it is very important to develop this.

Shin et al. [3] examined heat protective perfor mances of firefighters protective clothing andheat-resistant clothing circulated in the domestic setting. Song et al. [5] studied the effects of airlayers in the firefighters protective clothing on the heat protective performances under the flashfire.

Zhu et al. [6] investigated into firefighter protective clothing made of different material com-binations, based on the demand for radiant protective perfor mance and heat-moisture transferproperties, which are closely associated with comfort performance.

In this study, we aim to apply a new type of thermal layer with increasing thermal protectiveperformance to firefighters 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 ambientpressure, which leaves the original gel structure virtually intact. Aerogel has an extremely fineand highly porous structure, composed of individual features only a few nanometers in size. Bymass, it is 99.8% air, making it the least dense man-made substance. Aerogels with very higherinsulation are widely applied in construction, aerospace, defense and clothing [4].

In this paper, we studied the thermal protective performance of nonwovens treated with aerogeland used with spacers. Heat transmission on exposure to flame, heat transmission on exposureto radiant heat, and heat transmission on exposure to both flame and radiant heat methods wereused to measure the thermal protective performance of nonwovens treated with aerogels and usedwith spacers.

Finally we manufactured a firefighters protective clothing by using aerogel composite material,and the flash fire mannequin test method (ISO 13506) was used to measure the thermal protectiveperformance.

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 Alsoprepared the thermal layer at different thicknesses and assemblies.

D50 nanogels with particle size 711um, specific surface area 600800 m2/g and density 3045kg/m3 were purchased from Cabot Co. (Germ.) The details of the fabrics are illustrated inTable 1.

L. Jin et al. / Journal of Fiber Bioengineering & Informatics 4:3 (2011) 245252 247

Table 1: The characteristics of samples

Sample code Type of fiber Thickness (mm) GSM (g/m2)

SC 100% meta-Aramid 1.0 138.5

M1 100% meta-Aramid 2.9 108.2

M2 100% meta-Aramid 1.3 99.0

M3 100% meta-Aramid 1.2 88.8

W 100% Wool 3.5 140.8

M/P 90%meta/10%para 1.4 137.0

w1 100% Wool 1.3 81.0

w2 100% Wool 1.6 105.0

w3 100% Wool 2.0 107.5

w4 100% Wool 2.6 156.1

m1 100% meta-Aramid 1.1 91.2

m2 100% meta-Aramid 2.0 109.4

m3 100% meta-Aramid 3.0 137.0

s spacer 1.3 81.5

SC(SanCheong): Commercial material

2.2 Aerogels Treatment

The needle punched nonwovens were padded with 5 wt% aerogel dispersion in acetone. Afterdrying for 12 hours at room temperature, nonwovens treated with aerogels were dried undervacuum for 12 hours at 60 in oven. Both sides of samples were laminated by PTFE membranebecause of nonwovens treated with aerogel produced dust.

2.3 Test Method

The differences of thermal protective performance of nonwovens were evaluated by heat transmis-sion 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


dancy of samples was measure by LOI test. Three-layer assemblies of fabrics, namely, the outerlayer, 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 nonwovenstreated with aerogels and used with spacers. Finally we manufactured the firefighters protectiveclothing by using one of aerogel composite materials considering the thickness and weight, andthe flash fire mannequin testing method (ISO 13506) was used to measure the thermal protec-tive performance [8-11]. Fig. 1 is an image of flash fire mannequin testing system in dankookuniversity.

3 Result and Discussion

3.1 Thermal Protective Performance

In this study, we selected M1 sample to investigate the thermal protective performance by varyingthe 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 exposureto radiant heat and heat transmission on exposure to both flame and radiant heat methods. Thedata 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 (HTI24) ISO 17492 (HTI24) ISO 9151 (HTI24)

M1 0 0 17.2 23.3 16.0

M1 a 7.5 18.9 24.3 16.2

M1 b 35.0 20.2 25.4 16.7

M1 c 68.2 21.0 28.9 17.4

M2 32.6 17.3 25.2 13.7

M3 50.7 19.1 30.1 15.7

W 26.8 18.9 22.4 16.1

M/P 42.1 19.2 22.9 14.8

To investigate the thermal protective performance by changing the thickness of samples treatedwith aerogel, the M1, M2, M3 were prepared and then impregnated in an aqueous bath containingaerogel and padded through squeeze rollers. And the HTI value was measured by heat transmis-sion on exposure to flame, heat transmission on exposure to radiant heat, heat transmission onexposure to both flame and radiant heat methods.

From the results, M1 b presented higher HTI values than M2. It seemed that the thicknessof sample affects the thermal protective performance. The thicker samples exhibit the higherthermal protective performance. The thickness is a principal factor in thermal protective perfor-mance. However, the samples thickness is over a certain level (3 mm), and the thermal protectiveperformance could be reduced due to the convection [5]. As can be seen from Fig. 2, the HTIvalues of the flame transmission was higher as the thickness increased. The HTI24 values betweenthe thermal barriers with spacers and without were only 15% different. It seemed that thethermal barrier prevented flame transmission because spacers made air layers to insulate whilemaintaining the thickness.


Sample

SC m1 w2 m2 w3 m3 m4 m1/m1

m1/w1

HT

I 24

(sec

)

0

5

10

15

20

25

30

35Without spacerWith spacer

Fig. 2: Value of the HIT24 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 propertywere higher.

In the multi thermal barrier with 2 spacers, the HTI values of the m1/w1 were higher thanones 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 factorsaffecting heat transfer through multiple layers.

3.2 Flame Retardancy

To investigate the effect of the amounts of aerogel on the flame retardancy, the samples weretreated 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 theuntreated sample. It relates that the inorganic aerogel particles which attaches on the surface

Aerogel add-on (%)

0 20 40 60 80

LO

I (%

)

26

28

30

32

Fig. 3: LOI of meta-aramid needle punched non woven impregnated with different amounts of aerogel


of the samples could increase the flame retardant property. However, when the concentration ofaerogle 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 importantstep in the design of clothing for hazardous environments. In this paper, an automated systemfor testing the garments under flash fire is presented. [7] The system uses a size 40 regularmannequin made from a flame resistant polyester resin reinforced with fiberglass. The mannequinis suspended from the ceiling of an 5 5 m fire-resistant burn chamber and surrounded by twelveindustrial burners capable of producing a large volume, with simulated flash fire capable of fullyengulfing the mannequin in flames. The mannequin is instrumented with 110 individual sensorsdistributed over the surface of the body. In addition to measuring the heat transfer of themannequin with exposure of the test garment or protective clothing ensemble, these sensors alsoset the exposure level by directly exposing the mannequin to the flames in a test without thegarment. The test specimen is placed on the mannequin at ambient atmospheric conditions andexposed 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 calculatethe changing temperature of human tissue at two skin depths, one representing a second degreeburn injury point and the other a third degree burn injury point. A computer system controlsdata acquisition, calculation of surface heat flux, calculates the skin temperature distributionhistories, and predicts the skin burn damage for each sensor location. The computer produces afull 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 comparedit to the summary of second degree burn of both garments using the thermal barrier treatedwith aerogels and without. As can be seen from Figs. 4 and 5, the summary of second degreeof 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 thermalprotective 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/m2, 8 secondexposure)


heat resistant garment. Fig. 6 shows the aerogel garments before and after flash fire mannequintest. 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/m2, 8 secondexposure)

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 andmultilayer thermal barriers with or without spacers were studied to enhance the thermal protectiveperformance of flame resistant garment. The thermal protective performance was measured byheat transmission on exposure to flame, heat transmission on exposure to radiant heat and heattransmission on exposure to both flame and radiant heat methods. We found that the HTIvalues increased with increasing amount of aerogel. For similar thicknesses, the values HTI ofmulti-layered thermal barrier with spacer are higher than those without spacers. This is becausethe spacers increase the total thickness of the constructions and the amount of air. The garmentusing the thermal layer treated with aerogel exhibited higher thermal protective performance thancommercial firefighters garment. The multilayer constructions and the incorporation of aerogelshave significantly enhanced the thermal protective performance.


References

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[4] Soleimani Dorcheh., M. H. Abbasi, Silica aerogel; synthesis, properties and characterizationjournal of materials processing technology, 2008, 199, 10-26

[5] Guowen Song, Clothing Air Gap Layers and Thermal Protective Performance in Single LayerGarment, JOURNAL OF INDUSTRIAL TEXTILES, Vol. 36, No. 3, 193-205

[6] Zhu Fanglong, Zhang Weiyuan, Chen Minzhi, Investigation of Material Combinations for Fire-fighters Protective Clothing on Radiant Protective and Heat-Moisture Transfer PerformanceFIBRES & TEXTILES , 2007, Vol. 15, No. 1 (60), 72-75

[7] D. Juricic, B. Musizza, Evaluation of fire protective garments by using instrumented mannequinand model-based estimation of burn injuries IEEE, 2007

[8] Protective clothing-Protection against heat and fire-Method of test: Evaluation of materials andmaterial 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 exprosureto both flame and radiant heat, ISO17492, 2003

[10] Protective clothing against heat and flame-determination of heat transmission on exposure toflame ISO 9151, 2007

[11] Protective clothing against heat and flame-Test method for complete garments-Prediction of burninjury using an instrumented manikin, ISO13506, 2008

effect of thermal barrier on thermal protective performance of firefighter garments

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