The heat related properties of protective clothing fabrics

Fire Safety Journal, 6 (1983) 129 - 141

The Heat Related Properties

129

of Protective

Clothing Fabrics*

B. V. HOLCOMBE

CSIRO Division o f Textile Physics, 338 Blaxland Road, Ryde, N.S.W. 2112 (Australia) (Received November 25, 1982; in revised form May 17, 1983)

INTRODUCTION

Wool and c o t t o n or rubberised c o t t o n tunics have been worn by firefighters all over the world since the inception of professional fire services. Most of the uniforms in use t o d a y have seen very little change in either material or design since they were originally introduced, and it is for this reason that many organisations representing firefighters would like to see some change. A number of synthetic fibres with claimed improvements in thermal stability has been introduced over the past 20 years. Some have been developed specifically for military or aerospace applications; however, the question of whether they are appropriate to civilian firefighting garments has n o t been clearly answered. There is ample evidence that the danger to firefighters from heat stress is far greater than that due to clothing flammability [1 - 3]. As well as protection afforded by the materials, factors such as cost, durability, appearance and c o m f o r t must be considered. An interesting summary of practical experiences with a range of t u r n o u t coat materials used by European fire services appeared in a recent issue of Fire [4]. It is clear from this article that no p r o d u c t as y e t introduced to supplant the earlier garments has received universal acceptance, despite the fact that almost all possible materials have been tried at one time or another by various organisations. There are no suitable International Standards specifically intended for a firefighter's t u r n o u t clothing; the only widely q u o t e d standard, the 'Protective clothing for *This paper is based upon a report presented to the N.S.W. Board of Fire Commissioners and the N.S.W. Fire Brigade Employees Union. 0379-7112/83/$3.00

structural firefighting', prepared b y the National Fire Prevention Association of the United States [5], has been criticised [6] on the grounds that it was drawn up to exclude fibres other than aramids. It has n o t received universal acceptance in the United States, largely as a result of the unnecessary stringency of its requirements, and is currently under review, particularly with respect to permitting the use of treated c o t t o n and wool fabrics which have proven more than adequate in the past. The heat exposure experienced by structural firefighters during fireground operations is generally infra-red radiation, or radiant heat. All objects (even cold ones) emit a certain a m o u n t of this radiation. The firefighter is only concerned with those sources which radiate enough heat to p u t his life at risk. These are generally such things as glowing e m b e r s , heated walls, smoke, and other objects close to the source of the fire. The flames themselves produce some radiant heat, as there is a c o m p o n e n t of infra-red radiation in the energy released during combustion. The intensity of the radiation at the fireground depends upon a great number of factors, including the area and height of the fire (or heated surfaces), its temperature, and the amount of smoke present. Figure 1 shows the results of an investigation of the intensity of fuel fires as a function of the size of the fire and the distance from it [7]. For any given situation, distance from the source is the critical factor as far as the firefighter is concerned. A table which shows the typical conditions of United States firegrounds appears in Fig. 2 [8]. This has been prepared from studies by t w o groups [9 - 11], and includes tolerance times to burn injury at various flux © Elsevier Sequoia/Printed in The Netherlands

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that the useful working time will be largely determined by the onset of pain in the hands or face, or, where these areas are covered by gloves and breathing apparatus, the limits set by heat transfer through the clothing. At the upper limit of the 'hazardous' category, that is, at fluxes in the region of 10 to 13 kW/m 2, the tolerance time of human skin to second degree burns is less than 10 seconds. The 'emergency' category, extending from the 'hazardous' level to 1 0 0 - 2 0 0 kW/m 2, corresponds to conditions which might be encountered within a flashover or explosion. Here the exposure is not just radiant heat, as some flames will also be present. Intense heat flux will normally only persist for one or two seconds [13, 14]. At 200 kW/m 2, the tolerance time to second degree burn is about 0.15 s; at 100 kW/m 2, 0.4 s. A firefighter caught in these conditions without special equipment would be forced to evacuate. Without breathing apparatus and complete protection, he would suffer lung damage and burns to exposed parts of the body. There would also be some superficial damage to his clothing, the extent and nature of the damage depending on the type of material involved.

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I 6 8 FROM FIRE (m)

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Fig. 1. The radiant intensity o f fuel fires as a f u n c t i o n o f fire size and distance.

levels derived from the work of Stoll and Chianta [ 12]. The 'routine' conditions are roughly equivalent to what might be experienced outdoors on a hot summer day, and apply to firefighters operating hoses or other appliances at some distance from the source. 'Hazardous' conditions might be expected during entry of burning rooms or close proximity to a fire, and it is in such situations 0-5 1.0 2.0 l'_ .... I .... [

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131

In an exposure of this type, the greatest danger is from toxic gases or bronchial damage due to the heated air. There are no known reports of instances where a firefighter died in the course of d u t y solely as the result of ignition and combustion of his protective clothing. Invariably where burn injury is one of the causes of death, the victim was either trapped first, collapsed from suffocation, or was caught in a spill of flammable solvent. In such circumstances, no clothing can protect the wearer indefinitely. The following describes a study in which a wide range of materials, which might be considered for use in firefighters' protective clothing, was evaluated in terms of the protection offered against the types of heat exposure normally present at the fireground. In addition, a number of these materials were tested when combined with several different underwear fabrics in order to investigate the behaviour of garment assemblies in the real clothing situation.

2. TEST M E T H O D S

All the materials were tested for a range of basic textile properties, and some other less c o m m o n features which are appropriate to an occupation such as fireflghting where there is exposure to various sources of heat. These are listed below. (1) Weight per unit area was determined from the average of three 100 cm 2 specimens. (2) Thickness was determined in accordance with AS 1587 [15], using a pressure of 6.9 pascals. This pressure is very light, and was deliberately chosen as it comes as close as allowed by the test apparatus to the conditions in the front of a protective garment where the outer shell of the clothing is in contact with a garment beneath and w i t h o u t compression of its external surfaces. (3) The resistance to the loss of dry heat from the body, as distinct from the loss associated with sweat secretion, was measured by the double plate m e t h o d of BS:4745 [16]. This m e t h o d is more appropriate for multilayer assemblies than the single plate method. (4) Resistance to intense radiant heat was determined by the m e t h o d of ISO 6942 [17]. This specifies a number of heat flux levels at which the test may be carried out,

and the flux is chosen in accordance with the requirements of the application. The heat source consists of six silicon carbide rods arranged parallel and close together and operating at a temperature of about 1100 °C. The heat flux is varied by moving the position of the source relative to the test specimen. The tests reported here were carried out at a radiant flux intensity of 20 kW/m 2, which is probably the upper limit of radiant heat exposure which the firefighter would encounter in fireground operations. At this flux level, bare skin suffers second degree burn damage in 3.7 s. Heat fluxes are measured by means of a small aluminium block calorimeter of known mass. The block is insulated on all sides except its face, which is radiused to ensure contact with the specimen, and the temperature rise is measured by an internally m o u n t e d platinum resistance probe. The fabric or fabric assembly is m o u n t e d across the front face of the calorimeter and exposed to the heat source at the required heat flux level for a time sufficient for the heat flow through the test material to become constant. Figure 3 shows a photograph of the apparatus. The ratio of the incident heat flux to t h a t

Fig. 3. ISO 6942 radiant h e a t e x p o s u r e test apparatus.

132

at the rear of the specimen, referred to as the transmission factor, is calculated from the experimental data. ISO 6942 also requires t hat a separate test be carried o u t in which a specimen of fabric is exposed to t he heat flux of the test for three minutes, to determine w he t he r any change occurs in specimen appearance. If such a change is detected, even if it be only a change in colour, the test result is followed by a 'C', and the nature of the change recorded. (5) Resistance to intense convective heat was determined by a test currently unde r consideration by TC94/SC13/WG2 of the International Organisation for Standardisation. The exposure in both the 'r out i ne ' and 'hazardous' situations is p r e d o m i n a n t l y radiant heat, and it is only in the case of a flame c o n t a c t th at any significant convective heat is likely to be involved. Convective heat in the fireground sense refers t o h o t gases which can be the p r o d u c t of com bus t i on of fuels, or air heated by the fire itself. T he y are normally only a danger to the firefighter when he is in very close p r o x i m i t y to the source o f the fire (as when caught by a flashover), or in a region where forced draughts from the fire are duc t e d towards him. The test, used to simulate convective heat exposure (shown in Fig. 4), employs a Meker burner approximately 38 m m in diameter. The axis o f the burner is vertical, and the fabric to be tested is aligned horizontally and exposed at a distance of 5 cm above the burner surface. The flux level chosen for this test was 100 kW/m 2, which is within the 'emergency' category and typical of the levels occurring in a flashover. The a m o u n t of energy transferred through the fabric is measured with a small copper calorimeter, and the time required for absorption of energy sufficient to cause a second degree burn in h u man skin is r e p o r t e d as the Estimated Burn Time (EBT100). The subscript indicates the incident heat flux value ( ot he r levels of incident heat flux are under consideration). (6) Ease o f ignition was tested in accordance with the second m e t h o d described in ISO DP 6940. This is currently at the draft proposal stage as an International Standard.

Fig. 4. Convective h e a t e x p o s u r e test a p p a r a t u s .

In this test, a specimen 80 X 200 mm is oriented vertically on a pinned frame, and a small gas flame 40 mm in length is brought into c o n t a c t with its surface. Ignition is defined as a result in which either the flame on the specimen persists for a period of 5 s after removal of the igniting flame, or the specimen burns t o the t op or vertical edges after removal of the igniting flame, up to a m axi m um of 20 s flame application. In the work r e p o r t e d here, the test was used as a screening test for protective clothing materials which should be difficult to ignite. Materials which ignite readily under these test conditions would not normally be tested furt her for radiant and convective heat transfer. (7) In addition to the single layer tests, a series of multiple layer fabric assemblies were tested to dem onst rat e how materials might perform in the conditions where t h e y would normally be used, t hat is, in combination with an underwear or underwear and some ot her material such as a jacket lining or shirt. A n u m b e r of the outerwear fabrics chosen to represent a cross-section of all major fibre types were combined with a single underwear material and the tests were repeated. Different underwear fabrics were

133

also tested in combination with a single outerwear material to demonstrate the influence of various underwear materials on heat transfer performance.

3. D I S C U S S I O N A N D I N T E R P R E T A T I O N O F T H E RESULTS

The results of all tests on single layer fabrics appear in Table 1. Table 2 lists the results for the series of outerwear fabrics tested in combination with a single underwear material, whilst Table 3 lists the results for the series of underwear fabrics tested in combination with a single outerwear material. In order to demonstrate the underlying mechanism of the performance of the different materials in each test, several graphs have been prepared in which all materials, including both single and multi-layer combinations, are plotted together. These appear as Figs. 5 to 8. No thermoplastic materials (e.g. polyamide or polyester) were included in the outerwear data. There are several important reasons for this which are of significance to the professional firefighter. The foremost is that they invariably fail intense heat related tests. Thermoplastic fibres exposed to heat soften, melt and coalesce. In so doing, t h e y form a solid conducting path through the fabric which considerably increases the rate of heat transfer to the underlying layers. If fabric containing thermoplastic fibres is in contact with the skin, the molten material releases its latent heat of melting as it resolidifies after the heat exposure ceases. As a consequence, burn injury can be more severe than with non-thermoplastic fibres, and there is the added problem of adherence of solid polymer to the wound. It is for this reason that protective clothing standards strongly recommend that under no circumstances should thermoplastic materials form any part of the firefighter's clothing, even down to underwear and socks [18]. Some of the underwear used in the fabric combination tests were blends containing thermoplastic fibres; these were only included to illustrate the heat transfer mechanism, and should not be regarded as acceptable for actual use.

The percentage of thermoplastic fibres which can safely be used in blends with nonthermoplastic fibres is of some consequence to firefighters. Unfortunately little work has been carried out to ascertain the minimum percentage of thermoplastic fibre required in a blend to cause a 'melt/drip' hazard in intense heat conditions. Some convective heat tests at this laboratory established t h a t wool/ polyester blends with polyester contents of only 5% formed holes much more rapidly than 100% wool fabrics. However the fabrics were light-weight (less than 200 g/m2), and the extrapolation of this finding to heavier weights requires further investigation. Until such information is available, it is suggested t h a t the thermoplastic content in any blend with non-thermoplastic fibres should not exceed 10%. The transmission factor determined by Method B of ISO 6942 is the ratio of heat transmitted to the heat incident on the fabric for radiant heat exposure. The inverse of transmission factor is a measure of the resistance of the fabric to intense radiant heat transfer. This inverse has been plotted against thickness in Fig. 6 rather than transmission factor itself to illustrate more clearly the behaviour of the fabric in resisting radiant heat transfer. In this test, the only damage observed with all of the fabrics was slight scorching in a few cases, and none sufficient to result in substantial loss of structural integrity. Method A is a very severe test, as there is no calorimeter or heat sensor behind the fabric to c o n d u c t heat away from it. After exposure for three minutes to a radiant heat flux of 20 kW/m 2, as required by the method, most fabrics were damaged, the degree of damage ranging from slight scorching through to charring. In view of the enormous disparity between the length of exposure and the time required for a second degree burn at this level of flux intensity (180 s and 3.7 s respectively), the test is quite unrealistic, and no wearer could ever survive such an exposure w i t h o u t a self-contained and enormously complex protective system. To report the damage to individual fabrics is impractical, as every fabric performs differently. Since the use of the appearance change indication 'C' on its own is of little value, this has been omitted from the data.

C o n s t r u c t i o n , flame r e s i s t a n t treatment

2×1 twill

plain weave 3×1 twill

plain weave p u n t o di R o m a knit melton melton melton 2×2 twill 2X2 twill

NI6

N17 N18

Wool W1 W3 W4 W5 W6 W7 W8

plain weave needle felt 3 x l twill 2×2 twill herringbone herringbone needle felt n e o p r e n e b a c k e d needle felt plain weave plain weave

Aramid N1 N3 N4 N5 N7 N8 N12 N13 N14 N15

Cotton/Cellulosic C1 2×1 twill, P r o b a n * * C2 3×1 twill, P r o b a n C3 3Xl twill, P r o b a n C4 3Xl twill, P r o b a n C6 3×1 twill, P r o b a n C8 3×1 twill C14 2Xl twill C15 3×1 twill, P r o b a n C16 plain weave S13 viscose plain weave $9 f.r. p o l y n o s i c plain weave

Code

Fabric details a n d test results

TABLE 1

natural gold It green dk green natural black natural

natural yellow natural natural khaki khaki green green natural lemon lemon natural natural

red dk green gold gold navy gold loomstate khaki white navy It green

Colour*

139 304 513 770 843 296 270

219 285 153 191 118 174 294 654 151 203 200 184 275

304 342 342 253 346 286 247 336 150 98 152

Weight (g/m 2)

0.58 1.46 2.59 4.81 4.02 1.20 0.79

0.90 5.45 0.38 1.12 0.86 0.93 5.00 3.53 1.15 0.88 1.05 0.61 0.75

1.02 1.09 1.21 1.09 1.22 1.14 1.18 1.13 0.72 0.20 0.52

Thickness (mm)

0.007 0.029 0.057 0.111 0.081 0.023 0.009

0.015 0.106 0.004 0.022 0.017 0.019 0.121 0.089 0.028 0.019 0.023 0.011 0.012

0.012 0.013 0.019 0.013 0.016 0.017 0.019 0.019 0.012 0.003 0.005

Body heat (K m 2 / W )

0.61 0.47 0.40 0.41 0.65 0.65

0.73

0.58 0.29 0.60 0.58 0.65 0.58 0.33 0.32 0.62 0.61 0.60 0.62 0.60

0.65 0.62 0.63 0.61 0.60 0.63 0.62 0.62 0.65 0.76 0.70

R a d i a n t TF2o

H e a t resistance p r o p e r t i e s

3.1 5.6 6.3 9.9 7.8 4.3 4.4

3.7 13.3 3.2 3.7 3.2 3.9 10.4 15.6 2.9 3.3 3.5 2.9 4.2

3.3 3.7 3.7 3.8 3.7 3.7 3.9 3.9 2.6 1.9 2.5

C o n v e c t i v e EBTloo (s)

2.5 7.0 d.n.i. d.n.i. d.n.i. d.n.i. 7.5

d.n.i.

d.n.l.

d.n.i. d.n.i. d.n.l. d.n.i. d.n.i. d.n.i. d.n.l. d.n.1. d.n.l. d.n.l.

d.n.1.

d.n.i. d.n.i. d.n.i. d.n.i. d.n.i. 3.5 3.5 d.n.i. 2.5 1.5 d.n.i.

Ignition time (s)

b-a 50

2Xl twill, Z i r p r o t melton, Zirpro melton, Zirpro melton, Zirpro plain weave, Z i r p r o 2 x l twill, Z i r p r o 2 x l twill, Z i r p r o melton herringbone, Zirpro 2X2 h e r r i n g b o n e , Z i r p r o diagonal t r i c o t , Z i r p r o n e o p r e n e c o a t e d 2 x l twill, Z i r p r o melton melton

green It b r o w n mid brown natural natural mustard natural grey/blue white It b r o w n It b r o w n

red black dk green It green navy black navy navy gold khaki orange red natural navy

217 262 1770 626 1133 557 232 229 470 1274 644

269 676 653 481 150 261 264 510 322 312 405 528 760 451

1.12 1.10 3.14 5.52 3.72 3.62 7.04 7.22 0.99 1.95 1.07

1.17 3.70 2.58 2.38 0.72 0.71 1.07 2.75 1.12 0.86 1.45 1.07 3.22 2.70

"

0.022 0.021 0.043 0.119 0.052 0.090 0.187 0.214 0.015 0.029 0.015

0.019 0.087 0.054 0.048 0.011 0.014 0.017 0.063 0.021 0.012 0.023 0.016 0.065 0.062

0.75 0.59 0.37 0.29 0.47 0.46 0.30 0.31 0.39 0.46 0.56

0.65 0.41 0.44 0.46 0.71 0.66 0.69 0.48 0.64 0.65 0.59 0.68 0.42 0.49

* d k = dark, It = light. * * P r o b a n A l b r i g h t a n d Wilson r e g i s t e r e d t r a d e m a r k , t Z i r p r o IWS registered t r a d e m a r k .

O t h e r materials a n d b l e n d s S1 3 5 / 6 5 a r a m i d / f . r , r a y o n 2Xl twill $3 8 0 / 2 0 a r a m i d / n o v o l o i d 2x 1 twill $5 leather $7 a r a m i d / n y l o n n e e d l e felt 88 asbestos plain weave SlO novoloid/glass plain weave Sll a r a m i d n e e d l e felt S12 a r a m i d n e e d l e felt $14 glass 5×1 twill S17 ceramic s a t e e n S18 ceramic s a t e e n

Wll W12 W13 W14 W15 W16 W17 W24 W25 W26 W27 W28 W29 W30

2.9 4.3 14.1 13.3 12.3 11.3 5.7 6.4 5.4 7.9 4.3

4.1 8.9 8.2 7.2 4.0 4.3 4.5 8.4 5.2 3.5 4.7 10.9 9.1 7.2

d.n.i. d.n.i. d.n.i. d.n.1. d.n.i. d.n.l. d.n.i. d.n.i. d.n.i. d.n.i. d.n.i.

d,n.i. d.n.i. d.n.l. d.n.i. d.n.i. d.n.l. d.n.i. d.n.l. d.n.i. d.n.i. d.n.i. d.n.i. d.n.i. d.n.i.

136 TABLE 2 Outerwear materials in combination with underwear WU1 Code

WU1 C1/WU1 C2/WU1 C6/WU1 C14/WU1 C16/WU1 N1/WU1 N4/WU1 N5/WU1 N7/WU1 N15/WU1 Wl/WU1 W3/WU1 W6/WU1 Wl4/WUI W30/WU1 S7/WU1 S8/WU1 S9/WU1 S12/WU1 S13/WU1

Construction, flame resistant treatment

Colour*

wool single jersey cotton 2×1 twill, Proban cotton 3Xl twill, Proban cotton 2Xl twill, Proban cotton 2Xl twill cotton plain weave aramid plain weave aramid 3×1 twill aramid 2×2 twill aramid herringbone aramid plain weave wool plain weave wool punto di Roma knit wool melton wool melton, Zirpro wool melton aramid/nylon needle felt asbestos plain weave f.r. polynosic plain weave aramid needle felt viscose plain weave

nat/It br red dk green navy loomstate white natural natural natural khaki lemon natural gold natural It green navy natural natural It green grey/blue navy

Weight (g/m 2)

Thickness (mm)

226 530 568 572 473 376 445 379 417 344 429 365 530 1069 707 677 852 1359 378 455 324

1.56 2.36 2.49 2.52 2.55 2.15 2.49 1.88 2.43 2.17 2.21 2.00 2.72 5.20 3.64 4.01 6.81 4.70 1.98 8.27 1.72

Heat resistance properties Body heat Radiant (K m2/W) TF20

Convective EBTm0 (s)

0.035 0.048 0.047 0.046 0.045 0.046 0.056 0.038 0.055 0.042 0.048 0.044 0.062 0.130 0.082 0.096 0.157 0.075 0.042 0.158 0.040

3.9 4.3 4.8 4.8 6.3 6.7 7.8 6.0 8.3 7.5 6.9 6.8 9.7 11.4 10.7 13.0 19.6 19.7 5.8 13.1 5.6

0.57 0.46 0.45 0.43 0.47 0.45 0.43 0.44 0.43 0.43 0.43 0.51 0.46 0.26 0.39 0.40 0.24 0.34 0.50 0.26 0.53

*dk = dark, It = light, nat = natural.

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4 5 FABRIC THICKNESS (mm)

8

FABRICTHICKNESS{mm)

Fig. 5. The relationship between resistance to dry heat loss from the body and thickness for protective clothing materials.

radiant heat transfer and thickness for protective clothing materials.

Description of the damage sustained by s p e c i m e n s in t h e c o n v e c t i v e h e a t e x p o s u r e test has also been omitted, both because the length of exposure required to meet the second degree burn criteria varied, and the need for full description of behaviour and damage to avoid misinterpretation. The general observation from these results is t h a t t h e p a r a m e t e r w h i c h g o v e r n s b o t h

protection from intense heat and loss of dry h e a t f r o m t h e b o d y is f a b r i c t h i c k n e s s . F i g u r e 7 is a p l o t o f i n t e n s e r a d i a n t h e a t resistance against resistance to body heat loss, and shows that the two mechanisms are d i r e c t l y r e l a t e d , t h a t is, b o t h a r e s t r o n g l y dependent upon fabric thickness. Regression lines have been drawn through t h e p o i n t s in F i g s . 5 t o 8; d e t a i l s o f t h e s e

F i g . 6. T h e r e l a t i o n s h i p

between

resistance to intense

137 TABLE 3 Underwear materials in combination with outerwear C14 Code

C14 C14/CU2 C14/CU5 C14/CU6 C14/CU8 C14/CUll C14tNU1 C14/WU1 C14 IWU4 C14tWU5 C14/WU7 C14/WU8 C14/BU3 C14/BU5 C14]BU7 C14/BU8 C14/BU9 C14/SU4 C14/SU6 C14/SU9 C14/SU11 C14/SU13 C14/SU14

Weight (g/m 2)

Thickness (mm)

Heat resistance properties

loomstate white pink It green natural white natural nat/lt br natural natural

247 472 331 456 536 402 458 473 458 628

1.18 2.46 1.80 3.54 3.02 2.26 3.12 2.55 5.07 4.14

0.019 0.038 0.030 0.070 0.048 0.038 0.072 0.045 0.126 0.096

0.62 0.48 0.56 0.43 0.46 0.53 0.44 0.47 0.37 0.35

3.9 6.5 4.6 8.0 8.1 6.1 6.3 6.3 7.2 8.7

natural natural white

502 526 458

4.41 3.14 3.08

0.106 0.067 0.065

0.34 0.41 0.41

7.9 7.1 6.9

white

494

3.47

0.069

0.38

7.8

natural

545

3.60

0.077

0.48

10.6

red

474

4.36

0.098

0.37

12.0

white

450

2.31

0.035

0.50

6.6

white white

374 565

2.35 3.49

0.042 0.076

0.46 0.44

6.1 14.8

white

389

2.23

0.044

0.54

7.7

white

475

2.77

0.050

0.48

7.3

white navy

538 496

3.19 4.36

0.056 0.100

0.46 0.34

11.9 11.2

Construction, flame resistant treatment

Colour*

cotton 2Xl twill cotton l X l rib cotton single jersey cotton brushed interlock cotton interlock cotton interlock aramid l X l rib wool single jersey wool modified rib tuck wool punto di Roma, Zirpro wool brushed interlock wool superwash interlock 75/25 wool acrylic l X l fancy rib 75/25 cotton/polyester fancy rib 50/50 wool/polypropylene modified pique 65/35 polyester/cotton brushed interlock 90110 cotton/polyurethane single jersey polyamide fancy 1×1 rib 85/15 P.V.C./acrylic brushed interlock 85/15 P.V.C./acrylic cellular knit 50/50 polyester/viscose brushed interlock polypropylene interlock 65/35 polyester/viscose brushed interlock

Body heat Radiant (K m2/W) TF20

Convective EBTl00 (s)

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Fig. 8. The relationship between second degree burn time during convective heat exposure and thickness for protective clothing materials.

138 TABLE 4 Regression details for t h e graphical p r e s e n t a t i o n s Figure

Slope

Intercept Correlation coeff,

Mean square deviation

5 6 7 8

0.0242 0.333 12.9 1.64

--0.009 1.31 1.48 2.92

0.0001 0.055 0.077 6.18

0.97 0.92 0.89 0.74

regression lines appear in Table 4. Despite some scatter, the correlation coefficients are highly significant at the 99.9% level, indicating that there is a strong linear relationship between each pair of parameters plotted. The relationship in Fig. 8 is not as strongly defined as the others, but there is still a strong statistical association between the two parameters. It should be noted that none of the aramid fabrics (other than some needle felts which are restricted to use as insulating liners) are more than about half the thickness of the wool meltons, and therefore appear to offer lower levels of protection. The properties of the wool fibre enable it to be readily made up into thick fabrics which retain good textile properties such as handle, abrasion resistance, and structural rigidity. This is not the case with aramids, which are normally made up as multi-layer constructions to achieve a thickness consistent with an acceptable level of protection. The typical combination is a medium weight outer fabric (around 200 g/m2), with a needle felt liner and perhaps an inner liner. The multi-layer concept can be employed with fabrics in any fibre or combination of fibres. The penalty is cost of making-up. There is a small gain in performance with multi-layer constructions in that each layer does not necessarily lie in direct contact with the next, and the extra gaps increase the overall insulation level of the garment. Examination of the results of the ease of ignition test leads to several conclusions relevant to understanding flammability. Cotton tends to ignite more readily than most other fibres, although in dense constructions it can be difficult to ignite and will not burn rapidly. Only those cotton fabrics which

were flame-resist treated did not ignite. All Zirpro* treated wool fabrics did not ignite. Of the untreated wool fabrics, most of those weighing in excess of about 250 g/m 2 failed to ignite, whilst the lighter weights ignited. It could be concluded that light-weight wool materials should not be used in environments where there is risk of flame; however, if ignition does occur, the flame propagates very slowly, and would not be regarded as hazardous. All aramids fail to ignite, as do the specialty fabrics tested (with the exception of the viscose liner fabric S13). All materials are degraded by the flame to the extent that they are easily broken apart in the region of flame application.

4. M E T A B O L I C H E A T LOSS C O N S I D E R A T I O N S

The body is constantly generating heat, known as metabolic heat, even when at rest. Under stress, metabolic heat o u t p u t may increase to as much as 20 times the resting level. In the firefighting situation, there is the additional heat input to the body from the surroundings. Most of the heat absorbed by the outer clothing reaches the body by conduction and radiation through the various layers and air gaps between them. For the body to remain in a comfortable state, all this heat must be passed out to the surroundings. Two main routes are involved. The first is conduction through the clothing to the outside, where heat is removed by convection and radiation. The second is by the evaporation of water at the skin surface. The water vapour then passes out from the clothing either directly through the clothing itself or is carried out through openings such as cuffs and neck by the circulation of air beneath the clothing. In conditions where the air temperature is greater than that of the body, heat loss by conduction cannot occur, and the only means of cooling is by the evaporation of moisture. If the moist air is not removed, the vapour pressure (or humidity) builds up within the clothing until a point is reached where the air becomes saturated, and moisture released at the skin surface forms liquid sweat instead of evaporating. If conditions such as this persist

139

over the whole b o d y for any length of time, the temperature of the b o d y rises and heat stress inevitably results. The only way of alleviating this impasse is to remove some of the b o d y heat by other means such as strategic ventilation of the clothing which employs b o d y movement to exchange the hot, moisture laden air between garments with the drier air of the surroundings. The hidden aspect of heat protection is that it is achieved at the expense of b o d y cooling. As Figs. 5 - 8 show, the loss of dry heat by the b o d y and the transfer of radiant and convective heat through textile materials to the b o d y are all determined primarily by the thickness of the material. Thus increasing the thickness of the clothing system, to give greater protection against intense heat, correspondingly reduces the ability of that clothing to dissipate metabolic heat. It is important to be aware of the difference between requirements of brigades in Northern Europe or the United States and those of warmer climates such as Australia, principally with regard to climatic conditions. Impervious outer materials such as PVC or vapour barriers within the garment offer a practical solution to the problem of water repellency and chemical resistance in cold climates, but their use in h o t summer weather introduces far more problems in terms of heat stress than it solves. It is probably in the design of the clothing that the greatest gains can be made with any new uniform. Movement of the b o d y induces air m o v e m e n t through the clothing, the socalled 'bellows ventilation'. This can be harnessed to pump the hot, moisture-laden air from within the clothing to the outside through the openings around cuffs and neck, and below the jacket or t u r n o u t coat. There has been a good deal of work carried out at laboratories such as the Hohenstein Institute in Germany [19] to demonstrate that vents in regions such as underarm, back and behind legs can considerably increase bellows ventilation. One aspect of ventilation which is being investigated in several European countries, notably Germany and Sweden, is the use of a bib-and-brace overall rather than the belted trouser. The overall is a loose fit and not gathered in at the waist, allowing the air in the upper part of the b o d y beneath the shirt

and underclothing to pass down into the leg region and to leave the clothing through the jacket/overall overlap. Further physiological studies are desirable. 5. C O N C L U S I O N

There are several important conclusions from the data presented in these tables and graphs: (1) the resistance of protective clothing materials to the loss of b o d y heat is dependent upon the thickness of the material, and the influence of fibre t y p e is small enough to be neglected; (2) the resistance of protective clothing materials to penetration by radiant heat of an intensity which might be found under fireground conditions is dependent upon the thickness of the material, and is n o t influenced significantly by the type of fibre involved so long as the fibre itself is n o t substantially degraded. Such degradation only occurs after exposures well in excess of that required to cause burn injury to human skin; (3) the resistance of protective clothing materials to penetration by convective heat of an intensity which might be found in flashover or backdraught conditions is largely dependent u p o n fabric thickness, and fibre t y p e plays a relatively minor role insofar as most materials degrade after exposures greater than a few seconds, and inevitably char or form holes. The extent and nature of this degradation is determined b y a combination of fabric construction and fibre type; (4) all materials were severely degraded in the area contacted by the flame during the test for ease of ignition. A small number ignited in this test; they were included to demonstrate h o w the weight of the material influences ignition, and would n o t normally be considered for use in clothing for protection from intense heat. In the course of duty, the professional firefighter in an urban environment faces hazards which include contact with falling objects, contact with projecting objects which can puncture both garments and skin, exposure to heat, flames and h o t objects, water, corrosive liquids, toxic gases and combustion products, and even molten metals and live electrical wiring. Apart from the risk of direct physical injury, he is also faced with

140

the more subtle danger of heat stress and heart strain due to strenuous work in hot environments, or simply excessive exposure to heat which overloads his metabolic system. The ideal firefighter's uniform should incorporate all the following requirements: (1) adjustable ventilation cooling; (2) resistance to abrasion and impact damage; (3) some protection from impact; (4) radiant and convective heat resistance; (5) resistance to spark damage; (6) comfort in all weather conditions; (7) resistance to chemicals; (8) water repellency; (9) smart appearance; (10) ease of cleaning; (11) durability; (12) ease of donning and doffing, and finally (13) reasonable cost. No product on the market is able to meet all of these requirements. No conventional textile material for example can resist chemical attack and repel water w i t h o u t the addition of either a chemical treatment or the incorporation of an impervious layer or a surface coating such as PVC. Some materials which have good heat resistance properties have very poor durability or are not cost effective. No garment or garment system can possibly provide complete protection from all likely conditions of heat exposure and at the same time dissipate sufficient metabolic heat to maintain a safe heat balance in the body. The International Standard ISO 2801, Clothing for protection against heat and fire -- General recommendations for users and those in charge o f such users [18], discusses the question of protection and endurance in some detail. It is worth reiterating the c o m m e n t in Section 2 of this Standard, which states: "A very large number of variable and interdependent factors affect the time that such clothing can offer protection in an area of heat and fire (state of health, training, physical effort, atmospheric conditions, air speed, etc.). For one and the same garment, this period of protection may vary enormously from one operator to another." The firefighter's t u r n o u t system should ultimately be a compromise between the requirements for an acceptable level of heat

protection and a comfortable metabolic state. The garments chosen to fulfill these requirements will fall short of expectations in some other areas, but it is to be hoped that wearer acceptance will be achieved with at least partial satisfaction of most other requirements. ACKNOWLEDGEMENT

The laboratory work of Mariette Plante is gratefully acknowledged. REFERENCES 1 A. E. Washburn, D. W. Harlow and S. Horn, United States fire fighter deaths in the line of duty during 1979, Fire Command, 47 (1) (1980) 30. 2 H. P. Utech, Injuries show what protection improved clothing should offer, Fire Eng., 125 (1972)47. 3 J. H. Veghte, Designing protective clothing, Part 1, Fire Service Today, 49 (3) (1982) 11. 4 J. Warden, Firemen's uniforms -- the case for establishing a common standard, Fire, 74 (919) (1982) 427. 5 NFPA No. 1971, Protective Clothing for Structural Firefighting, National Fire Protection Association, Boston, MA, November, 1975. 6 H. P. Utech, Are Federal Standards Adequate, Occupations at High Burn Risk: a summary report, NI O S H contract No. 210-77-0218, Miami, April, 1977. 7 B. H~igglund, The heat radiation from petroleum fires, FoU-brand, 1 (1977) 18. 8 B. N. Hoschke, Standards and specifications for firefighters' clothing, Fire Safety J., 4 (1981) 125. 9 N . J . Abbott, T. E. Lannefield, R. E. Erlandson and S. Schulman, Coated Fabrics Update, Proceedings o f the Symposium, March 31 - April 1, ! 9 76, American Association of Textile Chemists and Colorists, Research Triangle Park, NC, 1976, pp. 13 - 18. 10 G. C. Coletta, I. J. Arons, L. E. Ashley and A. P. Drennan, The Development o f Criteria for Firefighter's Gloves, Volume H: Glove Criteria and Test Methods, DHEW(NIOSH) publication No. 77-134-B, February 1976. 11 N . J . Abbott and S. Schulman, Protection from fire: Nonflammable fabrics and coatings, J. Coated Fabrics, 6 (1976) 48. 12 A.M. Stoll and M. A. Chianta, Method and rating system for evaluation of thermal protection, Aerospace Medicine, Nov. (1969) 1232. 13 B. N. Hoschke, A. W. Moulen, B. V. Holcombe, S. J. Grubits and J. J. Madden, The burn hazard from exploding hydrogen-filled meteorological balloons, J. Consumer Product Flammability, 7 (1980) 1. 14 A. Hausman, Flame-resistant garments for rescuers, Ann. Mines Belg., 5 (1980) 537 - 580 (French/Dutch).

141 15 Australian Standard A S 1587, Methods for Measurements o f Textile Fabrics -- Length, Width, Thickness and Mass per Unit Area, S.A.A.,

Sydney, 1973. 16 British Standard BS:4745, Thermal Resistance o f Textile Materials, B.S.I., London, 1971. 17 International Standard ISO 6942, Clothing for Protection Against Heat and Fire -- Method o f Evaluation o f Thermal Behaviour o f Materials and Material Assemblies when Exposed to a

Source o f Radiant Heat, ISO, Switzerland, 1981. 18 International Standard ISO 2801, Clothing for Protection Against Heat and Fire General Recommendations for Users and those in Charge o f such Users, ISO, Switzerland, 1973. 19 K. H. Umbach, Verbesserung des Trageskomforts yon Herren-bekleidung durch optimierte Kleidungsventilation, Hohensteiner Forschungs-

-

bericht, Hohensteiner Institute, Hohenstein, January, 1981.