Safety Clothing for the Aluminium Industry

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1 Safety Clothing for the Aluminium Industry Viðar Magnússon 1, Guðmundur Gunnarsson 2, Hörður Jónsson 3 1 Foxhall á Íslandi e.h.f., Kalmannsvöllum 3, IS-300 Akranes, Iceland. Tel , vidar@foxhall.is. 2 IceTec, Keldanholt, IS-112 Reykjavík, Iceland. 3 Consultant, Bakkaflöt 3, IS-210 Garðabær Introduction Workers in the primary aluminium industry are in many places exposed to hazards from molten aluminium splashes, which can lead to serious burns if the aluminium is trapped against the body or sticks to the clothing used (Sasser 1979). It is therefore essential that the workers wear properly designed clothing made of appropriate materials. The primary requirements of materials for protective clothing against molten metal splashes is that they should be flame retardant and repel molten aluminium (Benisek and Edmondson 1981). Methods to evaluate the resistance of materials against molten metal splashes were developed about years ago (Mehta and Willerton 1977), (Sasser 1983). Extensive tests of different materials were carried out at that time and the results were published (Benisek and Edmondson 1981), (Brewster and Barker 1983). However since then there have been very few published test results in the literature. In this presentation we will first discuss the energy needed to cause burns and relate that to the energy released when molten aluminium cools. Then we describe tests methods to evaluate the resistance of materials against molten metal splashes and present some test results on materials developed in the last years. Proper design of protective clothing is then discuseed briefly. The limitations of the materials presently available are then discussed and possibilities in developing improved materials described. Skin temperature, burns and molten aluminium The average temperature of the skin is about 30 C. If the temperature of the skin rises to 45 C or higher we start to feel pain. If the skin temperature rises to 55 C, 1 st degree burn will occur after 20 seconds, followed by 2 nd and 3 rd degree burns (Benisek 1983). The degree of burning depends on the intensity of the heat transfer to the skin and its duration, but it seems to be accepted that second degree burn will start when the skin has received 8,5 J/cm 2. A 1 g splash of molten aluminium at 700 C releases 1100 J of energy (heat) when cooled to 30 C. If a splash of this size would be caught close to the skin inside a well insulated garment, for example a boot, it could cause a second degree burn in an area that measures 11,5 x 11,5 cm 2. This is of course a hypothetical example since all the energy of the cooling splash will not be transmitted to the skin. But even if only 1 % of the energy is transmitted to an area that is 1 cm 2 it will cause a very severe and uncomfortable burn in that area, resulting probably in absence from work for some time.

2 Splashes of molten aluminium can be much larger than in the hypothetical example above, making it obvious that measures have to be taken to protect workers in the primary aluminium industry from molten aluminium splashes, large and small. Preventive measures have been proven effective, but even though the frequency of molten aluminium splashes may have decreased it is nonetheless necessary to equip the workers with effective protective clothing. The testing method A test method for the assessment of resistance of materials against molten metal splashes is described in European standard EN:373 (1993)(Staðalráð Íslands 1993). In this test method a test piece is placed over a piece of a PVC film. The PVC film can be regarded as a skin simulant. The test piece is inclined 60 (see Figure 1) and a certain quantity of molten aluminium is poured on it at a certain speed. Damage to the fabric and skin simulant is then examined and the fabric is said to pass the test if the skin simulant is not damaged. Fabrics can then be classified according to the quantity of aluminium it can withstand. The classification and requirement of materials for protective clothing for workers where there is danger of molten metal splashes is described in European standard EN:531 (1995), see Table 1 (Staðalráð Íslands 1995). Figure 1. Schematic picture of the pouring apparatus. To meet a certain performance level it is sufficient that the fabric can pass a test with the minimum quantity of aluminium shown in Table 1. According to standard EN:531 it is stated that protective clothing that is claimed to offer protection against molten aluminium splashes should at least meet performance level D1 in Table 1.

3 Table 1. Performance level of fabrics against molten aluminium splashes, according to standard EN:531 (1995) Performance level Mass of molten aluminium that does not damage PVC film (g) Min. Max. D D D3 351 ASTM in America has also developed a testing method for the evaluation of the resistance of materials against molten metal splashes (ASTM 1996b). This method is similar to the European test method except that the heat transfer through the material is measured with a calorimeter when molten aluminium is poured on the material. Fabrics used for protection against molten aluminium splashes. Different kinds of clothing materials are used in industries where there is danger of molten aluminium splashes. The American Foundrymens association recently issued guidelines for protective clothing in foundries (Kohlhoff 1999). For protection against molten aluminium splashes the following materials are recommended; treated wool, 100% untreated cotton 100% untreated wool Vinex. The materials used should comply with the requirements of ASTM standards F1002 (ASTM 1996a) when tested with ASTM method F955(ASTM 1996b). The following materials are described as unsuitable; Nomex (molten aluminium sticks to it) Phosphorous treated cotton Nylon Polyester Adanur also claims that the following materials are unsuitable for molten metal protection; Nomex, Kermel, Flamex II (70/30 cotton/polyester), Trinex (50/30/20 modacrylic/polyester/rayon) (Adanur 1995). Good protection against molten aluminium is obtained by using Vinex (85/15 polyvinylalcohol/rayon) (Adanur 1995). However, Vinex has the disadvantage that it shrinks on contact with molten aluminium. Extensive test were carried out in the UK about 20 years ago on different materials for molten metal protection (Benisek and Edmondson 1981). An important conclusion from this work is that evaluations based only on flame retardance of the fabric can be completely misleading. As an example it is claimed that fabrics from aramids, or glass fibres cannot be considered for protection against molten metal protection. Of the materials tested, by Bensiek and Edmondson, wool was found to offer the best protection for molten metal protection. Untreated cotton offer slightly lower protection.

Several companies now offer fabrics for molten metal protection based on Viscose FR from Lanzing. Foxhall s criteria for selection of materials.

Foxhall considers this to be insufficient and requires that the clothing material should meet performance level D2, in addition to other requirements of standard EN:531.

4 Several companies now offer fabrics for molten metal protection based on Viscose FR from Lanzing. Foxhall s criteria for selection of materials. According to standard EN:531, the clothing material for protection of against molten aluminium should meet performance level D1. Foxhall considers this to be insufficient and requires that the clothing material should meet performance level D2, in addition to other requirements of standard EN:531. Foxhall has further constraints. The clothing should be comfortable and it should not shrink when molten aluminium is poured on it. Evaluation of candidate materials Several different materials have been tested according to standard EN:373 in search of materials that meet Foxhall s requirements that the fabrics should meet performance level D2. Some of the results are described and discussed below. Figure 2. PVC film and specimen of Pyrovatex treated cotton (290 g/m2). Tested with 213 g of aluminium. Figure 3. PVC film and specimen of a fabric made of Viscose FR, wool, and cotton (315 g/m2). Tested with 208 g of aluminium. Pyrowatex treated cotton is a common material for protective clothing used in the aluminium industry, but as can be seen in Figure 2, the performance of this material is unsatisfactory. The aluminium partly stuck (not shown) to the fabric resulting in extensive damage to the fabric and the PVC skin. Another result of a test of a fabric used for protective clothing is shown in Figure 3. This fabric is made of viscose, wool and cotton and it repels molten aluminium, but a hole is formed in the material resulting in damage of the PVC film.

An example of a fabric that repels molten aluminium and where there is no damage to the film, is shown in Figure 4. The viscose used in this sample is a special blend of cellulose and silica.

5 Figure 4. PVC film and specimen of a fabric made of Viscose FR, polyvinylalcohol and modacrylic (280 g/m 2 ). Tested with 208 g of aluminium. Figure 5. PVC film and fabric specimen made mainly of viscose FR and wool (300 g/m 2 ). Tested with 207 g of aluminium. An example of a fabric that repels molten aluminium and where there is no damage to the film, is shown in Figure 4. The viscose used in this sample is a special blend of cellulose and silica. However this material does not fulfil the requirements shown above since it shrinks considerably upon contact with the molten aluminium. The fabric selected by Foxhall for its protective clothing is made mainly of Viscose FR and wool. An example of a test result of this fabric is shown in Figure 5. This material repels molten aluminium and there is no damage to the PVC film. This material does not meet performance level D3 according to standard EN: 531 (1995). However, if a piece of knitted underwear (composed of Kermel, wool and Viscose FR) is inserted between the fabric and the PVC film then this clothing assembly meets the requirements of performance level D3, see Figure 6. These results show that although the fabric chosen by Foxhall offers good protection against molten aluminium when used alone, much better protection is obtained by using knitted underwear under an outer garment of the materail selected by Foxhall.

Figure 6. PVC film, knitted underwear made of Kermel, wool and 25 Viscose FR and specimen of a fabric made mainly of Viscose FR and wool (300 g/m 2 ). Tested with 354 g of aluminium.

6 Figure 6. PVC film, knitted underwear made of Kermel, wool and 25 Viscose FR and specimen of a fabric made mainly of Viscose FR and wool (300 g/m 2 ). Tested with 354 g of aluminium. Design of protective clothing for molten metal splash protection. In the design of garments for molten aluminium protection it is of utmost importance to minimise the risk of aluminium getting trapped on, in or under the clothing. Open pockets should therefore not be used. Pants should cover boots to minimise the risk of aluminium getting trapped in the boots. Further development When materials are tested according to EN:373 (1993) they are laid flat in the testing apparatus. This does not necessarily mimic real life situations since in practice there is always the risk of formation of unintentional folds. We have tried to mimic this in some tests by making folds in the lower part of the test specimen. Molten aluminium is then poured on the upper part of the fabric while fastened in the testing apparatus. The molten aluminium then runs down the test specimen and over the fold. We have found that if the folds are small then there is no damage to the PVC film. However, if the fold is larger, then molten aluminium may get trapped in the fold and then the aluminium will burn its way through the fabric and into the skin simulant. What is needed is development of a material that can better resist molten metal splashes when folded. Foxhall has started the development of such a fabric. There is no standard test to test the resistance of folded materials against molten metal splashes. Therefore Foxhall has decided, as a first step in the development of an improved fabric, that it should meet the requirements of performance level D3.

7 Acknowledgments The work desribed in this paper was supported by The Icelandic Research Council (Rannís). Magnús Valdimarsson is thanked for performing the tests and for his contribution to all the pictures. References Adanur, S. Safety and Protective clothing. Í. WELLINGTON SEARS HANDBOOK OF INDUSTRIAL TEXTILES. Technomic Publishing; 1995; p ASTM. Standard performance specification for protective clothing for use by workers exposed to specific molten metal substances and related thermal hazards. F ed. ASTM; 1996a Standard test method for evaluating heat transfer through materials for protective clothing upon contact with molten substances. F ed. ASTM; 1996b. Benisek, L. Virgin Wool Products With Flame-Retardant Finish. Melliand Textilberichte International Textile Reports. 1983; 64(8): Benisek, L. and Edmondson, G. K. Protective Clothing Fabrics.1. Against Molten-Metal Hazards. Textile Research Journal. 1981; 51(3): Brewster, E. P. and Barker, R. L. A Summary of Research on Heat-Resistant Fabrics for Protective Clothing. American Industrial Hygiene Association Journal. 1983; 44(2): Kohlhoff, Fredrick H. PPE Guidelines for Melting and Pouring Operations. Modern Casting, May 1999, S May; Mehta, P. N. and Willerton, K. Evaluation of Clothing Materials for Protection Against Molten- Metal. Textile Institute and Industry. 1977; 15(10): Sasser, B. J. Protective Clothing for Molten Aluminum Exposure. Journal of Metals. 1979; 31(12): Evaluating Clothing Materials for Molten-Metal Exposures. Astm Standardization News. 1983; 11(7): Staðalráð Íslands. Protective Clothing - Assessment of resistance to molten metal splash. ÍST EN 373:1993 ed. Staðalráð Íslands; Protective clothing for industrial workers exposed to heat (excluding firefigters' and weders' clothing). ÍST EN 531:1995 ed. Staðalráð Íslands; 1995.

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