1.Introduction:

It has been a long time since it was discovered that Freon gas was destroying the ozone layer over Antarctica. The ozone layer intercepts ultraviolet radiation from the sun and its destruction has become a serious environmental and social problem. Although the law of cause and effect between UV radiation and skin cancer has not been clarified in the field of medical science, there is a report from THE SKIN & CANCER FOUNDATION of AUSTRALIA which outlines that the number of melanoma, one type of skin cancer, found in Australia is about twice that found in America. Also a lot of sheep in pastures in Australia are suffering from skin cancer or blindness. The UV radiation which comes out of appliances that we use on a daily basis, like fluorescent lamps, is not considered a serious problem, because of its small volume. However, from industrial machines, such as welding machines, very strong and harmful short wave length UV radiation is emitted. The effect of UV radiation to eyes has become a matter of great concern and the safety standard of eye protectors has been established. But the safety standards for skin protection have yet to be given careful consideration. The UV radiation which comes out of welding machines is getting stronger, as those machines are becoming more efficient and have more uses. In addition, the operating hours of these machines are increasing. Therefore it is an urgent task to develop safety standards for those people working around welding machines. In order to pursue a safer working environment, our company developed tough cloth which limits the transmittance of UV radiation and then went on to manufacturing safer working clothes.


2. The effect of UV radiation to the human body:

UV radiation has different wave lengths and can be classified into three patterns. UV-A 315~400nm, UV-B 280~315nm, UV-C 100~280nm. UV-C is more harmful than UV-A or UV-B, because the shorter the wave length, the greater the energy it possesses. Since UV-C and parts of UV-B, the UV short wave lengths, were absorbed into the ozone layer and rarely reached the surface of the earth, those types of UV radiation had not been considered dangerous until recently, when it was found that those UV waves could reach the surface of the earth, because of the destruction of the ozone layer. At the present time, the effect of UV-C to the human body is not clear. UV-B can penetrate the outer layer of skin slightly, while UV-A penetrates deep into skin tissue. The table below shows various harmful effects that UV radiation has on our skin.

Sunburn is a common effect when our skin suffers from UV radiation. But it could develop a blister and become a real burn, if the skin received a large enough dose of UV radiation. As explained above, the shorter the wave length, the stronger and more harmful it becomes. Up to the present, the connection between UV radiation and skin cancer has not been proved clinically. However the statistics show that residents in low latitude areas tend to get skin cancer more often compared to residents in high latitude areas. Also people who work under the sunlight for a long period of time are more likely to develop skin cancer than those who work indoors. In the case of human beings, noses, foreheads and shoulders are the parts of the body which are easily exposed to UV radiation, and noses, cheeks and lower lips are the parts which are likely to get skin cancer. Considering these facts, we come to the conclusion that there are some connections between UV radiation and skin cancer.


3.Ultraviolet radiation from welding arcs and safety standards:

The present welding processes which are conducted Shielded metal arc welding, carbon dioxide(gas shielded) arc welding, Metal Active Gas(MAG) welding, Metal Inert Gas(MIG) welding, Tungsten Inert Gas(TIG) welding, Self-Shielded arc welding and so on. 3 welding Spectrum Charts using some of these welding processes are shown below. As these charts show,

UV-B and UV-C, which have short wave lengths and usually don't exist in nature, are generated in large quantities. From a long time ago it was taken for granted that workers in such welding work shops would get ophthalmia or skin erythema from exposure to strong Ultraviolet radiation. However, American Conference of GI Hygiene(ACGIH) is advising on the establishment of Threshold Limit Values(TLV) of Ultraviolet radiation which human bodies are exposed to. TLV is a safety standard for workers exposed to Ultraviolet radiation from both artificial and natural light sources, and in order to prevent serious injuries and diseases, it shows the limit of the spectrum range of UV radiation. Wave lengths from 200 to 400 nm, when workers work for 8 hours being repeatedly exposed to UV radiation. As for harmful UV radiation emissions from welding machinery, it is considered that manual welding and semi-automatic welding are riskier than any other welding process because workers have to be much closer to the light source in those 2 processes than in the others.

4.The development of protective worksuits:

To develop protective worksuits which intercept harmful short-wave-length UV radiation, an experiment was conducted as follows. The purpose was to determine the strength and transmittance of UV radiation of various materials.

(1) Methods:

• 1. Radiant source: 400W high pressure mercury lamp arc tube
• 2. Ultraviolet radiation emission apparatus:
  • The Arc tube is placed in the center of an equilateral decagonal tube box.
  • This box is revolved with a motor at a speed of 6rpm.
  • A vent hole was put at the bottom and a ventilator at the top of the box to prevent ozone generation.
• 3. Transmittance measuring instrument
• 4. Irradiance meter and Ultraviolet radiation irradiance meter
• 5. Spectrodiometry
• 6. CIE standard sources
• 7. Tension measuring instrument
• 8. Scanning electron microscope
• 9. Sample fibers -100% cotton fiber -Tetrose fiber and cotton blend -Aramid fiber

(2) Results:
At the point of tensile strength against UV radiation, Aramid fiber was the best and even after a 200-hour irradiation it showed 70% of its original strength. On the other hand, the Cotton fiber and the Tetrose fiber cotton blend showed less than 50%. Also in regard to transmittance, the Aramid fiber was the best followed by the Cotton fiber, and then the Tetrose fiber and cotton blend. At present, the Cotton fiber is widely used, and the transmittance was 2.64%. Aramid fiber (color; navy blue) showed 0.074% transmittance and it meant that the result was about 1/35 of the Cotton fiber's. The reason for these facts is that the molecular coupling of Aramid fiber's benzene ring creates a very strong material. After the photomicrograph test of these subjects, it was shown that the Cotton fiber was already worn out after a 50-hour exposure and the surface of the cloth became like fish scales after a 200-hour exposure. The surface of the Tetrose fiber and cotton blend was broken to pieces after a 50-hour exposure and had many transverse circular cracks around it after a 200-hour exposure. In contrast, after UV radiation emissions the Aramid fiber had small longitudinal cracks first and they developed into lines after a 200-hour exposure. However there were no major tears or damages found.

Cotton fiber 0-hour	Ultraviolet radiation emission 200-hour
Aramid fiber 0-hour	Aramid fiber Ultraviolet radiation emission 200-hour

5.Aramid Fiber

As the results show, it was found that Aramid fiber is suitable for uniform cloth to protect such workers as welders when exposed to harmful ultraviolet radiation produced at close range. Aramid fiber is a type of nylon known as “aromatic polyamide fiber", made of benzene rings. In 1974, the Federal Trade Committee(FTC) named this kind of fiber“Aramid" to distinguish from nylon, and, in 1977, the International Standards Organization(ISO) officially approved this “Aramid" fiber as a new type of synthetic fiber. Aramid fiber is divided into two broad classes in its molecular structure: para-type which is straight, and meta-type which is zigzag. We chose aromatic polyamide heat-resisting fibers of the meta-type, which is an organic synthetic fiber, mainly consisting of polimeter-phenylene-isofutal-amide. This kind of fiber has a high efficiency comparable to polyethylene in the strength of its elasticity, the rate of elasticity, specific gravity, touch, and color, etc. It also has thermal resistance which allows it to begin to break up and carbonize at 400℃ without melting in the air, and incombustibility of Limiting Oxygen Index(LOI)30 and nonflammability.


6.Conclusions

According to the recommendatory index of ACGHI, cotton uniforms, being most widely used today, are not adequate enough to resist ultraviolet radiation. Even when using a welding machine of low ultraviolet radiation, a worker in a cotton uniform can only operate it for several hours. In contrast, wearing a uniform made of Aramid fiber(especially, in navy blue), it is possible to operate almost all kinds of welding machines for more than 8 hours. However, even when wearing a uniform made of Aramid fiber, workers using MAG and MIG machines, which emit a high level of ultraviolet radiation, can only operate for 1~2 hours. Also, it is necessary to put on an additional protector made of Aramid fiber on top of the uniform. Thus, we selected Aramid fiber as an optimal uniform cloth to protect welders from ultraviolet radiation, and are working on developing and producing better protective uniforms.