出版社：National Institute of Occupational Safety and Health
摘要：The tuffaceous sediments are widely distributed in Japan, and have utilized for building stone at every where for many centuries. The production of the tuffaceous sediments at Oya, Tochigi Prefecture, is regarded as the largest in Japan. This tuf- faceous sediment called Oya-ishi , contains many altered volcanic rock fragments. We have experienced that there are only 19% of oxygen in the air at some level of quarries where exposed large amount of altered materials in tuffaceous sediments. The accidents due to oxygen deficiency have happened and will be happened where the worksite is narrow and ill-ventilation, especially in places where are absorbent and/or dilution agents of oxygen. We found that the strong absorbent in the quarry is the altered volcanic material called Miso . The Miso is confirmed the mixture of ferrous dioctahedral and ferrous trioctahedral smectite which are situated in deep portions of the quarry, and are stable under the reducing environment. The Miso is commonly dark blue in colour in unweathered deep places, but easily turns to black within a few hour and finally to brown in a few weeks. The oxidized Miso is re- cognized as the mixture of ferric dioctahedral and ferric trioctahedral smectite without any other impurities such as iron oxides. The ferrous smectites being stable under the reducing condition, absorb oxygen to become the stable ferric smectites under the normal condition, and oxygen is consumed by this reaction. It may be a first report that ferrous iron in the structure of minerals is so easily and spontaneously oxidized to ferric iron in them under the normal temperature and environment.
