Noteworthy Keyword
【Asbestos】
Asbestos

The asbestos health problem had been pointed out in Japan dozens of years ago. When great number of buildings collapsed due to the Kobe earthquake a decade back, the risk of health hazard caused by asbestos exposure emerged during demolition. Nevertheless, the measure to reduce exposure to asbestos did not last long. Similar health problem materialized at the end of June this year. There was a report from the Ministry of Health, Labour and Welfare that cancer development caused by asbestos has increased about 1.6 times since the beginning of this year. In addition, a news reported about employees, who worked at JR factories and died of mesothelioma; thus workmen’s compensation was certified to them. However, the major event which caused asbestos panic happened on the latter part of June. The report showed that 78 employees died from asbestos exposure at a major machine factory previously located at Amagasaki in Osaka. More eye-opening events took place when the neighboring residents of the factory also manifested the same symptoms. The wife of an employee, who died of mesothelioma, died of mesothelioma as well. The cause was assumed to be related to the laundering of her husband’s work clothes. A number of similar death cases were reported from many factories and workshops, where asbestos was handled. Moreover, asbestos was known to be mainly used in the infrastructures of schools and public facilities.

Asbestos has been appreciated as a magical mineral since the ancient time. It is a low-cost, highly heat-resistant mineral, and a good conductor of electricity. Furthermore, it is reactant against chemicals, such as acid and alkali (chlorine). It has been used abundantly as asbestos products and asbestos cement products - for fire prevention, heat-retention, electric insulation, polish-proof, and for prevention of noise. Now, the problem in many facilities is the kind of asbestos called "air-borne asbestos". In the past, asbestos was directly sprayed and attached to wall and ceiling for the purpose of heat-retention and insulation. However, the use of asbestos was prohibited, by principle, in Japan in 1975. On the other hand, building materials, such as the interior of wall or ceiling, flooring material, outer wall, and coating material of the back side of edge of the eaves, roof material, or chimney material, asbestos is still widely used.

Asbestos is the silicic acid compound of the shape of a fiber produced naturally.Asbestos includes mainly needle-like crystal structure of Chrysotile (white asbestos), amosite (brown asbestos) and crocidolite (blue asbestos). Among them crocidolite asbestos is the strongest toxic. Asbestos is defined by needle-like crystal whose width / length is smaller than 1/3 (Length is longer). Width is 5-10μm, while length is 10-50μm. There is a rock wool of similar substance, which is called the artificial mineral. It is called non-asbestos because there is no human body hazard like asbestos.

The typical human body hazard which asbestos causes is mesothelioma. A tumor develops near the surface, such as pleura or peritoneum, which epithelizes the internal organ especially the lung. It causes difficulty in breathing. After aspiration of asbestos, symptoms will develop in 20-30 years. Since it takes a long time to develop, it is called “A quiet time bomb” or “A 20-year murder”. Many cases show no symptoms until the disease develops to an advanced stage. The problem with asbestos is that it has particles that easily scatters and can be inhaled. So, anti-scattering preventive measures are now developed by Occupational Health and Safety Law, the Clean Air Act, and laws related to wastes disposal and public cleaning.

Whether or not asbestos is included in air-borne or building materials, as long as there are available construction records for such facilities, many health hazard related cases can be judged based on the date these facilities were constructed. The building materials used and construction parts can also be traced back from these facts. This can be distinguished from the year when construction method and building materials using asbestos was banned. However, in certain cases when judgment cannot be made due to limited available data, it must rely on the actual measurement. Presently, asbestos in air-borne and building materials is analyzed through a combination of the dispersion staining method using mainly a phase contrast microscope and the technique using the X-ray diffractmeter. Airborne concentration is measured by collecting air for four hours at 10L/m and using a phase contrast microscope. The standard airborne concentration is below 10p/L. If more than 1% of asbestos in air-borne or building materials is found, it is defined as asbestos hazard.


before
Methods for disposal of arsenic
top of contents next
Yellow sand or Dust and sandstorm