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 Stone crushers, popularly known as 'blue metal units' are essential industries, producing crushed stones of different grades for roads and other civil constructions. The raw material is the large amount of silica available in quarries. Most stone crushers in India are labour-intensive, small-scale units, with capital investments of Rs.5 to Rs.10 lakh and widely-varying production capacities between 30 and 300 tonnes per day. Stone crushing generates an enormous quantity of dust during all stages of operations: the drilling of the rock, blasting, loading of trucks, transport, fugitive dust loss from trucks on bad roads, dumping into crushers, actual crushing, screening, transfer on to conveyor systems, etc. Much of the dust is very fine, more than 20% being of less than 10 microns, which is
respirable.
The dust concentration is particularly intense down stream of a crusher. Wind currents cause secondary dust emissions by re-entertaining the dust deposits on the ground. Even when the crushers are not functioning, as during nights and holidays, the wind raises the accumulated dust from the ground, in what is known as "background concentration". Apart from the dust, the high silica content (sometimes 85%-95%) is particularly harmful. The workers in the crushing units are susceptible to bronchial infections and, even worse, deadly silicosis. Dust deposit on crops can affect yields and on the land can change the soil characteristics so much as to make it uncultivable.
 The Tamil Nadu Pollution Control Board (TNPCB) has been campaigning to spread awareness of the environmental problems associated with the operations among the 1500 or so crushing units located in the State. Kancheepuram district alone has about 500 units, mostly near Tiruchoolam. Erode district has 92 units, mostly in clusters in Morattupalalyam, Perundurai taluk, and Bhavanisagar, Satyamangalam taluk. In response to the TNPCB's request, the National Environmental Engineering Research Institute (NEERI), Nagpur, conducted a study during 1997-98 and recommended some anti-air pollution measures, which the Board decided to accept.
According to K. Elankumaran, Erode District Environmental Engineer, very few units in the district have adopted pollution control measures, mainly due to lack of awareness among the owners. The TNPCB conducted an awareness seminar for owners in the district, the first of its kind, in May and advised them in this regard. The Ministry of Environment and Forests and the Central Pollution Control Board (CPCB) have prescribed pollution control measures and standards. According to the standards, suspended particulate matter (SPM) measured three-to-10 meters from any process equipment should not exceed 600ug/M3. All units in the country have to comply by providing dust containment-cum-suppression systems and constructing wind-breaking walls.
The National Productivity Council (NPC), on its part, has demonstrated suitable dust suppression and containment systems. According to V.S.S. Baskaramurthy, NPC Senior Deputy Director, Chennai, the systems comprise building enclosures around dust sources and spraying water as a fine mist through special nozzles to settle the dust. According to him, these measures are simple to adopt and involve low capital investment and no operating cost. The CPCB has also prescribed development of a green felt around the units, for which the NPC has suggested high foliage trees like neem, tamarind, gulmohar, flame of the forest or any suitable local variety. Cashew, mango, lemon and sapota (chikku) may also be grown for commercial benefit.
Taking note of the badly-pitted, narrow road conditions in the units, aggravating the SPM problem, the CPCB has insisted on metalled roads within the premises, with regular cleaning and wetting, besides wetting of materials. It has also reduced the permitted drop height of dusty materials. Fine dust in the crushing area should be cleaned and the dump should be covered with tarpaulin to arrest erosion by wind. As an occupational safeguard, all workers should be provided nose masks.
 Mr. S.K. Yoganathan, an office bearer of Erode District Stone Crushers and Quarry Owners Association, says he has complied with the set standards. But the special spray nozzles were not available with Indian manufacturers. The Union Government has started taking stringent action against units that do not comply with the standards. It is pointed out that dust pollution from the crushers is much too high even when the units are not functional. For instance, the dust haze along the Delhi-Alwar highway was thick enough to impair visibility, posing a high threat of road accidents. That was why Government had decided if the units do not comply with the standards within the stipulated time, they may even be closed.
G. Anne Josephine
(Tamil Nadu Pollution Control Board)
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