Manufacturing Process for Chrysotile Asbestos Cement Corrugated Sheets

The manufacture of A.C. Sheets is based on the principle of famous “Hatschek” process and is well established in India. In brief the manufacturing process shall involve the following stages: -

Pretreatment of Chrysotile Fibre:

Chrysotile fibre bags of different grades are put in fully enclosed full automatic PLC controlled Bag Opening Device. To minimize the exposure risk of Chrysotile Fibre to the worker, manual handling of Chrysotile Fibre is completely avoided by using a fully enclosed fully automatic PLC Controlled Bag Opening Device with bag shredder through which compressed fibre bags are automatically cut.

Chrysotile fibre passes through the enclosed lump breaker and closely connected screw conveyor to be automatically discharged in the mill and the empty bags are automatically fed in the connected Bag shredder where these are shredded and fed to the Edge runner Mill through a duct 25% to 30% water is added in the mill. The fully automatic Bag opening Device, Lump Breaker, Screw Conveyor, Bag Shredder and mill are completely closed integrated unit. The wet chrysotile fibre along with shredded bag particles are discharged from the mill to a closely connected bucket elevator which discharges the wet chrysotile fibre along with shredded bag articles to a storage in which has a screw conveyor attached at the bottom for discharging the wet chrysotile fibre into a batch weighing Hopper placed on electronic load cells which in turn discharge the pre-determined weighed wet chrysotile fibre into the Hydro-disintegrater where he wet chrysotile fibre is mixed with 2000% of water to form asbestos slurry. The whole system of mill, Bucket, Elevator, Storage Bin, Batch weighing Hopper and Hydro-disintegrater is closely connected and integrated unit as a whole. The automatic Bag Opening Device, Edge runner mill and Cement-fly Ash feeding points are provided with suction hoods. These hoods are connected to a pulse jet bag filter unit through a duct. The entire system is designed keeping in mind zero dust generation and no manual handling of chrysotile fibre is done either dry or wet.

Preparation of slurry:

The treated fibre along with predetermined quantities of fly-ash, cement and pulp are charged into a mixing vessel to form slurry.

Sheet making:

The slurry is then fed into the vat from where layers of slurry are deposited on rotating sieve cylinders inside the vat. This is then transferred to a moving end loss polyester felt which deposits the layer on a rotating drum. The required thickness is achieved by successive transfer of slurry films and the sheets so formed are cut and picked up by the conveyor.

Sheet Moulding:

The sheets from the conveyor are automatically cut at the ends to the desired size and conveyed to the atmospheric corrugators’ machine where the sheets are corrugated and placed in the steel template. The wet edge trimming and cutting including damaged sheets are automatically fed to waste pulped through waste conveyor where the green sheets are re- pulped and returned back to the machine continuously in a closed circuit.

Drying and Curing:

50 corrugated sheets along with templates are loaded on to a trolley and transported to a drying chamber. After drying for 10 – 12 hrs, the sheets are striped from the templates. Thereafter, the sheets are air cured for 28 days.

Source: http://acpma.com/production-process.html

Uses in West not relevant to India

The health issues recorded in the Western countries in the past and which are being highlighted and debated by the anti-asbestos lobbies relate to extensive and uncontrolled usage of the Blue and Brown varieties of Asbestos fibre falling within the amphibole category.

Friable low-density asbestos insulation boards were also used as inner roof to provide better fire protection. These products consisted of asbestos upto 90% in loosely bound form. Such applications exposed workers to uncontrolled inhalation of loose asbestos dust in high concentrations which led to health related problems. Once the ill effects of such applications were documented, such usages were stopped in the western countries decades ago.

Those experiences in the West, do not apply to India, where warm climatic conditions never required such asbestos containing thermal insulation of buildings.

In India, we only use Chrysotile (white) asbestos fibre for the manufacture of asbestos-cement sheets and asbestos-cement pipes which contain a very small quantity of Chrysotile fibre (only 8 –10%). The other raw materials used are cement 45%, fly ash 30 –35% and wood pulp. The asbestos fibres are firmly locked-in or encapsulated within the cement matrix during manufacture so that fibres cannot be emitted into the atmosphere under normal use and thus, poses no health risk to the general public or environment. Several studies abroad have concluded that use of Chrysotile in the manufacture of Asbestos Cement Products under controlled conditions is safe for the workers, environment and the general public.

Source: http://acpma.com/uses-in-west.html

Asbestos & Health

Chrysotile is an inert material and is not toxic to touch, smell or ingestion. Chrysotile fibre can be an occupational health hazard only when its dust is respirable and becomes airborne and when such a dust is inhaled in excessive amounts over a prolonged period. Chrysotile fibre is not a hazard when proper dust control procedures are in operation. Low level exposure to chrysotile, within the limits stipulated by the national and international health authorities poses no measurable risk.

Health risk at a workplace due to inhalation of respirable dust is not unique to chrysotile fibre. Virtually all respirable materials are potential health risks when used in uncontrolled conditions. Chrysotile is only one among such fibres.

In the Western world, during the period of ignorance asbestos fibres of all types including amphibole varieties, in loose form, was extensively sprayed on ceilings and structures to conserve heat. It has been proven by later scientific studies that the health problems that were evidenced in the subsequent decades in the West were due to unregulated and irresponsible usage of asbestos, largely consisting of amphibole varieties. Mining, production and usage of these amphibole varieties of asbestos have subsequently been given up.

In today's well controlled and regulated industrial plants using only Chrysotile type of fibre, occurrence of such diseases do not arise. Nor are any health risks associated with the products containing chrysotile-cement mix, such as corrugated roofing sheets, plain sheets, pressure pipes, etc. etc. as the chrysotile fibre is bonded with cement and cannot escape in to the surrounding environment.

Indian Experience

Permissible Exposure Limit Value (PELV) - As technology has advanced the exposure of workers to Chrysotile fibre in the manufacturing process is kept well below the Permissible Exposure Value (PEV) of 1 f/cc as stipulated by the Ministry of Labour in the Factories Act.

During 2004 & 2005 The Directorate General Factory Advice Service and Labour Institutes (DGFASLI), under the Ministry of Labour, Government of India, undertook studies on "Health Status of Workers in the Asbestos Industry" and "Status of Work Environment in Asbestos Products Manufacturing Industry".

These studies covered 9 factories using Chrysotile fibre in the manufacturing process. A total of 702 workers in the age group of 20 to 50 years were covered. The studies concluded that the workplace emission levels in these industries, were well below the stipulated levels of emission, that is, 1 fibre/cubic centimetre and that no case of asbestosis was detected during the study. (asbestosis is a respiratory disease associated with excess inhalation of asbestos fibre of various types over a prolonged period). Click here for DGFASLI Reports

References:

• Gaensler EA, Asbestos-Related Disorders - Clinical and Epidemiological Aspects, Proceedingsof the Fleischner Society Eighteenth Annual Symposium on Chest Disease. Montreal 1988,17-31.
• Doll R. Mortality from Lung Cancer in Asbestos Workers. British Journalof Industrial Medicine, 1985, 12:81
• Berry G.Newhouse ML.Turok M; combined Effects of Asbestos Exposures and Smoking on Mortality from Lung Cancer in Factory Workers. Lancet 1972, 2:476
• Wagner J.C. et al, British Journal of Industrial Medicine 45: 305-308 (1988).
• Peter Elmes; Mesotheliomas and Chrysotile; The Annals of Occupational Hygiene Vol.38, No.4, August 1994, 547-553
• The National Study on Status of Work Environment in Asbestos Products Manufacturing Industry, 2005.
• The National Study on Status of Workers in the Asbestos Industry, 2004.

Source: http://acpma.com/asbestos-health.html 

Asbestos Cement Products: Truth held hostage – Understanding the facts about White Asbestos

Fact – Dictionary defines fact as verified information about past or present circumstances or events which are presented as objective reality.

In case of present usage of Asbestos, facts are often misrepresented and contorted to present a picture far from reality.   The differentiation of types of asbestos fibers is deliberately ignored by certain anti-asbestos groups.   They omit to mention that White Asbestos, which is only used now, is completely safe under controlled conditions. 

The Asbestos Cement industry has always supported an extensive range of domestic and commercial requirements of the society. Yet the industry has been under constant threat of several myths and negative propaganda. The awareness about asbestos are at a very low level and most people even do not know that there are different types of asbestos and risk potential differs by product and process. It occurs in a number of different forms and the risks posed by them vary considerably... from minimal to severe.

The Asbestos Cement industry, a Rs. 4,500 crore industry, generates employment for about 3 Lakh people in India and contributes over 20 % of the turnover to the government’s exchequer by way of direct and indirect taxes.  Still the usage of asbestos (even white asbestos) has been made by certain groups of vested interests as a contentious issue. It is a misconception that asbestos is hazardous to health, whereas the fact is that today it is not the mixed varieties of asbestos, but it is only Chrysotile (White fibre) variety which is used as approved by national and international scientific authorities and governments. Only safe white fibre is used in India and the unsafe blue and brown fibres are banned. Asbestos Cement products are eco friendly and contain only 8% of white asbestos while the rest consists of Fly ash (30%), cement (40%), water (20%) and pulp (2%). Chrysotile is a natural mineral without any known hazards under controlled usages in Asbestos Cement manufacturing process.

Various organizations are working on a negative propaganda against asbestos and are being funded by multinationals from European Union who want to promote their substitute products in the Indian market. These organizations get active support from steel sheet and pipe manufacturers’ lobby in India which commercially benefits by the increased sale and market share of metal roofing sheets and metal pipes, if manufacture of Asbestos Cement Sheets and Asbestos Cement Pipes is discontinued in India. The campaigns by these organizations are not based on any scientific evidence in India or elsewhere, and are totally dictated by vested commercial interests. The Activists try to create hysteria by quoting data and experience of past Asbestos usage notably in the European Union, which has no relevance at all in Indian usage.

International and national anti-asbestos bodies allege that asbestos is a dangerous substance and can cause lung cancer. However, there has not been any case of death or lung cancer in asbestos cement plant in India. One of the studies conducted in 2004-05 by Central Labour Institutes of the Ministry of Labour, Govt of India, has not found any asbestos-related diseases in 8 factories.   Nor is there any evidence to show that people who lived under the asbestos cement roofing - even for decades - have had any adverse health effects.

The various inspections and studies of the government agencies from time to time and the health records of employees, including the retired employees has been the testimony to the claim that manufacture and use of asbestos cement products are not a health hazard to the employees or the users. All the production facilities are fully automated where the workers have no direct exposure to asbestos fibre. Workers have no chance of inhaling the fibre as the fibres are bound to cement, besides, workers are provided with all kinds of precautions like masks, in addition to proper environment engineering controls.

When it comes to products asbestos cement such as corrugated roofing sheets, pipes, etc. the asbestos fibers are bonded with cement and have no chance of getting airborne and polluting the environment. 

It can thus be concluded that Chrysotile asbestos is just as safe, if not safer, than the replacement products. There is no proof to the contrary, from either a scientific or a medical point of view. Chrysotile makes it possible to offer families roofs that are well built, safe, and affordable and that will not go up in smoke or be perforated by rust after a few years. Asbestos sheets provide a safe, heat protective, least-noisy roof to millions of poor people, farmers and their poultry and cattle. These are cost effective, durable and energy efficient. AC products serve the developing countries by providing durable and low cost house roofing’s and water pipe systems.

Source: http://www.allvoices.com/contributed-news/7471101