Control at source
Transport, charge and discharge of asbestos and cement bags should be planned so as to avoid damage to the bags and injury to people; and provisions should be made for recovery of material after spills or transport incidents.
- Stores should be designed and maintained in order to minimize dust emission.
- Sources of dust emission (manufacturing machines, conveyors) should be enclosed at maximum.
- The exhaust ventilation should be located as close as practicable to the emission sources.
- It should be possible to introduce water inside of the bags prior to opening the bag by injection through a hole cut into the plastic, or immediately after removing the sewing string. However, the amount of water added to the bag must be controlled; otherwise the weight of bag is increased too much for easy handling.
Engineering and technical measures
Manual debagging and pouring stations could be incorporated a hood and exhaust ventilation. The hood for debagging should cover both sides and the back of space above the table, leaving only an adequate opening at the front so the bag could be cut, shaken and stacked inside. The airflow of exhaust systems should be calculated to ensure the hood under negative pressure and the exhausted air should be treated by appropriate air cleaning devices (fabric filter or cyclone-fabric filter).
- The asbestos in paper bag could be fed into the grinder without opening them.
- The conveyors should be designed to transfer the bags just to debagging and pouring stations, at the appropriate height to avoid unfavorable movement and posture.
- dry grinder should be enclosed and connected to exhaust ventilation system. The pouring and discharging point should be also incorporated a hood. The fiber treated in dry grinder must be conveyed to the next piece of equipment or silo using an enclosed conveyor or another safety device. It is improper procedure to discharge the treated fiber onto the floor or into the bags to be transported manually to the next stage. The grinder could be improved by water injection inside the machine.
- Even for the grinder and mixer using asbestos or asbestos-cement slurry, it should be used a cover to prevent material from splashing because the slurries can dry out and dust can then become airborne due to foot or vehicle traffic.
- In the plant using clinker grinder, clinker powder should be discharged to conveyor and transported directly to mixer. Even this is not feasible (i.e. 2 workshops are far each from other); using conveyor ensures the separation workers from grinder, which is a very high noise source. The conveyor should be covered and incorporated with exhausted hoods at both its beginning and end. It should be applied the noise control measures as maintaining and lubricating periodically machines, installing rubber layer and anti-vibration springs, building strong machine stands which has high cement concentration, and is isolated from the foundation by dry sand, isolating control room from manufacturing areas, etc.
- In production line using saturated steam curing, the flue gas containing some toxic gases as CO, SO2, NOx must be treated before discharging into the environment. The standards TCVN 6006-95 and TCVN 6007-95 on boiler safety must be ensured.
- It should ensure proper guarding of the moving parts, proper railing of platform and ladder. It should provide the safety posters and safety operation regulations at workplaces.
- Workshops and stores should be well designed to meet all the standards for heat prevention and air ventilation. Workshops, stores and equipment must be incorporated by anti-thunder system. All facilities of fire prevention and fire extinguishing should be provided according to standard TCVN 3990-84.
- Housekeeping and waste handling
- Regularly maintain good housekeeping over machines, equipment, ventilation system, air cleaning devices and floor.
- The empty bags should be cut and reused as raw material or deposited in plastic bag or container and then should be buried in approved landfill site. Used asbestos bags must not be reused for other purposes.
- The sheet debris is considered as solid waste and should be grinded and returned to process. In case it is not possible, this material should be wetted, collected and disposed of. The process water and scrubber water can be collected in silos and reused after a simple settling process. The solid settled in silos and settling tanks can be returned to the process using as raw material.
- The dry dust from air cleaning devices could be collected in thick nylon bags, labeled, well tied and buried in approved landfill site.
Personal protective equipment
- The employer must respect all regulations on PPE required in Circular No 10/1998/TT-BLDTBXH Mai 28, 1998, Circular No 955/QD-BLDTBXH September 22, 1998 and No 1320/1999/QD-BLDTBXH October 6, 1999.
- The employer must provide at no cost to workers, and require the use of protective clothing, at least 2 pieces per quarter. The clothing should be loose-fitting, comfortable, long-sleeved, good material which minimizes general heat stress and discomfort. The clothing should be cleaned, laundered and should not be taken outside the factory. The clothing should be laundered regularly inside the factory, and in case laundering outside, they should be vacuum cleaned or wetted and put in nylon bag.
- For the workers, especially who work in manual transportation, maintenance, waste solid collection, debagging and grinding, the employer should provide personal protective equipment including cloth-masks, helmets, gloves, etc. When the airborne concentration is over the permissible limits, workers should wear special mask or semi-mask. This equipment should be selected, used, maintained, stored and replaced in accordance with guidance set be the competent authority and should not be taken outside the workplace.
Workplace monitoring and personal monitoring
The competent authority, e.g. the National Institute of Labor Protection, the National Institute of Occupational and Environmental Health, the Construction Hospital, should carry out monitoring annually. Employers should have representative data on airborne concentration of reparable and total fiber, dust or both; on microclimate factors, noise level and lighting at overall workplaces. Based on monitoring data, the competent authority and employer should decide the implementation of necessary measures in order to improve working conditions ensuring all factors of working environment in permissible limits. Where concentrations of fibers and dusts may vary from on work operation or phase to another, personal sampling should be collected in workers’ breathing zone in order to evaluate the risk to the individual worker. Personal sampling should have been taken for maintenance and housekeeping operations. Working environment monitoring may implement by the followed methods or by international techniques:
- Concentrations of asbestos fiber should be measured according to standards “TCVN6504: 1999 – Air quality – Determination of the number concentration of airborne inorganic fibers by phase contrast optical microscopy – Membrane filter method” or “TCXDVN 268:2002 – Air quality- Determination of the number concentration of asbestos fibers by phase contrast optical microscopy – Membrane filter method”.
- Total dust concentration should be measured according to standards “TCVN 5704:1993 – Air quality at workplace- Determination of dust content method” or “TCVN 5067:1995 – Air quality – Weigh method for determination of suspended dust content”.
- Concentration of certain toxic gases emitted from boiler area (CO, NOx, SO2) should be measured according to standards “TCVN 8186:1989 – Ambient air – Determination of mass concentration of carbon monoxide- Gas chromatographic method”, “TCVN 6137:1996 – Ambient air – Determination of mass concentration of nitrogen dioxide – Modified Griess-Saltzman method”. Mass concentration of sulfur dioxide may be determined by several ways depending on its content in air.
- Noise levels should be measured according to standards “TCVN 3985:1999- Acoustics- Allowable noise levels at workplace”.
- Microclimate factors should be measured according to standard of Ministry of Health 3733/2002/QD-BYT.
The results of workplace and personal monitoring should be collected in a systematic way, and retained for at least 20 years. Records should include all relevant data such as detail of site, raw material, product, method of use including the engineering control measures. Workers or their representatives should have access to monitoring record relevant to their own exposure and to the purpose of prevention and protection. All relevant parties should be encouraged using this database for the purpose of scientific and epidemiological research, choice of technology and mitigation measures of working environment.
At present, the published data of working environmental quality in AC roofing tile enterprises is mainly by different projects or surveys. For example, the survey results of project “Mitigation measures in Building materials industry” (2003) of Ministry of Construction show that most of AC roofing tile production stages are polluted by total dust, including sheet formation area that is affected by dust from other areas. If comparing with asbestos fiber concentration threshold value required by Ministry of Health (0.5 fiber/cm3, 1-hour average), rate of over allowable limit samples at asbestos related workplaces is rather high, especially at asbestos stores (100%) and asbestos crushers (67,5%). Following survey data of project “Assessment of environment status of roofing tile production enterprises and impacts to people’ health. Recommendations and options” (2003) implemented by Ministry of Natural Resource and Environment and Ministry of Education and Training, there are more than 80% of enterprises using open asbestos crushers and raw material mixers so create dust dispersion all over. The percentage of enterprises applying dust and wastewater treatment facilities is only about 30%. Most enterprises are considered polluted; especially 78% of enterprises are polluted with asbestos fiber in workplaces. The highest number of asbestos fibers in the workplace assessed as the heaviest polluted area is 4.2 fibers/cm3 that means 8.7 times higher than the standard value required by Ministry of Health. The survey results of 23 AC roofing tile production enterprises carried out by Ministry of Health (2005) show that the asbestos fiber concentrations are 4-10 times higher than the standard value in 10 enterprises, and higher than 1- 1.5 times in 13 enterprises.
Surveillance of workers’ health
Health surveillance programs for workers should be consistent with the requirements of Circular No 13/BYT-TT, October 24, 1996 of Ministry of Health. All workers should have the right of pre-assignment medical examination, periodic medical examination, occupational diseases examination and employment cessation medical examination. All employees must be examined every year. Occupational diseases examination and periodic medical examination could be carried together or separately. In special circumstances (e.g. when there is some suspicion of occupational diseases), the examining doctor may specify more frequent examinations. Frequency of chest X-ray should be in accordance with years since first exposure, age of employee and exposure dust concentration.
Beside of the minimum medical examinations required by Ministry of Health, the workers exposed to hazardous factors should have a complete physical examination with emphasis on:
- Examination on asbestosis, lung cancer and mesothelioma;
- Examination on silicosis: clinical examination, pulmonary function test, chest X-ray;
- Chronic bronchitis examination: clinical examination, pulmonary function test;
- Occupational deafness examination: eyes, ears and throat examination, hearing test.
- Workers having occupational diseases should have personal file, should be examined and treated in specialized centers approved by Ministry of Health like the Building Hospital, provincial preventive centers.
According to several surveys and epidemiological studies of National Institute of Occupational and Environment Health, the clinic examination shows that the workers in asbestos roofing plants have 9 symptoms of respiratory disease including permanent cough and expectoration, chest tightness, chest pain, sinusitis, rhinitis, acute and chronic bronchitis, pneumonia; the risk having these symptoms, respiratory disease, lung function disorder syndrome and other unusual symptoms of workers exposed to asbestos dust is higher than that of workers exposed to cement dust. The results of occupational disease have showed the most common occupational disease in asbestos roofing plants should be silicosis.
Following survey data of project “Assessment of environment status of roofing tile production enterprises and impacts to people’ health. Recommendations and options” (2003) implemented by Ministry of Natural Resource and Environment and Ministry of Education and Training, by chest X-ray examination for 1,032 workers having the longest exposure time to asbestos it had discovered 4 cases of light asbestosis (1/0t and 1/1s). At that time, this is the unique specific data regarding to health impact of asbestos exposure in Viet Nam. There are also some cases of lung cancer, silicosis, injury or malformation of lung, but they are not specific symbol of asbestosis exposure.
According to the summary of provincial and local health reports during two years 2005 and 2006, there are defined 270 cases of mesothelioma, one asbestos- related disease.
Information, training and consultation.
Information, instruction and training should be realized in many ways: broadcasting station, posters, documents, training courses (inside or outside company) or workshops/conferences to inform to different audience groups.
All companies should carry out the OHS information, training in accordance with the Circular No 08/BLDTBXH-TT April 11, 1995 and Circular No 23/BLDTBXH-TT September 19, 1995 of Ministry of Labor, Invalids and Social Affaires. The content of information, training and education should be designed properly for each scope: employer, supervisors and employees, and as a minimum, meet the requirements of the competent authority. It is recommended that the information and training contain the following:
- Applicable laws, regulations and codes of practices;
- Labels and material safety data sheets;
- Preventive and control measures of hazards and risks;
- Working environment monitoring data in related workplace;
- Potential acute and chronic health affects which may result from exposure to hazardous and risk factors, especially to asbestos;
- The responsibilities of manufactures, supplies, installers, employers and workers, as well as the need for cooperation between them, etc.
Awareness raising activities related to asbestos exposure could carry out by enterprises of other organizations. The National Institute of Labor Protection, with its duty of implementation of workers protection measures, deploys the project namely “Developing propaganda and awareness raising activities on safety use of asbestos chrysotile for workers in AC roofing tile production enterprises”. Beside activities as organization of training courses on safety use of asbestos chrysotile, design and distribution of leaflets, posters, training materials, etc, the project will host the conference “Asbestos in production and safety measures” in August 2008.