About Silicosis

Silicosis is the commonest and one of the most serious occupational diseases. It is irreversible fibrosis of the lungs caused by inhalation of free silica dust. It is estimated that about 3 million people working in various types of mines, ceramics, potteries, foundries, metal grinding, stone crushing, agate grinding, slate pencil industry etc., are occupationally exposed to free silica dust and are at potential risk of developing silicosis. Silica exposure also predisposes to development of pulmonary tuberculosis, which is an important public health problem in the country. Some of the landmark studies carried out by NIOH are as follows:

Slate pencil cutting is a cottage type of industry, located in the Mandsaur district of M.P. Slate pencils are made by cutting slate stone on a circular electric saw and during this process, clouds of dust are generated pervading the work environment. An environmental and epidemiological study consisting of clinical examination, pulmonary function test, chest X-ray and laboratory investigations, carried out in slate pencil workers revealed following results:

The air borne free silica dust levels were several times higher than the limits prescribed under the Factories Act. Radiological evidence of silicosis was observed in 54.6% slate pencil workers and progressive massive fibrosis.

(PMF) was found in 17.7% slate pencil workers. About 50% of the workers suffering from silicosis were below 25 years of age and had worked for less than 7 years. Immunological studies among workers having silicosis showed increase in the levels of serum IgG and serum IgM. Pulmonary function test showed high prevalence of obstructive type abnormality and these abnormalities were seen even in workers with normal chest radiograph.

Follow up examination of these workers after an interval of sixteen months revealed rapid progression of the disease and it was related to the stage of silicosis during initial examination. About 4% of the subjects who had participated in the initial survey died during the intervening period. Their mean age at the time of death was 34.7 (18-55) years and the mean duration of work was 11.75 (3-20) years. All the deceased subjects were male and were suffering from PMF.

Agate grinding and polishing is a traditional vocation in the Khambhat Taluka of Gujarat and Jaipur (Rajasthan). Following sporadic reports of silicosis and deaths among the agate grinders, NIOH carried out detailed clinico-radiological survey of agate workers which showed that the problem of silicosis was most severe among the agate grinders.

The prevalence of silicosis in male and female agate grinders was 39.8% and 34.2% respectively. About 19% of the male agate grinders and 22% of female agate grinders developed silicosis within five years. The overall prevalence of tuberculosis amongst male and female agate grinders was 37.4% and 40.3% respectively. Pulmonary function abnormalities were found in about 51% grinders.

The mean "total" and "respirable" dust concentrations during agate grinding were 25.4 (14.5 - 35.1) and 2.74 (1.73 - 4.04) mg/M3 respectively, which are much higher than the prescribed limits. The free silica contents of the dust was 60%.

An environmental and epidemiological survey carried out in stone quarry workers revealed evidence of silicosis in 22.4% workers. About 32% workers showed radiological evidence of tuberculosis. Most of the cases of silicosis were found in the workers who had worked for over 10 years.

The mean total dust concentrations in two quarries were 3.38 and 3.72 mg/M3 and respirable dust concentrations in two quarries were 0.80 and 0.85 mg/M3 respectively with about 70% free silica.

Radiological examination of mica processing workers revealed evidence of pneumoconiosis of category 1 or more in 6.23% workers and evidence of pleural thickening was found in 4.3% workers. In female mica processing workers the prevalence of pneumoco-niosis was 2.7%.