Asian-Pacific Regional Network on Occupational Safety and Health Information (ASIA-OSH). Mineral dusts and prevention of silicosis, vol 4; No.2, September 1997
Eradication of the silicosis problem in Singapore.
By Lee Hock Siang.
Updated by PAP/SUT/TRS.
Approved by BKL. Last updated on 12 February 2001
When Singapore launched its industrialisation programme in the 1960s, the importance of protecting workers from occupational health hazards was foreseen. The government established the Industrial Health Unit in 1970. Focusing attention on the problem of silicosis in Singapore was the new Unit. The Unit is now known as the Department of Industrial Health (DIH), Ministry of Labour.
The DIH keeps the statistics on all reported and verified occupational diseases. The Factories Act of 1970 made silicosis an industrial disease that should be reported. Silicosis was the leading occupational disease in the early 1970s, and it was the leading occupational respiratory disease in the 1970s and 1980s (Figure 1). At end of 1995, 362 cases of silicosis had been verified, 8% of which were contracted in granite quarries (Table 1).
High risk of silicosis in granite quarries in the 1970s
In 1970, there were 25 granite quarries employing about 1,200 workers. Quarry operations involve drilling, blasting and stone breaking at the quarry face; the granite rocks are then loaded and transferred to the crushing plant for crushing and screening. Dust monitoring carried out in 1968 and 1971 revealed very high dust levels.
A radiological survey of 1,188 granite quarry workers in 1965 revealed that 8% had silicosis. A follow-up survey of 1,230 quarry workers, carried out in 1971, showed that 15% had silicosis (1).
Consultation with WHO
The government took a serious view of the situation, and in 1972 a World Health Organization (WHO) consultant in industrial hygiene was engaged to study the dust control problems in granite quarries. The consultant concluded that there was a serious dust hazard in the quarries and recommended that: 1) quarry operators should be required to take action to reduce dust levels 2) each quarry should submit a plan of action 3) regulations should be developed for the control of dust in quarries 4) quarry operators should establish a dust monitoring programme.
All of these recommendations were implemented by the government.
Study on the sources and extent of dust emission
Following the WHO Study, the Singapore Institute of Standards and Industrial Research (SISIR) in 1972, in cooperation with the Granite Quarry Owners and Employers Association of Singapore, carried out a survey covering 21 quarries. The report published in 1973 (2) found that only one of the quarries had an effective dust control system and that 50% of the larger quarries had very high levels of dust emission. The major sources of dust emission were drilling operations, crushing units, screen units, transfer points and loading points.
In both the WHO and SISIR reports, local exhaust ventilation together with the wet method were recommended as effective means of dust control in quarries.
The Sand and Granite Quarries Regulations were enacted in 1971. Licensees of any quarry were required to install dust extraction systems, to provide dust masks and to provide quarry workers with annual chest X-ray examinations.
Silicosis was declared a compensable occupational disease under the Workmen's Compensation Act in 1972.
The Abrasive Blasting Regulations enacted in 1974 prohibited the use of sand as an abrasive for blasting. Hence there have been only very few cases of silicosis among sandblasters in Singapore.
To focus attention on the problem and to create awareness among both workers and management, in 1973 the Ministry of Labour launched a campaign against silicosis which included a mobile exhibition and media coverage. Quarry owners were called upon to take preventive measures to protect the health of their workers.
Implementation of dust control measures
Between 1972 and 1973, the government formally requested all the then 25 granite quarries to install local dust exhaust systems (3). Despite the expected technical and financial problems, the number of quarries which installed such systems increased from 12 in 1974 to 21 in 1976. SISIR was responsible for the design of most of the dust control systems. By 1979, all granite quarries had installed dust control systems.
Regular monitoring of dust exposure is essential in order to assess occupational exposure and to evaluate the effectiveness of dust control measures. There was a significant decline in dust levels, particularly after the implementation of dust control measures in 1973 (Table 2).
In a study of 201 quarry workers from five granite quarries, carried out in 1988, the prevalence of respirator usage was about 60 70% among drillers and crusher attendants, who were the more exposed group of workers (4).
Pre-employment and annual chest X-rays have been a legal requirement for granite quarry workers since 1972, and for all silica-exposed workers in factories since 1985. Chest X-ray screening is useful in the early detection of silicosis. As a result, a large number of silicosis cases were detected in 1973.
Decline of silicosis cases
There was a sharp decline in the number of new cases of silicosis after 1975, and a further decline after 1990 (Figure 1). In the 1990s, occupational asthma has replaced silicosis as the most common occupational respiratory disease (5). Only one case of silicosis was verified in 1995 and three cases in 1994. The persons concerned had previously been working in granite quarries for many years.
A radiological survey of 219 workers currently employed in six operating granite quarries, carried out in 1990, showed that the prevalence of silicosis among drilling and crushing workers was 12.5%, the prevalence among maintenance and transport workers being 0.8% (6). Among those first exposed to granite dust in 1979 or later, no cases of silicosis were detected, possibly suggesting that the reduction in dust levels achieved since 1979 has been successful in preventing silicosis among active quarry workers over the ten-year period.
Phasing out of granite quarries
In recent years, the government has stopped renewing the licenses of many quarries. The number of quarries has declined from 25 in 1970 to three in 1995.
Silicosis was a significant problem among granite quarry workers in Singapore during the early years of industrialisation. The government recognised the problem and sought the assistance of experts to study it and to recommend solutions. Legislation was introduced in 1972, and dust control measures were enforced. Public education was carried out at the same time. Dust levels fell significantly after 1973, and this was followed by a decline in the number of silicosis cases. Today, silicosis is no longer an important disease in Singapore.
1. Supramaniam JMJ, Devi S, Yeoh SA, Chew PK, Chow KW. A Radiological Survey of Granite Quarry Workers in Singapore. Proceedings of the 8th SEAMEO-Tropmed Seminar: The First Symposium on Occupational Health in South-east Asia, May 1971: 98 102.
2. Leow SB. Investigation into the Dust Emission from Granite Quarries in Singapore and Pulau Ubin. Singapore Institute of Standards and Industrial Research, 1973.
3. Tan KT. A Review of Dust Control in Granite Quarries. Singapore Community Health Bulletin 1979;20:34 9.
4. Chia SE. A Study of the Usage of Respirators Among Granite Quarry Workers in Singapore. Singapore Medical Journal 1989;30:269 72.
5. Lee HS, Phoon WH, Wang SYT, Tan KP. Occupational Respiratory Diseases in Singapore. Singapore Medical Journal 1996;37:160 4.
6. Ng TP, Phoon WH, Lee HS, Tan KT. An Epidemiological Survey of Respiratory Morbidity Among Granite Quarry Workers in Singapore: Radiological Abnormalities. Annals Academy of Medicine Singapore 1992;21:305 11.
Lee Hock Siang
Department of Industrial Health
Ministry of Labour
18 Havelock Road #05-01
REPUBLIC OF SINGAPORE
Originally posted to Pedal Ubin Mailing List, 15th March 2004