Silica dust hazards in Vietnamese foundries - Asian-Pacific Newsletter on Occupational Health and Safety

2. Overview: Current situation in Vietnamese foundries

2.1) Metal casting and its typical pollutants

2.2) NILP studies, 1981-1985.

2.3) Results of initial foundry investigations in 1998

2.1 Metal casting and its typical pollutants

Metal casting is a process in which molten metal is poured into heat-resistant moulds. The basic principles of foundry technology have changed little in thousands of years. However, in industrially developed countries, many stages of the process have been mechanized or automated. In Viet Nam, foundry technology is by those standards obsolescent. Manual labour is still the rule, except where mechanized equipment is necessary. In addition, lack of or ineffective dust-control systems makes the working environment more hazardous.

A brief description of the main foundry processes helps to establish the background to the current situation in Vietnamese foundries:

Making a pattern of the desired article. Traditional wooden patterns remain the most common practice in Viet Nam. Pollutants include noise and wood dust from sawing and cutting machines.

Making the mould and core and assembling the mould. There are two types of moulds: A "green" sand mould is made from silica sand, coal dust, clay, and organic binder. Green sand mould does not need drying. A dry mould, on the other hand, uses silica sand, clay, and water, painted with molasses and coal dust. The mould is then dried in an oven. Moulds are also distinguished by their form: on a sand floor or in a flask. Normally, casting on a sand floor is used for small articles, flasks for casting large ones. The danger of dust in the moulding process is minimal because the moulding sand is usually damp – except where sand mixer and muller, which are often significant sources of dust, are involved.

Melting the metal. Iron melting is often done in a cupola. Scraps of iron, coke, and limestone, charged in layers, provide the raw material. A fan blows air into the cupola. Melting, at temperatures of 1200-1250⁰C, requires 5 to 6 hours, depending on the capacity of the cupola. The molten iron is poured into ladles which, in turn, are used to pour the material into moulds. Pollutants include fumes, toxic gases, dust, and noise. Where induction furnaces are substituted for cupolas, there is less pollution. Steel melting furnaces employ an electric arc. Raw materials include steel bars, steel scrap, and additives. The temperature in the furnace can be adjusted by changing the elevation of the electrode. When steel is melted at temperatures of 1400-1450⁰C, ingots are often added to adjust the carbon component in the steel. Aside from that, the process is similar to that of iron casting. Pollutants include fumes, toxic gases, dust, and noise. Less dust is generated in steel melting than in iron melting. Very often, however, melting furnaces without hoods emit dust and fumes inside the station, polluting upper zones such as that where crane cabins are located.

Cooling the casting and removing the mould. After cooling, the casting is removed, or "shaken out" of, the mould either manually or using a vibrating grid. The sand is collected, treated, and either re-used or dumped. This workstation is especially hazardous because in contact with hot metal sand changes its crystal structure, becoming more toxic. Exposed to high levels of dust and work intensity, workers at this station are at high risk of silicosis.

Cleaning the casting. After removal from the mould, the casting is cleaned. Cleaning includes removal of burnt-on moulding sand, cutting away surplus metal, and surface finishing. Cleaning tools include pneumatic hand chisels, grinders, and welding or cutting torches. This process is a major source of dust and noise. Advanced technology uses steel shot-blasting or, better, water or water and sand shot-blasting in an enclosed cabinet, eliminating exposure to hazardous silica dust.

2.2 NILP studies, 1981-1985.

From 1981 till 1985, Thai Quang Hoe and others from the NILP carried out State Research Project #58.01.02.02: "Study and application of technical measures to protect workers from silicosis in foundries in Viet Nam".

The project selected Tran Hung Dao, a manufacturer in Hanoi, together with eight other foundries throughout the country as pilot sites for study. Dust concentration measurements were conducted mainly at the Tran Hung Dao mechanical company. Silicosis and general health studies were carried out on a total 1,520 workers.

Some study results follow.

Environmental measurements

Table 1: Dust concentrations (mg/m3) in foundry work stations

Work station	Total dust concentration (mg/m³)	Portion (%) of respiratory dust (2-5 mm )	Percentage (%) of free silica (SiO₂ )
Materials mixing	14.8-41.1	1-8.6	80
Making moulds	7.8-27.8	25	24
Metal-melting furnace	1-7.9	14.3	24
Removing castings	7.4-14.8	25	64
Cleaning castings by hand	7.9	25.8	32
Crane cabin	5.3	-	40
Handling used sand	22-32	14.2	40

Source: NILP,1982

Comments

The percentage of free silica (SiO₂) in foundry dust fluctuates between 24 and 80 per cent, depending on the process stage. Average proportions of free silicaare highest (80 per cent) at the materials-mixing stage, while they are lowest (24 per cent) in the mould-making and furnace stages. During removal of castings, it averages 64 per cent.

Dust concentrations are highest (22-32 mg/m3) during sand handling, while they are lowest (1-7.9 mg/m3) during the melting and pouring of iron into the mould. Dust concentrations (7.4-14.8mg/m3) are relatively moderate at the mould- and core-removing stages, but they are especially dangerous because they contain a high percentage of free silica. The average proportion of respiratory dust is highest (< 5 m m) during the cleaning of castings (25.8 per cent) and lowest (1-8.6 per cent) during materials mixing.

These studies indicate that air in foundries is polluted by dust with a high percentage of free silica and a very high portion of respiratory particles. Removal of castings from moulds and cores and cleaning of castings are particularly dangerous stages in the foundry process.

This is the main reason for the high rate of silicosis among foundry workers.

Results of silicosis studies

From 1982 till 1985, NILP researchers selected 1,520 workers for medical examinations, including chest X-rays, from the following factories: Hanoi Mechanical Company, Foundry Company Number 1 (Ho Chi Minh City), Ha Son Binh Mechanical Company (Hatay Province), Quang Trung Mechanical Company (Hanoi), Mai Dong Mechanical Company (Hanoi), Instrumental Company Number 1 (Hanoi), and Ha Nam Ninh Mechanical Company (Hanam Province).

Among the 1,520 workers examined (831 men and 689 women), 608 workers were found to be suffering from silicosis (370 men and 238 women). Percentage of silicosis cases is 40 per cent (608/1,520) of which men occupied 24.3 per cent (370/1,520) and women 15.7 per cent (238/1,520). Men suffered 60.8 per cent and women 39.2 per cent of the 608 silicosis cases.

Silicosis was distributed in terms of degree of severity as follows:

Table 2 Silicosis cases, distributed by degree of severity

Silicosis, degree of severity	Number of silicosis cases	Percentage (%)
1/Op 1p 1/2p 2p 2/3p 3p 1m 2m A	180 150 98 86 76 14 11 12 4	29.6 24.4 16.1 14.2 12.5 2.3 1.81 1.97 0.16
Total	608	100.0

Note: These categories are based on ILO International Classification of Radiographs of Pneumoconioses (1980). Severity is described as profusion from 0/- to 3/+, based on assessment of the concentration opacities by comparison with the standard radiographs. P,m and A define the greatest diameter of the predominant opacities

Table 3 Silicosis cases, distributed by working history (in years)

Working years	Examined	Silicosis cases	Percentage %
Working years	Examined	Silicosis cases	Compared with examined	Compared with sufferers
< 5 6-10 11-15 16-20 21-25 26-30 >30	286 453 430 187 82 53 29	44 113 240 95 55 40 21	15.4 24.9 55.8 50.8 67 75.5 72.4	7.2 18.6 39.5 15.6 9.0 6.6 3.5
Total	1 520	608		100

Table 4 Silicosis cases, distributed by skill rank

Skill rank	Numbers of examined workers	Numbers of silicosis cases	Percentage %
Skill rank	Numbers of examined workers	Numbers of silicosis cases	Compared with numbers of silicosis cases	Compared with numbers of examined same skill
II III IV V VI VII	249 244 713 206 98 10	33 168 263 94 42 8	5.4 27.6 43.3 15.5 6.9 1.3	13.3 68.9 36.9 45.6 42.9 80
Total	1 520	608	100	-

Note: Skill rank is a common occupational classification in Viet Nam. Ranks in the foundry vary according to the job performed. For example, in the moulding stage a worker of the 2^nd rank can make simple moulds, while workers of higher make more complicated shapes.

Table 5 Development of silicosis among 122 cases observed from 1980 to 1984

Year	Number of silicosis cases	Silicosis degree
		p				m		A
		1p	2p	3p	Total	1m	2m	A
1980	122	100	19	1	120	1	1	0
1984	122	90	13	0	103	11	7	1

Note: P, m, and n are abbreviations for Latin words. P stands for puntiformis; m stands for micro nodularis; and n stands for nodulavis. The figures indicate the degree of silicosis classified according to ILO/WHO Classification.

Comments

The studies involved a significant number of workers in various foundries ranging in size from medium to large scale, and the following remarks can be made with some confidence:

A high proportion of foundry workers (40 per cent) suffer from silicosis. This represents a clear warning regarding employee health.

Although the percentage of sufferers is high, the illness does not develop much from one degree to another. Few people suffered from silicosis of m and A degrees, and none were at the n, B, or C stages. This suggests worker health was generally bad because they had to stop working when the illness had not yet developed to a more severe stage. They were released from the production line because they were unable to work.

The incidence of silicosis is related to skill ranking in the same way that it is to number of working years. That means the higher the skill rank, the higher the incidence of silicosis. And it means that very few skilled workers are found on the production line in foundries. Production-line workers are mainly of rank II, III, IV (see Table 4).

Among 122 afflicted workers, after 3-4 years, only 18 per cent of the cases had developed a more severe form of the illness. This rate is not very high. Nevertheless, prevention measures should be considered.

2.3 Results of initial foundry investigations in 1998

Comprehensive statistic data about Vietnamese foundries has never before been available. This study means to provide, among other information, the following:

number of foundries
number of workers working in foundries
number of workers suffering from silicosis
number of work-related accidents in foundries
technological state of foundries, including dust-abatement measures

In order to collect information, the Project has used as collaborators organizations such as the Trade Unions Net, which is active in provinces, industries, health departments, and health centres. However, given limited time and its wide range of concern, the Project has not received as many reports as expected. So far, only 20 provinces and 61 cities have reported, and 6 provinces reported not having a foundry. All relevant ministries – the Industry, Construction, Transport, Agriculture and Rural Development, and National Defense ministries – have submitted good reports.

Although only 30 per cent of provinces and cities and some ministries reported, it was in these areas that most foundries and foundry workers were concentrated. Therefore, the available data. presented in Table 6, can serve as the basis for analyzing foundries in Viet Nam.

Distribution of foundries and workforce by province and industry

The Agriculture and Rural Development Ministry led the list, with 15.7 per cent equals 13 of the 83 foundries. The National Defense and Industry ministries accounted for 12 out of 83, or 14.5 per cent. The Transport Ministry accounted for 8 of the total, or 9.6 per cent, while, with 6 out of 83, Hanoi accounted for 7.2 per cent. Provinces such as Can Tho, Nam Dinh, Son La, Nghe An and Thai Binh had only one foundry each, accounting for 1.2 per cent each.

However, simple foundry numbers did not accurately represent the magnitude of the industry in each case. Production capacity and worker numbers were also important. Among a total of 4,028 workers, the Industry Ministry stood at the top of the list, with 32 per cent. The Defense Ministry was next with 11.9 per cent, followed by Quang Ninh with 8.4 per cent, Dong Nai with 7.9 per cent, Hai Phong with 7.8 per cent, Hanoi with 6.6 per cent, and the remaining provinces and industries together accounting for 25.4 per cent.

No child labourers were found in state-owned foundries.

Incidence of silicosis

Statistic data indicate that, among a total of 4,028 workers, 383 (317 male and 66 female) suffered from silicosis. In other words, 9.5 per cent of the total were victims, 7.9 per cent of the total being male and 1.6 per cent female. Of the 383 actual sufferers, 82.8 per cent were male and 17.2 per cent were female.

The Industry Ministry had the greatest number of sufferers, with 171 out of the total 383, or 44.6 per cent. The National Defense Ministry was next, with 62, or 16.2 per cent; followed by Hanoi with 47, or 12.3 per cent; Quang Ninh with 29, or 7.6 per cent; the Construction Ministry with 22, or 5.7 per cent; the Transport Ministry with 17, or 4.4 per cent; Hai Phong with 13, or 3.4 per cent; and the remaining provinces and industries with only an insignificant portion. (Figure 1)

Some provinces with large numbers of foundry workers have yet to identify silicosis victims. But any conclusions regarding incidence of silicosis, in these cases, must await investigation of local examination and X-ray procedures. For example, the 1998 figures are only about one-quarter those reported in 1985, with reported female victims 9.8 times fewer. (See Table 2.)

The following factors may be responsible for the apparent change in the incidence of silicosis:

The 1985 data came from high-capacity foundries employing significant numbers of workers. These workers had all received medical examinations including chest X-rays. Where silicosis existed in this sample population, it was identified. The 1998 data, on the other hand, are merely statistics reported by provinces and industries. In many cases, workers exposed to silica dust had not been given medical exams and chest X-rays.
Some technological improvements have been made, however, and dust concentrations at the mould-making stage, for example, have been much reduced. This would also help to explain the figures concerning females, since a disproportionate number of women are employed in mould making.

Work-related accidents

Given insufficient statistic data, it is difficult to evaluate work-related accidents. However, it is obvious that accident rates remain high in provinces such as Da Nang (19), Can Tho (16), and Cao Bang (12). Common foundry accidents include burns from hot metal and pinching from crane chains.

Recommendations: Methods of information collection and assessment

The collection of information on foundries should continue, using Form 3 (See Annex 3) to update the existing data.
The Presidium of the VGCL requires that trade unions in cities, provinces and industries with foundries be given the responsibility for administering Form 3 and sending the collected data to the NILP every year before the end of November.
The NILP needs financial support from the VGCL, with about 20 million VND required to pay those who fill in Form 3 and send the data to the NILP for assessment.
The results of data collection and assessment should be disseminated to national taskforces on the elimination of silicosis.

Table 6. Statistics on Vietnamese foundries (1998)

Updated by PAP/SUT/TRS. Approved by BKL. Last updated on 21 November 2000