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epidemiological data
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
4 (not assignable)
Rationale for reliability incl. deficiencies:
secondary literature

Data source

Reference Type:
Clinical and Experimental Studies of the Effects of Pulverized Fuel Ash — A Review
Bonnell, J.A. et al.
Bibliographic source:
Ann. occup. Hyg., 23, 159-164.

Materials and methods

Study type:
cross sectional study
Endpoint addressed:
repeated dose toxicity: inhalation
Test guideline
no guideline followed
Principles of method if other than guideline:
Radiological studies of workers exposed to pulverized fuel ash (PFA) undertaken in the Midlands and South Wales between 1950 and 1961 are reviewed. A study of 246 boiler cleaners (not previously published) undertaken in the Midlands Region between 1974 and 1977 is described.
GLP compliance:

Test material

Constituent 1
Reference substance name:
Ashes (residues), coal
EC Number:
Molecular formula:
Not applicable (UVCB substance)
Ashes (residues), coal
Details on test material:
- Name of test material (as cited in study report): Pulverized fuel ash (PFA)


Type of population:
Ethical approval:
not specified
Details on study design:
- Type: Radiological studies on power station workers between 1950 and 1961 in South Wales and the Midlands, and between 1974 and 1977 in the Midlands alone.

Study 1)
Pilot survey to assess the occurrence of pneumoconiosis among personnel employed in the large pulverized coal fired stations in South Wales and the Midlands (1950-1951):
- In South Wales 572 men had an occupational history taken and had their chests X-rayed.
- In the Midlands 727 men were X-rayed only.

Study 2)
Since no pneumoconiosis was found in the general work force in 1950/1951, it was decided to concentrate further investigations on those employed in dusty environments. In 1954 a list of 142 men employed in dusty environments in nine power stations in South Wales was provided by the station managers; 137 of these men agreed to attend for a chest X-ray. This group included 72 boiler cleaners and 23 ash plant and coal plant attendants.

Study 3)
The third survey carried out in South Wales in 1957 which included a chest X-ray and an occupational history was based on a similar procedure.
A list of 135 men exposed to dusty conditions was obtained from the station manager. They were boiler cleaners, laggers and their mates, silica bricklayers and mates, and men from the ash and coal plant. Sixty-eight of these men had previously been X-rayed, 34 on two occasions, 34 on one occasion and 67 were X-rayed for the first time in 1957.

Study 4)
A fourth survey was carried out in South Wales in 1960-1961. 152 men attended for chest X-ray; 100 of these were employed as boiler cleaners, ash men, coal plant attendants, and precipitator and maintenance men. There were 22 men who had worked underground in coal mines for a varying number of years, and seven cases of pneumoconiosis were found amongst them. All had been previously X-rayed.

Study 5)
In 1974, a radiological survey of boiler cleaners was undertaken in the Midlands.
Owing to changes in pay structure boiler cleaning had become a full time job done by a mobile task force. In the past it was undertaken by ash plant attendants as part of a range of duties. Three readers composed the panel for interpretation of the X-rays, and included a radiologist, a chest physician with a special interest in industrial disease and a senior assessor of the Local Pneumoconiosis Medical Panel. The X-rays were taken on a single machine by the same radiographer. The study included a health questionnaire elicited by the Board's nursing staff.
A total of 281 employees were seen, 35 of whom were eliminated because they had less than one year's service in this category of employment.
This group represented 1652 man years of boiler cleaning, the average being 6.7 man years.
The consumption of cigarettes and tobacco was averaged out at 20 cigarettes daily (in the 67% who smoked) over a life time; 81 were non-smokers (33%).

- Disease(s): Pneumoconiosis

Exposure assessment:
not specified
Details on exposure:
The surveys were performed on the personnel employed in the power stations. Occupational lung diseases vary upon the different types of dust exposures. Many jobs in power stations involved exposure to the following types of dust:

Laggers are exposed to the special hazards of asbestos, although these exposures have been significantly reduced since the introduction of alternative lagging materials in 1968 and the strict adherence to the codes of practice for stripping asbestos since 1967.

Silica brick dust
Bricklayers and their mates who enter boilers to chip away worn and broken silica bricks are exposed to silica brick dust. Brick-lined boilers are a feature of the older type of stationary and moving grate boilers and not of the modern pulverized fuel type.

Pulverized fuel (PF)
Men working in the vicinity of the coal mills or of the pipes conveying PF from these mills to the boilers may be exposed to this dust. There are, however, strong safety incentives to keep PF levels to a minimum due to the high risk of explosion.

Pulverized fuel ash (PFA)
In spite of the fact that ash handling is mechanical and plant is enclosed, ash escapes and is deposited, sometimes in considerable quantities, on any surface available to it. Exposure therefore occurs when the dust is disturbed by electrical and mechanical fitters during maintenance. The men who would be expected to be most exposed to PFA are those involved in the maintenance and cleaning of boilers and precipitators. Boiler cleaning in modern pulverized fuel stations is done primarily by remote control, but there is a requirement for a small proportion of the work to be done by hand.

Results and discussion

Radiological studies of workers exposed to PFA undertaken between 1950 and 1961 did not reveal the existence of any pneumoconiosis (occupational lung disease) except in men with an occupational history of coal mining.
In a study of 246 boiler cleaners undertaken between 1974 and 1977 four men had category one or less pneumoconiosis which could only be explained on the basis of their employment with the Central Electricity Generating Board.

Confounding factors:
Most of the workers at the power stations had a occupational history of coal mining.
Other possible confounding factors were not specified.
Strengths and weaknesses:
Workers were exposed to different types of dust, not only to PFA.

Any other information on results incl. tables

Study 1: 1950/51:

This survey showed that there was no pneumoconiosis in the general population of the stations unless they had previously worked in coal mines. In the South Wales power stations 57 men were found to have pneumoconiosis and in the Midlands one man had the disease. Each one of these had worked underground as a coal miner for many years.

Study 2: 1954

Eleven men out of 137 were found to be suffering from pneumoconiosis and all had worked in coal mines. The severity of their disease was related to the length of time worked in the collieries. Nine of this group had been X-rayed 3 years previously and showed no evidence of any progression on this occasion. The remaining two were from power stations not previously surveyed.

Study 3: 1957

In this survey (135 workers), there were 10 cases of pneumoconiosis and 2 of pulmonary tuberculosis. Of the 10 cases of pneumoconiosis, 9 had worked as coal miners for many years, all had worked for more than 10 years and 6 for more than 20 years. The one man with pneumoconiosis who had not been a coal miner had worked for over 40 years as a ship's boiler cleaner. There were five cases of pneumoconiosis who had been X-rayed in previous surveys, but none showed any progression.

Study 4: 1960/61

Out of 152 men attended for chest X-ray, six men had simple pneumoconiosis and showed no progression. One man had advanced pneumoconiosis (progressive massive fibrosis) when X-rayed in the first pilot survey in 1950-1951; he was not X-rayed in 1954 or 1957, but showed definite progression in 1961 compatible with the usual course of the disease. Of the 152 men, 87 had been X-rayed on previous occasions, 53 of them on three or four occasions. It was pointed out by Dr Davies at the time that there were many imperfections in these surveys, no firm deductions could be made from a statistical point of view because they were done on a voluntary basis. However, it is significant that over 1700 films of 1465 workers in power stations in South Wales and the Midlands were examined by experienced doctors in co-operation with the Medical Research Council Pneumoconiosis Unit and no case of pneumoconiosis was found in this large number, except in men who had worked for many years underground in coal mines and the single case of the ship's boiler cleaner. Furthermore, the extent of the X-ray changes in these men were directly related to the number of years that they had worked in coal mines underground.

Study 5: 1974

Of the 246 men studied, there were 15 (6%) with category 1 or less pneumoconiosis, established radiologically. Eleven of the men (4.5%) had occupational exposure to dust before working for the Central Electricity Generating Board (CEGB) which could explain the radiological findings. In four men (1.5%) the radiological findings could be explained only on the basis of their employment with the CEGB. Three of this group had pleural plaques in keeping with previous or incidental exposure to asbestos. In addition, there were three other men with pleural plaques and no evidence of pneumoconiosis. Seventeen of these 18 men were followed up in 1977 and did not show any radiological progression.

Applicant's summary and conclusion

The results of all these studies indicate that PFA is unlikely to give rise to pneumoconiosis under similar working conditions.