Industrial Dust Diseases

The term "pneumoconiosis" refers to a group of lung diseases caused by the inhalation and retention in the lungs of dusts. The most commonly occurring type of pneumoconiosis, apart from asbestosis, is coal workers' pneumoconiosis, arising from the inhalation of coal dust. There is a long delay of at least 10 years between exposure and onset of the disease and hence most new cases or deaths from pneumoconiosis reflect the working conditions of the past. In the case of asbestos, the latent period for onset of disease may be from 15 to 60 years.

There are a number of prescribed industrial diseases. This means that if a person can show good reason to believe that he is suffering this disease as a result of industrial exposure, he shall be liable for compensation.

The word silicosis comes from the Greek word silex, meaning flint. Hippocrates and Pliny referred to this disease making it perhaps the oldest known occupational disease. .

Greater understanding of the causes of industrial lung disease, as well as enforcement of legislation by the Health and Safety Executive, have reduced the risk of industrial dust disease. Exposure today is nowhere near the scale found in the 1950s and 1960s. This cannot remove all risk from all occupations. In addition, some people may suffer exposure in ignorance or through neglect. Industrial lung disease has a very marked male preponderance but this is most likely related to occupation rather than inherent susceptibility.

An industrial lung disease may not present until some time after exposure has finished. Therefore, an employment history should include past as well as current occupations. This also accounts for a continuing high incidence of industrial lung disease despite much better working conditions.

Disease from exposure to asbestos accounts for over 3,500 deaths each year. It is the commonest cause of death relating to work in the UK and is about the same as the number of deaths on the roads. Although the use of asbestos has been banned, much of the material still exists, particularly in buildings. There is still the potential to kill those who are unknowingly exposed to the fibres in their work, or those who choose to ignore the controls that provide effective protection during work with asbestos.

In 2003, asbestosis was cited on 113 death certificates. In 2004, Disablement Benefit for asbestosis was awarded to 750 people. The annual number of mesothelioma deaths has increased from 153 in 1968 to 1,874 in 2003. This will probably continue to rise until between the years 2011 and 2015. There were 75 new cases of disablement in 2004 due to asbestos-related lung cancer and 132 reports of the disease. These numbers are substantially lower than the likely annual total number of deaths inferred from the number of mesotheliomas.

There were 1,160 new cases of pneumoconiosis, excluding asbestosis, assessed in the Industrial Injuries Scheme in 2004. These numbers are rising but almost certainly due to publicity about compensation as the mining industry in this country has been in decline for many years and 65% of claimants are over 65 years old. Chronic bronchitis and emphysema became prescribed diseases in September 1993 for coal miners with a specified level of lung function impairment and a minimum of 20 years underground exposure to coal dust. The numbers have fluctuated considerably, based more on publicity and relaxation of criteria to be able to claim rather than upon incidence.

There are 3 types of asbestos, all of which are dangerous but the blue and brown asbestos are more dangerous than white asbestos. Much of the asbestos found in buildings may contain 2 or more types. Undisturbed asbestos in good condition is not a risk to health but if it is disturbed the asbestos fibres can break down into sharp fibres that can inhaled. If these fibres lodge in the lungs they do not dissolve but can work their way to the periphery leading to several diseases, some of which are fatal.

Those at risk

Many of those now suffering from asbestos-related disease were exposed to very high levels of asbestos in the more traditional industries such as shipbuilding, construction and boiler work but 25% of the deaths from the disease are in people who have spent some of their working lives in the building and maintenance trades. Such people were often unaware that they were dealing with asbestos and exposed to risk.

Those who continue to be at risk from exposure to asbestos include heating and ventilating engineers, roofing contractors, fire and burglar alarm installers, general maintenance workers, electricians, plumbers, carpenters, joiners, plasterers, painters and decorators, gas fitters, demolition workers, telephone engineers, computer installation engineers, site managers, surveyors, janitors and those others who disturb the fabric of buildings in their day to day work

Presentation of asbestosis

Asbestosis usually presents as shortness of breath with a dry cough. Initially dyspnoea is only on exertion. Symptoms may be preceded by repetitive inspiratory basal crackles as is typical of pulmonary fibrosis. Clubbing of the fingers is a later feature. The rate of progression depends upon the level of exposure and eventually results in increasing disability and death from cardiorespiratory failure. In smokers, there is a 40 to 50% risk of death from bronchial carcinoma.

Investigations

CXR shows a ground-glass opacification, small nodular opacities, "shaggy" cardiac silhouette, and an ill-defined diaphragmatic contour.¹ It produces a restrictive pattern of lung function with reduced volumes/transfer factor. In later stages, there is reduced arterial oxygen saturation.

Sputum microscopy may show asbestos bodies. These confirm exposure to asbestos but their significance in diagnosing asbestosis is uncertain.²

Lung cancer is a common disease amongst smokers but it has an increased incidence in those with asbestosis.³ All types can cause the disease with some evidence of more danger from blue and brown. It is commoner amongst those who also smoke but may occur in non-smokers. The presentation and investigation of lung cancer is discussed elsewhere. The prognosis for most common cancers has improved significantly in recent years but lung cancer is a significant exception.

This malignancy may arise in the chest or abdomen. There is evidence of increased risk from exposure to blue or brown asbestos fibres with the disease being triggered from low or short exposures to asbestos.

Presentation

Mesothelioma often presents with pain, or a dull ache, and shortness of breath. There is tiredness, anorexia, weight loss, fever and occasional drenching sweats. Pleural effusion is common and a mass may be palpable due to direct extension through the chest wall.

Investigation

CXR often shows pleural effusion and thickening with a lobulated outline. CT provides a better image.¹

Pleural aspiration or pleural biopsy should give a definitive diagnosis.

Coal miners are exposed to a variety of dusts and in addition they have a higher incidence of smoking than the general population. Coal workers pneumoconiosis refers to disease from inhalation of coal dust. Silicosis is a particular problem of coal miners but about 10% of cases of silicosis occur in the construction industry.

Tiny particles of coal dust, just 2 to 5 microns in diameter, become retained in the alveoli. They are engulfed by macrophages but eventually the system is overwhelmed and an immune response follows. This produces pulmonary fibrosis. If this is associated with rheumatoid arthritis it is called Caplan's syndrome. Morbidity and mortality are related to the type of coal dust and the duration of exposure. Dust that is high in silica increases the risk of fibrosis.

Presentation

The clinical picture is one of increasing dyspnoea and history and examination that are typical of pulmonary fibrosis.

Silicosis can be divided into 4 distinct clinical presentations:⁴

• Acute silicoproteinosis occurs after intense exposure to silica. It is rapidly progressive and aggressive, often being fatal.
• Accelerated silicosis occurs with inhalation of high concentrations of silica over a short period. Symptoms may occur 2 to 5 years later. There is pulmonary fibrosis and nodularity.
• Simple chronic nodular silicosis, is fairly benign and follows more than 10 years of low level exposure to silica. Pulmonary nodules tend to be well circumscribed and are usually 1 to 3 mm in diameter. Patients are often asymptomatic, with normal pulmonary function and the diagnosis is an incidental finding on CXR. Macrophage destruction increases the risk of tuberculosis.
• Complicated chronic nodular silicosis, is characterized by the coalescence of the small nodules into large conglomerate opacities over 1cm in diameter, that may obstruct airflow.

The rate of progression and severity of the diseases is influenced by the amount of silica that is inhaled, the level and duration of exposure and also whether other minerals are present in the inhaled dust. A high percentage of free silica gives a high degree of pulmonary fibrosis.⁵

Investigations

CXR and pulmonary function tests are required. CT is often helpful.

Those who work with metal grinding or welding have a risk of inhalation of metallic particles. These are usually iron. Iron has a high atomic number and so it absorbs x-rays and produces very impressive shadows on chest x-ray but it has little effect on pulmonary function and little long term morbidity.

Farmer's lung, also called extrinsic allergic alveolitis and hypersensitivity pneumonitis, is an incurable, allergic lung disease caused by the inhalation of spores found in moldy crops, such as hay, straw, corn, silage, grain, and tobacco.

The signs and symptoms of Farmer's lung are most severe within 12 to 48 hours after exposure to the moldy crop. In some cases, symptoms may last for two weeks, or in cases where repeated exposure to moldy crops has occurred, farmers may develop chronic farmer's lung.
Signs and symptoms include:

• Shortness of breath
• Chronic cough
• Tiredness, weakness, or depression
• Headaches
• Occasional fever or night sweats
• General feeling of ill health

If a patient is suspected of having an industrial lung disease, it is important to take a good occupational history, going back over many years and looking also at hobbies and pastimes. CXR and lung function tests are required. If it seems reasonable that there is an occupational disease then referral to a chest physician with such an interest is indicated. There may be considerable financial implications but a tribunal may be required to make a decision. This requires an expert opinion. Nowadays, with both tribunals and courts, a single joint expert is preferred to partisan experts. It is cheaper, easier and more satisfactory to have a single expert who is responsible to the court, even if paid by one side.

The Health and Safety Executive have a Working Group on the Assessment of Toxic Chemicals (WATCH) to consider the evidence on the occupational exposure and health effects of substances, including whether a maximum exposure limit (MEL) or occupational exposure standard (OES) would be appropriate. If limits are indicated, they set them.

It is probably impossible to prevent all industrial dust diseases but they can certainly be reduced by following appropriate safety precautions including adequate ventilation and keeping down the level of dust in the workplace along with the wearing of facemasks as required. Not smoking will also reduce the risk or severity of such disease.