Now that the rains have stopped and the dry season is here, dust has become a permanent feature of the atmosphere. It is a common feature in the cities and towns. Dusts have a very damaging effect on human lungs
What are the lungs?
The lungs are the organs of breathing: they are responsible bringing oxygen from the atmosphere into the body through a series of branching air tubes and exchanging it for carbon dioxide that is released back into the atmosphere.
The lungs are constantly exposed to danger from the dusts we breathe. Luckily, the lungs have another function – they have defence mechanisms that protects them by removing dust particles from the respiratory system. For example, during a lifetime, a coal miner may inhale 1,000 g of dust into his lungs. When doctors examine the lungs of a miner after death, they find no more than 40 g of dust. Such a relatively small residue illustrates the importance of the lungs' defences, and certainly suggests that they are quite effective. On the other hand, even though the lungs can clear themselves, excessive inhalation of dust may result in disease.
What happens when we breathe in dust?
The lungs are protected by a series of defence mechanisms in different regions of the respiratory tract.
When a person breathes in, particles suspended in the air enter the nose, but not all of them reach the lungs. The nose is an efficient filter. Most large particles are stopped in it, until they are removed mechanically by blowing the nose or sneezing.
Some of the smaller particles succeed in passing through the nose to reach the windpipe and the dividing air tubes that lead to the lungs [more information about how particles entering the lungs].
These tubes are called bronchi and bronchioles. All of these airways are lined by cells. The mucus they produce catches most of the dust particles. Tiny hairs called cilia, covering the walls of the air tubes, move the mucus upward and out into the throat, where it is either coughed up and spat out, or swallowed.
The air reaches the tiny air sacs (alveoli) in the inner part of the lungs with any dust particles that avoided the defences in the nose and airways. The air sacs are very important because through them, the body receives oxygen and releases carbon dioxide.
Dust that reaches the sacs and the lower part of the airways where there are no cilia is attacked by special cells called macrophages. These are extremely important for the defences of the lungs. They keep the air sacs clean. Macrophages virtually swallow the particles. Then the macrophages, in a way which is not well understood, reach the part of the airways that is covered by cilia. The wavelike motions of the cilia move the macrophages which contain dust to the throat, where they are spat out or swallowed.
Besides macrophages, the lungs have another system for the removal of dust. The lungs can react to the presence of germ-bearing particles by producing certain proteins. These proteins attach to particles to neutralize them.
Dusts are tiny solid particles scattered or suspended in the air. The particles are "inorganic" or "organic," depending on the source of the dust. Inorganic dusts can come from grinding metals or minerals such as rock or soil. Examples of inorganic dusts are silica, asbestos, and coal.
What are the reactions of the lungs to dust?
The way the respiratory system responds to inhaled particles depends, to a great extent, on where the particle settles. For example, irritant dust that settles in the nose may lead to rhinitis, an inflammation of the mucous membrane. If the particle attacks the larger air passages, inflammation of the trachea (tracheitis) or the bronchi (bronchitis) may be seen.
The most significant reactions of the lung occur in the deepest parts of this organ.
Particles that evade elimination in the nose or throat tend to settle in the sacs or close to the end of the airways. But if the amount of dust is large, the macrophage system may fail. Dust particles and dust-containing macrophages collect in the lung tissues, causing injury to the lungs.
The amount of dust and the kinds of particles involved influence how serious the lung injury will be. For example, after the macrophages swallow silica particles, they die and give off toxic substances. These substances cause fibrous or scar tissue to form. This tissue is the body's normal way of repairing itself. However, in the case of crystalline silica so much fibrous tissue and scarring form that lung function can be impair. The general name for this condition for fibrous tissue formation and scarring is fibrosis. The particles which cause fibrosis or scarring are called fibrogenic. When fibrosis is caused by crystalline silica, the condition is called silicosis.
What are the diseases of dusty operations?
The classic diseases of "dusty" occupations may be on the decline, but they have not yet disappeared. Workers today still suffer from a variety of illnesses caused by dust they inhale in their work environments. For practical purposes, we limit this document to dust. We do not take into consideration combined effects arising from exposures to dusts, gases, fumes and vapours.
Some types of lung diseases caused by the inhalation of dust are called by the general term "pneumoconiosis." This simply means "dusty lung."
The changes which occur in the lungs vary with the different types of dust. For example, the injury caused by exposure to silica is marked by islands of scar tissue surrounded by normal lung tissue. Because the injured areas are separated from each other by normal tissue, the lungs do not completely lose their elasticity. In contrast, the scar tissue produced following exposure to asbestos, beryllium and cobalt completely covers the surfaces of the deep airways. The lungs become stiff and lose their elasticity.
Not all inhaled particles produce scar tissue. Dusts such as carbon and iron remain within macrophages until they die normally. The released particles are then taken in again by other macrophages. If the amount of dust overwhelms the macrophages, dust particles coat the inner walls of the airways without causing scarring, but only producing mild damage, or maybe none at all.
Some particles dissolve in the bloodstream. The blood then carries the substance around the body where it may affect the brain, kidneys and other organs.
How can we protect the lungs from dust?
To avoid respiratory or other problems caused by exposure to dust, hazardous substances should be substituted with non-hazardous substances. Where substitution is not possible, other engineering control methods should be introduced. Some examples are:
• use of wet processes
• enclosure of dust-producing processes under negative air pressure (slight vacuum compared to the air pressure outside the enclosure)
• exhausting air containing dust through a collection system before emission to the atmosphere
• use of vacuums instead of brooms
• good housekeeping
• efficient storage and transport
• controlled disposal of dangerous waste
Use of personal protective equipment may be vital, but it should nevertheless be the last resort of protection. Personal protective equipment should not be a substitute for proper dust control and should be used only where dust control methods are not yet effective or are inadequate. Workers themselves, through education, must understand the need to avoid the risks of dust.
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