timberland bots Hazard prevention and control in the work environment
Airborne contaminants can occur in the gaseous form (gases and vapours) or as aerosols, which include airborne dusts, sprays, mists, smokes and fumes. Airborne dusts are of particular concern because they are associated with classical widespread occupational lung diseases such as the pneumoconioses, as well as with systemic intoxications such as lead poisoning, especially at higher levels of exposure. There is also increasing interest in other dust related diseases, such as cancer, asthma, allergic alveolitis and irritation, as well as a whole range of non respiratory illnesses, which may occur at much lower exposure levels. This document has, therefore, been produced to aid dust control and the reduction of disease.
Whenever people inhale airborne dust at work, they are at risk of occupational disease. Year after year, both in developed and in developing countries, overexposure to dusts causes disease, temporary and permanent disabilities and deaths. Dusts in the workplace may also contaminate or reduce the quality of products, be the cause of fire and explosion, and damage the environment.
As a matter of social justice, human suffering related to work is unacceptable. Moreover, appreciable financial losses result from the burden of occupational and work related diseases on national health and social security systems, as well as from their negative influence on production and quality of products. All these adverse consequences, which are economically costly to employers and to society, are preventable through measures which have been known for a long time, and which are often of low cost.
The aim of this document is to help educate and train people in the prevention and control of dust in the workplace. It also aims at motivating employers and workers to collaborate with each other, in tandem with occupational health professionals, for the prevention of the adverse effects caused by dust in the workplace. Of course, dust is only one among the many workplace hazards, which include other aerosols (such as fumes and mists), gases and vapours, physical and biological agents, as well as ergonomic factors and psychosocial stresses.
Definitions and examples
Dusts are solid particles ranging in size from below 1 m up to around 100 m, which may be or become airborne, depending on their origin, physical characteristics and ambient conditions. This document does not deal specifically with other aerosols (such as fumes and mists), with very fine particles resulting from chemical reactions in the air, or with air pollution outside the workplace. However, in many cases similar principles of control apply to these as to dusts.
Examples of hazardous dusts in the workplace include:
mineral dusts from the extraction and processing of minerals (these often contain silica, which is particularly dangerous);
metallic dusts, such as lead and cadmium and their compounds;
other chemical dusts, such as bulk chemicals and pesticides;
vegetable dusts, such as wood, flour, cotton and tea, and pollens;
moulds and spores.
Asbestos is a mineral fibre, which is particularly dangerous, and is found, for example, in maintenance and demolition of buildings where it had been used as insulation material.
In occupational hygiene, particle size is usually described in terms of the aerodynamic diameter, which is a measure of the particle’s aerodynamic properties. Whether or not an airborne particle is inhaled depends on its aerodynamic diameter, the velocity of the surrounding air, and the persons’ breathing rate. How particles then proceed through the respiratory tract to the different regions of the lungs, and where they are likely to deposit, depend on the particle aerodynamic diameter, the airway dimensions and the breathing pattern. If a particle is soluble, it may dissolve wherever it deposits, and its components may then reach the blood stream and other organs and cause disease. This is the case, for example, of certain systemic poisons such as lead. There are particles which do not dissolve, but cause local reactions leading to disease; in this instance, the site of deposition makes a difference. When a relatively large particle (say 30 m) is inhaled, it is usually deposited in the nose or upper airways. Finer particles may reach the gas exchange region in the depths of the lungs, where removal mechanisms are less efficient. Certain substances, if deposited in this region, can cause serious disease, for example, free crystalline silica dust can cause silicosis. The smaller the aerodynamic diameter, the greater the probability that a particle will penetrate deep into the respiratory tract. Particles with an aerodynamic diameter > 10 m are very unlikely to reach the gas exchange region of the lung, but below that size, the proportion reaching the gas exchange region increases down to about 2 m.
The depth of penetration of a fibre into the lung depends mainly on its diameter, not its length. As a consequence, fibres as long as 100 m, have been found in the pulmonary spaces of the respiratory system.
Whenever exposure to airborne dust needs to be quantitatively evaluated, instruments must be used which select the right size range for the hazard concerned. the particles likely to reach the gas exchange region of the lung. For example, if silica is present, it is necessary to measure the respirable fraction of the airborne dust.
Mineral dusts are generated from parent rocks by any breaking down process, and vegetable dusts are produced by any dry treatment. The amount, hence the airborne concentration, is likely to depend on the energy put into the process. Air movement around, into or out of granular or powdered material will disperse dust. Therefore handling methods for bulk materials, such as filling and emptying bags or transferring materials from one place to another, may constitute appreciable dust sources. Coarse materials usually have a dust sized component as a result of attrition. If dust clouds are seen in the air, it is almost certain that dust of potentially hazardous sizes is present. However, even if no dust cloud is visible, there may still be dangerous concentrations of dust present with a particle size invisible to the naked eye under normal lighting conditions.
Unless its generation is prevented or it is removed from the air, dust may move with ambient air and reach even persons who are remote from the source and whose exposure is unsuspected.
Damp materials are less likely to release airborne dust, but of course this does not apply if they dry up later.
This document is concerned with preventing disease. Nevertheless, safety hazards (which pose immediate danger of accident) cannot be overlooked. Any airborne flammable dust in sufficient concentrations can explode. Combustible dust on the ground may become airborne and increase and propagate an explosion which is started by flammable gas ignition. This can occur with vegetable and organic materials, as well as with metal and other oxidizable dusts. Static electricity can also pose hazards. Preventive measures include good housekeeping to prevent build up of dust deposits, prevention of ignition, provision of explosion relief valves, dusting with non flammable dusts, and confinement in low oxygen environments.