The existence and nature of respiratory hazards

The composition of normal air consists of approximately 78% nitrogen, 21% oxygen, and a small percentage of inert gases such as argon. When harmful substances are present in the air—defined as any gaseous or particulate matter not normally found in clean air at concentrations exceeding those set by national occupational hygiene standards—this can pose a significant respiratory hazard.

Harmful substances in the air typically take on five main forms:

1. Dust: These are tiny solid particles suspended in the air, often generated by mechanical processes like cutting or grinding. Examples include coal dust, cement dust, and asbestos fibers. Dust particles can be hazardous when inhaled over long periods, leading to conditions like pneumoconiosis.
2. Smoke: This refers to very fine solid particles that form through the condensation of gases or vapors. Smoke is generally smaller in size than dust and is commonly produced during activities like welding. It often contains metal oxides and can be highly dangerous when inhaled.
3. Fog: These are tiny liquid droplets suspended in the air, usually formed from sprayed liquids. Common examples include paint mist or chemical mists used in industrial settings.
4. Gases: These are harmful substances that exist in gaseous form under normal temperature and pressure. Examples include chlorine, carbon monoxide, hydrogen sulfide, and sulfur dioxide. Exposure to these gases can lead to serious health effects, depending on the concentration and duration of exposure.
5. Vapors: These are gases that result from the evaporation of substances originally in liquid or solid form. Common examples include benzene, toluene, gasoline, and mercury vapor. Vapors can be particularly dangerous because they are often invisible and easily inhaled.

Dust, smoke, and fog are collectively known as airborne particles or aerosols. These particles are usually odorless, and their ability to remain suspended in the air depends on their size. The smaller the particle, the longer it stays airborne and the greater the chance it will be inhaled into the lungs. While the human respiratory system has natural defenses to remove larger particles, fine particles measuring less than 10 microns in diameter can bypass these defenses and reach the deep parts of the lungs, including the alveoli. Over time, this accumulation can lead to chronic lung diseases.

Respiratory dust is defined as the fine dust that can penetrate deep into the lungs. Particles visible to the naked eye are typically larger than 10 microns, which makes them less likely to be inhaled deeply. However, when concentrations are high, such as in welding smoke, the particles may appear visible. Once dispersed into a larger space, however, the smoke becomes invisible due to lower concentration.

China Labor Insurance Network