Characteristics of Dust Particles in Gaseous Medium Quiz

Terminal Velocity of Particles

• The terminal velocity of coarse particles (> 200 μm) is determined by Newton's Law: VN = √(8mg)/(3m2) where VN is the terminal velocity, m is the mass of the particle, g is the acceleration due to gravity, and m1 and m2 are the masses of the particle and air, respectively.

Classification of Particulates

• Particulates can be classified as Respirable (< 7 μm) and Nonrespirable (> 7 μm) from a health hazard point of view.
• Harmfulness of dust can be classified into:
  • Fibrogenic Dusts: Pulmonary dust that is harmful to the lower respiratory system, e.g., silica, quartz.
  • Carcinogenic Dust: Pulmonary dust that harms the upper respiratory system, e.g., radon daughters, asbestos, arsenic.
  • Toxic Dust: Poisonous to body organs, tissues, etc., e.g., Beryllium, Arsenic, Lead.
  • Radioactive Dust: Injurious due to alpha and beta radiation emissions, e.g., uranium, radium, thorium.
  • Explosive Dust: Combustible when airborne in sufficient quantities, e.g., metal dust, coal dust, sulphide ore dust.

Factors that Determine the Harmfulness of Dust

• Composition of dust, including chemical and mineralogical composition.
• Concentration of dust in the atmosphere.
• Particle size.
• Exposure time: usually, exposure to dust for over 20 years could lead to dust-related illnesses, though it is possible after shorter durations.
• Individual susceptibility: health status and other individual peculiarities influence the degree of harmfulness of dust.

Pathological Effects of Dust

• The human respiratory system has built-in safeguards to protect the sensitive tissue in the lungs from the harmful effects of dust particles.
• In the upper respiratory system, filters involve:
  • Hairs in the nasal passage filter out larger particles (over 10 μm in size).
  • The mucous membrane lining the nose and throat traps more dust particles.

Characteristics of Dust

• Dust particles have sizes, shapes, and structural features.
• Parameters to characterize dust include:
  • The number of particles per unit volume.
  • The size distribution of the particles.
  • The mass of dust per unit volume.
  • The surface area of dust per unit volume.
  • The chemical composition of the dust.
  • The mineralogical nature of the particles.

Formation and Movement of Rock Dust Particulates

• Formation and movement of rock dust particulates depend on:
  • Brittleness of the substance (B).
  • The hardness of the substance (Vicker's hardness H).
  • The force applied to the substance.
• A Dustability Index is defined as D = f(B) / f(H).
• A Dust Forming Index is also defined as: DFI = f(B) × f(I) / f(H) = D × f(I) where I is the induced factor causing dust production.