Free Silica

Free Silica

Main Industries and Occupations at Risk

  • Mining, quarrying and tunnelling of siliceous rocks (e.g. granite, sandstone, slate, mica, silica containing coal or metal ores);
  • Abrasive blasting using siliceous grains (e.g., sandstone, sand, quartzite and flint);
  • Stone cutting, dressing, polishing, cleaning and monumental masonry (including tombstone engraving) using granite and sandstone;
  • Construction (e.g., jack hammering, drilling of silica or silicon dioxide-containing material like sand, sandstone, quartz and granite);
  • Maintenance and repair of refractories (furnace linings);
  • Manufacture of ceramics (chinaware, porcelain, earthenware) and refractories;
  • Foundries (mould breaking and fettling);
  • Rubber milling (using calcium carbonate containing silica);
  • Enamelling using quartz, feldspar, metal oxides and carbonates;
  • Manufacture of abrasive soaps.


Health Effects

Acute Silicosis

  • Rare;
  • Due to inhalation of high concentrations of very fi ne free silica dust particles (e.g., manufacture of abrasive soaps, tunnelling and sandblasting);
  • May develop within a few months with severe dyspnoea, cough, mucoid sputum, fever, weight loss and cyanosis;
  • Fatal within a year.

Chronic Silicosis

  • Most of the cases are asymptomatic, presenting after 10 – 20 yrs;
  • Some may have dyspnoea, cough and wheezing;
  • Silicotics may develop progressive massive fibrosis.


  • Crystalline silica dust is an IARC Group 1 carcinogen
  • Cancer of lung;
  • Higher risk of lung cancer especially in smokers.


  • Silicotics are more prone to developing pulmonary tuberculosis.
  • There is also an association with scleroderma and chronic renal disease.

Medical Examinations


  • Any work where workers are exposed to airborne free silica

Types of Tests and Frequency of Examinations:

  • Pre-placement medical examination: within 3 months of exposure
    • Clinical examination shall include a detailed medical and work history with emphasis on:
      • i.  past, present and anticipated future exposure to silica;
      • ii.  respiratory system.
    • Test:
      • i.  Full size chest x-ray examination.
    • Unfit for exposure to silica:
      • i.  Workers with history of pulmonary tuberculosis;
      • ii.  Workers who are unable to wear respirators.
  • Periodic medical examinations: every 36 months
    • i.  Clinical examination shall include a detailed medical and work history with emphasis on the respiratory system;
    • ii.  Full size chest x-ray examination