Respirable Free Silica

Crystalline silica (also known as free silica) is a growing concern in the construction industry due to the causative link with silicosis. It is bio-insoluble and toxic, which is a nasty combination when it enters the human lung. Silicosis can present in chronic form, after 10 or more years of low level exposure; accelerated form after 5 to 10 years of moderate exposure; or acute form which can be fatal within months.
Silicosis is incurable, with limited symptomatic relief available to sufferers. As such, preventative action is critical, and risk assessment and determination of appropriate safety measures is paramount to the health of employees and the liability of employers.
Crystalline silica can be found as quartz (extremely common), cristobalite or tridymite (both uncommon naturally, but common in high temperature industries). All three forms are easily identifiable by X-ray diffraction. As crystalline silica is primarily hazardous when it reaches the lungs, the respirable fraction or PM4 in most industries, is the fraction of interest.
The PM4 fraction is the size fraction in which the particles have an equivalent aerodynamic diameter of 4 µm. An equivalent aerodynamic diameter is the diameter of a sphere with unit density that has aerodynamic behavior identical to that of the particle in question. The actual diameter of the particulates will vary depending on density and morphology.

For full respirable crystalline silica determination, Microanalysis uses an adaptation of the SWeRF method to determine the size distribution, abstract the fraction of interest and then determine the crystalline silica content of the respirable fraction.

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Microscopic Mite - Big Trouble

Grain mites (also known as flour mites) are typically about 600 µm long (about 6 human hair widths) and are one of the most common mites that infest food and feed products. Microanalysis was recently involved in work to identify possible human irritants in dusts as part of an occupational exposure investigation.
A surface dust sample was refined in our laboratory to abstract the respirable (PM4) fraction which was subsequently placed in an electron microscope for examination.
Amongst the chaff, the usual suspects of quartz, kaolinite and mica particles could be observed; but one stood out – a grain mite. These mites are responsible for extensive damage to grain, primarily through the germ and can be responsible for spreading fungal spores through large volumes of grain. Grain mites are known to cause allergic responses in certain individuals and can cause severe itching to the skin.
Scientist abroad – Nimue Pendragon

I recently had the pleasure of spending six weeks gallivanting around the countryside of England, Wales, Scotland and the Republic of Ireland. From London to Dover to Clovelly to Pembroke, then Rosslare to Limerick and Knock to Edinburgh before exploring the lowlands, Speyside, the highlands and the isles - the amazing geological formations, isolated ecosystems and interesting evolutionary paths of flora and fauna were fascinating and delightful.
A few interesting facts I learned:
  • The cliffs of Dover are formed from soft calcite limestone formed from the skeletal remains of coccolithophores, a form of tiny planktonic algae;
  • Clovelly in North Devon is a tiny cobbled town which is too steep for cars to access, so the main form of transport is by donkey;
  • Pembroke is the origin of the Welsh Corgi;
  • New Ross, Ireland, was the birthplace of Patrick Kennedy, the grandfather of J F Kennedy;
  • The conflict in Ireland resulted in incredible innovation despite the adversity; and
  • The mountains of the Scottish Highlands were formed during the Caledonian orogeny, and are bisected by the Great Glen Fault.  
Pictured: The chalk cliffs of Dover, dotted with flint and quartz porphyroblasts.

SEM Image Of The Month

Pollen of Papaver Rhoeas, or Corn Poppy
Thought to originate in southern Europe, the corn poppy is found in west Asia, north Africa and Europe. A common garden poppy, the flowers are associated with Remembrance day and appear on a variety of international currency. P. rhoeas contains the alkaloid rhoeadine which is a mild sedative and antitussive.

Image by Sandy Lam (false colour).
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