Silica (RCS) is twenty times more toxic than coal dust

silica rcs

SILICA (RCS) respirable crystalline silica
Respirable mine dust in high concentrations cause lung disease due to overloading the defences of the respiratory system as particles start to deposit in the lung.

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Silica airborne particles are 20 times more toxic to the lungs than coal dust alone; nevertheless, Silicosis is the world’s oldest known occupational disease. Workers who are exposed and inhale invisible Silica (RCS) particles are at increased risk of developing serious – and often deadly – silica related disease.


In the United States the Mines Safety and Health Administration (MSHA) has introduced a new rule that has lowered the concentration limit for respirable coal dust from 2.0 mg/m³ to 1.5 mg/m³.In regard to Silica the Occupational Safety and Health Administration (OSHA) new rule has been brought in and is expected that MSHA will follow suit. The new limit from OSHA’s new rule cuts the permissible exposure limit (PEL) in half from 100 to 50 micrograms (as an 8-hour time weighed average)


HEPA filtration system is effective at controlling respirable dust exposure as long as the operator remains inside.


The health risks associated with exposure to RCS can be controlled with the use of effective systems installed in environmental cabin/enclosures to isolate workers. Respirable crystalline silica (RCS) is one of major issues brought to the attention of the Queensland Parliament - Coal Workers’ Pneumoconiosis Select Committee Inquiry. The select committee will be looking at evidence of silica exposures of Brisbane's tunnel workers.

Dr Cohen has given evidence stating: “Silica is probably more dangerous than coalmine dust. We talked about the toxicities earlier. Quarriers, tunnelers, metal miners—anyone who is disturbing the earth’s crust and drilling through rock is at risk for quartz and silica exposure. There should be industrial hygiene monitoring of the exposure levels. We just lowered our exposure level to silica from 0.1 milligram per metre cubed to 50 micrograms or 0.05 milligrams per metre cubed because of the horrendous diseases that occur from silica.
Aside from the diseases we have already talked about for coalmine dust, silica is actually a lung carcinogen. It is an International Agency for Research on Cancer, IRAC, class 1 human carcinogen. It causes renal disease and causes other autoimmune diseases like rheumatoid arthritis and other things.”

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Picture of HVAC evaporator contaminated with dust

To mitigate exposure to respirable dust a multitude of controls must be used. Then it should follow that fresh air pressurisation systems should be installed with HEPA filters in a two-stage setup: primary and return air stages to filter outside fresh air and also to filter the air that is inside the enclosure to same HEPA standard.

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Picture of Breathe-Safe system to control respirable dust - HEPA fresh air fiter and HEPA return air filter located close to feet of operator (Trap airborne particles from shoes & clothes).

This process maintains the HVAC system dust free thus extending the lifecycle of the system and maintains the cooling capacity by avoiding air restrictions caused by dust contamination.These aspects must be considered, as it will result in costs reduction over the service life of the system. Specifically, reduce the overall costs of servicing & repairs of the HVAC system due to dust ingress contamination.
Finally, Its widely known and common practice that respirable fibres (Asbestos) must be removed using HEPA vacuum cleaners. The same principle applies in controlling respirable particulate inside the cabin.

Find out more about HEPA fresh air pressurisation technical guide.

HEPA chart