How to Control Cabin Respirable Mine Dust Exposures and Comply with Occupational Exposure Limits (OEL)

“Imagine having to breathe through a tiny tube that will continue to shrink in size over time: this is one of the many health risks posed from respirable mine dust”

In recent times, the exposure level to respirable dust that any machine operator [fixed or mobile plant] is exposed to has become a WHS imperative due to the resurgence of Black Lung disease amongst Queensland’s Coal Workers.

Coal Worker Pneumoconiosis or Black lung disease can be preventable when exposures to coal and silica dust are limited.

The Queensland’s Parliamentary Select Committee has finished their inquiry with a full report and 68 recommendations. The Inquiry into the re-identification of Coal Workers Pneumoconiosis calls for an immediate reduction to coal and silica dust occupational exposure limits (OEL).

Recommendation 19 proposed new (OEL) exposure:
• for coal dust – 1.5mg/ m3 air, and
• for silica – 0.05mg/m3 air.
The new exposure limits adhere to the results of years of research and analysis of mine workers in the US recognising respirable mine dust exposure as the issue of most concern. Coal mine dust is made up of a mixture of substances: coal, silica and other elements like iron; Silica being the most toxic to human health. The definition of “respirable dust is particles with a diameter of <10 microns which easily evade our respiratory defence mechanisms”.

These [respirable] invisible particles are produced by blasting, crushing, drilling, long wall mining and handling recently extracted minerals and by-products.

There are new findings for fresh respirable silica at mine /quarry sites being highly reactive due to becoming electrostatically charged. Once in the body these highly reactive particles pierce lung tissue and will continue to damage surrounding lung tissue over time. 

The following are five key factors for maintaining and operating enclosed cabins and booths based on the findings by NIOSH.

  • Ensure good cab enclosure integrity to achieve positive pressurisation against wind penetration into the enclosure.
  • For effective mitigation respirable dusts requires high efficiency filters (HEPA) on the pressurised intake air supply into the cab.
  • Use high efficiency (HEPA) respirable dust recirculation filter (return air filter)
  • Minimize dust sources in the cab by using good housekeeping practices, such as periodically cleaning soiled cab floors, using a sweeping compound on the floor, or HEPA vacuums to remove dust from foot well and cloth seat (Never brush or use compressed air)
  • Keep doors and windows closed during equipment operation.

The only international standard to address airborne particles is EN15695 which is designed for tractors / sprayers handling hazardous particulate substances such as pesticides with 4 classifications that reflect the integrity of the cabin and the functioning of the pressurising system.

The main categories that are relevant to mining / quarry are category 3 & 4 which infer the following:

  • Pressurised system (air conditioned over pressure)
  • Sealed cabin /enclosure (pre-set minimum > 20 pascals)
  • HEPA filtration tested to EN1822
  • Digital display

Recommendation 19 means that several engineering controls will have to be put in place. Breathe-Safe can assist with installing a system that can effectively isolate a worker and effectively control respirable mine dust and other contaminants within enclosures or cabins.

Breathe-Safe key features & safety facts:

  1. Cabin sealing: Excellent cabin integrity is required to maintain optimum positive pressure and prevent contamination from wind penetration.
  2. Pre-cleaner: Expels up to 90% of airborne debris and extends the lifecycle of the fresh air HEPA filter.
  3. HEPA filter Stage one: Removes respirable mine dust before pressuriser.
  4. Pressuriser: Increases cabin pressure to push against external airborne particulate contamination
  5. HEPA filter Stage two: Return air filter removes respirable dust from inside the cabin; from shoes & clothes
  6. Display panel: To INFORM operator that PROTECTIVE system is working and when system requires maintenance.

A two stage HEPA system when installed will reduce overall maintenance costs associated with HVAC – Climate Control as it will remain dust free.

For more information http://breathe-safe.com.au/index.php/news/174-how-to-control-cabin-respirable-mine-dust