Respirable silica and dust exposure monitoringPetroleum and gas safety alert no. 91 | 09 July 2019 | Version 1
The Petroleum and Gas (P&G) Inspectorate has undertaken proactive worker exposure monitoring in collaboration with Queensland Government’s Safety in Mines Testing and Research Station (Simtars). This involved conducting personal respirable dust and silica sampling at two hydraulic stimulation work sites. Hydraulic stimulation involves handling and pumping large volumes of silica sand. During the monitoring a number of workers wore sampling devices that monitored their personal respirable dust and quartz (silica) exposures during their work shifts.
What is silica?
Silica is a mineral found in the earth’s crust. Quartz, the crystalline form of silica, has been associated with lung disease and is present in soil, bricks, sandstone, concrete and sand.
The Safe Work Australia Workplace Exposure Standard for respirable crystalline silica is currently 0.1 mg/m3 for a 40 hour work week. Best practice aims to keep exposures as low as reasonably practicable to minimise the risk of getting a silica-related disease.
Respirable silica dust, when inhaled, can present a significant health risk. It is 100 times smaller than a grain of sand and is not visible to the naked eye (Figure 1). If the inhaled dust contains a proportion of silica there are a range of health effects:
- chronic bronchitis – inflammation of the airways resulting in cough and irritation
- lung cancer – occurs with heavy exposure to silica with smokers having a higher risk
- scleroderma – a disease of the connective tissue of the body resulting in the formation of scar tissue in the skin, joints and other organs of the body
- emphysema – destruction of the lung tissue and loss of surface area for the exchange of gases such as oxygen and carbon dioxide
- silicosis – scarring of the lung tissue causing shortness of breath and interfering with the exchange of gases which takes place in the air sacs. Usually requires 10 or more years exposure unless the dust concentration is very high. (Figure 2)
Key findings from the onsite monitoring
- two of the 35 workers exceeded the shift adjusted regulatory limit, one in particular measured three times the limit. A number of workers fell within the action zone (50-100% of the adjusted regulatory exposure limit exposure).
- workers who exceeded the shift adjusted regulatory limit for respirable silica were positioned downwind of sand proppant transfer operations.
- over reliance on respiratory protective equipment (RPE) worn inconsistently and sometimes removed when communicating with other workers. RPE is a lower order risk control.
- some workers unable to achieve effective RPE seals due to facial hair.
- reloading of the bulk loader with the use of compressed air potentially exposed workers in the vicinity to airborne dust containing a high percentage of silica. (Figure 3).
- exclusion zones for work areas with high level of silica dust exposure.
- vehicle and structure doors and windows closed when not being accessed.
- control excessive dust generated by vehicle movements.
- carry out RPE awareness, training and fit testing for employees.
- undertake silica dust monitoring during hydraulic stimulation activities
- implement higher order controls to reduce risk to as low as reasonably practicable for employees (e.g. isolation, engineering controls and elimination).
Planned actions from the P&G Inspectorate
- inspect hydraulic stimulation sites to assess effectiveness of silica dust controls.
- conduct second round of silica dust monitoring in collaboration with Simtars.
- undertake compliance action consistent with Resources Safety and Health Compliance Policy 2017.
- dust reduction strategies to concentrate on reduction / capture at the source. Use of respiratory protection may not be adequate even if appropriately chosen, worn and fitted.
- scheduling of the refill of bulk loaders when no other workers are on lease site. In the event that this cannot occur mandatory RPE should be worn by all workers on the lease.
- investigate alternate methods to reload without the use of compressed air.
- investigate remote control technologies in order to increase the distance between the worker and source.
- ensure workers position themselves upwind of dust generating activities.
- ensure regular housekeeping is conducted in all operator cabins, offices and crib rooms using wet cleaning methods and vacuum cleaning with HEPA filters.
- inform workers about the risk associated with exposure to respirable dust and silica.
References and further information
Figure 1: Electron microscope image of a human hair (diameter of 40 micrometres) and respirable silica dust particles (10 micrometres). Source: Australian Tunnelling Society Air Quality Working Group
Figure 2: Chest X-ray image of a worker’s lungs, showing advanced stage silicosis (scarring and nodules – white against healthy lung tissue - black).
Figure 3: Dust plume.
Authorised by Bill Date - Chief Inspector
Contact: Don Harris, Principal Inspector, Drilling, +61 7 4531 8521 email@example.com
Issued by the Queensland Department of Natural Resources, Mines and Energy