Best Practice When Air Sampling for Silica: The Deadly Dust

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By: Tim Turney, Contributor

Silica dust is a scourge on industrial working environments that can be a deadly presence if not controlled appropriately. Silica is abundant as a constituent part of many of the organic materials found in construction, mining, quarrying and manufacturing worksites; and it is found naturally formed as quartz.

Recently, silica dust has begun to receive more attention, as the effects of the compound are becoming more widely visible—with records of the long latency illnesses it can cause. Inhalation of Respirable Crystalline Silica (RCS), a carcinogen, can cause silicosis, lung cancer, progressive massive fibrosis and other irreversible diseases. OSHA estimates 2.3 million Americans annually are exposed to the dust.

In April this year, The U.S. Department of Labor (DoL) announced that its Mine Safety and Health Administration (MSHA) had issued a final rule to better protect the nation’s miners from health hazards associated with exposure to respirable crystalline silica, following an earlier Silica Enforcement Initiative in 2022¹. This final ruling has lowered the permissible exposure limit (PEL) to 50 micrograms per cubic meter, calculated as an eight-hour, time weighted average (TWA) to protect miners from silica dust which has been “known as a health hazard for decades”².

The action level is 25 micrograms per cubic meter, half the PEL. This is the level at which a written exposure control plan, worker training and scheduled personal air monitoring must be implemented. If a worker is exposed to the action level for more than 30 days a year, medical surveillance is also required.

Choosing the correct air sampling pump and combining gravimetric monitoring with real-time solutions will maximize the ability to protect employees, ensure compliance and save lives. (photo courtesy Casella)

Know the Control Measures

Now that the dangers of silica dust are getting the necessary attention, employers need to be informed on the processes and control measures to protect employee health and minimize exposure to punitive damages.

If, as a company, it is known there is an issue with silica dust, control measures should be put in place. Monitoring the air for silica dust levels can be done to quantify the risk before control measures have been put in place or after control measures have been put in place (to ensure they are effective); and to monitor residual risk for air monitoring. There are air sampling pumps and real-time monitoring solutions available.

Hierarchy of Controls

The hierarchy of controls sets the precedent for the process employers should take to minimize employee exposure to workplace hazards, from most effective to least effective.

• Elimination: Removal of the hazard entirely. The stoppage of using silica dust-bearing materials eliminates exposure altogether, making elimination the preferred solution. For example, if sand is used for abrasive blasting, switch to metallic shot.
• Substitution: This involves using a safer alternative to the hazardous source. For instance, switch to a material with a lower silica concentration. When considering a substitute, it is essential to compare the potential new risks with the original risks.
• Engineering Controls: These controls modify equipment or the workspace to prevent hazards from coming into contact with workers. Examples include protective barriers, ventilation systems (LEV) and equipment design. Engineering controls are most effective when they’re part of the original equipment design and require minimal user input.
• Administrative Controls: These establish work practices to reduce exposure duration, frequency or intensity. Examples include exclusion zones, regular breaks, shift rotations and good housekeeping.
• Personal Protective Equipment (PPE): PPE includes items like gloves, masks and overalls. In the case of Respiratory Protective Equipment (RPE), it is the last line of defense and should only be used when other controls are not feasible. RPE requires proper training, fit and consistent use.

Monitoring

The hierarchy of controls sets the precedent for the process employers should take to minimize employee exposure to workplace hazards, from most effective to least effective. (photo courtesy NIOSH)

Air sampling pumps are typically used for compliance purposes in accordance with well-established U.S.³ methods, which are also recognized on a global basis. The pump itself should comply with the latest version of the ISO standard and be calibrated (for flow rate) both before and after use, because it is vital the volume of air sampled is accurate to calculate the exposure level.

Choosing the right pump – Aside from conforming to the latest standards, the personal air sampling pump selected must have the appropriate filter and sampling head according to the prescribed method mentioned above. A sample pump collects an air sample by pulling air through a sampling head (in this case, a cyclone head for the respirable fraction, the smaller sized fraction which is more hazardous and that is capable of penetrating into the lungs). Different cyclone heads are available that work on differing flow rates to achieve the respirable fraction; always check the manufacturer’s guideline to select the correct flow rate.

Collect a representative sample & calibrate – The flow of air may deviate throughout the day, so all pumps should be calibrated with representative sampling media before use. It is also necessary to calibrate the pump at the end of the day to make sure flow has not deviated by more than 5%. Calibrate the whole sample train, not just the pumps, to ensure accurate measurement.

Real-Time Monitoring

Gravimetric sampling, the type most commonly used with air sampling pumps, can take weeks to produce results, due to laboratory analysis required on the samples. Real-time dust monitors provide a solution and can be deployed to make assessments and adjustments to control measures before the gravimetric sample is taken.

Real-time instruments provide immediate information about exposure levels that can alert employees to exposure levels exceeding safe quantities. With real-time results, employers move through the assessment process faster and at a lower cost—through accurate reporting and instant validation of the measures in place.

Real-time instruments will not tell you the proportion of silica within the total dust, but known types of material will have an estimated proportion of silica within them, which gravimetric sampling can do. The benefit of real-time monitoring is the ability to know when exposure is occurring and where the sources of exposure are, because of the real-time reading.

For silica, gravimetric analysis is still required for compliance, but incorporating real-time monitoring can speed up the process.

Conclusion

Choosing the correct air sampling pump and combining gravimetric monitoring with real-time solutions will maximize the ability to protect employees, ensure compliance and save lives. Protecting employees’ wellbeing is the legal and moral duty of employers. Consult with a qualified occupational hygienist where necessary; adhere to the pump user manual; and follow the steps outlined above to ensure employees’ safety is looked after and legislation is complied with. IHW

Tim Turney is Global Marketing Manager at air sampling equipment manufacturer, Casella (www.casellasolutions.com).