Silica Can Be an Environmental and Health Threat

Not many people would think dust would be a threat to health. You probably knew it can affect allergies, but would it really be considered a threat?  Yes, if that dust was silica.  On our sister blog, Analyzing Metals, we discussed how working in the metal foundries industry can be a threat to one’s health because of exposure to silica dust known as respirable crystalline silica (RCS). Inhaling RCS can lead to silicosis, lung cancer, chronic obstructive pulmonary disease, and kidney disease. These dusts are produced by casting sand, fettlings and kiln linings.

Silica is actually a common naturally occurring element found in sand and quartz. When silica-containing rocks and minerals are blasted, chipped, cut, ground, and drilled, small particles are released into the air, which can then be breathed in and land in workers’ lungs.

The US Occupational Safety and Health Administration (OSHA) estimates that 34,591 foundry workers are currently exposed to respirable crystalline silica.  However, crystalline silica can be found in a many more industries. Workers around asphalt roofing materials, concrete products, cut stone, and clay products, especially in the railroad, shipyard, and oil and gas industries, can be exposed to this harmful silica.  In fact, even workers in dental laboratories and jewelry manufacturing are exposed to RCS.

Because of this threat, OSHA has issued standards to protect workers that must be complied with by June 23, 2018. The OSHA Fact Sheet, OSHA’s Crystalline Silica Rule: General Industry and Maritime, outlines the standards:

• Measure the amount of silica that workers are exposed to if it may be at or above an action level of 25 μg/m3 (micrograms of silica per cubic meter of air), averaged over an 8-hour day;
• Protect workers from respirable crystalline silica exposures above the permissible exposure limit of 50 μg/m3, averaged over an 8-hour day;
• Limit workers’ access to areas where they could be exposed above the PEL;
• Use dust controls to protect workers from silica exposures above the PEL;
• Provide respirators to workers when dust controls cannot limit exposures to the PEL;
• Restrict housekeeping practices that expose workers to silica where feasible alternatives are available;
• Establish and implement a written exposure control plan that identifies tasks that involve exposure and methods used to protect workers;
• Offer medical exams — including chest X-rays and lung function tests — every three years for workers exposed at or above the action level for 30 or more days per year;
• Train workers on work operations that result in silica exposure and ways to limit exposure; and
• Keep records of workers’ silica exposure and medical exams

Silica can be monitored by collecting a total dust sample and sending it to a laboratory for analysis, typically using X-ray diffraction (XRD) techniques. (OSHA offers information about the process for collecting an air sample to measure airborne silica.)

In addition, both personal and area dust monitoring equipment can be used to help limit exposure.

Personal real-time aerosol monitoring instruments measure aerosol concentration in real-time, with relative humidity compensation.  The ability to quickly identify unsafe particulate levels for personal exposure is critical in the prevention of health effects. As I mentioned, respirable particles can settle deep in the lungs, potentially resulting in serious health and respiratory problems. The hazards associated with particulate exposure exist within both the concentration of the particulate and the size. So when considering portable particulate monitoring solutions, make sure they address both particle size and concentration in real time.

Fixed Particulate Detection instruments offer real-time particulate monitoring for site remediation or perimeter monitoring.  These types of Dust Monitors utilize a highly sensitive light-scattering photometer (nephelometer) technology. The intensity of the light scattered by airborne particles passing through the sensing chamber is linearly proportional to their concentration. This optical configuration produces optimal response to particles, providing continuous measurements of the concentrations of airborne particles. Most monitors incorporate a temperature and relative humidity (RH) sensor coupled with an internal heater to mitigate the positive bias with elevated ambient RH.

It only takes a very small amount of the very fine respirable silica dust to create a health hazard.  Real-time monitoring is essential to reducing exposures and protecting workers.

You can learn more about global air quality regulations and solutions for successfully complying with those regulations, on the Air Quality Analysis Information page in our Environmental Learning Center.