Rules of Exposure

How fabricators should prepare for OSHA’s new silica standards


OSHA’s new rules for respirable crystalline silica exposure in manufacturing environments went into effect in June 2018. If you’re using sand or other silica-containing abrasive materials in your manufacturing processes, now is the time to make sure your facility is in compliance.

When permissible exposure limits cannot be met, employees must be provided PPE, such as a powered air purifying respirator or PAPR.

The Trouble with Silica

Sand has long been used as a cheap, effective abrasive material for processes such as deburring, glass etching, surface cleaning, and rust and mill scale removal. Recently, growing concerns about silica exposure have prompted many manufacturers to look for alternate abrasive materials for these processes – and for good reason.

Any facility still using sand in their abrasive blasting processes needs to be ready for the new silica standards that went into effect in June 2018.

When in solid form, as sand or quartz, silica is not dangerous. In fact, it is one of the most common elements on earth, making up 12 percent of the earth’s crust. However, when it is broken down into tiny, inhalable particles – known as respirable crystalline silica, or RCS it can have significant health impacts on workers.

The most serious of these is silicosis, a highly debilitating lung disease. Silicosis develops when inhaled particles of silica prompt the development of scar tissue in the lungs. Over time, this scar tissue leads to reduced lung function. This can happen over a period of years or decades with continued exposure to silica.

At first, workers may notice some shortness of breath when they exert themselves. As time goes on, exertion becomes more difficult and workers may develop extreme fatigue and chest pain as oxygen levels are reduced. Eventually, silicosis can lead to respiratory failure.

RCS is linked to other health effects, including lung conditions such as chronic obstructive pulmonary disease (COPD) and lung cancer. RCS exposure is also linked to kidney disease, cardiovascular impairment and various autoimmune disorders.

These standards cover workers using abrasives in manufacturing environments as well as shipyard workers who may use abrasives while preparing surfaces or stripping paint from ship hulls.

The New Standards

Because of these concerns, OSHA has cut the permissible exposure limits (PELs) for RCS in half for most workers. Standards for General Industry and Maritime went into effect June 23, 2018. These standards cover workers using abrasives in manufacturing environments as well as shipyard workers who may use abrasives while preparing surfaces or stripping paint from ship hulls. Similar standards for construction (including workers stripping paint from bridges and other infrastructure, for example) went into effect in June 2017.

For enclosed abrasive applications, make sure the dust collector can handle large volumes of abrasive dust.

Employers utilizing abrasives must keep two important limits in mind.

  • PEL: A time-weighted average concentration that must not be exceeded during any 8-hour work shift of a 40-hour workweek. OSHA has set a PEL of 50 micrograms of RCS per cubic meter of air (50 µg/m3).
  • Action level (AL): The airborne level of silica that creates a hazard to workers. The action level for workplace exposure to RCS is 25 micrograms per cubic meter of air (25 µg/m3) calculated as an 8-hour time-weighted average exposure.

OSHA requires employers to take active steps to reduce silica exposure. These include:

  • Establish and implement a written exposure control plan that identifies tasks that involve exposure and methods used to protect workers.
  • Conduct exposure monitoring.
  • Limit access to areas where workers may be exposed above the PEL.
  • Train workers on work operations that result in silica exposure and ways to limit exposure.
  • Make PPE available to employees when working in areas where they will be exposed above the AL (and mandatory for workers in areas where engineering controls cannot be used to meet the PEL).
  • Initiate a medical surveillance program for employees who are at or above the AL on 30 or more days per year (enforcement of this standard starts June 23, 2020).

Controlling Silica Exposure

Abrasive blasting and related processes can produce extremely high concentrations of RCS. As large abrasive particles rub against each other and the material being abraded, they are ground down into smaller and smaller particles, eventually becoming small enough to be respirable.

OSHA requires employers to use engineering and process controls wherever possible to keep exposures below PELs and provide PPE when it is not technically feasible to meet PELs through engineering controls alone. The best way to control RCS produced by abrasive processes depends on what kinds of processes are used and how easily they can be contained.

Large, outdoor applications – such as stripping paint off of bridges or ship hulls – can typically be tented to contain silica dust. An integrated dust collection system pulls excess particulates out of the air inside the enclosure. Workers inside the enclosure must have PPE to prevent inhalation of silica-containing dust.

In a manufacturing environment, abrasive blasting of parts and components is generally contained in an airtight enclosure to prevent silica dust from escaping into the ambient air of the facility. These enclosures must also be connected to a dust collector. Backup methods may be needed to control small amounts of particulate that may leak out of the enclosure. This is especially true in facilities where multiple stations or processes contribute to silica exposure; while only tiny amounts may escape from each station, the cumulative effect can quickly put the facility as a whole out of compliance.

Meeting the New Standard

Because the new standard sets the limits so low, many companies are finding that strategies used to meet previous PELs for RCS are no longer adequate to meet the new standard. While traditional ventilation systems may have been enough before, the new standard requires more technically challenging approaches similar to those used in cleanroom environments.

There are several steps companies using silica-based materials in manufacturing should take now.

Abrasive blasting and related processes can produce extremely high concentrations of respirable crystalline silica.

Consider changing materials or processes. While sand is cheap and readily available, the cost of meeting the new standard may make alternate abrasive materials more attractive for companies that have not already made the switch. Some of the most commonly used alternatives include coal slag, steel shot or grit, crushed glass or walnut shells.

Keep in mind that dust capture and control will still be needed even with these alternate materials to meet the OSHA “general duty” clause for workplace safety. However, dust levels may not need to be reduced to the stringent levels now needed for silica dust. (Note that while crushed glass does contain silica, it is in amorphous, rather than crystalline, form due to the rapid cooling of molten glass during manufacturing. Amorphous silica dust is not covered by the new RCS standard, but still needs to be controlled under the general duty clause.)

Perform an evaluation of current exposure levels. Look at concentrations of silica dust in the ambient air of the facility and in the breathing zone for employees with the greatest risk of exposure. Ambient air can be tested using dust concentration meters placed at strategic locations around the facility.

Centralized, ducted dust collectors can collect silica dust from multiple enclosures or stations. The system design must be optimized for effective collection of RCS in abrasive blasting.

Wearable devices can be used to get a better understanding of individual exposure levels for employees working directly with or near silica-producing processes. Chemical analysis of the collected particulate may be needed to determine the exact concentration of silica in mixed samples.

Adjust airflows to reduce the spread of silica dust. An evaluation should include examination of airflow patterns in the facility that can spread silica dust. Once airborne, tiny particles of silica can stay suspended in the air for days and travel far from their source. Prevent the spread of dust by using physical enclosures and negative air pressure (produced by a dust collector) to keep dust contained to the area where it is produced.

Train personnel in good housekeeping processes. If the air filtration system is effective, there will not be silica dust buildup on horizontal surfaces. If dust does accumulate in areas, use housekeeping practices that will not stir up dust, and provide PPE to employees working directly with silica dust.

Don’t use high-velocity fans. Large fans, high-velocity ventilation systems and personal cooling systems that use high-speed airflow are likely to just stir up silica dust without capturing the tiny particles that make up the respirable fraction. Turbulent airflow created by fans or high-velocity ventilation or HVAC systems will just spread these tiny particulates around.

Invest in a good dust collection and filtration system. Processes that create silica dust should be enclosed wherever possible and hooked up to a dust collector equipped to handle abrasive dust. A pre-filter that keeps larger particulates from reaching the main filters can increase filter life. A HEPA after-filter ensures that RCS does not escape past the main filters. Some systems also have a dust monitor integrated into the dust collector that alerts operators if dust is leaking past the main filters.

Computer modeling can be used to model airflow in the facility to see how dust moves in the environment and determine the optimal approach to mitigation. Shown here are diagrams of a facility before and after dust mitigation was introduced.

Finally, make sure the system is using a laminar (non-turbulent) airflow within the collection chamber to avoid the problems described with high-velocity ventilation systems. Airflow within the enclosure or hood should be smooth and slow; airflow within the ductwork itself must be fast enough to prevent dust from dropping out before it reaches the filters.

Consider adding an ambient air filtration system. Source capture should be used wherever possible to prevent silica dust from escaping into the ambient air of the facility. However, with the new low standard employers may find that source capture alone is not enough. A hybrid system that includes source capture and ambient air filtration is often needed to get concentration levels in ambient air below PELs when working in indoor environments.

Provide PPE for employees when PELs cannot be met. Remember, PPE should be used as a last resort when PELs cannot be met through other engineering and process controls. When using PPE, a powered air purifying respirator (PAPR) system is the best choice in most cases.

For companies using silica in their processes, a qualified air quality system designer can help determine the most cost-effective and efficient way to manage silica dust. RoboVent’s VentMapping engineering process uses computer modeling to optimize system design.

Meeting the new RCS standard will be challenging for many employers, but it is certainly not impossible. For any facility not yet ready to meet the new RCS standard, it’s time to conduct an evaluation and get a new silica strategy in place.

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