New respirable crystalline silica rules due in June

Jon Lawson

In a move to help all silica dust-producing operations comply with impending rule changes, a specialist in industrial dust control is reminding companies that the US Occupational Safety and Health Administration (OSHA) respirable crystalline silica (RCS) dust emissions Final Rule [OSHA §1910.1000 Respirable crystalline silica] compliance deadline for general industry and maritime is on June 23, 2018.

Due to the small size, RCS of PM10 (particulate matter ≤10 microns [μm]) can penetrate the body’s natural defences (mucus membranes, cilia, etc.), reaching deep into the lungs. Invisible to the naked eye and able to travel long distances on ambient air currents, workers are often unaware of lingering RCS and take off protective masks, risking exposure and potentially contracting silicosis over time.
Silicosis is a chronic and irreparable disease that affects millions of workers in a wide variety of industries. Without proper protection, workers with extensive exposure can experience a buildup of RCS deep in the lungs, restricting lung capacity. Silicosis can potentially lead to more harmful and life-threatening lung ailments such as pneumonia, pulmonary tuberculosis and lung cancer.
With this in mind, not only does the Final Rule require regular monitoring by the employer, but it also sets personal exposure limits (PEL) and suggests engineering controls and particulate isolation rather than putting the entire onus of wearing uncomfortable respirators on the employees. By doing this, regulators also limit fugitive dust emissions from leaving the site line and exposing the wider public.

“The RCS regulations are touching a wide range of industries,” said Jerad Heitzler, Foundations Training Manager at Martin Engineering. “Some operations can implement a single solution, whereas others create dust throughout the entire process and require unique solutions at each stage.”

Companies are required to follow OSHA’s rules of compliance by using a personal dust monitor worn by a trained employee to monitor the amount of RCS and determine whether the exposure is under the average 'action level' of 25 µg/m3 (micrograms of RCS per cubic meter of air). Plants must protect workers if they have an amount of RCS dust above the PEL of 50 µg/m3, averaged over an 8-hour day. To control these levels, OSHA provides guidelines regarding methods of compliance, advising companies to do the following:

Use engineering controls - these include isolating dust in sealed chute systems and dust collectors, and/or using water-based atomised suppression systems. Provide respirators – compliance cannot be achieved by respirators alone, but respirators must be provided for use in areas where engineering controls cannot adequately limit exposure. Limit access to high exposure areas where workers could be exposed to dust concentrations above the PEL. Develop a written exposure control plan – and have it available along with monitoring results. Offer medical exams to highly exposed workers, and review the regulation for compliance details.

Non-compliance could result in fines, disruption in production and legal action by federal or state agencies or workers. If PEL readings are at or above the permissible exposure level, plants must take action with isolation or engineered controls. And fines for first offences can be steep. For example, following the construction industry deadline of June, 23rd 2017, some general contractors and developers faced fines of US$40K- $70K.  

Solutions are available. Engineering controls are retrofitted equipment or newly designed systems that reduce or eliminate exposure to RCS. An example of this is Martin Engineering’s modern conveyor transfer chute design, which shapes the flow of cargo, controls transfer speed and minimises disruption.  

Isolation to control dust exposure entails enclosing the material handling system through the transfer and sealing in particles to help prevent them from escaping. On a fast moving, high volume conveyor, air flow through the settling zone should be controlled to minimise its escape. An effective transfer zone slows the air down, allowing the material and dust time to settle. New modular structures deliver the versatility to adapt to virtually any material transfer, enabling the construction of a transfer chute and settling zone of varying heights and lengths to meet specific needs. Specially configured dust curtains can also be installed to promote quick settling, and top-mounted dust bags release excess air while capturing particles that remain in the air stream. 

For heavy duty applications with short ducting runs that exceed the volume of a dust bBag, an integrated air cleaner is a compact dust collector located directly above the conveyor transfer point. It captures agitated dust in a filter, then uses a reverse pulse of air to return dust to the main cargo stream.
The system is not sealed if the chute skirting doesn’t retain contact with the belt. Mounted on the outside of the chute with optional quick release clamps for safer access and maintenance, ApronSeal double skirting provides a dual seal to further reduce the escape of dust. The patented design features a secondary sealing strip that rides the belt to deliver an extra layer of protection against dust emissions and spillage.  

For hydrophobic materials, the surfactant dust system can apply dust-suppressing surfactant and crusting agents using strategically placed spray nozzles and a fully automated system to avoid waste. Able to be placed almost anywhere within the cargo stream from loading to discharge, the sprayed surfactant agents reduce the surface tension of water, improving its ability to wet surfaces and form fine droplets that reduce dust emissions. 

Another concern operators should be aware of is carryback. Without thorough discharge of bulk materials from the head pulley, fines can stick to the belt or get caught in cracks and divots, dropping off randomly and potentially creating fugitive dust along the entire return path. Having the proper primary and secondary cleaners is key to reducing carryback. For extra cleaning of tacky or powdery cargo, operators may consider installing a Washbox Cleaning System consisting of a powder-coated steel enclosure equipped with rollers, spray bars, inspection doors and secondary cleaners. 

“Compliance not only protects workers, but also protects the bottom line from fines, downtime and lawsuits,” said Heitzler. “Investing in long-lasting and field-proven equipment translates to a sensible ROI and peace of mind over the long term.”



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