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Reducing Worker Exposure to Refractory Ceramic Fibers

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Reducing Worker Exposure to Refractory Ceramic Fibers 30 Safety First Reducing Worker Exposure to Refractory Ceramic Fibers Hazards are ever-present in the Refractory ceramic fibers (RCFs) Health Effects and Exposure Limits steel plant environment, and belong to a broad group of materi- a heightened awareness and als called synthetic vitreous fibers, Health effects from exposure to emphasis on safety is a necessary which includes many different types RCFs can include skin itching and priority for our industry. This of manufactured fibers produced by irritation due to contact with fibers. monthly column, coordinated by the melting and subsequent fiber- These fibers can also cause irrita- members of the AIST Safety & ization of kaolin clay, sand or other tion of the eyes, nose and throat, Health Technology Committee, naturally occurring minerals. Also which may lead to coughing and focuses on procedures and referred to as man-made mineral discomfort. These effects are typi- practices to promote a safe fiber (MMMF) or man-made vitre- cally temporary and dissipate after working environment for everyone. ous fiber, some common examples exposure.4 include fiberglass, mineral wool and More concerning is exposure alkaline earth silicate wool. through inhalation of respirable Specifically, RCFs are a group of dust and fibers. In addition to irri- man-made amorphous or crystalline tation of the respiratory tract, the fibers typically produced through National Institute for Occupational melting and spinning silicon oxide, Safety and Health (NIOSH) has aluminum oxide and certain other determined that occupational metal oxides to form a lightweight exposure to RCFs is associated with fiber. adverse respiratory effects, and may RCFs are widely used in the pose a carcinogenic risk based on steelmaking industry due to their the results of chronic animal inhala- Author physical properties, which include tion studies.1 Scott Shinn low thermal conductivity and high Several agencies have estab- technical service specialist — thermal shock resistance. Uses of lished occupational exposure lim- personal safety division, 3M, Maplewood, Minn., USA RCFs include high-performance and its (OELs) for refractory ceramic high-temperature insulation materi- fibers, both compulsory and volun- als for furnace linings, ladle covers, tary. These OELs are summarized heat curtains and mold linings, to in Table 1.2 name a few. RCFs, along with other Currently the U.S. Occupational high-temperature insulating wool, Safety and Health Administration provide many benefits to the steel (OSHA) does not have specific expo- production and casting industry. sure limits for refractory ceramic These include protecting workers, fibers, relying instead on the per- equipment and property from exces- missible exposure limit (PEL) of sive heat, improving the efficiency 15 mg/m3 (5 mg/m3 respirable) of furnaces and process equipment, 8-hour total weight average (TWA) and reducing energy usage. limit for total respirable dusts and However, like other man-made particulates not otherwise regulat- AIST.ORG and naturally occurring fibers, they ed. However, OSHA has endorsed I can become friable (easily broken the High Temperature Insulation Comments are welcome. or crumbled) when cut or damaged, Wool (HTIW) Coalition voluntary If you have questions about this or when they are at the end of use- product stewardship program (PSP topic or other safety issues, please ful life and pose an exposure and 2017) for RCF products.5 The prod- contact [email protected]. health risk to workers. uct stewardship program estab- Please include your full name, lishes a Recommended Exposure IRON & STEEL TECHNOLOGY I company name, mailing address Guideline (REG) of 0.5 fibers per and email in all correspondence. cubic centimeter (f/cm3) respirable refractory ceramic fibers, consistent JUL 2019 31 Table 1 Exposures should be controlled using a combi- Summary of Published Occupational Exposure Limits: nation of engineering and administrative controls. 8-Hour Time-Weighted Average (TWA) Engineering controls include adequate general dilu- Federal OSHA PEL 15 mg/m3 Total dust tion ventilation, use of local exhaust ventilation for Inert or nuisance dust 5 mg/m3 respirable fraction point of generation dust control and use of power ACGIH TLV 0.2 f/cc (1) tools with emission controls to minimize dust/fiber Refractory ceramic fibers A2 - Suspected Human Carcinogen generation during cutting and shaping of insulation NIOSH REL 5 mg/m3 (total) products. Administrative controls can include proper Synthetic vitreous fibers 3 f/cm3 (2) work and material handling procedures, worker train- State of California PEL ing, and good housekeeping practices. 0.2 f/cc (3) Refractory ceramic fibers 1. Respirable fibers > 5 μm aspect ratio ≥ 3:1 as determined by the membrane filter method at 400–450X magnification Suggested Material Handling and Housekeeping (4 mm objective), using phase contrast illumination. Practices 2. Fibers ≤ 3.5 μm in diameter and ≥ 10 μm in length. 3. Fibers per cubic centimeter of air at 25°C and 760 mm Hg • Limit use of power tools unless in conjunction with pressure. To be considered a fiber for this limit the glass particle local exhaust ventilation. Use hand tools whenever must be longer than 5 μm, have a length to diameter ratio of 3 or possible. more, and have a diameter less than 3 μm. • During handling or transport, avoid contact with rough surfaces and avoid dragging materials. Pieces should be fully lifted to help prevent release of fibers. with the proposed NIOSH recommended exposure • Use a brush under local exhaust ventilation or limit (REL) in the 2006 NIOSH Criteria Document a HEPA vacuum to clean insulation products of for occupational exposure to RCF. excess dust after cutting or machining. Both California OSHA and the American • Do not use compressed air to clean product or Conference of Government Industrial Hygienists work areas. (ACGIH®) have established a TWA OEL of 0.2 f/cm3.3 • Clean work areas with a HEPA vacuum. If sweeping This limit is primarily based on lung function changes must be used, utilize wet sweeping methods. and pleural thickening observed in RCF produc- • Clear waste insulation materials and clean work tion workers. ACGIH has also designated refractory areas regularly. ceramic fibers as a suspected human carcinogen.4 NIOSH has established a recommended exposure limit (REL) of 3 f/cm3 for synthetic vitreous fibers as Personal Protective Equipment (PPE) a 10-hour TWA. In 2006, NIOSH proposed an REL of 0.5 f/cm3 for respirable refractory ceramic fibers, When engineering and/or administration controls further stating that due to a residual risk of cancer are not adequate or feasible to control worker expo- that may still exist at this level, efforts should be made sures to RCF, use of appropriate and properly selected toward reducing exposures to less than 0.2 f/cm3.1 PPE can be utilized. Gloves and protective clothing should be worn to help prevent skin contact. Either disposable or reusable (launderable) clothing can be Workplace Exposure Controls used. If using launderable clothing, take care not to carry RCF into areas where others may be exposed. Employers using RCF insulation or handling RCF- Dedicated changing areas and laundry facilities are containing products during insulation installation or recommended. In addition, proper donning/doffing removal should assess worker exposures to RCF dust techniques can help minimize release of fibers. JUL and fibers. When assessing worker exposures to RCF, Proper eye protection should be used when per- 2019 respirable fiber counts are preferred over gravimetric forming activities that generate RCF dust and fibers, I measurements. Employers should also be aware that and with some operations safety glasses may be suf- IRON & STEEL TECHNOLOGY RCF insulation exposed to temperatures more than ficient. However, in operations that generate larger 900°C may see some conversion of amorphous silica to amounts of dust, a dust goggle may be the better crystalline silica. Bulk material testing or air sampling option. A face shield can also be used to provide methods can be used to determine crystalline silica additional protection for eyes and face. Reducing content. If respirable crystalline silica is present, refer risk of eye contact from extremely small particles I to the OSHA respirable crystalline silica standard, can be difficult to address as these particles tend to AIST.ORG 29 CFR 1910.1053, for employer requirements. stay suspended in air longer and can accumulate on top of hard surfaces, including hard hats. These fine 32 Safety First particles can sometimes reach the eyes through gaps Conclusion between the eyewear frame and workers’ skin. Recent advances in safety eyewear design, including foam There is no doubt that insulating materials manufac- linings on safety glasses and safety goggles, can help tured with RCFs provide the steel industry with many prevent these fine particles from reaching the eyes. benefits associated with thermal heat management In the U.S., if respiratory protection is required, the and energy savings. While there are inherent risks employer must implement an effective written respira- associated with the use and handling of these materi- tory protection program in accordance with require- als, proper worker training, material handling, house- ments in OSHA’s Respiratory Protection Standard keeping and maintenance procedures can be used to 29 CFR 1910.134. A particulate respirator with a reduce these risks and help provide a safe working minimum filter efficiency of 95% is recommended for environment. filtering of RCFs (NIOSH Respirator Selection Logic 2004). Measured airborne fiber concentrations should be used as the basis for determining the appropriate References respirator with the minimum assigned protection fac- tor needed to reduce exposures to an acceptable level. 1. “Criteria for a Recommended Standard: Occupational Exposure to A recent trend seen in many industries, especially in Refractory Ceramic Fibers,” Department of Health and Human Services, Centers for Disease Control and Prevention, and National Institute for the metal and metalworking industry, is the use of Occupational Safety and Health, DHHS (NIOSH) Publication No.
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