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Life and Work: Respiratory Exposure Concerns

With the increased public awareness that COVID-19 has brought to respiratory issues, it’s timely for technical leaders to review safety recommendations regarding exposure to particulate matter less than 10 microns. As an engineer working in industry, you may need to protect your own health and/or advocate on behalf of others.
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This article was written to encourage you to protect your own health, and to encourage you to advocate for your co-workers who, lacking the credentials of an engineer, may not have as strong a voice as you do.

In recent years, there have been many new discoveries regarding particulate matter less than 10 microns (PM10) and less than 2.5 microns (PM2.5). Women need to be especially aware of exposures and personal protective equipment (PPE), because respirators sometimes do not fit women’s faces well, and being shorter in height can, in some situations, lead to increased fume and dust exposure. Adding to these considerations is the fact that some fine powders and fumes that were not classified as hazardous even 10 years ago now require more stringent controls.

Life And Work: Respiratory Exposure Concerns
Example from an OSHA publication of a powered air purifying respirator (PAPR). Many different masks and helmet designs are available.

Tiny but dangerous

The risks of inhaling fine particulate matter in everyday life and at work have long been public knowledge. “Killer smogs” were common in the 1940s, and Congress passed the first Air Pollution Control Act in 1955. The U.S. Bureau of Mines set its first standards for breathing masks after World War I. As reported by Riccelli (2020), both mild steel and stainless steel welding fumes have recently been classified as group I carcinogens. Welders have exhibited lower resistance to pneumonia, and welding fumes have been found to contain PM2.5 particles.

Fine particulate matter in relation to Covid-19 has been in the news since articles on wildfires and air pollution surfaced this summer. While there are multiple contributing factors under discussion with respect to the Covid-19 correlations, scientific studies in the U.S. and Europe have indicated higher Covid-19 risk in areas of higher air pollution.

Particles less than 10 microns are categorized as “inhalable particles.” For some groups of materials, particles between 1 micron and 5 microns can penetrate the lung to the bronchi and bronchioles, and particles less than 1 micron can reach the alveoli and can cause immunological and inflammatory reactions. Inflammation and/or other long-term adverse health effects in the lungs caused by fine particulate exposure have been reported in several articles.

Advances in 3D metal printing drove a renewed look at fine powder safety standards over the past five years. Most 3D printing processes start with metal powder that is subsequently sintered to produce the final part. If you were exposed to fine powder before 2015, there could have been new discoveries about safety in the interim.

However, powders exhibiting these fine particle sizes have been present in industry for decades before the industrialization of 3D metal printing.

This article will highlight some PPE and exposure considerations; encourage those with past respiratory exposure to particles less than 10 microns to talk with their doctors; and encourage engineers to serve as advocates for their co-workers, such as machine operators, technicians, and hands-on maintenance personnel.

Height and gender can make a significant difference in respiratory exposure. Shorter workers tend to have shorter arms, and their heads are closer to standard height lab benches — and to the dust created when moving, pouring, or sampling powders. 

Greater use of powder-based processes

In the mid-1990s, the powder metallurgy processes that were designed for specialty high-temperature applications metals (such as tungsten) became more prevalent in selected iron and nickel-based applications, as an alternative to machining and/or casting. Powder-based processing typically involves compacting powder under high pressure and heat-treating (or sintering) it to produce the required density and properties. Computer-controlled 3D metal printing processes also typically start with powder. Ceramics can be sintered and/or 3D printed as well, starting from fine powder. As these powder metallurgical processes became common for these additional materials, the possibility for employee respiratory exposure grew.

So how about particle size — is 5 micron or 1-micron powder rare? The answer is no. There are many industrial facilities with particles less than 5 microns. And even if the average particle size is 15 or 30 microns, there may be a percentage below 5 microns or below 1 micron. Also, some powders are friable, and may fracture into smaller particles in transport. In near net shape processes, fine particles aid sintering, so removing these particles would be detrimental to the yield and/or would require significant process adjustments.

Therefore, in some industries, fine particles collected from sieving loss or other operations are sometimes added back into the material if they are chemically pure. Even metal powders designed to have an average particle size greater than 30 microns may contain fine satellite particles < 3 microns, held in place either by electrostatic forces or by mechanical attachment, see articles by Mellin (2016) and Arrizubieta (2020).

PPE and exposure concerns for women

Height and gender can make a significant difference in respiratory exposure. Shorter workers tend to have shorter arms, and their heads are closer to standard height lab benches — and to the dust created when moving, pouring, or sampling powders. Women need to make sure they have a respirator that fits, and they may wish to advocate for a quantitative fit test instead of a qualitative fit test if they expect to be talking or moving while using the respirator.

A quantitative fit test includes a challenge agent outside the mask, while the person reads aloud a specific paragraph, as described in OSHA Standard 1910.134 Appendix A . You may need to be an advocate for yourself and/or for a co-worker if the respirators your company initially decides to stock do not fit properly. You may find that you are the only employee at your site who needs a different brand of respirator. And yes, employees who were fit in the past with a qualitative fit test may not have been fully protected if their tasks involved talking or head movement.

Accumulation of risk: Tracking industrial respiratory exposure is complex, since changing jobs or even just changing projects can expose you to different materials. In regions of high job mobility, such as California, employees may work at many plants and companies over a short time period. Changing life conditions, such as commuting method and lifestyle habits, also add to an individual’s exposure history. Don’t forget to account for hobbies: Recreational sources of particle exposure could include woodworking, gardening, chalk, and metal oxide exposure from artist materials and even flour exposure from cooking. There are also situations where debris from work clothing can become a significant home contaminant, if the clothing is not segregated and laundered carefully.

It can be difficult to determine the cause of a respiratory issue if you have respiratory exposure from work and additional exposure from home. It should be noted that current material safety data sheets (MSDS) can be obtained, but past changes in particle size or material composition can be difficult to obtain. Without this information, it can be difficult to ascertain the details of past exposure.

The bottom line: If you read through the discussion above and find you have had significant exposure to industrial fine powders or other industrial respiratory irritants, consider creating a data packet of the MSDS’s to discuss with your doctor. Comprehensive toxicology reports and journal articles are available on many materials. References by Naqvi (2008) and by Yates (2018) describe cases in which special additional tests such as SEM analysis on lung biopsy samples and bronchoalveolar lavage (BAL) were helpful in diagnosing industrial exposures. Your doctor may also suggest that you obtain a home oximeter or pulmonary peak flow unit, both of which are quite affordable.

Given the hazards of fine particles and the unknown effects of industrial respiratory exposures on COVID-19 comorbidity, all engineers working in industry need to be vigilant in protecting their health. Deciding to wear a mask at work or home when it is not required can bring unwanted questions, and sometimes pushback from your employer. Remember that the proactive employees and unions from the past were instrumental in bringing us up to the level of safety we have today. Some materials that appeared nonhazardous 10 to 20 years ago are now routinely handled with either passive or powered respirators in some well-informed companies. This is the time to raise questions to protect your health and that of your co-workers.  


Arrizubieta, Jon Iñaki et al, Study of the Environmental Implications of Using Metal Powder in Additive Manufacturing and Its Handling, Metals 2020, 10, 261; doi:10.3390/met10020261 

Bukowski, Thomas J. 2014. Women and PPE: finding the right fit. Safety and Health.

CBS News. 2018. Baker’s asthma: Edmonton study to examine long-term health hazards of flour dust.

Cole, Matthew, et al. 2020. Air pollution exposure and COVID-19. IZA Institute of Labor Economics. Discussion Paper 13367.

Flynn Jr., James H. and Holder, Charles D. (Eds.). 2001. A Guide to Useful Woods of the World, Appendix B, ISBN 1-892529-15-7. Forest Products Research.

Mark, Saralyn. 2020. Account for gender/sex to make PPE safer for women. Stat.

Mellin, Pelle et al. 2016. Nano-sized by-products from metal 3D printing, composite manufacturing, and fabric production. Journal of Cleaner Production.

Mizutani, Rafael Futoshi et al. 2016. Hard metal lung disease: a case series. Jornal Brasileiro de Pneumologia 42(6):447-452. doi:10.1590/S1806-37562016000000260.

Naqvi, Asghar, et al. 2008. Pathologic spectrum and lung dust burden in giant cell interstitial pneumonia (hard metal disease/cobalt pneumonitis): review of 100 cases. Arch Environ Occup Health 63(2): 51-70.

Riccelli, Maria Grazia, et al. 2020. Welding fumes, a risk factor for lung diseases. International Journal of Environmental Research and Public Health 17.7: 2552.

Spelce, David, et al. 2018. History of U.S. respirator approval. Journal of the International Society for Respiratory Protection 35(1): 35-46.

U.S. Occupational Safety and Health Administration (OSHA). Standard 1910.134, Appendix A Fit Testing Procedures (Mandatory). 

Wu, Xiao, et al. 2020. Exposure to air pollution and COVID-19 mortality in the United States. medRxiv 2020.04.05.20054502; doi: 10.1101/2020.04.05.20054502. April 24 revision.

Yates, Deborah, et al. 2018. A case of unsuspected hard metal lung disease in a thermal sprayer in NSW, Australia. European Respiratory Journal 52: Suppl. 62, PA1219.


  • Lisa Maiocco, SWE

    Lisa Maiocco has a B.S. and M.S. in materials engineering from the Massachusetts Institute of Technology and the Thayer School of Engineering at Dartmouth College, respectively. She has worked in industry and R&D as a metallurgist, manufacturing engineer, and Six Sigma black belt for 25 years, and is a member of the SWE Boston Section. The author acknowledges Diana ben-Aaron, Ph.D., for her technical review and editing of the manuscript.