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Public transit systems play a vital role in connecting workers to their jobs. In 2024, passengers made a total of 7.66 billion trips on U.S. public transit vehicles, 50 percent of which were to and from work, according to the American Public Transportation Association’s 2025 Public Transportation Fact Book (PDF). But transit systems are also workplaces in themselves. More than 430,000 people worked for the nation’s roughly 6,700 public transit organizations in 2023, APTA states.

According to Doug Fallon, MSPH, CIH, CSP, and Trenell Boggans, MSPH, CIH, CSP, many occupational and environmental health and safety professionals are unfamiliar with the scale of work undertaken by public transit workers, as well as the hazards they encounter. “I had no appreciation for the amount of effort that goes into keeping the system running every day,” Fallon told SynergistNOW. He was recalling the time just before he became a senior industrial hygienist for the Washington Metropolitan Area Transit Authority. “I figured, if I, living in D.C., am this ignorant to it, then probably a lot more people are.” WMATA, also known as Metro, operates the Metro Bus and Metro Rail systems in the Washington, D.C., metropolitan area. The organization was named the Transit Agency of the Year in 2025.  

“We have designated groups that are out in the field day in, day out, making sure that the trains run smoothly from an infrastructure standpoint,” said Boggans, also an industrial hygienist at WMATA. “The tracks don't keep themselves maintained. There are people who work behind the scenes and make sure that things keep running.”

Hazards in Transit

Transit workers’ jobs are diverse, encompassing vehicle operations and maintenance, facilities construction and maintenance, warehousing, general administration, and, at large agencies, police. The hazards they face are equally varied. According to a 2015 Bureau of Labor Statistics report, the most common work-related illnesses and injuries reported by transit workers were related to transportation incidents; ergonomic stressors; slips, trips, and falls; and workplace violence.  

Though not covered by the BLS report, transit workers may also be exposed to hazardous substances and environmental agents. As part of a years-long project, Fallon and Boggans have gained an understanding of a particular hazard in the Metro Rail system: tunnel dust.  

Fallon explained that tunnel dust is mainly produced from the friction between train wheels and tracks. “Because it's a subway, there's a lot of starts and stops, so there's a lot of braking and then accelerating,” he said. “That all generates a lot of dust, mostly metal dust and other constituents from the brakes.” Fallon and Boggan’s sampling has revealed that dust in the Metro Rail tunnel system contains several potentially hazardous components, including lead, thought to come from brass in the brake pads on older trains, as well as iron and manganese, from the steel used in parts of the rail network. Heavy metals are common components of subway tunnel dusts due to similar rail operations across different transit systems, but each system’s profile is unique. Fallon and Boggan focused further sampling efforts on quantifying the risks from airborne exposure to Metro's tunnel dust.

Silica is another component of Metro’s tunnel dust. While some subway systems are primarily structural steel, Metro’s underground tracks are mostly built in concrete. WMATA workers must demolish and restore concrete almost constantly to maintain the system’s structures and rails. This produces silica exposures similar to those found in the construction industry, with the added challenge that the work is often occurring underground in enclosed areas.  

Critically, sampling revealed one hazardous substance not present in Metro’s tunnel dust. “There was always concern that the old rail brakes had asbestos in them because that was pretty common for old trucks and other heavy equipment,” Fallon explained. “We didn't find any asbestos, thankfully.”

Who Is Exposed?

Fallon and Boggans’ sampling of settled dust as well as particulate in personal and ambient air enabled them to identify the most exposed workers. Boggans explained that WMATA’s Track and Structures team is responsible for maintaining and inspecting Metro Rail tracks, including rails, ballast, and ties, as well as the structures that support and allow access to the tracks, such as concrete decking and pads, tunnel walls, catwalks, and pedestrian bridges. “Based on our work, they’re our most exposed group, so we have worked closely with them to make sure that they have the tools to do their day-to-day work safely,” Boggans said.

“A big part of their work is activities that generate some of this dust, like concrete demolition or rail cutting and grinding,” Fallon added. As such, Metro has invested heavily in hazard controls for the Track and Structures departments, especially when their work disturbs silica-containing materials. Metro’s silica exposure control plan dictates when ventilation, dust mitigation, and respiratory protection are required, and it empowers supervisors to act when needed to protect employees. All tools used by these departments for concrete work have either a vacuum attachment or water suppression, and each employee is provided with a powered-air purifying respirator for enhanced comfort and protection.  

Other groups encounter tunnel dust either during maintenance activities or their daily assignments in underground stations. These include employees tasked with maintenance of tunnel ventilation, station heating and cooling, communication and signaling, and power transmission systems, as well as those in customer-focused roles, such as station managers. Air sampling for these employees provided enhanced awareness and reassurance of the air quality in underground environments. “We can now provide them more detail of what they're actually exposed to,” Fallon said. He explained that air sampling results in the stations have not revealed any concentrations that exceed OSHA permissible exposure limits for hazardous materials detected in the dust.  

To help address any lingering concerns among these groups, Metro has added tunnel dust to its hazard communication training, provides enhanced hygiene supplies for tunnel workers, and administers a robust voluntary-use respirator program for those who desire extra protection.  

Next Steps

Transit workers may be exposed to hazards of great concern for OEHS professionals, such as lead and silica. But awareness of this is rare. “I don't think there's much known about the transit industry coming from an industrial hygiene perspective, unless you're already in it,” Boggans said.

The desire to increase appreciation for transit workers and the hazards they face is one reason why Fallon and Boggans will present an educational session at AIHA Connect 2026. In “The Mission of WMATA to Understand Tunnel Dust,” they will share their sampling methods, findings, conclusions, and planned further actions. “What can we do, as IHs, to mitigate hazards and make sure that our employees who are down in those unique environments, are working safely?” Boggans asked.

Subway train tunnels are unique environments with specific hazards, and different systems have slightly different dust compositions, based on their history and environment. Other OEHS professionals working in transit can use Fallon and Boggans’ findings as a starting point to identify hazards in their own systems. Professionals working in freight or commercial rail, highway construction, or mining may also find their work applicable.  

But the pair also hopes to receive feedback and advice from other OEHS professionals, no matter their industry. Boggans noted that AIHA Connect brings together professionals from many backgrounds and experiences. “Having those other perspectives is going to be beneficial in and of itself,” he said. “Sometimes you stare at a picture so long on your own. You get somebody else who's coming in to look at the picture too, they're going to have fresh eyes and be able to see something you went blind to.”

Almost everyone has taken a train at some point in their lives, Boggans observed, yet few know about the work that makes this possible. “Name three occupational hazards you can think of in the transit industry,” he said. “If you can’t, you should come to our education session.”

Doug Fallon and Trenell Boggans will present “The Mission of WMATA to Understand Tunnel Dust” on Monday, June 1st, from 3:15 to 4:15 p.m. Central time. AIHA Connect 2026 will be held June 1–3 at the Ernest N. Morial Convention Center in New Orleans. To view the conference agenda or to register, visit aihaconnect.org.