National Academies Press: OpenBook

Air Quality in Transit Buses (2023)

Chapter: Day 2 Session 3

« Previous: Day 2 Session 2
Page 41
Suggested Citation:"Day 2 Session 3." National Academies of Sciences, Engineering, and Medicine. 2023. Air Quality in Transit Buses. Washington, DC: The National Academies Press. doi: 10.17226/27033.
×

Session 3

Other Strategies for Mitigating Transmission Risks

Moderators

Nathan Edwards, MITRE (formerly), U.S. Partnership for Assured Electronics (USPAE) (current)

Mariela Garcia-Colberg, TRB

Nathan Edwards opened the discussion on broader air quality challenges within transit systems with the TCRP Planning Committee members answering audience questions.

Q: How do we think about this problem of air quality and transit—as an engineering problem or a system design problem?

In response, Brian L. Sherlock noted that air quality issues have been ignored in transit, while thermal comfort has been explored. Transit has been ignoring air exchanges in vital, foundational considerations. Others have shown that there could be virtually no air exchanges; for instance, buses are almost sealed boxes. Groups with the necessary expertise are needed to advise the industry to have regulatory capacity because market forces will not accomplish that. The complexity is such that agencies and unions cannot be expected to do complex engineering fixes. The amount of money within transit that gets spent on improving air quality needs to increase to come up with high-enough-quality products to get people on to transit. Convincing the broader public of the need for transit and for transit to be safe needs to be the goal.

Ariel Piedmont noted the challenge is going to be changing the incentives, so that the bus design includes a good mix of filtration, minimum introduction of outside air, and consideration of airflow as vertical as opposed to horizontal inside the bus. Once the objectives for better airflow are stated it becomes easier to engineer to address those concerns.

Q: How do we think about mitigating the other emerging contaminants in public transportation, such as fire, wildfire, smoke, smoke from fentanyl or vaping, or marijuana that is being used on the back of the buses? What about other emerging industrial gases and other challenges that we see? How do we think about that in terms of technology and operations?

Jose-Luis Jimenez noted that the contaminants mentioned are aerosols and particles and they can be mitigated with the same technologies discussed for COVID-19 and other infectious diseases. Mitigation of gases, however, requires other methods. Ultimately there needs to be some level of ventilation and internal filtration inside buses.

Page 42
Suggested Citation:"Day 2 Session 3." National Academies of Sciences, Engineering, and Medicine. 2023. Air Quality in Transit Buses. Washington, DC: The National Academies Press. doi: 10.17226/27033.
×

Also, there are energy recovery ventilators that can use the cool air exiting the bus to cool the air entering the bus, which is more efficient.

Kit Conway noted, as someone who works at a public transit agency, that it is about going back to basics, that is, increasing the circulation of airflow, especially fresh air from outside the vehicle, and improving filtration as much as possible. Beyond that, the more sophisticated technologies take an expert.

Ken Bogen (of Versar, Inc.) discussed a paper by Yadav et al. titled “Synthesis and Biological Evaluation of Some Novel 1-Substituted Fentanyl Analogs in Swiss Albino Mice,” Interdisciplinary Toxicology, 2014 7(2): 93–102 (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4427721/) that presents the size distribution of fentanyl that is aerosolized and gives the size distribution of the particulates. The researchers exposed mice to aerosolized fentanyl. In a substantial fraction of the crystalline particulates of fentanyl, which has extremely low vapor pressure, about one fourth of the particles are going to have aerodynamic diameters of less than one-half micron, so it is not clear that N95 masks are going to be all that effective in mitigating that kind of a risk. For that reason, ventilation and negative pressure are among the various control options that are used in law enforcement in other contexts trying to deal with fentanyl.

Q: How have the transit bus filtration and air quality enhancements been communicated to the ridership and the public, and how has that kind of information affected ridership by their improvements or decreases?

Brian L. Sherlock responded that the ridership is remaining low because people are confused about whether the air inside the bus is safe. The public will not be convinced until the transit industry uses principles such as the vertical airflows that can isolate the passengers by using excellent filtration. The huge push to overhaul the fleets and go to battery electric designs means replacing all the buses, which provides the opportunity to resolve those air quality problems. To protect the operator, use positive pressure isolation, high-quality filtration, and the barriers that are effective against assault and COVID-19. But for the passengers’ protection, buses need to get away from longitudinal flow that carries viral shedding from one end to the other. Transit can, using roughly similar HVAC hardware with larger filters for lower restriction and decent flow rates, change the air direction from longitudinal to vertical.

Kit Conway noted that there are members of the riding public who are paying attention to air quality improvements. Following good science and sound judgment and sharing that with the public, even if they do not understand it initially, is important.

Brian Alberts (APTA liaison) commented that the American Public Transportation Association (APTA) is trying to be on the forefront of this issue. A communication that went out after APTA did a health and safety commitments program that started soon

Page 43
Suggested Citation:"Day 2 Session 3." National Academies of Sciences, Engineering, and Medicine. 2023. Air Quality in Transit Buses. Washington, DC: The National Academies Press. doi: 10.17226/27033.
×

after the pandemic required that transit agencies had to commit to having better air quality on their buses and in their trains. Members could put a seal on their buses and trains that said they were committed to helping and increasing air quality. Transit agencies are trying to communicate to the public that it is relatively safe to ride a bus again.

Q: Regarding some of the gaps that we have in standardization or testing methods, what do you believe is needed to push that forward?

Brian L. Sherlock noted that the current Altoona Testing, the independent testing performed by The Altoona Bus Research and Testing Center responsible for testing new model buses, should be expanded to look at the performance of various subsystems and that there are some huge costs associated with some of the bad design elements. There is a lot of good news coverage that we can generate by proper testing and proper intellectual resourcing, which eventually leads to standards that give the public a better idea of why they should pay increased amounts to support transit.

Allison Laurie Barrett commented that, as an air quality specialist in this field, the biggest issue is getting consistent monitoring, as changing the parameters slightly and suddenly can lead to very different results. Pushing those results out to the public can lead to significant issues if the science has changed. It can be difficult to communicate this in a way that is accessible to everyone.

Jason DeGraw noted that because indoor air quality is primarily about controlling contaminants, the only thing that really correlates with better indoor air quality is trying to control the contaminants. Making things more airtight has had the unintended effect of creating what is now called “sick building syndrome,” in which building occupants experience acute health effects that appear to be linked to time spent in a building. Air quality can be the first thing that gets value-engineered out, and creating better indoor air quality only happens intentionally.

Q: What is acceptable air quality in transit?

Jason DeGraw noted that acceptable and healthy are not the same thing. The conversation before the pandemic on air quality was about acceptable and not about healthy.

Ariel Piedmont commented that it is helpful to state what is acceptable, and more guidance may be needed. It is hard to tell an engineer to create a space that will not infect anyone.

Kit Conway noted that, rather than setting some number for transit for what is acceptable or healthy, using CO2 monitor readings as a proxy for indoor air quality would empower riders to make their own decisions about what numbers they are

Page 44
Suggested Citation:"Day 2 Session 3." National Academies of Sciences, Engineering, and Medicine. 2023. Air Quality in Transit Buses. Washington, DC: The National Academies Press. doi: 10.17226/27033.
×

comfortable with. Having an understanding of how the air in a space is being treated would make riders more comfortable. Getting that information in the hands of those people is maybe one way to think about it from a different angle.

Piedmont noted that it is hard to give that to a population in a single number.

DeGraw said that, typically, do not scrub out the CO2 along with the bioaerosols and the bioeffluents, if using the CO2 as a marker.

Jose-Luis Jimenez (not a member of the Planning Committee) noted that CO2 is not just an indicator of virus but it also by itself leads to cognitive decline and is an indicator of other indoor quality issues. Scientists are saying CO2 should be kept below 700 if there is no filtration, but if there is filtration, that it can go to 1,000 or 1,500, but 2,000 is too high, and the ventilation should be increased. CO2 monitoring is more useful in places where there is no filtration.

Brian L. Sherlock noted that there is no absolute answer, but there are practical answers. For instance, a MERV 13 filter could be an absolute, or the lowest performance acceptable. Also, incremental improvements could be made, such as adjusting the airflow direction, adding electrostatics to filters for improved filtration, and fixing the airflow around the exterior of a bus. Transit currently lacks a meaningful standards program that utilizes an iterative process that looks at what is practically possible within the current level of engineering and then make those standards flexible.

Q: What can the Transit Cooperative Research Program do moving forward with this topic of air quality and transit buses?

Allison Laurie Barrett noted that TCRP is best at getting input from anyone who has a good idea about a project or a research topic and then making sure that the best of those topics gets researched and then published in a manner that is accessible to the people who can most put them to use.

Tyler Baker agreed that TCRP helps connect best practices with transit operators.

Ken Bogen added that TCRP could gather consensus on some key research questions and the quantification of related data.

Brian Alberts noted that TCRP comes up with research problem statements and then moves forward with that research. For example, from this Insight Event, two topics to include could be (1) what is acceptable and what is healthy air quality and (2) vertical versus horizontal airflow.

Kit Conway noted TCRP could outline a basic threshold for what the transit agency should be thinking about or doing to keep people safe in the context of air quality. Small agencies, especially, struggle with the question of what they should be

Page 45
Suggested Citation:"Day 2 Session 3." National Academies of Sciences, Engineering, and Medicine. 2023. Air Quality in Transit Buses. Washington, DC: The National Academies Press. doi: 10.17226/27033.
×

focusing on and what the bare minimum is. Developing a checklist that could include the first three things transit should do regarding air quality would be a big help to small agencies that may not have the people with the time, energy, or resources to think about these things.

Jason DeGraw added [from his own perspective and not that of his employer] that the key to having good standards and guidelines is to have proper metrics that can be used to assess a situation. For example, building energy uses “energy use intensity” (EUI), meaning an indicator of the energy efficiency of a building’s design and/or operations. EUI is one number and is easy to evaluate. Having a similar number for transit could potentially simplify a lot of what has been discussed at this Insight Event.

Ariel Piedmont added that TCRP could introduce a venue for sharing the problem-solving going on among transit systems that would lead to peer review and dissemination of these ideas.

Mariela Garcia-Colberg concluded the TCRP Insight Event by noting that the panel will meet again to follow up regarding some of the problem statements discussed during the event, including the need for transit guidance, standards, testing, and better metrics. The transit industry also needs to know how to discern how effective various products are for cleaner air and reduced disease transmission and how to work with manufacturers to design the transit vehicle of the future. It is the task of TCRP to identify topic ideas and present them to the TCRP Oversight Project Selection Commission (TOPS), https://www.apta.com/research-technical-resources/tcrp/tcrp-oversight-and-project-selection-tops-committee/, which decides which topics will move into research. Finally, Garcia-Colberg thanked all in attendance.

Page 41
Suggested Citation:"Day 2 Session 3." National Academies of Sciences, Engineering, and Medicine. 2023. Air Quality in Transit Buses. Washington, DC: The National Academies Press. doi: 10.17226/27033.
×
Page 41
Page 42
Suggested Citation:"Day 2 Session 3." National Academies of Sciences, Engineering, and Medicine. 2023. Air Quality in Transit Buses. Washington, DC: The National Academies Press. doi: 10.17226/27033.
×
Page 42
Page 43
Suggested Citation:"Day 2 Session 3." National Academies of Sciences, Engineering, and Medicine. 2023. Air Quality in Transit Buses. Washington, DC: The National Academies Press. doi: 10.17226/27033.
×
Page 43
Page 44
Suggested Citation:"Day 2 Session 3." National Academies of Sciences, Engineering, and Medicine. 2023. Air Quality in Transit Buses. Washington, DC: The National Academies Press. doi: 10.17226/27033.
×
Page 44
Page 45
Suggested Citation:"Day 2 Session 3." National Academies of Sciences, Engineering, and Medicine. 2023. Air Quality in Transit Buses. Washington, DC: The National Academies Press. doi: 10.17226/27033.
×
Page 45
Next: Appendix A: Program Agenda »
Air Quality in Transit Buses Get This Book
×
 Air Quality in Transit Buses
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

With a major drop in U.S. transit ridership since the start of the COVID-19 pandemic, an increased understanding of infectious disease in confined spaces and the role of droplets and particles in transmission has been increasingly important to the bus industry. A combination of experiments, models, and simulations in fluid dynamics has been employed to understand how aerosols move in spaces containing people.

TRB's Transportation Insights 2: Air Quality in Transit Buses provides a summary of a June 2022 in-person TRB Transit Cooperative Research Program (TCRP) Insight Event.

READ FREE ONLINE

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    Switch between the Original Pages, where you can read the report as it appeared in print, and Text Pages for the web version, where you can highlight and search the text.

    « Back Next »
  6. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  7. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  8. ×

    View our suggested citation for this chapter.

    « Back Next »
  9. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!