Curtains Up! Safety Measures and Costs

Watch the recorded program here.


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Asked and Answered: Q&A with our ASHRAE Experts:


1. Can you address the possible interference of ozone when measuring aldehydes?

It depends on the sampling method. This resource might be useful as it addresses interference of ozone when sampling aldehydes using DNPH cartridges.

This study showed that ozone does not significantly interfere with the sampling.

2. Are there commercial HVAC HEPA filters available which contain antiviral components in the filtration medium?

Not for HEPA, but for some lower efficiency filters. Whether these are actually worth the additional cost is an unresolved question. Filters can be bagged and disposed of as ordinary waste. Eye and respiratory protection and gloves should be worn when servicing HVAC filters during the pandemic, and persons performing maintenance should wash well afterwards, but no other special precautions are believed to be necessary even for ordinary filters.

3. There a lot of pollutants to consider regarding Indoor Air Quality, how can this related to MERV 13 to mitigate the risk of Indoor pollution according to ASHRAE?

Mechanical filters remove one component of indoor air pollution – particles that have direct health affects and/or that may serve as the delivery mechanism for chemicals and microbes. Ventilation and gas-phase air cleaning (for example with activated carbon or other sorbent media filters) address gaseous pollutants and odor.

4. Thanks for presenting this as we are concerned about risk and protecting artists, staff and patrons. Are HVAC/ air quality standards or recommendations required of other public buildings that are already open to public (e.g, restaurants, bars, movie theatres, hospitals)? If not, very curious why?

Yes, many states and cities have established requirements for reopening various types of facilities. These include things like occupancy limitations and HVAC performance requirements (ventilation and filtration). In some cases, occupancy limits have been tied to ventilation.

See LCA’s COVID-19 Resources for links to Illinois and Chicago guidelines on reopening.

5. In terms of risk of infection, is there any consensus on what is an acceptable level of risk that is deemed reasonably safe?

Views of what is acceptable have not been formally established. Many have considered reduction to less than 10% for a single exposure and in some cases lower. Another is a "public health" approach that is based on reducing the R_0, the basic reproductive number of a disease to less than 1, which means that an average infected person infects less than one other person, which will cause an epidemic to end. E.g assuming one infector, less than one predicted infection. The outcome of analyses using the Wells/Riley model for a number of different occupancy types is 4 -6 air changes per hour. The HSPH/CU recommendations Marwa showed were developed for schools, but more generally applicable.

6. I understand VOCs are a concern from air cleaners. Can you expand if possible what cleaners to avoid? I found this article from Berkeley Lab on VOCs in cleaning/sanitization

I think the link is actually to surface cleaning products, but it is an important issue. Any of the air cleaners that add reactive substances to the air have the potential to produce either particles or organic compounds. These agents themselves have health effects. Included are ions (positive, negative, bipolar), dry hydrogen peroxide, photocatalytic oxidation, "cold plasma" and others. A recent paper reported both particle and organic contaminant generation by a bipolar ionization unit.

Zeng, Y., Manwatkar, P., Laguerre, A., Beke, M., Kang, I., Ali, A.S., Farmer, D.K., Gall, E.T., Heidarinejad, M. and Stephens, B., 2021. Evaluating a commercially available in-duct bipolar ionization device for pollutant removal and potential byproduct formation. Building and Environment, 195, p.107750.

Another recent paper reported increases in oxidative stress biomarkers resulting from exposure to negative ions.

Liu, W., Huang, J., Lin, Y., Cai, C., Zhao, Y., Teng, Y., Mo, J., Xue, L., Liu, L., Xu, W. and Guo, X., 2021.

7. When Marwa showed the filter of MERV 7 + 11 to achieve MERV 13, what particle size was that based on?  And did this account for anticipated virus distribuion between the different ranges?

See ASHRAE Building Readiness guidance.

It addresses filter performance based on particle sizes for different MERV. It's based on the typical respiratory aerosol particle size distribution.

8. It is my understanding that COVID spreads directly between people. If we need the air to come back to the air handler, is that really doing anything at all?

Within 3 - 6 feet, larger aerosol particles that have a tendency to settle can strike eyes, nose, mouth of a susceptible person who is close to an infected person. However, a significant amount of the infectious material in the air can remain suspended for a long time and move far from the source. Perhaps 50% of close range exposure comes from these particles and they can also cause infections at a distance. Ventilation, filtration lower the ambient concentration. There have been multiple cases of superspreading incidents that confirm this mode of transmission, which is why WHO and CDC acknowledged it last October.

9. We have small kiosks and an air cleaner of suitable size could not keep it clean, probably because it's too leaky. (air outside is "dirty" so it's easy to tell) for Covid should a person consider the leakiness of a space?

Within 3 - 6 feet, larger aerosol particles that have a tendency to settle can strike eyes, nose, mouth of a susceptible person who is close to an infected person. However, a significant amount of the infectious material Leakage would not subtract from the air cleaner clean air delivery rate of the air cleaner. Whether that leakage is a problem depends in part on where the air comes from. Would help if I could visualize the scenario more clearly.

10. We have been very conservative to achieve a calculated risk below 5% which is hard to achieve. Like you said there is no formally established acceptable baseline.

Given all the factors affecting infection risk - airborne, close contact, uncertainty in infectivity, etc., anything under 10% is probably within calculation uncertainty.

11. Will you be discussing resources to help us measure outside airflow, calculate time needed to flush out space etc.?

More appropriate for technicians/engineers, but there is information on flushing in the ASHRAE Building Readiness guidance.

A technician with the right instruments can do an outdoor air flow measurement or in some systems the flow measuring station may already be there. Alternatively, decay of carbon dioxide concentration over time can be used to estimate the outdoor air change rate. Harvard School of Public Health has described a number of techniques in its schools guidance.

12. This all seems to assume these are stand alone, large theatres. What about storefronts? 30-50 seaters in a residential building

The same general principles in the ASHRAE Core Recommendations apply. An important question is whether HVAC was upgraded for the theater occupancy. If ventilation low and cannot be increased, that could be addressed temporarily by reduced occupancy and in-room air cleaners.

13. How much of your recommendations can be eased, if say, in an orchestra rehearsal room, mandatory vaccination is implemented?

I would be guided by what public health authorities say - CDC, etc. Vaccines are not 100%, so even if everyone is vaccinated, there is still risk. There are not many recommendations we made that are not good permanent upgrades. Portable air filters could be removed eventually, and some control changes like disabling demand controlled ventilation could be undone.