Fixing the Air We Breathe Indoors

On May 15, ASHRAE — the association of engineers who work in heating, air conditioning, and ventilation — set out its Proposed Standard 241P, Control of Infectious Aerosols.

They are soliciting comments on it until May 26 from the public. Links and instructions for comments can be found here.

This standard, which was put together over six months — lightning speed for ASHRAE, which often takes years to develop new standards due to its painstaking process — was built on years of work by the organization on indoor air quality and included some input from public health experts.

According to ASHRAE:

The standard will address long-range transmission of infectious aerosols and provides minimum requirements for:

  • Equivalent outdoor air (combined effect of ventilation, filtration, and air cleaning) for use during Infection Risk Mitigation Mode
  • Room air distribution to reduce risk
  • Characterization of filter and air cleaner effectiveness and safety
  • Commissioning, including development and implementation of a Building Readiness Plan
  • System operation in Infection Risk Mitigation Mode during periods of high risk
  • Maintenance tasks and their minimum frequency
  • Residences and health care facilities

ASHRAE issued some recommendations early in the pandemic that provided guidelines for the kind of filtration that should be used in buildings to minimize transmission of airborne viruses. Those guidelines, though very good, were based on ongoing work on indoor air quality and did not include the kind of comprehensive work they brought to this new standard.

These standards, once incorporated into building codes and other regulations for buildings, will be a major step forward in making sure that the indoor air is safe to breathe. In a world in which many people spend most of their time indoors, that is a crucial element of public health.

These standards will minimize the transmission of airborne diseases including, but not limited to, Covid.

The Centers for Disease Control also issued some ventilation recommendations on May 12 after the end of the pandemic emergency status in the United States. While these are reasonable standards, they are rooted in the recommendations from ASHRAE and others that were in place in 2020. They do not include the more detailed new standards proposed by ASHRAE.

The CDC could and should have issued similar guidelines about indoor air quality in 2020, when it became obvious that most Covid transmission was airborne and that poorly ventilated indoor locations were the places with the highest risk.

The John Snow Project — which is named after the man who figured out that cholera spread in contaminated water — has a detailed explanation of the CDC guidelines. They also have other good advice on protecting ourselves from the ongoing Covid pandemic.

Another excellent resource is the Corsi-Rosenthal Foundation. The founders, Dr. Richard Corsi and Jim Rosenthal, came up with the Corsi-Rosenthal box, which is an inexpensive air cleaner system based on a box fan and HEPA filters. It’s open source and there are instructions on how to build one on their website.

I have noticed that some conventions (including ASHRAE’s) are making and using Corsi-Rosenthal boxes to help keep the air clean. Conventions can be super-spreader events for Covid, since they draw a lot of people and many of the facilities that host them have very poor indoor air quality. (A recent conference that my partner attended had CO2 readings of up to 2000 ppm in small conference rooms in a hotel. At that level of CO2, which is considerably above the outdoor air of 450 ppm, people are sharing their lung exhalations.)

The CDC guidelines are late and far too many people are not paying attention to the pandemic anymore. The ASHRAE standards are excellent, but we will all have to push for governments to adopt them and apply them to old buildings as well as new construction.

However, it is possible that in the future we will not all be regularly sharing airborne viruses in our schools, offices, and public buildings. While not all contagious diseases are airborne, enough of them are that this can make a huge difference in our public health.

Now we need to put some real money behind a working public health system — the CDC failure in this pandemic has been a national disgrace and our local agencies are always underfunded.

It would be nice if the next pandemic (and there will be another one) is handled more rationally and successfully than this one. Indoor air quality would give us a good start.

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