The New York Times – “…But fear of the risk of transmission indoors has fueled a market for expensive devices that promise to scrub surfaces — and even the air — clean of the virus. But most of those products are overkill and may even have unintended harmful consequences, experts warned. Some school districts have focused on virus-proofing their ventilation systems, and the C.D.C. has produced an exhaustive set of recommendations for businesses trying to keep employees from becoming infected with the virus. But “the conversation on risk reduction is beyond ventilation,” said Joseph Allen, an expert on building safety at the Harvard T.H. Chan School of Public Health. “It’s a layered defense approach where no one strategy in and of itself is sufficient, but collectively they can reduce risk.” Dr. Allen proposed these measures for managing larger buildings:

• Eliminate exposure whenever possible — for example, by encouraging staff to work from home;
• Permit entry only to those who need to be physically present in the building;
• Adopt strategies like adding air filters and disinfecting surfaces;
• Manage the flow of people going through the building — for example, the number of those in elevators at a time;
• Require the use face coverings and other personal protective equipment as appropriate indoors.

Researchers at the Massachusetts Institute of Technology have created an app to determine how many people can safely congregate in a given space and for how long. But regardless of these precautions, the optimal strategy is simply to wear a mask indoors, said Martin Bazant, a chemical engineer at the M.I.T., adding, “That’s a much bigger effect than any of those strategies would provide.” [h/t Pete Weiss]