If you’re working in an office or eating in a restaurant, and someone 30 feet away exhales tiny particles of the coronavirus, those particles can drift and infect you. Picture cigarette smoke wafting across a room. Same thing. The precautions global and federal agencies are advising aren’t good enough. ­Social distancing — keeping six feet away — and washing your hands won’t protect you from this airborne virus. That isn’t fear-mongering. It’s science.

To defeat COVID-19 and reopen our economy, we all need to become radical indoor environmentalists, shifting our attention from outdoor air quality to the air we breathe indoors.

New research from the ­National Academy of Sciences contends that airborne transmission of the virus is “highly virulent,” the “dominant” way it spreads.

On Monday, 239 scientists jointly announced research showing “beyond any reasonable doubt” that “viruses are released during exhalation, talking and coughing in micro-droplets small enough to remain aloft in the air” and that can spread across a room.

They didn’t say what proportion of infections are caused that way, but the evidence may explain how one “super-spreader” in a room can ­infect dozens of other people.

The scientists, including engineering experts, urged countries battling the virus to make buildings healthier, by improving ventilation and installing air-cleaning technologies.

Here’s the takeaway: Indoor air quality is the key to reopening safely.

The scientists cited research showing how three families at three different tables in a restaurant in China all became infected with the ­virus. One person at table A came in with it, and when he talked, he emitted viral droplets that were carried across the room in a stream of air-conditioned air, infecting diners at two other tables.

In a restaurant, you’re maskless and more vulnerable. The mounting evidence on airborne transmission underscores the importance of masks and eye glasses or goggles. Viral particles can invade eye membranes too. The journal Lancet reports that “eye protection is typically under-considered.”

As for improving indoor safety, kudos to Gov. Cuomo for becoming an indoor environmentalist. At his June 29 briefing, he expressed concern about the airborne virus particles circulating in malls.

Unfortunately, he went too far, mandating that they install specific equipment — HEPA filters — in their air conditioning, before they’re allowed to reopen.

Mall owners are pushing back against the HEPA mandate, saying the filters won’t work with their existing systems or will cost too much.

Airlines use HEPA. Most recycle about 30 percent of cabin air through HEPA filters, and exhaust the other 70 percent out of the plane. The cabin air is replaced about every three minutes. So a plane is an unlikely place to become infected by airborne COVID-19: A passenger msut still worry about people seated close by and about contaminated surfaces, but not dirty air.

Unfortunately, few indoor spaces can be fitted like airplanes to turn over air in three minutes. But there are other, newer technologies that can be installed to combat airborne viruses.

“Healthy buildings should be the first line of defense” against the coronavirus, says Joseph Gardner Allen from Harvard’s School of Public Health. And against indefinite lockdowns.

Reopening plans proposed by most states and the Centers for Disease Control and Prevention overlook the problem of airborne spread and don’t consider high-tech remedies.

What the United States needs is a Green Indoor Deal, an infrastructure-spending plan to equip workplaces. It would be a bargain compared to prolonged unemployment benefits.

It could also help schools ­reopen. School-aged kids pose the lowest infection risk. Yet Mayor Bill de Blasio is insisting kids learn from home half the time. Why? The CDC recommends that students’ desks be spaced six feet apart, making it impossible to fit the whole class in one room. It’s going to be a nightmare for parents.

The CDC’s antiquated six-foot rule ignores that the virus can spread through the air and the technologies to battle that.

You may wonder why you haven’t heard this information from the CDC or the World Health Organization. They’re behind on the science. On Tuesday, WHO grudgingly acknowledged “the emerging evidence.”

It’s airborne, and it’s time to deal with that.

Betsy McCaughey is the chairwoman of the Committee to Reduce Infection Deaths and author of the forthcoming book “The Next Pandemic.”