As a September 1st deadline approaches for all 1600 public schools in the city (housed in 1300 buildings) to be tested for airflow, just over half of those school buildings continue to stand by for approval to reopen. The School Construction Authority president Lorraine Grillo said 340 schools have been inspected so far by Schools Ventilation Action Teams, with another 270 expected to be inspected by the end of Thursday.

Of the schools already inspected, 99 have received a final report, with 8% having at least one problematic classroom and the rest "just fine" for reopening, said Grillo. At one unidentified school in Brooklyn, a classroom was flagged for having windows that were nailed shut.

"That is going to be taken care of today," said Grillo, once again joining Mayor Bill de Blasio for a daily news conference on Thursday.

The SCA has formed more than 100 teams comprised of ventilation experts and engineers to determine airflow, considered a key way to filter out contaminants inside school classrooms. De Blasio has emphasized that the teams are another added layer of inspection that's been carried out by the city Department of Education, working with the Division of School Facilities and custodial staff to determine if classrooms are ready to go.

The city Department of Education plans to release its inspection results for each school publicly on the agency's website starting on September 4th.

"We're literally going to list the status of every single school as they go through the inspections and we'll be adding to the list every day as more inspection results are analyzed and completed," said de Blasio, adding the data would be delineated by schools ready to reopen versus schools with classrooms that aren't ready.

HVAC systems across schools are being upgraded with either a MERV-13 filter or a HEPA filter as a way of mitigating contaminants. HEPA filters were approved to be used in HVAC systems in public schools following an update by the CDC's updated guidance released last week. DFS currently has a supply of filters, according to Grillo.

While MERV filters can be installed in the HVAC system to filter small particle aerosols, epidemiologist Stephen Morse told us even that is not a perfect solution. "I’m assuming these are older systems," he said. "These filters provide good protection against fine-particle aerosols, but most HVAC systems are generally too high up in the room to prevent droplet transmission at close quarters, which is how we believe most of the transmission occurs." Opening windows, distancing, and wearing masks will also be important.

Classrooms without windows will be assessed for whether it's safe to use, based on guidance from the CDC or Environmental Protection Agency.

On Wednesday, pictures taken from a Manhattan high school surfaced showing a tissue placed on a stick as a tool to determine airflow. At a news conference in the Bronx that same day, de Blasio said the so-called "tissue test" is backed by the Centers for Disease Control and standard operating procedure.

As a way of further dispelling any misunderstanding, de Blasio invited George Roussey, senior director for technical design with the SCA, to clarify that the test is the standard way of determining the right amount of airflow sifting through a classroom.

"The tissue test is a qualitative method to see that the systems are running. So they're actually going into every space to see that the mechanical systems are actually running. If they don't see any air movement then they know that that particular area needs to be fixed," said Roussey. "We're also checking for operability for windows and other pieces of mechanical equipment."