Air filtration calculations for determining how quickly CT scan rooms can be used between patients.
Note: your building engineers will know this stuff. Don’t be hesitant to ask them for the numbers.
The current pandemic continues to keep us on our toes in relation to how we give the best patient care while keeping ourselves safe at the same time.
Note: this article deals with wait time on air turnaround, not the wait time to let your wiped-down room dry. That is based on the chemicals you use to disinfect (Sani-Wipes or other cleaners.)
For total room turnaround times (TATs), you need to know two things;
- How long it takes for your disinfecting chemicals to dry on walls, equipment, etc.
- How long it takes for your air handler to filter all the air in the room
Knowing how quickly your air handler turns over and filters the air in your imaging exam rooms is equally important with a suspected airborne virus.
Coronavirus, or Covid-19, has been classified as an airborne virus by the CDC. Once you scan a suspected or confirmed Covid patient in your imaging room, you need to know how long you have to wait before you can image the next patient.
Let’s discuss your CT Room and How Long to Wait Between Covid Scans.
Air Filter Basics
There are two basic types of air filters:
These create a physical barrier which traps or captures small particles
These use a high-voltage charge to attract and capture contaminants.
There are a few air filters that are hybrids which combine both methods. Some of these use activated carbon elements to deter odor.
These filters use ultraviolet light to kill airborne bacteria and viruses. A common place to find these filters is in a tuberculosis ward.
Air filters can be built into the heating and cooling system or can be used as a freestanding unit inside the room being filtered.
Note: the EPA and the American Lung Association do not recommend the use of ozone generators. These rely on ozone
How to Determine Your TAT for CT
You need three data points to calculate the amount of time needed to filter the air in your CT room.
Note: HEPA filters are still only 99.9%
- You need the total square footage of your CT scan room.
- You need the air return rate measured in CFM (cubic feet per minute).
Take your total room sq foot and divide by the air return rate. That gives your air handler turnaround time.
I add an additional 25% for safety and filter loading variances.
According to the CDC, minimum total air change per hour is six cycles. Six cycles in 60 minutes (one hour) means turning the air every ten minutes, at a minimum.
Our data shows we turn our air every 4-5 minutes, so we’re good.
Why HEPA Filters?
These High-Efficiency Particulate Air filters were first invented during World War II. Their design was “highly efficient” in preventing radioactive particles from escaping laboratories.
These filters are usually made of different types of synthetic fibers because there is no construction standard to date. The efficiency rating specifically designates the ability to filter out 99.97% of all particles at a size of 0.3 micron or larger.
But Covid-19 is Smaller than 0.3 micron!
Yes, the Covid-19 virus has been measured with the use of an electron microscope to be approximately 0.125 microns.
But not to worry!
NASA has verified through a process called diffusion, particles as small as the Covid-19 (and other nano-particles) get captured “virtually 100%” of the time.
When used alone, HEPA-rated media provides superior performance for removing virtually 100% of particulates.JL Perry, JH Agui, R. Vijayakumar – NASA
The University of Minnesota also tested this by using HEPA filters to catch particles of silver that were roughly 5-30 times smaller than Covid-19.
Their conclusion showed showed a capture rate of 99.99%.
Wait Time for EVS to Enter CT Scan Room?
After the scan is completed, terminal cleaning may be performed by EVS personnel according to the CDC. They should delay entry into the room until sufficient time has elapsed for enough air changes to remove potentially infectious particles.
We do not yet know how long SARS-CoV-2 remains infectious in the air. But you now know how long it takes to filter your air.
After this time has elapsed, EVS personnel may enter the room and should wear a gown and gloves when performing terminal cleaning.
A facemask and eye protection should be added if splashes or sprays during cleaning and disinfection activities are anticipated or otherwise required based on the selected cleaning products.
Shoe covers are not recommended at this time for personnel caring for patients with COVID-19
This article, CT Room – How Long to Wait Between Covid Scans, has been written to help you determine how much time needs to pass between scanning suspected or known Covid-19 patients.
Talk to your building engineers and find out the data for yourself. While you’re at it, ask about the rest of your modalities too.
You need to know the TAT on all rooms in your department for this pandemic and any future suspected airborne diseases.