Introduction: Creating a Negative Pressure Room in Your Home
This guide offers step-by-step instructions on how to construct a negative pressure room in your own home using recourses you likely already have! The device works by sucking air out of the room by using a fan or other pressure management device. The air is then pushed through a filter, which can catch harmful airborne particles such as viruses and hold them during their activation period, after which time they are no longer a threat.
In light of the current COVID-19 medical crisis, precautionary plans must be taken to prepare for hospitalizations exceeding bed capacities and to create safe environments to treat less severe cases in the home. A key component of treating these cases is the health and safety of the healthcare provider. One of the core components of reducing the spread of airborne viruses such as COVID-19 between an infected patient and a healthcare provider is an airborne infection isolation room (AIIR). The purpose of an AIIR is to stop the virus from leaving the room, trapping it in air filters where it is deactivated and disposed of. This is achieved by creating a negative pressure environment inside the room and subsequently forcing all air out of the room through a filter and not through alternative routes such as heating, ventilation, and air conditioning (HVAC) vents, open doors/windows, or gaps around a door.
Without proper isolation rooms, infected patients pose a serious risk to people around them, including healthcare providers, family members, and other bystanders. Unfortunately, most hospitals lack the facilities needed for a large number of patients with airborne infections to be housed safely. In lieu of substantial AIIR facilities in most hospitals, many people will face COVID-19 in their own homes, this guide will offer step-by-step instructions to create a safe negative pressure AIIR room inside any home to protect the other residents of the house.
There are many ways in which a device of this nature can be constructed, and many different kinds of rooms in which it can be constructed as well. We will just cover one option in this description, a box fan model that utilizes a window in the room; however, other options and instructions can be found in this guide.
- Filter: (1) HEPA HVAC filter
- These filters can be found in a variety of sizes and for a variety of prices. We recommend using the Honeywell HRF-H2 filter, however a similar model can be found at Walmart, or on Amazon. It is useful for the filter to be the same size as the fan that you plan to use, but this is not a requirement.
- Pressure Management: (1) Box Fan, (1) extension cord, if necessary
- Attachments: (1) Roll of Duct Tape
- Coverings / Connections: (2) Plastic trash bags, (1) medium sized piece of cardboard - size depends on window size
Step 1: Fan and Filter Preparation
Overview: Once you have assembled your materials, the first step is to attach your filter to your fan in a way that ensures that all air that passes through the fan must pass through the filter before being exhausted through the window to the outside. In these steps you will use plastic strips (trash bags cut into strips) and duct tape to secure the filter to the exhaust face of the fan.
- Cut the plastic trash bags into long, wide strips. If you place the filter over the front of the fan, these strips should be wide enough to ensure that there are no gaps between the output face of the fan and the intake face of the filter.
- Tape the strips around the border of the fan output face, creating a skirt.
- Attach the top of the skirt around the borders of the filter using tape, effectively closing the gap between the fan and the filter in an air-tight environment.
Step 2: Room and Window Preparation
In this step you will create a way for all air that passes through the fan+filter combination to exit through a nearby window. To ensure that all air leaves the room you will connect the fan+filter combination to an air-tight window covering, this covering will have an opening that is the same size as the filter, to allow air to be blown out of the window.
- Identify any openings in the room through which air could escape. This includes HVAC vents, door cracks, etc...
- If the HVAC vent in the room is an exhaust it is okay to leave it as is. If the HVAC vent in the room is a return to the HVAC system of the residence, block off this vent using plastic and tape.
- Leave the cracks around the door to the room open; this will ensure that some fresh air is able to enter the room.
- Take a piece of cardboard and determine if this piece is large enough to cover the width of the window; if not, make sure that you have extra plastic available to close the gap.
- On your piece of cardboard, trace a shape that is the same size as your filter's output face, in the example this shape was traced in the center of the cardboard piece.
- Cut out the shape of your filter that was traced on the cardboard using scissors or an exacto-blade.
- Open the window in the room, to the height of the cardboard.
- Attach the cardboard with filter hole to the open window using remaining plastic and tape. Ensure that there are no gaps or cracks in between the window sill and the covering.
Step 3: Fan + Filter Attachment to Window Covering
In this step you will attach the fan + filter combination to the window covering you created in the previous step, and ensure that all air leaving the fan passes through the filter, and that all air leaving the filter is directed through the window.
- Using books or other props as shown in the photos, elevate your fan + filter device to the height of the window covering and opening. Secure the fan+filter combination in place, the system should be stable without risk of tipping or falling.
- Make sure that you are able to plug in your fan, or have the necessary extension cords to reach a nearby outlet.
- Using tape and plastic (if necessary) attach the output face of the filter to the hole cut in the cardboard, ensure that there are no gaps or cracks.
- The only way that air should be able to leave the room now should be through the fan+filter combination. The only way that air should be able to enter the room is through small cracks around the door to the room.
- If possible, check the window from the outside to identify any remaining gaps.
Step 4: Device Testing
Test before use! After turning on your fan, wait a few minutes from outside the room and test to see if a negative pressure environment has been created inside the room.
- Plug in your fan inside (using the extension cord if necessary) and let it run in the room with the door closed for a minimum of 5 minutes. If the room is very large you will need to run the fan longer at the maximum setting.
- If you do not have a digital pressure gauge you can evaluate using a smoke / tissue test to see whether a room is under negative pressure, as follows:
- Standing outside of the room, a tube containing smoke (can use a match or candle) or a lightweight tissue is held near the bottom of the negative pressure room door, about two inches in front of the door.
- Hold the smoke source parallel to the door.
- Take care to release the smoke from the source slowly to ensure the velocity of the smoke from the tube does not overpower the air velocity.
- Observe: If the room is at negative pressure, the smoke or tissue will be pulled under the door and into the room. If the room is not at negative pressure, the smoke will be blown outward or will stay stationary.
Step 5: Acknowledgements
Our team would like to acknowledge the department of Applied Physical Sciences at the University of North Carolina at Chapel Hill for its resources and faculty that assisted the Negative Pressure Project development. We would like to kindly thank Dr. Goldberg for his mentorship and for helping our team pivot through COVID-19 to achieve our desired goals. We would also like to recognize Innovate Carolina for providing financial assistance for the class materials. Lastly, we would like to acknowledge our families for tolerating hours of intrusive prototyping in our homes, and our peers who provided valuable feedback throughout the last weeks of the semester.