Coronavirus, Ebola, and The Hidden Role of Air Changes and HEPA Filters in Hospitals

When a new, infectious disease takes way, treatment centers must be armed and ready to contain and treat infected patients. 

As COVID-19, better known as Coronavirus, continues to spread, hospitals need to be able to treat these patients without allowing the virus to spread further. Preventing the transmission of these respiratory pathogens requires infection control procedures and protocols, including safer work practices, personal protective equipment, and, most importantly, proper ventilation control.

So, how can hospitals ensure no airborne particles escape these rooms and infect other patients or the general public? This can be done through a combination of air changes, high-efficiency particulate air (HEPA) filters, upblast fans, and maintaining negative pressures within these units.

What are the designated air changes in a typical patient’s room?

A standard single patient room calls for a minimum of 6 air changes an hour with a neutral door pressure. This means all of the air in the room will be cycled 6 different times each hour. The neutral pressure means the air from the room is able to flow freely between the room and hallway.

What are the air changes in infectious isolation rooms and COVID-19 Biocontainment Rooms?

For standard infectious isolation rooms, you will have 12 air changes per hour(double a typical patient room) with a -.01 pressure at the doors. This ensures when the door opens air flows into the room from the hallway instead of out.

Note: Rooms that house patients with compromised immune systems will often have a positive pressure to ensure air from the hallway does not enter the room. 

When you start looking at rooms that house patients with more serious diseases like COVID-19 or Ebola these safety measures increase again.

A Biocontainment room generally has a -.03 pressure at the doors (3x’s the standard) on every room and 12 air changes per hour to prevent the air from flowing out of the room into the hallways. There’s also what is known as an anteroom (buffer room between the infectious isolation room and the hall), which also maintains a negative pressure and will generally have 10 air changes per hour. This greatly reduces the risk of air escaping from the room.

HEPA Filters, how do they work?

In an infectious control room, you can find HEPA filters in the rooms exhaust. As air changes occur and that air flows out of the room, it moves through a HEPA filter that removes partials down to  .3 microns in size and sometimes even smaller. How small is .3 microns? For scale, consider that the width of a human hair is typically greater than 5 microns or 16.67 times larger than the particles HEPA filters pull out.

A large up-blast fan pushes air from the room through the HEPA filter and out of the building with an exit velocity of 3000 ft per minute. After this air flows through the HEPA filter, it’s diluted with outside air and shot up high enough, so it’s safe for the surrounding area.

Medical facilities have these units tested using a  device called a photometer. This device is able to detect if any particles at .3 or larger are getting through the filter.

How frequently do HEPA filters need to be changed?

Due to the high cost associated with HEPA Filters, many companies opt to have pre-filters installed to extend the life of there HEPA filters. These pre-filters are changed out on an annual basis but can extend the life of the HEPA filter up to 5 years in some cases. When pre-filters are not installed, however, HEPA filters should generally be changed once a year. This prevents the buildup of dirt and contaminants in the filters. Since HEPA filters are thick in frame, they can impede airflow in HVAC systems, causing inconvenient breakdowns or malfunctions if they are not properly maintained.

When filters are changed out, the old filters are decontaminated, bagged, sent to biowaste and destroyed.

Additional Information

If you need additional information about how your facility should adhere to the latest standards regarding COVID-19 or any other airborne infectious diseases, visit  the ASHRAE COVID-19 Preparedness Resources page or refer to the ASHRAE resources below:

• ANSI/ASHRAE Standard 62.1-2019, Ventilation for Acceptable Indoor Air Quality – Outlines minimum ventilation rates and other measures intended to provide IAQ that is acceptable to human occupants and that minimize adverse health effects.
• ANSI/ASHRAE Standard 62.2-2019, Ventilation for Acceptable Indoor Air Quality in Residential Buildings – Defines the roles of and minimum requirements for mechanical and natural ventilation systems and the building envelope intended to provide acceptable indoor air quality in low-rise residential buildings.
• ANSI/ASHRAE/ASHE Standard 170-2017, Ventilation of Health Care Facilities – Ventilation guidance, regulation, and mandates to designers of health care facilities. It addresses hospital spaces, outpatient spaces, and nursing home spaces.
• ANSI/ASHRAE Standard 52.2-2017, Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size – Establishes a method of laboratory testing to measure the performance of general ventilation air-cleaning devices in removing particles of specific diameters.
• ANSI/ASHRAE Standard 55-2017, Thermal Environmental Conditions for Human Occupancy – Specifies conditions for acceptable thermal environments and is intended for use in design, operation, and commissioning of buildings and other occupied spaces.
• ANSI/ASHRAE Standard 185.2-2014, Method of Testing Ultraviolet Lamps for Use in HVAC&R Units or Air Ducts to Inactivate Microorganisms on Irradiated Surfaces – Establishes a test method for measuring the intensity of ultraviolet lamps on irradiated surfaces under typical HVAC&R operating conditions.
• ANSI/ASHRAE Standard 161-2018, Air Quality within Commercial Aircraft – Defines the requirements for air quality in air-carrier aircraft and specifies methods for measurement and testing in order to establish compliance with the standard.
• ASHRAE Guideline 28-2016, Air Quality within Commercial Aircraft – Serves as a companion to ANSI/ASHRAE Standard 161, Air Quality within Commercial Aircraft. Includes additional research and supporting information for guidance in assessing and assuring good air quality within the aircraft cabin.

At Rasmussen Mechanical Services,  we’re here to help ensure your indoor air systems are working the way they should. Whether you work in an office building, school or a hospital, our experts can help you ensure you are set up the right way. This ensures your staff stays happy, comfortable and healthy. Give us a ring at 1-800-237-314, or visit our website to learn how we can help you.