“Reoccupying a building during the COVID-19 pandemic should not, in most cases, require new building ventilation systems,” says guidance from NIOSH and the Centers for Disease Control and Prevention (CDC). “However, ventilation system upgrades or improvements can increase the delivery of clean air and dilute potential contaminants.”
Vaccines may be the tool in the safety toolbox everybody’s talking about, but NIOSH recommends using multiple mitigation strategies in the workplace to reduce the spread of COVID-19. Besides masking, distancing and hand washing, another option is ventilation modification.
At the request of several health organizations, NIOSH has addressed ventilation Frequently Asked Questions and updated some existing FAQ answers on:
- carbon dioxide (CO2) monitoring
- technologies that claim to be effective for reducing the risk of virus exposure, and
- info and calculations for choosing portable High Energy Particulate Air (HEPA) cleaners.
Indoor CO2 monitoring reveals the quality of your building’s ventilation.
Cost effective monitoring can be done with handheld meters, used in combination with HVAC systems that don’t have modulating setpoints based on CO2 concentration. When taking this approach, the HVAC outdoor air dampers should be set to introduce more outdoor air than code requires. It may take collaboration with your building’s maintenance staff to get this just right.
To accurately measure CO2 concentration levels in individual rooms, the meter should be used with the HVAC operating and the room at normal occupancy.
According to NIOSH, good ventilation is anything below 800 parts per million (ppm). If readings are above that, it’s time to work on solutions to increase outdoor air flow. If you’re unable to get it below 800 ppm, it may require using enhanced filtration, such as HEPA air cleaners.
If you’re on target, don’t forget to take periodic measurements and watch for any trends. If the ventilation airflow (outdoor air or total air) is unchanged and occupancy capacity hasn’t increased, any future readings that reach 110% of your benchmark indicate a potential problem and should be investigated.
Before increasing your building’s total ventilation, take into consideration:
- enclosure characteristics of the building
- HVAC system capabilities
- level of control and/or building automation
- local COVID-19 transmission rates
- any employee health conditions that may be affected (check with HR), and
- weather conditions and outdoor air quality.
According to NIOSH, HEPA filters are more than 99% effective at capturing human-generated particles associated with COVID-19.
Portable HEPA filtration units with a fan system are “a preferred option” for auxiliary air cleaning, especially in high-risk settings such as public waiting areas. If you’re considering using them, take a look at EPA’s Guide to Air Cleaners.
When choosing a portable HEPA unit, the size of the room matters. The product description should indicate the largest room size, or suggested room size, in square feet that the unit is appropriate for. If the ceiling height is more than 8 feet, multiply the room’s square footage by the ratio of the ceiling height divided by eight. So a 300-square-foot room with an 11-foot ceiling will require an air cleaner labeled for a room size of at least 415 square feet (300 × [11/8] = 412.5).
For units that only tell you their air flow rate in cubic feet per minute (cfm), there’s a 2/3 formula to follow. A 300-square-foot room with an 8-foot ceiling needs at least 200 cfm of air flow (300 × [2/3] = 200). If the ceiling height is taller, multiply that result by the ratio of the ceiling height divided by eight. If that 300-square-foot room had an 11-foot ceiling, it requires an air cleaner that can provide at least 275 cfm of air flow (200 × [11/8] = 275).
There’s also such a thing as ducted HEPA systems. See the CDC/NIOSH discussion here.
The CDC doesn’t have a position on ionization, dry hydrogen peroxide or chemical fogging disinfection systems.
Before considering any of these, be cautious and do your own research. These “emerging technologies” don’t have much of a documented track record when it comes to cleaning/disinfecting large volumes of fast-moving air.
Because employees, and even members of the public, would be exposed to ions, reactive oxidative species or chemicals as part of the air cleaning process, don’t be afraid to ask for testing data that demonstrates a clear protective benefit under conditions consistent with the intended use.
There should be safety data that’s applicable to all employees, including those with health conditions that could be aggravated by air treatment. Also, documented performance data should be available from more than one independent, third-party source. Unsubstantiated claims, or limited case studies with only one device in one room and no reference controls, should be questioned.
If considering products that may generate ozone, verify that the equipment has UL 867 standard certification (Standard for Electrostatic Air Cleaners) for production of acceptable levels of ozone, or better yet UL 2998 standard certification (Environmental Claim Validation Procedure for Zero Ozone Emissions from Air Cleaners) which validates that no ozone is produced.
The CDC and American Society of Heating, Refrigerating and Air Conditioning Engineers both say you should avoid counting on temperature or humidity to control transmission of COVID.
On the other hand, there are studies that suggest preventing excessively dry air could help the body’s immune system stay effective. If humidification is used to maintain workplace comfort, double-check with the people most familiar with the specs of your building to verify that condensation or moisture accumulation won’t cause problems.