Guidance on Ventilation Systems and Occupancy Limits

After a review of the best available scientific evidence and federal and state guidelines, we recommend focusing efforts for preventing the spread of COVID-19 on key public health practices, including social distancing, face coverings, hand hygiene, isolation and quarantine protocols, and proper cleaning and disinfection of surfaces. When all faculty, staff and students adhere to these preventive measures, the potential for spread of the virus that causes COVID-19 is significantly decreased.

Adequate ventilation and avoidance of crowded indoor spaces can also play a role in decreasing the potential for transmission of the virus within enclosed spaces.

Campus Ventilation Systems

Early in the pandemic, Facilities took the following measures to improve ventilation systems in campus buildings:

  • Reprogrammed air supply units and maximized the amount of outside air supplied to building interiors with mechanical ventilation systems. If you work or study in a building with a mechanical ventilation system, you will receive the maximum amount of outside air that can be provided by the system. The amount of outside air supplied will be balanced with maintaining reasonable temperature and humidity levels to ensure occupant comfort and decrease the potential for microbial growth, including mold. 
  • Continuously operate ventilation systems that serve laboratory spaces 24 hours/7 days a week. 
  • Operate systems serving offices and academic spaces in a “flush” mode for two hours pre and post occupancy.
  • Regularly service ventilation systems to replace filters and verify function of the system.
  • Assessed rooms used for assembly and large, open work areas, such as classrooms and open office areas, to determine whether some activities should be restricted in any of these spaces.

Ventilation Flow Chart

Ventilation Guidance Flow Chart
*Click to enlarge.*

Occupancy Limits and Spacing  

The ability to maintain six-foot distancing, the ventilation system, and the type of activity (e.g., laboratory research, exertion, office work, etc.) are all factors in determining the recommended occupancy limits in Princeton buildings.

The following general principles apply to indoor spaces:

No mechanical ventilation
Windows closed
No mechanical ventilation
Windows open
Mechanical ventilation
Inadequate fresh air or filtration
Laboratories with standard lab ventilation Mechanical ventilation adequate fresh air or filtration
1 person

150 ft
per person

150 ft2
per person

125 ft2
per person

100 ft2
per person

  • Masks and six-foot distancing are required at all times.
  • Occupancy in a room with no mechanical ventilation or operable windows is limited to one individual.  If the room will be used by another person following the initial use, it must remain unoccupied for at least one hour prior in between uses. Work surfaces must be disinfected before and after each use.
  • Any space with no mechanical ventilation but equipped with operable windows that are open during occupancy is limited to one person per 150 ft2.   
  • Laboratories, machine shops, fitness centers and other spaces deemed to have adequate ventilation and where occupants regularly move about are limited to one person per 125 ft2.
  • Spaces equipped with a mechanical ventilation system that supplies adequate outside air as determined by current indoor air quality standards* can be occupied at 100 ft2/person.
  • Spaces with a mechanical ventilation system that cannot provide enough outside air to meet current standards* or sufficiently filter recirculated air can be occupied at 150 ft2/person.  These spaces should not be occupied for more than 4 hours continuously.

Maximum Room Capacity

Maximum occupancy signs must be posted at the entrance to each room or space, except for dorm rooms, that will be occupied by staff and students. Departments are expected to enter the occupancy number for each posted space.

Auditoriums, Lecture Halls, and Classrooms with Fixed Seating

  • Students shall be spaced a minimum of six feet apart.
  • Rooms will be provided with adequate outside air or adequately filtered air via a ventilation system to support occupancy of the space.

Classrooms without Fixed Seating

  • Students shall be spaced a minimum of six feet apart, at 1 student per 64 ft2.
  • Rooms will be provided with adequate outside air or adequately filtered air via a ventilation system to support occupancy of the space.

Instructional Laboratories

  • May be occupied at a density of 1 student /125 ft2
  • Rooms will be provided with adequate outside or filtered air via a mechanical ventilation system, depending upon the type of laboratory.

Meeting, Conference or Seminar Rooms without Fixed Seating

  • Occupants shall be spaced a minimum of six feet apart.
  • For rooms with adequate mechanical ventilation, the occupancy limit is 1 person per 100 ft2.
  • Spaces with a mechanical ventilation system that does not provide outside air in accordance with current standards or MERV-13 recirculated air can be occupied at 150 ft2/person. These spaces should not be occupied for more than 4 hours continuously.

Residential College and Other Student Social/Activity Space—Studies, Common Areas, Lounges, Activity Rooms, etc.

  • Students shall be spaced a minimum of six feet apart.
  • When people will be actively moving around the space, the limit is 1 person per 125 ft2.
  • For rooms with adequate mechanical ventilation, the occupancy limit is 1 person per 100 ft2.
  • Spaces with a mechanical ventilation system that does not provide outside air in accordance with current standards or MERV-13 recirculated air can be occupied at 150 ft2/person.  These spaces should not be occupied for more than 4 hours continuously.

Research Laboratories, Machine Shops, Maker Spaces

  • Occupants shall be spaced a minimum of six feet apart.
  • Occupancy is limited to 1 person per 125 ft2.
  • If an essential task unavoidably prevents adherence to these guidelines, EHS must be contacted prior to the activity to perform a risk assessment.

Shared Work Spaces

  • Spaces with adequate ventilation can be occupied at 1 person/100ft2.
  • Spaces with a mechanical ventilation system that does not provide outside air in accordance with current standards or MERV-13 recirculated air can be occupied at 150 ft2/person

Cubicles:

  • People with standing desks in adjoining cubicles must be 8 feet apart (person-to-person).
  • If the person-to-person distance between seated people in adjoining cubicles is less than six feet, the cubicle wall must be at least five feet high. The cubicle wall should extend 32 or more inches above the workstation surface.
  • In work spaces with no partitions, maintain a minimum of 8 feet between chairs.
  • While masks or face coverings are not required in private cubicles, masks are strongly recommended, if you are closer than six feet from the person in the adjoining cubicle
  • Shared workstations must be disinfected before and after use.

Other Open Spaces with Study Carrels or Workstations

  • Maintain a minimum of 8 feet distance between chairs.
  • Unused carrels and workstations should be marked, “do not use.”

FAQs

How much outside air is provided to our campus buildings?

*Wherever possible, the University meets or exceeds the outside air parameters recommended by ANSI/ASHRAE Standard 62.1-2019 on Indoor Air Quality. 

Ventilation systems in our older buildings may not provide the amount of outside air specified by this standard. However, all of our air handler units have been set to provide the maximum amount of outside air while maintaining reasonably comfortable temperature and relative humidity levels.

Is air in my office recirculated from other parts of the building? 

With the exception of laboratories and machine shops, the ventilation system in most buildings on campus provide a mix of outdoor and recirculated air.  Even the most stringent indoor air quality standards for classrooms, offices and assembly areas allow for a mix of outside and recirculated air.

Recirculated air is filtered before it is delivered back to occupied spaces. The quality of a filter is based upon its ability to capture small particles. The MERV (Minimum Efficiency Reporting Values) rating is a measurement of a filter's ability to capture particles of a certain size and range from 1 to 16. The higher the MERV rating the better the filter is at trapping certain size particles. When possible, our ventilation systems are equipped with MERV-13 filters, as recommended by CDC. All air filters are periodically cleaned and replaced by trained Facilities staff to ensure proper function

 

For more information, see the FAQs for COVID-19 Health and Safety