Introduction

On March 11, 2020, the World Health Organization (WHO) declared Coronavirus Disease 2019 (COVID-19) a global pandemic [1], and on March 13, 2020, the United States declared a national emergency concerning COVID-19 [2]. COVID-19 has had disruptive impacts on all aspects of daily life. With an objective of mitigating the spread of COVID-19, the United States Centers for Disease Control and Prevention (CDC) has issued guidelines recommending that persons practice social distancing (maintaining a physical separation of at least 6 feet between two persons) [3].

The CDC social distancing guidelines introduce new challenges, as well as raise questions, as society attempts to return to 'a new normal'. Once such challenge is related to building designs, particularly public buildings, as people begin returning to their daily routines. Will current building designs enable people to safely return to their routines while maintaining the recommended 6 feet of separation? When designing a new building, does the planned design promote social distancing? To address these questions, cove.tool has developed a new analysis method focused on social distancing.

The newly developed method provides a quantitative metric for buildings, called the COVID Occupancy Assessment Score (henceforth COVID Score for brevity), that reflects the potential to maintain social distancing within a given building design. This metric can be used to optimize floor plans such that they encourage social distancing to the greatest extent possible. For example, a score of 100% for a floor would indicate that at every point on that floor, two persons would be able to maintain at least 6 feet of separation in all directions surrounding each point.

This metric refers to the AIA Re-occupancy Assessment Tool and the LEED Safety First: Re-Enter Your Workspace Pilot Credit for calculating the occupancy under social distancing guidelines.

The COVID Occupancy Assessment analyzes the floor area of the entire building to provide recommendations for the maximum number of building occupants (per level and for the whole building), the percentage of floor area in which a building occupant can safely practice social distancing, and a heatmap visualization of risky locations (purple; those less likely for two people to maintain recommended separation) and safe locations (blue-green; those with enough unobstructed space for two people to adequately maintain a 6-foot separation).

The remainder of this article is structured as follows. First, the calculation of the COVID Score is discussed. The discussion then shifts to explaining how to interpret the results, including the heatmap. Finally, two example cases are presented to demonstrate how this method can be used in practice.

Methodology

The COVID Occupancy Assessment is a grid-based analysis. First, each floor of the analyzed building is divided into 1-foot x 1-foot grid cells. Then, from the center of each grid cell, the presence of obstructions, namely, walls, windows, and furniture, is checked in all directions. If an obstruction is present, the distance from the grid center to the obstruction is determined, and this information is used in calculating the COVID Score for that grid cell.

After the COVID Score has been calculated for each grid cell comprising the floor, the scores are assigned to a color to generate a heatmap. The purpose of this heatmap is to provide a visual representation of the COVID Scores for the entire floor.

The COVID Scores for the individual grid cells comprising a floor are averaged, providing the COVID Score for that floor (COVID-floor = average of COVID-grids). The COVID Scores for all the floors are then averaged to provide an overall COVID Score for the building (COVID-building = average of COVID-floors). The COVID Scores for the floors and for the building are also used to provide recommendations for the maximum occupancies for each floor and for the building as a whole, respectively.

This method is based on the fact that the area of a circle with a 6-foot radius is 113.097 square feet (pi x r-squared, where r is the radius of the circle), which is larger than the area of a 10-foot x 10 foot room (100 square feet). The 6-foot radius, representing the recommended physical separation for social distancing, allows for human access (i.e., travel) through an area at the tangents of the circles formed by

the radius, including that of a close-packing arrangement of the circles.

Moreover, this principle can be used as a guide for identifying the building and fire code occupancies, as well as their respective occupant levels, that would be affected by using the CDC-recommended physical separation distance of 6 feet. In the following examples, to simplify the calculations and for the purposes of this exercise, a nominal area of 100 square feet per person is used rather than the area of a circle with a 6-foot radius (113.097 square feet), as a comparison for the stated allowable occupancy levels in the building code.

Interpreting the Results

The COVID assessment provides two results. The first is the COVID Score, which is presented as a percentage, and it represents the amount of open space of each floor and of the whole building that is most capable of maintaining social distancing between people. The second is the Recommend Occupancy, which is the suggested maximum occupancy of each floor and provided as a sum total for the whole building to safely maintain proper social distancing measures for each occupant. Each floor is analyzed individually and color coded with a heatmap grid for visualizing risky (purple) to safe (blue-green) locations. The resulting values and heatmap diagram vary according to the density of each floor level and the layout of interior partition walls and furniture.

COVID Score and Heatmap

Regarding the COVID Score heatmap, note that the intention of the diagram is not to indicate where people should not be. Rather, the riskier locations are those that have a lower potential for maintaining social distancing. The percentages provide a total score for each floor and for the whole building, and these percentages represent the potential to maintain social distancing. It is easiest to read the diagram as though each grid cell represents a person standing in the middle of it, as described in the following example.

There are three conditions that simulate the major scenarios for occupant safety.

  1. If nothing obstructs the circle boundary around a grid cell, then that grid cell receives a score of 100%. If an object obstructs the circle, then that grid cell receives a score that is less than 100% according to the extent of obstruction.
  2. At an interior wall, the grid is 50% obstructed; thus, a grid cell next to an interior wall receives a score of 50%.
  3. Obstructions also have an effective radius that simulates the potential to hinder a person from maintaining social distancing but not directly blocking them from doing so.

Recommended Occupancy

Example 1

Using the building code assembly occupancy for an unconcentrated space that

has tables and chairs—such as a restaurant—of 15 square feet per person, it can

easily be calculated that a restaurant occupancy designed to accommodate 100

people would be allowable with 1,500 square feet of floor space (100 occupants x

15 square feet per person as per the existing code).

That same 1,500-square-foot restaurant with the 6-foot radius of physical

distancing would only be able to accommodate 15 people seated in the restaurant

(1,500 square feet divided by 100 square feet of physical distancing per person). It

should also be pointed out that in a restaurant in which tables placed 6 feet apart,

the physical distancing would be violated when restaurant staff or others enter

the space of the 6-foot table separation because there would only be at most 3 feet of

separation.

Example 2

This example considers the layout of an elementary school classroom. A standard classroom is typically 30 foot x 30 foot (900 square feet) with a typical student load starting with 15-17 students for each classroom for standard social distancing calculations. However, with social distancing measures, the layout of desks constricts the available safe space for maintaining a physical separation between students and teachers. Testing three layout options results in Recommended Occupancies as low as 6 and at most 7.

Conclusions

Reaching a 'new normal' in the presence of COVID-19 is going to require developments in many facets of life, ranging from better understandings of the mechanism of action of COVID-19 to new medical advancements and the development of new protective measures. To help support social distancing to mitigate the spread of COVID-19, cove.tool has been actively developing new analysis methods to help optimize safer designs. This article has presented the newly developed COVID Occupancy Assessment Score, along with examples of how to interpret the results. Calculate the COVID Score for your project!

References

  1. https://www.who.int/news-room/detail/27-04-2020-who-timeline---covid-19
  2. https://www.whitehouse.gov/presidential-actions/proclamation-declaring-national-emergency-concerning-novel-coronavirus-disease-covid-19-outbreak/
  3. https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/social-distancing.html
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