Can We Maintain Social Distancing and Still Get People onto Office Floors?
Colin Wilson, associate director for Tetra Tech’s High Performance Building Group’s Brisbane, Australia, office and global vertical transportation lead, discusses how social distancing, when applied to elevators, may have us rethinking how we return to the office after COVID-19 restrictions are lifted.
With restrictions easing in many parts of Australia and other countries, Tetra Tech’s focus is turning towards a return to the workplace. Health departments in many countries have issued guidelines on physical distancing with typical recommendations of between 1.5 meter (m.) (5 feet [ft.]) distance from others and provide 4 square meters (sq. m.) (43 square feet [sq. ft.]) of area for each person where possible.
The following graph illustrates these physical distancing requirements applied within a typical commercial office, which includes a 21-passenger elevator (lift car) of internal dimensions 2 m. wide (6.5 ft.) and 1.7 m. deep (5.6 ft.), with 1.5 m. (5 ft.) distancing possible; however 4 sq. m. (43 sq. ft.) per person is greater than the available car area.
From the graph, we can appreciate why Safe Work Australia’s guidelines confirm the restrictions may limit elevators to an occupancy of 1 or 2 passengers at any time to meet the physical distancing requirements. To avoid doubt for all users, it would be good practice to identify standing zones with each elevator.
These requirements will have a significant impact on how people access and move, from commercial office buildings to hospitals, universities, and retail centers.
In commercial office buildings, a 21-passenger elevator—similar to the sketch above—would be expected to transport up to 15 passengers in a morning peak period to enable our offices to be loaded efficiently over a one-hour timeframe. With a reduced number of passengers in an elevator, the time taken to fully occupy an office building will be significantly longer.
The impact is best explored stepping through an example building.
Taking a commercial office building comprising of a ground floor and 11 upper levels of 1,550 sq. m. (16,685 sq. ft.) each, occupied at 1 person per 12 sq. m. (130 sq. ft.), this could be serviced by five, 21-passenger elevators using a destination control call algorithm and achieving a Property Council of Australia Premium Grade classification.
During the morning peak, the peak design arrival rate would reach 14 percent of the building population, or 198 people, in a 5-minute period with each elevator carrying an average of 13 passengers.
The average waiting time during the period would be in the order of 23 to 25 seconds and an expected queue length of 25 to 35 people (refer to graphs below).
With car loading reduced to two passengers per elevator, the outcome is significantly different, as the arrival rate of passengers very quickly exceeds the reduced capacity of the elevator system, resulting in long waiting times and passenger queues on the ground floor foyer (refer to graphs below).
With a passenger queue length exceeding 600 people, the required waiting area in the foyer to meet physical distancing requirements would need to accommodate a linear queue of at least 900 m. (2,950 ft.) or provide an area of at least 2,400 sq m. (25,834 sq. ft.). There is unlikely to be any commercial office buildings capable of providing the required space to accommodate these waiting passengers while meeting prescribed physical distancing requirements.
Until the current physical distancing requirements are relaxed, there will be a responsibility on building owners and tenants to ensure workers and visitors can enter and exit buildings safely. This will require a significant reduction in the arrival rate of people to office buildings to ensure the passenger demand does not significantly exceed the transportation capacity of the elevator systems in order to maintain acceptable queues in and around elevator waiting areas.
To be successful, building owners need to determine the maximum steady state transportation capacity of the elevator system in their building and ensure the arrival rate does not exceed this value.
Through simulation, the steady state transportation capacity can be determined by increasing the passenger demand incrementally until a time when the queue lengths and waiting times increase exponentially. This is illustrated below for our example office building.
In this example, when the arrival rate exceeds 3.5 percent of the building population, the queue length increases significantly, indicating passenger demand is exceeding capacity. An arrival rate of 3.5 percent or more will generate significant congestion in the entry foyer with a risk of breaches in physical distancing requirements likely to occur.
With this limited capacity, the elevator system will only be able to move approximately 42 people every five minutes during a morning peak. Restricting arrival rates to this level in buildings will be challenging but necessary for building owners, managers, and tenants if the current physical distancing guidelines are to be followed.
This example focuses only on the morning peak period. Reducing car loading to two people per elevator will have a similar detrimental impact on elevator performance during midday lunch peaks and evening down peaks and should be considered by every building owner before a large-scale return to the workplace occurs.
Despite the reduced elevator performance imposed by physical distancing, there are some measures building owners and tenants should consider to ease the transition back to office spaces, including:
- Explore options to compartmentalize the elevator car interior with acrylic glass—like those being applied in retail—allowing more passengers to be transported per elevator. It may be possible to create three or four passenger compartments and significantly increase transportation capacity over those available under current restrictions.
- Review the elevator’s internal dimensions for your building to determine the number of passengers each elevator can accommodate while complying with physical distancing requirements. Place standing zone signage with 1.5 m. (5 ft.) separation in elevators noting the distance is measured from the outer most point of the body.
- Stagger work hours for all employees in the building, including arrival to work, lunch breaks, and departures in the evening. It would be beneficial to provide each floor with a nominated timeframe for each peak period as this will limit the number of stops an elevator will be required to make, restricting mixing of employees from different tenancies.
- Restrict passengers from waiting for elevators on the ground floor; create waiting zones outside the foyer, allowing extra space for elevator passengers to exit with sufficient space without exceeding 4 sq. m. (43 sq. ft.) per person in lobbies (with a lobby width of around 2.5 m. (8.2 ft.). A five-car lobby would have an area of around 20 sq. m. (215 sq. ft.) and only able to hold 5 people without breaking physical distancing requirements).
- Reduce the number of people activating the elevator by having a concierge on the main entry floor to enter calls for patrons, reducing the number of people touching elevator buttons/screens. If concierge service is not offered, then building owners could encourage building occupants to use a personal stylus, or similar device, to activate elevator call buttons where possible.
- A number of buildings have multiple building entry points at ground level; therefore, an opportunity exists to assign an entrance for tenants located within an elevator group or rise (low, medium, or high-rise). This would enable building owners to monitor and control the arrival rate to the designated elevator group and ensure the arrival rate does not exceed the elevator’s transportation capacity. Buildings with a single elevator group may designate alternate entry points as either building entry or exit points.
- Limit cross traffic during peak period. For example, restrict morning down traffic trips for coffee breaks during the designated up peak periods. This could be improved by increasing existing food delivery services or implementing a new food and beverages delivery service.
- Where buildings have two main ground level entry floors (i.e. an upper and lower ground arrangement), consider restricting occupants to one entrance only to improve traffic handling performance.
- For buildings with escalators, encourage users to keep 4 steps (1.6 m. or 5.25 ft.) from other users by placing signage at the entrance to escalators.
- Investigate the use of stairs for inter-floor traffic where the building layout permits. This option should be reviewed with input from a building certifier and/or fire engineer to ensure fire safety, accessibility, security, and physical distancing requirements can all be maintained.