Increased Risk of COVID-19 Transmission in Indoor Ice Rinks

Ventilation in indoor ice arenas poses a double threat during the COVID pandemic. Poor air circulation encourages the spread of the airborne coronavirus while also trapping air pollutants released by ice-resurfacing equipment such as Zambonis.

Air quality inside ice arenas has been studied for many years. Ice-resurfacers, powered by gasoline or propane, release pollutants, including carbon monoxide, nitrogen dioxide, organic compounds and particulates, which are all known to cause harmful health effects.

Air flow and thermal inversion

Figure 1: Smoke released from a smoke generator has been shown to settle about 10 ft above the ice surces. Adapted from Toomla et al. 2019.

The cool air near the ice pad and the warmer air above create a thermal inversion; this restricts air movement from the ice to other areas in the arena. Air flows are further hindered by boards and plexiglass barriers along the rink that can extend 9 to 12 ft. above the ice surface.

A recent study shows the air stagnation caused by using a smoke generator on the ice surface. After about two minutes, the smoke settled at about 10 ft above the ice.

COVID-19 circulation

A person infected with COVID-19 releases what are called ballistic droplets of viral material when they cough or shout, as well as smaller-sized particles, called aerosols, when they breathe, speak or sing. Ballistic droplets usually settle quickly, causing a risk of transmission when people are are less than 6 feet apart. Aerosols (less than 100 micrometers) can stay airborne for long periods, creating a risk of transmitting the virus over a large area.

While dynamics and spatial distribution of SARS-CoV-2 aerosols have not been studied in indoor ice arenas due to safety restrictions, past studies have shown that similarly sized aerosols were detected at breathing height above the ice in an indoor arena. Using the building’s heating, ventilation and air conditioning (HVAC) system was found to lower airborne bacteria levels by only 25% from periods with no mechanical ventilation.

Heating, ventilation and air conditioning

HVAC systems bring outdoor air into indoor ice rinks, diluting airborne contaminants and maintaining indoor air-quality requirements. Minimum ventilation in sports arenas, set by the American Society of Heating, Refrigeration and Air-conditioning Engineers' (ASHRAE) Ventilation for Acceptable Indoor Air Quality, Standard 62.1-2007, is 0.3 CFM/ft2 ice. Based on these standards, an NHL-sized rink (16,327 ft2) needs 16,330 CFM OA. In tests, this high outdoor-supply air has been shown to completely mix in the upper zone of the arena, as well as the stands around the ice. However, the thermal inversion over the ice pad reduced the efficiency of the air exchange to 27%.

Risk models

Figure 2: Probability of COVID-19 infection after 60 minutes of skating with or without a mask in an indoor ice rink operated at 20,000 CFM (A) and 2,500 CFM (B) HVAC outdoor air supply.

To measure how poor ventilation affects the transmission risk of SARS-CoV-2 while skating in indoor ice arenas, infection probability was modeled for various scenarios. They looked at the impact of:

HVAC supply air flow,
the number of COVID-19-infected people on the ice, and
mask use.

Ice rinks are often shared by two teams, with potentially 50 people on the ice. At a 7% COVID-19 test positivity rate (as in Connecticut in early January 2021), four COVID-19 infected people could be skating at a given time. In both high- and low-HVAC ventilation scenarios, the probability of infection increased 2.4 to 3.5 times for one infected skater versus five on the ice. The importance of wearing a mask is reinforced with these estimates – the probability of infection was found to be 1.5 to 2.5 greater for people not wearing a cloth mask compared to skaters assumed to be wearing a mask.

Also, the elevated levels of combustion-derived pollutants in indoor ice arenas can possibly increase the risk of COVID-19 infection, while temperature (55-65°F) and humidity (33-47%) levels designed to preserve the integrity of the ice surface may also stabilize SARS-CoV-2 aerosols.

Conclusions

Poor air quality and movement and mixing of the air can lead to elevated levels of airborne contaminants at the breathing height of skaters on the ice pad;
Temperature and humidity conditions inside ice arenas are within the range of conditions that may increase the survival of SARS-CoV-2 in aerosol;
Co-exposure to elevated levels of air pollutants, such as fine particulates and nitrogen dioxide, may worsen the severity of COVID infection;
Highly aerobic activity like skating will enhance respiration rate, increasing the release of potentially infectious aerosol if COVID-19 infected individuals are on the ice; and,
Highly aerobic activity will also enhance the risk of transmitting SARS-CoV-2 through increased breathing in of airborne contaminants.

It’s reasonable to suspect that the use of indoor ice arenas will increase the exposure of skaters to SARS-CoV-2 aerosols. Athletic activities inside ice arenas may pose an increased risk of COVID-19 transmission compared to athletic activities in other indoor and outdoor environments.