How can outdoor dining spaces be adapted for colder weather without exacerbating COVID-19 transmission and other safety risks?
“Winterizing” a restaurant and its outdoor space has probably never been more important for foodservice operators than in 2020. It’s a delicate balance; it’s tough to survive without the kind of space offered by winter patio dining, but it also has clear and inherent risks in the time of a pandemic.
The availability of outdoor space was vital for the industry and many individual operators over the summer of 2020. It allowed restaurants to maximize their space in a safe and socially-distanced manner, thus mitigating revenue losses. It also responded to consumer feedback, as many members of the public indicated they feel safer eating outdoors than in.
Moving forward, several cities have created new regulations to extend patio season by allowing winterized patios. Canada’s National Collaborating Centre for Environmental Health (NCCEH) has published a study, authored by Angela Eykelbosh, that was aimed at assisting foodservice operators in getting ready for winter patio dining.
The conclusion? There are numerous innovative ways to mitigate the specific risks of winter patio dining, which include the threat of COVID-19 transmission from other tables and the risk of carbon monoxide exposure due to the inappropriate use of fuel-burning patio heaters.
Challenges of winterizing patios
Based on dialogue with environmental health experts within the NCCEH and partner agencies and other professionals (NCCEH collaborators), a number of potential challenges related to outdoor winter dining were identified:
- Enclosure, decreased ventilation, and the potential for increased COVID-19 transmission
- Trying to fit more people into an outdoor space (i.e., non-compliance with physical distancing requirements) and the potential for COVID-19 transmission
- Increased risk of fire and carbon monoxide (CO) exposure due to the misuse of fuel-burning heaters
- Structural safety of temporary structures during inclement weather or heavy/wet snowfall
- Egress in case of an emergency
- Obstructing other users’ rights of way, particularly people with disabilities
Risk of transmission
SARS-CoV-2, the virus that causes COVID-19, can be transmitted via a number of different methods. Currently, public health evidence suggests that being in close contact with an infected individual creates the highest risk of transmission, and that the large majority of cases can be traced to a known case.
The risk of close-range droplet transmission can be mitigated by using masks, physical barriers that fully separate the breathing zones of those interacting and, of course, physical distancing. Enhancing and/or efficient ventilation is recommended to reduce the risk of short-range aerosol transmission. However, ventilation or air cleaning devices are unlikely to have any effect on reducing the risk of close-range droplet transmission.
Maskless diners in the same party are at high risk of infection if one member is ill and shedding the virus in their respiratory particles (within-party transmission). However, in a restaurant setting, the principal public health concern is to protect one party from infecting another. Hand-washing and limiting the numbers at any one table should help to limit this, but some enhanced degree of risk is inevitable when interacting this way.
The outdoor risk is generally accepted to be less than indoors, but it’s still present and is generally associated with crowding. A report found that indoor close contacts were almost 19-fold more likely to result in transmission than close contacts that occurred outdoors. However, while it seems that being outdoors may greatly reduce the risk of COVID-19 transmission, this isn’t necessarily true for restaurant patios where people are stationary together, particularly if they’re pretty full.
Enclosed outdoor dining
During the winter, partial or full enclosure may be necessary to protect clients from the elements and allow food to retain heat. There are two undesirable conditions to be avoided:
- “Tight” enclosure with limited air exchange that increases the risk of particle accumulation and short-range aerosol transmission between parties.
- Drafty conditions. For example, lowering two opposite walls of a tent (as opposed to two adjacent walls) can result in funnelling wind through the structure, and increases the likelihood of respiratory transmission.
Ventilation rates vary with outdoor conditions, and this lack of control is a key issue in being able to provide a safe environment for diners.
One option is to treat the patio space as an indoor space and manage it with a mechanical ventilation system that meets the standards for indoor spaces. However, this option may not be feasible for a variety of reasons. Another is adapting outdoor enclosures based on day-by-day weather. For example, “buttoning up” on windy days to reduce draftiness and opening up on still days to promote air flow.
Diners also play a role in comfortable outdoor dining and restaurants can reflect this with certain measures. For example, adding a weather widget to the restaurant’s website, or a reminder to dress warmly to apps used for booking reservations.
When does outdoor become indoor?
This question is a critical factor in assessing COVID-19 transmission risk. A problem is that there’s no universal definition. Colorado classifies temporary outdoor structures according to the presence of a roof, the number of walls, and the configuration of wall panels and the resultant air flow. For example, a structure with a roof and two adjacent walls is considered “indoor,” whereas structures with a roof and two non-adjacent walls, or two adjacent walls and no roof, are considered “outdoor.”
In contrast, Manitoba deems a space to be enclosed or indoor if more than 25% of its floor area is covered by an impermeable barrier, and more than 50% of its perimeter is more than 50% enclosed. In turn, New York City defines a partial enclosure as two walls, and full enclosure as four, but a full enclosure can only have 25% occupancy.
The issue of heating
In most cases, only electric heaters are permitted for use inside of tents, as long as the appropriate fire and electrical safety measures are in place. Although electric heaters are not without risk, fuel-burning heaters are unsafe to use within enclosures as they generate dangerous carbon monoxide. Propane heaters can be risky as combustion products may still enter the tent. In general, a number of inquiries to the NCCEH and its partners suggested that fuel-burning patio heaters are being used improperly due to lack of knowledge, as well as lack of safer options.
There are a number of themes and approaches to outdoor winter dining that were raised to the NCCEH, each with their own challenges, pros, and cons.
- Single-party enclosures. These can be dining pods, bubbles, domes, yurts, igloos, or cocoons designed to partially or fully enclose a single party of diners. These options reflect the public’s desire to restrict social interactions to known persons only, while still enjoying a public setting. Single-party enclosures might also be more space-efficient than multi-party structures with physical distancing and occupancy limitations. The key concern here is the potential for “airborne” transmission in small enclosed spaces, and it of course relies on diners sticking to their own bubbles or close-contact units.
- Park and eat. In-car dining proposals have included driving into a designated area (e.g., a re-purposed parkade or other large space), where customers could eat from one or multiple food service providers, usually while enjoying other forms of entertainment as well (concerts, movies, fireworks, etc.).
- Convertible or modular designs. For multi-party dining, designs can be convertible or modular, and therefore able to scale to party size or be moved or reconfigured to address physical distancing concerns.
- Creative heating options. These suggestions have been varied, and ranged from well-known technological solutions (e.g., electric space heaters, radiant floor heating) to highly personalized options like electric blankets, heated tables/chairs, electric capes, and even personalized hot potatoes to tuck into one’s pocket for later consumption. Carbon monoxide concerns, again, must be considered.
- Treating outdoor space as indoor space. Treating enclosed patios as an extension of the indoor space with equivalent heating and ventilation. This involved either a dedicated heating and ventilation system for the outdoor space or modification to the restaurant’s existing system.
- Passive ventilation. A number of entries proposed to use the stack effect to passively ventilate enclosures. Here, air warmed by heaters near the floors, occupant body heat, or hot food would be allowed to rise and pass through transoms or vents created in the roof of the enclosures, theoretically helping to clear accumulated aerosols.
- “Sterilization” approach. Another possibility could be using ultraviolet (UV) irradiation to “sterilize” surfaces after each party of diners leaves. The effectiveness of this solution would be dependent on the surfaces present and the maintenance of the UV unit.
Conclusions to draw
While patios are allowed to remain open, there are a number of creative means to provide comfortable outdoor dining that should not increase the risk of transmission beyond that of an indoor restaurant.
There are, however, a number of key risk communication issues for outdoor winter dining:
- Dining out heightens COVID-19 transmission risk because it requires unmasked, face-to-face interaction, and this risk exists both indoors and outdoors. The most effective way to reduce transmission risks remains to avoid close contact with those outside one’s own “bubble”.
- Single-party structures appear to be a popular and nearly ubiquitous option to prevent between-party transmission. Although use of single-party structures effectively eliminates this risk, it does not mitigate (and may slightly accentuate) the risk from those seated at the same table, particularly if an infection is present among the party.
- Tents or enclosures should be designed with passive ventilation in mind, and should allow for rapid reconfiguration to modulate airflow as weather conditions change.
- Devices that generate heat via combustion should never be used in enclosed spaces. Operators should familiarize themselves with the risks of CO poisoning and ensure that outdoor heating devices are used safely.
- Operators may also wish to consider a mix of heating strategies, including some of the personalized options like bring-your-own-blanket, as well as enhancing communication with patrons to ensure that they can dress for the weather.
The information discussed here is a response to a specific inquiry related to an environmental health issue. It is not a comprehensive evidence review and does not supersede federal, provincial or local guidance or regulations, and/or the advice of a medical professional.
The NCCEH is hosted at the BC Centre for Disease Control in Vancouver and funded by the Public Health Agency of Canada. It is one of six National Collaborating Centres created to foster linkages within the Canadian public health community.