This guidance provides a uniform definition for outdoor operations as used in CDPH-Cal/OSHA industry guidance related to the prevention of transmission of COVID-19.
Specifically, this document defines outdoor operations to include operations that are conducted under a tent, canopy, or other sun shelter, as long as no more than 50% of the structure's perimeter has impermeable walls, allowing sufficient, unrestricted outdoor air movement resulting in cross-ventilation. Such walls must be non-adjacent or non-continuous. Of note, doors, windows and other portals do not make a wall "non-continuous." Adjacent walls are walls that touch each other and form a corner. This supersedes the definition in the July 13, 2020 Public Health Order.
Classification of Types of Outdoor Structures
As California starts to experience colder months, restaurants and other businesses that must continue to operate outdoors may wish to enclose more than one side of the operation to contain heat and avoid rain. This document outlines the parameters businesses must follow to reduce the risk of COVID-19 transmission for customers in these temporary structures and to qualify as outdoor operations under CDPH's guidance.
In general, the more people from different households a person interacts with at a gathering, the closer the physical interaction is, and the longer the interaction lasts, the higher the risk that a person with a COVID-19 infection, symptomatic or asymptomatic, may spread it to others. Public health studies have also shown that the risk of transmission is increased in indoor spaces, particularly when there isn't appropriate ventilation. Unlike indoor spaces, movement of wind and air in and through outdoor spaces can help reduce the concentration of virus in the air and limit spread of the virus from one person to another.
The table below explains the criteria the state uses to classify a setting as indoors or outdoors. In the table, an impermeable wall is defined as any material type that can reasonably restrict aerosols from passing through. A fabric curtain and a tarp or plastic barrier are considered an impermeable wall because the material would prevent aerosols from passing through. A permeable wall is one that is made of a material or design which does not significantly impede natural air flow. For example, barriers such as a lattice fence with widely separated slats or a coarse mesh screen will allow more air to flow freely and are not considered an impermeable wall. In addition to the composition of the barrier, air flow is affected by the height, number, and angle of the barriers, as well as the percentage of the space covered by impermeable barriers. For a barrier to be considered permeable, air must be able to flow across the length and width of the barrier.
Additionally, by having permeable walls on opposite ends of a structure, air is able to flow across the structure creating cross-ventilation, which can help to reduce airborne contaminants, including SARS-CoV-2. Open roofs may promote additional airflow out of a structure when strong winds are present above it. However, open roofs on their own do not provide sufficient airflow to constitute outdoor spaces for the purposes of CDPH-Cal/OSHA guidance.
Air circulation is decreased in the corner where the two "closed" adjacent walls meet and will confine air.
50% of the structure has non-adjacent impermeable walls
With at least 50% of the non-adjacent walls in a structure being open, the resulting air movement allows for droplets/aerosols containing the COVID-19 virus to disperse rapidly. Ceilings, roofs, umbrellas, or canopies are permitted.
* Any security barriers or other solid structures used to create a perimeter for a business can be no higher than three feet. Mesh fencing or other permeable materials that maintain cross-ventilation and do not significantly impede natural airflow may be used as a perimeter with no height restriction.
See visualization below for additional context:
COVID-19 continues to pose a severe risk to communities and requires all people in California to follow necessary precautions and to adapt the way they live and function in light of this ongoing risk.
The Blueprint for a Safer Economy has set limitations on indoor operations in a number of sectors including restaurants, bars, breweries, distilleries, gyms, fitness centers, museums, places of worship, family entertainment centers, and cardrooms due to features of the businesses and the behaviors that occur within them. These sectors are settings where groups convene and may mix with others for a prolonged period of time, increasing the risk of escalating the transmission rate of COVID-19. The rationale for restricting indoor operations is anchored in the science of disease transmission. Recent studies show that transmission is substantially greater in indoor settings due to the release of infectious particles into the air when someone speaks, coughs, sneezes, or sings, which is exacerbated in indoor spaces particularly when lacking appropriate ventilation.
Please note: Increased ventilation should be considered as an addition to, and not a replacement for wearing face coverings, maintaining at least six feet of distance between people, washing hands frequently, and limiting activities that bring together people from different households.
 The definition of "outdoor operations" set forth in this guidance pertains exclusively to the use of that term to classify a setting as indoors or outdoors under the California Blueprint for a Safer Economy. It does not pertain to nor is it meant to alter, modify, or supersede existing law on the definition or use of that term in any existing Title 8 regulation, including but not limited to Title 8 section 3395.
 See, e.g., Hiroshi Nishiura, et al., Closed environments facilitate secondary transmission of coronavirus disease 2019 (COVID-19); Hu Qian, et al., "Indoor transmission of SARS-CoV-2" [pre-print] published in medRxiv on April 4, 2020.