For over a year, the COVID-19 pandemic has destabilized life around the world, particularly in the built environment. According to a paper posted in April 2020 to the preprint website medRxiv, COVID-19 infection is 18 times more likely indoors than outdoors. The virus presents a lethal, unpredictable health and safety risk due to its high degree of infectiousness, its multiple modes of transmission, and its high incidence of asymptomatic infections (approximately 40–45 percent) that make contact tracing and other response strategies more challenging to conduct. While vaccines provide cause for optimism, their less than 100 percent efficacy, the mistakes in mass vaccination efforts, and rapid mutations of the SARS-CoV-2 virus will necessitate a comprehensive approach to infection control that does not exclusively rely on vaccination for the foreseeable future.

Developing and implementing a strong infection control plan has never been more urgent, not just as a matter of best practice but increasingly as a matter of regulatory compliance. In 2020, OSHA provided recommended guidance, allowing states and counties to establish their own requirements. The ensuing response was uneven, with some states like California, Oregon, Michigan, and Virginia promulgating emergency temporary standards on COVID-19 in workplaces while others relied on guidelines and recommendations. Critics charged that the overall OSHA response was fragmented, confusing, and ineffective, triggering worker complaints, mass outbreaks, and calls for reform.

As of early 2021, the Biden administration has signaled a much more active approach toward OSHA regulation, enforcement, and funding. On Jan. 21, President Biden issued an “Executive Order on Protecting Worker Health and Safety” stating that the administration would:

Concurrently, several states and counties have signaled a more aggressive approach to protecting worker health and safety. In late January 2021, Virginia became the first state to enact a permanent standard on COVID-19 in workplaces. Among other provisions, Virginia requires employers to comprehensively evaluate the hazards of all job tasks, create infectious disease preparedness and response plans, and maintain air handling systems in accordance with manufacturers’ instructions and American National Standards Institute (ANSI) and ASHRAE standards. Experts believe that Virginia could be a model for a forthcoming wave of federal and state-level OSHA permanent standards, complemented by heightened enforcement. COVID-19 PREVENTION PROGRAM DEVELOPMENT In recently published guidance, OSHA noted that the most effective COVID-19 prevention programs involve conducting a hazard assessment; identifying measures that limit the spread of COVID-19; adopting measures to ensure that workers who are infected or potentially infected are separated and sent home; and protecting workers who raise concerns about COVID-19 from retaliation.

For purposes of this discussion, I will focus on the first two aspects of COVID-19 prevention programs: hazard assessment and mitigation measures.

Hazard Assessment According to OSHA, a hazard assessment, also referred to as a job hazard analysis or JHA, consists of the following process: 1. collect existing information about workplace hazards 2. inspect the workplace for safety hazards 3. identify health hazards 4. conduct incident investigations 5. identify hazards associated with emergency and nonroutine situations 6. characterize the nature of identified hazards, identify interim control measures, and prioritize the hazards for control

OSHA has divided job tasks into four potential risk exposure levels:
• Lower risk: Jobs that do not require close contact (within 6 feet for a total of 15 minutes or more over a 24-hour period) with other people. Workers in this category have minimal occupational contact with the public and other coworkers.

• Medium risk: Jobs that require either frequent close contact (within 6 feet for a total of 15 minutes or more over a 24-hour period) or sustained close contact with other people in areas with community transmission.

• High risk: Jobs with a high potential for exposure to known or suspected sources of SARS-CoV-2.

• Very high risk: Jobs with a very high potential for exposure to known or suspected sources of SARS-CoV-2 during specific medical, postmortem, or laboratory procedures.

Subsequently, an employer must implement a hazard prevention and control process consisting of the following steps: 1. identify control options 2. select control options 3. develop and update a hazard control plan 4. select controls to protect workers during nonroutine operations and emergencies 5. implement selected controls in the workplace 6. follow up to confirm that controls are effective

Applying the hierarchy of controls for COVID-19 is fundamental to hazard prevention and control. Case reports and epidemiological studies have indicated that the primary means of SARS-CoV-2 disease transmission is the indoor spread of exhaled droplet aerosols. Consequently, the AIHA guidance document “Reducing the Risk of COVID-19 Using Engineering Controls” states, “Engineering controls that can keep infectious aerosols at very low levels indoors offer the greatest promise to protect non-healthcare workers and other vulnerable populations as we reopen our businesses and workplaces.”

Mitigation Measures: Dilution Ventilation and Filtration ASHRAE’s April 2020 position document on infectious aerosols (PDF) states: ASHRAE, AIHA, and other leading authorities emphasize that selecting, installing, and evaluating specific engineering controls should be based on a site-specific risk assessment in consultation with “a knowledgeable mechanical engineer and industrial hygienist familiar with ventilation controls and infection control,” as explained in the AIHA guidance document. Every building is unique, conditions and risk are dynamic, and there are no one-size-fits-all solutions. Nevertheless, research published in the American Journal of Infection Control indicates that dilution ventilation and filtration emerge in peer-reviewed scientific literature and public health guidance as the most consistently recommended engineering controls, not only for SARS-CoV-2 but also for other respiratory viruses like influenza, tuberculosis, and rhinovirus. The logic is clear and compelling: increasing outdoor air intakes, air exchange rates, and filtration levels to the highest level an HVAC system can sustainably handle reduces the time and space for airborne pathogens like SARS-CoV-2 to linger, spread, and infect others, similar to the “infinite dilution” benefits of outdoor environments. For generations, healthcare facilities have embedded dilution ventilation and filtration in their infection control systems and controls. Now, the pandemic is forcing non-healthcare facilities to operate based on the same core principles, representing a significant departure from traditional building operations optimized for cost, efficiency, and occupant comfort. Meanwhile, federal and state OSHA authorities have thrust ventilation and filtration controls front and center in their updated guidelines, recommendations, and standards given scientific consensus on the importance of airborne transmission of SARS-CoV-2. Verification of Engineering Controls Even within the scope of dilution ventilation and filtration-focused controls, the hazard prevention and control process is not straightforward due to often-competing health and safety, engineering, and financial considerations. For example, what is the relative risk reduction of increasing the volume of outside air, installing enhanced filtration in central HVAC systems, and using standalone HEPA-filtered air cleaners? Which of these controls are possible within the mechanical system’s design and operational capabilities? Will increased outside air introduce high levels of humidity, thereby causing other health and safety risks like mold and bacterial growth in the HVAC system, ducts, and occupied areas of the building? What is the capability of fans in the HVAC system to handle increased pressure load from increased filtration, and what will be the implications for maintenance, filter changes, and air leakage around the enhanced filtration? And are the benefits of these controls worth the costs associated with implementing them? Moreover, the lack of a widely accepted quantitative standard for ventilation endorsed by OSHA, ASHRAE, and other leading authorities creates further ambiguity for developing, implementing, evaluating, and enforcing critical engineering controls. Ideally, robust analytical tools and diagnostic solutions should guide the hazard prevention and control process and help assess costs and benefits. However, the pandemic has exposed a critical gap in the toolbox of industrial hygienists and mechanical engineers. Existing solutions fall into two main categories: quantitatively rigorous theoretical approaches like computational fluid dynamic modeling and Wells-Riley mathematical solutions, and qualitatively rigorous applied approaches heavily reliant on expert feedback. What has been lacking is a quantitatively rigorous applied approach capable of verifying the efficacy of engineering controls in real-world indoor environments. However, technology-enabled solutions are emerging to fill this gap. One recent example is a diagnostic solution leveraging DNA-tagged tracer particles that safely mimic airborne pathogen mobility and exposure levels. This type of technology-enabled solution has the potential to integrate a layer of science- and data-based verification into the hazard prevention and control process and to round out traditional approaches. CRITICAL COMPONENTS The COVID-19 pandemic represents a once-in-a-century public health risk, which is particularly acute in the built environment. In response, federal and state-level OSHA authorities are advancing increased regulation and enforcement actions to protect workers. Identification, assessment, and prevention of hazards, and the implementation of controls, are critical for developing and implementing infection control plans that are consistent with best practices and compliant with regulations. Given the airborne transmission risk of SARS-CoV-2, dilution ventilation and enhanced filtration should be critical components of a hazard control plan, strengthened by emerging technology that can verify efficacy throughout the decision-making process. IH and OEHS professionals should employ the scientific knowledge gained during this pandemic by utilizing the best industrial hygiene practices and means to verify ventilation and filtration controls as part of COVID-19 prevention plans. We are all under an obligation to apply effective infection control and management tools that demonstrate the effectiveness of the actions taken.

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