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Option 2. Management Mode for Respiratory Diseases

Following the COVID-19 pandemic, industry experts developed strategies to reduce airborne infectious disease transmission in buildings for the protection of public health and to facilitate keeping buildings operational during periods of heightened risk. One resulting standard — ASHRAE Standard 241-2023, Control of Infectious Aerosols — specifies an infection risk management mode with ventilation and filtration strategies for reducing occupant exposure to airborne pathogens that cause significant personal and economic damage each year.

Projects pursuing this option must design occupied spaces with the capability to operate in an Infection Risk Management Mode. This mode provides minimum equivalent clean airflow rates, calculated as the equivalent clean airflow rate per person multiplied by the anticipated number of people in a space. The building owner and facility manager must determine when to apply this mode of operation.

Commissioning requirements Include the requisite sequences of operation in design documents and ensure that Infection Risk Management Mode is included in the commissioning scope of work to verify that all equipment responds as intended.

Option 3. Design for Occupant Thermal Safety During Power Outages

During power outages when backup power is unavailable, mechanical cooling, heating, and ventilation become inaccessible. Designing spaces to sustain thermal habitability passively or through manual occupant controls allows the building to remain livable until power is restored.

Projects that pursue Option 3 have two paths to consider: One for extreme cold and one for extreme heat. Based on the project’s location, teams should determine which option, or both, are appropriate.

Thermal safety zones Designate thermal safety zones where thermal habitability can be maintained during a loss of power. Analyze conditions on the assumption that building occupants will congregate in the safety zones during an outage. This may increase the expected occupant density above normal assumptions for the space. Include enough thermal safety zones so the occupant density does not exceed one person per 20 square feet (1.9 square meters).

Example An office building has 400 employees. If 20,000 square feet (1,858 square meters) of space is identified as being thermally safe, teams must analyze the

U.S. Green Building Council LEED v5 Reference Guide for Building Design and Construction, April 2025 Launch Edition 517