Randall W. Whitesides, P.E.

Course Outline

Learning Objective

• Defining aspects of Indoor Air Pollution (IAP);
• Modern sources and transmission vehicles that contribute to IAP, including particulates and pathogens; and
• Current remedial engineering actions that can be taken to mitigate IAP.

Course Content

INTRODUCTION
Studies from the United States and Europe show that persons in industrialized nations spend more than 90 percent of their time indoors. The concentrations of many indoor pollutants routinely exceed those outdoors.

Heavy industry-related occupational hazards are heavily regulated. This course addresses IAP problems caused by contaminants in homes, commercial establishments, and offices.

Modern energy codes demand highly energy-efficient, nearly airtight building envelopes. While earlier construction allowed for natural draft dilution of indoor contaminants, modern self-contained envelopes require highly engineered mechanical ventilation to prevent the accumulation of pollutants and protect occupant health.

ENVIRONMENTAL TOBACCO SMOKE (ETS) & VAPING AEROSOLS
Background
Where allowed, environmental tobacco smoke and aerosols from Electronic Nicotine Delivery Systems (ENDS, or vapes) are major sources of indoor air contaminants. ETS is a dynamic, complex mixture of more than 4,000 chemicals in vapor and particle phases. Vaping aerosols introduce ultrafine particulate matter (PM2.5), heavy metals, and VOCs into the environment.

The U.S. Environmental Protection Agency (EPA) classifies ETS as a known human (Group A) carcinogen.

Architectural/Engineering Considerations
Health risks from ETS and ENDS cannot be eliminated by generally accepted ventilation methods. Total removal of tobacco smoke and vape aerosols through general ventilation is not feasible. The most effective solution is the total elimination of smoking and vaping from the indoor environment. Where smoking rooms are legally permitted, they must be highly depressurized and separately exhausted directly to the outdoors with zero recirculation.

The current version of ASHRAE Standard 62.1, Ventilation for Acceptable Indoor Air Quality, sets the minimum ventilation rates. It unequivocally states that prescribed ventilation air flow rates apply only to spaces that do not contain environmental tobacco smoke.

PRODUCTS OF COMBUSTION & OUTDOOR INFILTRATION
Background
Major combustion pollutants stem from malfunctioning heating devices, gas ranges, or the infiltration of outdoor pollution (e.g., motor vehicles, loading docks, and seasonal wildfire smoke).

The gaseous pollutants from combustion sources include carbon monoxide (CO), nitrogen dioxide (NO₂), and sulfur dioxide (SO₂). Recently, residential gas stoves have been identified as significant emitters of NO₂ , routinely pushing indoor air quality past safe outdoor exposure limits during normal cooking.

Furthermore, outdoor PM2.5 from seasonal wildfires is a major modern IAP threat, infiltrating buildings through makeup air intakes and envelope leaks.

Design and Maintenance Considerations
Vented appliances must be used, and the industry is heavily shifting toward building electrification (e.g., induction cooking, heat pumps) to eliminate indoor combustion entirely.

The location of outside air intakes must be carefully planned to avoid loading docks and street-level exhaust. To combat wildfire PM2.5, HVAC systems must be designed to accommodate higher-efficiency filtration (MERV 13 or higher) without unacceptable static pressure drops, and systems should feature controls that can temporarily reduce outside air intake during severe outdoor smoke events.

BIOLOGICAL AIR POLLUTANTS & PATHOGENS
Background
Biological air pollutants include allergens (dust mites, animal dander), fungi (mold), bacteria (Legionella), and human-shed viruses (such as SARS-CoV-2 and Influenza). High relative humidity encourages dust mite populations and fungal growth on damp surfaces.

Mechanical HVAC systems can serve as sites of microbial amplification if poorly maintained. Condensate drain pans, cooling coils, and humidifiers require strict hygiene.

Engineering and Maintenance Considerations
The COVID-19 pandemic permanently altered the engineering approach to biological IAP. Ventilation, filtration, and air cleaning are now primary defenses against airborne infectious diseases.

Additional Resources