CMI Indoor Air Quality Assessment 2 — Questions and Answers
Question 1: According to ACGIH guidelines, which relative humidity range is considered optimal to minimize mold growth while maintaining occupant comfort?
- 20–30%
- 30–50% (Correct answer)
- 55–70%
- 70–85%
Correct answer: 30–50%
ACGIH guidelines recommend maintaining indoor relative humidity between 30–50% to inhibit mold growth while keeping occupants comfortable. Below 30%, air becomes too dry, causing skin and respiratory irritation. Above 50–55%, conditions become increasingly favorable for mold colonization on building surfaces. Ranges above 70% represent very high mold risk and are well outside acceptable IAQ parameters.
Question 2: A carbon dioxide concentration above what level (ppm) in an occupied space typically indicates inadequate fresh air ventilation?
- 400 ppm
- 700 ppm
- 1,000 ppm (Correct answer)
- 2,500 ppm
Correct answer: 1,000 ppm
CO2 above 1,000 ppm in an occupied space indicates that exhaled air is not being adequately diluted by fresh outside air, signaling insufficient ventilation per ASHRAE 62.1 guidelines. Outdoor ambient CO2 is approximately 400–420 ppm, establishing the baseline. Levels of 700 ppm may suggest slightly reduced ventilation but are not the established threshold for action. Levels above 2,500 ppm are associated with measurable cognitive impairment and represent severe ventilation failure.
Question 3: When evaluating IAQ complaints in a building with a central HVAC system, what is the most important first component to inspect?
- Window seals and weatherstripping
- The condensate drain pan and coil for mold growth (Correct answer)
- The thermostat calibration setting
- Return air grille filter for dust buildup only
Correct answer: The condensate drain pan and coil for mold growth
The condensate drain pan and evaporator coil are the most critical HVAC components to inspect first because standing water in the drain pan combined with accumulated organic debris on the coil creates ideal mold growth conditions that can distribute spores building-wide. Window seals and thermostats do not significantly impact IAQ at scale. While dirty return filters matter, they are secondary to active mold growth on wet HVAC components that directly seed the air stream.
Question 4: VOCs (volatile organic compounds) in indoor air can contribute to IAQ complaints that mimic mold exposure. Which instrument is used to measure total VOC concentration?
- Particle counter
- PID (photoionization detector) (Correct answer)
- Hygrometer
- Manometer
Correct answer: PID (photoionization detector)
A PID (photoionization detector) uses ultraviolet light to ionize volatile organic compounds in air and measures the resulting ion current, providing a total VOC reading in parts per million. A particle counter measures particulate matter by size, not chemical composition. A hygrometer measures humidity, and a manometer measures air pressure differential — neither can detect VOC concentrations.
Question 5: During an IAQ assessment, what does a 'negative building pressure' condition indicate?
- The HVAC system is working at peak efficiency
- Outside air and potential contaminants are being drawn into the building (Correct answer)
- The building has excessive mechanical exhaust
- Indoor CO2 levels are below ambient outdoor concentrations
Correct answer: Outside air and potential contaminants are being drawn into the building
Negative building pressure means indoor air pressure is lower than outdoor pressure, causing outside air — along with pollutants, moisture, radon, or contaminants — to be drawn in through cracks, penetrations, and the building envelope. This is the opposite of peak HVAC efficiency, which typically involves positive or neutral pressure. Excessive mechanical exhaust would cause negative pressure, making it a contributing factor, not the definition of the condition itself.
Question 6: Which condition most directly links an IAQ complaint to a mold source rather than a chemical or particulate source?
- Symptoms worsen during winter months only
- Symptoms are limited to eye irritation
- Symptoms improve when occupants leave the building and return when they re-enter (Correct answer)
- Symptoms include only headaches without respiratory issues
Correct answer: Symptoms improve when occupants leave the building and return when they re-enter
Symptoms that resolve upon leaving the building and return upon re-entry establish a clear temporal and spatial link to an indoor exposure source, which is the hallmark pattern for building-related illness including mold exposure. Winter-only symptoms could indicate dry air or heating system issues. Isolated eye irritation or headaches are non-specific and could have many causes unrelated to mold or indoor air quality.
CMI Indoor Air Quality Assessment 2
According to ACGIH guidelines, which relative humidity range is considered optimal to minimize mold growth while maintaining occupant comfort?