RMS Commercial Building Mitigation 3 — Questions and Answers
Question 1: What is the recommended minimum pipe diameter for a commercial SSD system serving a floor area greater than 10,000 square feet?
- 2 inches
- 3 inches
- 4 inches (Correct answer)
- 6 inches
Correct answer: 4 inches
A 4-inch diameter pipe is the standard minimum for large commercial SSD systems to minimize airflow resistance and maintain system efficiency.
Question 2: In a commercial building, where should the radon fan discharge point be located?
- Into the mechanical room for dilution
- Into the HVAC return air plenum
- At least 10 feet above grade and away from windows and air intakes (Correct answer)
- At grade level near the building perimeter
Correct answer: At least 10 feet above grade and away from windows and air intakes
Fan discharge must be directed away from occupied areas, windows, and air intakes—typically at least 10 feet above grade—to prevent re-entry of radon.
Question 3: Which condition would most likely INCREASE radon entry in a commercial building with a sub-slab depressurization system already installed?
- Fan operating continuously
- HVAC system creating negative pressure relative to sub-slab (Correct answer)
- Slab crack sealed with epoxy
- Suction point located near sump pit
Correct answer: HVAC system creating negative pressure relative to sub-slab
If the building HVAC creates interior negative pressure greater than the SSD system's depressurization, radon can be pulled in through slab cracks and openings.
Question 4: What is the purpose of a diagnostic smoke test during commercial building radon mitigation planning?
- To locate the radon fan exhaust point
- To identify sub-slab communication pathways and air leakage routes (Correct answer)
- To test fire alarm system response to smoke
- To verify HVAC ductwork integrity
Correct answer: To identify sub-slab communication pathways and air leakage routes
Smoke tests help identify where sub-slab air communicates with the building interior and locate bypass pathways that can affect mitigation system performance.
Question 5: For a commercial building with a crawl space and conditioned slab areas, what combined mitigation approach is typically used?
- SSD only beneath the slab
- Crawl space encapsulation with sub-membrane depressurization plus SSD (Correct answer)
- HVAC air filtration with HEPA filters
- Block wall depressurization only
Correct answer: Crawl space encapsulation with sub-membrane depressurization plus SSD
Combined buildings require sub-membrane depressurization in the crawl space and sub-slab depressurization under slab areas for complete radon control.
Question 6: According to ANSI/AARST standards, what is the maximum recommended radon level in a commercial building before mitigation is considered successful?
- 4 pCi/L (Correct answer)
- 2 pCi/L
- 0.4 pCi/L
- 1 pCi/L
Correct answer: 4 pCi/L
ANSI/AARST and EPA use 4 pCi/L as the action level; post-mitigation levels below this threshold indicate a successful system.
Question 7: A commercial SSD system's fan is mounted on the rooftop. What is a key advantage of this placement?
- Easier access for homeowner maintenance
- Discharge is already at or above roofline, away from occupied zones (Correct answer)
- Lower electrical consumption due to cooler temperatures
- Reduced noise in mechanical rooms
Correct answer: Discharge is already at or above roofline, away from occupied zones
Rooftop fan placement ensures the radon discharge is above occupied levels and away from air intakes, eliminating the need for extended vertical exhaust piping.
RMS Commercial Building Mitigation 3
What is the recommended minimum pipe diameter for a commercial SSD system serving a floor area greater than 10,000 square feet?