RMS Diagnostic Testing & Troubleshooting 2 — Questions and Answers
Question 1: During a block-wall depressurization diagnostic, what is primarily being assessed?
- Whether hollow cores in block walls can be depressurized as a radon entry pathway (Correct answer)
- The R-value of the exterior wall insulation
- The structural integrity of the foundation wall
- Moisture levels in the masonry blocks
Correct answer: Whether hollow cores in block walls can be depressurized as a radon entry pathway
Block walls with hollow cores can serve as radon entry and transport pathways; diagnostics assess whether those cores communicate and can be effectively evacuated.
Question 2: A diagnostic test reveals very low sub-slab airflow despite a high-powered fan. What is the most likely cause?
- The sub-slab gravel bed is too thick
- The sub-slab fill has very low permeability such as clay or fine sand (Correct answer)
- The fan is oversized for the application
- The radon level is naturally below the action level
Correct answer: The sub-slab fill has very low permeability such as clay or fine sand
Low-permeability sub-slab materials like clay restrict air movement, resulting in poor pressure field extension regardless of fan power.
Question 3: If a mitigation system test pipe shows no pressure differential when the fan is running, what should be checked first?
- Whether the suction pit properly connects to the sub-slab environment (Correct answer)
- The indoor humidity level
- The exterior paint on the exhaust pipe
- The date of the original radon test
Correct answer: Whether the suction pit properly connects to the sub-slab environment
No pressure differential typically means the suction pipe is not properly connected to the sub-slab space, or the suction pit opening is blocked or sealed.
Question 4: A crawl space mitigation system shows adequate fan operation, but radon levels remain elevated. Which diagnostic finding is MOST likely?
- The fan is placed too close to the ground
- The vapor barrier has holes, gaps, or is not properly sealed to walls and piers (Correct answer)
- The fan exhaust is too close to a window
- The soil in the crawl space is too dry
Correct answer: The vapor barrier has holes, gaps, or is not properly sealed to walls and piers
An incomplete vapor barrier allows radon to bypass the system and enter the living space through gaps or unsealed edges.
Question 5: During troubleshooting, a technician measures higher-than-expected negative pressure but still finds elevated radon levels. What is the most plausible explanation?
- The fan is not powerful enough
- There is a radon source not addressed by the system such as radon in well water or an isolated sub-slab section (Correct answer)
- The manometer is malfunctioning
- Outdoor radon levels are unusually high
Correct answer: There is a radon source not addressed by the system such as radon in well water or an isolated sub-slab section
When system vacuum is confirmed but radon persists, an unconnected radon source such as radon-bearing well water or an isolated sub-slab zone is a key suspect.
Question 6: When should a contractor perform follow-up diagnostic verification after initial system installation?
- Only if the homeowner specifically requests it
- As part of post-installation verification before final sign-off on the job (Correct answer)
- After two years of system operation
- Only when the fan fails or makes noise
Correct answer: As part of post-installation verification before final sign-off on the job
Post-installation diagnostic checks confirm proper pressure field extension and system function before the technician certifies the job as complete.
Question 7: A mitigation system installed five years ago suddenly shows a significant drop in negative pressure. What is the most likely cause?
- Natural degradation of the concrete slab
- Fan motor wear or bearing failure reducing fan performance (Correct answer)
- Radon levels naturally decreasing over time
- Seasonal changes in outdoor temperature
Correct answer: Fan motor wear or bearing failure reducing fan performance
Fan motors and bearings degrade over time, causing reduced airflow and lower negative pressure, which is a common reason for gradual or sudden system performance decline.
RMS Diagnostic Testing & Troubleshooting 2
During a block-wall depressurization diagnostic, what is primarily being assessed?