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InterNACHI Certified Radon Tester study materials
InterNACHI Certified Radon Tester study resources

InterNACHI Certified Radon Tester practice questions

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Question 1Radon science and health effects

Radon is a radioactive gas produced by the decay of which element?

  1. Thorium
  2. Potassium
  3. Uranium Correct answer.
  4. Radium

Explanation

Radon-222 forms in the uranium-238 decay chain, where radium-226 decays into radon gas. Uranium in soil and rock is therefore the original source material. Thorium and potassium are radioactive but do not produce radon-222.

Question 2Radon science and health effects

Which type of radiation emitted by radon decay products poses the greatest health concern when inhaled?

  1. Gamma rays
  2. X-rays
  3. Beta particles
  4. Alpha particles Correct answer.

Explanation

Radon progeny such as polonium-218 and polonium-214 emit alpha particles, which deposit large amounts of energy over a very short distance in lung tissue. This localized damage to bronchial cells drives the lung cancer risk. Beta and gamma radiation penetrate farther but deposit far less energy per unit path.

Question 3Radon science and health effects

What is the primary route of human exposure to radon?

  1. Ingestion of contaminated well water
  2. Inhalation of indoor air Correct answer.
  3. Ingestion of contaminated food
  4. Absorption through skin

Explanation

The dominant exposure pathway is breathing indoor air containing radon and its decay products, which then irradiate lung tissue. Water and food contribute only a small fraction of total exposure in most homes. Skin absorption is negligible for this noble gas.

Question 4Radon science and health effects

Radon is chemically classified as which type of element?

  1. Noble gas Correct answer.
  2. Transition metal
  3. Alkali metal
  4. Halogen

Explanation

Radon belongs to group 18 of the periodic table, the noble gases, which are characterized by filled valence shells and very low chemical reactivity. This inert behavior is why radon migrates as a gas rather than bonding to soil minerals. Halogens, alkali metals, and transition metals all react readily.

Question 5Radon science and health effects

What is the most widely recognized long-term health effect of chronic radon exposure?

  1. Lung cancer Correct answer.
  2. Thyroid disease
  3. Skin cancer
  4. Leukemia

Explanation

Epidemiological studies of miners and residential populations consistently link prolonged radon exposure to elevated lung cancer risk, especially when combined with tobacco smoke. The alpha-emitting progeny irradiate the bronchial epithelium directly. Leukemia, skin cancer, and thyroid disease are associated with other exposure types.

Question 6Radon science and health effects

Which unit is commonly used in the United States to express indoor radon concentration?

  1. Becquerel per cubic meter (Bq/m3)
  2. Gray (Gy)
  3. Millirem per year (mrem/yr)
  4. Picocuries per liter (pCi/L) Correct answer.

Explanation

In the United States, radon in air is reported in picocuries per liter, where one picocurie equals 2.22 decays per minute. The SI equivalent, becquerels per cubic meter, is used internationally. Millirem and gray measure dose, not concentration.

Question 7Radon science and health effects

What is the approximate conversion factor between picocuries per liter and becquerels per cubic meter?

  1. 1 pCi/L = 370 Bq/m3
  2. 1 pCi/L = 3.7 Bq/m3
  3. 1 pCi/L = 37 Bq/m3 Correct answer.
  4. 1 pCi/L = 0.37 Bq/m3

Explanation

One picocurie is 0.037 decays per second, and one liter is 0.001 cubic meters, so 1 pCi/L equals 37 Bq/m3. This factor lets a tester compare U.S. and international data. The 3.7 figure applies to activity per unit volume in different units.

Question 8Radon science and health effects

Which radon decay product is a solid that can attach to dust particles and be inhaled?

  1. Helium-4
  2. Polonium-218 Correct answer.
  3. Radon-220 gas
  4. Radon-222 gas

Explanation

Radon progeny such as polonium-218 are solid metals that quickly attach to airborne particles, which can then lodge in the lungs. Radon itself is a gas and is largely exhaled before decaying. Helium is a stable, non-radioactive gas.

Question 9Radon science and health effects

A home measurement reads 148 Bq/m3. What is the approximate equivalent in picocuries per liter?

  1. 0.4 pCi/L
  2. 4 pCi/L Correct answer.
  3. 1.5 pCi/L
  4. 40 pCi/L

Explanation

Dividing 148 by the conversion factor of 37 Bq/m3 per pCi/L yields approximately 4 pCi/L. This is the familiar U.S. action level expressed in SI units. Multiplying instead of dividing would give the incorrect larger result.

Question 10Radon science and health effects

Which statement best describes the relationship between radon and tobacco smoking with respect to lung cancer risk?

  1. Radon exposure protects smokers from cancer
  2. The risks are entirely independent and cannot be combined
  3. The two risks combine multiplicatively, making smokers at far higher risk Correct answer.
  4. Smoking eliminates the risk from radon

Explanation

Epidemiological evidence shows the combined effect of radon and smoking is greater than additive, often described as multiplicative or synergistic. Smokers exposed to elevated radon face the highest absolute lung cancer risk. The two exposures do not cancel each other.

Question 11Radon science and health effects

Why does radon concentration tend to be higher in the lowest level of a home?

  1. Warm air rises and carries radon upward
  2. Sunlight generates radon near windows
  3. Upper floors have more ventilation openings
  4. Radon enters from soil and rock beneath the foundation and is denser than air Correct answer.

Explanation

Radon migrates from soil and rock into the structure through foundation cracks, sumps, and utility penetrations, so the lowest occupied level usually sees the highest concentrations. Radon is also denser than air, which limits upward mixing. Ventilation patterns in upper floors are secondary to the source location.

Question 12Radon science and health effects

What is the half-life of radon-222?

  1. 22 years
  2. 1600 years
  3. 3.8 hours
  4. 3.8 days Correct answer.

Explanation

Radon-222 has a half-life of about 3.8 days, short enough that concentrations respond quickly to changes in entry and ventilation but long enough to accumulate indoors. This timescale guides test duration and placement decisions. The other values correspond to different radionuclides.

Question 13Radon science and health effects

A short-term radon test is placed in a basement bedroom. Why might the result overstate the exposure of the occupants?

  1. The test device is calibrated only for living rooms
  2. Occupants may spend little time in that room Correct answer.
  3. Basements never contain radon
  4. Short-term tests cannot detect radon

Explanation

Exposure depends on both concentration and time spent in each area, so a high reading in a room rarely used does not reflect actual occupant dose. Testers should consider where people spend meaningful time. Device calibration is not room-specific, and short-term devices do detect radon.

Question 14Radon science and health effects

Which factor most directly increases radon entry into a home?

  1. Use of natural gas appliances
  2. A pressure difference drawing soil gas inward Correct answer.
  3. Bright interior lighting
  4. High outdoor humidity

Explanation

Heating systems, exhaust fans, and stack effects can lower indoor pressure relative to the soil, drawing soil gas containing radon through openings in the foundation. This pressure-driven flow is the main mechanism of entry. Humidity, lighting, and gas appliances do not drive soil gas movement.

Question 15Radon science and health effects

What is the typical primary source of radon in indoor air?

  1. Outdoor air infiltration
  2. Building materials in the walls
  3. Household cleaning products
  4. Soil and rock beneath and around the structure Correct answer.

Explanation

In most buildings, soil and rock surrounding the foundation are the dominant radon source. Building materials and outdoor air contribute only minor amounts in typical cases. Cleaning products contain no radon.

Question 16Radon science and health effects

Which statement about radon in well water is accurate?

  1. Waterborne radon is the dominant source in all homes
  2. Radon in water poses no risk because it cannot escape
  3. Radon released from water during showering can add to indoor air concentrations Correct answer.
  4. Radon cannot dissolve in water

Explanation

Radon dissolved in groundwater is released into indoor air when water is agitated, particularly during showering and washing. In homes with high-radon well water, this can meaningfully raise airborne concentrations. Soil gas remains the dominant source in most homes.

Question 17Radon science and health effects

Why do radon concentrations often vary seasonally in a home?

  1. Radon production in soil stops in summer
  2. Closed-house conditions in winter reduce ventilation and increase indoor levels Correct answer.
  3. Radon decays faster in cold weather
  4. Outdoor radon levels rise in winter

Explanation

In heating seasons, homes tend to be closed up, reducing air exchange and allowing radon to accumulate. Stack effect and pressure differences can also strengthen. Soil radon production does not stop seasonally, and decay rate is temperature-independent.

Question 18Radon science and health effects

Which statement best characterizes the dose-response relationship observed between residential radon and lung cancer?

  1. Risk only appears above 100 pCi/L
  2. Risk rises with increasing radon concentration in a roughly linear fashion Correct answer.
  3. Risk is identical at all concentrations
  4. Risk decreases as concentration rises

Explanation

Pooled analyses of residential studies show lung cancer risk increasing approximately linearly with radon concentration, with no identified threshold. This supports risk estimates down to low concentrations. A decreasing or flat relationship contradicts the evidence.

Question 19Radon science and health effects

Which radon decay product is often measured as a proxy for potential alpha energy concentration?

  1. Lead-210
  2. Radon-222
  3. Bismuth-214
  4. Polonium-218 Correct answer.

Explanation

Short-lived progeny such as polonium-218 and polonium-214 carry most of the potential alpha energy and are measured to estimate working levels. Polonium-218 is a principal short-lived contributor. Lead-210 is long-lived and less relevant to immediate dose, and radon-222 is the parent gas.

Question 20Radon science and health effects

A tester finds a reading of 2 pCi/L in a living area. How should this be interpreted relative to U.S. guidance?

  1. It is zero risk because it is below 4 pCi/L
  2. It indicates the detector malfunctioned
  3. It is above the action level and requires immediate mitigation
  4. It is below the action level but still carries some estimated risk Correct answer.

Explanation

The U.S. action level is 4 pCi/L, so a reading of 2 pCi/L is below it, yet risk estimates indicate some elevated risk exists even at low concentrations. Guidance recommends considering mitigation in the 2 to 4 pCi/L range. No threshold of zero risk has been established.

Question 21Radon science and health effects

Why is a radon test that lasts only a few days considered less representative of long-term exposure?

  1. Detectors expire within 48 hours
  2. Short tests always read low
  3. Short tests cannot detect alpha particles
  4. Radon concentrations fluctuate with weather, season, and occupancy Correct answer.

Explanation

Radon levels vary substantially over time due to weather, pressure changes, and how the home is operated, so a brief snapshot may not reflect the annual average. Longer tests reduce this variability. Short devices do detect alpha activity, and detectors do not expire that quickly.

Question 22Radon science and health effects

Which combination of conditions would most likely produce an elevated radon reading during a short-term test?

  1. Closed-house conditions with the detector placed in a low-level room Correct answer.
  2. A detector placed in a well-ventilated attic
  3. Testing during a windy day with doors open
  4. Open windows and a running whole-house fan

Explanation

Closed-house conditions minimize dilution from outdoor air, and low-level rooms are closest to the soil gas source, together favoring higher readings. Open windows, whole-house ventilation, and attic placement all reduce measured concentration. These choices reflect standard placement and closure guidance.

Question 23Radon science and health effects

Which statement best explains why radon progeny, rather than radon gas itself, deliver most of the lung dose?

  1. Progeny are gases that remain in the lungs longer
  2. Progeny are solids that deposit in the airways and decay there Correct answer.
  3. Progeny emit only gamma radiation
  4. Radon gas emits more alpha particles than progeny

Explanation

Because radon is a gas, much of it is exhaled before decaying, whereas its solid progeny attach to particles and deposit on airway surfaces, where their alpha emissions irradiate nearby cells. This deposition pattern concentrates dose in the bronchial epithelium. Progeny are not gases, and they do emit alpha radiation.

Question 24Radon science and health effects

A homeowner with a persistent 5 pCi/L reading asks what the result implies. Which interpretation is most defensible?

  1. The home is safe because readings below 10 pCi/L are ignored
  2. Mitigation is unnecessary unless readings exceed 20 pCi/L
  3. The reading must be an error because radon cannot exceed 4 pCi/L
  4. The home exceeds the U.S. action level and mitigation should be considered Correct answer.

Explanation

A confirmed long-term average above 4 pCi/L exceeds the U.S. action level, and guidance recommends mitigation. Readings above 4 pCi/L are common and physically plausible. No guidance sets a 10 or 20 pCi/L threshold below which action is unnecessary.

Question 25Radon science and health effects

Which reasoning best explains why two neighboring homes with similar construction can have very different radon concentrations?

  1. Local soil permeability, uranium content, and foundation pathways can differ markedly Correct answer.
  2. Only the age of the homes matters
  3. Radon concentration depends solely on outdoor temperature
  4. Radon concentrations are random and unrelated to geology

Explanation

Radon entry depends on the uranium content and permeability of the soil beneath each home, plus the specific cracks and openings in its foundation. Small differences in these factors can produce large differences in indoor concentration. Radon is not random, and no single variable such as age or temperature explains the variation.

Question 26Radon science and health effects

Which lung cancer risk estimate is most consistent with major pooled analyses of residential radon studies?

  1. About a 2% increase in risk per 100 Bq/m3 of long-term radon exposure
  2. No measurable increase in risk below 200 Bq/m3
  3. About a 16% increase in risk per 100 Bq/m3 of long-term radon exposure Correct answer.
  4. About a 50% increase in risk per 100 Bq/m3 of long-term radon exposure

Explanation

Pooled analyses of residential studies, such as the European and North American pooling projects, report a statistically significant excess relative risk of roughly 10–16% per 100 Bq/m3 of long-term radon concentration, after adjusting for smoking. This linear excess risk is consistent with the linear-no-threshold model used by radiation protection bodies.

Question 27Radon science and health effects

Which health effect is the primary concern associated with chronic exposure to elevated indoor radon?

  1. Leukemia
  2. Stomach cancer
  3. Skin cancer
  4. Lung cancer Correct answer.

Explanation

Radon and its solid decay products are inhaled and deposit in the lung, where alpha emission delivers dose to bronchial tissue. Epidemiological evidence from miners and residential studies consistently links radon exposure to lung cancer, making it the primary health concern.

Question 28Radon science and health effects

Which statement best describes the classification of radon by the International Agency for Research on Cancer?

  1. Radon is classified as a Group 2B possible human carcinogen.
  2. Radon is classified as Group 3, not classifiable as to carcinogenicity.
  3. Radon is classified as a Group 2A probable human carcinogen.
  4. Radon is classified as a Group 1 human carcinogen. Correct answer.

Explanation

IARC classifies radon and its decay products in Group 1, meaning there is sufficient evidence of carcinogenicity in humans. This classification is based on studies of underground miners and supported by residential epidemiological findings.

Question 29Radon science and health effects

In the linear-no-threshold model applied to radon, what is assumed about the risk at very low concentrations?

  1. Risk is assumed to decline with a threshold below which there is no effect.
  2. Risk is assumed to be proportional to dose with no safe threshold. Correct answer.
  3. Risk is assumed to be zero below the action level.
  4. Risk is assumed to decrease at low doses due to hormesis.

Explanation

The linear-no-threshold model assumes that excess cancer risk increases linearly with dose and that no threshold exists below which risk is zero. This conservative approach is used for radiation protection and radon guidance, even though individual risk at low concentrations is small.

Question 30Radon science and health effects

A non-smoker living for many years in a home with an average radon concentration of 200 Bq/m3 asks how this exposure compares with common risks. Which comparison is most appropriate?

  1. The radon-related lung cancer risk is comparable to or higher than typical accidental death risks and is a leading environmental cancer risk. Correct answer.
  2. The radon-related lung cancer risk is negligible compared with everyday hazards such as driving.
  3. The radon-related risk applies only to smokers, so a non-smoker faces no excess risk.
  4. The radon-related risk is similar to the risk from a few dental X-rays per year.

Explanation

At 200 Bq/m3, long-term exposure yields an excess lung cancer risk that is substantial for a non-smoker and is among the larger environmental cancer risks encountered in daily life. Risk communication often compares it with familiar hazards, but it remains a genuine public health concern rather than a negligible one.

Question 31Radon science and health effects

Why is the synergistic effect between radon and smoking important when interpreting radon risk for an individual?

  1. Smoking reduces radon risk because smoke particles clear the lungs.
  2. Smoking multiplies the radon risk, so smokers face a much higher absolute risk than non-smokers at the same radon level. Correct answer.
  3. Smoking and radon act independently, so risks are simply added.
  4. Radon risk is the same for smokers and non-smokers at equal exposure.

Explanation

Epidemiological data show a sub-multiplicative but strong interaction: smokers exposed to radon have much higher lung cancer rates than non-smokers at the same radon concentration. This means risk communication and testing recommendations should account for smoking status when interpreting the same measured radon level.

Question 32Radon science and health effects

Which statement best describes the evidence for radon as a cause of lung cancer in non-smokers?

  1. Evidence is limited to miners who also smoked.
  2. No study has found an association in non-smokers.
  3. The association in non-smokers is explained entirely by secondhand smoke.
  4. Pooled residential studies show a significant excess risk in non-smokers, supporting a causal link. Correct answer.

Explanation

Pooled analyses of residential radon studies include many lifelong non-smokers and find a statistically significant excess lung cancer risk with increasing radon concentration. This supports a causal interpretation that is not dependent on smoking, although the absolute risk is lower than for smokers.

Question 33Radon science and health effects

Which exposure pathway accounts for the majority of the radiation dose from radon in a typical home?

  1. External gamma exposure from radon in soil
  2. Absorption of radon through the skin
  3. Inhalation of radon progeny deposited in the lung Correct answer.
  4. Ingestion of radon in drinking water

Explanation

The dominant dose pathway is inhalation of radon decay products that attach to airborne particles and deposit in the respiratory tract, where alpha emissions irradiate lung tissue. Ingestion and external exposure contribute much less to the total dose in typical residential settings.

Question 34Radon science and health effects

In the context of radon health effects, what does the term 'working level' (WL) quantify?

  1. The potential alpha energy concentration from short-lived radon progeny Correct answer.
  2. The concentration of radon gas in picocuries per liter
  3. The air exchange rate of a building
  4. The permeability of soil beneath a home

Explanation

One working level is defined as any combination of short-lived radon progeny in one liter of air that releases 130,000 MeV of potential alpha energy. It is used in occupational and some residential contexts to express progeny concentration rather than radon gas concentration.

Question 35Radon science and health effects

A public health official is explaining why radon is considered a leading environmental cause of cancer mortality. Which statement is most accurate?

  1. Radon is a minor contributor compared with outdoor air pollution.
  2. Radon is the leading cause of all cancer deaths combined.
  3. Radon causes more cancer deaths than smoking.
  4. Radon is second only to smoking as a cause of lung cancer in the general population. Correct answer.

Explanation

Radon is widely described as the second leading cause of lung cancer after smoking and the leading cause among non-smokers in many countries. It is not the leading cause of all cancer deaths, but its contribution to lung cancer mortality is substantial.

Question 36Radon science and health effects

Which statement best explains why the dose from radon progeny can be high even when the radon gas concentration is moderate?

  1. Progeny are solid particles that can deposit in the lung and deliver alpha dose locally. Correct answer.
  2. Progeny emit gamma radiation that penetrates the whole body.
  3. Progeny are gases that diffuse rapidly into the bloodstream.
  4. Progeny have longer half-lives than radon gas and accumulate over years.

Explanation

Short-lived radon progeny such as polonium-218 and polonium-214 are solids that attach to aerosols and, when inhaled, deposit in the bronchial tree. Their alpha emissions deliver a localized dose to lung tissue that can be significant even at moderate radon gas concentrations.

Question 37Radon science and health effects

Why is the risk from radon exposure often described as stochastic rather than deterministic?

  1. The probability of cancer increases with dose, but the severity is not dose-dependent. Correct answer.
  2. The effect occurs only above a clear threshold dose.
  3. The effect is immediate and predictable in all exposed persons.
  4. The severity of lung damage increases directly with the dose received.

Explanation

Stochastic effects are those whose probability increases with dose while the severity of the effect does not depend on dose; cancer induction by radon is treated as stochastic. Deterministic effects, by contrast, have a threshold and increase in severity with dose.

Question 38Radon science and health effects

Which statement best characterizes the latency period for radon-induced lung cancer?

  1. Latency is irrelevant because radon causes immediate cell death.
  2. The latency period is often many years to decades after exposure begins. Correct answer.
  3. Cancer typically appears within months of exposure.
  4. Latency is shorter for radon than for smoking-related lung cancer.

Explanation

Radon-induced lung cancer, like other radiation-induced solid cancers, typically has a long latency period, often on the order of years to decades. This is why long-term exposure estimates, rather than short-term measurements alone, are used in risk assessment.

Question 39Radon science and health effects

A homeowner asks whether a radon level of 4 pCi/L is a safe threshold below which no risk exists. Which response is most scientifically defensible?

  1. Yes, 4 pCi/L is a threshold below which risk is zero.
  2. Yes, because the EPA action level is based on a biological threshold.
  3. No, because any radon level above zero is immediately dangerous to health.
  4. No, risk is treated as increasing with dose without a sharp threshold, and 4 pCi/L is an action level, not a safe/unsafe boundary. Correct answer.

Explanation

The 4 pCi/L action level is a policy recommendation, not a biological threshold; risk is modeled as increasing with dose even below that level. The most defensible response explains that lower levels carry lower risk but are not risk-free, and that mitigation is recommended at or above the action level.

Question 40Radon science and health effects

Which statement about the dose conversion convention used for radon is correct?

  1. Dose conversion factors are used only for waterborne radon.
  2. Dose conversion is unnecessary because radon gas itself is the only source of dose.
  3. Dose conversion factors differ between occupational and residential settings because of differences in aerosol conditions and breathing patterns. Correct answer.
  4. The same dose conversion factor applies to homes and mines without adjustment.

Explanation

Dose conversion factors for radon progeny depend on aerosol characteristics, unattached fraction, and breathing patterns, which differ between mines and homes. Consequently, different conventions are used for occupational and residential exposure when estimating dose from radon progeny.

Question 41Radon entry, transport, and building dynamics

In radon measurement, what does the term 'stack effect' describe?

  1. The upward movement of warm indoor air driven by indoor-outdoor temperature and pressure differences Correct answer.
  2. The diffusion of radon gas directly through concrete floor slabs
  3. The release of radon from well water when a faucet is opened
  4. The downward pull of outdoor air caused by wind passing over the roof ridge

Explanation

The stack effect occurs when warmer, lighter indoor air rises and escapes through upper openings, creating a slight negative pressure in the lower part of the building. This depressurization draws soil gas, including radon, in through foundation openings. It is strongest in cold weather when the indoor-outdoor temperature difference is large.

Question 42Radon entry, transport, and building dynamics

Which condition most strongly increases pressure-driven entry of soil gas into a house?

  1. A raised foundation with no basement
  2. A sealed and unvented attic
  3. A slight negative pressure in the lowest level relative to the soil Correct answer.
  4. A pressurized crawlspace relative to the soil

Explanation

Radon entry is largely pressure-driven: when indoor air pressure at the foundation is lower than soil gas pressure, soil gas is drawn inward. Common causes include exhaust fans, furnace combustion air, and the stack effect. A pressurized crawlspace or sealed attic does not create the pressure gradient needed for entry.

Question 43Radon entry, transport, and building dynamics

Which soil characteristic is generally associated with the greatest radon entry potential?

  1. Saturated clay with high organic content
  2. Compacted fill with no uranium-bearing minerals
  3. High permeability combined with elevated radium content Correct answer.
  4. Low permeability combined with low radium content

Explanation

Radon potential depends on both the source (radium/uranium in soil) and the ease of movement. Highly permeable soils allow soil gas to migrate readily, and elevated radium supplies the radon. The combination produces the greatest entry potential into a building.

Question 44Radon entry, transport, and building dynamics

What is the primary mechanism by which radon moves through soil toward a building foundation?

  1. Capillary action of liquid water carrying dissolved gas
  2. Convection of soil gas driven by pressure differences Correct answer.
  3. Photochemical breakdown of radium at the surface
  4. Settling of radon particles under gravity

Explanation

Radon is a gas that migrates primarily by bulk flow (advection/convection) of soil gas driven by pressure gradients. Diffusion also occurs but is much slower over typical distances. Pressure-driven flow is the dominant transport mechanism near foundations.

Question 45Radon entry, transport, and building dynamics

A tester measures elevated radon in a basement but low levels on the second floor during the same period. What best explains this pattern?

  1. Radon enters at the foundation and is diluted as it rises and mixes with outdoor air exchange Correct answer.
  2. Radon is heavier than air and settles on the lowest level
  3. The upper-floor detector is always defective
  4. Radon is destroyed by the higher temperature on upper floors

Explanation

Radon entry is concentrated at the soil-building interface, so the lowest level typically shows the highest concentrations. As air moves upward, dilution and air exchange with outdoors reduce concentrations. Radon is not heavy enough to settle significantly, and temperature does not destroy it.

Question 46Radon entry, transport, and building dynamics

How does a home's air-tightness generally affect indoor radon concentrations?

  1. Tighter homes always have lower radon because less outdoor air enters
  2. Air-tightness has no relationship to radon concentration
  3. Tighter homes tend to have higher radon because soil gas entry is less offset by air exchange Correct answer.
  4. Tighter homes prevent all soil gas entry

Explanation

In a tighter home, outdoor air exchange is reduced, so radon entering from the soil is diluted less and can accumulate. Air-tightness does not stop entry; it can actually increase the indoor concentration by reducing dilution. This is why weatherization should be paired with radon testing.

Question 47Radon entry, transport, and building dynamics

Which weather condition most often produces elevated short-term radon readings in a basement?

  1. Heavy rain that fully saturates the soil
  2. Cold winter periods with closed windows and a strong stack effect Correct answer.
  3. Mild spring days with continuous ventilation
  4. Warm, windy summer days with open windows

Explanation

Cold weather with closed windows increases the indoor-outdoor temperature difference, strengthening the stack effect and depressurizing the lower level. This draws more soil gas indoors while reducing dilution from outdoor air. Open windows and strong ventilation tend to lower readings.

Question 48Radon entry, transport, and building dynamics

What role does a sump pit typically play in radon entry?

  1. It prevents soil gas from entering the foundation
  2. It acts as a collection point that can channel soil gas into the basement if not sealed Correct answer.
  3. It filters radon out of soil gas before it enters
  4. It converts radon into a harmless compound

Explanation

A sump pit often provides a direct, low-resistance pathway from the soil beneath the slab into the basement. If the pit is open and unsealed, soil gas can readily enter the living space. Sealing the pit or using it as part of a sub-slab depressurization system addresses this pathway.

Question 49Radon entry, transport, and building dynamics

Why do foundation drain tiles and gravel layers sometimes increase radon entry?

  1. They create a permeable bed that transports soil gas to the foundation perimeter Correct answer.
  2. They block all soil gas from reaching the foundation
  3. They absorb radon into the gravel permanently
  4. They chemically generate radon from water

Explanation

Gravel and drain tile form highly permeable zones that allow soil gas to move easily toward the foundation. Where these zones connect to openings in the foundation, they can deliver radon-laden gas indoors. This is why sub-slab depressurization systems are often effective when they intercept these pathways.

Question 50Radon entry, transport, and building dynamics

Which phenomenon describes the entry of soil gas caused by a running bathroom exhaust fan?

  1. Backdrafting of the water heater alone
  2. Radon release from shower water
  3. Diffusion of radon through drywall
  4. Depressurization of the house drawing soil gas through foundation openings Correct answer.

Explanation

Exhaust fans remove indoor air and can slightly depressurize the house, especially in a tight home. The resulting pressure difference draws soil gas through foundation cracks and other openings. This is a pressure-driven entry mechanism, not diffusion or water release.