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W J Fisk

Publications and source records attributed to W J Fisk.

23 records · Page 2Linked to original sources
PubMed1993

Modeling radon entry into Florida slab-on-grade houses.

Radon entry into a Florida house whose concrete slab is supported by a permeable concrete-block stem wall and a concrete footer is modeled. The slab rests on backfill material; the same material is used to fill the footer trench. A region of undisturbed soil is assumed to extend 10 m beyond and below the footer. The soil is assumed homogeneous and isotropic except for certain simulations in which soil layers of high permeability or radium content are introduced. Depressurization of the house induces a pressure field in the soil and backfill. The Laplace equation, resulting from Darcy's law and the continuity equation, is solved using a steady-state finite-difference model to determine this field. The mass-transport equation is then solved to obtain the diffusive and advective radon entry rates through the slab; the permeable stem wall; gaps at the intersections of the slab, stem wall, and footer; and gaps in the slab. These rates are determined for variable soil, backfill, and stem-wall permeability and radium content, slab-opening width and position, slab and stem-wall diffusivity, and water table depth. The variations in soil permeability and radium content include cases of horizontally stratified soil. We also consider the effect of a gap between the edge of the slab and the stem wall that restricts the passage of soil gas from the stem wall into the house. Calculations indicate that the total radon entry rate is relatively low unless the soil or backfill permeability or radium content is high. Variations in most of the factors, other than the soil permeability and radium content, have only a small effect on the total radon entry rate. However, for a fixed soil permeability, the total radon entry rate may be reduced by a factor of 2 or more by decreasing the backfill permeability, by making the stem wall impermeable and gap-free, (possibly by constructing a one-piece slab/stem-wall/footer), or by increasing the pressure in the interior of the stem wall (by ensuring that there is a large pressure drop across the slab/stem-wall gap), thereby reducing radon entry into the wall from the soil. Use of an impermeable stem wall and a low-permeability fill in combination is predicted to reduce the radon entry rate by 71%.

Air Pollution, Indoor↗
PubMed1991

Effectiveness of radon control techniques in fifteen homes.

Radon control systems were installed and evaluated in fourteen homes in the Spokane River Valley/Rathdrum Prairie and in one home in Vancouver, Washington. Because of local soil conditions, subsurface ventilation (SSV) by pressurization was always more effective in these houses than SSV by depressurization in reducing indoor radon levels to below guidelines. Basement overpressurization was successfully applied in five houses with airtight basements where practical-sized fans could develop an overpressure of 1 to 3 Pascals. Crawlspace ventilation was more effective than crawlspace isolation in reducing radon entry from the crawlspace, but had to be used in conjunction with other mitigation techniques, since the houses also had basements. Indoor radon concentrations in two houses with air-to-air heat exchangers (AAHX) were reduced to levels inversely dependent on the new total ventilation rates and were lowered even further in one house where the air distribution system was modified. Sealing penetrations in the below-grade surfaces of substructures was relatively ineffective in controlling radon. Operation of the radon control systems (except for the AAHX's) made no measureable change in ventilation rates or indoor concentrations of other measured pollutants. Installation costs by treated floor area ranged from approximately $4/m2 for sealing to $28/m2 for the AAHX's. Based on the low electric rates for the region, annual operating costs for the active systems were estimated to be approximately $60 to $170.

Air Pollution, Radioactive↗
PubMed1990

Evaluation of radon mitigation systems in 14 houses over a two-year period.

Fourteen single-family detached houses in Spokane, Washington, and Coeur D'Alene, Idaho, were monitored for two years after high concentrations of indoor radon had been mitigated. Each house was monitored quarterly using mailed alpha-track radon detectors deployed in each zone of the structure. To assess performance of mitigation systems during the second heating season after mitigation, radon concentrations in seven houses were monitored continuously for several weeks, mitigation systems in all houses were inspected, and selected other measurements were taken. In addition, occupants were also interviewed regarding their maintenance, operation, and subjective evaluation of the radon mitigation systems. Quarterly alpha-track measurements showed that radon levels had increased in most of the homes during many follow-up measurement periods when compared with concentrations measured immediately after mitigation. Mitigation-system performance was adversely affected by (1) accumulated outdoor debris blocking the outlets of subsurface pressurization pipes; (2) fans being turned off (e.g., because of excessive noise or vibration); (3) air-to-air heat exchanger, basement pressurization, and subsurface ventilation fans being turned off and fan speeds reduced; and (4) crawl-space vents being closed or sealed.

Air Pollution, Radioactive↗
PubMed1988

Modeling the effects of exhaust ventilation on 222Rn entry rates and indoor 222Rn concentrations.

Continuous mechanical exhaust ventilation of moderately air-tight residences is common in Scandinavia and has recently been employed in several U.S. residences. Exhaust ventilation decreases the indoor pressure and, thus, increases the pressure difference which drives 222Rn entry. Relatively simple analytical (i.e. closed form) models were developed and used to examine the impacts of exhaust ventilation on 222Rn entry rates and concentrations in houses with either a crawl space or a basement. A more complex finite difference model was also developed for the house with a basement and yielded soil gas entry rates within 16% of those predicted with the analytical model. The models indicate that exhaust ventilation is suitable, but not optimal (from the perspective of indoor 222Rn), for houses with a vented crawl space. Exhaust ventilation is also indicated to be suitable for houses with basements surrounded by relatively impermeable soil (10(-12) m2 or less). If soil permeabilities are between 10(-12) and 10(-10) m2, exhaust ventilation may cause substantial increases in indoor 222Rn when soil gas 222Rn concentrations are above average. If soil permeabilities are greater than 10(-10) m2, exhaust ventilation is indicated to be inappropriate, unless some procedure is employed to inhibit soil gas entry. These conclusions should be considered tentative, since extensive verification of the models is still required.

Air Pollutants, Radioactive↗