Nazaroff W W, Doyle S M
Health Phys. 1985 Mar;48(3):265-81. doi: 10.1097/00004032-198503000-00003.
The transport of 222Rn from soil, through a vented crawl space, and into the living space of single-family residences was studied. Two houses were monitored in detail for periods of 5 and 7 weeks. With crawl space vents open, the average indoor 222Rn concentrations were 1.2 and 0.6 pCi 1.-1 (44 and 22 Bq m-3); with the vents sealed the averages rose to 2.2 and 1.0 pCi 1.-1 (81 and 37 Bq m-3). The data suggest that, of the Rn released into the crawl space from the soil beneath the house, a significant fraction, perhaps 50% or more, enters the living space. The effect of 3 meteorological parameters--wind speed, indoor-outdoor temperature difference, and rate of barometric pressure change--on Rn concentration and entry rate were examined. In 1 of the houses a higher temperature difference corresponded to a higher indoor concentration, suggesting that the increased infiltration rate is more than compensated by an increase in the Rn entry rate. On the other hand, a high wind speed tended to reduce the indoor concentration, presumably by increasing both cross-ventilation of the crawl space and the infiltration rate of the living space. Results suggest that Rn transport into the crawl space of at least 1 of the houses occurred by pressure-driven flow, rather than solely by molecular diffusion. The diffusion coefficient of 222Rn through polyethylene sheeting, such as was present on the ground beneath this house, was measured in the laboratory and found to range from 0.65 X 10(-7) cm2 s-1 at 11 degrees C to 1.6 X 10(-7) cm2 s-1 at 25 degrees C, implying that the maximum diffusive flux through the sheet was many times smaller than that necessary to account for the rate of Rn entry into the house. A third house was studied using a tracer gas injected into the crawl space at a controlled rate. The fraction of air leaving the crawl space that entered the living space ranged from 0.3 to 0.65, in good agreement with results for Rn transmission in the other 2 houses, assuming that the 222Rn flux into the crawl space was comparable to that which would have resulted from molecular diffusion from soil having a 222Rn diffusion length of 1.0 m. By sealing leaks in the floor of this house, the average infiltration rate was reduced by 25%, but the indoor concentration of the tracer gas remained constant.
研究了222Rn从土壤中通过通风的爬行空间进入单户住宅居住空间的传输情况。对两所房屋进行了为期5周和7周的详细监测。当爬行空间通风口打开时，室内222Rn的平均浓度分别为1.2和0.6 pCi l.-1（44和22 Bq m-3）；通风口密封后，平均值升至2.2和1.0 pCi l.-1（81和37 Bq m-3）。数据表明，从房屋下方土壤释放到爬行空间中的Rn，有很大一部分，可能50%或更多，进入了居住空间。研究了风速、室内外温差和气压变化率这三个气象参数对Rn浓度和进入率的影响。在其中一所房屋中，较高的温差对应较高的室内浓度，这表明增加的渗透速率被Rn进入率的增加所抵消。另一方面，高风速往往会降低室内浓度，大概是通过增加爬行空间的交叉通风和居住空间的渗透率。结果表明，至少有一所房屋的Rn进入爬行空间是由压力驱动的流动发生的，而不仅仅是通过分子扩散。在实验室中测量了222Rn通过聚乙烯薄膜（如该房屋下方地面上的薄膜）的扩散系数，发现在11℃时为0.65×10(-7) cm2 s-1，在25℃时为1.6×10(-7) cm2 s-1，这意味着通过该薄膜的最大扩散通量比解释Rn进入房屋的速率所需的通量小很多倍。对第三所房屋进行了研究，以控制速率向爬行空间注入示踪气体。离开爬行空间进入居住空间的空气比例在0.3到0.65之间，与其他两所房屋中Rn传输的结果非常一致，假设进入爬行空间的222Rn通量与从222Rn扩散长度为1.0 m的土壤中分子扩散产生的通量相当。通过密封该房屋地板上的漏洞，平均渗透率降低了25%，但示踪气体的室内浓度保持不变。
