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relatively poor counting statistics in the particular experiment. For dosimetric calculations, the particle size distribution during showering is therefore essentially the same as the normal house particle size distribution. This is not unexpected, because as radon gas is released from water droplets and decay products form, they interact with the normal home aerosol particles.
Integrated Measured 222Rn Concentration in the Shower
The 222Rn released to a shower from water was monitored in an ultra-high energy efficiency home with a private well (N. Harley, private communication). Integrated measurements spanned two 6-mo periods and indicate the average shower concentration. Data from this example home is presented.
The home monitored was in northern New Jersey and occupied by two adults and three children. The duration of all five morning showers was measured to be 60 minutes per day. The 222Rn concentration was measured at the bathroom cold-water tap and in water at showering temperature that was collected from the showerhead but near the tub surface to determine 222Rn loss. The long-term data are shown in table 5.3. The mean concentration in cold tapwater was 60,000 Bq m-3; on the average, 6,000 Bq m-3 remained in the drain water after spray from the showerhead.
The showerhead normally delivers water at 0.0053 m3 min-1 with a mean 222Rn concentration of 60,000 Bq m-3. The fraction of 222Rn lost (table 5.3) by the water to the air was 90% (the water concentration decreases from 60,000 Bq m-3 to 6,000 Bq m-3) as the water fell from the showerhead to the tub floor. Thus, the shower released to the air at an average of about 290 Bq 222Rn min-1.
Table 5.4 shows the time-integrated 222Rn concentration in the ventilator duct directly above the shower as measured with a passive, alpha-track detector. A small exhaust fan in the vent outlet operates during showering to remove water vapor from the home. The duct concentration approximates the concentration in the shower. The concentration over the two 6-mo intervals varied somewhat, as expected, because of different conditions in the shower.
From the preceding description of the aerosol particle size distribution as a result of showering, it is clear that the aerosol characteristics in showers are not substantially different from those found in the rest of the house in terms of particle number or size.
The annual dose to the bronchial airways of a person can be calculated from three factors:
A knowledge of the 222Rn concentration in the shower.
The estimated time spent in the shower per year (about 1% for illustrative purposes).
The central value of the 222Rn bronchial dose factor, given the equilibrium factor in the shower (0.05) is 0.004 mGy yr-1 per Bq m-3. This dose factor takes