One of the dodges the stone industry is using to minimize the risks of granite countertop Radon emission is that a little ventilation will solve the problem. The info below is from an University study were a 2 1/2 square foot opening was added to the normal leakage present in a home (ACH).
Now stop and think of the effect that a 2 1/2 square foot hole would have on our homes heat and cooling bill. Then consider how much of the Radon is still present even with this large amount of fresh air.
One of the reasons Radon levels are kept lower despite a continual exhalation of new Radon from granite is that outside air is continually leaking into a home at varying rates. Exactly how much fresh air coming in is usually a guess, but there have been studies showing from .5 ACH (Air Change per Hour, or how many times the air is completely replaced) to .035 ACH, with .35 ACH being that adopted by ASHRAE (American Society of Heating, Refrigerating and Air Conditioning Engineers).
In an effort to bring some facts to bear, there was a study done by two scientists at the University of Colorado. These two Physicists looked at the air exchange rates in multi room house models.
The Correlation Between Small Ventilation Rates And Indoor Radon Concentrations Using A Multi Room House Model.
Their model was six rooms, interconnected, but with one room having an operable window to outside air. With the window closed, the rooms reached the maximum levels quickly, around 12 hours, assuming an air sharing rate of .5 ACH between rooms and and leakage rate of .35 ACH (normal air leaks present in all homes). Their result mirrored the result they got from figuring the home as one large room. See graph 2.
In the next graph result, Figure 3, a window was opened 10″ six hours after the test started and left open for the duration of the test. Note that the Radon levels dropped severely in room 1, the one with the open window, but the other rooms didn’t drop that much in comparison. Air exchange for room 1 (open window) was 1 ACH. The air exchange remained at .5 ACH between rooms, with the same .35 ACH from leakage.
The next graph, Figure 4., had the air exchange between rooms increased to 2 ACH per hour which is thought to be a normal rate for rooms open to each other. Room 1 still had an open window and remained at 1 ACH. More Radon reduction, but only about 20% for the farthest room. Strangely enough, room 1 had a slight increase due to the Radon being brought in from the other rooms.
Figure 5., represented a “tight” house with an ACH of .1, exactly what Bill Brodhead was reporting in his concrete high rise condo Radon study. This ACH is reported to not be uncommon. The ACH between rooms remains at 2, with room 1 still having an open window and a 1 ACH rate. Now the Radon levels are much lower, with room 1 having a 60% drop, even room 6 is at half it’s normal Radon levels.
Finally, Figure 6 represents the same conditions in Figure 5 graph, with one exception, the window being open for only 24 hours. This affected the final values quite a bit, with a 30% Radon decrease in room 1 and a 26% decrease in room 6.
One of the conclusions was that a window opened 10″ will cut the Radon levels by 10% to 50% if the window remains open. What struck me as important was that even a large amount of ventilation did not eliminate the Radon buildup, but merely reduced it. With 1.3 pCi/L of Radon (the average level in US homes) having a death rate of 21,000 per year, it would seem that ventilation alone will not eliminate the danger.
The entire study can be found at http://www.uccs.edu/~physics/docs/multiroom.pdf
I would guess that an average window was around 36″ wide, which if opened 10″, would give you a 2 1/2 square foot hole in the wall. For those that argue that ventilation alone will solve the problem of hot granite emitting Radon in homes, this should give them some pause.
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