Schools

Case 3: Measurement in Schools

More and more schools are being tested for radon exposure to students and employees.  This is increasingly becoming mandatory in many states.  Radon can enter schools just as easily as homes, and in fact, the entry can be quite high if the heating ventilation and air conditioning system (HVAC) is not balanced.  The effects of the HVAC system on radon entry are two-fold:

• Schools are typically designed to have fresh air introduced into the building via the HVAC system which would serve to positively pressurize the building and reduce radon entry from the soil.  However, energy management strategies at times reduce or even shut off the addition of fresh air, either deliberately or when control components fail. 

• Also, large HVAC systems become unbalanced for a given room where more air is drawn out of the specific room than is supplied. This causes that particular room to be under negative pressure that can draw radon in, if the room is in contact with the soil. 

However, when these two conditions occur the HVAC system is still operating and recirculating air within the building.  The simple air movement within the building, regardless of whether fresh air is being added or the system is balanced can still significantly reduce the levels of radon decay products within the rooms, and hence risk exposure, even if the radon levels are elevated.  The following graphs present some comparisons of long-term radon and radon decay product measurements in two school buildings (click on each thumbnail to enlarge the picture).

School 1 The results shown are from long-term (>91 day) measurements of both radon & radon decay products in rooms that were > 4.0 pCi/L	School 2 Long-term radon & radon decay products in all occupied rooms.

The results shown in the graphs to the left are typical of results in buildings with high air circulation.

In the case of School 1 there were 8 rooms that would have been mitigated based on radon measurements alone.  However, the radon decay product measurements indicated that only one room was in excess of the guideline.

In the case of School 2, it was similarly found that for the most part the actual radon decay product exposures were well below the 0.02WL guidance, but in two cases there were rooms where the radon was elevated but the radon decay product exposure was significantly higher than indicated by the radon measurement alone. 

In the interest of focusing limited resources towards health risk reduction, the use of PGL devices that measure both radon and radon decay products, often eliminates unnecessary mitigation costs but can also highlight those locations where efforts should be exerted.  In other words, the use of radon decay product measurements in addition to radon can avoid both false positives and false negatives.

Caution: When doing follow-up measurements using radon decay product levels as a criteria it is important to also measure radon.  This insures that the lower radon decay product levels are a function of lower equilibrium factors and plate-out, rather than an a lower radon gas level during the time of the follow-up measurement.  That is why PGL provides devices through its manufacturing partners that measure BOTH radon and radon decay products!

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Last modified: 06/05/08