The two options you ask about are aimed at different outcomes and are in many respects similar. Both the C-NRPP and OCRMI short-term measurements are performed over a minimum of 48 hours. The difference is the reason behind the measurements.
The C-NRPP measurements are aimed at trying to gauge the long-term exposure of residents in a property to radon levels but extrapolating the levels found in a short-term test. The test is based upon the levels of a home that is currently inhabitable. These tests do not take into account the possible future use of the home. Neither do they take into account that fact that there may be a defect in the property that will allow radon into the home enabling a future build-up.
The OCRMI measurements are aimed at trying to identify those very defects so that valid information is provided to buyers BEFORE they make the decision to proceed with a purchase. The measurements are made in areas of the home that may be lived in at some time in the future. We believe that this is a necessary requirement for people who are thinking of purchasing a home.
Both types of measurement provide a traffic light report of the results, but the reporting is distinctly different.
There is not a huge difference between the recommendations made for the results that come in as Yellow or Red for the C-NRPP measurements. Both specify long-term testing. This is obviously inconvenient in a real-estate transaction.
The OCRMI Green-Amber-Red report gives distinctly different recommendations for each and specifies clearly the options available to the person who requested the measurement.
The reason we feel the OCRMI measurement protocol is the better choice is that a home purchase is made under the legal axiom “Caveat Emptor”. This means that the buyer should take all steps to ascertain the condition of the property they are intending to buy BEFORe they purchase it. We see no reason why you should be asked to purchase a property only to find out after you’ve bought it that there is a defect that requires a large expense to fix.
This is why the OCRMI protocol mimics many of the reasons why buyers should have a full home inspection performed before buying a home and doesn’t just look at the long-term health of the individual. Everyone knows radon is a cause of lung cancer. It is well known that long-term exposure to elevated levels increases the risk. We don’t see the reason for a long-term test if it is known that radon can enter the property through a defect in the building envelope. It is, in our opinion, better to know of the risk as soon as possible and then make a decision based upon a risk profile.