[Strawbale] Radiating earth
derek at unm.edu
Thu Jun 21 20:23:56 CEST 2012
Radon in houses is a serious problem on the national and international scale. Roughly five times as many people die each year from radon exposure as from fires (all causes). In the USA, that is 21000 deaths per year from radon-induced lung cancer, compared to a bit over 4000 deaths per year from house fires, commercial building fires, forest fires, and wild fires (combined). Given how much time, money, and attention we put on preventing fires and fire deaths, we ought to put five times as much on radon. We don't, because radon is invisible, slow, and has none of the drama of a fire.
I think "thoron" is a silly word, and using it only causes confusion, as is happening in this discussion. The word "thoron" was created more than a hundred years ago, when physicists still didn't understand much about radioactivity, nor what elements were radioactive. Some people still use the word "thoron" for one of the four most long-lasting isotopes of radon, but all of these isotopes ARE radon. It is symptomatic of the problems caused by this terminology, that we read, "I am not thinking about radon... [but] thoron". It's all radon, in different forms. In fact, the isotope of radon referred to as "thoron" is less of a health risk than several other radon isotopes.
Radioactive elements are very common in the Earth's crust, and anywhere that you find dirt or rock, it is possible to detect some level of radioactivity. In most places, scientists say, the diverse radioactive elements occur in low concentrations that cause no significant health risk. Of course, other people say that there is no safe level of radioactivity, but whatever you believe about that, you can't escape radiation and live a normal life on this planet. Most dirt is "safe", because the radioactive elements are spread out, are in solid form, and don't move. The problem with radon is that it is a gas, and can move and become concentrated in a house. All the radon gas from several meters of dirt underneath a house has the potential to migrate upwards through the soil and to concentrate in a house. Radon in a water supply can be pumped into the house.
Radon might enter a house as a gas that mixes with the inside air, or in its water. If in the water, radon can be released into the air during showers, and then breathed. Breathing radon gas brings it into the lungs, where the radioactivity can remain for the rest of your life. The radon will rapidly change to another radioactive element in your lungs, and therefore won't be breathed out.
The most stable isotope of radon has a half-life of 3.8 days. I won't go into a lengthy explanation of half-life, but this means that half the radon in a given sample will change into another radioactive element within 3.8 days. Half of what remains will change in the next 3.8 days, and so on. Most radon atoms will have decayed into another solid radioactive element within three weeks. Meanwhile, new atoms of radon are continually being created by other radioactive elements in dirt and water. 21 days doesn't seem like a lot of time for radon to migrate, but it is enough for it to concentrate and become a significant problem in some houses. (Radon 220, the isotope sometimes referred to as "thoron", has a half-life of 55.6 seconds. This means it has much less time to migrate and concentrate as a gas, which is why it is usually less of a health problem in houses than the longer-lived isotopes.)
As I said above, radon is a significant problem on the national scale. I don't know much about the geology of Europe, but I bet that there isn't a single country where no house has a radon problem. Every state in the USA and every province of Canada has locations with radon problems. However, the distribution of radon problems is highly variable from house site to house site. There are houses with severe problems located within 100m of houses with no problem. Some regions have more frequent problems than others. Testing a specific building site for radon is the only way to be sure.
We like to build tight houses (low air infiltration), because they are more energy efficient and more comfortable. Sadly, this increases the risks of several internal air quality problems, including radon. Strawbale houses can be built tight, loose, or in between. A well-built strawbale house, with low air infiltration, does nothing to protect the occupants from radon, when compared to a similarly tight house built with other materials. As others have mentioned, if you design and build the floor to prevent radon migration from the soil into the house, you can mitigate most radon problems. If there is significant radon in the water, I think the only solution is to find another source of water.
If the dirt around a house is safe to walk on and grow vegetables in, then I doubt that using it to plaster your interior walls could cause a significant radioactivity problem. From all dirt, some amount of radon will be released, but the mass of earth contained in a layer of plaster is pretty small. I don't know if anyone has ever measured the radon released by a 3cm thick layer of interior earthen plaster. I would be very interested in the figures, if anyone knows of any research. But my guess is that the radon release would be quite low, compared to the risk of radon from the mass of soil under the house and from domestic water. Pit houses, earth-sheltered houses, and any structures that bring a large mass of earth into contact with the house will increase the potential risk. Again, testing a specific site is the only way to be sure.
It is counter-productive to exaggerate the problems with radon, or to become paranoid about the risks. It's also a bad idea to minimize or ignore the potential problem with radon. Like most aspects of building, we want to do things in the proper way, not do too much or too little. I know of several owner-built houses that were found to have radon problems only after the builder wanted to sell the house. Testing was done on behalf of the buyer, which revealed that the builder's family had been exposed during the whole time they lived there. To me, it makes sense for every owner-builder to test their site before building. The cost of a test is a tiny fraction of even the most inexpensive home. It's far better to know in advance that your building site is safe for radon, or that you must design your house to mitigate a radon problem. Doing it after the house is built is hard and expensive. Not testing at all might expose your family to a risk that, with knowledge, you could have avoided.
On Jun 21, 2012, at 4:07 AM, Sara Tommerup wrote:
> I am not thinking about Radon from the bedrock, I am thinking about
> thoron (I guess it could be radon as well as it is what thoron breaks
> down to) radiating from the clay that we use in earth building
> On Thu, Jun 21, 2012 at 10:51 AM, Juliane Derry
> <julianederry at hotmail.com> wrote:
>> Hi Sara,
>> Here in Norway, there are also concerns about this radiation (we call it
>> This is a radiation present in most areas of dense rock (most of Norway).
>> This started becoming a problem in the 70s and 80s, as houses were built
>> more air tight than before. Older houses were leaky, and let the radiation
>> out through
>> windows and other small cracks all around the house. People now build solid
>> cement floors, and add a special membrane to keep this radon out of the
>> house to begin with.
>> Here is a link to some products. Even though it is in Norwegian, you could
>> ask a local place
>> about the names and product numbers.
>> I have wondered about this issue myself, and whether or not the air exchange
>> happens with the straw bale walls is sufficient to let the radiation go
>> right through the house?
>> You can get little dosimeters to place in the house, which measures the
>> content over time.
>> Anyone else have thoughts on this?
>> Juliane Derry
>> Oslo, Norway
>>> Date: Thu, 21 Jun 2012 10:36:44 +0100
>>> From: stommerup at gmail.com
>>> To: strawbale at amper.ped.muni.cz
>>> Subject: [Strawbale] Radiating earth
>>> Hi everybody,
>>> There is a real concern that radiation from earth in buildings are at
>>> harmful levels, especially in Germany and china. I would like to hear
>>> what you know and think of it as I am contacted by nervous clients
>>> about the matter. I have a hard time finding information on the
>>> subject. A German article was describing the high levels of radiation
>>> as being a big contributor to lung cancer which has freaked out the
>>> German population as it has a large amount of earthen houses. It is
>>> Thoron that is the suspect.
>>> If you know about how to stop radiation from walls, like paints or
>>> wall paper, etc, let me know also.
>>> Look forward to hearing from you.
>>> Sara Tommerup
>>> European strawbale building discussion list
>>> Send all messages to:
>>> Strawbale at amper.ped.muni.cz
>>> Archives, subscription options, etc:
> European strawbale building discussion list
> Send all messages to:
> Strawbale at amper.ped.muni.cz
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derek at unm.edu
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