Saturday, February 25, 2012

Cap and Boots (VII)

So far in this series about at old houses and their problems, we have taken a look at foundation and roof design shortfalls, antiquated wiring systems, lead plumbing components, lead in paint and varnish, asbestos, and then mold. If these issues weren't enough to give pause to those contemplating buying or living in an old house, there is another hazard, and this hazard is by no means confined to old houses. It is a hazard you can't see, hear, or smell, and it is estimated to be responsible for 21,000 deaths annually in the US.

If you've even wondered how a person might die from lung cancer without ever having smoked, been exposed to second hand smoke, lived near a refinery, etc., or worked in a coal mine or similar hazardous environment, well: have you heard of radon?

Radon, atomic symbol Rn,  is the second largest cause of lung cancer after smoking, and, if you do smoke and are exposed to radon gas in your living/working environment, well, your risks compound. It's one of those areas where synergy is not such a good thing.

Radon is an odorless, tasteless and invisible gas produced by the decay of naturally occurring uranium in soil and water. It was discovered in 1900 by Friedrich Earnst Dorn, and was the fifth radioactive element ever found. The source of radon is the radioactive decay of uranium - radon is in fact a form of ionizing radiation. It is also the only gas that is radioactive under normal conditions. Radon in the air is all but ubiquitous on the planet. It is in soil, it is in rocks, it is in the oceans, it is even in lakes, rivers, streams and groundwater. The source of radon for our homes has to do with the type of soil and bedrock where we live. If there is a lot of uranium present in the soil or bedrock upon which our homes are built, then there will be lots of radon produced as well. If your home relies upon groundwater, and there is radon present, then your tap water will have radon in it, the gas being emitted every time you turn on a faucet or have a shower.

However some geographic zones are much worse than others. Growing up on the West Coast of Canada, radon was, apparently, all but an irrelevancy and not subject to much conversation. Here in the East Coast, the situation is a little different. Here's a radon potentials map of the US:

If you live in one of the areas colored pink in the above illustration you live in an area with high radon levels. Iowa and the southern Appalachian Mountains in Pennsylvania are the worst locales for radon in the US. The light blue areas on the map have the lowest radon levels. I live in Western Massachusetts, which is rated 'medium' for radon exposure. According to one E.P.A. study I perused, 63% of homes in North Dakota have radon levels above a 'safe' standard.

As mentioned, some parts of Pennsylvania are quite bad for Radon, and in fact heightened radon contamination in homes was discovered by chance in the mid 1980's by events surrounding a certain Stanley Watras, a construction engineer at Bechtel's Limerick nuclear power plant in Pottstown, Pennsylvania:

"One day, on his way to work, he entered the plant and set off the radiation monitor alarms which help protect workers by detecting exposure to radiation. Safety personnel checked him out, but could not find the source of the radiation. Interestingly, because the plant was under construction at the time, there was no nuclear fuel at the plant. They discovered the source of radiation exposure when Watras's home was tested and was measured to have very high radon levels (2,700 pCi/L)."

Every time Watras went to work he had to spend 3~4 hours in the decontamination facility before he could even enter the work site - at a nuclear plant! According to his later testimony (in 1985) to the US House of Representatives Subcommittee on Natural Resources, Agriculture Research and the Environment, a clipping I snatched right off the document (available online):

The E.P.A designated 'safe' limit for radon exposure is 4 pCi/L - or picocuries per liter. The levels in Watras' home were 700 times the E.P.A.'s safety line. A picocurie is 0.000000000001 (one-trillionth) of a Curie, an international measurement unit of radioactivity. The term 'safe' however must be taken a bit provisionally, as even the E.P.A. states,

"Because there is no known safe level of exposure to radon, EPA also recommends that Americans consider fixing their home for radon levels between 2 pCi/L and 4 pCi/L. The average radon concentration in the indoor air of America's homes is about 1.3 pCi/L. It is upon this level that EPA based its estimate of 20,000 radon-related lung cancers a year."

At 4 pCi/l there will be approximately 12,672 radioactive dis-integrations in one liter of air, during a 24-hour period. By comparison, a radon level of 15 pCi/l has about the same risk of causing lung cancer as smoking a package of cigarettes a day.

Canada seems somewhat less plagued by radon over all, except for New Brunswick and Nova Scotia:


I do wonder though, looking at that map and comparing it to the US example, and considering the similarity of much of the underground geology, if the map suffers a bit from insufficient data.

Canada uses a different measure for radon gas levels, denoting the concentrations in Bq, or 'becquerels'. A becquerel is named after Henri Becquerel, who shared a Nobel prize with Marie Curie in 1903. The becquerel is an international method of measuring radiation. To convert picocuries to becquerels, divide by 27.027. If you convert the E.P.A. value of 4 pCi/l you obtain 148 Bq/m3. Notice that the map above shows a threshold line of 200 Bq/m3? It seems that various countries cannot quite agree yet upon what is 'safe' and what isn't. While in the US a suggested 'action level' for radon is 4 pCi/l or 148 Bq/m3, in Canada the "suggested" action level is 400 Bq/m3. The European Union recommends action be taken when concentrations reach 400 Bq/m3 (11 pCi/L) for old houses and 200 Bq/m3 (5 pCi/L) for new ones. County Kerry, Ireland apparently has tested houses in some spots where the radon levels are 13,797Bq/m3, which is some 70 times above the EU limit, equal to an exposure of 47 chest x-rays per day!

The risk of lung cancer increases by 16% per 100 Bq/m3 increase in radon concentration, according the the World Health Organization.

Radon is less an issue in the general environment than it is in our homes, where it tends to accumulate. According to a geology blog I was reading,

"Radon is a noble gas. This means it is very un-reactive in the environment and does not interact readily with other compounds or elements that are present around it. This means that in the environment radon travels all on its own and does not attach itself to other elements as a way to get around. This does not hinder the ability of radon to transfer from air to water and back again, in fact, radon transfers very readily...Radon accumulates in confined spaces such as in our houses or other buildings, particularly in basements as radon is heavier than air. In the open air there is no threat from radon, however, Canadians and many other cultures spend a great deal of their time inside, especially during winter (it is  -20 with wind chill as I write this). This is a major concern as all of this time spent indoors can greatly increase radon exposure."

 If you live in a place known to have high levels of radon gas, you should have your home tested. If you then learn that radon levels are above an acceptable threshold for your peace of mind, then you can either move or look into radon mitigation. Typically, radon mitigation involves:
  • improving the ventilation of the house
  • avoiding the passage of radon from the basement into living rooms
  • increasing under-floor ventilation
  • installing a radon sump system in the basement
  • sealing floors and walls
  • installing a positive pressurization or ventilation system
A common solution is the radon sump - drilling a hole or two in the concrete floor slab and fitting a vent pipe or pipes. This pipe is then routed outside of the house and has a vent fan attached. The fan creates negative pressure under the slab and sucks any radon out. To test, a few small holes are drilled elsewhere in the slab, the sump fan is turned on, and a smoke test applied to the small holes to check if there is suction. If it is working well, then the small holes are sealed back up. This a relatively inexpensive remedy in most cases - perhaps $1000~1500. In some houses the pipe (usually 4" pvc as smaller pipes have higher air flow rates and can be noisy) is routed internally until emerging out the roof, while in other cases is too much of a hassle to route the piping inside the walls, so the pipe emerges just above ground level and pvc pipe is then run up the exterior wall to the roof peak. If you are house hunting and notice that houses in the area in which you are viewing have 4" white pvc pipes running conspicuously up the walls, then you can be fairly sure that radon is a problem in that area.

However, if you live in an old house without a poured concrete foundation and slab floor, it is not so easy to seal off the radon. Old houses with stacked stone of brick foundations, and cracked concrete floors or dirt floors provide innumerable places for radon gas to penetrate:

In order to provide a barrier of some sort for the radon sump to work, typically the entire basement, floors and walls, needs to be sealed up with plastic sheeting. Depending upon how accessible the basement is and how complex the situation, the cost of sealing the basement with plastic, admittedly not a great long term solution, is going to vary.

In high radon areas, old houses with leaky foundations are going to be a hassle. The agriculture department of North Dakota State University has a humorous cartoon showing the ideal radon mitigation system for such places:

Humorous, of course, to those who don't own homes in such places.

If you live in an area with high radon levels, it is vastly preferable to have a basement that is poured concrete, with an under-slab vapor barrier, as it can be more readily sealed and a radon sump fitted. And of course, fitting of a radon sump in new construction is quite easy. If you have an old house and look for a long term solution, then replacement of the foundation is one option, albeit a costly one. Since crummy old foundations are sources of many problems in a house, complete replacement yields many benefits, and may be worth a serious look if the remained of the house has those almost-mythical 'good bones'.

One more post to come in this series. Thanks for coming by the Carpentry Way.

1 comment:

  1. Hi Chris,
    Interesting topic, here in ireland we install the radon sump and also a heavy gauge plastic sheet over the whole foundation just under the slab in areas of high Radon. The sheet is reinforced with a mesh of fibre inside and is taped around all openings, pipes etc..


All comments are moderated:

Anonymous comments will be deleted

Spam will be deleted

Comments containing links unrelated to blog content will be deleted