Presentation on theme: "Indoor Air Pollution —— Radioactivity from Radon Gas Group members: 刘佳颖，叶秋雯，裴伟."— Presentation transcript:
Indoor Air Pollution —— Radioactivity from Radon Gas Group members: 刘佳颖，叶秋雯，裴伟
Outline Introduction Where does radon come from? How does radon get inside buildings? The level and distribution of radon The Risk of Living With Radon Reducing Radon Risks
Introduction Although pollutant concentrations vary significantly from building to building, the levels of some common air pollutants often are greater indoors than outdoors. Since most people spend more time indoors than outdoors, exposure to indoor air pollutants is an important environmental problem.
What ’ s indoor air pollution? Indoor Air Pollution is the term used to describe the amount of contaminants in the air inside a building from sources such as cigarette smoking, fuel combustion for heating or cooking, certain wallboards, carpets, or insulation as well as the geology of the area (radon in soil or rocks beneath the structure).
What ’ s radon( 氡 )? Radon is a naturally-occurring radioactive( 放 射性的 ) but inert( 惰性的 ) gas part of the decay chain that starts with uranium( 铀 ) and ends with plumbum ( 铅 ).
Property of Radon Single atom gas Inert, colorless, odorless at ordinary temperatures Melting point: 202 degrees K Boiling point: 211 degrees K Atomic radius: 1.34 angstroms (the heaviest known gas) Half-life: 3.8days
Where does radon come from? Natural source: Earth and rock beneath home; Well water; Outdoor air; Artificial source: Daily life materials: leather; low density plastic (like plastic bags, etc.); paints Building materials: gypsum board (sheetrock), concrete block, mortar, sheathing paper (tarpaper), wood paneling, and most insulation.
Some uranium is present in all earth materials. On continental surfaces the rocks, sediments and soils typically contain between 1 and 3 parts per million (abbreviated ppm) of uranium. Some earth materials may have more.
Cracks in solid floors Construction joints Cracks in walls Gaps in suspended floors Gaps around service pipes Cavities inside walls The water supply
Radon from soil gas is the main cause of radon problems. How much of radon reaches the surface depends on the uranium content of the underlying earth materials together with their depth and permeability (that is, the presence of fractures and interconnected pore spaces that act as conduits for radon). Enter the lowest level of a building using whatever pathways are available. Soil
For structures with basements or slab-on-grade foundations, the entry points include Cracks and pores in floor slabs, walls, and floor-wall joints; Openings around sump pumps, floor drains, and pipes penetrating floors and walls.
Structures with a crawl space between the ground and lowest floor level may be less vulnerable to radon, which tends to escape to the outside air when appropriate vents are installed, but can still admit some of the gas through cracks in the flooring.
Water Radon can also enter into homes through the water system. This is mainly true for houses in which ground water is used as the main water supply.
Small public water works and private domestic wells often have closed systems and short transit times that do not allow radon to decay to harmless by-products before entering a home. Once inside, radon escapes from the water to the indoor air as people take showers, wash clothes or dishes, or otherwise use water. The areas most likely to have problems with radon in ground water are those with have high levels of uranium in the underlying rocks.
Water in rivers and reservoirs usually contains very little radon, because it escapes into the air. Thus homes that rely on surface water usually do not have a radon problem from their water. In big cities, water processing in large municipal systems aerates the water, which allows radon to escape, and also delays the use of water until most of the remaining radon has decayed.
The Average Level of Radon Found in a Home Based on a national residential radon survey completed in 1991, the average indoor radon level is about 1.3 picocuries( 皮居里 =10 -12 Ci) per liter (pCi/L) in the United States. The average outdoor level is about 0.4 pCi/L.
The safe level of radon There is no safe level of radon--any exposure poses some risk of cancer.
Zone 1 counties have a predicted average indoor radon screening level greater than 4 pCi/L (pico curies per liter) (red zones) Zone 2 counties have a predicted average indoor radon screening level between 2 and 4 pCi/L (orange zones) Zone 3 counties have a predicted average indoor radon screening level less than 2 pCi/L (yellow zones)
The Risk of Living With Radon Radon gas decays into radioactive particles that can get trapped in your lungs when you breathe. As they break down further, these particles release small bursts of energy. This can damage lung tissue and lead to lung cancer over the course of your lifetime.
Smoking combined with radon is an especially serious health risk. Children have been reported to have greater risk than adults of certain types of cancer from radiation, but there are currently no conclusive data on whether children are at greater risk than adults from radon.
Radon Risk If You Smoke/Never Smoke Radon Level If 1,000 people who smoked were exposed to this level over a lifetime*... If 1,000 people who never smoked were exposed to this level over a lifetime*... WHAT TO DO: Stop smoking and... 20 pCi/L About 260 people could get lung cancer About 36 people could get lung cancer Fix your home 10 pCi/L About 150 people could get lung cancer About 18 people could get lung cancer Fix your home 8 pCi/L About 120 people could get lung cancer About 15 people could get lung cancer Fix your home 4 pCi/L About 62 people could get lung cancer About 7 people could get lung cancerFix your home 2 pCi/L About 32 people could get lung cancer About 4 person could get lung cancer Consider fixing between 2 and 4 pCi/L 1.3 pCi/L About 20 people could get lung cancer About 2 people could get lung cancer (Reducing radon evels below 2 pCi/L is difficult.) 0.4 pCi/LAbout 3 people could get lung cancer Note: If you are a former smoker, your risk may be lower. * Lifetime risk of lung cancer deaths from EPA Assessment of Risks from Radon in Homes (EPA 402-R-03-003). ** Comparison data calculated using the Centers for Disease Control and Prevention's 1999-2001 National Center for Injury Prevention and Control Reports.
EPA ( Environmental Protection Agency 美国 环保署 ) estimates that radon causes thousands of cancer deaths in the U.S. each year.
Reducing Radon Risks There are two ways to protect your family from Radon. First, the hard way Holding Your Breath
Lower the Radon Level in Your Home Your Family Will Breathe A Lot Easier.
How to Lower the Radon Level The most effective way to lower the radon level is set a vent pipe system and fan, which pulls radon from beneath the house and vents it to the outside.
There are also other ways: Test your home for radon. Be careful when you choose building materials. Fill the gaps and cracks in the ground, floor, and walls. Pay more attention to the basement and the first floor where there is a high level of radon. Don ’ t smoke in the room, especially the one for children and elders.
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