Transcript Indoor Air Pollution

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).
Uranium-238 Decay Chain
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.
How does radon
get inside
buildings?
Cavities inside walls
Gaps around service pipes
Cracks in solid floors
The water supply
Construction joints
Cracks in walls
Gaps in suspended floors
Soil
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.
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=10-12Ci) 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 cancer
Fix 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
0.4 pCi/L
(Reducing radon
evels below 2 pCi/L is difficult.)
About 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.
Liu Jiaying: Collect Information& Draft ppt
Ye Qiuwen: Make ppt
Pei Wei: Presentation