Transcript Radon Measurement Training Program

Lesson 3
How does radon
enter a home?
Predicted average indoor
radon levels (U.S.)
Zone 1 (red):
greater than
4 pCi/L
Zone 2 (orange):
2-4 pCi/L
Zone 3 (yellow):
less than
2 pCi/L
This map cannot be used to determine the radon level of a
particular home. Homes with high levels of radon have been
found in all three zones. All homes—regardless of their zone—
Slide 4-1
should be tested.
Predicted average indoor
radon levels (Connecticut)
Zone 1 (red):
greater than
4 pCi/L
Zone 2 (orange):
2-4 pCi/L
Zone 3 (yellow):
less than
2 pCi/L
This map cannot be used to determine the radon level of a
particular home. Homes with high levels of radon have been
found in all three zones. All homes—regardless of their zone—
Slide 4-2
should be tested.
Requirements for radon
to enter a home
1. A source of radon
2. A mechanism to transport radon
from the source into the home
3. An opening or pathway into the
home
Slide 4-3
Level of radon
in a home
Depends on
• Strength of radon sources: most
important factor
• Distance of the sources from the
home
• Ease of transport into the home
• Ventilation in the home
• Environmental factors
Slide 4-4
Uranium decay series
Uranium-238
Thorium-234
Protactinium-234
Thorium-230
Radium-226
Radon-222
Slide 4-5
Sources of radon
• Soil and rock
– Uranium is present at about 0.5 to 5
parts per million (ppm) in common
rocks and soil
– Uranium decays into radium
– Radium decays into radon
• Groundwater
• Building materials containing
uranium and radium
Slide 4-6
Radon
from soil and rock
• Soil gas, including radon,
seeps from the ground into
the air in the home
• Usually enters through the
foundation
– Cracks in walls and
floors
– Drains
– Sump holes
– Dirt floors
– Construction joints
– Spaces around service
pipes
Slide 4-7
Radon
in groundwater
Usually a problem only in
small, closed water
systems
• Where underlying rocks
contain high levels of
uranium
• Where homes rely on
groundwater from
private wells or small
public waterworks as
the main water source
Slide 4-8
Radon in small, closed
groundwater systems
• Radon does not have time to
decay into harmless byproducts before entering a
home
• Once inside the home, radon
escapes from the water into
the air during normal
household activities:
– Showering
– Washing clothes or dishes
– Flushing toilets
Slide 4-9
Radon
in other water
Usually not a problem where
homes
• Use surface water (lakes,
streams, rivers, and reservoirs)
– Radon usually escapes into
the air before it reaches a
home
• Use groundwater from large public systems
– Water is aerated (mixed with air), which allows
radon to escape
– Longer transit times allow most of remaining
radon to decay into harmless products
Slide 4-10
Radon
in building materials
• Materials sometimes contain radium or uranium
– Brick
– Granite
– Concrete products
– Sheet rock
– Materials contaminated with radioactive refuse (rarely
used)
• Usually contribute little to indoor radon
Slide 4-11
Strength of
radon sources
Even homes next to each other may have
different radon sources, with different strengths.
Rock:
strong radon
source
Groundwater
containing radon
Rock:
strong
radon
source
Rock:
moderate
radon source
Soil: moderate to weak radon source
Slide 4-12
Radon
transport mechanisms
Push or pull radon into a home
Average contribution to
radon in a home
Diffusion
(1-4%)
Emanation
(2-5%)
Outgassing
(less than
1%)
Air pressure
differences
(85-90%)
Slide 4-13
Radon transport mechanisms
Air pressure differences
• Home creates small
vacuum (negative air
pressure)
– Draws in soil gas,
including radon
• Vacuum caused by
– Temperature differences
between outside and
inside air (stack effect)
– Mechanical systems
– Environmental factors
Slide 4-14
Air pressure differences
Stack effect
• Heated indoor air rises and
moves out of cracks and holes at
the top of the house
– Creates positive air pressure
at the top of the home
– Creates negative air pressure
(vacuum) at the bottom
• Vacuum draws in soil gas,
including radon
• Effect is greatest during coldest
months, when homes are closed
up
• Effect increases because
of thermal bypasses
Positive pressure


 Warm air 
Negative pressure
 Soil gas 
(including radon)
Slide 4-15
Air pressure differences
Mechanical systems
• Heating, ventilation,
and air conditioning
(HVAC) systems
– Air distribution
blowers
– Furnaces
– Boilers
– Wood-burning
fireplaces
– Woodstoves
– Other combustion
systems
• Home exhaust
systems (vent air to
outside)
– Clothes dryers
– Exhaust fans in
bathrooms,
kitchens, or attics
– Central vacuum
cleaners
Slide 4-16
Air pressure differences
Environmental effects
• Weather
–Seasons
–Rain, snow,
and frost
–Wind
• Other factors
that seal the
soil around a
home
Slide 4-17
Environmental effects
Seasons
Usually more radon enters in winter
Warm weather
• Open windows
• Equal pressure
indoors and outdoors
– L ess radon enters
• Good ventilation
dilutes radon
concentration
Cold weather
• Closed windows
• Lower pressure
indoors
– More radon enters
• Poor ventilation
traps radon inside
Slide 4-18
Complex effects of good
ventilation (open windows)
• Reduces vacuum effect
– Generally reduces radon
entry
– Dilutes radon in home
• But may also increase
stack effect
– Thereby increases radon
entry
When you
measure radon
in short-term
tests, should
windows be
open or closed?
Slide 4-19
Complex effects of good
ventilation (open windows)
• Reduces vacuum effect
– Generally reduces radon
entry
– Dilutes radon in home
• But may also increase
stack effect
– Thereby increases radon
entry
When you
measure radon
in short-term
tests, windows
must be kept
closed
Slide 4-20
Environmental effects
Rain, snow, and frost
• Rain, snow, and frost
can seal the soil
– Prevent radon from
escaping from around
the foundation
• Rain can force soil gas
into the home
Slide 4-21
Environmental effects
Wind
Don’t measure
radon during
high winds
because
Higher
results may
pressure
upwind
not show
typical levels.
Downwind draft effect
• Changes pressure around the home
• Higher pressure in soil as wind pushes
beneath soil
Lower
pressure
downwind
Slide 4-22
Environmental effects
Factors that seal the soil
Prevent
radon
escape into
outdoor air
• Asphalt or
concrete
driveways
• Concrete
patios
Slide 4-23
Radon transport mechanisms
Diffusion
Lower radon
concentration


Higher radon
 concentration 
Diffusion = movement
through materials
• Radon concentration is
higher at its source
(underlying soil or
foundation) than in
indoor air
• Radon moves from area
of higher concentration
to area of lower
concentration
Slide 4-24
Radon transport mechanisms
Emanation
Emanation = emission of gas from
a surface by radioactive decay
• Some rocks and other building
materials contain uranium or
radium
• As these elements decay, radon
may be created on their surfaces
• The radon may be emitted into a
room
• Emanation rate depends on
Uranium

Radium

Radon
– Amount of radioactive materials
– Surface area of the materials
Slide 4-25
Radon transport mechanisms
Outgassing
Slide 4-26
Radon transport
Pathways into the home
• Natural
– Pores or empty spaces in soil
– Cracks in underlying rocks
– Earthen areas in basements
• Artificial
– Fill below foundations
– Trenches for utility lines and plumbing
– Water drainage systems
– Other openings in foundations
Slide 4-27
Pathway characteristics
• Ease with which air moves through
the pathway
• Distance from radium (radon source)
• Connections with other pathways
Slide 4-28
Radon entry and levels
vary
• In space
– From geographic area to geographic area
– From home to home
– From level to level within a home
• In time
– From season to season
– From day to day
– From hour to hour
• With changes to the home (such as
additions)
Slide 4-29
Radon levels vary
• Usually highest in
lower levels of
home
• Higher readings in
upper levels
suggest unusual
radon entry factors
• Levels vary
because air
pressure factors
vary
– Temperature
– Rain, snow, and
frost
– Use of mechanical
exhaust systems
Because radon levels vary, testing
must be done over a period of time
Slide 4-30
Summary
How radon enters a home
Slide 4-31
Summary
• Every home should be tested for
radon
• Requirements for radon to enter a
home:
– Radon source
– Mechanism to transport radon
– Pathway
Slide 4-32
Summary
• Sources
– Soil and rock
– Groundwater
– Building materials
• Mechanisms
– Air pressure
differences
– Diffusion
– Emanation
– Outgassing
• Pathways
– Natural
– Artificial
• Variation in
radon levels
– In space
– In time
– With changes in the
home
Slide 4-33
Activity
For a hypothetical client, summarize how
radon enters a home
• Importance of testing every home
• Factors that determine the radon level in a
home
• Most common sources of radon
• Common mechanisms of radon entry
• Pathways into the home
• Variations in radon levels over space and
time
Slide 4-34