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Produced by John Krigger and Chris Dorsi

Illustrated by John Krigger, Bob Starkey,

Steve Hogan, and Mike Kindsfater

This edition compiled by Darrel Tenter

The Saturn Building Shell Field Guide

outlines procedures for improving the comfort,

durability, and energy efficiency of existing homes.

The companion volume Saturn Building Analyst Field Guide

describes the procedures used to analyze the

performance of existing homes.

The companion volume Saturn Mechanical Systems Field Guide

includes procedures for inspecting, servicing, and improving the

efficiency and safety of residential heating and cooling systems.

In compiling this publication, the authors have benefited from the experience

of many individuals who have reviewed our documents, related their

experiences, or published information from which we’ve gained insight.

Though we can’t name everyone to whom we’re indebted, we acknowledge the

specific contributions of the following people: Martha Benewicz, Michael

Blasnik, Anthony Cox, Rob de Kieffer, Rick Karg, Dave Like, Bruce Manclark,

David Miller, Rich Moore, Gary Nelson, Russ Rudy, Russ Shaber, Cal Steiner, Ken

Tohinaka, John Tooley, Bill Van Der Meer, and Doug Walter. We take full

responsibility, however, for the content and use of this publication.

Copyright 2007

Saturn Resource Management, Inc.www.srmi.biz

Printed in the U.S.

ISBN 978-1-880120-15-6

Ver. 032207

Saturn

Building Shell

Field Guide

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2: Air Sealing Homes

When Not to Air Seal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Air-Sealing Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61Caulking and Adhesives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62Liquid Foam. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64Air Barrier Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66Stuffing Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

Sealing Major Air Leaks and Bypasses . . . . . . . . . . . . . . . . . . . 68Major Air Leak Locations & Treatments . . . . . . . . . . . . . . . . 70

Sealing Duct Leaks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76Minor Air Sealing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80Air-Sealing Multi-Family Buildings . . . . . . . . . . . . . . . . . . . . 82

3: Installing Insulation

Insulation Safety Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

Attic Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85Preparing for Attic Insulation . . . . . . . . . . . . . . . . . . . . . . . . . 85Attic Ventilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86Blowing Attic Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87Insulating Closed Roof Cavities . . . . . . . . . . . . . . . . . . . . . . . 89Installing Attic Batt Insulation. . . . . . . . . . . . . . . . . . . . . . . . . 90Finished Knee Wall Attics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

Walk-Up Stairways and Doors . . . . . . . . . . . . . . . . . . . . . . . . . 94

Wall Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95Preparing for Blown Wall Insulation . . . . . . . . . . . . . . . . . . . 96Installing Wall Insulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98Insulated Wall Sheathing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

Floor and Foundation Insulation . . . . . . . . . . . . . . . . . . . . . . . 106

Preparing for Floor/Foundation Insulation . . . . . . . . . . . 107Installing Floor Insulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . 110Crawl-Space Foundation Insulation . . . . . . . . . . . . . . . . . . 113Basement Insulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

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8 Table of Contents

4: Windows and Doors

Window Shading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

Exterior Storm Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

Window Repair and Air-Leakage Reduction. . . . . . . . . . . . . 126

Window Replacement Specifications . . . . . . . . . . . . . . . . . . . 129Window Replacement Options. . . . . . . . . . . . . . . . . . . . . . . 129Window Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131Removing Old Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132Installing Replacement Windows . . . . . . . . . . . . . . . . . . . . 132

Window Safety Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . 135Windows Requiring Safety Glass . . . . . . . . . . . . . . . . . . . . . 135Fire Egress Windows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

Door Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

Door Repair Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

5: Mobile Homes

Mobile Home Air Sealing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142Shell Air-Leakage Locations. . . . . . . . . . . . . . . . . . . . . . . . . . 143Duct-Leak Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143Belly Pressure Test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

Mobile Home Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147Insulating Mobile Home Roof Cavities . . . . . . . . . . . . . . . . 147Mobile Home Floor Insulation . . . . . . . . . . . . . . . . . . . . . . . 152

Mobile Home Windows and Doors . . . . . . . . . . . . . . . . . . . . . 154Mobile Home Storm Windows . . . . . . . . . . . . . . . . . . . . . . . 154Replacing Mobile Home Windows . . . . . . . . . . . . . . . . . . . 155Mobile Home Doors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

Cool Roofs for Mobile Homes . . . . . . . . . . . . . . . . . . . . . . . . . . 156

Mobile Home Skirting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158

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6: Health and Safety

Customer Health and Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . 159Carbon Monoxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160

Smoke and Carbon Monoxide Alarms . . . . . . . . . . . . . . . . 161Moisture Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

Installing Whole-House Ventilation. . . . . . . . . . . . . . . . . . . . . 167Exhaust Ventilation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168Supply Ventilation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170Balanced Ventilation Systems. . . . . . . . . . . . . . . . . . . . . . . . 170Heat Recovery Ventilators . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

Lead-Safe Repair Work. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174Electrical Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176

Worker Health and Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177Commitment to Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178New Employees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179Driving. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180

Lifting and Back Injuries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180Respiratory Health. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181Hazardous Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183Falls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184

 Tool Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186Repetitive Stress Injuries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186

Appendices 188 Tools for Air Sealing and Insulating. . . . . . . . . . . . . . . . . . . . . 189Materials for Air Sealing and Insulating . . . . . . . . . . . . . . . . . 190R-values for Common Materials . . . . . . . . . . . . . . . . . . . . . . . . 191Calculating Loose-Fill Attic Insulation . . . . . . . . . . . . . . . . . . 192Calculating Wall Insulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198List of Tables and Illustrations . . . . . . . . . . . . . . . . . . . . . . . . . . 199Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204

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C HAPTER 1: DIAGNOSING SHELL & DUCT   AIR LEAKAGE 

The testing described here will help you analyze the existing airbarriers and decide whether and where air sealing or duct seal-ing is needed.

An air barrier that is aligned with the insulation forms thebuilding’s thermal boundary. The location and condition of theair barrier has a substantial effect on the insulation’s effective-ness.

The energy impact of duct leakage depends on whether theducts are located within or outside of the thermal boundary. Notall duct leaks are an energy problem.

1.1 AIR-LEAKAGE EFFECTS

Controlling shell air leakage is a key ingredient in a successfulhome-performance or weatherization job. The decisions youmake about sealing air leaks will affect a building throughout itslifetime.

✔ Air leakage through insulated assemblies reduces insula-tion R-value.

✔ Air leakage accounts for a significant percentage of abuilding’s heat loss.

✔ Air leakage moves moisture into and out of the house, andso exerts a wetting and/or drying effect.

✔ Air leakage causes house pressures that can interfere withthe venting of combustion appliances.

We depend on air leakage to provide outdoor air for dilutingpollutants and admitting fresh air. However, air leaks can alsobring pollutants into the home, which is why mechanical venti-lation works better than air leakage for providing fresh air. See“Installing Whole-House Ventilation” on page 167.

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Diagnosing Shell & Duct Air Leakage12

Building height and location, weather, and mechanical equip-ment all effect air leakage in a building. Strong winds may createa positive pressure on one side of a building, and a negative pres-sure on the opposite side. A forced air distribution system, a

chimney, or an exhaust fan may create a negative pressure in thebuilding.

Often air moves through abuilding as if it were a chimney;air enters low in the building(infiltration) and exits at the topof the building (exfiltration).

This is called the stack effect.The area between the air com-ing in at the bottom (infiltra-tion) and the air leaving thebuilding at the top (exfiltration)is called the neutral pressureplane. Not much air leakage

comes in or goes out near theneutral pressure plane. As thebuilding is tightened at the bot-tom, the neutral pressure planemoves up. As the building istightened at the top the neutralpressure plane moves down. For the best results, seal at both the

top and bottom of the building.

Air sealing or duct sealing may affect combustion-appliance venting by changing house pressures or reducing the availablesupply of combustion air. After all weatherization measures havebeen performed, technicians must conduct worst-case draft test-ing and re-check the safety of all combustion appliances.

1.1.1 Goals of Air-Leakage Testing

The first goal of air-leakage and pressure testing is to decide howmuch time and effort is required to achieve cost-effective air-

Infiltration

Exfiltration

Exhaust Air

Neutral Pressure Plane

Air leakage concepts: When

performing air sealing, it helps to

understand the effects of exhaust

appliances, the stack effect, and wind

effect.

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C HAPTER 2: AIR SEALING H OMES 

This chapter discusses the locations of air leaks and the methods

and materials use to seal them. Duct leakage and sealing isincluded because duct-sealing often falls under the job descrip-tion of a building-shell technician. Perform air-leakage testingand evaluation before beginning air-sealing or duct-sealingwork. See "Diagnosing Shell & Duct Air Leakage" on page 11.

Air sealing improves the building’s thermal boundary. Thisboundary should consist of an air barrier and the insulation,

which should be adjacent to each other. Air leakage in homesaccounts for 5% to 40% of annual heating and cooling costs. Air-sealing is one of the most important energy retrofits, and oftenthe most difficult.

The first step to improving a building’s airtightness is to formu-late a strategy. What building components already serve as airbarriers? How do we best seal the border areas between thesecomponents? What is our strategy for sealing various penetra-tions through the building shell? Answer these questions todevelop your air-sealing strategy. Another important part of thestrategy is considering ventilation. See "Evaluating Home Venti-lation" on page 22.

Air travels into and out of the building by three main pathways.

• Major air leaks, which are significant flaws in the home’s airbarrier.

• Minor air leaks, which are often seams between buildingmaterials.

• Through the building materials themselves (See table 1-4on page 28.

Reducing air leakage accomplishes several tasks.

• Saves energy by protecting the thermal resistance of theshell insulation.

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Air Sealing Homes60

• Increases comfort by reducing drafts and moderating theradiant temperature of interior surfaces.

• Reduces moisture migration into building cavities.

• Reduces the pathways by which fire spreads through abuilding.

2.1 WHEN NOT TO AIR SEAL 

Air sealing reduces the exchange of fresh air in the home, andcan alter the pressure balance within the home. Before air seal-ing, survey the home to identify both air-pollutants that may beconcentrated by air sealing efforts, and combustion appliancesthat may be affected by changes in house pressure. See "Control-

ling House Pressure" on page 48.

Don’t perform air-sealing when there are obvious threats to theoccupants’ health, the installers’ health, or the building’s dura-bility that are related to air-sealing. If any of the following cir-

Thermal boundary flaws:  The thermal boundary contains the air barrier and

insulation, which should be adjacent to one other. The insulation and the air

barrier are often discontinuous at corners and transitions. These areas merit

special attention.

rim joist area

 joint between collar beam and rafter 

cantilevered floor 

corner at garage ceiling

insulation

air barrier 

thermal boundary

 joint between porchand house

 joint between

finished-attic floorand kneewall 

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C HAPTER 3: I NSTALLING I NSULATION 

Insulation reduces heat transmission by slowing conduction,

convection, and radiation through the building shell. Insulationcombined with an air barrier forms the thermal boundary.

Installing insulation is one of the most effective energy-savingmeasures. You can ensure its effectiveness by following theseguidelines.

✔ Protect insulation from air movement with an effective airbarrier. Make sure that the air barrier and insulation willbe aligned (next to one another) using procedures outlinedon page 27.

✔ Protect insulation from moisture by repairing roof andsiding leaks, and by controlling vapor sources within thehome.

3.1 INSULATION SAFETY PROCEDURES

Comply with the following fireand electrical safety proce-dures before insulating.

✔ Inspect wiring, fuses,and circuit breakers toensure that wiring isn’toverloaded. Install S-type fuses where appro-priate to prevent circuitoverloading. Maximum ampacity for 14-gauge wire is 15amps and for 12-gauge wire is 20 amps. Do not coverknob-and-tube wiring with insulation.

S-type fuse: An S-

type fuse prohibits

residents from

oversizing the fuse

and overloading an

electrical circuit.

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Installing Insulation84

✔ Protect heat-producingfixtures such as recessedlights and exhaust fanswith lights or heaters.

Install an airtight box ifair leakage is suspected,or a metal collar if theyare airtight.

✔ Confirm that all wiresplices are enclosed inelectrical junction boxes.

If you plan to cover a junction box with insula-tion, mark its locationwith a sign or flag.

✔ Install insulation shields around unlined masonry chim-neys, B-vent chimneys, and manufactured chimneys. Seal

any bypasses around chimneys with metal and high-tem-perature caulk.

✔ Install insulation shields around all-fuel wood-stove chim-neys with 6 inches of space between the chimney and insu-lation.

✔ If shields are used as a barrier around heating producingdevices or masonry chimneys, fasten them securely to theceiling joist so they maintain 3 inches of clearance anddon’t collapse. Don’t allow metal shields to contact wiring.Cover the tops of shields while installing insulation, anduncover and clean them out afterwards.

✔ Wear an approved respirators or dust mask while blowinginsulation or installing batts. See page 181.

✔ Observe lead-safe weatherization practices with all tasksthat may disturb interior paint. See page 174.

Recessed light fixtures: Covering

recessed light fixtures with fire-

resistant drywall or sheet-metal

enclosures reduces air leakage andallows installers to safely insulate

around the box.

maintain 3-inchclearance

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C HAPTER 4: W INDOWS  AND DOORS

This chapter presents specifications and procedures for improv-

ing the energy performance of windows and doors. Detailedspecifications for window replacement provide guidance on thisoften-performed and potentially troublesome retrofit.

Windows and doors are a major concern to homeowners andenergy specialists alike. Windows and doors were once thoughtto be a major air-leakage problem. However, the widespread useof blower doors has shown that windows and doors don’t tend to

harbor large air leaks. But heat losses and gains, by conduction,convection, and radiation through windows, are often quitehigh. Unfortunately, the cost to improve windows is also high,so the payback from window improvements may not be asattractive as other retrofits. In older buildings, though, the win-dows and doors may be in such poor condition that their repairis essential to a building’s survival even if it’s not an energy-sav-

ing measure.

All tasks relating to window and door improvement, repair, andreplacement should be accomplished using lead-safe weather-ization methods. See "Lead-Safe Repair Work" on page 174.

4.1 WINDOW SHADING

Much of the solar energy that strikes a home’s windows will passthrough the glass and enter the living space. It may be welcomein cold weather, but this solar heat accounts for up to 40% ofsummer overheating in many homes. To reduce cooling costs, itworks far better to block solar heat before it enters the homethan to cool the home after it overheats.

Window shading increases comfort and reduces the cost of cool-ing, and is one of the most cost-effective weatherization mea-sures in hot climates. Not all windows cause overheating, so youshould direct your efforts towards windows where the most heatenters.

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Windows and Doors122

• Windows that face east or west and so are exposed to low-angle sun. South side windows if sun strikes them directly.

• Windows with no shade from landscaping or roof over-hangs.

• Large windows.

Exterior Window Treatments

Sun screens, made of mesh fabric that is stretched over an alu-minum frame, are one of the most effective window-shadingoptions. They absorb or reflect a large portion of the solar

energy that strikes them, while allowing a slightly diminishedbut acceptable view out of the window.

Sun screens are installed on the outside of the window, and workwell on fixed, double-hung, or sliding windows. They aren’t suit-able for jalousie windows. For casement and awning windows,the sun screen should be mounted on the movable window sashrather than on the window frame. Sun screens are easily con-structed in the shop or on the job.

Sun screens: Installed on the window’s exterior, sun screens absorb solar heat

before it enters the home. This strategy is superior to interior window treatments,

which reflect heat back after it has entered.

Rolling the spline

Sun screen

spline

frame

fabric 

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C HAPTER 5: MOBILE  H OMES

Mobile homes typically use more energy per square foot than

site-built homes. Fortunately, their consistent constructionmakes them more straightforward to weatherize.

Insulation upgrades save the most energy in mobile homes,though sealing shell and duct air leaks presents good opportuni-ties, too. Mobile home heating retrofit and replacement areoften cost-effective when a customer’s energy usage is high.

Typical Components of a Mobile Home: 1–Steel chassis. 2–Steel outriggers and

cross members. 3–Underbelly. 4–Fiberglass insulation. 5–Floor joists. 6–Heating/

air conditioning duct. 7–Decking. 8–Floor covering. 9–Top plate. 10–Interior

paneling. 11–Bottom plate. 12–Fiberglass insulation. 13–Metal siding. 14–Ceiling

board. 15–Bowstring trusses. 16–Fiberglass insulation. 17–Vapor barrier. 18–

Galvanized steel one-piece roof. 19–Metal windows.

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Mobile Homes142

5.1 MOBILE HOME AIR SEALING

The location and relative importance of mobile home air leakswas a mystery before blower doors. Some mobile homes are

fairly airtight, yet many are incredibly leaky. Air leakage servesas ventilation in most mobile homes. Observe the minimum ventilation requirements outlined in “Calculating MinimumVentilation Level” on page 23.

A duct airtightness tester, which pressurizes the ducts is the bestway to measure and evaluate duct air sealing. For assessingmobile home duct tightness, the blower door used in conjunc-

tion with a pressure pan does a good job of detecting air leaks.See "Pressure-Pan Testing" on page 46.

Most mobile home duct sealing is performed through the belly.This work is more difficult once the belly has be re-insulated.Inspect the ductwork and seal any major leaks, such as discon-nected trunk lines, before insulating the belly.

Mobile home shell air leakage is often substantially reducedwhen insulation is installed in roofs, walls, and belly cavities.Prioritize your efforts by performing these tasks in this order.

Table 5-1: Air-Sealing Locations & Typical CFM50 Reduction

Air-Sealing ProcedureTypicalCFM50 

Reduction

Patching large air leaks in the floor, walls and ceiling 200–900

Sealing floor as return-air plenum 300–900

Sealing leaky water-heater closet 200–600

Sealing leaky supply ducts 100–500

Installing tight interior storm windows 100–250

Caulking and weatherstripping 50–150

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C HAPTER 6: H EALTH   AND S AFETY 

This chapter introduces some of the most pressing hazards that

your clients face in their homes, as well as those you face atwork.

When you discover serious safety problems in a customer’shome, you should inform the customer about the hazards andsuggest how to eliminate them. Major hazards and potentiallylife-threatening conditions should be corrected before you beginwork in the dwelling unless the you are making the corrections

as part of their work.

6.1 CUSTOMER HEALTH AND SAFETY

House fires, carbon monoxide poisoning, moisture problems,and lead-paint poisoning are the most important health andsafety problems that are related to building repair work. When

these are noted in the home, inform the customer verbally andin writing as appropriate.

✔ Inspect the home for fire hazards such as improperlyinstalled electrical equipment, flammable materials storednear combustion appliances, or malfunctioning heatingappliances. Discuss the problems with the client, and per-form repairs if possible.

✔ Test combustion appliances for carbon monoxide produc-tion and other related hazards. Test the ambient air for car-bon monoxide. Solve the problems causing these hazards.

✔ Find moisture problems and discuss them with the client.Never make moisture problems worse. See page 163.

✔Practice lead-safe repair techniques. See page 174.

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Health and Safety160

6.1.1 Carbon Monoxide

Carbon monoxide (CO) is released by combustion appliances,automobiles, and cigarettes as a product of incomplete combus-tion. CO is the largest cause of injury and death in the U.S. fromgas poisoning, resulting in more than 500 deaths per year. Addi-tional people are injured or sickened by lower concentrations ofthe gas. The symptoms of low-level CO exposure are similar tothe flu, and may go unnoticed.

CO blocks the oxygen-car-rying capacity of the blood’s

hemoglobin, which carries vital oxygen to the tissues.At low concentrations (5-to-50 ppm), CO reduces nervereaction time and causesmild drowsiness, nausea,and headaches. Higher con-

centrations (50-to-3000ppm) lead to severe head-aches, vomiting, and evendeath if the high concentra-tion persists. The effects ofCO poisoning are usuallyreversible, except for expo-

sure to very high levels, which can cause brain damage.The EPA’s suggested maximum 8-hour exposure is 9 ppm inroom air. Room levels of CO at or above 9 ppm are usually asso-ciated with the use of malfunctioning combustion applianceswithin the living space, although cigarette smoking or automo-bile exhaust are also common CO sources.

Causes of Carbon Monoxide

CO is a common problem in low-income housing, affecting 20%or more of residential buildings in some regions. Offendingappliances include: unvented gas space heaters, kerosene space

10

20

30

40

50

60

70

80

90

1 2 3 4

Collapse

HeadacheDizziness

Impaired judgement

Fatal

Hours of Exposure

    C    O    p

   e   r   c   e   n   t    b    l   o   o    d   s   a   t   u   r   a   t    i

   o   n

 1 0 0

200

 400

 8 0 0

 1 6 0 0

  3  2 0 0

Effects of CO:  This graphs curves

represent different exposure levels in

parts per million.