Carbon Monoxide Testing + Response Reference

Why this matters

Carbon monoxide kills 400+ people in the US annually + sends 50,000+ to the ER. It's odorless, colorless, tasteless - only a detector OR symptoms reveal it. Service techs encounter potential CO sources constantly: furnaces, water heaters, boilers, generators, fireplaces, vehicles in garages. The tech who tests + responds correctly saves lives. This is the field card.

CO basics

Carbon monoxide forms during incomplete combustion of any fuel:

• Natural gas, propane, oil, wood, coal, gasoline, charcoal
• Insufficient oxygen = CO production
• Cracked / damaged equipment = release into living space

Physical properties:

• Odorless, colorless, tasteless
• Slightly lighter than air (mixes well)
• Binds to hemoglobin 200-250× stronger than oxygen
• Displaces oxygen in blood

Effects on body:

• Mild (low ppm exposure): headache, fatigue, dizziness
• Moderate: confusion, nausea, vomiting
• Severe: loss of consciousness, death

CO levels + effects

Concentration measured in parts per million (ppm):

• 0-9 ppm: typical urban background; safe
• 10-35 ppm: low concern; investigate sources
• 35-70 ppm: headache after 6-8 hours; nausea in some
• 70-150 ppm: headache + nausea in 1-3 hours
• 150-200 ppm: severe headache; possible disorientation
• 200-400 ppm: severe symptoms within 1-2 hours
• 400-800 ppm: significant danger within 1 hour
• 800-1600 ppm: unconsciousness within 1 hour
• 1600+ ppm: rapid loss of consciousness; death possible

OSHA limit (workplace): 50 ppm TWA (8-hour time-weighted average).

CO detectors

Two types:

Battery-operated standalone:

• Plug-in OR battery
• Audible alarm at threshold
• Limited lifespan (5-7 years; sensor degrades)
• Required by code in many jurisdictions

Combination smoke + CO:

• Both sensors in one unit
• Easier maintenance
• Same lifespan limits

Hard-wired with battery backup:

• Required in new construction (some jurisdictions)
• Network with smoke detectors
• Battery backup on power loss

Placement (per UL + NFPA):

• One on each level
• Outside sleeping areas
• Not within 15 ft of combustion appliance (false alarms from low-level normal exposure)
• Not in kitchen
• Not in bathroom (humidity affects sensors)

CO detection during service

When servicing combustion equipment, test the equipment + the living space:

Combustion analyzer:

• Measures CO in flue gas
• Measures O2 + CO2 + efficiency
• Inserted into flue near appliance
• Pro-grade tool

Ambient CO meter:

• Handheld; measures room air
• Some can also be combustion analyzers
• Carry on truck

Quick check sources:

• Near furnace draft inducer / flue
• Above water heater draft hood
• In garage (vehicle exhaust)
• Near gas range when operating
• Around fireplace

During HVAC service

For furnace service:

• Measure flue gas CO (should be under 100 ppm air-free; under 50 better)
• Measure ambient CO around furnace
• Verify draft (no spillage from draft hood)
• Verify combustion air sufficient

For water heater:

• Same checks
• Draft hood spillage test (match held; flame draws upward into hood)
• Spillage = backdraft = CO release

For boiler:

• Flue gas CO
• Ambient
• Combustion adjustments per manufacturer

CO alarm sounding - first response

If you arrive + customer's CO alarm is going off:

1. Get everyone OUTSIDE immediately

• Don't search for source first; evacuate first
• Include pets

1. Call 911

• Fire department responds with calibrated meters
• Medical evaluation for anyone with symptoms

1. Verify outside / fresh air

• Don't go back in
• Wait for fire department

1. Do NOT operate suspected sources

2. Open doors / windows as you exit (ventilation)

Don't try to identify source while everyone is inside affected area.

CO source identification

After ventilation + safety:

Most common sources:

Cracked heat exchanger (gas furnace):

• Most common residential CO source
• Combustion gas leaks into supply air
• CO distributed throughout house
• Replacement furnace usually required

Blocked / failed flue:

• Animal nest, ice, fallen debris
• Combustion products back up into house
• Combustion appliance must be shut down + flue cleared

Backdrafting:

• Negative pressure pulls flue gas back into house
• Caused by exhaust fans, fireplace draft, return air leakage
• House air-sealed too tight without combustion air

Damaged appliance:

• Improperly burning (yellow flame, sooting)
• Misadjusted combustion
• Worn components

Vehicle in garage:

• Engine running with garage door open insufficient
• Attached garage shares some air with house
• Common holiday season CO incidents

Generator improperly placed:

• Inside home OR garage
• Near windows / doors
• Kills people during power outages

Charcoal grill / camp stove inside:

• Sometimes used during power outages
• Can fill home with CO quickly

Long-term low-level exposure

Customer reports:

• Frequent headaches
• Fatigue
• "Feels worse at home"
• Pets / kids more affected
• Symptoms improve when away from home

Investigate:

• CO detector working (test + replace battery)
• Furnace flue gas reading
• Combustion appliances inspection
• Garage / attached spaces

Low-level chronic exposure damages organs over time; not just acute hazard.

When you find a CO problem

If your testing reveals CO in living space:

Shut down the source:

• Turn off suspected appliance
• Don't relight
• Verify with customer

Notify customer:

• "Your [appliance] is producing CO. It's not safe to use until repaired."
• Don't underplay; don't catastrophize

Document:

• CO levels measured (location + reading)
• Conditions (when running, idle, etc.)
• Source identified
• Customer notification (verbal + written)

Recommend:

• Repair OR replacement
• Until then, do NOT operate
• If gas: don't relight pilot
• Provide alternate heat / hot water if needed

Follow-up:

• Schedule repair promptly
• Verify CO clear after repair
• Test detectors functional

When customer ignores

If customer wants to keep using a CO-producing appliance:

• Document refusal
• Get customer's signature on warning
• Notify management
• Sometimes refuse to continue work / leave appliance operational
• Local regulations may require utility notification

You can't force customer to comply; you can document + protect yourself.

CO from non-equipment sources

Attached garage:

• Vehicle warming up (cold mornings especially)
• Even brief operation = CO in garage = into house

Wood-burning fireplace:

• Damper closed / partially closed
• Cool flue (cold weather; backdraft)
• Burning wet wood (more CO)

Wood / pellet stove:

• Improper installation
• Inadequate clearance
• Damper issues

Gas oven for heating:

• Some customers try in power outages
• Significant CO release
• DON'T

References

• NFPA 720 (Carbon Monoxide Detection + Warning)
• NFPA 54 (National Fuel Gas Code)
• UL 2034 (CO Alarm Standard)
• OSHA 1910.1000 (Air Contaminants)
• Manuall internal: Combustion Fundamentals, Smoke + CO Detectors