13.3 | FINDING THE SOURCE OF CO AFTER AN ALARM
Carbon monoxide is an odorless, invisible gas, which often makes it difficult to locate the source of CO after an
alarm. These are a few of the factors that can make it difficult to locate sources of CO:
1. House is well ventilated before the investigator arrives,
2. Problem caused by “backdrafting”,
3. Transient CO problem caused by special circumstances.
Because CO may dissipate by the time an investigator arrives, it may be difficult to locate the source of CO.
13.4 | POTENTIALS SOURCES OF CO
1. Fuel-burning appliances like: portable heaters, gas or wood burning fireplace, gas kitchen range or
cooktop, gas clothes dryer
2. Damaged or insufficient venting, corroded or disconnected water heater vent pipe, leaking chimney pipe or
flue, or cracked heat exchanger, blocked or clogged chimney opening
3. Improper use of appliance/device: operating a barbecue grill or vehicle in an enclosed area (like a garage or
screened porch)
4. Transient CO Problems: “transient” or on-again-off-again CO problems can be caused by outdoor
conditions and other special circumstances. The following conditions can result in transient CO situations:
a. Excessive spillage or reverse venting of fuel appliances caused by outdoor conditions such as:
i. Wind direction and/or velocity, including high, gusty winds. Heavy air in the vent pipes (cold/humid
air with extended periods between cycles),
ii. Negative pressure differential resulting from the use of exhaust fans,
iii. Several appliances running at the same time competing for limited fresh air,
iv. Vent pipe connections vibrating loose from clothes dryers, furnaces, or water heaters,
v. Obstructions in or unconventional vent pipe designs, which can amplify the above situations.
b. Extended operation of unvented fuel burning devices (range, oven, fireplace).
c. Temperature inversions, which can trap exhaust close to the ground.
d. Car idling in an open or closed attached garage, or near a home.
These conditions are dangerous because they can trap exhaust in your home. Since these conditions can come
and go, they are also hard to recreate during a CO investigation.
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