If the atmosphere is greater than 25 ppm, SCBA must be used.

This level is based on the recommmendations of the American Conference of Governmental Industrial Hygienists.

Levels of 100 ppm or greater are lethal 

A reading of 9 ppm or less -- tell the occupant that our detection equipment did not register an eleveted level of carbon monoxide (CO).

A reading 9 to 100 ppm -- tell the occupant that a potentially dangerious level of CO has been detected.

A reading of 100 ppm or greater -- notify the occupant that a potentially lethal level of CO has been detected


Carbon monoxide can escape from any fuel-burning appliance, furnace, water heater, fireplace, woodstove, or space heater.

Most newer homes are built very air-tight, thus cutting down on the supply of fresh air to your furnace - and creating an oxygen starved flame. Tight closing replacement windows and doors, as well as additional insulation can cause similar problems in older homes.

Carbon monoxide can spill from vent connections in poorly maintained or blocked chimneys. If the flue liner is cracked or deteriorated, CO can seep through the liner and into the house - slowly creeping up to dangerous levels. If a nest or other materials restrict or block the flue, CO will mostly spill back into the house. 

Locating Carbon Monoxide Detectors

According to the 2005 edition of the carbon monoxide guidelines, NFPA 720, published by the National Fire Protection Association, sections and, all CO detectors “shall be centrally located outside of each separate sleeping area in the immediate vicinity of the bedrooms,” and each detector “shall be located on the wall, ceiling or other location as specified in the installation instructions that accompany the unit.”

CO detectors can be placed near the ceiling or near the floor because CO is very close to the same density as air.

Detectors have a limited life and need to be replaced every five years. 

The gas sensors in CO alarms have a limited life span, typically two to five years. The test button on a CO alarm only tests the battery and circuitry, not the sensor. Alarms over five years old should be replaced. 

CO alarms should be tested with an external source and they should be checked on installation and at least annually during the manufacturer’s warranty period. Newer models may signal their need to be replaced after the warranty period.