The Silent Killer

Carbon Monoxide (CO) the Silent Killer

We have all heard about incidents with carbon monoxide (CO) in the local news.  Many home inspectors are not familiar with the sources or the “acceptable” exposure levels.  The sources are very straight forward, improperly vented combustion appliances and motor vehicles.  Any home with combustion appliances; stoves, furnaces, water heaters, dryers, or an attached garage should have at least one CO detector. So what are the acceptable levels?  It depends on who you ask.  OSHA says you can be exposed to 50 ppm as an average during an 8-hour workday.  NIOSH says 35 ppm and has a 200 ppm ceiling (maximum) limit.  The ACGIH says 25 ppm.  But these are all workplace requirements. In the home, the EPA is the one that sets the “recommended” limits.  This limit is set at 9 ppm for occupants in a home.  Other entities have the same 9 ppm limit; WHO and ASHRAE.  There are studies that indicate that even low level exposures can have long term health effects especially if the occupants already have re-existing pulmonary (lung) or circulatory (heart) conditions. At low level concentrations the symptoms are; fatigue in healthy people and chest pain in people with heart disease.  At higher concentrations symptoms include impaired vision and coordination, headaches, dizziness, confusion, and nausea. Exposures can cause flu-like symptoms that clear up after leaving home. Acute effects are due to the formation of carboxyhemoglobin in the blood, which inhibits oxygen intake. At moderate concentrations, angina, impaired vision, and reduced brain function may result. At higher concentrations, CO exposure can be fatal. CO detectors do not function like smoke detectors.  They have a certain concentration of CO that must be attained over a certain time period.  One manufacturer for example has the following requirements for the alarm to sound (threshold):
Parts Per Million Detector Response Time, Minutes
30 +/- 3ppm No alarm within 30 days
70 +/- 5ppm 60-240
150 +/- 5ppm 10-50
400 +/- 10ppm 4-15
CO detectors should be placed much like smoke detectors; bedrooms, hallways, one per floor minimum, etc.  Consult manufacturer’s installation instructions for proper placement. Courtesy of AHIT