Carbon Monoxide Indoors will Cause Poisoning

Carbon monoxide indoors will result in poisoning, when the amount of carbon monoxide in the air, often referred to as “ambient air” exceeds nominal levels. While carbon monoxide detectors are required when those levels exceed 70 ppm (parts per million) lower levels if they persist for any significant period of time, can cause poisoning. While levels such as 50 ppm may not be dangerous to most people unless they persist for more than an hour, they can still result in concentrations of carbon monoxide in the blood which can result in a poisoning response.  Carbon monoxide in the blood is reported as a percentage, many times using the technical term of carboxyhemoglobin, abbreviated COHb. There is evidence that a carboxyhemoglobin even below ten can initiates the body’s defenses, triggering serious cell damage. Most often that cell damage shows up as brain damage.

Sources of Carbon Monoxide Indoors

Worldwide, the biggest source of carbon monoxide indoors is cooking fires, as in many countries they still cook with charcoal and other fuels that are improperly vented. In the United States, the primary sources of carbon monoxide indoors relates to gas burning appliances. These gas burning appliances are often part of the homes “heating and ventilating” equipment, “HVAC”. Both gas furnaces and gas hot water heaters can pose serious risk of carbon monoxide exposure if the such appliances are not vented properly. Proper venting is not just limited to venting of the exhaust, but can also be related to venting of the oxygen supply for the appliance to burn. One of the ironies of carbon monoxide poisoning is that absence of oxygen is the key ingredient to both the creation of carbon monoxide from the burning of gas or other fuel, but also to the pathology in the body from inhalation of carbon monoxide.

The fuel burning appliance and the human body both require oxygen to generate energy. In the gas hot water heater, the fuel that is burned is natural gas or methane. In the human body the fuel that is burned is glucose, blood sugar. Both fuels are primarily carbon based. Neither chemical reaction will occur properly if sufficient oxygen is denied in the process. Both processes involve oxidation, the oxidation of carbon into carbon dioxide, CO2. In the appliance, when there is insufficient oxygen, only one oxygen atom will bind with the carbon atom, resulting in carbon monoxide, CO. In the human body, rather than creating CO, the presence of the carbon monoxide interrupts the oxidation process, causing injury through the mechanism of hypoxia as a result of the shortfall in oxygen. This process creates ischemic injury to the cell, similar to what might happen in a stroke.  When the cell that ceases to function is in the heart, the heart may stop beating, resulting in quick death. When it happens in the brain, long term brain damage can result.

Indoor Ambient Air Quality Guidelines

The World Health Organization has published guidelines for levels which carbon monoxide cannot exceed in indoor (ambient air.) Each time the WHO takes a look at those guidelines, they lower the amount of carbon monoxide that is allowed. For the current guidelines, click here:  The levels allowed under this guideline are designed to only prevent COHb levels of exceeding 2.5%, even though levels below that could still be harmful to some people.  WHO levels are

  • 100 ppm for 15 min
  • 60 ppm for 30 min
  • 30 ppm for 1 h
  • 10 ppm for 8 h

It is important to note that the levels at which most residential carbon monoxide detectors will alarm are considerably higher, and might allow for COHb levels to get as high as 7%.