Carbon Monoxide - The Silent Killer

Every year, the news is filled with stories of family home or schools or businesses that have high levels are Carbon Monoxide present and the effects are almost always sickness or in some cases death.  We have talked about some of these in the past (see links below) but this page serves as a place to capture everything in one spot.

Don't just take my word for it, here are links to government and health organizations around the world and what they think about Carbon Monoxide (CO) and your health:

I realize it is from the UK, but the information is so good I wanted to capture it directly as shown on

Low levels of carbon monoxide

The symptoms of exposure to low levels of carbon monoxide (CO) can be similar to those of many other conditions, such as food poisoning and flu. However, unlike flu, carbon monoxide poisoning does not cause a high temperature (fever).

The most common symptoms include:

Your symptoms may be less severe when you are away from the source of the carbon monoxide.

The longer you inhale carbon monoxide, the worse your symptoms will be. You may lose balance, vision and memory. Eventually, you may lose consciousness. This can happen within two hours, if there is a lot of carbon monoxide in the air.

Long-term exposure to low levels of carbon monoxide can also lead to neurological symptoms, including:

  • difficulty thinking or concentrating
  • frequent emotional changes  for example, becoming easily irritated, depressed or making impulsive decisions

High levels of carbon monoxide

If you have breathed in high levels of carbon monoxide gas, it is likely that you will experience more severe symptoms. These may include:

  • impaired mental state and personality changes (intoxication)
  • vertigo – the feeling that you or the environment around you is spinning
  • ataxia – loss of physical co-ordination, caused by underlying damage to the brain and nervous system
  • breathlessness and tachycardia (a heart rate of more than 100 beats per minute)
  • chest pain caused by angina or a heart attack
  • seizures – an uncontrollable burst of electrical activity in the brain that causes muscle spasms
  • loss of consciousness – in cases where there are very high levels of carbon monoxide, death may occur within minutes

At-risk groups

Certain people in your household may be affected by carbon monoxide poisoning more quickly than others. Those at particular risk include:

  • babies and young children
  • pregnant women
  • people with heart or breathing problems

Pets may be the first to show signs of carbon monoxide poisoning because they are vulnerable to the effects of the gas. The smaller an animal or a person is, the faster this will affect them.

If your pet suddenly becomes ill or dies unexpectedly, and death is not related to old age or an existing health condition, you should investigate the possibility of a carbon monoxide leak.

What Levels of CO Cause an Alarm


Underwriters Laboratories Inc. Standard UL2034 requires residential CO Alarms to sound when exposed to levels of CO and exposure times as described below. They are measured in parts per million (ppm) of CO over time (in minutes). UL2034 Required Alarm Points*:

  • If the Alarm is exposed to 400 ppm of CO, IT MUST ALARM BETWEEN 4 and 15 MINUTES
  • If the Alarm is exposed to 150 ppm of CO, IT MUST ALARM BETWEEN 10 and 50 MINUTES.
  • If the Alarm is exposed to 70 ppm of CO, IT MUST ALARM BETWEEN 60 and 240 MINUTES.

Note* Approximately 10% COHb exposure at levels of 10% to 95% Relative Humidity (RH). The unit is designed not to alarm when exposed to a constant level of 30 ppm for 30 days. 


CO Alarms are designed to alarm before there is an immediate life threat. Since you cannot see or smell CO, never assume it’s not present.

  • An exposure to 100 ppm of CO for 20 minutes may not affect average, healthy adults, but after 4 hours the same level may cause headaches.
  • An exposure to 400 ppm of CO may cause headaches in average, healthy adults after 35 minutes, but can cause death after 2 hours.


How Do Low Levels oF CO affect us?

In our research it appears that there is not a single standard to be applied across all people because it affects everyone differently.  The effects of high levels (greater than 70 parts per million PPM) of CO are well documented and universally agreed up as something to be avoided.  In fact, the standard CO detectors that are purchased from the store are required NOT to alarm at a level less than 70 PPM and even then only after that level is observed for more than 1 hour.  In other words, you could have 60 PPM levels of Carbon Monoxide in your home indefinitely without the detector going off and that is the way it is designed.  In fact, the US Consumer Product Safety Commission tests CO monitors to make sure they are meeting standards.  One of the tests is a 30 DAY test at 30 PPM.  If one of the alarms were to go off, they would actually be failing the test.  See more of those results here:

So, why no alarm until 70 PPM and only then after an hour or more?  The reason is simple, it's to avoid nuisance calls to emergency services for "safe" levels of CO in the home.  It's understandable, but we feel it might be leaving out some crucial information for the health of you and your family.  The CPCS has the following on their website to give us an indication why these off the shelf alarms behave as they do.

While the CPCS states that less than 70 PPM is an acceptable and safe level, many other organizations don't agree as you can see in the table below.  Many show 11, 25, 35, and 50 PPM and even as low as 9 PPM as being an unacceptable level of CO in an indoor environment.  

ANSI/ASHRAE Addenda a, b, c, d, and g to ANSI/ASHRAE Standard 62.1-2004

So what can we do when the CO detectors readily available simply ignore anything below 70 ppm?  That is where a Low Level CO "Health" monitor comes into play.  While more expensive to purchase than a standard CO detector, the CO monitors we offer show measured levels as low as 7 ppm and will give an audible and visual alarm as low as 10 ppm.  While not all health and government organization can agree on what is acceptable, we feel that the homeowner should be able to make that decision for themselves and providing the means to detect and measure lower levels of CO concentration allows them to do so.



What is carbon monoxide?

Carbon monoxide, or CO, is an odorless, colorless gas that can cause sudden illness and death.

found at

found at


The following excerpt taken from

Carbon monoxide poisoning occurs after enough inhalation of carbon monoxide (CO). Carbon monoxide is a toxic gas, but, being colorless, odorless, tasteless, and initially non-irritating, it is very difficult for people to detect. Carbon monoxide is a product of incomplete combustion of organic matter due to insufficient oxygen supply to enable complete oxidation to carbon dioxide (CO2). It is often produced in domestic or industrial settings by motor vehicles that run on gasoline, diesel, methane, or other carbon-based fuels and from tools, gas heaters, and cooking equipment that are powered by carbon-based fuels such as propane, butane andcharcoal. Exposure at 100 ppm or greater can be dangerous to human health.

Symptoms of mild acute poisoning will include light-headedness, confusion, headaches, vertigo, and flu-like effects; larger exposures can lead to significant toxicity of the central nervous system and heart, and death. Following acute poisoning, long-term sequelae often occur. Carbon monoxide can also have severe effects on the fetus of a pregnant woman. Chronic exposure to low levels of carbon monoxide can lead to depression,confusion, and memory loss. Carbon monoxide mainly causes adverse effects in humans by combining with hemoglobin to form carboxyhemoglobin (HbCO) in the blood. This prevents hemoglobin from carrying oxygen to the tissues, effectively reducing the oxygen-carrying capacity of the blood, leading to hypoxia. Additionally, myoglobin and mitochondrial cytochrome oxidase are thought to be adversely affected. Carboxyhemoglobin can revert to hemoglobin, but the recovery takes time because the HbCO complex is fairly stable.

Treatment of poisoning largely consists of administering 100% oxygen or providing hyperbaric oxygen therapy, although the optimum treatment remains controversial. Oxygen works as an antidote as it increases the removal of carbon monoxide from hemoglobin, in turn providing the body with normal levels of oxygen. The prevention of poisoning is a significant public health issue. Domestic carbon monoxide poisoning can be prevented by early detection with the use of household carbon monoxide detectors. Carbon monoxide poisoning is the most common type of fatal poisoning in many countries. 

What are the symptoms of CO poisoning?

The most common symptoms of CO poisoning are headache, dizziness, weakness, nausea, vomiting, chest pain, and confusion. High levels of CO inhalation can cause loss of consciousness and death. Unless suspected, CO poisoning can be difficult to diagnose because the symptoms mimic other illnesses. People who are sleeping or intoxicated can die from CO poisoning before ever experiencing symptoms.

Who is at risk from CO poisoning?

All people and animals are at risk for CO poisoning. Certain groups — unborn babies, infants, and people with chronic heart disease, anemia, or respiratory problems — are more susceptible to its effects. Each year, more than 400 Americans die from unintentional CO poisoning, more than 20,000 visit the emergency room and more than 4,000 are hospitalized due to CO poisoning. Fatality is highest among Americans 65 and older. (emphasis mine)

Are some people at greater risk of CO poisoning than others?

Yes, some people are at greater risk of CO poisoning. People at greater risk include individuals with:

  • respiratory conditions (such as asthma and emphysema);
  • cardiovascular disease;
  • anemia (such as sickle cell anemia); and
  • individuals engaging in strenuous physical activity;
  • the elderly, children and fetuses.


How can I prevent CO poisoning from my home appliances?

  • Have your heating system, water heater and any other gas, oil, or coal burning appliances serviced by a qualified technician every year. (emphasis mine)

So, you can't see it, you can't taste it, you can't smell it, and it makes you feel sick.  This time of the year a lot of things can make you feel sick, but not all of them will kill you if not addressed.  Unfortunately there are stories every year about families that have been affected by Carbon Monoxide poisoning.  I found 4 within the last month.  I want to share them here and highlight something they all share in common: 

CO scare at Rutland home - "Fire officials say they did find unsafe levels of carbon monoxide in the home and determined it was due to a faulty furnace."  The carbon monoxide detector probably saved their lives

Day after Mooresville family replaces batteries, CO alarm sounds "Ted Freshwater looks over the gas furnace that is a suspect in the CO poisoning at the home on Sunday morning. Carbon monoxide sent four familiy members to the hospital Sunday morning. They had been sick for a few days."  “Everything didn’t really point back to (carbon monoxide) until after the fact, unfortunately,”

He said inspectors found a crack in an internal part of the furnace Monday afternoon and would replace the unit later this week. It’s unclear when the crack appeared.

Furnace problem sends 8 to hospital in Des Moines "...she had a headache for the last four days"

"Brown said the occupants of the home could’ve easily been killed by the CO gas had the 911 call not been placed. “Our meters read 500 parts per million and it alerts at 25 parts per million, so it was way over…1,200 parts per million in a home is immediately dangerous to life and health,” Brown said.

The source of the gas leak was traced to home’s furnace [emphasis mine]. Brown said it appeared moisture from the air conditioner dripped onto the heat exchanger, causing rust and the buildup of carbon monoxide."  In other words - the heat exchanger had rusted through and the furnace was putting carbon monoxide in deadly levels into the home.  

2 Minnesota men died of carbon monoxide poisoning "a damper on the furnace of the rural Springfield home was not functioning properly."  So it doesn't appear to have been a heat exchanger, but part of the furnace that appeared to be functioning normally was in fact the cause of death for 2 people.

What Should I DO?

So what's the takeaway?  What's the lesson we should learn here?  Furnace safety matters.  It's a life or death situation for some people.  Annual preventative maintenance and inspections are one great way to keep your family safe.  Carbon monoxide detectors are another.  Low Level monitors provide you the information and warning when any levels are present and give you the information to make important health decisions for your family.

I keep talking about this subject because it's important, and like I said before, people don't necessarily understand the potential danger.  We have received more phone calls and gone through more trouble related to failed heat exchangers that we find than any other problem we encounter.  People are furious that we have told them they have a dangerous situation and shut down their equipment.  People call angry that we've left their elderly parents without heat "for no good reason".  They call insisting we're trying to rip them off and don't believe they have an issue.  They won't let us come back to show them again when we offer, either.  We've been called unethical, liars, cheats, you name it, but we're going to keep informing customers when we find cracks in heat exchangers because it truly is a safety issue.

The reason for their frustration is fairly simple - the furnace appears to still be running fine, and they have carbon monoxide detectors that aren't going off.  

The reason for our insistence on addressing the issue with a new heat exchanger or new equipment is also fairly simple -- what seems like a small crack or hole could in fairly short order become a crack or hole large enough to kill them and their family.  Literally.  

What else can we do to prevent these kinds of tragedies?  Get your boiler or furnace tuned up by a professional technician every year.  This will not only make sure everything is in good operating order to greatly reduce the chance of CO poisoning, but they also help improve efficiency, and reduce breakdowns in the heating equipment we depend on through the winter.

Part of our Precision Furnace Tune-up is a Heat exchanger safety inspection.  The heat exchanger is the part of your furnace or boiler that is responsible for keeping the combustion products (including Carbon Monoxide) seperated from the air in your home.  If that part of your furnace becomes compromised by a hole or a crack, you could find yourself in a situation not unlike the folks in the stories listed above.  Making sure your furance is safe and reliable are our top priorities when we work on your equipment.  After all, this could be your lives at stake as we see in the recent news.

I'll leave with this parting thought: if your furnace or boiler was a car driving at 60 miles an hour, it would drive over 100,000 miles per year.  You would definitely have your car checked out at least every 100,000 miles - probably get the tires changes and the oil and filters too.  Make the investment in your peace of mind and get your equipment checked out today.