Carbon Monoxide

• Carbon monoxide?
• Yes it is  dangerous?
• How is it made?

What is Carbon Monoxide

Carbon monoxide is a gas composed of one Carbon atom and one Oxygen atom. It's chemical symbol is CO. Carbon monoxide is also flammable and burns with a blue flame.

Why is it so dangerous

Firstly, CO is colorless, odorless and tasteless. In fact we cannot sense it's presence at all. We just feel ill if we breath it in.

In order to elaborate, we must first understand a bit about how oxygen gets to our muscles and body tissues. We all know we breath in air to live and that we breath out carbon dioxide and water vapor. Our blood absorbs the oxygen from the air we inhale to our lungs, and returns the carbon dioxide, which we exhale. Medical science has discovered that a molecule called hemoglobin, a constituent part of our blood, is the carrier of these gasses. Hemoglobin has a great affinity for many gasses, including oxygen, carbon dioxide as above, and of course, the topic of this discussion, Carbon monoxide.

In oxygen rich conditions, such as normal inhalation (with no carbon monoxide present), each hemoglobin molecule combines with oxygen atoms. Up to 4 at a time, in a very loose affinity. While at the same time, giving up any Carbon Dioxide it may be carrying. Oxygenated hemoglobin, or oxy hemoglobin, which is red in color, is circulated through our arteries to the tissues and muscles in our body, the loose affinity with the oxygen allows the oxygen to be readily given up within our body tissues where it is used to produce the energy which in turn allows our body to function. The hemoglobin molecule picks up carbon dioxide at the same time as the oxygen is released and turns a blue/purple color in the process. The deoxygenated hemoglobin is returned to the lungs via our veins, where it is exhaled. Since there are millions of hemoglobin in our blood, this process takes place on a massive scale, in terms of numbers of atoms and molecules. It carries on for as long as we breathe normal air.

The explanation also shows how our arteries are red and our veins are blue. (blue blood has lots of carbon dioxide) Red blood (usually) contains oxygen. we don't bleed blue blood, because as soon as it is in the open the blood becomes oxygenated.

I said above, that the hemoglobin molecule has an affinity for many gasses. Unfortunately for us, hemoglobin has a much higher affinity for Carbon Monoxide than it does for oxygen. In fact 2 to 300 times more affinity. So when Carbon Monoxide is present in the air we breath, the results are, that the hemoglobin combines with the carbon monoxide molecules instead of the Oxygen this is called carboxyhaemoglobin and is cherry red in color. Not only that, because of the higher affinity, the hemoglobin forms a strong bond with the CO, keeping it locked in on the journey through the body, resulting in a cumulative effect. So long as CO is present in the atmosphere we breath, the worse the situation becomes. The blood is effectively being clogged up with CO, this means that there are progressively less and less hemoglobin molecules able to carry oxygen to the tissues and muscles. This results in the the person quickly becoming incapacitated and sudden exertion can lead to collapse, preventing escape from the dangerous conditions.
The lack of oxygen can cause tissue and muscle damage. Even in slight exposure.
Although you may make an apparent full recovery, it could take several years for the damage to show up, by which time the CO incident has been forgotten and the damage attributed to something else. In severe cases, it is even worse than this. Recent medical research has shown that the uptake of carbon monoxide in the membranes of our brain causes these membranes to break down releasing further poisonous and dangerous chemicals, leading to long term brain damage. A few cases have been recorded, where victims of CO poisoning have apparently made a complete recovery, only to be admitted to hospital a few days later, with Parkinson's like disease. Only very recently have these problems been linked to CO Poisoning. Longer term, victims can suffer cognitive and learning difficulties. Again, the past these were attributed to growing older and other medical conditions, but now it is known to be caused by the long term effects of CO poisoning.
The lifespan of a person who has had a carbon monoxide incident can be severely shortened.

Symptoms of CO poisoning

The symptoms of CO poisoning are initially very similar to having the flue and therefore it is difficult to diagnose, especially to those unaware that they have been, or are, exposed to CO. Possible vomiting is the only factor which is different. (You are not physically sick) when you get the flue Table 1, gives an indication of the effects of CO Poisoning.

How is carbon monoxide produced in our home?

Carbon Monoxide is produced, to a greater or lesser extent, as a by-product of burning fossil fuels. If a fuel is burned completely, carbon monoxide is not produced. However, manufacturers have yet to create a fuel burning appliance which is 100% efficient in terms of combustion and does not produce at least some Carbon Monoxide. A modern boiler can have up to 100PPM (parts per million) of CO in the flue gasses, but typical concentrations are more like 5 to 10 PPM. and whilst the combustion efficiency of a modern non condensing Boiler is about 95%, the actual boiler efficiency is in the order of 80% as there is excess air present as well as lost energy from the water content of the flue gasses

If the appliance is faulty or needs serviced, the CO production gets much worse than normal.

I will be using a hypothetical natural gas boiler in this explanation, since Natural gas is 95% composed of a very simple hydrocarbon, Methane, chemical symbol CH₄.
The chemical symbol tells us that the Methane molecule consists 1 carbon atom and 4 Hydrogen atoms.
So methane is burned in our boiler.

Burning, or more correctly, Combustion, is an exothermic heat producing) chemical reaction whereby the gas combines with oxygen from the air to form oxidized components, transforming the chemical energy of the gas to heat energy, where it is used in our boiler. Complete combustion of Methane CH₄ produces Water in gaseous form H₂o and carbon Dioxide CO₂.

Incomplete combustion can produce Soot, or Carbon C. Carbon Dioxide. Carbon Monoxide our poisonous gas and water vapor

The chemical combustion equation for the complete combustion of Methane ( CH₄ ) is:-

CH₄+2O₂ >> 2H₂0+CO₂ + heat

This tells us that for each molecule of methane burned, two molecules of oxygen are required. Producing two molecules of water and one molecule of carbon dioxide.
Now a molecule is a very small amount, so you should multiply the above equation by millions even billions.
It so happens that a gas molecule, whatever it may be, methane, oxygen, carbon dioxide etc, occupies about the same volume as any other gas molecule, so it is easier to consider the above equation in terms of volume. i.e. one volume of methane combines with two volumes of oxygen to produce one volume of carbon dioxide and two volumes of water( in gaseous form).
Our typical boiler may burn 100 cubic feet of methane in one hour. (enough to heat the average home)
So the combustion equation would be :-

100ch4+200O2 >> 200 H2O + 100 CO2.+ lots of heat
i.e. 100 cubic feet of gas combines with 200 cubic feet of oxygen to produce 200 cubic feet of water vapor and one hundred cubic feet of carbon dioxide and gives out lots of heat in the process.

Since air is composed of only 21% oxygen( see table 2 for the full composition, this means that if we need 200 cubic feet of oxygen we actually have to supply 1,000 cubic feet of fresh air.
So our boiler, when working normally will entrain 1000 cubic feet of air every hour.

Now consider what would happen if our hypothetical boilers air pathways became partially blocked. There are many reasons this could occur, dead leaves, dust, dog and cat hairs, clothes piled up over the boiler to name just a few. The following discussion illustrates what would happen with just a simple 5% reduction in the air supply.
We are still burning 100 cubic feet of gas, but now we can only get 190 cubic feet of oxygen. Remembering that each side of the equation must balance, in order to preserve mass.

An incomplete combustion equation is:-

100CH₄ + 190 O₂ >> 100H₂0+ 80CO₂+20CO.

100 cubic feet of methane combines with 190 cubic feet of oxygen to produce 100 cubic feet of water vapor, 80 cubic feet of Carbon Dioxide and 20 cubic feet of Carbon monoxide.
It is possible that the boiler could be producing carbon as well, but this only occurs in severe cases. even then it is still common to come across soot up boilers.

Remembering again, that the air is composed of only 21% of oxygen, 190 cubic feet of Oxygen is actually 190/.21 or 905 cubic feet of air. 190 of oxygen and 715 of mainly nitrogen. so in this case, the concentration of CO in the flue gases will be 20/(715+100+80+20)20/915 or approximately 2%. 2% =20,000 Parts per million, refer to table one and you can see that if we tried to breathe this stuff in, we would be dead in less than a minute. Fortunately, the gasses are contained in the flue of the boiler, and are directed to outside. But what if the flue were faulty? You need to ensure that the appliance is not only regularly serviced, but checked, to ensure the flue ways are clear and internal joints sealed. Which is why you must only get a properly trained Gas Engineer to do the work. Normally a gas boiler entrains much more air than it can use for combustion. This air bypasses the combustion process and dilutes the flue gasses. However Excess air as it is called is kept to a minimum, as it severely decreases the efficiency of the boiler, since it is being heated up only to be ejected out the flue.