I am often asked if a person was alive during the fire. It is a fairly simple question to answer in most cases, using deductive reasoning, which goes something like this: A human is a mammal. Mammals need to breathe to live. Humans breathe through the nose and mouth down into the bronchi of the lungs. Fires produce particulates in the air. When one breathes the particulates, there is sooting around the nose and mouth into the lungs. Therefore I can say yes the individual was alive during the fire, if that sooting is present. This is a process of top down thinking. It is based on a premise known to be true, leading towards a conclusion that must also be true. If you read the premise above, it can lead to only the one conclusion.
There is a certain amount of carbon monoxide in the atmosphere, somewhere between 0.05 to 5 parts per million. In our blood systems there is a cell whose purpose is to carry oxygen throughout the body. This cell is called hemoglobin or the red blood cell. Carbon monoxide has a better than 200 times greater affinity than oxygen to latch on to a red blood cell thus depriving the body of oxygen. This combination of carboxyhemoglobin is the percentage measurement of how many red blood cells have been replaced with carbon, depriving oxygen to the cells in the brain and throughout the body. Normal levels of carboxyhemoglobin are between five and for heavy smokers up to twelve percent. There are many factors that would indicate how quickly a person would be affected and die when over these limits. Carboxyhemoglobin is a necessary piece of evidence in any fire death.
The Merriam-Webster Dictionary defines it as “a substance used to accelerate a process (as in the spreading of fire).” The most common accelerants appreciated in fire investigations are volatile organic compounds such a gasoline, kerosene, lighter fluid or other combustible liquids. One might ask, how does one know that accelerants were used? In many cases investigators use a dog specially trained to detect multiple types of accelerants. Fire investigators study fire first by looking at patterns. They are trained to find the origin of the fire, calculate the heat of the fire and determine how it spread. They also collect samples at the point of origin and test for accelerants.