Smoke inhalation in forensic investigations
Smoke inhalation refers to the breathing in of gases, vapors, and particles produced during combustion or pyrolysis. It poses significant dangers, particularly during fires, as many individuals die from smoke inhalation rather than burns. Forensic investigations into fire-related deaths often involve examining the airways of victims to ascertain the cause of death and whether they were alive when the fire started. A key indicator of smoke inhalation is the presence of soot in the lungs, which suggests breathing occurred during the fire. Additionally, carbon monoxide poisoning is a frequent cause of death in such scenarios, as it binds more readily to hemoglobin than oxygen, depriving the body of necessary oxygen. The examination of carboxyhemoglobin levels in the blood can further assist forensic pathologists in determining the circumstances surrounding a death. Understanding smoke inhalation's effects is crucial for both forensic analysis and fire safety awareness.
Subject Terms
Smoke inhalation in forensic investigations
DEFINITION: Breathing in of gases, vapors, and particles created by combustion (burning) or pyrolysis (breakdown of material by heat in the absence of enough oxygen to support combustion).
SIGNIFICANCE: By examining the airways of a person who has died in a fire, a forensic pathologist can determine the cause of death and whether the individual was dead before the fire started or died during the fire.
Smoke inhalation has been known to be potentially deadly for centuries. For example, the Roman writer and naturalist Pliny reported in the first century CE that prisoners were executed by being placed over a smoking fire. Of the people who die in fires, two to three times as many die from smoke inhalation as die from burns. When large numbers of people are killed in a fire, deaths most often occur because people are trapped in the building and succumb to smoke inhalation. For example, all eighty-seven deaths in the 1990 fire at the Happy Land social club in New York City were caused by smoke inhalation, and up to half of the one hundred people who died in the Station nightclub fire in West Warwick, Rhode Island, in 2003 were killed by smoke.
How Smoke Inhalation Causes Death
Smoke inhalation damages the body in multiple ways, all of which may cause or contribute to death. Inhaling hot smoke burns the tissues that line the airways. Thermal burns from smoke tend to occur only in the mouth and upper part of the trachea (windpipe). Nevertheless, if the smoke is hot enough, when it reaches the larynx (voice box), it can trigger a spasm that closes the windpipe and causes asphyxiation.
If the smoke contains toxic gases, it can also cause chemical burns. When a fire burns certain synthetic polymers, such as PVC (polyvinyl chloride) pipe, poisonous hydrogen chloride gas is created; burning wool, silk, nylon, and polyurethane create deadly hydrogen cyanide gas. Exposure to either of these gases can cause death. In addition, soot and particles in smoke can trigger a reaction in the airways similar to an asthma attack. The airways narrow, and the individual begins to wheeze in an attempt to get enough air.
One of the most common causes of smoke inhalation death is carbon monoxide (CO) poisoning. In a normally functioning lung, oxygen from the air is transferred to a molecule called hemoglobin that is found in red blood cells. Hemoglobin holds the oxygen as the red blood cell travels through the circulatory system. When the red blood cell reaches an oxygen-deficient cell, hemoglobin releases the oxygen molecule and picks up a molecule of carbon dioxide (CO2). CO2 is a normal cellular waste product. The red blood cell carries it to the lungs, where it is released and breathed out of the body. The hemoglobin molecule then picks up another oxygen molecule and the cycle repeats.
In a fire, a large amount of carbon monoxide, a colorless, odorless gas, is produced through incomplete combustion, or pyrolysis. Hemoglobin binds to CO two hundred times more easily than it binds to oxygen. When CO enters the lung, it rapidly binds to hemoglobin, making it impossible for the hemoglobin to pick up any oxygen molecules. Once the CO is bound to hemoglobin, it remains tightly attached, so that over time less and less oxygen can be picked up in the lungs and carried to cells, and little CO2 is removed.
When the level of CO in a person’s blood reaches about 30 percent, the person becomes confused; this state may contribute to the inability to escape from a fire. As the amount of CO increases (many victims of smoke inhalation have as much as 80 percent of their hemoglobin bound to CO), the body is simply too depleted of oxygen for cells to continue to function. Breathing air with 100 parts per million of CO can be fatal in half an hour; air with 5,000 parts per million of CO causes death within a few minutes. Carbon monoxide poisoning causes asphyxiation at the cellular level.
Signs of Foul Play
Typically in the United States, when a person dies in a fire, an autopsy is performed to determine the cause of death whether the fire was accidental or arson is suspected. In addition to looking for external burns, the pathologist looks for signs of damage to the tissues lining the airways. The presence of soot in the lungs indicates that the victim was breathing after the fire started. The amount of carboxyhemoglobin in the blood may also be measured after death. Carboxyhemoglobin is a substance formed within red blood cells when hemoglobin is exposed to and bonds with carbon monoxide. This process typically takes place in instances of carbon monoxide poising or during fires. A large presence of carboxyhemoglobin in the blood indicates that a deceased person died in a fire.
Sometimes fires are set to cover up or destroy of other crimes, such as murder. As long as remains recovered from a fire scene include airways that can be examined, however, a forensic pathologist can determine whether the victim was alive at the time the fire started. If death occurred before the fire began, the body will show no signs of airway burns, even if the external body is charred. No soot or particulate matter will be found in the airways and lungs, and the level of CO in the blood will be less than 15 percent.
Bibliography
Faith, Nicholas. Blaze: The Forensics of Fire. New York: St. Martin’s Press, 2000.
MacDonald, Jake. “After the Inferno: Winnipeg’s Arson Squad Can Tell How a Fire Started and Often Who Started It, by Sifting Through the Ashes and Reading Scorch Marks on the Wall.” Saturday Night, May 20, 2000, 24-32.
Redsicker, David R., and John J. O’Connor. Practical Fire and Arson Investigation. 2d ed. Boca Raton, Fla.: CRC Press, 1997.
Shusterman, Dennis. “Predictors of Carbon Monoxide and Hydrogen Cyanide Exposure in Smoke Inhalation Patients.” Journal of Toxicology: Clinical Toxicology 34 (January, 1996): 61-72.
Tanner, Robert. “New Science Challenges Arson Convictions.” The Washington Post, December 31, 2006; p. A08.
Žiūkaitė, Gabrielė. "Homicides Disguised as Fire Deaths." Acta Medica Lituanica, vol. 30, no. 1, 16 May 2023, pp. 86–96, doi: 10.15388/Amed.2023.30.1.10. Accessed 16 Aug. 2024.