English version machine-translated from the Vietnamese original — under review.
Smoke kills—everyone knows that. But not many people fully understand why. We know that we cannot breathe smoke because of its toxic effects. We know it smells unpleasant, but that is about all.
Besides being chemically toxic, hot smoke can harm the skin, eyes and lungs and lead to disability. Beyond that, it can obscure visibility, hindering escape from fires. Explosions or flashovers can occur if the concentration of smoke particles is high enough and they are heated to their ignition temperature.
COMPOSITION OF SMOKE
When a building and its contents begin to burn, whether smouldering or flaming - smoke is produced. Typically, this smoke consists of a large number of different molecules and particles forming large clouds. All common fuel sources, from the building structure to the furnishings, contain carbon and hydrogen, while most modern materials (plastics and polymers) also contain sulfur and nitrogen. Recycled materials may contain other potentially harmful compounds. The nitrogen and sulfur compounds generated in a fire are highly toxic. Among the products of combustion are hydrogen sulfide, sulfur dioxide, hydrogen chloride, ammonia and various organic products. Black soot forms from incompletely burned carbon. More than one hundred known toxic substances are produced in a fire inside a building.
CO and HCN
In a typical non-hazardous residential fire, carbon monoxide (CO) and hydrogen cyanide (HCN) are the two most dangerous compounds.
CO and HCN act through different mechanisms. CO binds very tightly to haemoglobin in the blood and prevents oxygen from being transported and carbon dioxide (CO2) from being removed. The result is asphyxiation. HCN acts on the mitochondria of cells, particularly in the nervous system. Its mechanism of action is more complex, but essentially it halts the production of adenosine triphosphate (ATP), the biochemical that drives most processes in the cell. With ATP being recycled 10 times per second, HCN is more destructive than CO because it acts almost immediately and shuts down cell functions.
At high temperatures, CO2 is usually produced. At low temperatures, incomplete combustion occurs and CO is produced instead. HCN is produced at a higher rate at lower temperatures.
In the early stage of combustion, as the fire spreads, the production of CO and HCN begins. The oxidation of HCN leads to the formation of other toxic compounds and more CO. Sprinklers, where present, will contain 88 percent of fires until firefighters arrive. As water cools the fire, the formation of HCN is still promoted. In a similar way, restricting oxygen promotes the formation of CO instead of CO2. The best approach is to fully extinguish the flames and put out the embers, but this will always take more time.
Long-term effects of smoke inhalation
Less well known than the immediate dangers of smoke are the effects of exposure to high concentrations of smoke over long periods. CO binds to other molecules, particularly myoglobin and mitochondrial cytochrome oxidase. This leads to significant damage to the heart and nervous system. Cyanide kills brain cells by reducing their ability to produce energy. Many firefighters' heart attacks are suspected to be caused by cyanide poisoning. The higher the cyanide concentration, the faster death occurs.
Among the medium- and long-term symptoms of smoke inhalation are hoarseness (vocal cord damage), coughing, shortness of breath, worsening asthma symptoms and reduced lung function. The most comprehensive reference on this subject is a study of the health effects on the responders to the 9/11 attacks. Smoke can cause or contribute to cancer, autoimmune diseases, sleep apnoea and sarcoidosis.
In summary:
Smoke from building and interior furnishing fires contains more than 100 toxic substances, of which CO and HCN are generally the most dangerous. Although the immediate effects of smoke inhalation can be death or permanent injury, the long-term effects are also very serious. Therefore, efforts to control smoke protect the long-term health of the public and of firefighters alike.
Based in Nevada, the author is an expert in actuators and fire and smoke containment, and manages fire and smoke products for Belimo Americas. Felker is also vice chairman of the Smoke and Fire Task Force of the Air Movement and Control Association International. He is a member of the International Code Council, the National Fire Protection Association and the Society of Fire Protection Engineers, and a life member of ASHRAE. He is a co-author of the book “Dampers and Airflow Control,” published by ASHRAE Special Publications in 2010.
