Basics of Chemistry and Firefighting

Fire Behaviour As a firefighter you must have an understanding of the Science of Fire: Combustion:is a chemical process in which a substance reacts rapidly with oxygen and gives off heat. The original substance is called the fuel, and the source of oxygen is called the oxidizer. Fire Heat Temperature Combustion is a chemical process in which a substance reacts rapidly with oxygen and gives off heat. The original substance is called the fuel, and the source of oxygen is called the oxidizer.

Fire Triangle The triangle illustrates the three elements a fire needs to ignite: heat, fuel, and an oxidizing agent (usually oxygen). A fire naturally occurs when the elements are present and combined in the right mixture,[2] meaning that fire is actually an event rather than a thing. A fire can be prevented or extinguished by removing any one of the elements in the fire triangle. For example, covering a fire with a fire blanket removes the oxygen part of the triangle and can extinguish a fire.

Smoke The composition of smoke depends on the nature of the burning fuel and the conditions of combustion. Carbon and hydrogen are almost completely oxidized to carbon dioxide and water  Presence of such smoke, soot, and/or brown oily deposits during a fire indicates a possible hazardous situation, as the atmosphere may be saturated with combustible pyrolysis products with concentration above the upper flammability limit, and sudden inrush of air can cause flashover or backdraft.

Backdraft or Flashover

Fire Classes

Fighting Fire Temperature Reduction- surface cooling/absorption Fuel Removal – wildland fire/ overhaul Oxygen Exclusion – carbon dioxide excludes amount of oxygen available to fire Chemical Flame Inhibition - Dry chemical extinguishers put out fire by coating the fuel with a thin layer of dust, separating the fuel from the oxygen in the air. The powder also works to interrupt the chemical reaction of fire, so these extinguishers are extremely effective at putting out fire. Ventilation -  is a part of structural firefighting tactics, and involves the expulsion of heat and smoke from a fire building, permitting the firefighters to more easily and safely find trapped individuals and attack the fire. If a large fire is not properly ventilated, not only will it be much harder to fight, but it could also build up enough poorly burned smoke to create a smoke explosion, or enough heat to create a flashover. Contrarily, poorly placed or timed ventilation may increase the fire's air supply, causing it to grow and spread rapidly. The flashover may cause the temperature inside the building to peak at over 1000 °C (1850 °F).[1]

Hazardous Materials Safety First City of Ottawa – awareness level vs operations

Hazard Types Thermal hazards: heat - cold Radiological hazards: Chronic vs Acute Asphyxiation hazards: CO cyanide Chemical Hazards: Poisons, corrosive, irritants, convulsants, carcinogens, sensitizers Etiological/biological hazards Mechanical

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