Basic Fire Science Flashcards
What are the four components of the fire tetrahedron?
Fuel
Heat
Uninhibited chemical chain reactions
oxidizing agent
Fires can be prevented or suppressed by controlling or removing
one or more of the sides of the tetrahedron.
A fuel is
any substance that can undergo combustion.
The majority of fuels encountered are
organic. Which simply means that they are carbon based
Combustion of liquid fuels and most solid fuels takes place
above the fuel surface in a region of vaports created by heating the fuel surface.
Gaseous fuels do not require ______ or _____ before combustion can occur.
vaporization or pyrolysis
In most fire situations, the oxidizing agent is
the oxygen in the earth’s atmosphere.
Many chemical oxidizers contain readily released oxygen. List three examples:
Ammonium nitrate fertilizer
potassium nitrate
hydrogen peroxide
Every fuel-air mixture has an optimum ratio at which point the combustion will be most efficient. This ratio occurs at or near the4 mixture known by chemists as the
Stoichiometric ratio
Self sustained combustion occurs when
sufficient excess heat from the exothermic reaction radiates back to the fuel to produce vapors and cause ignition in the absence of the original ignition source.
Lower explosive (flammable) Limit
LEL
The minimum percentage of fuel in air in which combustion can occur is the lower explosive limit of the material.
Upper Explosive Limit
UEL
There is also a maximum percentage of fuel in air in which combustion can occur.
Complete combustion of hydrocarbon fuels containing only hydrogen and carbon will produce
carbon dioxide and water
When less air is available for combustion, as in ventilation controlled fires, the production of ______ increases as does the production of ______
Carbon monoxide increases as does the production of soot and unburned fuels.
Combustion products exist in all three states of matter:
solid, liquid and gas.
Solid material makes up the ash and soot products that represent the
visible “smoke”
Many of the other products of incomplete combustion exist as vapors or as extremely small tarry droplets or aerosols. These vapors and droplets often condense on surfaces that are cooler than the smoke, resulting in
smoke patterns that can be used to help determine the origin and spread of fire.
Soot and tarry products often accumulate more heavily on
ceramic-tiled surfaces than on other surrounding surfaces due to the heat conduction properties of ceramic tile. Those surfaces that remain the coolest the longest tend to collect the most condensate.
Smoke is generally considered to be
the collection of the solid, liquid, and gaseous products of incomplete combustion.
_______ flows occur because hot gases are less dense than cold gases. This causes the hot gases to rise, just as a hot air balloon rises.
Buoyant Flows
What causes a fire plume to increase in diameter as it rises?
As the hot gases rise, they mix with or entrain the surrounding air so that the flow of gases in the plume increases with height above the fire and at the same time the temperature of the plume is reduced by the entrainment of air. It is the entrainment of air into the plume that causes the plume to increase in diameter as it rises.
When a fire plume reaches the ceiling of a room, the gases turn to move laterally along the ceiling jet as a
ceiling jet.
The buoyancy of gases in a compartment fire causes flow into and out of a compartment through vents. In a compartment fire with a single vent opening, hot gases flow out through the upper portion of the opening, and fresh air enters in the lower portions of the opening.
Vent flows
The heat transfer rate per unit area
Heat flux