ESD No. 1 North Lake Travis Fire & Rescue

ESD No. 1 North Lake Travis Fire & Rescue

Fire Behavior / Fire Science ESD No. 1 North Lake Travis Fire & Rescue

Main Topics • Types of Energy • Types of Heat Transfer • Fire Triangle • Fire Tetrahedron • Phases of Fire

Introduction Firefighters encounter a variety of conditions when responding to a fire. Wildland Fires – may endanger a structure Structural Fires – may expose another structure Flames – may expel gases causing a life hazard Fire in room of origin – potential for flashover Fire explosion – caused by non-ventilated building (backdraft) ESD No. 1 North Lake Travis Fire & Rescue

Introduction A basic understanding of the science of fire will help the firefighter to perform his/her duties safely and effectively. ESD No. 1 North Lake Travis Fire & Rescue

Fire is a rapid chemical reaction that produces energy. ESD No. 1 North Lake Travis Fire & Rescue

There are various types of energy found in nature, such as: Chemical – energy released as a result of a chemical reaction (ie., combustion) Mechanical – energy an object in motion has (ie., snow in an avalanche) Electrical – energy as a result of current flowing (ie., through a wire) Heat – energy transferred between two mediums with different temperatures (ie., sun and earth) Light – energy as visible wavelengths produced by chemical reaction (ie., flashlight) Nuclear – energy released as a result of fission (ie., split atoms) or fusion (ie., compressed atoms) ESD No. 1 North Lake Travis Fire & Rescue

Two Stages of Energy Kinetic – energy possessed by a moving object Potential – energy stored in an object that can be released at a later time ESD No. 1 North Lake Travis Fire & Rescue

Heat is the tendency of energy transferred from one body to another when the temperatures are different – usually from hot to cold. • Heat transfers by three ways: • Conduction • Convection • Radiation ESD No. 1 North Lake Travis Fire & Rescue

Conduction If you place a pot on a hot stove, the pot heats. This is a transfer of excited atoms (the heat source), moving to slower atoms (the pot), causing them to accelerate. This is a point-to-point contact method of heat transfer. ESD No. 1 North Lake Travis Fire & Rescue

Convection When you hold your hand over the stove, you can feel the energy (heat) from the flame even though the flame isn’t touching your hand. Convection is the transfer of energy by the movement of heated gases (air in this case) or liquids. ESD No. 1 North Lake Travis Fire & Rescue

Radiation Go outside during a clear day and you feel the warmth of the sun. The electromagnetic waves that hit you result in heating your body. The sun’s energy travels through a vacuum and we feel it affects. Radiation is the cause of most exposure fires. ESD No. 1 North Lake Travis Fire & Rescue

Combustion Defined as the process of rapid oxidation, resulting in fire. Oxidation can also be slow, as in rusting, or instantaneous, as in an explosion. ESD No. 1 North Lake Travis Fire & Rescue

Oxidation • Rapid oxidation can occur in two forms: • Smoldering fires • Steady state fire (also called free-burning fires) ESD No. 1 North Lake Travis Fire & Rescue

Fire Triangle The Fire Triangle is an illustration that shows that oxygen, fuel, and heat in certain proportions create fire. If any one of the three elements are removed, a fire cannot exist. ESD No. 1 North Lake Travis Fire & Rescue

Fire Triangle As research methods of combustion improved over the years, It was found that the fire triangle only accurately portrayed The smoldering mode of combustion. ESD No. 1 North Lake Travis Fire & Rescue

Fire Tetrahedron Modern fire science recognized that in order to support flaming combustion a fourth element needed to be added to the Fire Triangle. ESD No. 1 North Lake Travis Fire & Rescue

Fire Tetrahedron A chemical chain reaction is required to continue flaming combustion. As with the fire triangle, if any of the four elements of the Fire Tetrahedron is removed, the fire is extinguished. ESD No. 1 North Lake Travis Fire & Rescue

PHASES OF FIRE ESD No. 1 North Lake Travis Fire & Rescue

Incipient Phase Steady-state Phase Hot-smoldering Phase ESD No. 1 North Lake Travis Fire & Rescue

Incipient Phase • The earliest phase of a fire, beginning with the actual ignition. • Limited to the original materials of ignition • Flame temperature may be over 1000°F, yet the room temperature may be only slightly increased. ESD No. 1 North Lake Travis Fire & Rescue

Incipient Phase Rollover Sometimes called flameover, rollover occurs when unburned gases released during the incipient phase accumulate at the ceiling level. The superheated gases are pushed, under pressure, away from the fire area where they mix with oxygen. When their flammable range is reached they ignite. ESD No. 1 North Lake Travis Fire & Rescue

Steady-state Phase • Also called the free-burning phase, is generally when sufficient oxygen and fuel are available for fire growth and open burning to a point where total involvement is possible. • Flame-spread is early part – around 1300°F • Clear burning is accompanied by high temperatures with little or no smoke (ie., propane fire) ESD No. 1 North Lake Travis Fire & Rescue

Steady-state Phase Flashover Occurs when flames flash over the entire surface of a room or area. It is caused by the buildup of heat from the fire. When unburned combustibles simultaneously reach their ignition points, simultaneous ignition occurs and the area becomes fully involved. ESD No. 1 North Lake Travis Fire & Rescue

Hot-smoldering Phase After steady-state phase, flames may stop if the area of confinement is sufficiently airtight. The fire is reduced to embers. The area becomes filled with dense smoke and gases. Superheated gases may accumulate. ESD No. 1 North Lake Travis Fire & Rescue

Hot-smoldering Phase Backdraft Also known as smoke explosion, the superheated gases in the hot-smoldering (or steady-state) phase(s) are rapidly ignited by introduction of oxygen. As oxygen is introduced, the stalled combustion resumes, sometimes as an explosion. ESD No. 1 North Lake Travis Fire & Rescue

Conclusion An essential part of firefighting is for us (as firefighters) to continuously study and comprehend fire science and fire behavior. The days or “Squirt the wet onthe red,” are over.

Questions or Comments?

ESD No. 1 North Lake Travis Fire & Rescue