Which factors contribute to a fire’s dynamics, and how do investigators use that knowledge to pinpoint the origin of a fire?
The study of fire dynamics examines how fires grow and move. It plays an important role in fire investigation, taking chemistry, fluid mechanics, heat transfer, and the science of fire itself to point toward the fire’s ultimate source.
The Fire Tetrahedron
To evaluate the path of destruction wrought by a fire and form a hypothesis about its origin, investigators draw on their knowledge of fire chemistry.
For a fire to ignite and spread, it requires four components, known as the fire tetrahedron:
- Fuel: This could be a material like loose paper or untreated wood, or even an accelerant like gasoline or kerosene.
- Oxygen: Fire needs oxygen to grow and spread. Without adequate oxygen, the fire dies.
- Heat: As the fire grows and spreads, it increases in temperature.
- Unbroken chemical reaction: The fire needs all three of the above components to continue burning. Remove one, and the fire goes out.
The Room Where It Happens
Depending on the location of the fire and the items surrounding the original flame, the fire may behave differently according to the dynamics of the room.
For example, if a candle in the living room is knocked over and sets a curtain on fire, that flame will climb up the curtain toward the ceiling. Once the fire and smoke reach the top of the room, it’s much easier for that fire to engulf the whole room. Should you enlist engineering consulting services to investigate a fire in your home, they’ll take the dimensions and setup of the room where it started into consideration.
How Heat Moves
The mechanics of heat transfer are another essential component of fire dynamics. The three main methods of heat transfer are conduction, convection, and radiation.
Conduction
You may have heard that some materials, like metal, are better conductors than others. That means they’re highly adept at transferring heat from a higher-energy spot, such as a hot metal spoon, to a lower-energy location. Conduction requires direct contact to move heat.
Convection
Convective heat transfer uses the air as a medium to move heat; it’s the method your oven most likely uses to heat up and bake food. If a heating element makes the air hot enough, it could ignite nearby objects.
Radiation
Instead of using a medium to move heat, radiation utilizes electromagnetic waves that make nearby molecules move faster. As those molecules speed up, they heat up—this could cause a fire, depending on the objects nearby. Your microwave uses radiation to heat food quickly.
The study of fire dynamics encompasses a variety of scientific principles, and its importance in fire investigations cannot be overstated. Investigators and consultants move through the fire scene and apply their knowledge of fire chemistry and mechanics to map out the fire’s path and determine its source.
