Chapter 6 Fire Patterns Flashcards
A fire pattern is _____________
The visible or measurable physical changes or identifiable shapes formed by a fire effect or group of fire effects.
___________are the observable or measurable changes in or on a material as a result of exposure to the fire.
Fire Effects
The mass loss of material is often used as an indication of
the duration and intensity of the fire.
The rate of mass loss is generally dependent on
the heat flux to the material surface
Fire growth rate
rate of heat release of the material itself
When exposed to elevated temperatures, wood undergoes pyrolysis, a chemical decomposition that drives off
gases
water vapor
various pyrolysis products as smoke.
(the solid residue that remains is mainly carbon)
The rate of charring of wood varies widely depending upon variables, including:
Rate and duration of heating
Ventilation effects
Surface to mass ratio
Type of wood
Moisture content
The rate of charring and burning of wood in general has no relation to its age once
the wood has been dried.
No specific time of burning can be determined based solely on
depth on char.
Analysis of the depth of charring is more reliable for evaluating_____, rather than for establishment of specific burn times or intensity of heat from adjacent burning materials.
fire spread
________ is characterized by the loss of surface material resulting in cracking, breaking, and chipping or in the formation of craters on concrete, masonry, rock, or brick.
Spalling
_________ is the breakdown in surface tensile strength of material caused by changes in temperature, resulting in mechanical forces within the material.
Fire-related Spalling.
A mechanism of spalling is the _____ or _______ of the surface while the rest of the mass expands or contracts at a different rate.
expansion or contraction
Another factor in the spalling of concrete is loading and stress in the material at the time of the fire. Because these high-stress areas may not be related to the fire location
spalling of concrete on the underside of ceilings may not be directly over the origin of the fire.
_________ is the basic chemical process associated with combustion.
Oxidation
The melting of certain metals may not always be caused by fire temperatures higher than the metals’ stated melting point; it may be caused by
alloying.
Alloying refers to the mixing of, generally , two or more metals in which one or more of the metals is in a liquefied state, resulting in an alloy.
Nearly all materials ____ when heated.
expand
Bending and buckling of steel beams and columns occurs when the steel temperature exceeds approximately
900 degrees
_________ is a phenomenon whereby the soot particulate forms identifiable patterns on such surfaces of the smoke alarm as the internal and external surfaces of the smoke alarm cover near the edges of the “horn” sound oulets, the edges of and “horn outlets of the interior “horn” enclosures.
Enhanced Soot deposition on smoke alarms
Acoustic Soot Agglomeration
(there will be a buildup of soot around the alarm horn)
A ______ is a distinct and visible fire effect generally apparent on non-combustible surfaces after combustible layers have been burned away.
Clean Burn
Clean burn patterns produced by burning away of soot can be produced by direct flame contact or intense radiated heat. The carbon will be oxidized to gases and disappear from the surface.
________ of gypsum wallboard involves driving the free and chemically bound water out of the gypsum as well as other chemical and physical changes to the gypsum component itself.
Calcination
Calcination involves a chemical change of the gypsum to another mineral,______
anhydrite
What causes window glass to break in a fire?
If a pane of glass is mounted in a frame that protects the edges of the glass from radiated heat of fire, a temperature difference occurs between the unprotected portion of glass and the protected edge.
The temperature difference can cause cracks that start at the edge of the glass.
