Trial Prep - General questions Flashcards
What is a rapid oxidation process, which is an exothermic chemical reaction resulting in the evolution of light and heat in varying intensities
Fire
Define “fire”
A rapid oxidation process, which is an exothermic chemical reaction, resulting in the evolution of light and heat in varying intensities
Four sides of the fire tetrahedron
heat
fuel
oxidizing agent
uninhibited chemical chain reaction
oxygen % required for flaming fire
at least 14-16%
oxygen % required for smoldering fires
as little as 8%
define temperature
the degree of sensible heat of a body as measured by a thermometer
a measure of the degree of molecular activity relative to some reference point (freezing point of water)
define “heat”
a form of energy characterized by the vibration of molecules and capable of initiating and supporting chemical changes and changes of state
or. the amount of energy require to maintain or change the temperature of an object
what are the two units of heat energy?
joule
calorie (1 cal = 4 J
Define “heat transfer”
energy that is transferred between objects due to a temperature difference
which direction does heat transfer move?
from the hotter object to the colder object
Heat transfer is measured in units of what?
Watts
How many watts are in a megawatt?
1,000,000 W
Define “heat flux”
The measured rate of heat transfer to or from a defined area or surface.
does high pressure always flow to low pressure, or low to high?
high to low
what law does this represent?
PV=nRT
Ideal gas law
what is the key point to Ideal Gas Law?
If the pressure increases, then temperature increases.
if the temperature increases, then the pressure increases.
and the same if there is a drop
Name the 3 modes of heat transfer
Conduction
Convection
Radiation
What type of heat transfer involves the movement of a fluid?
convection
Which type of heat transfer is with electromagnetic waves?
radiation
which mode of heat transfer is through direct contact
conduction
Define “Thermal Conductivity”
the rate at which heat passes through a specified material
Does steel have a high or low thermal conductivity?
high
what are the two types of convection heating?
Natural (think of a car radiator and how fresh air goes across it)
Forced (heater with a mechanical fan)
How is smoke and radiation heat associated?
smoke consists of tiny, dark, solid carbon particles and each one is radiating heat.
this means, the dirtier and darker the smoke, the more radiation it will emit (high emissivity)
Define Pyrolysis
The chemical decomposition of a compound into one or more substances due to heat alone.
Remember that “radiant heat created pyrolysis products and these products burned”
What are the two types of changes to fuel turning to vapor?
phase changes which is reversible (melting or evaporation)
Thermal decomposition which is irreversible (pyrolysis)
What is the term for the amount of heat released when a known amount of a substance burns completely?
Heat of Combustion
Define “heat of combustion”
the amount of heat released when a known amount of a substance burns completely
Define “Heat Release Rate”
the amount of heat energy released by the fire per unit time
What units are used to measure HRR?
kW or MW
How is HRR used to define a fire?
often used to describe the “size” of a fire
What is the single most important factor in characterizing fire behavior
HRR because it helps explain the thermal conditions in a room or how it might ignite other nearby fuels via heat transfer
What four things control the HRR of an object
- chemical and physical properties
- geometry of the fuel and containment
- ventilation
- surrounding fuels
What is the approx. peak HRR of a cigarette?
5 W
What is the approx. peak HRR of a match?
80 W
What is the approx. peak HRR of a upholstered sofa?
3MW to 5 MW
At what phase of a fires development is the idealized HRR curve highest?
fully developed or post flash-over
Define “ignition”
the process of initiating self-sustained combustion
What are the 2 types of ignition?
piloted ignition and autoignition
What is piloted ignition?
when an external ignition source ignites flammable vapors
What does a competent ignition source include?
- enough energy
- will be in contact with the fuel long enough to raise it to the fuel’s ignition temperature
Define “thermal Inertia”
the measure of how fast the surface temperature of a material will rise
what is the measure of how fast the surface temperature of a material will rise?
thermal inertia
What 3 things determine an objects thermal inertia?
- thermal conductivity - the material’s ability to conduct heat
- the material’s density
- the material’s capacity to store heat
Does low kpc (thermal inertia) mean fast or slow ignition
fast.
what is the measurement for something considered thermally thin?
a thickness of 2mm or less