Exam 4 Flashcards
what are the three most common ignition sources in major fires according to the text’s Table?
Electrical, Smoking, Friction
fire triangle
essential elements for combustion: fuel, oxidizer, ignition source
ignition
ignition caused when flammable mixture coming in contact with a source of ignition with sufficient energy or gas reaching a temperature high enough to cause the gas to autoignite
decomposition fire
fires where the fuels have their own oxidant and can burn without air present; ethylene oxide, acetylene, propylene oxide
autoignition temperature
temperature at which a vapor ignites spontaneously from the energy of the environment
flash point
lowest temperature at which a liquid gives off enough vapor to form an ignitable mixture with air
flammability limits
vapor-air mixtures will ignite and burn only over a well-specified range of compositions
mechanical explosion
explosion resulting from the sudden failure of a vessel containing high-pressure nonreactive gas
deflagration
explosion in which the reaction front moves at
detonation
explosion in which the reaction front moves at >Ma1 in the unreacted medium
BLEVE
boiling-liquid expanding-vapor explosion. when a vessel that contains liquid at room temperature above its atmospheric pressure boiling point ruptures
(explosive) overpressure
pressure above ambient that is caused by an explosion or shockwave
LOC
limiting oxygen concentration. minimum oxygen concentration required to propagate a flame
MIE
minimum ignition energy; minimum energy input required to initiate combustion
auto-oxidation
process of slow oxidation with accompanying evolution of heat
siphon purging
alternate to sweep-through purging: filling a vessel with compatible liquid, then adding a purge gas to the vapor space of the vessel as the liquid is drained.
bonding
electrically connecting two adjacent objects to drop their voltage to 0 relative to each other
grounding
electrically connecting an object to the ground to drop its voltage to zero relative to the ground
explain how a deflagration and a detonation are related along with their differences
both are explosions. Detonations produce a shock wave moving at speed >Ma1 with a maximum pressure of ~10atm lasting less than 1ms. Deflagrations produce a pressure wave lasting many ms with a max pressure of 1-2atm.
explain the important aspects of the various purging techniques including vacuum, pressure, vacuum/pressure, and sweep-through
vacuum: uses less inert gas bc oxygen is reduced primarily by vacuum.
pressure: faster than vacuum purging (bc of higher P differentials), but uses more inert gas
vacuum-pressure: uses less inert than pressure purging.
sweep-through: simultaneous addition of inert at one opening and withdrawal at another. Used for vessels not rated for pressure or vacuum.
explain the difference between bonding and grounding
bonding electrically connects two objects to drop their voltage to zero, while grounding electrically connects objects to a grounded object (metal rod buried in ground)
which will generate higher static voltages and energies given all other factors are unchanged: laminar or turbulent flow?
turbulent flow will generate higher static voltages since charge separation occurs when two materials come into friction. Turbulent flow has higher velocity, and streaming current is proportional to the square of fluid velocity.
what is relaxation time in the context of static electricity? what categories of materials have long relaxation times? Why is that important?
time required for a charge to dissipate by leakage; polar materials have long relaxation times bc polar groups can hold charge longer
for pressure below ambient, how do the LFL and UFL typically change with pressure?
x
for pressures above ambient, how do the LFL and UFL typically change with pressure?
UFL increases as P increases
P has little effect on LFL
for pressure below ambient, how do the LFL and UFL typically change with pressure?
very low pressures have little effect on LFL and UFL
for temperatures above ambient, how do the LFL and UFL typically change with temperature?
As T increases,
LFL decreases and
UFL increases.
