Exam 4

Question 1

what are the three most common ignition sources in major fires according to the text’s Table?

Answer 1

Electrical, Smoking, Friction

Question 2

fire triangle

Answer 2

essential elements for combustion: fuel, oxidizer, ignition source

Question 3

ignition

Answer 3

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

Question 4

decomposition fire

Answer 4

fires where the fuels have their own oxidant and can burn without air present; ethylene oxide, acetylene, propylene oxide

Question 5

autoignition temperature

Answer 5

temperature at which a vapor ignites spontaneously from the energy of the environment

Question 6

flash point

Answer 6

lowest temperature at which a liquid gives off enough vapor to form an ignitable mixture with air

Question 7

flammability limits

Answer 7

vapor-air mixtures will ignite and burn only over a well-specified range of compositions

Question 8

mechanical explosion

Answer 8

explosion resulting from the sudden failure of a vessel containing high-pressure nonreactive gas

Question 9

deflagration

Answer 9

explosion in which the reaction front moves at

Question 10

detonation

Answer 10

explosion in which the reaction front moves at >Ma1 in the unreacted medium

Question 11

BLEVE

Answer 11

boiling-liquid expanding-vapor explosion. when a vessel that contains liquid at room temperature above its atmospheric pressure boiling point ruptures

Question 12

(explosive) overpressure

Answer 12

pressure above ambient that is caused by an explosion or shockwave

Question 13

LOC

Answer 13

limiting oxygen concentration. minimum oxygen concentration required to propagate a flame

Question 14

MIE

Answer 14

minimum ignition energy; minimum energy input required to initiate combustion

Question 15

auto-oxidation

Answer 15

process of slow oxidation with accompanying evolution of heat

Question 16

siphon purging

Answer 16

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.

Question 17

bonding

Answer 17

electrically connecting two adjacent objects to drop their voltage to 0 relative to each other

Question 18

grounding

Answer 18

electrically connecting an object to the ground to drop its voltage to zero relative to the ground

Question 19

explain how a deflagration and a detonation are related along with their differences

Answer 19

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.

Question 20

explain the important aspects of the various purging techniques including vacuum, pressure, vacuum/pressure, and sweep-through

Answer 20

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.

Question 21

explain the difference between bonding and grounding

Answer 21

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)

Question 22

which will generate higher static voltages and energies given all other factors are unchanged: laminar or turbulent flow?

Answer 22

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.

Question 23

what is relaxation time in the context of static electricity? what categories of materials have long relaxation times? Why is that important?

Answer 23

time required for a charge to dissipate by leakage; polar materials have long relaxation times bc polar groups can hold charge longer

Question 24

for pressure below ambient, how do the LFL and UFL typically change with pressure?

Answer 24

x

Question 25

for pressures above ambient, how do the LFL and UFL typically change with pressure?

Answer 25

UFL increases as P increases

P has little effect on LFL

Question 26

for pressure below ambient, how do the LFL and UFL typically change with pressure?

Answer 26

very low pressures have little effect on LFL and UFL

Question 27

for temperatures above ambient, how do the LFL and UFL typically change with temperature?

Answer 27

As T increases,
LFL decreases and
UFL increases.