QUESTIONS WITH FULL SOLUTION GRADED
A+
◉ what is arcing. Answer: electric discharge across a gap through a
medium
◉ what is sparking. Answer: luminous particles form and spatter
when arc occurs
◉ how is mechanical energy generated. Answer: friction or
compression
◉ what is heat flux. Answer: Energy transfer over time per unit of
surface area, kilowatts/meter(squared) kilojoules/meter(squared) x
sec
Btu/feet(squared) x sec
◉ ways of heat transfer. Answer: conduction, convection, radiation
◉ what is conduction. Answer: Transfer of heat through and
between solids, direct contact
,◉ what is convection. Answer: Transfer of heat by circulation within
a medium like gas or liquid
◉ what is radiation. Answer: Transfer of heat by electromagnetic
energy
§ Can become dominant mode of heat transfer when fire grows in
size
§ Includes light waves, radio waves, x-rays
§ Significant effect on ignition of objects located away from the fire
§ Radiant heat systems usually located under a room
◉ factors that affect radiant heat transfer. Answer: nature of exposed
surface
distance between heat source and exposed surface
temp diff between heat source and exposed surface
◉ what is a passive agent. Answer: o Materials that absorb heat and
do not contribute to fuel
o Ex. Fire doors and fire walls, dry wall gypsum
◉ 3 types of fuel. Answer: gas, liquid, solid
,◉ what is heat of combustion. Answer: total amount of thermal
energy released when a specific amount of fuel oxidizes (measured
in Kj/g)
◉ what is heat release rate. Answer: total amount of heat released
per unit time (measured in kW)
◉ which state it the most dangerous and why
solid/ liquid/ gas. Answer: gas because it is in a ready state for
ignition
◉ what must happen to liquid before it can burn. Answer: must
vaporize
◉ flammable lq vs combustible lq. Answer: comb; any liquid with
flashpoint above 37.8*C
flamm; any liquid with flashpoint below 37.8*C
◉ flash point vs fire point. Answer: flash; min temp at which lq gives
off enough vapors to ignite, cannot sustain combustion, commonly
used to indicate flammability haz
, fire; temp at which enough vapors are generated to sustain
combustion reaction, usually a few degrees above flash point
◉ what temp does wood pyrolysis occur at. Answer: 204*C
400*F
◉ at what ox concentration can materials ignite (as low as what %).
Answer: 14%
◉ what is flammable range. Answer: the entire range of possible gas
or vapor fuel concentrations in air that are capable of burning
--range between UFL (too rich to burn) and LFL (too lean to burn) in
which a substance can be ignited
◉ what is chemical flame inhibition. Answer: occurs when an
extinguishing agent interferes with the chemical reaction
-application forms stable product and terminates the reaction
◉ what is self sustained chemical reaction. Answer: free radicals
break off and combine with oxygen or fuel materials