a |
velocity of sound (length/time) |
A |
area (length2) or Helmholtz free energy (energy/mole); or process component availability; or arrhenius reaction rate pre-exponential constant (time−1) |
At |
tank cross sectional area (length2) |
ΔA |
change in Helmoltz free energy (energy/mole) |
AEGL |
acute exposure guidance level |
B |
adiabatic reactor temperature increase (dimensionless) |
C |
mass concentration (mass/volume) or capacitance (Farads) |
C0 |
discharge coefficient (unitless), or concentration at the source |
C1 |
concentration at a specified time (mass/volume) |
Cp |
heat capacity at constant pressure (energy/mass deg) |
Cppm |
concentration in parts per million by volume |
CV |
heat capacity at constant volume (energy/mass deg) |
Cvent |
deflagration vent constant (pressure1/2) |
Cx |
concentration at location x downwind from the source (mass/volume) |
〈C〉 |
average or mean mass concentration (mass/volume) |
d |
diameter (length) |
dp |
particle diameter (length) |
df |
diameter of flare stack (length) |
D |
diffusion coefficient (area/time), or diameter (length) |
D0 |
reference diffusion coefficient (area/time) |
Dm |
molecular diffusivity (area/time) |
Dtid |
total integrated dose due to a passing puff of vapor (mass time/volume) |
Ea |
activation energy (energy/mole) |
ERPG |
emergency response planning guideline (see Table 5-4) |
EEGL |
emergency exposure guidance levels (see Section 5-5) |
f |
Fanning friction factor (unitless) or frequency (1/time) |
f(t) |
failure density function |
fv |
mass fraction of vapor (unitless) |
F |
frictional fluid flow loss term (energy mass) or force or environment factor |
FAR |
fatal accident rate (fatalities/108 hours) |
FEV |
forced expired volume (liters/sec) |
FVC |
forced vital capacity (liters) |
g |
gravitational acceleration (length/time2) |
gc |
gravitational constant (mass length/force time2) |
G |
Gibbs free energy (energy/mole) or mass flux (mass/area time) |
GT |
mass flux during relief (mass/area time) |
ΔG |
change in Gibbs free energy (energy/mole) |
h |
specific enthalpy (energy/mass), or height (length) |
hL |
fluid level above leak in tank (length) |
hL |
initial fluid level above leak in tank (length) |
hs |
leak height above ground level (length) |
H |
enthalpy (energy/mole) or height (length) |
Hf |
flare height (length) |
Hr |
effective release height in plume model (length) |
ΔH |
change in enthalpy (energy/mole) |
ΔHc |
heat of combustion (energy/mass) |
ΔHv |
enthalpy of vaporization (energy/mass) |
I |
sound intensity (decibels) |
ID |
pipe internal diameter (length) |
IDLH |
immediately dangerous to life and health (see Section 5-5) |
I0 |
reference sound intensity (decibels) |
Is |
streaming current (amps) |
ISOC |
in-service oxygen concentration (volume percent oxygen) |
j |
number of inerting purge cycles (unitless) |
J |
electrical work (energy) |
k |
non-ideal mixing factor for ventilation (unitless), or reaction rate (concentration1-m/time) |
k1, k2 |
constants in probit a equations |
ks |
thermal conductivity of soil (energy/length time deg) |
K |
mass transfer coefficient (length/time) |
Kb |
backpressure correction for relief sizing (unitless) |
Kf |
excess head loss for fluid flow (dimensionless) |
Ki, K∞ |
constants in excess head loss, given by Equation 4-38 |
KG |
explosion constant for vapors (length pressure/time) |
Kj |
eddy diffusivity in x, y, or z direction (area/time) |
KP |
overpressure correction for relief sizing (unitless) |
KSt |
explosion constant for dusts (length pressure/time) |
KV |
viscosity correction for relief sizing (unitless) |
K0 |
reference mass transfer coefficient (length/time) |
L |
length |
LEL |
lower explosion limit (volume % fuel in air) |
LFL = LEL |
lower flammability limit (volume % fuel in air) |
LOC |
limiting oxygen concentration (volume percent oxygen) |
LOL |
lower flammable limit in pure oxygen (volume % fuel in oxygen) |
m |
mass |
mf |
mass fraction |
m0 |
total mass contained in reactor vessel (mass) |
mLR |
mass of limiting reactant in Equation (8-36) (mass) |
mTNT |
mass of TNT |
mv |
mass of vapor |
M |
molecular weight (mass/mole) |
M0 |
reference molecular weight (mass/mole) |
Ma |
Mach number (unitless) |
MOC, MSOC |
Minimum oxygen concentration or maximum safe oxygen concentration. See LOC |
MTBC |
mean time between coincidence (time) |
MTBF |
mean time between failure (time) |
n |
number of moles or reaction order |
OSFC |
out of service fuel concentration (volume percent fuel) |
p |
partial pressure (force/area) |
pd |
number of dangerous process episodes |
ps |
scaled overpressure for explosions (unitless) |
P |
total pressure or probability |
Pb |
backpressure for relief sizing (psig) |
PEL |
permissable exposure level (see Section 2-8) |
PFD |
probability of failure on demand |
Pg |
gauge pressure (force/area) |
Pmax |
maximum pressure for relief sizing (psig) |
Ps |
set pressure for relief sizing (psig) |
Psat |
saturation vapor pressure |
q |
heat (energy/mass) or heat intensity (energy/area time) |
qf |
heat intensity of flare (energy/time area) |
qg |
heat flux from ground (energy/area time) |
qs |
specific energy release rate at set pressure during reactor relief |
Q |
heat (energy) or electrical charge (coulombs) |
Qm |
mass discharge rate (mass/time) |
instantaneous mass release (mass) |
|
Qv |
ventilation rate (volume/time) |
r |
radius (length) |
R |
electrical resistance (ohms) or reliability |
Sachs scaled distance, defined by Equation 6-31 (unitless) |
|
Rd |
release duration for heavy gas releases (time) |
rf |
vessel filling rate (time−1) |
Rg |
ideal gas constant (pressure volume/mole deg) |
Re |
Reynolds number (unitless) |
S |
entropy (energy/mole deg) or stress (force/area) |
Sm |
material strength (force/area) |
SPEGL |
short term public exposure guideline (see Section 5-5) |
t |
time |
td |
positive phase duration of a blast (time) |
te |
emptying time |
tp |
time to form a puff of vapor |
tv |
vessel wall thickness (length) |
tw |
worker shift time |
Δtv |
venting time for reactor relief |
T |
temperature (deg) |
Ti |
time interval |
TLV |
threshold limit value (ppm or mg/m3 by volume) |
Tm |
maximum temperature during reactor relief (deg) |
TMEF |
target mitigated event frequency (1/year) |
TQ |
threshold quantity (mass) |
Ts |
saturation temperature at set pressure during reactor relief (deg) |
TWA |
time weighted average (ppm or mg/m3 by volume) |
u |
velocity (length/time) |
ud |
dropout velocity of a particle (length/time) |
ū |
average velocity (length/time) |
〈u〉 |
mean or average velocity (length/time) |
U |
internal energy (energy/mole) or overall heat transfer coefficient |
UEL |
upper explosion limit (volume % fuel in air) |
UFL = UEL |
upper flammability limit (volume % fuel in air) |
UOL |
upper flammable limit in pure oxygen (volume % fuel in oxygen) |
v |
specific volume (volume/mass) |
vf |
specific volume of liquid (volume/mass) |
vg |
specific volume of vapor (volume/mass) |
vfg |
specific volume change with liquid vaporization (volume/mass) |
V |
total volume or electrical potential (volts) |
Vc |
container volume |
W |
width (length) |
We |
expansion work (energy) |
Ws |
shaft work (energy) |
x |
mole fraction or Cartesian coordinate (length), or reactor conversion (dimensionless), or distance from the source (length) |
Xf |
distance from flare at grade (length) |
y |
mole fraction of vapor (unitless) or Cartesian coordinate (length) |
Y |
probit variable (unitless) |
YG |
gas expansion factor (unitless) |
z |
height above datum (length) or Cartesian coordinate (length) or compressibility (unitless) |
ze |
scaled distance for explosions (length/mass1/3) |
Greek Letters
α |
velocity correction factor (unitless) or thermal diffusivity (area/time) |
β |
thermal expansion coefficient (deg−1) |
δ |
double layer thickness (length) |
ε |
pipe roughness (length) or emissivity (unitless) |
εr |
relative dielectric constant (unitless) |
ε0 |
permittivity constant for free space (charge2/force length2) |
η |
explosion efficiency (unitless) |
Φ |
nonideal filling factor (unitless), or phi-factor for calorimeter thermal inertia (dimensionless) |
γ |
heat capacity ratio (unitless) |
γc |
conductivity (mho/cm) |
Γ |
dimensionless activation energy |
χ |
function defined by Equation 10-10 |
λ |
frequency of dangerous episodes |
λd |
average frequency of dangerous episodes |
μ |
viscosity (mass/length/time), or mean value, or failure rate (faults/time) |
μV |
vapor viscosity (mass/length/time) |
ψ |
overall discharge coefficient used in Equation 10-14 (unitless) |
ρ |
density (mass/volume) |
ρL |
liquid density (mass/volume) |
ρref |
reference density for specific gravity (mass/volume) |
ρV |
vapor density (mass/volume) |
σ |
standard deviation (unitless) |
σx, σy, σz |
dispersion coefficient (length) |
τ |
relaxation time, or dimensionless reaction time |
τi |
inspection period for unrevealed failures |
τ0 |
operation period for a process component |
τr |
period required to repair a component |
τu |
period of unavailability for unrevealed failures |
ζ |
zeta potential (volts) |
Subscripts
a |
ambient |
ad |
adiabatic |
c |
combustion |
f |
formation or liquid |
g |
vapor or gas |
H |
higher pressure |
i |
initiating event |
j |
purges |
L |
lower pressure |
m |
maximum |
s |
set pressure |
o |
initial or reference |
Superscripts
° |
standard |
′ |
stochastic or random variable |