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## Nomenclature

### Greek Letters

### Subscripts

### Superscripts

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a | velocity of sound (length/time) |

A | area (length^{2}) or Helmholtz free energy (energy/mole); or process component availability; or arrhenius reaction rate pre-exponential constant (time^{–1}) |

A_{t} | tank cross sectional area (length^{2}) |

ΔA | change in Helmoltz free energy (energy/mole) |

B | adiabatic reactor temperature increase (dimensionless) |

C | mass concentration (mass/volume) or capacitance (Farads) |

C_{0} | discharge coefficient (unitless), or concentration at the source (mass/volume) |

C_{1} | concentration at a specified time (mass/volume) |

C_{m} | concentration of dense gas (volume fraction) |

C_{p} | heat capacity at constant pressure (energy/mass deg) |

C_{ppm} | concentration in parts per million by volume |

C_{v} | heat capacity at constant volume (energy/mass deg) |

C_{vent} | deflagration vent constant (pressure^{1/2}) |

C_{x} | concentration at location x downwind from the source (mass/volume) |

<C> | average or mean mass concentration (mass/volume) |

d | diameter (length) |

d_{p} | particle diameter (length) |

d_{f} | diameter of flare stack (length) |

D | diffusion coefficient (area/time) |

D_{c} | characteristic source dimension for continuous releases of dense gases (length) |

D_{i} | characteristic source dimension for instantaneous releases of dense gas (length) |

D_{0} | reference diffusion coefficient (area/time) |

D_{m} | molecular diffusivity (area/time) |

D_{tid} | total integrated dose due to a passing puff of vapor (mass time/volume) |

E_{a} | activation energy (energy/mole) |

ERPG | emergency response planning guideline (see Table 5-6) |

EEGL | emergency exposure guidance levels (see Section 5.5) |

f | Fanning friction factor (unitless) or frequency (1/time) |

f(t) | failure density function |

f_{v} | mass fraction of vapor (unitless) |

F | frictional fluid flow loss term (energy mass) or force or environment factor |

FAR | fatal accident rate (fatalities/10^{8} hours) |

FEV | forced expired volume (liters/sec) |

FVC | forced vital capacity (liters) |

g | gravitational acceleration (length/time^{2}) |

g_{c} | gravitational constant (mass length/force time^{2}) |

g_{o} | initial cloud buoyancy factor (length/time^{2}) |

g_{x} | buoyancy factor at location x (length/time^{2}) |

G | Gibbs free energy (energy/mole) or mass flux (mass/area time) |

G_{T} | mass flux during relief (mass/area time) |

ΔG | change in Gibbs free energy (energy/mole) |

h | specific enthalpy (energy/mass) |

h_{L} | fluid level above leak in tank (length) |

h^{0}_{L} | initial fluid level above leak in tank (length) |

h_{s} | leak height above ground level (length) |

H | enthalpy (energy/mole) or height (length) |

H_{f} | flare height (length) |

H_{r} | effective release height in plume model (length) |

ΔH | change in enthalpy (energy/mole) |

ΔH_{c} | heat of combustion (energy/mass) |

ΔH_{r} | release height correction given by Equation 5-65 |

ΔH_{v} | 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) |

I_{0} | reference sound intensity (decibels) |

I_{s} | 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 (concentration^{1-m}/time) |

k_{1}, k_{2} | constants in probit a equations |

k_{s} | thermal conductivity of soil (energy/length time deg) |

K | mass transfer coefficient (length/time) |

K_{b} | backpressure correction for relief sizing (unitless) |

K_{f} | excess head loss for fluid flow (dimensionless) |

K_{i}, K_{∞} | constants in excess head loss, given by Equation 4-38 |

K_{G} | explosion constant for vapors (length pressure/time) |

K_{j} | eddy diffusivity in x, y or z direction (area/time) |

K_{p} | overpressure correction for relief sizing (unitless) |

K_{St} | explosion constant for dusts (length pressure/time) |

K_{V} | viscosity correction for relief sizing (unitless) |

K_{0} | reference mass transfer coefficient (length/time) |

K* | constant eddy diffusivity (area/time) |

L | length |

LEL | lower explosion limit (volume %) |

LFL = LEL | lower flammability limit (volume %) |

LOC | limiting oxygen concentration (volume percent oxygen) |

LOL | lower flammable limit in pure oxygen (volume %) |

m | mass |

m_{f} | mass fraction |

m_{0} | total mass contained in reactor vessel (mass) |

m_{LR} | mass of limiting reactant in Equation (8-34) (mass) |

m_{T} | total mass of reacting mixture in Equation (8-34) (mass) |

m_{TNT} | mass of TNT |

m_{v} | mass of vapor |

M | molecular weight (mass/mole) |

M_{0} | 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) |

p_{d} | number of dangerous process episodes |

p_{s} | scaled overpressure for explosions (unitless) |

P | total pressure or probability |

P_{b} | backpressure for relief sizing (psig) |

PEL | permissable exposure level (see Section 2.8) |

PFD | probability of failure on demand |

P_{g} | gauge pressure (force/area) |

P_{max} | maximum pressure for relief sizing (psig) |

P_{s} | set pressure for relief sizing (psig) |

P^{sat} | saturation vapor pressure |

q | heat (energy/mass) or heat intensity (energy/area time) |

q_{f} | heat intensity of flare (energy/time area) |

q_{g} | heat flux from ground (energy/area time) |

q_{s} | specific energy release rate at set pressure during reactor relief (energy/mass) |

Q | heat (energy) or electrical charge (coulombs) |

Q_{m} | mass discharge rate (mass/time) |

instantaneous mass release (mass) | |

Q_{v} | ventilation rate (volume/time) |

r | radius (length) |

R | electrical resistance (ohms) or reliability |

Sachs scaled distance, defined by Equation 6-29 (unitless) | |

R_{d} | release duration for heavy gas releases (time) |

RHI | reaction hazard index defined by Equation 14-1 |

r_{f} | vessel filling rate (time^{–1}) |

R_{g} | ideal gas constant (pressure volume/mole deg) |

Re | Reynolds number (unitless) |

S | entropy (energy/mole deg) or stress (force/area) |

S_{m} | material strength (force/area) |

SPEGL | short term public exposure guideline (see Section 5.5) |

t | time |

t_{d} | positive phase duration of a blast (time) |

t_{e} | emptying time |

t_{p} | time to form a puff of vapor |

t_{v} | vessel wall thickness (length) |

t_{w} | worker shift time |

Δt_{v} | venting time for reactor relief |

T | temperature (deg) |

T_{d} | material decomposition temperature (deg) |

T_{i} | time interval |

TLV | threshold limit value (ppm or mg/m^{3} by volume) |

T_{m} | maximum temperature during reactor relief (deg) |

T_{s} | saturation temperature at set pressure during reactor relief (deg) |

TWA | time weighted average (ppm or mg/m^{3} by volume) |

TXD | toxic dispersion method (see Section 5.5) |

u | velocity (length/time) |

u_{d} | dropout velocity of a particle (length/time) |

average velocity (length/time) | |

<u> | mean or average velocity (length/time) |

U | internal energy (energy/mole) or overall heat transfer coefficient (energy/area deg time) or process component unavailability |

UEL | upper explosion limit (volume %) |

UFL = UEL | upper flammability limit (volume %) |

UOL | upper flammable limit in pure oxygen (volume %) |

v | specific volume (volume/mass) |

v_{f} | specific volume of liquid (volume/mass) |

v_{g} | specific volume of vapor (volume/mass) |

v_{fg} | specific volume change with liquid vaporization (volume/mass) |

V | total volume or electrical potential (volts) |

V_{c} | container volume |

W | width (length) |

W_{e} | expansion work (energy) |

W_{s} | shaft work (energy) |

x | mole fraction or Cartesian coordinate (length), or reactor conversion (dimensionless), or distance from the source (length) |

x_{t} | is the distance from the source to the transition (length), |

x_{v} | is the virtual distance (length), and |

x_{nb} | is the distance used in the neutrally buoyant model to compute the concentration downwind of the transition. (length) |

X_{f} | distance from flare at grade (length) |

y | mole fraction of vapor (unitless) or Cartesian coordinate (length) |

Y | probit variable (unitless) |

Y_{G} | gas expansion factor (unitless) |

z | height above datum (length) or Cartesian coordinate (length) or compressibility (unitless) |

z_{e} | scaled distance for explosions (length/mass^{1/3}) |

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) |

ε_{r} | relative dielectric constant (unitless) |

ε_{0} | permittivity constant for free space (charge^{2}/force length^{2}) |

η | explosion efficiency (unitless) |

Φ | nonideal filling factor (unitless), or phi-factor for calorimeter thermal inertia (dimensionless) |

γ | heat capacity ratio (unitless) |

γ_{c} | conductivity (mho/cm) |

Γ | dimensionless activation energy |

χ | function defined by Equation 9-10 |

λ | frequency of dangerous episodes |

λ_{d} | average frequency of dangerous episodes |

μ | viscosity (mass/length/time) or mean value or failure rate (faults/time) |

μ_{V} | vapor viscosity (mass/length/time) |

Ψ | overall discharge coefficient used in Equation 10-15 (unitless) |

ρ | density (mass/volume) |

ρ_{L} | liquid density (mass/volume) |

ρ_{ref} | reference density for specific gravity (mass/volume) |

ρ_{V} | vapor density (mass/volume) |

ρ_{x} | density at distance x downwind from source (mass/volume) |

σ | standard deviation (unitless) |

σ_{x}, σ_{y}, σ_{z} | dispersion coefficient (length) |

τ | relaxation time, or dimensionless reaction time |

τ_{i} | inspection period for unrevealed failures |

τ_{0} | operation period for a process component |

τ_{r} | period required to repair a component |

τ_{u} | period of unavailability for unrevealed failures |

ζ | zeta potential (volts) |

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 |

° | standard |

′ | stochastic or random variable |