Source Models Flashcards
Most incidents in chemical plants result in spills of?
Toxic, Flammable, and explosive materials
Typical incidents might include?
- Rupture or breakage of a pipeline
- A hole in a tank or pipe
- Runaway reaction
- Fire external to the vessel
Once the incident is known, _______ are selected to describe how the hazardous materials were discharged from the process
Source models
Is usually done as part of Quantitative Risk
Analysis (QRA) in the design phase to define the limits of the
design envelope and to ensure that the resulting engineering
design to mitigate or remove the hazard is overdesigned.
Source Modelling
Source Modelling is usually done as part of __ in the ____-
Quantitative Risk Analysis, Design phase
The resulting engineering design to mitigate or remove the hazard is _____
overdesigned
Describes the physical and chemical processes occurring during the release of a material
Hazardous material event model
A release could be?
- Outflow from a vessel
- evaporation from a liquid pool
Source models provide?
description of the rate of discharge,
total quantity discharged,
total time of discharge and
state of discharge
Characterized by the amount of material released
Strength of a source
What governs source strength?
Physical state of material
Containment pressure
Temperature
A release may be:
Continuous
Instantaneous
Source strength is total mass released (kg)
instantaneous
Source strength is rate of mass released (kg/s)
Continuous
Constructed from fundamental/empirical equation representing the physiochemical process occurring during release of materials
Source models
Only can be applied once the incident has been identified
Source models
Technical information needed:
Rate of discharge
total quantity discharged
State of discharge
Other Types of Hazardous Material Event Models
- Dispersion Model
- Fire & Explosion Model
- Effect Model
To describe how the material is transported downwind and dispersed to some concentration levels
Dispersion Model
To convert the source model information into energy hazard potentials
Fire & Explosion model
Example of Energy hazard potential
Thermal radiation
Explosion overpressure
Evaluate potential loss/damage on people, properties and environment
Effect model
Mode of Release (2)
Wide aperture release
Limited aperture release
Releasing a substantial amount of material in a short time
Wide aperture release
Large hole developing in process unit
Wide aperture Release
Examples of WAR
Overpressure explosion, explosion of a storage tank
Slow release of material that causing non-immediate effect to upstream
Limited Aperture Release
Examples of LAR
Leaks in flanges, valves and pumps
Ruptured Pipes, cracks, relief systems
Number of possible release points from a chemical vessel
Relief valve
Hole
Crack
Valve
Severed or Rupture Pipe
Pump Seal
Flange
Pipe Connection
Types of Release
Gas/Vapor Leak
Vapor or Two-Phase Vapor/Liquid Leak
Liquid or Liquid Flashing into Vapor
Influences type of release
Physical State of a material
Source models describing a material release:
- Flow of Liquid through a hole
- Flow of liquid through a hole in a tank
- Flow of Liquid through Pipes
- Liquids Flashing
- Liquid pool evaporation or boiling
- Flow of gases/vapor through holes from vessels or pipes
A tank that develops a hole. Pressure of the liquid contained in the tank is converted into kinetic energy as it drains from the hole.
Liquid flow through a hole (Ambient Conditions)
Frictional forces of the liquid draining through the hole convert some of the kinetic energy to thermal energy
Liquid flow through a hole (Ambient Conditions)
Uses mechanical energy balance for the flow of incompressible liquids through pipes (density is constant)
Flow of liquid through pipes
Driving force for the movement of liquid across pipes
Pressure gradient
Friction forces between he liquid and the wall of the pipe convert?
Kinetic energy into thermal energy
Frictional forces results in a decrease in the liquid ______ and a decrease in the liquid ______
velocity and pressure
Normally occurs when a liquid stored under pressure above their normal boiling point experiences sudden ambient environment causing the liquid to flash into vapor sometimes explosively
Flashing
If the tank develops a leak, the liquid will?
Partially flash into vapor
The process is rapid and is assumed to be adiabatic
Partial flashing
Rate of evaporation from a pool depends on:
- liquid’s properties
- subsoil’s properties
A key note is if liquid is released into a?
contained pool or not
The pool height = volume spilled/cross sectional area of the containment structure
Contained pool
Release is not contained then it is called?
Freely spreading pool
US EPA Offsite Consequence Analysis Guide recommends a pool depth of ? for not contained pools
1 cm
The vapor above the pool is blown away by prevailing winds as a result of vapor diffusion
Evaporation from a pool for Non-boiling liquids
The amount of vapor removed through the process of evaporation from a pool (Non-boiling liquids) depends on:
Partial vapor pressure of the liquid
Prevailing wind velocity
area of the pool
Energy contained within the gas or vapor as a result of its pressure is converted into kinetic energy as the gas escapes and expands through the hole
Flow of Vapor though Holes
What do change as the gas or vapor exits through the leak?
Density, pressure and temperature
Is modeled using two special cases
Vapor flow through pipes
Vapor flow through pipes is modeled using two special cases:
Adiabatic and isothermal
Corresponds to rapid vapor flow through an insulated pipe
adiabatic case
Corresponds to flow through an uninsulated pipe maintained at a constant temperature
Isothermal case
Example of isothermal case
Underwater pipeline
