TOXIC RELEASE AND DISPERSION Flashcards
TOXIC RELEASE AND DISPERSION
During an accident, _____can release _____ quickly and in significant enough quantities to spread in dangerous clouds throughout a plant site and the local community
Process equipment, toxic materials
Rupture of pressure vessel as a result of ?
excessive pressure caused by a runaway reaction
rupture of pipeline containing
toxic materials at a high pressure
rupture of a tank containing
toxic materials above its atmospheric boiling point
What serious accident emphasize the importance of planning emergencies and designing plants to minimize the occurrence and consequences of toxic release
Bhopal Tragedy
Are routinely used to estimate the effects of a release on the plant and community environments
Toxic release models
Why must chemical engineers understand all aspects of toxic release?
- To prevent the existence of release situations
- To reduce the impact of a release if one occurs
Understanding all aspects of toxic release of a ChE requires what?
Toxic release model
Describes the airborne transport of toxic materials away from the accident site and into the plant and community
Dispersion models
After a release of the airborne, toxic material is carried away by the wind in what characteristics?
Plume or Puff
Where does the maximum concentration of toxic material is located?
At the release point (may not be at ground level)
Concentrations downwind are ____ because of ______ and dispersion of the toxic substance with ____
less, turbulent mixing and air
What is the purpose of the toxic release model?
Provide a tool for performing release mitigation
Parameters affecting atmospheric dispersion of toxic materials: (5)
- Wind speed
- Atmospheric stability
- Ground conditions (buildings, water, trees )
- height of the release above ground level
- momentum and buoyancy of the initial material released
Are used to estimate the concentrations downwind of a release in which the gas is mixed with fresh air.
Neutrally Buoyant Dispersion Models
These models apply to gases at low concentrations, typically in ppm range
Neutrally Buoyant Dispersion Models
2 types of neutrally buoyant vapor cloud dispersion models
- Plume models
- Puff models
Describes the steady-state concentration of material released from a continuous source
Plume models
The release of a continuous puffs
Plume
Were originally developed for dispersion from a smoke stack
Plume models
Plume can develop when ?
There is a leak in a large tank
If there is a leak in a large tank what could develop?
Plume
Describes the temporal concentration of material from a single release of fixed amount of material
Puff model
Used when you have essentially an instantaneous release and the cloud is swept downwind
Puff model
Describe a plume
Puff model
Pasquill-Gifford or
Gaussian Dispersion Models
Guassian Dispersion Model or?
Pasquill-Gifford
Because of fluctuations and turbulence, _____ is constantly changing (PG Model)
Diffusivity
These equations don’t do a good job in predicting dispersion
Traditional transport phenomena equations
This assumes that the materials spread out in a normal Gaussian -type distribution
Pasquill-Gifford or Gaussian Dispersion Model
According to Pasquill-Gifford Model, as the plume is swept downwind, the concentration profile?
spreads out and decreases
This applies only to neutrally buoyant dispersion of gases in which turbulent mixing is the dominant featureof the dispersion
Pasquill-Gifford or Gaussian Dispersion Model
Pasquill-Gifford or Gaussian Dispersion Model is valid only for a distance of ? from the release point
0.1 to 1 km
Best suited for instantaneous or continuous ground-level releases of dense gases
Dense Gas Dispersion: Britter and McQuaid Model
In this model, the release is assumed to occur at ambient temperature and without aerosol or liquid droplet formation
Dense Gas Dispersion: Britter and McQuaid Model
Dense Gas Dispersion: Britter and McQuaid Model reuires specification of? (7)
Initial Cloud Volume
Initial Plume Volume Flux
Duration of release
Initial gas density
windspeed at a height of 10 m
distance downwind
ambient gas density
Any gas whose density is greater than the density of the ambient air though which it is being dispersed
dense gas
A gas with a molecular weight greater than that of air
dense gas
A gas with low temperature resulting from autorefrigeration during release
Dense gas
Lessening the risk of a release incident by acting on the source in a preventive and protective way
Release Mitigation
Reducing the likelihood of an event that could generate a hazardous vapor cloud
preventive way
reducing the magnitude of the release and/or exposure of local persons or property
Protective way
6 Release Mitigation
- Inherent Safety
- Engineering Design
- Management
- Early Vapor Detection
- Countermeasures
- Emergency response
Inventory reduction
chemical substitution
process attenuation
Inherent safety
Physical integrity of seals and construction
Process Integrity
Emergency Control
Spill containment
Engineering design
Policies and procedures
Training for vapor release
Audits and Inspections
Equipment testing
routine maintenance
management of change
Security
Management
Sensors
Personnel
Early vapor detection
Water sprays and curtains
steam or air curtains
deliberate ignition
foams
countermeasures
