Lecture 5 Flashcards
During an accident, process equipment can release _______ quickly and in significant enough quantities to spread in dangerous clouds throughout a plant site and the local community.
toxic materials
___ are routinely used to estimate the effects of a release on the plant and community environments.
Toxic release models
____ describe the airborne transport of toxic materials away from the accident site and into the plant and community.
Dispersion models
The maximum concentration of toxic material occurs at the ___ (which may not be at ground level)
release point
Parameters affecting atmospheric dispersion of toxic materials:
-wind speed,
-atmospheric stability,
-ground conditions (buildings, water, trees),
-height of the release above ground level,
-momentum and buoyancy of the initial material released.
__ estimate the concentrations downwind of a gas release that has mixed with fresh air to become neutrally buoyant.
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.
-is simply the release of continuous puffs.
-were originally developed for dispersion from a smoke stack.
Plume models
-describes the temporal concentration of material from a single release of a fixed amount of material.
-are used when you have essentially an instantaneous release and the cloud is swept downwind
-can used to describe a plume.
Puff models
applies only to neutrally buoyant dispersion of gases in which the turbulent mixing is the dominant feature of the dispersion. It is typically valid only for a distance of 0.1-10 km from the release point.
Pasquill-Gifford or Gaussian Dispersion Model
The model is best suited for instantaneous or continuous ground-level releases of dense gases. The release is assumed to occur at ambient temperature and without aerosol or liquid droplet formation.
Dense Gas Dispersion: Britter and McQuaid Model
is defined as any gas whose density is greater than the density of the ambient air through which it is being dispersed.
dense gas
is defined as “lessening the risk of a release incident by acting on the source (at the point of release) either
(1) in a preventive way by reducing the likelihood of an event that could generate a hazardous vapor cloud or (2) in a protective way by reducing the magnitude of the release and/or the exposure of local persons or property.”
Release mitigation
Inherent Safety
-Inventory reduction
-Chemical substitution
-Process attenuation
Engineering Design
-Physical integrity of seals and construction
-Process integrity
-Emergency control
-Spill containment
