iDRM Home » Key Concepts » iDRM Training Modules » 12 - Consequence Analysis  · 

Module 12: Consequence Analysis: Points to be taken

This module was prepared by the Disaster Management Institute Bhopal in cooperation with the Indo-German bilateral cooperation - InWEnt Capacity Building International and GTZ-ASEM.


Download the brochure of module 12 - Consequence Analysis: Points to be taken
Consequence analysis of the released hazardous chemicals into the environment is one of the vital parts of the overall emergency management. The module tries to highlight the important consideration for consequence modelling and insists that consequence analysis should be done by considering all possible variables, as one variable may change the impact zones.
[More]

 

This module is mainly targeted to:


Content

1 Introduction
2 Worst-case release scenarios
       2.1 Definition
       2.2 Worst-case releases of toxic substances
       2.3 Worst-case releases of Flammable substances
3 Alternative-case release scenarios
       3.1 Number of release scenario
       3.2 Mitigation systems for alternative release scenarios
       3.3 Alternative releases of toxic substances
       3.4 Alternative releases of flammable substances
4 Estimating off-site receptors
5 Conclusion


Glossary

AEGL:

Acute Exposure Guideline Levels (AEGLs) are Toxic Levels of Concern (LOCs) is used to predict the area where a toxic gas concentration might be high enough to harm people. The AEGLs are under development by the National Research Council's National Advisory Committee on AEGLs of USA. AEGLs take into account sensitive individuals and are meant to protect nearly all people. As of October 2005, the final AEGL values for more than 20 chemicals have been released, interim AEGL values for more than 60 additional chemicals have also been established, and proposed AEGL values for more chemicals are under review. The committee's objective is to define AEGLs for the 300+ extremely hazardous substances. The guidelines define three-tiered AEGLs as follows:

 

AEGL-1: The airborne concentration of a substance above which it is predicted that the general population, including susceptible individuals, could experience notable discomfort, irritation, or certain asymptomatic non-sensory effects. However, the effects are not disabling and are transient and reversible upon cessation of exposure.

 

AEGL-2: The airborne concentration of a substance above which it is predicted that the general population, including susceptible individuals, could experience irreversible or other serious, longlasting adverse health effects or an impaired ability to escape.

 

AEGL-3: The airborne concentration of a substance above which it is predicted that the general population, including susceptible individuals, could experience life-threatening health effects or death.

Cloud cover:

Cloud cover, the proportion of the sky that is covered by clouds, in order to estimate the amount of incoming solar radiation at the time of a chemical release. Solar radiation is an important influence on puddle evaporation rate because heat from the sun can warm a puddle and speed up evaporation.

ERPG:

The Emergency Response Planning Guidelines (ERPGs) are Toxic Levels of Concern (LOCs) that you can use in ALOHA to predict the area where a toxic gas concentration might be high enough to harm people. The ERPGs were developed by the ERPG committee of the American Industrial Hygiene Association. The ERPGs were developed as planning guidelines, to anticipate human adverse health effects caused by exposure to toxic chemicals. The ERPGs are three-tiered guidelines with one common denominator: a 1-hour contact duration. Each guideline identifies the substance, its chemical and structural properties, animal toxicology data, human experience, existing exposure guidelines, the rationale behind the selected value, and a list of references.

 

ERPG 1: The maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour without experiencing other than mild transient adverse health effects or perceiving a clearly defined, objectionable odour.

 

ERPG 2: The maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour without experiencing or developing irreversible or other serious health effects or symptoms which could impair an individual's ability to take protective action.

 

ERPG 3: The maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour without experiencing or developing life-threatening health effects.

Stability class:

Meteorologists have defined six atmospheric stability classes, each representing a different degree of turbulence in the atmosphere. When moderate to strong incoming solar radiation heats air near the ground, causing it to rise and generating large eddies, the atmosphere is considered unstable (relatively turbulent). Unstable conditions are associated with atmospheric stability classes A and B. When solar radiation is relatively weak or absent, air near the surface has a reduced tendency to rise and less turbulence develops. In this case, the atmosphere is considered stable (less turbulent), the wind is weak, and the stability class would be E or F. Stability classes D and C represent conditions of more neutral stability (moderately turbulent). Neutral conditions are associated with relatively strong wind speeds and moderate solar radiation.

Threat zone:

Threat zone represents the area within which the hazard level (toxicity, flammability thermal radiation, or overpressure) is predicted to exceed your Level of Concern (LOC) at some time after a release begins.


References

  1. Hazard Identification and Risk Analysis Code of Practice, BIS IS 15656: 2006, Bureau of Indian Standards.
  2. ALOHA software for consequence analysis developed by US EPA.
  3. Center for Process Safety of the American Institute of Chemical Engineers (AIChE). Guidelines for Evaluating the Characteristics of Vapor Cloud Explosions, Flash Fires, and BLEVEs. New York: AIChE, 1994.
  4. Center for Process Safety of the American Institute of Chemical Engineers (AIChE). Guidelines for Use of Vapor Cloud Dispersion Models, Second Ed. New York: AIChE, 1996.
  5. Center for Process Safety of the American Institute of Chemical Engineers (AIChE). International Conference and Workshop on Modeling and Mitigating the Consequences of Accidental Releases of Hazardous Materials, September 26-29, 1995. New York: AIChE, 1995.
  6. Technical background document for off-site consequence analysis for anhydrous aqueous ammonia, chlorine, and sulfur dioxide , Chemical emergency preparedness

 

 
Locations of visitors to this page