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Consequence Analysis. Dr. AA Department of Chemical Engineering University Teknology Malaysia. Consequence Analysis. Determine the amount / rate of release Source modelling Model the dispersion Effect of Chemicals released Toxic Effect Fire Explosion Estimate Fatality : Probit

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Consequence Analysis

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consequence analysis

Consequence Analysis

Dr. AA

Department of Chemical Engineering

University Teknology Malaysia

consequence analysis1
Consequence Analysis
  • Determine the amount / rate of release
    • Source modelling
  • Model the dispersion
  • Effect of Chemicals released
    • Toxic Effect
    • Fire
    • Explosion
  • Estimate Fatality : Probit
  • Estimate injury / health effect
    • Heat Effect / Toxic Effect
  • Estimate Losses



estimation of fatality probit analysis1
Estimation of Fatality: Probit Analysis
  • The dose level of the various hazard events against fatality can be conveniently determined using Probit Analysis.
  • It is a graphical and Look-up Table approach to determine probability of fatality
probit analysis
Probit Analysis
  • The probit variable Y is computed from:

Y = k1 + k2 ln V

  • Values of constants k1, k2 and causative variable V (representing the dose) are given in table
  • Once the probit is obtained, it can be converted into % fatality
probit fire and explosion
Probit: Fire and Explosion

Here, te is the effective time duration (s), t is the time duration of pool burning (sec), Ie is the effective radiation intensity (W/m2), I is the radiation intensity from pool burning (W/m2), te is the effective time duration (s), po is peak overpressure (N/m2), J is impulse (Ns/m2), C is concentration (ppm) and T is time interval (min).

effect of thermal radiation on structures tno 1992
Effect of Thermal Radiation on Structures TNO, 1992

Damage Level 1 – Surfaces of exposed materials catch fire and structural elements collapse or rupture

Damage Level 2 - Surfaces of exposed experience serious decoloration as well as peeling and structural elements undergo substantial deformation

toxic effect criteria1
What Concentration are considered dangerous?

PEL, TLV etc designed for workers are overly conservative – designed for long-term exposure, not for short-term, emergency condition

Some guidelines

AIHA: ERPG - Emergency Response Planning Guideline


Nat Acad Sci : EEGL (emergency exposure guidance level) and SPGEL(short term public emergency guidane)

TLV, PEL etc

For design of ERP, the ERPG, SPEGL, EEGL are more directly relevant for general public

Toxic Effect Criteria
erpg see pp201 202 crowl louvar

Max airborne concentration below which it is believed nearly all individuals could be exposed for up to 1 hour without experiencing effect other than mild transient adverse health effect or perceiving a clearly defined objectionable odor.


… without experiencing or developing irreversible or other serious health effects or symptoms that could impair their ability to take protective action


… without experiencing or developing life threatening health effects (similar to EEGL)

Sometimes called TEEL

Example : Ammonia - ERPG 1,2,3 = 25,200,1000 ppm

ERPG (see pp201-202 Crowl & Louvar)
EEGL – Emergency Exposure Guidance Level

Defined as concentration of gas, vapour aerosol that is judged acceptable and that allows exposed individuals to perform specific tasks during emergency condition lasting from 1 to 24 hours.

National Research Council committee on Toxicology (USA) has submitted EEGL for 44 chemicals.

NERC also developed SPEGL (Shor term public emergency guidance)

Defined as acceptable concentration for exposure for members of general public

Generally SPGEL is 10-50% of EEGL


Concentration for acute toxicitymeasures for common industrial gas

Defined as a condition “ that poses a threat of exposure to airborne contaminants when that exposure is likely to cause death or immediate or delayed permanent adverse health effect or prevent escape from such an environment”.

Considered as a maximum concentration above which only a highly reliable breathing apparatus providing maximum protection is permitted.

toxic end point
EPA promulgamated a set of toxic end points to be used for air dispersion modeling for toxic gas releases as part of EPA RMP

Toxic end points follows (in order of preference)


LOC (level of concern) - the maximum concentration of an extremely hazardous substance in air that will not cause serious irreversible health effects in the general population when exposed to the substance for relatively short period.

Toxic End Point