individual and societal risk

1. PRESENTED BY
SRUTHI P M
MTECH HSE
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2. INTRODUCION
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3.  Risk: The likelihood of a specific effect within a
specific period.
 There are two methods of risk determination
 Qualitative risk determination
 Quantitative risk determination
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4. QUANTITATIVE RISK DETERMINATION
 Risk indices are single numbers or tabulation of
numbers which are correlated to the magnitude of
risk.
 Some risk indices are relative values with no specific
units, which only have meaning within the context of
the risk index calculations.
 The main two risk sets are
 Individual risk
 Societal risk
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5. Individual risk(IRx,y): Probability of death per year of
exposure to an individual at a certain distance from the
hazardous source. It is usually expressed in the form of
iso-risk contours.
IR x,y =ΣIR (x,y,i)
IR (x,y,i)= Σfi*pfi
Pfi is obtained using probit equation. AlChe/CCPS is
used for converting probit equation to probability ie pfi
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6. Different probit functions used for calculation
The probit models are generally expressed as
Pr =k1+k2(ln V)
Probit equations are available for a variety of exposures,
including exposure to toxic materials, heat, pressure and
radiation,impact and sound.
P=a+bln cnt
Esignberg also provides a probit function for fatalities
due to direct effect of overpressure as follows.
Pr=-77+6.91(ln P0)
For first degree burn
Pr= -39.83+3.0186ln (q4/3t)
For lethality
Pr=-36.38+2.56 ln tq4/3
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8. Societal risk: Societal risk is a measure of risk to a
group of people. It is most often expressed in terms of
the frequency distribution of multiple casualty events.
(FN curve).
Number of people affected by all incident
outcome cases can be estimated using the following
equation
Ni=ΣP (x,y)*pfi
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10.  There are three cylinders in a factory. First cylinder is
filled with LPG in the horizontal cylinder. Second
cylinder is filled with cyclohexane in the vertical
cylinder. Third cylinder is filled with Benzene in the
vertical cylinder. The wind speed in the region is 4.1
m/s. The ambient temperature is 25˚C. Determine the
individual risk and societal risk.
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11.  Assume the values of frequencies of incident outcome
cases as
 BLEVE of LPG -8x10-4
 VCE of cyclohexane -6x10-5
 Pool fire of Benzene-2.67x10-4
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12. BLEVE of LPG
 For LPG,
Consider the case of lethality,
Pr=-36.38+2.56 ln tq4/3
Assume t= 82.58 sec. q=10800w/m2
Pr1 = -36.38+2.56 ln 82.58x(10800)4/3
=6.62
From the conversion table
Pf1= 0.95
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13. VCE of cyclohexane
 For cyclohexane,
Consider the case of 1st degree burning,
Pr2=-39.83+3.186ln tq4/3
q=4200 t=9.25
Pr2=-39.83+3.186ln 9.25x(4200)4/3
=2.7
pf2= .01
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14. Pool fire model of benzene
Pr= a+bln cnt
here a=-9.82 b=0.71 n=2
(from World Bank)
Assume c=1000ppm t=600 min.
Pr3=-9.82+0.71 ln(1000)2 x600
=4.53
pf3=0.32
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16. Individual risk
At A
IR x,y = f1*pf1+f2*pf2
=8x10-4x0.95+6x10-5x0.01
=7.606x10-4
At B
IR x,y = f1*pf1+f2*pf2+f3*pf3
=8x10-6x0.23+6x10-5x.01+2.67x10-4x0.32
=8.46x10-4
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17. At C
IR x,y = f1*pf1+f3*pf3
=8x10-4x0.95+2.67x10-4x0.32
=8.45x10-4
At D
IR x,y = f2*pf2+f3*pf3
=6x10-5x.01+2.67x10-4x0.32
=8.604x10-5
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18. Societal risk
Assume
P a=1000, P b= 2000, Pc=3000, Pd= 4000
N1=P a*pf1+P b*pf1+ Pc*pf1
=1000x0.95+2000x0.95+3000x0.95
=5700
N2=P a*pf2+P b*pf2+Pd*pf2
=1000x0.01+2000x0.01+4000*0.01
=70
N3=P b*pf3+Pc*pf3+Pd*pf3
=2000x0.32+3000x0.32+4000x0.32
=2880
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