Types of Risk Assessment
CEL899: Environmental Risk
Assessment
1st Semester 2012-13
Health-based risks
Basic Concepts of Environmental Risk and
Definitions
•
•
Dr. Arun Kumar
•
(arunku@civil.iitd.ac.in)
•
For humans
High chances of happening
with small consequences;
Chronic
(i.e.,
long-term
exposure) at low doses.
Chemical exposure or microbial
infection
Ecological risks
•
•
For aquatic species and
physical environment
Due to human interaction
or natural actions on
environment, such as oil
spills or hurricane
Department of Civil Engineering
Indian Institute of Technology Delhi, Hauz Khas (India)
August 16, 2012
Source, Medium, and Receptor
Source
•
Medium
Medium
Receptor
1.
2.
3.
•
•
•
•
Cyclic in nature as receptors also contribute to source and medium.
August 16, 2012
Water
Air
Soil
Food
•
•
•
Humans,
aquatic species,
Physical
environment
4.
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
3
• Background risk (Rbkgd):
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
4
Total Risk
• Total Risk (Rtotal):
– This is the risk what people are exposed to from a
given medium (such as water, air, soil, etc.)
• Incremental risk (Rincr):
– This is the risk due to addition of an external pollutant
in the medium or occurrence of any event (events
such as oil spill, contamination of water with poison,
release of carbon monoxide gas in a closed room)
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
Exposure Route
Water Ingestion route (say drinking of water)
Air Inhalation route (say breathing of air)
Soil Ingestion route (say eating of soil from hand or
from food, etc.
Food Ingestion route (say eating of leafy or root
vegetable and fruits)
Background, Incremental, and Total Risk
August 16, 2012
2
Medium -----
Exposure Route
Oil spill or any
other accident
Natural minerals
Industry
Humans
•
•
•
•
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
5
– This is the total risk a person or any receptor
is exposed from a given medium
– It represents both background and
incremental risk
Rtotal = Rbkgd + Rincr
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
(Eq. 2)
6
1
Acceptable Risk
Acceptable Risk-Notation
• Acceptable Risk (Racceptable):
– This is the allowable risk a particular contaminant can
result in on any receptor.
– It is used to compare if Rtotal is higher or smaller than
the Racceptable risk estimate.
– Calculate risk ratio (“r”) and compare it with 1.
r=
Risk ratio
•
•
August 16, 2012
– If exposed population (P) = 1000, it means that
excess risk is allowable for
= [(10-6)(person/person)]*(1000 person) = 1/1000 (i.e.,
0.001 additional cases of cancer )
(or 1 out of 1000 people are expected to have excess
cancer risk.)
Rtotal
(Eq. 3)
Racceptable
No concern ( r<1)
Concern (r>1)
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
• Say, acceptable risk over life time = 1 :10,00,000 (i.e.,
one in a million)
=> Out of one million exposed, the risk of getting a
particular effect in excess is acceptable for only one
person over a lifetime.
7
August 16, 2012
Problem 1
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
8
Problem 1: Solution
• In U.S. excess lifetime risk of getting a cancer is
1×10-6 (i.e., acceptable risk) and background risk
of getting a cancer is say 1×10-5 .
• (2) Calculation of risk ratio
r= (1.1×10-6)/ (1×10-6)
= 1.1 >1 (=> concern) (answer)
– Calculate total risk of getting a cancer?
– Calculate risk ratio?
Solution:
(1) Here, Incremental risk of getting a cancer = 1×10-6
Background risk of getting a cancer = 1×10-5
So, total risk of getting a cancer (using Eq. 2)
= (1×10-5) +( 1×10-6) = 10-6 (1+10) =1.1×10-5 (answer)
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
9
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
10
Problem 2: Solution
Problem 2
Demand
type
Ghat 1
Ghat2
Background
waterborne
risk
1:10,000 (i.e., 10-4)
1:10,000 (i.e., 10-4)
The WWTP discharges 103 virus particles/100 mL after Ghat
1 (which are pathogenic). Say, a person baths at Ghat 1
(upstream of a discharge point) and also baths at Ghat 2
(downstream of the discharge point). Background risk of
getting a waterborne disease = 1:10,000 (i.e., 10-4)
Incremental
waterborne
risk
0 (as WWTP discharge Say X (as WWTP discharge will
can not influence the affect downstream water quality)
upstream
water Here, X >0 (i.e., positive)
quality)
Total
waterborne
risk
=Background risk
incremental risk
=10-4+0 =10-4
Which ghat can pose higher total risk to a person?
Comment
Here, Ghat 2 will pose higher risk than Ghat 1 as Ghat
2 water quality is affected by WWTP discharge.
WWTP discharge (wastewater effluent discharge)
River “AA”
Ghat 1
August 16, 2012
Ghat 2
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
11
August 16, 2012
+ =Background risk + incremental
risk
=10-4+X =X+10-4
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
12
2
Overall risk ratio for environment is given by:
Risk Estimation for Environment with Different Receptors
Say our environment consists of humans, aquatic life, and
physical environment (say river) and we want to do
environmental risk assessment. We need to develop risk
ratio for all three receptor types and then use them together
to come up with overall environmental risk ratio estimate.
Receptor type
Total Risk
Acceptable Risk
Risk
ratio
Humans
Risktotal,H
Riskacceptable,H
rH
Aquatic life
Risktotal,aq
Riskacceptable,aq
raq
Physical
environment
(say for river)
Risktotal,river
Riskacceptable,river
Rriver
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
Nr
renvt =
Renvt
∑w r = w r + w r
i i
i =1
Risk ratio for environment
11
2 2
+ ...
(Eq. 4)
wi
Importance weights for different receptors (say wH for humans, waq for
aquatic species)
ri
Risk ratio for different receptors (say rH for humans, raq for aquatic species)
Nr
Total number of receptors
If renvt < 1 => no concern
If renvt > 1 => concern.
13
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
14
Slope Factors (For carcinogens, i.e., substance
which can cause cancer)
Overall risk ratio for environment with three receptors=>
Slope Factor = Response/Dose
Receptor type
Risk ratio
Weightage
Risk ratio * weightage
Humans
rH
wH
rH * wH (say A)
Aquatic life
raq
waq
raq * waq (say B)
Physical
environment
for river)
rriver
wriver
rriver * wriver (say C)
Response
(or risk)
Dose (mg/d/kg body weight)
(say
•
Overall risk ratio renvt = A+B+C
for environment
•
•
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
Slope factor (SF) is also known as carcinogen potency factor.
– Depends on medium under consideration. So SF for say inhalation
exposure route can not be used for ingestion rate.
If renvt < 1 => no concern; and If renvt > 1 => concern
August 16, 2012
Say
= [0.001 risk / (mg/d/kg body weight)]
15
For example: chloroform is a carcinogen with slope factor (oral, i.e., for
ingestion route) = 6.1×10-3
Source: www.epa.gov/iris (Integrated Risk Information System)
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
16
Acceptable Daily Intake (For non-carcinogens,
i.e., substance which cannot cause cancer)
Reference Concentration (For noncarcinogens, i.e., substance which cannot
cause cancer)
• Acceptable daily intake
• This is denoted as RfC and it represents value for which no
effect is observed and a chemical concentration is within
safe limit (Source: www.epa.gov/iris).
• This can be used to calculate acceptable daily intake value
= Reference concentration in water (mg/L)*water
ingestion rate (L/day)
(Eq. 5a)
• Or Acceptable daily intake
= Reference concentration in air (mg/m3)*air inhalation rate (m3/day)
(Eq. 5b)
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
17
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
18
3
Stages of Risk Assessment
Stages of Risk Assessment
• Hazard Identification– Defining hazard and nature of harm
Hazard Identification
• Exposure assessmentDose-response
assessment
Exposure
assessment
– Determination of concentration in environment and estimation of
ingestion or inhalation rate of a contaminant
• Dose-response assessment-
Risk characterization
– Quantification of effect due to exposure of a particular contaminant.
A relationship between dose and response is used.
• Risk characterization– Estimating of the potential impact of a hazard based on the severity
of its effects and the amount of exposure.
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
19
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
20
Hazard Identification
CEL 899- Environmental Risk
Assessment
• Hazard– A descriptive term;
– Refers to intrinsic capability of the waste or a contaminant to cause
harm and it is a source of risk.
• Depends on
– Toxicity,
– Mobility and persistence in medium under consideration
– For example: Arsenic can cause greater chances of excess cancer
from ingestion route than from inhalation route.
Hazard Identification
Dr. Arun Kumar
arunku@civil.iitd.ac.in
• A waste or contaminant is not harmful or causes
no risk unless the exposure is occurred through a
medium.
Department of Civil Engineering
Indian Institute of Technology Delhi, Hauz Khas (India)
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
22
Data Needs during Hazard Identification Process
Hazard Identification
• This process examines the data for all contaminants
detected at a site and consolidates the date to determine
chemicals-of-concern (or pathogens-of-concern).
• This process helps in knowing spatial and temporal
distribution of concentration over space.
1. History of the contaminated site or medium
2. Land use of the medium
3. Contamination levels in media (air, groundwater, surface
water, soilds and sediments)
4. Environmental characteristics affecting fate and transport
of chemicals and microorganisms
–
Geologic, hydrologic, atmospheric, topographic, etc.
5. Potentially affected receptor (humans, aquatic species,
physical environment)
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
23
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
24
4
Data Needs during Hazard Identification Process
6. Data from short-term tests in living organisms
Grouping of animal and human data into different
groups:
7. Data from long-term animal studies
1.
2.
3.
4.
5.
8. Data from human studies
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
25
EPA Categories for Carcinogenic Groups
D
No
classification
E
No
evidence
B2
No evidence
in humans
C
Possible
carcinogen
Case: Carcinogenicity
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
26
Initial Screening Procedure-Steps
1. Sort the contaminant data by medium (say groundwater,
soil, surface water) for different types of contaminants
B
Probable
carcinogen
B1
Linked
human data
Sufficient evidence of carcinogenicity
Limited evidence of carcinogenicity
Inadequate evidence
No data available
No evidence of carcinogenicity
A
Human
carcinogen
2. Tabulate mean and range of concentration values for all
contaminants observed at the site
3. Identify the reference concentration (for noncarcinogens); slope factor (for carcinogens) for each
potential exposure route, and
4. Calculate toxicity score for each contaminant in each
medium.
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
27
Formula for calculating toxicity scores for
chemicals
For carcinogens
TS = C max × SF
(1a)
(1b)
Toxicity score
Cmax
Maximum concentration of a chemical
RfC
Reference concentration (chronic, i.e., for long-term exposure) (only for
non-carcinogens) (source: www.epa.gov/iris/)
SF
Slope factor (or carcinogenic potency factor) (only for carcinogens)
(source: www.epa.gov/iris/)
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
28
Following chemicals are found from a contaminated site.
Rank these chemicals from high to low using toxicity as
a criterion (for a oral ingestion route).
TS
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
Class Problem 1-Noncarcinogenic Chemicals
For non-carcinogens
C
TS = max
RfC
August 16, 2012
29
Chemical
Cmax
(mg/kg)
Oral RfC Calculated toxicity score
(mg/kg)
(using Eq. 1a on Slide 9)
Chlorobenzene
6.4
2×10-2
=6.4/ [2×10-2]
=320
Chloroform
4.1
1×10-2
=4.1/ [1×10-2]
=410
1,2Dichloroethane
Not
detected
at site
Not
applicable
Not applicable
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
30
5
Class Problem 1 contd.
Class Problem 1-Carcinogenic Chemicals
Total toxicity score = sum of all individual toxicity scores (eq. 2)
Chemical
Calculated toxicity
score (using Eq. 1)
(from Slide 9)
Ratio (toxicity
score/Total toxicity
score)
Chlorobenzene
=6.4/ [2×10-2]
=320
=[3.2×102]/[7.3×102]
=0.4384(rank 2)
Chloroform
=4.1/ [1×10-2]
=410
=[4.1×102]/[7.3×102]
=0.5616 (rank 1)
Not applicable
Not applicable
1,2-Dichloroethane
=(3.2×102)+(4.1×102)
=(7.3×102) (from Eq. 2)
Total toxicity score
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
31
Class Problem 1 contd.-Carcinogenic Chemicals
Following chemicals are found from a contaminated site.
Rank these chemicals from high to low using toxicity as
a criterion (for a oral ingestion route).
Chemical
Cmax
(mg/kg)
Oral SF [1/(mg/kg)]
Chlorobenzene
6.4
Not applicable (not a Not applicable
carcinogen)
Chloroform
4.1
6.1×10-3
1,2Dichloroethane
Not
9.1 ×10-2
detected
at site
August 16, 2012
Calculated
toxicity
score (using Eq. 1b
on slide 9)
=4.1* [6.1×10-3]
=2.5×10-2
Not applicable
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
32
Calculated Toxicity Score-Chloroform
Total toxicity score = sum of all individual toxicity scores
Chemical
Chlorobenzene
Chloroform
1,2-Dichloroethane
Total toxicity score
August 16, 2012
Calculated
toxicity score
(using Eq. 1b on
Slide 9)
Ratio (toxicity score/Total
toxicity score)
Not applicable
Not applicable
2.5×10-2
=[2.5×10-2]/[2.5×10-2]
=1.00 (rank 1)
Not applicable
Not applicable
33
Screening for microorganisms
Campylobacter jejuni
E.coli O157:H7
Salmonella spp.
Shigella spp. (B4 and
A21 strains
pooled)
Vibrio cholerae
August 16, 2012
Dose-response ratio
(alpha/beta)
References
0.0191
Haas et al. (1999); Teunis et
al.(1996)
×
1.781×10
4.899×10
2.5×10-2
August 16, 2012
Dose-response ratio
(alpha/beta)
Rank based on doseresponse ratio (from
high to low value)
Campylobacter jejuni
0.0191
1 (highest concern)
Salmonella spp.
Haas et al. (1999)
-5
Haas et al. (1999)
-3
Haas et al. (1999); Soller et
al. (2004)
×
1.76 10-9
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
34
Pathogen
E.coli O157:H7
0.099 10-6
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
Screening for microorganisms-Contd….
Rank microorganisms based on “dose-response ratio”
parameter from low to high
Pathogen
As a carcinogen
4.1×102
Here, chloroform acts as both carcinogen as well as noncarcinogens.
⇒There are two values for toxicity scores.
⇒For ranking chloroform, use high toxicity score value to
include both aspects of chloroform.
=(2.5×10-2)
=(2.5×10-2) (using Eq. 2 on slide 11)
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
As a non-carcinogen
Shigella spp. (B4 and
A21 strains
pooled)
Vibrio cholerae
Teunis et al.(1996)
35
August 16, 2012
×
1.781×10
(=0.000018)
4.899×10
10-6
0.099
(=0.000000)
4 (lowest concern)
-5
3
-3
2
(=0.004899)
×
1.76 10-9
(=0.00000) (approx.)
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
4 (lowest concern)
36
6
So many contaminants…how to handle all of
them
From overall pool of contaminants to pool of
priority contaminants
Overall pool of
all contaminants
Pool of screened
contaminants
Pool of screened
contaminants
Overall pool of all
contaminants
N3
Pool of priority
contaminants
Number of contaminants reduces due to use of multiple
sequential criteria------
>
Pool of priority
(selected)
contaminants
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
37
August 16, 2012
Use of Surrogate chemicals or Indicator
Microorganisms during Hazard Identification
Process
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
38
CEL 899- Environmental Risk
Assessment
1. Surrogate chemicals or indicator microorganisms
•
Used to characterize different chemicals and microorganisms
2. Criteria for selection:
•
•
•
Environmental Risk Zonation
It should be most toxic persistent and mobile
The most prevalent in terms of spatial distribution and
concentration
Those involved in the more significant exposures
Dr. Arun Kumar
arunku@civil.iitd.ac.in
Department of Civil Engineering
Indian Institute of Technology Delhi, Hauz Khas (India)
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
39
Class Problem 1Risk = Severity * Probability (loss)
Risk
• Risk is a function of severity and probability of
loss due to happening of an event or en exposure.
Calculate risk estimates for following activities:
Table 1
Activity
• Risk = Severity * Probability of loss
• = (S)*(P)=K
Severity of outcome
(worker-days lost)
Probability of
outcome
Risk
(=worker-days lost)=K
A
20
0.1
=20*0.1=2.0 (K1)
B
10
0.2
=10*0.2=2.0 (K2)
C
30
0.3
=30*0.3=9 (K3)
Here, K1= K2 < K3
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
41
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
42
7
Severity versus Probability (i.e., “Risk Plane”)
Risk=Severity * Probability = Say K
Figure 1
Severity (S)
Region
2
Region
3
Increasing
K values
(K1 < K2<K3)
Region
4
K3 = Risk3
Region 1
K1 = Risk1
Never
High
• See that K1 < K2<K3
Probability of happening the severity (P)
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
43
• As we go up from K1 to K3, risk value
increases (as indicated by the direction of
arrow in Fig. 1)
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
44
• Region 4:
– The region with high risk value and have all
those combinations of “S” and “P” which can
result in high risk value (See upper right corner
of the Fig. 1)
– “Not acceptable region”
45
• Region 3:
– The region with medium risk value (K2>K1 and
K2< K3) and have all those combinations of “S”
and “P” which can result in medium risk value
(See this region between regions 2 and 4 in
Fig. 1)
– “Provisionally acceptable region”
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
46
• Risk evaluation:
– For worst case credible case; not for worst conceivable
case
– Otherwise it might not represent the worst case (i.e.,
sensitive sub-population, say children, elderly, and
pregnant women)
• Risk plane
• Region 2:
– The region with medium risk value, higher than
that in Region 1
– “Acceptable region”
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
– The region with small risk value and have all
those combinations of “S” and “P” which can
result in small risk value (see lower left corner
of the Fig.1.)
– “Safe region”
1 (below K1 line)
2 (between K1 and K2)
3 (between K2 and K3)
4 (above K3 line)
August 16, 2012
August 16, 2012
• Region 1:
• See fours regions:
– Region
– Region
– Region
– Region
– When severity is high, probability of happening that
effect is low (i.e., happens only for the extreme case)
– The “Never” value of P happens only for asymptotically
high value of “S”
– The “High” value of P can happen for very small value
of “S”
– Both of these cases are examples of “Extreme events”
• Lines with constant “R” or “K” values are called
“Iso-risk” line (i.e., line with equal risk at every
point (S, P) of this line.)
K2 = Risk2
Line with equal
“K” values
• The general trend:
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
47
– Generally used for illustration purposes and also for
policy making (i.e., for developing guidelines,
convention, and acceptable limits for risk assessment)
– For conducting “Preliminary Hazard Analysis”
– For developing “Risk Assessment Matrix”
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
48
8
Development of Risk Assessment Matrix
Step 2: Develop “Risk Plane” into matrix of different cells (i.e.,
zoning) (the matrix = “Risk Assessment Matrix”)
Step 1: Subjective classification of severity and
probability for different targets (our case: humans)
Subjective levels
Severity
Negligible < marginal <critical <catastrophic
Probability
Impossible <improbable< remote< occasional<probable
<frequent
Probability levels are defined for certain exposure levels
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
49
Guidelines
1. Don’t make too many cells.
2. Limit risk zoning to desirable categories of risk
resolution
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
50
Risk Assessment Matrix
Table 2
Severity
of
consequence
Probability of mishap
F
(Impossible )
E
(Improbable
)
D
(Remote)
C
(Occasional)
B
(Probable)
A
(Frequent)
I
(Catastrophic)
II( Critical)
III (Marginal)
IV (Negligible)
Zone 1: “Avoided”
Zone 2: “Accepted by waiver”
Zone 3: “Routinely accepted”
4(severity levels)* 6 (probability levels)
=>24 cells are optimum without much confusion
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
51
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
52
• In Table 2=>
• See different classes of probability of mishap from
“F” to “A” (i.e., 6 levels)
– Here, probability of mishap increases as we go towards
level “A”
• See different extents of severity of consequence
from level “I” to “IV” (i.e., 4 levels)
– Here, severity of loss increases as we go towards level
“I”
• Now, we have a risk matrix (i.e., Table 2) with 24
cells showing different combinations of “S” and
“P” levels.
– Known as “Risk Assessment Matrix with 24 cells”
• Here, we used “Risk Plane” (Figure 1 from Slide
#4) and divided into different levels of “S” and “P”,
and thus we created a risk assessment matrix.
– This is called “Zoning of the risk plane”.
• So we have 6*4= 24 cells and total of 24
combinations resulting in 24 risk values.
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
53
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
54
9
•In Table 2=>
Advantages and Limitations of Risk Assessment Matrix
•Black colour region “Zone 1”
•=> Imperative to take action to reduce risk levels
•Grey colour region “Zone 2”
• => Operation requires written communication for
limited time exposure by management
•White colour region “Zone 3”
•=> Operation permissible and no significant risk
Transition from Zone 1 -> Zone 2-> Zone 3
(don’t jump from Zone 1 to Zone 3)
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
55
•Advantages
•A good tool for representing interrelationship of severity
and probability of happening the severity
•Avoids unknowingly selecting intolerable and senseless
risk
•Helps in making operation-based decisions for optimum
use of resources
•Limitations
•It does not help in identifying hazard.
•It can be used only for comparative purposes. It can not
be used for risk quantification, unless data is available.
August 16, 2012
(C) Dr. Arun Kumar, Civil Engg. IIT
Delhi (India)
56
10