(IAQ)
What is Risk Assessment?
 Risk assessment: provides information on the health risk
 Characterizes the potential adverse health effects of human exposures to
environmental hazards
 Extent to which a group of people has been or may be exposed to a
certain chemical is determined
 Extent of exposure is then considered in relation to the kind and degree
of hazard posed by the chemical, thereby permitting an estimate to be
made of the present or potential health risk to the group of people
involved
 Risk management: is the action taken based on the risk
assessment
Purpose of Risk Assessment
 Characterizes the types of health effects expected
 Estimates the probability (risk) of occurrence of these
health effects
 Estimates the number of cases with these health
effects
 Provides an acceptable concentration of a toxicant in
air, water, or food
 Covers cancerous as well as non cancerous chemicals
Process of Risk Assessment
 Hazard identification : A determination is made as to whether human
exposure to the agent in question has the potential to increase the incidence
of cancer
 Dose-response assessment: A quantitative relationship is derived between
the dose, or more generally the human exposure, and the probability of
induction of a carcinogenic effect
 Exposure assessment: An evaluation is made of the human exposure to the
agent. Exposure assessments identify the exposed population, describe its
composition and size, and present the type, magnitude, frequency, and
duration of exposure
 Risk characterization: The exposure and dose-response assessments are
combined to produce a quantitative risk estimate and in which the strengths
and weaknesses, major assumptions, judgments, and estimates of
uncertainties are discussed
Characterization of Risk Assessment
Hazard
Assessment

Data
Response
Assessment
Exposure
Assessment
Technical
hazard
Characterization
Technical
Population
Dose
response
Characterization
Technical
Exposure
Characterization
Integrative
analysis
Risk
characterization
summary

What is Risk?
 Hazard is the potential of an entity (or activity) to cause harm to nature, property, or
people.
 Risk from a hazard:
risk (harm/unit time) = frequency (event exposure/ unit time)
* Consequence (harm/event exposure])
What is Total Risk?
 Total risk:
R = i =1N∑ R
i= 1,2,3,…,n
where, i is hazard
 For low value of C , R = f x Ch
 For high value of C, R = f x Chn where n is some known number that reflects the
roles of disruptions by severe accidents, as well as the public perception
How to calculate frequency (f)?
 Frequency (f) = Exposure / Unit time
= Daily amount of air pollutant inhaled over a life time
/ person’s weight
= (Breathing rate ( m3 / day) x indoor concentration ( µg/ m3) )
/ ( Weight of an individual in kg)
= (B x C) / W
where,
B is breathing rate,
C is indoor concentration,
W is weight of an individual.
 Units of frequency is ( µg / kg-day)
How to calculate Consequence (C) ?
 Consequence (c) = Life time excess cancer risk / Daily exposure to 1 µg of the
pollutant/weight of an individual
= βa x Kah x I
where,
βa = “potency” of the pollutant for inhalation in (µg/kg-day)-1
Kah = a conversion factor expressing the ratio of the risk to a human
to the corresponding risk to an animal based on inhalation
toxicity
I = a factor relating inhalation data to risk if other pathways were
also available, also known as data potency
What is lifetime excess cancer risk ?
 It is expressed as follows:
R = (B x d). (βa x K ah x I )
W
Example of lifetime excess cancer risk
 Risk to an adult from the exposure to tetrachloroethylene is calculated as follows by
using the given information B = 20 , W = 70 , d = 3.5 , βa = 9.2 x 10-6 , Kah = 1 ,
I = 1 By using the above formula and substituting the above given values in the
formula we get the lifetime excess cancer risk to an individual is R = 9.2 x 10 -6.
 The above value of risk implies that an individual has a 9.2 chance in a million of
getting cancer over his or her lifetime because of the daily exposure to
tetracholoroethylene at a concentration level of 3.5 µg/m3 of air. If an individual has
a life span of 70 years, then chance of getting cancer in any one year is 9.2/70 = 0.13
in a million
Why are risk studies conducted on Animals?
 While carrying out experiments there are risks from a spectral of real, suspected or
conjured hazards related to chemical and biological substances.
 The effect from a single substance on humans under controlled conditions cannot be
studied.
 Therefore, studies are conducted on test animals that are subjected to massive doses
of a substance on a relatively short time scale.
 These test conditions carried out on animals like rats and monkeys are atypical of
human exposures.
 The results of these animal studies are extrapolated for applications to human
conditions by the use of mathematical models.
 The mathematical models are actually equations which are formulated and solved
for applications to animal test conditions
Understanding Risk Factors
 EPA Reference Dose: Maximum daily acceptable oral
dose of a toxic substance, smaller numbers mean a
pollutant is more toxic
 Carcinogenic Potency factor or Carcinogenic Slope
Factor: a way to measure the safe dose of a toxin. The
EPA says that this chemical is safe to this dose with a
95th percentile of certainty. Higher numbers are safer.
Risk Factors of Various Pollutants
Toxic Air Pollutants
EPA reference dose
(mg/kg-day)
Antimony
4*10-4
Arsenic
3*10-4
Cadmium
Cobalt
5.71*10-5
6*10-2
Lead
4.29*10-4
Magnesium
1.15*10-6
Manganese
1.43*10-5
Mercury
8.57*10-5
Nickel
2*10-2
Carcinogenic Potency
(kg –day / mg)
6.3
Risk Factors of Various Pollutants
Toxic Air Pollutants
EPA reference dose
(mg/kg-day)
Selenium
5*10-3
Vanadium
7*10-3
Biphenyl
5*10-2
Acenaphthene
6*10-2
Carcinogenic Potency
(kg –day / mg)
6.1*10-1
Benzo-anthracene
Benzo pyrene
6.1
6.1*10-3
Chrysene
Fluoranthene
4*10-2
Fluorene
4*10-2
Naphthalene
4*10-2
Risk Factors of Various Pollutants
Toxic Air Pollutants
EPA reference dose
(mg/kg-day)
Pyrene
3*10-2
Phenanthrene
3*10-2
Carcinogenic Potency
(kg –day / mg)
5-methyl chrysene
4.1*10-1
Acetaldehyde
7.7*10-1
Acetophenone
5.71*10-6
Acrolein
5.71*10-6
Benzene
2.9*10-2
Benzyl chloride
1.7*10-1
Bromoform
3.85*10-3
Risk Factors of Various Pollutants
Toxic Air Pollutants
Carbon disulfide
Chlorobenzene
EPA reference dose
(mg/kg-day)
2*10-1
5.71*10-3
8.05*10-2
Chloroform
Cumene
2.57*10-3
Cynide
2*10-2
4.1*10-1
Di methyl sulfate
Ethyl benzene
2.86*10-1
Ethyl chloride
2.86
Ethylene dibromide
Carcinogenic Potency
(kg –day / mg)
7.7*10-1
Risk Factors of Various Pollutants
Toxic Air Pollutants
EPA reference dose
(mg/kg-day)
4.55*10-2
Formaldehyde
Hexane
5.71*10-2
9.5*10-4
Isophorone
Methyl bromide
1.43*10-3
1.64*10-2
Methylene chloride
Phenol
6*10-1
Toluene
1.14*10-1
2.03*10-3
Tetrachloroethylene
Styrene
Carcinogenic Potency
(kg –day / mg)
2.86*10-1
Risk Factors of Various Pollutants
Toxic Air Pollutants
Xylenes
EPA reference dose
(mg/kg-day)
2
Vinyl Acetate
5.71*10-2
HCL gas
5.71*10-3
HF gas
7*10-4
Carcinogenic Potency
(kg –day / mg)