Risk Assessment- Occupational Health and Safety
SCENARIO: Hydrazine is an inorganic compound which is dangerously unstable and
carcinogenic. It is probably toxic as well, but some chronic exposure parameters are uncertain at
this time. Hydrazine is used in preparing polymer foams, rocket fuels, fighter aircraft fuels, and in
the reaction that rapidly inflates vehicle air bags.
You are asked to carry out a risk assessment in two parts:
(1) An explosion scenario at the facility
which addresses the short term exposure of nearby residents to hydrazine in their water supply for a
limited period of time; and
(2) Chronic exposure of nearby residents through the water supply on
an on-going basis as a result of leakage from the plant. Years later, a risk assessment of various
chemicals in the food and water is being performed. Provide the assessment for the combined risk
using the excel sheet (3).
Part 1: Resident carcinogen scenario following explosion at the plant resulting in hydrazine
contamination of the aquifer used for drinking water
Hydrazine dissipates in air within hours, but it can reach the water supply and is thought to remain
there for up to 40 days, presenting a risk for persons drinking well-water containing hydrazine.
The initial (highest) concentration in water at day 1 is 600μg/L, with the concentration reaching
undetectable limits by day 40. Assume constant rate-of-dissipation, so calculate the exposure
assessment as a mean concentration of 300μg/L for the full 40-day exposure. Also assume
contact rate of 2L/d, body weight of 70kg, absorbance and relative retention of 1.0. Show all work
including units.
(a) Given that an explosion has taken place, calculate the expected lifetime incremental risk of
death from cancer per person exposed as specified above for these 40 days.
(b) Given that an explosion has taken place, calculate the hypothetical number of additional
deaths from cancer due to this cause among 50,000 residents exposed through drinking water.
Part 2: Resident carcinogen scenario from continued low-level hydrazine contamination of
the aquifer used for drinking water through leakage. Assume that the continuous leakage of
hydrazine into the ground water from the plant for 12 years results in a constant
concentration in the aquifer of 10.0 µg/L.
(a) What would be the lifetime risk of cancer death for the residents from this exposure
scenario, assuming the parameters
(b) How many people would die from this exposure if the population were 50,000?
(c) Advise this population about how to reduce their intake to acceptable levels if the risk was
147 times more than the de minimis level (note: There is more than a single answer – only
provide one).
Part 3: Years later, soil and water samples are taken and a combined risk assessment is
performed for various chemicals (Note: bioconcentration factor provided in excel sheet to
convert soil values to food values). Using the given excel sheet, answer the following questions:
(a) What is the combined HI and cancer risk to the community from these new chemicals?
(b) Removing the most hazardous combined carcinogenic compounds first, list the chemicals
need to be removed to bring the values to acceptable values?
(c) Removing the most hazardous non-carcinogenic chemicals first, which ones need to be
removed to bring the values to acceptable values?