Upload
daoud-saleem
View
214
Download
1
Embed Size (px)
Citation preview
Western University
Faculty of Engineering
DEPARTMENT OF CHEMICAL AND BIOCHEMICAL ENGINEERING
CBE 9185 - RISK ASSESSMENT AND MANAGEMENT IN ENGINEERING SYSTEMS
Assignment #2 Question1: Bayes Problem
Transplant operations for hearts have the risk that the body may reject the organ.
A new test has been developed to detect early warning signs that the body may be
rejecting the heart. However, the test is not perfect. When the test is conducted on
someone whose heart will be rejected, approximately two out of ten tests will be
negative (the test is wrong). When the test is conducted on a person whose heart
will not be rejected, 10% will show a positive test result (another incorrect result).
Doctors know that in about 50% of heart transplants the body tries to reject the
organ.
*Suppose the test was performed on my mother and the test is positive (indicating
early warning signs of rejection). What is the probability that the body is
attempting to reject the heart?
*Suppose the test was performed on my mother and the test is negative (indicating
no signs of rejection). What is the probability that the body is attempting to
reject the heart?
Western University
Question2:
Case study:
Transportation accidents involving hazardous materials, HazMat, occur every day in the United
States and around the world. On May 01, 2001, in Ramona, Oklahoma, an accident occurred
which resulted in the release and explosion of hydrogen gas. A semitrailer that contained
horizontal mounted gas filled cylinders and a pickup truck were involved in the accident. Both of
these vehicles were traveling northbound on Interstate 75 south of the town of Ramona, OK.
According to witnesses, the pickup truck veered into the path of the semitrailer causing it to go
out of control flipping on its side,and traveling 300 ft before it came to rest, the pickup truck also
ran off the road causing a rupture in the vehicles gas line igniting a fire.
During the initial stages of the accident, relief valves were broken off causing a leak of the
hydrogen gas. According to the National Transportation Safety Board (NTSB) report the
semitrailer driver was killed and the pickup truck driver was seriously injured.
At 14 : 15, the 911 dispatch center was notified of the incident,and the local fire department
(Ramona Volunteer Fire Department) was notified; at 14 : 16, the Washington County
Emergency Management Agency (EMA) started responding to the scene; between 14 : 16
and 14 : 21, an Air Gas employee driving southbound sees the vehicle and notifies the Air Gas
corporation; the driver of the pickup truck was extricated from the vehicle by local bystanders.
14 : 21 the Washington County Emergency Medical Service (EMS) requests assistance from a
private hazardous materials response team; 14 : 22, the Chief of the local fire department
arrives and directs the firefighters to “cool” the burning cylinders; the Washington County EMA
requests additional manpower for mutual aid companies. 14 : 22 other firefightersnot involved in
active firefighting attempt to extricate the truck driver.14 : 25 the Emergency Operations Center
(EOC) and emergency plan are activated by the Washington County EMA. 14 : 30 Washington
County EMA and Oklahoma State Patrol officer trained in hazardous materials arrives on scene.
14 : 40 extrication attempts halt because of the lack of water to suppress the fire coming from the
cylinders. The Washington County EMA and Phillips Petroleum DART commander advise the
firefighters to stay away from the ends of the burning tanks in the event of an explosion. 15 : 00
the Air Gas executive team arrives on scene and offers assistance to the incident command team.
15 : 11the Tulsa OK HazMat team is requested to aid. 15 : 15 the truck driver is extricated from
the vehicle. 15 : 30–15 : 35 the Tulsa Hazardous Materials team arrives on scene and assumes
command. 1600 Air Gas executive team member and safety director offers assistance to the Tulsa OK HazMat team with their own response team called AERO. 17 : 15 the AERO team
members arrive on scene. 18 : 30–18 : 40 the scene is declared controlled and the Tulsa OK
HazMat team goes into service. At 00 : 20 the AERO team advises command that the cylinders have vented and are properly cooled. 00 : 55 command is turned over to the Oklahoma State
Patrol, active firefighting, Hazardous Materials response is terminated, 06 : 00 the highway
then reopens.
Western University
Draw an event tree that can be used to represent the major events in this accident
sequence and can be used in the future by emergency response personnel to
determine what the critical events in the sequence were
Question3:
Case Study: Chernobyl
On 25 April, 1986, prior to a routine shutdown, the reactor crew at Chernobyl 4 began
preparing for an experiment to determine how long turbines would spin and supply power to the
main circulating pumps following a loss of main electrical power supply. This test had been
carried out at Chernobyl the previous year, but the power from the turbine ran down too rapidly,
so new voltage regulator designs were to be tested.
Multiple operator actions, including the disabling of automatic shutdown mechanisms, preceded
the attempted experiment on the morning of April 26. By the time that the operator began to shut
down the reactor, it was in an extremely unstable condition. The design of the control rods
caused a dramatic power surge as they were inserted into the reactor.
The interaction of extremely hot fuel with the cooling water led to fuel disintegration, along with
rapid steam production and an increase in reactor pressure. The design characteristics of the
reactor were such that substantial damage to even three or four fuel assemblies could—and
did—result in the failure of the reactor vessel. Extreme pressure in the reactor vessel caused the
1000 ton cover plate of the reactor to become partially detached. The fuel channels were
damaged and the control rods jammed, which by that time were only halfway down. Intense
steam generation then spread throughout the entire core.
The steam resulted from water being dumped into the core because of the rupture of the
emergency cooling circuit. A steam explosion resulted and released fission products to the
atmosphere. A second explosion occurred a few seconds later that threw out fuel fragments
and blocks of hot graphite. The cause of the second explosion has been disputed by experts, but it
is likely to have been caused by the production of hydrogen from zirconium–steam reactions.
Two workers died as a result of these explosions. The graphite (about a quarter of the 1200 tons
of it was estimated to have been ejected) and fuel became incandescent and started a number of
fires, causing the main release of radioactivity into the environment. A total of about 14 EBq (14
× 1018 Bq) of radioactivity was released, over half of it being from biologically inert noble gases.
About 200–300 tons of water per hour was injected into the intact half of the reactor using the
auxiliary feed water pumps. However, this was stopped after half a day because of the danger of
it flowing into and flooding units 1 and 2. From the second to tenth day after the accident, some
5000 tons of boron, dolomite, sand, clay, and lead were dropped on to the burning core by
helicopter in an effort to extinguish the blaze and limit the release of radioactive particles.
It is estimated that all of the xenon gas, about half of the iodine and cesium, and at least 5% of
the remaining radioactive material in the Chernobyl 4 reactor core (which had 192 tons of fuel)
was released in the accident. Most of the released material was deposited close to the reactor
complex as dust and debris. Lighter material was carried by wind over the Ukraine, Belarus,
Russia, and to some extent over Scandinavia and Europe.
Western University
The casualties included firefighters who attended the initial fires on the roof of the turbine
building. All these were put out in a few hours, but radiation doses on the first day were
estimated to be up to 20,000 mSv, causing 28 deaths—6 of which were firemen—by the
end of July 1986.
The Soviet Government made the decision to restart the remaining three reactors. To do so, the
radioactivity at the site would have to be reduced. Approximately 200,000 people (“liquidators”)
from all over the Soviet Union were involved in the recovery and cleanup during the years 1986
and 1987. Those individuals received high doses of radiation, averaging around 100 mSv.
Approximately 20,000 of the liquidators received about 250 mSv and a few received 500 mSv.
Later,their numbers swelled to over 600,000 but most of them received only relatively low
radiation doses.
Causing the main exposure hazard were short-lived iodine-131and caesium-137 isotopes. Both
of these are fission products dispersed from the reactor core, with half-lives of 8 days and 30
years, respectively (1.8 EBq of I-131 and 0.085 EBq of Cs-137 were released).
About 5 million people lived in areas contaminated (above 37 kBq/m2 Cs-137), and about
400,000 lived in more contaminated areas of strict control by authorities (above 555 kBq/m2 Cs-
137).
Approximately 45,000 residents were evacuated from within a 10 km radius of the plant, notably
from the plant operators’ town of Pripyat on May 2 and 3. On May 4, all those living within a
30 km radius—a further 116,000 people from the more contaminated area—were evacuated and
later relocated. Approximately 1000 of those evacuated have since returned unofficially to live
within the contaminated zone. Most of those evacuated received radiation doses of less than 50
mSv, although a few received 100 mSv or more.
Reliable information about the accident and the resulting contamination was not made available
to affected people for about 2 years following the accident. This led the populace to be distrustful
of the Soviet Government and led to much confusion about the potential health effects. In the
years following the accident, a further 210,000 people were moved into less contaminated areas,
and the initial 30 km radius exclusion zone (2800 km2) was modified and extended to cover
an area of 4300 km2. This resettlement was owing to the application of a criterion of 350 mSv
projected lifetime radiation dose, although,in fact, radiation in most of the affected area (apart
from half a square kilometer) fell rapidly after the accident so that average doses were
less than 50% above normal background of 2.5 mSv/year.
Recent studies have found that the area surrounding the reactors is recovering, although
background radiation levels are approximately 35 times normal background level. In fact, in
2010, the area surrounding the reactor site was opened for tourism.
Draw an event tree OR Decision tree that can be used to show how selected one
can be used to analyse the accident or prevent such one.