4
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?

CBE9185Risk+Assessment Assignment 2 (1)

Embed Size (px)

Citation preview

Page 1: CBE9185Risk+Assessment Assignment 2 (1)

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?

Page 2: CBE9185Risk+Assessment Assignment 2 (1)

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.

Page 3: CBE9185Risk+Assessment Assignment 2 (1)

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.

Page 4: CBE9185Risk+Assessment Assignment 2 (1)

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.