CHE 320 Safety, Engineering Ethics and Professionalism
Fall 2017
CHE 320 Homework #4 Due Tuesday, November 14, 2017 at the start of class (10:00 AM) (Not a Canvas submission, turn in
a physical copy at the beginning of class)
Your written responses must be neatly typed, and free of major grammatical and spelling errors.
Calculations may be done by hand, but to receive credit they must be neat and organized and you must
show all of your work.
Chapter 1: Introduction and Case Studies
1) Make a table of the seven major plant disasters that were discussed in class and the Crowl textbook. In this table, list the major cause(s) of each accident and at least one specific process or equipment
modification which would have prevented the accident from occurring (“don’t do that” is not an
acceptable answer). Complete sentences are not required, but please type or write clearly.
2) During a plant startup, the supervising manager yelled across the crowded control room to an operator: “Hey, you!! Shut down pump PD103 now!!!” The operator shut down the pump as requested. To
everyone’s surprise and dismay, a huge explosion and fire occurred several minutes later. Firefighters
from the fire department in the neighboring city were able to put out the blazing fire at the plant.
Unfortunately, a large holding tank and much of the surrounding equipment were completely
destroyed, mostly because it took so long for the city fire crew to arrive on scene.
Investigation revealed that the operator had turned off pump PB103 (which was not actually running at
the time), not PD103. As a result, a holding tank full of cyclohexane overflowed onto a flat concrete
slab under the tank. A few minutes later, the vapors from the spilled cyclohexane were ignited by the
motor of a plant maintenance truck that had been left idling over the lunch hour. The control-room
operator claimed that he had followed his orders. Who is “responsible” for this accident? List at least
four major mistakes or poor procedures that contributed to the extensive fire damage at the plant.
3) A very hot oil was accidentally pumped into a tank that contained some residual water. The liquid water flashed to saturated steam (vapor), and the resulting increase in pressure ruptured the tank. The
cylindrical tank had a rated bursting pressure of 0.3 psig, and was 6 m high and 8 m in diameter.
Estimate the minimum amount of water, in US gallons, which was in the tank. (ans: ~48 gal)
Hint: Water vapor acts as an ideal gas at atmospheric pressures.
Chapter 6: Fires and Explosions
4) Crowl Problem 6-3. An Excel or other spreadsheet will greatly simplify the calculations. Which mixture has the largest flammability region (i.e. is most likely to burn)?
5) Phosgene (CAS 75-44-5) is an important industrial precursor for polyurethanes and various other compounds. It was also used as a chemical weapon in World War II, and is a common hazard in many
industrial plants. Download a safety data sheet (SDS) for phosgene from Sigma-Aldrich or another
reputable website.
a. Based on the SDS, draw an NFPA diamond diagram for this compound (a color print is not
CHE 320 Safety, Engineering Ethics and Professionalism
Fall 2017
required, as long as the hazard classes are in the correct order).
b. List the major health hazards which might be expected for everyday work with phosgene. c. What is the TLV-TWA for phosgene? Your text has TLV data tabulated in the Appendix.
Note: Because it is a hazardous gas, phosgene is often sold as a solution in toluene – don’t
confuse the TWA for phosgene with the TWA for the toluene solvent.
d. What symptoms would you expect to observe if a co-worker was exposed to phosgene concentrations above the TLV-C? Would you need any special protective equipment to rescue
your co-worker? If you’re unfamiliar with the medical terms, you should learn what they mean
(Wikipedia?)
6) You wish to place a 600-gallon tank of liquid propane, C3H8, near your house to supply your furnace. You are concerned that the tank may rupture, and the resulting vapor cloud explosion would damage
your house. It would be prudent to calculate the minimum distance from your house to place the tank.
Assuming only limited minor structural damage would occur from the explosion, please determine:
a. The mass (in kg and moles) of propane in the tank, assuming it is completely full. b. The equivalent mass of TNT for the propane, assuming the explosion efficiency is 7%. c. The tolerable overpressure, po, for the explosion. d. The minimum distance, r, between the tank and your house (ans: ~1000 feet)
The ΔHcombustion for propane is 488.3 kcal/gmole, and the density of liquid propane is 0.50 g/cm³.
Chapter 7: Concepts to Prevent Fires and Explosions
7) Explain, in a sentence or two, the purpose of “inerting”. What safety hazard does the procedure mitigate? Why should air never be used to inert a vessel?
8) How are “grounding” and “bonding” different? What is the main goal of grounding or bonding equipment?
9) A 10,000 liter propane storage tank is being taken out of service for maintenance. Before the maintenance work can begin, the vessel must be emptied of propane, depressurized, and then inerted
by sweep-purging using pure nitrogen. Please determine the following:
a. The maximum allowable out-of-service fuel concentration before the tank can be opened. b. How long will the nitrogen have to flow to inert the tank, if N2 is delivered at 0.5 kg/min? c. What is the total mass (in kg) of nitrogen required to do the job?
10) Think of a significant accident that occurred in your life (e.g. an automobile collision, a bad fall, kitchen disaster, etc.) Who was ultimately responsible for the accident? Were you aware of the root
cause or hazard before the incident? Over what length of time did it occur? How do you feel now,
when you reflect on that incident? What “lessons learned” could be gleaned from the event?
Note that “ultimately responsible” means the person(s) who created a situation or system that allowed
CHE 320 Safety, Engineering Ethics and Professionalism
Fall 2017
the incident to occur, not necessarily who was there when it happened.
No written answer is required for this question (no points), but please ponder it for a few moments.
Extra Credit Opportunity
11) EXTRA CREDIT (12 pts): Choose a video produced by the US Chemical Safety Board (www.csb.gov) which pertains to an industry in which you’d like to work. After watching the video
carefully, summarize the following in a short paragraph:
a. Where and when the incident occurred b. The root cause(s) that initiated the incident c. Recommendations offered by the CSB to prevent similar incidents d. Was the hazard obvious before the incident? Why or why not?
Please provide the complete title of the video you chose to watch, and use complete and
grammatically correct sentences in your writing. Full credit will only be granted if an in-depth
answer is provided.
12) EXTRA CREDIT (12 pts): Choose a second video produced by the US Chemical Safety Board (www.csb.gov) which pertains to an industry in which you’d like to work. After watching the video
carefully, summarize the following in a short paragraph:
a. Where and when the incident occurred b. The root cause(s) that initiated the incident c. Recommendations offered by the CSB to prevent similar incidents d. Was the hazard obvious before the incident? Why or why not?
Please provide the complete title of the video you chose to watch, and use complete and
grammatically correct sentences in your writing. Full credit will only be granted if an in-depth
answer is provided.
