School of Engineering

Faculty of Science and Engineering

ENGG8401 - Safety and Risk Engineering Tutorial 1

Important points:

· You can make appropriate assumptions for the data you believe

missing. However, state your assumptions clearly.

1. a) During a job interview for a Safety Advisor position, the employer tells you that based on the plant safety record, the chance of getting killed by the process is 1 in every 750 years. Calculate the corresponding (i) FAR and (ii) Fatality rate assuming normal working hours. Would you accept an offer from this employer? Why?

b) Assume that you accepted the offer of employment, however, after several weeks on the job you determine that the plant manager runs the plan with an iron fist. Also, a number of unsafe practices are performed at the plant, including some that could lead to catastrophic results. You bring up these problems to your immediate supervisor, but he decides to do nothing for fear that the plant manager will be upset. After all, he says, “we’ve operated this plant for 40 years without an accident”. What would you do in this situation?

2. A chemical plant has three units: Unit A with FAR of 1; Unit B with FAR of 2 and Unit C with FAR of 3.

a) What is the overall FAR for the plant, if workers expose to all units simultaneously?

b) Assume now that the units are far enough apart that an accident in one would not affect the workers in another. If a worker spends 20% of his time in process Unit A, 40% in process Unit B, and 40% in process unit C, what is his overall FAR?

3. A university has 1200 full-time employees. In a particular year this university had 38 reportable lost-time injuries with a resulting 274 lost workdays. Compute the OSHA incidence rate based on injuries and lost workdays.

4. A car leaves New York City and travels the 2800-mi distance to Los Angles at an average speed od 50 mph. An alternative travel plan is to fly on a commercial airline for 4.5 hr. What are the FARs for the methods of transportation? Which travel method is safer, based on the FAR?

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 5. Agasolinetankinastandardautomobilecontainsabout14galofgasolineandcan be filled in about 3 min. The molecular weight of gasoline is approximately 94, and its vapor pressure at 77oF is 4.6 psi (0.303 atm). Estimate the concentration (in ppm) of gasoline vapor as a result of this filling operation. Assume a ventilation rate 3000 ft3/min. The TLV for gasoline is 300 ppm (Consider Ф as 0.5).

6. A drum contanins 42 gal of toluene. If the lid of the drum is left open (lid diameter

is 3 ft), determine the time required to evaporate all the toluene in the drum. The

temperature is 85oF. Estimate the concentration of toluene (in ppm) near the drum

if the local ventilation rate is 1000 ft3/min. The pressure is 1 atm. (Consider the

mass transfer coefficient (K) as 0.95 ft/min; ������������ = 0.047 ��������� ; M=92.13 lbm/lb- ���������������������

mol; Rg = 0.7302 ft3.atm/lb-mol.oR; ������������������������ = 53.95 lbm/ft3)

7. ATLV-TWAforasubstanceis150ppm.Aworkerbegingsaworkshiftat8amand completes the shift at 5 pm. A one-hour lunch break is included between 12 noon and 1 pm, when it can be assumed that no exposure to the chemical occurs. The data were taken in the work area at the times indicated. Has the worker exceeded the TLV specification?

Time Concentration (ppm)

8:10 110

9:05 130 10:07 143 11:20 162 12:12 142

1:17 157 2:03 159 3:13 165 4:01 153 5:00 130

8. Air contains 4 ppm of carbon tetrachloride and 25 ppm of 1,1-dichloroethane. Compute the mixture TLV and determine whether this value has been exceeded.