246
10 Illustrative Case Study
Task:
(a) Use the Gaussian model for gas propagation by turbulent diffusion given in
Appendix D.2 to calculate the maximum air concentration of HCN expected at
the neighboring site. Assume that average wind conditions are 1.5 m/s, stable
conditions of σ y = 18 m and σ z = 9 m prevail, and a leak in the reactor releases
2 kg HCN over 1 hr. Considering the obtained result, estimate the consequence
of the release scenario using the consequence categories given in Table 7.8 in
Chap. 7. Assume a maximum allowed short-term exposure limit of 3.8 ppm
HCN (ECHA, 2019b).
(b) Regarding effects on process operators on-site in the chemical plant, how would
you estimate the consequence of a release of HCN using the consequence
categories given in Table 7.8 in Chap. 7 and the data provided in step 1?
10.2.4.2 Probability Analysis
As a result of the risk identification step, the process deviations and failures that
lead to loss events and to the release of HCN are known. Fault tree analysis can
be used to estimate the probability of release of HCN during the synthesis step
of 3-amino-2-isopropylthio benzonitrile if probability data for the single events
are available (from historical records and reliability analysis). This would result
in a quantitative probability estimation. The task below, however, will focus on
qualitatively assessing the probability.
Task: Figure 10.5 shows an incomplete fault tree with the release of HCN as the
top event.
(a) Insert the missing intermediate events and the corresponding Boolean operators
(OR and AND). Note that this tree is rather a simplified model and does not
contain an exhaustive list of initiating events.
(b) Comment on the assumption used in the fault tree analysis that all events are
independent. Is this realistic?
(c) Qualitatively estimate the probability of release of HCN using the probability
categories proposed in Table 7.9 in Chap. 7. Format your solution in a table with
probability categories assigned to potential: process failures, process deviations,
preventative safeguard failures, loss events, mitigative safeguard failures, and
resulting consequences.
10.2.5 Risk Evaluation (Step 5)
Task: Based on the outcomes of the risk analysis step, evaluate the level of risk for
people at the neighboring manufacturing site and for operators at the manufacturing
10 Illustrative Case Study
Task:
(a) Use the Gaussian model for gas propagation by turbulent diffusion given in
Appendix D.2 to calculate the maximum air concentration of HCN expected at
the neighboring site. Assume that average wind conditions are 1.5 m/s, stable
conditions of σ y = 18 m and σ z = 9 m prevail, and a leak in the reactor releases
2 kg HCN over 1 hr. Considering the obtained result, estimate the consequence
of the release scenario using the consequence categories given in Table 7.8 in
Chap. 7. Assume a maximum allowed short-term exposure limit of 3.8 ppm
HCN (ECHA, 2019b).
(b) Regarding effects on process operators on-site in the chemical plant, how would
you estimate the consequence of a release of HCN using the consequence
categories given in Table 7.8 in Chap. 7 and the data provided in step 1?
10.2.4.2 Probability Analysis
As a result of the risk identification step, the process deviations and failures that
lead to loss events and to the release of HCN are known. Fault tree analysis can
be used to estimate the probability of release of HCN during the synthesis step
of 3-amino-2-isopropylthio benzonitrile if probability data for the single events
are available (from historical records and reliability analysis). This would result
in a quantitative probability estimation. The task below, however, will focus on
qualitatively assessing the probability.
Task: Figure 10.5 shows an incomplete fault tree with the release of HCN as the
top event.
(a) Insert the missing intermediate events and the corresponding Boolean operators
(OR and AND). Note that this tree is rather a simplified model and does not
contain an exhaustive list of initiating events.
(b) Comment on the assumption used in the fault tree analysis that all events are
independent. Is this realistic?
(c) Qualitatively estimate the probability of release of HCN using the probability
categories proposed in Table 7.9 in Chap. 7. Format your solution in a table with
probability categories assigned to potential: process failures, process deviations,
preventative safeguard failures, loss events, mitigative safeguard failures, and
resulting consequences.
10.2.5 Risk Evaluation (Step 5)
Task: Based on the outcomes of the risk analysis step, evaluate the level of risk for
people at the neighboring manufacturing site and for operators at the manufacturing