Qualitative Risk Analysis
Risk analysis can be both qualitative and quantitative. The former (qualitatively)
assesses and combines their probability of occurrence and impact. The latter (quantitatively)
numerically analyzes the effect on overall project objectives of identified risks.
With this risk analysis, two questions need to be answered:
- What is the probability of the event occurring?
- If the event occurs, what will be its impact?
For the first risk - escape plot discovery:
- The greatest risk was with the tunnel itself and with a deep tunnel the utmost
liability and most likely part of it to be discovered was the trap door. The probability
was very high as it was a "top prize" the ferrets were looking for. The impact
of its detection was catastrophic. With only one entrance, it was critical to
make sure the trap door to the tunnel entrance was concealed to the closest of
- Nosy ferrets were also a very high risk, as they had unrestricted access,
could wander anywhere, and uncover something. They could lie in wait hiding and
listening to conversations. With many factories in operation the probability of
discovery was high. The impact of this was that all escape-related work had to
be closely guarded and POWs had to be alerted to the ferrets' presence.
- A slightly lesser risk was ineffectively hiding traces of the tunnel, particularly
the sand. The probability of discovery was very high as sand was so hard to conceal.
The impact of discovering sand was that the ferrets would be alerted to tunneling
activity. This would increase the ferocity of the searches but would not reveal
the tunnel's exact whereabouts.
- The probability of discovering sand was high because there was such a massive
volume that had to be dug, hauled to the entrance, extracted out of the shaft
and transported to a hiding place. A long tunnel (330 feet/100 m) would
generate close to one hundred cubic metres of sand.
For the second risk - dangers with tunnel engineering:
- The probability of collapse was high and cave-ins were common. The impact
of collapsing tunnels was extremely dangerous to the men inside it.
- The probability of bad air was very high and increased with the growth of
the tunnel. The impact of bad air saturated in carbon dioxide could seriously
injure or even kill.