A wild animal is on a hair trigger in the sense that an untrained person would not know the actions or gestures that could provoke action in the wild animal; if you consider a scenario where massive flooding causes the enclosures of the zoo to break open and the animals to get free, the animals would be in totally unknown conditions and stressed out, which is extremely dangerous for humans exposed to or near these animals. This is what happened in a zoo in Tbilisi, the capital of the country of Georgia (link to article):
Georgia mobilized its special forces on Sunday and warned residents in the capital not to leave their homes after lions, tigers and bears — among other animals — escaped during floods that have claimed at least 12 human lives. Heavy rains and wind hit Tbilisi overnight on Saturday, turning a normally small stream that runs through the hilly city into a surging river. Officials said 12 people were known to have died and about two dozen others were missing. The surging floodwater destroyed enclosures at the zoo, killing some animals and letting loose others. Georgian Culture Minister Mikheil Giorgadze told NBC News: "The special forces are doing everything to control the situation. We are all mobilized"