When confronted with a crisis like the ongoing nuclear accident in Japan, individuals are faced with some difficult choices. Usually, the authorities tell them to take very modest precautions, like not drying your laundry outdoors if you live close to the plant. Individuals themselves can take additional precautions, but risk causing knock-on effects if they do.
An obvious example is trying to move farther from the accident site. It probably improves your personal safety to be farther away, but may be an ineffective approach if everyone tries to do it at once. That actually creates a stronger personal incentive to take early action. If you leave early – before most people are excessively concerned – you might actually make it. If you wait until the government tells everyone to leave, you might find yourself stuck in a relatively chaotic mass of scared people.
A less dramatic example is avoiding certain potentially risky activities, like consuming products from pastured animals. After nuclear accidents in other places, things like milk, wool, and meat have been contaminated. It is pretty clear why that is a risk – animals that graze across a wide area of pasture get exposed to whatever level of fallout has accumulated over all that land. The same is probably true of fish and other marine organisms that either filter large amounts of water or eat other animals that do.
All told, the situation in a disaster area may be a bit of a prisoner’s dilemma. The best choice for you may be to flee and/or take precautions, but doing so could cause problems for others. Furthermore, trying to do either of those things at the same time as everyone else is more difficult than taking action before others do. That risks creating a ‘run on the bank’ scenario, however, as people farther and farther from the disaster area rush to deplete pharmacies of potassium iodide, or to purchase air-filtering equipment.