Answer:
The health hazard of directly going to these places to take direct readings and observations.
Step-by-step explanation:
The Chernobyl accident was a catastrophic radioactive accidents, with an immediate fatal effect on some victims (mostly firemen and law enforcement officers). Scientists investigating the effects of the radiation left on the venues of the accident face a health risk if they intend to carry out a full scale on-field testing and experiment. Some of the relocated occupants of these places, that have long been relocated, have shown some health effect of the radiation. And scientist studying and working on these places for too long stand a risk of developing health complications if they are exposed to the radiations for too long.