We should avoid becoming unduly alarmed about the leakage or escape of cancer causing materials during a flood.

In the USA and other developed countries, standards are very strict and materials are classified as carcinogens when workers who have handled them daily for decades are found to be at elevated risk.
It is well for TPTB to be cautious about even small risks, when large numbers of workers are exposed.

The position in a flood is rather different, since even with increasing flooding it should still be a relatively rare and fairly brief event, not at all comparable to a lifetime of occupational exposure.

Remember that bugging out also carries risks, of auto accidents, of greater exposure than remaining indoors, and of course of your home being looted whilst unattended.