During the morning Self-Defense Force helicopters drop water four times on the spent-fuel pools of units 3 and 4. They measure radiation field of 3.75 Sv/h above Unit 3. In the afternoon it is reported that the unit 4 spent-fuel pool was filled with water and none of the fuel rods were exposed.
And there is a notable point -- 300 feet 2 above Unit 3 in the air there is a dose reading of 375 R per hour.
375 Rem is 3.75 Sievert
An hour in that sort of radiation is almost certain death.
Since radiation levels are subject to the inverse square law, at 150 feet above Building 3 the dose would be 15 Sieverts an hour, deadly, and enough to make anyone sick very quickly. Which is why the helicopters stayed so high up when dropping water.