<P> Contrary to safety regulations, bitumen, a combustible material, had been used in the construction of the roof of the reactor building and the turbine hall . Ejected material ignited at least five fires on the roof of the adjacent reactor 3, which was still operating . It was imperative to put those fires out and protect the cooling systems of reactor 3 . Inside reactor 3, the chief of the night shift, Yuri Bagdasarov, wanted to shut down the reactor immediately, but chief engineer Nikolai Fomin would not allow this . The operators were given respirators and potassium iodide tablets and told to continue working . At 05: 00, Bagdasarov made his own decision to shut down the reactor, leaving only those operators there who had to work the emergency cooling systems . </P> <P> Approximate radiation intensity levels at different locations at Chernobyl reactor site shortly after the explosion are shown in the below table . A dose of 500 roentgens (~ 5 Sv) delivered over an hour is usually lethal for human beings . </P> <Table> <Tr> <Th> Location </Th> <Th> Radiation (roentgens per hour) </Th> <Th> Sieverts per hour (SI Unit) </Th> </Tr> <Tr> <Td> Vicinity of the reactor core </Td> <Td> 30,000 </Td> <Td> 300 </Td> </Tr> <Tr> <Td> Fuel fragments </Td> <Td> 15,000--20,000 </Td> <Td> 150--200 </Td> </Tr> <Tr> <Td> Debris heap at the place of circulation pumps </Td> <Td> 10,000 </Td> <Td> 100 </Td> </Tr> <Tr> <Td> Debris near the electrolyzers </Td> <Td> 5,000--15,000 </Td> <Td> 50--150 </Td> </Tr> <Tr> <Td> Water in the Level + 25 feedwater room </Td> <Td> 5,000 </Td> <Td> 50 </Td> </Tr> <Tr> <Td> Level 0 of the turbine hall </Td> <Td> 500--15,000 </Td> <Td> 5--150 </Td> </Tr> <Tr> <Td> Area of the affected unit </Td> <Td> 1,000--1,500 </Td> <Td> 10--15 </Td> </Tr> <Tr> <Td> Water in Room 712 </Td> <Td> 1,000 </Td> <Td> 10 </Td> </Tr> <Tr> <Td> Control room </Td> <Td> 3--5 </Td> <Td> 0.03--0.05 </Td> </Tr> <Tr> <Td> Hydropower Installation </Td> <Td> 30 </Td> <Td> 0.3 </Td> </Tr> <Tr> <Td> Nearby concrete mixing unit </Td> <Td> 10--15 </Td> <Td> 0.10--0.15 </Td> </Tr> </Table> <Tr> <Th> Location </Th> <Th> Radiation (roentgens per hour) </Th> <Th> Sieverts per hour (SI Unit) </Th> </Tr>

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