The radiation levels in the worst-hit areas of the reactor building have been estimated to be 5.6 roentgens per second (R/s) (1.4 milliamperes per kilogram), equivalent to more than 20,000 roentgens per hour. A lethal dose is around 500 roentgens (0.13 coulombs per kilogram) over 5 hours, so in some areas, unprotected workers received fatal doses within minutes. However, a dosimeter capable of measuring up to 1,000 R/s (0.3 A/kg) was inaccessible because of the explosion, and another one failed when turned on. All remaining dosimeters had limits of 0.001 R/s (0.3 µA/kg) and therefore read "off scale." Thus, the reactor crew could ascertain only that the radiation levels were somewhere above 0.001 R/s (3.6 R/h, or 0.3 µA/kg), while the true levels were much, much higher in some areas. Approximate radiation levels at different locations shortly after the explosion:

location	radiation (roentgens per hour)
vicinity of the reactor core	30,000
fuel fragments	15,000–20,000
debris heap at the place of circulation pumps	10,000
debris near the electrolyzers	5,000–15,000
water in the Level +25 feedwater room	5,000
level 0 of the turbine hall	500–15,000
area of the affected unit	1,000–1,500
water in Room 712	1,000
control room, shortly after explosion	3–5
Gidroelektromontazh depot	30
nearby concrete mixing unit	10–15

Because of the inaccurate low readings, the reactor crew chief Alexander Akimov assumed that the reactor was intact. The evidence of pieces of graphite and reactor fuel lying around the building was ignored, and the readings of another dosimeter brought in by 4:30 a.m. were dismissed under the assumption that the new dosimeter must have been defective. Akimov stayed with his crew in the reactor building until morning, trying to pump water into the reactor. None of them wore any protective gear. Most, including Akimov, died from radiation exposure within three weeks.

Plant layout

based on the image of the plant

level	objects
49.6	roof of the reactor building, gallery of the refueling mechanism
39.9	roof of the deaerator gallery
35.5	floor of the main reactor hall
31.6	upper side of the upper biological shield, floor of the space for pipes to steam separators
28.3	lower side of the turbine hall roof
24.0	deaerator floor, measurement and control instruments room
16.4	floor of the pipe aisle in the deaerator gallery
12.0	main floor of the turbine hall, floor of the main circulation pump motor compartments
10.0	control room, floor under the reactor lower biological shield, main circulation pumps
6.0	steam distribution corridor
2.2	upper pressure suppression pool
0.0	ground level; house switchgear, turbine hall level
-0.5	lower pressure suppression pool
-5.2, -4.2	other turbine hall levels
-6.5	basement floor of the turbine hall