Three decades on, disagreement continues over how many people died as a result of radiation released by the explosion in Chernobyl reactor four.
Estimates vary wildly, from 4,000, as declared in a study published in 2006 by the UN, up to 200,000, as reported by environmental body Greenpeace.
Both sides claim they have hard evidence and scientific research to back up their findings, but if this is so, why does such a gap exist? Surely at this stage, so long after the accident, we must know how many were killed by Chernobyl?
It is important that we should have this information, because it will teach us a great deal about the effects of radioactivity on human beings.
Much of our understanding of this comes from uranium miners, radiation plant workers, survivors of the Hiroshima and Nagasaki bombs, and accidents in nuclear power plants, such as Three Mile Island in the US and, more recently, Fukushima in Japan.
The greater the exposure to radiation, the higher the risk. In Chernobyl’s case, the exposure was colossal for some. Early responders, including plant workers and firefighters, developed acute radiation sickness, which killed 28 out of 134 suffering from it.
Data accumulated by the UN Scientific Committee on the Effects of Atomic Radiation and the World Health Organisation suggest that an additional 4,000 additional deaths from cancer will occur among other groups exposed to the the highest levels of radiation.
These include 240,000 “liquidators” sent in to clean up radioactive materials afterwards, 116,000 evacuees who were living near the plant, and 270,000 residents who continue to live in areas with high levels of fallout.
There might be more cancer deaths directly attributable to Chernobyl, but these will be lost in the general cancer statistics, the 2006 report says.
Greenpeace used data provided by a large number of experts from the region, claiming cancer rates are all much higher as a result of Chernobyl. It says the death toll in Belarus, Russia and Ukraine could reach 200,000.
Unfortunately, there is no match-up between the two reports. At least some of this is caused by having to estimate incidences on the basis of uncertain exposure levels, says Dr Ciara McMahon of the Environmental Protection Agency. Models are used but predictions can still vary greatly even within a single study.
Perhaps the biggest killer in number terms over time, however, will not be radiation. It may well be the stress and anxiety among the estimated 5 million living in contaminated areas or among those forcibly removed from their homes in the days following the explosion.These deaths will remain hidden in the statistics.