On April 26, 1986, a series of explosions rocked the Soviet Union’s Chernobyl nuclear power station, precipitating a catastrophic release of radioactive material into the environment. Explore some surprising facts about history’s worst nuclear accident, the effects of which are still being felt.

1. The reactor’s emergency safety systems had been turned off.
The Chernobyl nuclear power station in present-day Ukraine consisted of four 1,000-megawatt reactors, plus two additional reactors that were under construction. On the night of April 25-26, 1986, Soviet technicians initiated a turbine test on Unit 4 just prior to a routine shutdown for maintenance. In order to perform the test, they unwisely disabled the emergency core cooling system and other key safety equipment. A chain of operating mistakes then ensued, resulting in a buildup of steam that caused the reactor to overheat. At 1:23 a.m., two to three rapid-fire explosions blew its steel and concrete lid right off and sent a fireball shooting high into the sky. This initial release of radioactive material was then compounded by several fires that broke out, including one inside the reactor core that raged for 10 days. All told, the accident at Chernobyl released at least 100 times more radiation than the atomic bombs dropped on Hiroshima and Nagasaki.

2. The cleanup was much deadlier than the original blasts.
Though massive, the explosions at Chernobyl killed only two plant operators directly and reportedly prompted a third to die of a heart attack. By comparison, 28 workers and firefighters succumbed to acute radiation poisoning during the first few months of the cleanup, and dozens of others were badly sickened. Heavy radioactive fallout, which spread as far west as France and the United Kingdom, likewise took a toll. Thousands of children who drank irradiated milk contracted thyroid cancer, at least 15 of whom ended up dying. Chernobyl almost certainly caused other premature cancer deaths as well, though the number remains hotly disputed. In 2005, the United Nations-backed Chernobyl Forum predicted that the accident would claim up to 4,000 lives in total, whereas Greenpeace put the number at 93,000.

3. The Soviet Union attempted a cover-up.
In the immediate aftermath of the Chernobyl meltdown, the Soviet authorities largely kept their own citizens in the dark and made no attempt to alert neighboring countries. On April 28, however, the cover-up began falling apart when Swedish air monitors detected large amounts of radiation in the atmosphere that seemed to have originated in the USSR. Pressed for an answer, the Soviets admitted that an accident had killed two people at Chernobyl, but they also lied that the situation was now under control. It took until May 6 for the authorities to close schools in Kiev, the Ukrainian capital located about 65 miles from the plant, and to warn residents to stay inside. The full story of what happened at Chernobyl would not come out until years later.

4. Huge numbers of people still can’t go home.
About 36 hours after the accident, the Soviet authorities started evacuating some 115,000 people who lived nearby, though not before many had already begun to suffer from vomiting and headaches. Believing they would soon be allowed to return home, they left behind assorted pets and valuables. Much to their surprise, however, all land within an 18.6-mile radius of the plant was subsequently closed off, and checkpoints were established to control access. This so-called exclusion zone was expanded in later years, leading to the evacuation of an additional 220,000 people. Though a few hundred residents have returned illegally, the vast majority of the area remains devoid of humans.

5. Chernobyl may have actually been a boon for wildlife.
As forests reclaimed land previously given over to industry and agriculture, and without people around to shoot and poison them, moose, red deer, wolves, lynx, bears, eagles and other megafauna reportedly began taking refuge in the exclusion zone around Chernobyl. This area “has paradoxically become a unique sanctuary for biodiversity,” the Chernobyl Forum declared in 2005. Yet even as some species apparently thrive, the radiation has been shown to cause significant and potentially deadly abnormalities in others, such as birds with deformed beaks.

6. The plant didn’t close until years later.
When Unit 4 exploded, the other three reactors at the Chernobyl nuclear power station were likewise shut down. But they were all restarted within a year and a half or so, despite international condemnation over their alleged design flaws and widespread contamination at the site. Thousands of plant operators continued trudging into work every day, only to see a turbine hall fire prompt the closure of Unit 2 in 1991. Then, in 1995, newly independent Ukraine agreed to shutter the remaining two reactors in return for financial assistance from the Group of 7 leading industrial nations (which includes the United States). Unit 1 stopped operating in 1996, and Unit 3 was the last to close in 2000.

7. Chernobyl has become a macabre tourist attraction.
Though people still can’t live there, the Ukrainian authorities opened up the exclusion zone to tourism in 2011. Since then, guides regularly take in visitors to view wildlife, as well as to explore the hastily abandoned ghost towns that dot the landscape, such as Pripyat, which once had a population of more than 45,000. In order to minimize exposure to radiation, the guides carry dosimeters and instruct their customers not to eat or smoke outside.

8. The cleanup is still taking place.
At great risk to their own health, emergency workers dropped sand, lead and boron into the reactor core and cleaned up flammable debris, among other desperate attempts to stop the release of radioactive material in the frantic few days after the accident. They also chopped down and buried acres of pine forest, bulldozed villages and even slaughtered abandoned pets for fear they would leave the area and cause further contamination. The workers then entombed the reactor in a gigantic concrete structure, known as the sarcophagus, which over time has begun to deteriorate and spring leaks. If all goes well, a new 32,000-ton arch will be pushed on top of the sarcophagus sometime next year. According to the Ukrainian government, however, the site will not be completely cleared until around 2065. Meanwhile, radioactive particles will remain in the environment for hundreds of generations to come.