Kyshtym disaster

At the epicenter of the explosion, contamination exceeded 1,000 X-rays per hour (1,000 R/h), or 10,000 millisieverts per hour (mSv/h).

An excerpt from the article 42 facts about Kyshtym disaster

Within 100 meters of the blast's epicenter, gamma radiation exceeded 360 R/h, exceeding the annual norm by 18 million times. It thus took about 30 minutes to receive a lethal dose.

Within a radius of 55 kilometers from the epicenter of the explosion, gamma radiation exceeded the annual norm by 1080 times - it could take 3 to 5 years to receive a lethal dose of radiation.