A rocket exploded on August 8 in the Russian military range of Nyonoksa, injuring four people and killing two. Russian’s defense ministry reported that the explosion caused a fire, but that no radioactive or toxic material was released.
However, this doesn’t seem to match with what was measured in the city of Severodvinsk, 30 kilometers (19 miles) east of the naval base of Nyonoksa. According to the Associated Press, the local authorities reported a small increase in radiation levels, though they did not link it to the explosion at the military base.
According to the authorities, they registered a level of 2 microsieverts per hour for about 30 minutes, before it returned to the natural background level of between 0.1 and 0.4 microsieverts per hour. Despite the spike being 5-20 times the background dose, it is nowhere near deadly or even harmful.
A level of 2 microsieverts per hour is equivalent to eating 20 bananas in an hour, due to the slightly radioactive nature of bananas (it's the potassium). It’s also equivalent to getting two arm X-rays within an hour. The amount of cosmic rays you receive during 20 minutes onboard a flight is roughly 2 microsieverts. A dental X-ray will put you well in the 5 microsievert range.
The maximum yearly dose permitted for US radiation workers is 50 millisieverts, which is 25,000 times the spike recorded in the town. Even if the spike were to be constant for a year, they would still be getting less than half of what a radiation worker receives, way below the limit of the level linked to an increased risk of cancer.
Despite the situation in the town not being alarming, Greenpeace has appealed to Russia’s consumer watchdog to look into what might have caused the spike. According to Reuters, the bay near the base has been shut down to shipping for the next month. This shouldn’t affect Severodvinsk or the larger city of Arkhangelsk.