A company spokesman said the above-ground area was evacuated when explosions used to mine potash released a large amount of dust, Euronews.com reported Wednesday.
Seven miners were trapped at the site near Unterbreizbach, but four were rescued. The victims were ages 24, 50 and 56, officials said.
"After the explosions, we carry out checks to see how much carbon dioxide is in the mine," mine owner Rainer Gerling said. "This was the actual job of these employees, and they were then surprised by the amount of CO2 on the site."
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