To put these numbers in perspective, using units that are used in teh US this would be 40 mRem / hr. The adminstrative control dose in a nuclear environment is 300mRem / year (so you are allowed 10 hrs at this exposure level). Radition workers are allowed 5 Rem /year (125 hrs at this level).
To put this in further perspective exposure of 50 Rem at one time have clearly observable health impacts (well short of death). This would require 125 hrs of exposure at this level.
So, these levels are serious, and need to be considered carefully in emergency management, but they are manageable.
The quote is wrong, the measured dose was 400 millisievert, Not 400 microsievert.