PSY/CS330 Human Factors
04/30/2001
Day 1-5
Three Mile Island - The Disaster
uMechanical Failure
lNO water was getting to the emergency pump - the lines were closed
uone light signaling that lines were closed was covered by a maintenance tag.
uother light - who knows?
lThe relief valve did not close
uWith valve open, radioactive water escaped to drain tank.
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uHuman Factors Issue
lVisibility of alerts
lPlacement is also an issue
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lRelief valve lights indicated commanded state not actual state - that they were switched to close that that they did close
The relieve valve did not close
The relief valve could have been manually closed but the operator could not tell if the valve was open only that the power to the valve was off .

With over 100 alarms going off - think - what is the supposed limit of short term memory - 7+-2.