There is a result in Cognitive biases potentially affecting judgement of global risks, p. 17, which is about intervals given by engineers about points of dam failure. It really doesn't make your claim, but it does look like the kind of thing that could be misremembered in this way. Quoting the relevant paragraph:

Similar failure rates have been found for experts. Hynes and Vanmarke (1976) asked seven internationally known geotechical engineers to predict the height of an embankment that would cause a clay foundation to fail and to specify confidence bounds around this estimate that were wide enough to have a 50% chance of enclosing the true height. None of the bounds specified enclosed the true failure height. Christensen-Szalanski and Bushyhead (1981) reported physician estimates for the probability of pneumonia for 1,531 patients examined because of a cough. At the highest calibrated bracket of stated confidences, with average verbal probabilities of 88%, the proportion of patients actually having pneumonia was less than 20%.