Digital Inclinometer: Graphic
To insure the safety of those involved, emergency response structural engineering teams arrived early in the disaster and continually assessed the stability of the building.
One of the ways structural engineers assessed the danger of collapse was by using a device called a digital inclinometer. These electronic levels were strapped to support columns, walls, etc., in the building and indicated in fractions of degrees the angle at which these parts of the building were leaning. Changes in the angles were monitored closely and rescue crews were warned as necessary.
Support columns in buildings are designed to bear weight coming straight down on them. If because of the sinking of the foundation, or the effects of some natural or man-made disaster they are caused to lean, their ability to support weight dramatically decreases. The angle at which the support columns in the Federal Building were leaning was a measure of how much of the remaining weight they could bear, which areas of the building were particularly dangerous, and an indicator of when parts of the structure needed to be shored up.