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This is the final highway accident report (NTSB-HAR-71-1) from the National Transportation Safety Board, adopted in December 1970. It covers the collapse of the U.S. 35 bridge between Point Pleasant, West Virginia, and Kanauga, Ohio, on December 15, 1967, which killed 46 people. The Board found that the cause was a cleavage fracture in eyebar 330 at joint C13N. That fracture grew from a flaw produced over 40 years by stress corrosion and corrosion fatigue, in a spot that could not be seen or found by inspection.
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(2) A black acicular oxide covered much of the preexistent crack surface. (3) No distinct fractographic features such as fatigue striations were found after the oxide was removed. (4) Near the tip of the pre-existent crack, there were many small branching cracks, suggesting that the crack growth was by stress-corrosion cracking. Area scans and line scans were made with the electron microprobe. In the area scan work, the resulting x-rays emitted by elements on the surface were displayed and photographed on a cathode ray tube. By selective control of the x-ray detection, those due to separate elements could be identified. This permitted the general distribution of the elements in the crack fracture surface to be determined. It was found that aluminum, chlorine, potassium, and sulfur were prominent at the outer lip of the crack (the original pinhole surface), and except for the aluminum and potassium, generally decreased in concentration as one proceeded along the crack surface. Figure 22 shows the pattern of concentration for sulfur. An examination of the area near the crack tip showed higher concentrations of sulfur and chlorine on the pre-existent crack surface than on the freshly cracked ductile fracture. Sulfur in the freshly cracked area was found to be identified with sulfide inclusions in the metal. Line scans across the entire crack and into the freshly opened surface confirmed this result. A test to distinguish sulfide from sulfate ions showed that both were present on the pre-existent crack surface. A chemical test using sodium azide gave only a very weak indication of sulfide in the crack surface, and no detectable indication in the freshly opened crack. The conclusion of this study reads in part as follows: "The crack morphology is quite typical of that normally associated with stress-corrosion cracks. No evidence was found to suggest that the crack may have been associated with corrosion fatigue. A pit near the mouth of the crack was identified as the possible origin of the crack... Also, the highest chlorine concentrations were found at both the mouth and tip of the crack, whereas sulfur was greatest just at the mouth of the crack. Examination of the secondary crack in the eyebar corroborated the work done by Lane et. al. on eyebar No. 330. The failure mechanism was probably sulfide-stress corrosion. Hydrogen sulfide in the atmosphere from industrial or exhaust gases could have dissolved in moisture condensed on the bridge. H2S could then react with the steels and form iron sulfide in the oxide scale. Restricted areas where moisture would remain for long periods would become sulfide
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