case of stress corrosion cracking, hydrogen embrittlement may also lead to a decrease in the threshold stress intensity factor for crack propagation or an increase in the sub-critical crack growth velocity of the material. The most visible effect of hydrogen in materials is a drastic reduction in ductility during tensile tests. It may increase, decrease or leave unaffected the yield strength of the material. Hydrogen may also cause serrated yielding in certain metals such as niobium, nickel and some steels (3). Case studies One of the worst disasters caused by stress corrosion cracking was the fall of the Silver Bridge, WV in 1967, when a single brittle crack formed by rusting grew to criticality. The crack was on one of the tie bar links of one of the suspension chains, and the whole joint failed quickly by overload. The event escalated and the whole bridge disappeared in less than a minute, killing 46 drivers or passengers on the bridge at the time. See also References Mars G. Fontana, Corrosion Engineering, 3rd Edition, McGraw-Hill, Singapore, 1987 A. R. Troiano, Trans. American Society for Metals, 52 (1960), 54 T. K. G. Namboodhiri, Trans. Indian Institute of Metals, 37 (1984), 764 A. S. Tetelman, Fundamental Aspects of Stress Corrosion Cracking, eds., R. W. Staehle, A. J. Forty and D. Van Rooyan, National Association of Corrosion Engineers, Houston, Texas, (1967), 446 N. J. Petch and P. Stables, Nature, 169 (1952), 842 R.A. Oriani, Berichte der Bunsen-Gesellschaft für physikalische Chemie, 76 (1972), 705 C. D. Beachem, Metall. Trans., 3 (1972), 437 D. G. Westlake, Trans. ASM, 62 (1969), 1000 Corrosion Fracture mechanics