Here is an y2k anecdote involving the nuclear industry, sounds very similar to example Houston gave about oil company:
A midwestern US fossil facility was testing a boiler feedwater control loop for date rollover to Year 2000. The control console date was set in a fashion similar to testing a PC - it was changed to 12/31/99, 23:58, and then powered down. A few minutes later, it was powered back up - with the only resultant problem being the year shown as 1980 (a typical older BIOS response). The logic loop (PLC and other instrumentation) continued to function normally. Boiler levels were simulated up and down to drive feedwater regulating valves; again, no problem. Then, the technicians reset the console clock to 12/31/99, 23:58, and did NOT power down. When the clock rolled over to 01/01/2000, there was no problem. The technicians powered down the console and then restarted it - and guess what happened? The console rebooted with a date of 01/01/80, the downstream PLC (which had not been powered down) apparently saw this as a significant mismatch with it's own clock (time as a function of integers rather than actual date), and interpreted this condition as a gross control failure. The feedwater regulating valves were driven shut, and the boiler trip logic was initiated (the 'fail safe' condition for the boiler). In a 'live' situation, the plant would have tripped.
Source for this anecdote: accsyst.com
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