Wrong Code Downloaded to PLC Causes Plant to Shutdown

Event Year: 1997 Reliability: Likely But Unconfirmed
Country: United Kingdom
Industry Type: Food & Beverage

When making minor changes to a PLC program, the PLC and Slave PLC were loaded with the new program and made the Master. The new Slave, previously the Master, was also loaded halfway through this download. The Master PLC stopped working and the plant was shut down.

On a previous training course, the instructions were always to download to both units. However, a colleague, unaware of what had been taught on the training course, had discovered that it was possible to run different programs on the Master and Slave on a previous occasion, as long as they were not too dissimilar.


The plant was shutdown for 1

Action Description: All new starters were told of the procedure used when downloading software and why. This was done only after they had been on their formal training with the software supplier. The software supplier was told of the problem and how the problem would be avoided in the future. This was incorporated into their training. Additionally, the organisation developed a policy of not having more than one person working on a PLC at the same time. At the time of the incident there were two developers working on the same PLC (working on different priority jobs). This caused confusion when trying to troubleshoot the problem.