Some system has redundancies and some system doesn’t.

Here is an article where plant operators accidentaly left a sodium hydroxid pump in manual mode. Dumpibg way too much of it in one go causing chemical burns to the customers. There were Ph alarms but nobody heard them. https://www.google.co.uk/amp/s/www.telegram.com/article/2007...

This is the website of an other water treatment company explaining what processes they have in place to prevent an issue like the above: https://www.mwra.com/01news/2007/042507nosodiumhydroxide.htm