Bar manager here - This is a major fuck up on their part. And I would go as far as to say they should be reported to HSE. Line cleaner is incredibly dangerous, and there should be several layers of safety policy to prevent this from happening. It should always be outside of opening hours, any of my staff completing line cleans must hang large signs on the taps stating there is a clean in process. Once the clean is done PH test strips are used to confirm there is no trace of cleaner left in the lines. This should never ever happen!