The jury at the inquest into the death of Joan Blaber criticised the hospital's management for failings which they say could have led to her "safety being compromised".
The conclusion in full says: "Joan Catherine Blaber died six days after ingesting cleaning fluid on 17th September 2017 in the following circumstances.
"Mrs Blaber was admitted to the Royal Sussex County Hospital on 22nd August 2017 with symptoms of minor strokes.
"By the 7th September 2017 she was making progress and doctors were considering options, but general frailty and health issues meant she was unable to be discharged.
"On 17 September 2017, Mrs Blaber's clear water jug was replaced with a solid green water jug containing a cleaning fluid. This was later used to dilute cordial which she drank whilst taking her medication.
"Evidence leads us to believe there was widespread confusion surrounding the water jug system that was in place and that jugs were being misused.
"Understanding and implementation of cleaning procedures were inconsistent and inadequate amongst agency and Trust cleaning staff.
"Furthermore we find that management failed to direct and monitor staff, adhere to and enforce the control of Substances Hazardous To Health Regulations (COSHH) leading to ongoing breaches of regulation.
"In-house training for facilities and estates was not optimised due to the failure to monitor post-training practices, adequate training was also not guaranteed to the same standard for agency staff.
"Management missed an opportunity to learn and disseminate lessons from a 2016 incident on the same floor of the hospital involving the drinking of cleaning fluid which had been entered into the DATIX incident database.
"Based on the evidence, we find this contributed to inappropriate practices in the hospital which were not addressed due to a culture of non-reporting.
"Serious communication failures in the hospital opened the way to misunderstanding of procedures, errors in practice and resulted in a failure to implement lessons that could have been learned.
"We found this contributed to Mrs Blaber's safety being compromised."
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