Speaking to The News, Dr Martinus said the culture of "hiding things" had worsened at Grey Hospital.
He said everyone made mistakes, but if one clinician made an error, others should pick it up and correct it. "That's not happening."
An avoidable patient death usually followed a series of errors.
"You've got to discuss things openly and identify all the problems, apologise to the proper people if necessary, and then try and correct it.
"But because of what they call the medico-legal environment, that's discouraged at all levels - at the hospital level, at the medical and nursing level - it's discouraged to discuss things openly.
Dr Martinus said he had referred to the Health and Disability Commissioner several sentinel cases - events threatening life or resulting in unexpected death or major loss of function.
Dr Martinus worked at Grey Hospital for five-and-a-half years, leaving last year.
WCDHB chief executive David Meates said yesterday the board took the issues Dr Martinus raised very seriously but Dr Martinus was "ill-informed" and his criticism of junior doctors was "inappropriate".
He said DHBs had internal and external accountability. Since 2010 the WCDHB's reporting of sentinel events had increased significantly, not as a result of increased incidents of harm but because of better reporting of incidents, he said.
The WCDHB reported four sentinel events last year, compared to two the previous year - both of which were suicides, which are no longer reported.
Mr Meates said all DHBs, including the West Coast and Canterbury, had a policy of open disclosure which recognised "the learnings that come from investigating incidents and also recognises our obligation to patients and their families to do so".
