Nine out of ten people who took their own lives and were known to mental health services were assessed as posing a low or no risk of suicide, an official said.
Oscar Donnelly from the Northern Health and Social Care Trust is leading a bid to reduce the number of deaths to zero.
When people presented to services and were cleared they were fine at the time they were seen, he said.
"We know that 90 per cent of the people who take their lives who are known to mental health services, at their last risk assessment they were seen as at low or no risk of suicide."
"That is because we risk assess people on how they present at this minute, and they are fine at this minute, and they are grand, and they have no idea why they tried to kill themselves yesterday, but they are fine now.
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"But actually they are not fine, because nothing has changed between today and yesterday.
"Whatever happened to them yesterday could happen to them tomorrow."
Mr Donnelly chairs the regional Towards Zero Suicide Patient Safety Collaborative.
The new initiative is designed to take better account of changeable factors like whether someone drinks alcohol or has periods of low mood.
Mr Donnelly said "gate-keeping" to try to decide who receives services was useless.
He added: "Safety planning is a more dynamic form of risk assessment that allows us to seek to protect someone."
Risk factors include being male and unemployed, living in deprivation or with long-term health conditions.
Mr Donnelly added: "You are looking at those dynamic risks that can change the suicide risk very quickly, that can escalate it, and you are looking at putting in place measures that will actually help to mitigate against those and you are making sure that the person knows that.
"So you are educating them about it themselves, and suicide risk, and their family, so that when you send them home from accident and emergency with their loved ones, that they know and understand what is happening.
"My analogy for this is, we would not put someone in an inpatient ward or even into a supported living scheme without telling the staff who are responsible for their care, actually what their needs are, what the risks are and how they can safely care for them.
"But people are sent home all the time without that knowledge.
"Part of that can be because the person says we don't want the family to know, but part of the skills in the training of people is to have a conversation that takes you there, so what we do at the minute is we ask people.
"If the conversation is right and the risk assessment is right, it becomes a natural part of it."
Suicide levels in Belfast are 24 per 100,000, while those in other areas are about 14 per 100,000, Mr Donnelly said.
Rates have not gone up in recent years and there is no evidence of an epidemic or spike in numbers.
Chief medical officer Dr Michael McBride said: "There is no poverty of ambition around anyone working in this sector, at whatever level, to make real inroads."
Families have expressed concern about how suicide is reported by the media, and the potential impact that could have on other vulnerable people and communities, the senior official added.
