An internal company investigation failed to find a reason for the incident in which Houston's dozer went over the bench's crest and fell approximately 20m.
Another investigation into the tragedy by the Queensland Mines Inspectorate is still in progress.
"At BMA, there is no way of avoiding the tragic facts over the past few years," Palmer told a Bowen Basin Mining Club luncheon in Mackay.
"In 2015 we lost Laurie Donovan. In 2017 we lost Daniel Springer, and we lost Allan Houston just over six months ago.
"As a leader you never want to receive the call that one of your people has been hurt or killed at work.
"And my phone buzzed early on New Year's morning, while I was back home in Childers, with news of Allan's fatal accident.
"And I can assure you it was an experience that will stay with me forever."
Palmer said that internally, over the past six months, BMA had been reviewing and resetting its safety standards and refocusing on its life-saving critical controls.
"To be candid, we recognise we have more work to do - and we can't ever be complacent about safety," he said.
"Safety never stops - but at BMA we are encouraged by the statistics for the last quarter, which tell us that we are improving by setting standards we can be proud of.
"And I am committed to maintaining this momentum."
Palmer said BHP and BMA were also active participants in the industry-wide safety reset and were working closely with the Queensland government, the Queensland Resources Council, and fellow operators.
"Next month, as we do annually, we will be participating in the Queensland Mining Industry Health and Safety conference - with a particular focus on reforms that will strengthen the safety culture in the resources sector," he said.
"As we always say to our people, our achievements and performance mean nothing - if we don't all go home safe at the end of the day."