The savagery and heartache of Sept. 11 is the wound that never heals. It’s a scab that opens up with the flashback of memories.

I experienced a rush of emotions the moment I walked in to the museum during a recent visit.

I’m moved by the depth of the location of exhibits underground — at the precise footprint of the World Trade Center towers. Right on bedrock. It’s a powerful symbol.

I applaud the museum’s efforts to demonstrate the horror of that day and educate the public with video messages and authentic relics.

The museum didn’t try to soften the evil of what occurred on Sept. 11. It didn’t sugar-coat anything.

I saw the bare, steel beams, the charred remains of what was the World Trade Center buildings.

How the once mighty, beautiful structures and architecture were pulverized into twisted pieces and shards of steel and concrete. It’s a reminder that the towers and 2,600 people were reduced to rubble, vaporized.

One of the most poignant exhibits — the one that hit me in the gut and brought me back to the loss and heroism of that day — is the remains of Ladder 3.

The front of the cab is totally destroyed.

I immediately thought of Ladder 3 Capt. Pat Brown, who lost all the men on his day and night tour that day. What a leader he was, Paddy Brown. He was a teacher, a ­motivator.

For me, it’s all about the people. Paddy Brown was a decorated FDNY hero well before 9/11. He was a Vietnam War veteran.

Men who weren’t even scheduled to work that day would follow him into that burning tower. They would follow him anywhere. Now he and all his men were gone.

Ladder 3 is a wreck when you see it. It brings back searing memories to think all the people we lost.

Even the FDNY bunker gear and equipment packs an emotional wallop.

When I saw the gear on display, it instantly reminded me of the agonizing recovery effort at Ground Zero. Finding remains was a painstaking, tedious process. Remains were hard to come by.

But the bunker gear we found held more of the human remains of our brothers.

The damaged “survivors’ staircase” from the North Tower is right there — near the entrance of the museum. The last group of survivors that evacuated when the building collapsed descended down that staircase. What a lesson.

One of the more uplifting exhibits is a room with a verse from Virgil: “No Day Shall Erase You From the Memory of Time.” The words are inscribed against a cheery, blue-tiled wall.

Every one remembers what a gorgeous, cloudless day that Sept. 11 morning was — before the terrorists crashed the planes into the towers. The display and verse to me is a symbol of the beauty of the day and darkness that followed. The contrast between good and evil.

There are visual reminders of FDNY heroism everywhere. The museum did an excellent job of paying tribute to firefighters’ tremendous sacrifice.

I spent 32 years in the Fire Department. I knew how many firefighters tried to save people that day. I knew how heavy the losses would be when the building collapsed.

We lost 343 people.

There is no group that made a greater sacrifice than the FDNY in trying to save strangers on Sept. 11.

For me, the Sept. 11 tragedy has been a source of pride and pain for so many of the great men I worked with who died that day. There was so much grief for the families the guys left behind.

It’s going to be difficult for a lot of families to experience the museum.

I dread going back. But I feel an obligation to the men who lost their lives and respect for the people they left behind.

I understand there’s been controversy about mentioning that the terrorists were self-described Muslim extremists in one of the museum videos. But it was necessary to explain who the evil people who perpetrated the crime were.

It’s not an insult to Islam to point out the evil of a small group of extremists who killed innocent people that day.

Tom Von Essen was the city fire commissioner on Sept. 11, 2001.