"We watched this wee girl go through all her treatment and all sorts of things and that motivated us."
Having done the climb five times before Mr Glenn is well aware of the challenges it poses.
"It's not easy, you're carrying over 20kg of of stuff up there.
"Being in full firefighting gear keeps heat out but it keeps it in as well. The temperature gets pretty high and your heart rate gets pretty high."
The training regime for the climb consists of 20-minute bursts in full gear scaling an escalator, three times a week.
"Normally we hit 14 or 15 mins for the climb, but we try and train a bit harder than the actual climb will be."
Personally Mr Glenn has raised $6,500 for the cause, with the national total exceeding $1 million.
Fire crews from all around the world including the Fire Department of New York will be getting stuck in to generate as much support as possible for the Leukaemia & Blood Cancer Foundation.
Mr Glenn said catching up with like-minded firefighters from different countries was a perk of being involved, but it doesn't distract from the key driver.
"The social side is huge, having a few beers with guys from across the world is great, but that's not the main motivation.
"[Charlotte] comes fundraising with us, with all her beads. She's completely cured now but she still has a way to go to fully recover.
"We've seen her at her absolute worst, and now she's a normal 6-year-old girl and she's just gorgeous."
The Sky Tower will be lit up in red to mark the challenge.
