He and a woman were stationed on the 14m-tall slide with an experienced operator, who discussed sharing ride posts before he "disappeared" and left Mr Martin and the woman running the slide on their own.
Another female worker had soon afterwards asked Mr Martin to work her ride, a rock-climbing wall, as the job aggravated her injured back.
Within half an hour the giant slide tower suddenly deflated, tumbling up to 15 children to the ground.
"I just swapped. There was no one to find and tell we were swapping, everyone just seemed to disappear. The lady who stayed at the slide the whole time, I think she was there on her own when it collapsed," Mr Martin said.
"Now I feel like I'm getting blamed for that ride, what happened to those children. I did a favour for a lady because she couldn't do it.
"I didn't know what had happened until I was told hours later. I still feel guilty, just like the lady who was left doing the slide on her own."
Mr Martin said there had been little supervision of the "hundreds and hundreds" of children "running wild" in the inflatable rides area, where a tangle of live power cords had been snaking underfoot throughout the day.
"The power apparently went out a few times. There was heaps of cords, and power packs for the air pumps, and kids with water everywhere. You could just tell something was going to go wrong sooner or later."
WorkSafe inspector Mark Donaghue had interviewed Mr Martin and his partner about their work on Saturday, and the couple had been told of a string of similar incidents on the giant slide at other events.