The family apartment was one of 12 flats to vanish in seconds as a massive explosion tore through the three-storey building just before 7pm on Thursday evening.
His mother, sister and grandmother had all been home, but not Bernhard. When he raced to the scene a few minutes later, all he saw was a pile of rubble where a dozen family homes had stood.
Rescue workers said last night that six people had been killed by the collapse of the block after a gas explosion. They said they had given up hope of finding survivors.
Three people were still missing under the rubble last night.But amazingly, soon after dawn yesterday, Bernhard's sister Michaela, 15, was dug out alive. She was taken to hospital where doctors said she was in a stable condition.
"I saw this mass of destruction when I arrived yesterday and I have been here all night. We are all hoping that there are people buried in there who are still alive. At least my sister is OK, she was in the flat with my mother and grandmother," said Mr Schachner, 18.
The scene of the explosion yesterday resembled an earthquake site. This quiet estate on the edge of Wilhelmsburg, a sedate town of 7,000 inhabitants 35 miles south-west of Vienna, with its manicured trees and carefully mowed lawns, had suddenly been turned into a place of havoc and death.
Stunned relatives and neighbours stood watching, their faces tense and drawn as the rescue operation continued. Sniffer dogs explored the rubble as first aid workers offered hot drinks and rolls.
A pall of grey masonry dust hung in the freezing air as khaki-clad soldiers, firemen and women and paramedics in red uniforms worked in the hope that each chunk of masonry they removed would bring them nearer a survivor.
Neighbouring buildings were pockmarked from flying debris and a minivan's windows had been blown out, and its windscreen shattered into a spider's web of fractured glass. Yet next to the mini-van another car was completely untouched.
A white curtain dangled from the jaws of a mechanical digger as its steel teeth bit into the rubble, bringing up mangled sections of wall and floor, and the destroyed remains of the inhabitants' lives.
A stream of dumper trucks flowed out of the site, each piled high with masonry. The corner of a beige patterned mattress poked out of one heap while on another truck sheets of pink writing paper stood out against the drab rubble.
By yesterday morning two people had been rescued alive. As well as Michaela Schachner, an elderly woman was found. But surgeons had to amputate her legs to pull her free and her condition was critical.
"This is a disaster for the area," said state official Doctor Josef Sodar, in charge of co-ordinating the rescue work. "We think eight people are still missing and hope they are still alive. We worked through last night with great determination and we will do that again tonight."
Looking at the remains of the apartment building, it was hard to believe anyone could still be alive underneath. But late yesterday morning the site fell silent as rescue workers equipped with sonar detection devices went to work, checking the rubble for signs of life.