The captain of the boat discovered the men's bodies on Sunday evening. They had been in charge of looking after a cavity in the boat which is designed to ensure it remains stable, fire department spokesman Franz Resperger said. He added that the job was hard and unpleasant and that as it was not possible to enter the cavity with respirators, it had to be well ventilated.
According to Resperger the boat is owned by a German shipping company and the crew was Russian or Ukrainian.
He added that the rescue team at first assumed there had been a gas leak but that air measurements taken in the cavity were so far inconclusive and it is not clear if the men died from a lack of oxygen or from breathing in poisonous gases.
"The oval hatch through which one reaches the cavity is only about 40 by 25 cm big, so only one person can go through at a time. It took us some time to bring the three bodies out,” Resperger said.
He added that at present “it's a complete mystery why these people died”.
The captain last had contact with the three men at Tulln. He was uninjured.
Resperger described the cavity as an empty space around four meters high, with a floor space of around four to six metres. Two of the sailors had gone down the hatch but when they failed to reappear on deck the third climbed down to find them. His body was found on the ladder.