[edit] I found an academic paper that discusses the safety of these heaters - dated 1973. I'd guess that they've gradually disappeared thanks to better heating systems and improved safety regulations. The paper: http://hej.sagepub.com/content/32/4/120.abstract
You are of course right in pointing out that central heating often goes along with central water heating and that heating is often based on fossil fuels such as gas.
My hot-water + heating system is gas-fired, but the boiler is in a utility closet vented to the outside.
Fortunately she was only scared but otherwise ok. Quite the bang, I've had a healthy respect for old Junckers products that have gas lines fed into them since.
Jacques, if you happen to come to Poland again, shoot me an e-mail, I'll buy you a beer :).
That might be quite soon actually. I'll be travelling to Krakow and on another trip I'll be going to Bialestok.
My cell is + 31 6 30 366 241, I won't have email during those days. Send me a text please so I'll be able to reach you when I'm there.
Let me continue this conversation via e-mail then.