Installing Ceiling Fans - suspended platerboard ceiling

I had 4 ceiling fans sent over to my apartment in Almeria and took my joist detector with me so I could make sure I was fixing them securely. Then shock hooror I discovered that the ceilings are made of something that looks like plasterboard but thicker and are suspended from the reinforced concrete by poles which are stuck or glued in some way.

I asked others who had them already fitted in the apartment block and it seems they are just fitted using butterfly bolts or similar. Here in UK we would never consider doing this but the "plasterboard" is thicker and maybe interlocking but I can't tell without seeing how it is put up. In any case I have now installed 2 of these and there seems to be no problem as they are solidly fixed to the ceiling with no wobble etc.

My question is whether anyone else has come across this problem or does anyone know how these ceilings are fixed to the concrete and is it considered safe to just use these type of buttfly bolts to attach the fans.

The older ceilings are supended by horse-hair dipped in 'yeso' .( a type of plaster which sets like concrete. ) In addition each plaster panel is 'yesoed' to the next & are interlocking. Newer ceilings are suspended by galvanised wire but are still stuck together. It tends not to be done now since the advent of suspended ceilings where the panels are supported by the metal dividing bars. The panels though are still the heavy plaster ones.

Many thanks Gus - That makes sense now and is probably why people feel safe to just attach fans  to the ceiling. My wife will sleep easier knowing that it is unlikely the fan will coem crashing down on here head.!

 Personaly I always insert a lenght of  wood [ 2"x 1"] in old money into the ceiling void and fix the fan to it, this ' spreads the load'

Funnily enough that was my first thought and , in fact, the first one I fitted there was a big enough hole where someone had previously been messing about and I was able to make up a little template of 1/4" ply  x 1.1/2" wide and fit it through the hole so the toggle bolts would rest on the wood and not the " plaster". 

In the other room the hole was much smaller form the electrics so I just decided to use the two toggle bolts and see what happened.

I then realised that using wood may be helpful for fixing e.g. screwing into, but I don't think it would actually spread the load at all as surely the load is spread over the entire ceiling if it is all bonded together.

Anyway, I appreciate the feedback and when I return, hopefully soon, I will confidently fit the other two fans without two much worry. lol