where can i find (free) industry safety blocks?
 
i need prohibid-blocks, mandatory-blocks etc.

Are you looking for "signage"?  Like "No Smoking" or "Hearing Protection Required Beyond This Point"?

yes


no smoking
no open fire
speed limit 10km
no photographs
no cellphone
safetyglasses required
helmet required
safety boots required
...

Look at this and check on the two links referenced.
http://www.cadforum.cz/cadforum_en/qaID.asp?tip=4660

these are the one i need but...those are .gif-files...
can they be used in CAD??
 
 

Not in AutoCAD without converting to another format like jpg.
 
Early releases of AutoCAD (like r14) had the GIFIN command but it was replaced with the IMAGE command in later releases and support for GIF files got dropped.