Hazard symbols exporting blurred

[CHewitt]

Hi, so I keep having a recurring issue that two symbols that I use when exported to PNG or PDF come out blurred and unreadable which can be seen below.

However it is only these two symbols that are effected, all the others are okay. The only fix that I've come across is reducing the resolution/dpi when exporting but that means that if you attempt to zoom in everything becomes blocky and low resolution as it would.

Is there any way I can keep a highish resolution (I'm using 300 at the moment) and have these symbols clear? 

Thanks.

[RobertBorchert]

how complex are those symbols and are they using non standard fonts. In the export have you tried embedding the fonts?