having worked as an acoustic engineer many moons ago, here are my suggestions. Generally, to get sound atten, panels will be to be filled with a sound absorb compound. this would normally be a ridgid fibreglass panels similar to what is used in roofing, however this has a sound rateing, and is stiff. this will also take care of the fire hazard you have as well. panels should be skinned with a perfferated metal. to give venterlation, acoustic louvers would be installed, so that air could come in, and sound will not get out. Having a fan only will let sound out.
(sorry if there is spelling mistaked i typed this up really quick on my way out the door)