When spraying butyrate or urethane, you always want to take precautions to protect your skin, your eyes, and lungs.  The best way to do this is to wear rubber gloves, safety goggles, a Tyvek suit, and use a fresh air breathing unit.  The fresh air isn't necessary with the butyrate, as it is an air dry system.  A disposable charcoal mask will suffice.  However, the drying agent in the urethane primer and paint is a catalyst.  The base of these catalysts is an isocyanate.  And spraying an isocyanate without using a fresh air breathing system can be detrimental to your lungs. Unprotected exposure to isocyanates can cause severe asthma attacks - some severe enough to kill.  Some symptoms to look out for - eye irritation, nasal congestion, dry or sore throat, cold-like symtoms, cough, shortness of breath, wheezing, or chest tightness. Bottom line - Be safe!  Wear the masks, suits, gloves, and goggles when spraying any kind of butyrate or urethane system.