Cost-Effective Ventilation for Large Spray-Painting Operations

摘要

Ventilation air serves several purposes during spray painting of objects in an enclosed space. By removing particles of overspray, air movement protects the texture of surfaces already painted and those yet to be painted. By diluting and removing solvent vapors and by removing overspray, it limits the exposure to personnel present while paint is applied. In achieving these ends, the ventilation stream carries the solvent vapors and overspray solids into the external environment as it is exhausted. Inside the enclosure the movement and condition of ventilation air must conform to standards that ensure worker safety, both from explosion and fire hazards that would result from excessive accumulation of solvent vapors, and from toxicity caused by absorption or inhalation of solvent vapors or of fine overspray particles. Coatings applied to Air Force (AF) aircraft are an epoxy primer and a urethane topcoat. In general, the most toxic constituent of each (strontium chromate in the primer and isocya-nates in the topcoat) remains in the droplets as they dry, so management of particles is critical to meeting standards for personnel exposure. The Lower Explosion Limit (LEL) of paint solvent is typically an air concentration of 1 to 2% by weight (10,000-20,000 ppm), whereas the Personal Exposure Limit (PEL) of the constituents is typically 100 to 5,000 ppm (measured as an 8-hr, time-weighted average). Thus, compliance with exposure standards ensures compliance with fire and safety standards in AF facilities, and the same may be expected (but should be verified) in facilities applying more-benign coatings.