Spray polyurethane foam (SPF) roof systems have unique chemical components, application techniques and worker protection requirements not commonly found in a majority of roof systems. Although several hazards common to many roof system installations are equally common with SPF roof system installations, roofing contractors face unique challenges when implementing controls to minimize SPF hazards because of the unconventional nature of SPF materials.
Airless spray equipment is used by an applicator to apply a two-component mixture to form an SPF roof system base. Component A of the mixture typically is methylene diphenyl diisocyanate (MDI) or a similar isocyanate-based compound that forms a liquid that expands and cures into a closed-cell foam when combined with the mixture's B side, a polyol resin.
Isocyanates are a group of chemicals used in the manufacture of polyurethane plastics, synthetic rubbers, foams, paints, varnishes and adhesives. Polyol resin is a chemical used to formulate polyurethanes; in the case of an SPF roof system, it is a high-density polyurethane foam.