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.
Additional chemicals may be present in SPF to promote a chemical reaction between the A and B sides, create its foaming characteristic, act as a flame-retardant and give the foam proper consistency, among other things. Two 55-gallon drums, each containing one part of the two-component mix, usually are housed in insulated vans or trailers with transfer pumps or pressurized holding tanks and other necessary equipment for delivering high-pressure SPF to the applicator at roof level.
The mixed components are sprayed in lifts or layers onto the roof surface through a specially designed spray gun to allow for proper curing and uniform material application. After the SPF has cured, a protective surfacing, such as a coating, is applied using less-sophisticated airless spray equipment or a brush and roller.
When a material is applied with airless spray equipment, there is a possible danger of inhaling a contaminant's or chemical's respirable particles. Limiting worker exposure to gases, vapors, fumes, dusts and mists is required in the Occupational Safety and Health Administration's (OSHA's) construction regulations 29 CFR §1926.55, Subpart D, "Occupational Health and Environmental Controls."
Subpart D requires "feasible" engineering or administrative controls to first be used to minimize worker exposure and then personal protective equipment (PPE) if those controls are insufficient or infeasible. Fortunately, because SPF roof system installations occur outdoors, airborne concentrations of contaminants to which a worker may be exposed are minimized.
Manufacturer safety data sheets (SDSs) for SPF components provide specific information regarding the hazardous chemicals present in the A and B sides that could pose an inhalation risk to workers, as well as the recommended respiratory protection to minimize or eliminate that risk.
The hazard of most concern from the A side is respiratory sensitization. Certain individuals may become sensitized to isocyanates after repeated overexposures above the permissible exposure limit or, in rare cases, a significant one-time exposure. Subsequent exposure of these individuals to even minor concentrations of isocyanates can result in wheezing, shortness of breath, coughing, chest tightness and, in some cases, asthma attacks. According to the American Chemistry Council Center for the Polyurethanes Industry (ACC CPI), asthma attacks in such instances may be life-threatening; therefore, manufacturers recommend sensitized individuals avoid subsequent respiratory or even skin contact with isocyanates at any concentration level.
A review of several SDSs for SPF's isocyanate component indicates respiratory protection is required at all times to avoid possible symptoms such as respiratory irritation, chest discomfort and reduced pulmonary function. Control methods for respiratory hazards described in SDSs include a minimum air-purifying respirator with dust filter and organic vapor cartridge. It is critical filter and cartridge replacement schedules be established and adhered to so respirator function is maintained.
Isocyanates do not have a distinctive odor or taste, so a worker would not be aware of a malfunction or improper air-purifying respirator operation. Supplied air respirators using breathing air from an uncontaminated source are recommended in some SDSs when MDI levels exceed those at which an air-purifying respirator may be effective. Excessive MDI levels typically will not be present in a majority of SPF roof system installations because of natural ventilation though weather conditions and building configuration may restrict dispersal of SPF mists.
Some coatings applied to SPF roof systems present similar inhalation hazards particularly when applied with airless spray equipment. Workers and contractors generally are aware of the health concerns involved with spraying solvent-based, flammable coatings and may ignore the inhalation hazards related to acrylic or waterborne SPF coatings. However, a review of the SDSs for a variety of coatings indicates manufacturers universally recommend respiratory protection for all spray applications of their products. At a minimum, half-mask or full-face air-purifying respirators with dust filters and organic vapor cartridges are required.
Another hazard often overlooked when using airless spray equipment involves material being injected into the skin from contact with pressurized fluids. System pressure produced by SPF spray equipment can exceed 2,000 pounds per square inch, and airless sprayers for coatings also operate at high pressures. Failure of hoses or couplings has the potential to release liquids at significant pressure sufficient to inject material under skin.
Contact with a spray gun tip also may cause an injection injury. ACC CPI recommends applicators do the following:
Contact with chemicals used in SPF roof system installations should be avoided to the extent possible. Other PPE critical to minimize exposure includes a full-body protective coverall, a spray sock or hood for head protection, goggles or full-face piece for eye and face protection, and chemical-resistant gloves made with butyl, nitrile, chloroprene rubber or polyvinylchloride.
As with all hazardous chemicals workers encounter at job sites, SDSs for such products must readily be accessible during workers' shifts so critical information is available to avoid injuries or complications from exposure. SDS maintenance is just one component of an OSHA-mandated written hazard communication program under 29 CFR §1910.1200 for the protection of workers from chemical exposures in the workplace.
OSHA requires fall protection in construction when workers are at heights of 6 feet or more. Conventional fall-protection systems include guardrails, safety nets and personal fall-arrest (PFA) systems. When workers are engaged in low-slope roofing work, they also may be protected by a warning-line system and one of the three conventional systems mentioned (when work takes place outside the warning line) or a warning-line system and a safety-monitoring system. On low-slope roofs 50 feet wide or less, a safety-monitoring system may be used alone. In addition, workers exposed to falls through holes, such as skylights, must be protected with the use of guardrails around holes, covers over the holes or PFA systems.
During an SPF roof system installation, the use of most fall-protection systems can be a challenge. SPF typically is applied with an applicator handling the spray gun and a second worker (helper) minding the cumbersome hoses that supply the gun. The helper also may perform other tasks during spraying such as moving fall-protection equipment or holding shields or screens to prevent overspray and protecting building components as the spray is directed in their vicinities. Fall-protection systems, such as warning lines or guardrails placed directly on a roof, that demand constant relocation as the system is installed (and can interfere with the uniformity of SPF application) add to the challenge of an SPF roof system application.
Use of a safety monitor alone complies with OSHA rules only when a roof's width is 50 feet or less. The issue of roof hatch or skylight fall protection as an SPF system is applied near these components inevitably demands the use of PFA systems with a lifeline to manage—a safety monitor is not an option at these areas.
Some innovations in fall protection may help with regard to unprotected sides or edges (without a minimum 39-inch parapet height). Fall-protection system manufacturers have developed innovative attachment hardware for guardrails that can be more effective to facilitate SPF and other roof system installations. A benefit is guardrail baseplates are eliminated through the use of clamping devices or other special hardware that secures guardrail end posts with minimal or no intrusion into the roof field. Spray application can take place without the need to move fall-protection equipment, and edge protection always is in place.
Figure 1 shows a parapet wall clamping system made by ACRO Building Systems that uses common 2- by 4-inch wooden toprails and midrails. Similar products include FIXFAST USA's Turbo-Rail System shown in Figure 2 and Guardian Fall Protection's Alligator Parapet Roof System shown in Figure 3. Other similar products are offered by manufacturers, including Garlock Safety System's TurboCable Fall Protection System; Miller® by Honeywell's EPIC Barrier System; Safety Rail Co. LLC's SRC Parapet Clamp; Perimeter Protection Products LLC's Parapet Wall/Slab Clamp; Capital Safety's Portable Construction Guardrail; and AES Raptor® LLC's RaptorRail.™ Some fall-protection system manufacturers also produce specialty hardware for installing their guardrail systems on exterior walls when parapet clamping devices cannot be used.
Although a number of available fall-protection products simplify edge protection for workers, skylight fall protection remains an issue during SPF roof system installations. Skylights protected by integrated metal cages or screens generally will offer sufficient protection from falls. Workers may need to rely on the use of PFA systems using lifelines with rope-grab lanyards or self-retracting lifelines to be compliant with OSHA rules.
The realities of SPF roof system installations point to a greater emphasis that must be placed on fall-protection options for workers installing these systems. Earlier versions of fall-protection equipment were not compatible with SPF roof system installations; consequently, compliance was neglected. Manufacturers have responded to this issue and now offer products more in tune with many work processes in the roofing industry. Similarly, products for worker protection from other SPF-related hazards such as disposable coveralls, gloves and full-face respirators have been specially designed to allow for ease of use and cost-effective protection.
Harry Dietz is NRCA's director of risk management.