All roof system installations have common hazards, such as falls, that must be controlled. However, some unique hazards specific to spray polyurethane foam (SPF) roof systems must be assessed and managed on SPF roofing projects.
To complete an SPF roof system installation, workers use airless spray equipment to apply a two-component mixture to form the base of an SPF roof system. Airless spray equipment uses hydraulic pressure rather than compressed air in conventional spray equipment to apply the material to a roof surface. An airless pump pushes the SPF material through a hose and then through a fine hole in a spray gun tip, spraying the material in a fan pattern.
Generally, the advantage of airless spraying is the material is sprayed without altering its physical properties (as may occur when spraying with compressed air) to atomize the material, reducing viscosity by using solvents to thin it. The result is a more uniform application with consistent thickness and limited overspray.
Component A of the two-component mixture generally is referred to as MDI—shorthand for the compound methylene diphenyl diisocyanate or a similar isocyanate-based liquid compound that expands and cures into a closed-cell foam when combined with component B, a polyol resin. Isocyanates are a group of chemicals used in the manufacture of paints, varnishes, adhesives, synthetic rubber, polyurethane plastics and foams. Polyol resin is a chemical used in the formulation of polyurethanes that produce a high-density polyurethane foam in SPF roof systems.
Additional chemicals may be present in SPF that serve a variety of functions, such as promoting the chemical reaction between A and B components, creating foaming characteristics, acting as a flame-retardant and establishing proper foam consistency. 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 high-pressure holding tanks and other auxiliary equipment for delivering high-pressure SPF to the applicator at the roof level.
The mixed components are sprayed in lifts, or layers, onto a roof surface through a specially designed spray gun to achieve proper depth and allow for proper curing and uniform material application. After the SPF has cured, a protective surfacing, such as an acrylic, butyl, silicone or urethane coating, is applied using a brush, roller or more simple airless spray equipment than needed for SPF.
Potential health hazards
As with nearly all products workers are exposed to on a job site, the safety data sheets (SDSs) supplied by product manufacturers provide specific information regarding the presence and nature of any hazardous chemicals. SDSs also will (among other things) describe the precautions to take to minimize or eliminate exposures, the type of personal protective equipment (PPE) that may be needed, the first-aid procedures to employ in emergency situations, and any special spill or cleanup requirements.
Because not all SPF products have precisely the same chemical components, workers must be familiar with the SDS that matches the product they are using, and employers must ensure the correct SDSs are accessible to workers in the field. Employer mandates from the Occupational Safety and Health Administration (OSHA) for hazardous chemicals in the workplace are found in OSHA Hazard Communication standard 29 CFR §1910.1200. One of the most important obligations for roofing contractors is to maintain current versions of SDSs for all chemicals used in the workplace and have those SDSs easily accessible for workers on all job sites.
The American Chemistry Council®'s Center for the Polyurethanes Industry (ACC CPI) notes MDI in liquid, vapor or aerosol form can be harmful to health and notes the four possible routes of exposure are inhalation, contact with eyes, contact with skin and ingestion.
The hazard of greatest concern regarding MDI in SPF is respiratory exposure. Because the installation method involves spraying, mists containing MDI particles become airborne and are more likely to be inhaled by workers in proximity to the spray operation.
In a majority of exposures, MDI merely irritates the nose and lungs, but higher concentrations may cause breathing difficulty. Certain individuals may become sensitized to MDI after repeated overexposures above the permissible exposure limit or, in rare cases, a significant one-time exposure. Such individuals who experience a subsequent exposure to even minor concentrations of MDI may show symptoms of wheezing, shortness of breath, coughing, chest tightness and, in some cases, asthma attacks.
Although asthma attacks in sensitized individuals are rare, according to ACC CPI, they may be life-threatening. MDI manufacturers recommend sensitized individuals avoid subsequent inhalation of MDI or even skin contact with isocyanates at any concentration level. The National Institute for Occupational Safety and Health (NIOSH) notes early recognition of isocyanate sensitization is critical to reduce the risk for any long-term or permanent respiratory problems for sensitized individuals. Of most significance, some workers who have become sensitized to isocyanates never should have any contact with such products regardless of engineering controls or PPE being considered, according to a 2004 NIOSH Health Hazard Evaluation Report.
Component B of the SPF mixture also presents inhalation hazards that may cause irritation of the respiratory tract, cough, sore throat and a runny nose. Some chemicals in component B may cause an irregular heartbeat and vision problems. Subpart D in OSHA's Safety and Health Regulations for Construction standard 29 CFR §1926.55 requires feasible engineering or administrative controls first be used to minimize worker exposures. If those controls are not feasible or are insufficient, PPE must be used.
Ventilation equipment often is considered an engineering control during spray operations. However, ventilation for roof applications is provided by the nature of the environment itself; additional equipment such as fans typically are ineffective or cause application problems.
To protect workers, appropriate PPE must be used. A review of several SDSs for SPF materials indicates respiratory protection is required at all times to avoid inhalation hazards. Control methods for respiratory hazards described by manufacturers in SDSs include a minimum air-purifying respirator with dust filter and organic vapor cartridge. Isocyanates don't have a distinctive odor or taste as some other materials do, so a worker may not be aware of a malfunctioning respirator or spent filter. It is critical replacement (change-out) schedules for filters and cartridges be established and adhered to so proper function is maintained and worker protection is assured.
When contaminant levels exceed those at which an air-purifying respirator may be effective, supplied air respirators using breathing air from an uncontaminated source are required. Natural ventilation on a roof may diffuse the concentration levels of most airborne contaminants during SPF roof system installations, but workers must be aware of weather conditions and building configurations that may not allow for quick dispersal of contaminants.
It is important to note use of a respirator demands a written respiratory protection program under OSHA's Respiratory Protection Standard 29 CFR §1910.134 along with a number of other requirements to ensure workers can safely use the proper type of respirator and maintain it.
Similar inhalation hazards exist for workers spraying the protective outer coating on the SPF. Health concerns involved with spraying flammable, solvent-based coatings are fairly obvious, but workers and roofing contracting companies may not be as concerned with hazards related to waterborne or acrylic SPF coatings. However, a review of the SDSs for a variety of these coatings indicates manufacturers universally recommend respiratory protection during spray application of their products. At a minimum, half-mask or full face-piece air-purifying respirators with dust filters and organic vapor cartridges are required.
According to ACC CPI, skin contact with component A can cause irritation and sensitization manifested by reddening of the skin, itching, swelling and rash. It's important to note skin contact alone may lead to respiratory sensitization.
To minimize skin exposure, it is critical to use the following PPE:
A skin hazard often overlooked when using airless spray equipment involves material being injected into skin from contact with pressurized fluids. System pressure produced by SPF spray equipment can exceed 2,000 pounds per square inch; airless sprayers for coatings also operate at high pressures. Injury can result from the spray tip coming in contact with body parts and injecting material into the body at a contact point. This type of injury requires emergency medical attention because though it may appear as a cut or puncture, it is much more serious because chemicals may have entered the body at the cut site acting as a poison that can lead to amputation or more significant harm.
Adhering to the following safeguards will avoid skin injuries:
If MDI gets on skin, ACC CPI suggests washing with soap and warm water and refrain from using solvents to remove it.
Eye contact with SPF's component A may cause stinging or swelling of the eyes along with redness and watering or tearing. Some chemicals in component B also may cause blurry or foggy vision, and halos may appear in the field of vision around bright lights. Eye protection is the best way to avoid getting SPF components in the eyes. If material does get in the eyes, ACC CPI suggests a continuous flow of low-pressure water be applied and to see a doctor.
If a worker ingests SPF components, he or she should see a doctor immediately. It is important to not induce vomiting but rinse the mouth with water.
A safe workforce
Using PPE to control hazards during SPF roof system installations keeps workers safe and healthy. Many of the hazards related to the exposures that come with SPF roof system installations cannot be engineered out of a project but can be controlled with proper PPE.
The use of chemicals during an SPF roofing project also requires adherence to OSHA's Hazard Communication standard, such as developing chemical inventory lists, maintaining up-to-date copies of SDSs for all chemicals found in the workplace, and training workers about chemical hazards and prevention of injuries related to the chemicals.
Purchasing the proper PPE and following procedures OSHA requires for PPE use translate to a safe and healthful workforce.