Polyurethane is a widely utilized polymer found in numerous products, including foams, adhesives, and protective coatings. Concerns about inhalation safety depend significantly on the material’s state: liquid application, fully cured, or physically damaged. This analysis focuses on the distinct hazards presented during each phase.
Hazards During the Application Phase
The most severe inhalation hazard occurs during the application of liquid polyurethane products, such as spray foam insulation or two-part coatings. This acute risk is primarily due to highly reactive chemicals called isocyanates, including methylene diphenyl diisocyanate (MDI) and toluene diisocyanate (TDI). These chemicals are highly hazardous to the respiratory system before they have fully reacted and cured.
Inhaling isocyanate vapors or aerosols can cause irritation and inflammation of the respiratory tract, leading to symptoms like coughing, wheezing, and chest tightness. Repeated exposure, even at low levels, can lead to respiratory sensitization, which may result in occupational asthma. Once sensitized, a person can experience a severe allergic reaction from very small subsequent exposures.
The application process, especially spraying or heating, increases the airborne concentration of these reactive compounds. Spraying, in particular, creates fine liquid aerosols that can be easily inhaled deep into the lungs. Furthermore, liquid polyurethane coatings often contain volatile organic compounds (VOCs) that add to the inhalation burden during the application and initial curing period.
Off-Gassing from Cured Polyurethane
Once polyurethane has fully cured, the acute hazards from isocyanates largely disappear. A different concern emerges: the release of residual chemicals known as Volatile Organic Compounds (VOCs). This process, known as off-gassing, involves the slow leaching of these compounds from finished products like new furniture, mattresses, or flooring. While less acutely dangerous than isocyanate exposure, off-gassing presents a chronic concern, especially in enclosed indoor spaces.
The VOCs released can include substances like formaldehyde, toluene, and benzene. Exposure to these compounds can lead to immediate effects such as headaches, dizziness, and irritation of the eyes, nose, and throat. Chronic exposure is associated with long-term respiratory and central nervous system effects.
The duration of off-gassing is variable. The most noticeable odors dissipate relatively quickly, often within a few days or weeks. However, the slow, low-level emission of some harmful VOCs can persist for months or even years from solid materials. Proper ventilation during the initial period is important to reduce the concentration of these airborne chemicals.
Respiratory Risks from Dust and Heat
Physical disruption of cured polyurethane, such as through sanding or cutting, creates two distinct inhalation hazards. Sanding generates fine polymer dust particles that are physical irritants to the lungs. These small particles can carry residual chemicals and penetrate deep into the respiratory system, causing irritation and potential long-term effects.
A far more dangerous scenario is exposure to fire or extreme heat, which causes thermal decomposition. Polyurethane contains nitrogen, and when it burns, it produces highly toxic gases. This includes common asphyxiants like carbon monoxide (CO), which prevents oxygen uptake in the blood. The decomposition also generates hydrogen cyanide (HCN), an extremely fast-acting chemical asphyxiant. Both carbon monoxide and hydrogen cyanide are major contributors to fire toxicity and death in structure fires. The concentration of these toxic gases is influenced by the fire’s ventilation conditions, with oxygen-limited environments potentially increasing the yield of hydrogen cyanide.
Protecting Yourself from Inhalation Exposure
Mitigating inhalation exposure requires protective measures tailored to the material’s current state. During the liquid application phase, which carries the highest acute risk, specialized respiratory protection is mandatory. Workers applying two-component products must use a National Institute for Occupational Safety and Health (NIOSH)-approved respirator with organic vapor cartridges, or a supplied-air respirator when spraying isocyanates.
Adequate ventilation is essential to reduce the concentration of airborne isocyanates and solvents during application and initial curing. This often requires forced-air exhaust systems that remove vapors directly from the work area. Skin and eye protection, such as chemical-resistant gloves and coveralls, should also be used to prevent absorption and sensitization.
To manage chronic exposure from off-gassing in new products, it is advisable to “air out” new items, like foam mattresses or furniture, in a well-ventilated area before bringing them indoors. When working with cured polyurethane, such as during sanding, a simple dust mask is insufficient to protect against fine polymer particles and residual chemicals. A properly fitted respirator with a P100 particulate filter should be used to prevent inhalation of the fine dust.