Is Methylene Diphenyl Diisocyanate safe in indoor air?

Methylene diphenyl diisocyanate (MDI) is a suspect carcinogen, primarily due to its metabolite methylene dianiline (MDA), which is a known animal carcinogen.

Why here

MDI can be metabolized in the body to MDA following inhalation exposure from indoor air sources, such as during the application or off-gassing of MDI-containing products.

What would have to be true

Inhalation exposure to MDI, leading to the formation of its metabolite MDA. NIOSH recommends minimizing work-related exposure to MDI due to the potential carcinogenicity of MDA.

Methylene diphenyl diisocyanate (MDI) is an irritant to the eyes, skin, and respiratory tract.

Why here

MDI can be released into indoor air as vapor or aerosol during the application of MDI-containing products such as spray foams, sealants, adhesives, and coatings, or from uncured materials, leading to direct contact with mucous membranes and skin.

What would have to be true

Exposure to airborne MDI can cause irritation, with symptoms like eye tearing, nose and throat irritation, and cough.

Methylene diphenyl diisocyanate (MDI) can cause respiratory sensitization and asthma, even at low concentrations, particularly in individuals who have become sensitized.

Why here

MDI is a key component in polyurethane products such as spray-applied foam sealants, adhesives, and coatings used in residential and other indoor settings. Inhalation exposure can occur during application due to aerosols and vapor, and from off-gassing of uncured material.

What would have to be true

Exposure to airborne MDI, especially above 0.08 µg/m³ (California OEHHA Chronic Inhalation REL) or above 20 ppb (0.02 ppm), can lead to sensitization and trigger asthmatic symptoms. Once sensitized, even very low concentrations may trigger symptoms.

Inhalation of methylene diphenyl diisocyanate (MDI) can cause respiratory sensitization, leading to asthma and severe asthma attacks upon subsequent exposure, even at low concentrations.

Why here

MDI is used in consumer products such as spray-applied foam sealants, adhesives, and coatings, where aerosols or vapors can be inhaled during application or from off-gassing during curing.

What would have to be true

Inhalation of MDI vapors or aerosols, potentially at concentrations below the odor threshold, from products like spray foams or coatings. Sensitization can occur from a single high-dose exposure or repeated low-level exposures.

Inhalation of methylene diphenyl diisocyanate (MDI) vapors or mist can irritate the mucous membranes of the respiratory tract (nose, throat, lungs), causing symptoms such as runny nose, sore throat, coughing, chest discomfort, and shortness of breath.

Why here

MDI is present in consumer products that can release vapors or aerosols during use (e.g., spray applications, heating, foaming), leading to direct inhalation.

What would have to be true

Inhalation of MDI vapors or mist at concentrations above occupational exposure limits (TLV), or even below for individuals with pre-existing bronchial hyperactivity.

Repeated inhalation exposure to polymeric methylene diphenyl diisocyanate (pMDI) aerosol can lead to specific target organ toxicity, causing irritation and changes in the lungs and nasal cavity.

Why here

While primarily an occupational concern, prolonged or repeated consumer exposure to off-gassing MDI from products like insulation or coatings could lead to similar effects.

What would have to be true

Repeated inhalation of pMDI aerosol at concentrations of 0.2 mg/m3 or higher over extended periods (e.g., 6 hours/day, 5 days/week for 2 years in animal studies).