Is Spray Foam Insulation Safe After It Cures?

Is spray foam insulation safe? It depends on the stage

Professional spray foam is made on site from two liquids. The A-side is polymeric MDI (methylene diphenyl diisocyanate). The B-side is a resin blend that, depending on the product, carries amine catalysts, a blowing agent and a flame retardant such as TCPP. The two meet in the gun, react and expand within seconds; Spray Foam 101 shows the equipment.

Once reacted, the MDI is bound into a polyurethane polymer, so the safety question has a different answer at each stage.

During spraying: why everyone leaves

The Center for the Polyurethanes Industry (CPI), the industry's own trade group, says "MDI is typically the greatest concern during spray application." Spraying turns it into vapor and a fine aerosol, and EPA notes these "can migrate through the building if the area is not isolated and properly ventilated."

Isocyanates are the reason this matters. EPA states they "have been reported to be a leading chemical cause of work-related asthma." Sensitization is the bigger worry: once a person is sensitized, "even low concentrations of isocyanates can trigger a severe asthma attack," and EPA says there is "no recognized safe level of exposure" for that person.

The B-side carries its own irritants. EPA notes that amine catalysts "may be sensitizers and irritants that can cause blurry vision (halo effect)," and CPI says several have an ammonia-like odor.

So the crew wears supplied-air respirators and full protective clothing, the work area is sealed off with exhaust fans holding it under negative pressure, and the house is empty. CPSC staff say residents should vacate "for at least 24 hours." CPI says the same for high-pressure foam and notes that recommendations vary by product, so get the time for your product in writing. The full step-by-step is in how long to stay out after spray foam.

Is spray foam toxic after it dries?

Foam is dry to the touch in minutes, but dry isn't cured. EPA's wording is careful: "When spray foam has been correctly applied and cured, it is usually considered to be relatively inert." CPI's own health and safety guide adds that additives "may emit from the cured foam after application at measurable quantities."

The best independent data comes from the National Institute of Standards and Technology (NIST). In a 2017 report for the Consumer Product Safety Commission, NIST measured emissions from several foams in small test chambers:

• Amine catalysts and most other volatiles decayed exponentially, fastest in the first 100 hours.
• TCPP from closed-cell foam also fell quickly, and the total released was tiny: under 8 micrograms out of roughly 300,000 micrograms in the sample.
• TCPP from open-cell foam stayed roughly constant and was still measurable more than 24 months after application. It rose with temperature: in a test house, the average at about 83°F was 3.4 times the level at about 71°F.

An earlier NIST paper found open-cell samples emitting TCPP at concentrations about 100 times higher than closed-cell after 100 hours. NIST cautions that chamber results shouldn't be used to predict whole-house levels. The pattern still holds: most of what you can smell leaves within days, and the slow, lasting emission is a flame retardant, mostly from open-cell foam in hot spaces. If anyone in the house is sensitive, that's a fair question to raise before choosing open-cell.

EPA also says "the potential for off-gassing of volatile chemicals from spray polyurethane foam is not fully understood." Anyone who tells you cured foam emits nothing at all is overselling it.

Emissions certifications

Some spray foam products carry third-party certifications such as UL GREENGUARD Gold, which tests chemical emissions from samples of the product. There's also an ASTM test method written specifically for spray foam, ASTM D8142. It measures blowing agents, formaldehyde, residual solvents, some amine catalysts and TCPP from foam samples, but not isocyanates.

If indoor air quality is a priority, ask whether your product holds an emissions certification and ask to see it. Know its limit: the test is run on correctly made samples. It can't vouch for foam that was mixed off-ratio in your attic.

When spray foam isn't safe

Good chemistry turns into a bad result in a few predictable ways:

• Off-ratio foam. CPI states that if foam is "applied off-ratio, the insulation product will not cure properly and unreacted chemicals may be emitted." It often shows: discolored, chalky, sticky or shrinking foam. See off-ratio spray foam.
• Passes sprayed too thick. Reaction heat builds in the core, which can scorch the foam and leave odors that don't clear. See is spray foam flammable.
• Poor containment and ventilation. Vapors drift into the rest of the house, and odor soaks into framing, insulation and belongings.
• Heating, grinding or burning cured foam. EPA says plumbers and electricians "should not heat or grind spray foam," and that fires involving spray foam "may release isocyanates, hydrogen cyanide, amines, and other toxic chemicals."
• Trimming too early. EPA warns that cutting or trimming foam as it hardens can generate dust, so early trimming is a job for protected workers only.
• DIY kits used without the gear. Two-component kits use the same chemistry. See DIY spray foam kits vs professional.

Who should be extra careful

CPSC staff single out people with "a history of skin conditions, respiratory allergies, asthma, or prior isocyanate sensitization." Their advice is to review the product information carefully and, "if necessary, consider alternative insulation products."

We agree. If someone in the house is already sensitized to isocyanates, for example from work with isocyanate paints or coatings, cellulose, fiberglass or mineral wool may be the better choice. Anyone else with asthma or allergies should take the product's safety data sheet (SDS) to a doctor before the job, not after.

What to ask before the job

1. What is the exact product? Ask for its technical data sheet (TDS) and SDS. CPSC staff advise getting copies of the product literature.
2. What is the re-occupancy time for that product, in writing?
3. How will the work area be sealed off and ventilated, and will the HVAC system be shut down?
4. What respiratory protection does the crew wear, and what safety training have they had?
5. What is the product's maximum pass thickness, and how do you check the mix before spraying my house?
6. Will you record the drum lot numbers for my job?
7. Does the product hold a third-party emissions certification?
8. Who do I call if a strong odor doesn't fade, and what does the warranty cover?

When you come home, a mild smell near the foam is normal and should fade; see spray foam smell. Foam that looks wrong deserves a closer look: how to spot bad spray foam. For vetting the installer, see how to choose the right spray foam contractor.

FoamGuard is ACC SPF-Safety trained and records drum lot numbers on every job. Want a number for your own project? Price My Project or call (814) 208-3478.