When discussing a specific product, it's best to refer to the product's MSDS (Material Safety Data Sheet).
- Online I found the 2007 MSDS for LP's OSB Sheathing which listed contents including Phenol-Formaldehyde Resin along with Formaldehyde.
- I then called for an explanation and the company forwarded the 2009 MSDS which no longer included the Formaldehyde, as they changed their formulation.
- The contents listed are Wood Dust, Phenol-formaldehyde Resin, and Polymeric Diphenylmethane Diisochyanate.
Polymeric Diphenylmethane Diisochyanate?
I consulted a biochemist, Professor Janis Lochner at Lewis and Clark, regarding this last chemical and was told that it is considered a hazardous substance according to OSHA 29 CFR 1910.1200.
- The hazard alert code was extreme and the primary risk was due to inhalation.
- The OSHA standard is for occupational exposure, at which point workers may be exposed to more of the monomer or dimer form (simple molecule combining to form the polymer).
- The hazardous component is the methylene diphenyl diisocyanate (MDI) which is manufactured and used worldwide with 2.8 metric tons produced each year.
- With a little more research I found "The primary hazard of this solution is the threat to the environment. Immediate steps should be taken to limit its spread to the environment. Since it is a liquid it can easily penetrate the soil and contaminate nearby streams or groundwater."
I also spoke with Professor Suzanne Paulson, an atmospheric scientist at UCLA. Her additional comments were:
- If the stuff is successfully polymerized (forms long chains), it should not off-gas because its volatility should be too low. Material that didn't polymerize could off-gas particularly when the material is new.
- Oxidation by air pollutants could cause breakdown and volatilization if the stuff isn't sealed in with something (paint etc.), but it is hard to say if its oxidation products would be more toxic than some other organics that get oxidized.
I always prefer to minimize my exposure to the emissions from newly manufactured articles. There tend to be a lot of these emissions in indoor air.
3 possible explanations
So there are 3 explanations for the odor you are experiencing:
- it is either the "free formaldehyde" in the material offgassing or
- it is the off-gassing of the non- polymerized MDI.
A third explanation is that you bought OSB that was produced before 2009, which was before LP redesigned their mix and used more formaldehyde (possibly urea-formaldehyde).
Given the current market conditions this last possibility could be the problem.
Sealing the panel
As a note, MDI is listed to be reactive to water so you should do a test before applying it.
Another approach would be to let the off-gas before using them.
It is so challenging these days when buying manufactured products, which is why the less that is done to a product the more environmentally safe it is, which is something to consider in your solution for this.
What you should know about formaldehyde
Formaldehyde is found in many household products such as glues, permanent press fabrics, paper product coatings, and the adhesives in particleboard, fiberboard, and plywood.
- Acute exposure is irritating to the eyes, nose, and throat and subsequent exposures may cause allergic reactions of the skin, eyes and respiratory tract.
- Long-term exposure to low levels in the air can cause asthma-like respiratory problems.
The National Institute for Occupational Safety and Health (NIOSH) considers 20 ppm of formaldehyde to be immediately dangerous to life and health (IDLH) and has set the permissible exposure limit (PEL) for formaldehyde in the workplace at 0.75 parts formaldehyde per million parts of air (0.75 ppm) measured as an 8-hour time-weighted average. http://www.osha.gov/OshDoc/data_General_Facts/formaldehyde-factsheet.pdf
There are two types of formaldehyde adhesives found in manufactured wood products such as plywood, and oriented strand board (OSB).
- Urea formaldehyde adhesives are the more toxic type. They are water resistant but not waterproof and so until recently were used for interior interior wood products.
- Phenol formaldehyde (phenolic) resins are considered the "safe resin." They are waterproof and were used only for exterior grade wood products, though they are now used for interior products as well.
Phenol formaldehyde resin is a chemical reaction of phenol and formaldehyde forming a polymer, which is a large molecular chain of the 2 ingredients whose properties are completely different than either ingredient and relatively inert and stable, properties that contribute to its waterproofness.
- In the process of making the resin the formaldehyde used is a very small amount, typically less than 0.1 percent of the mix.
- In manufacturing the adhesive, the resin is mostly used without additives and when it is added to the wood chips it is cured at high temperatures and pressure.
How much "free" formaldehyde (not polymerized) is left after the process of making the resin and then making the OSB can only be measured by the off-gassing.
The Engineered Wood Association (APA) developed a method for testing the emissions using newly manufactured OSB and found that formaldehyde levels were below 0.1 part per million with emissions approaching zero as the panels aged. This is well below the PEL values developed by OSHA for formaldehyde emissions in the workplace.