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Re: GBlist: HCHO in Materials


At 10:07 AM 5/23/97 -0700, you wrote:
>Just received a copy of the California study, "Determination of
>Formaldehyde and Toluene Diisocyanate Emissions from Indoor Residential
>Sources",.... [snip]
>The highest emissions rate among the building products was from a product
>described as a commercially-applied, two-coat "acid-cured floor
>finish"--when wet, the base coat's initial emission rate was 1,050,000

The California study is a valuable addition to the literature on
formaldehyde emissions. It updates the vast existing data base with a fairly
large set of values for a range of sources. Formaldehyde content of products
and the formulations have been modified significantly in recent years
effectively to reduce emissions and exposure. Data on emissions from
products currently in the supply chain is valuable. However, I have a few
cautions about oversimplification of the results or misapplication by
extrapolation or over-generalizastion.

While comparison of results is more reasonable when all of the tests are
conducted in the same chambers and analized by the same methods, there are
many reasons to make such comparisons cautiously. The report itself warns:
"Direct product-to-product comparisons can be made for only a few of the dry
products...." One reason is that different loading rates were used for the
various wet products (for practical reasons related to the testing method),
and loading rate is an extremely important variable in emissions testing.

Please always be careful to consider the time at which emissions tests are
taken relative to the age and environmental history of the product. (ASTM
Std 5116-90 is very clear about the requirements for reporting these
details. Refer to it for guidance on the factors and variables that must be
considered in interpreting test results.) 

It is also extremely important to distinguish between wet products and dry
products, as done in the report. 

The initial emission rate of a wet product is high by design. It is applied
in liquid form and dries after application. The final emission rate of the
floor finish product (at 15 to 22 hours, according to the report) was 1/100
of the initial rate. The "final" rate is a function of the study design
(length of period of the study) and not uniform among studies. We are
interested in initial emissions, emissions decay profiles, and total
lifetime emissions. The time of the study was very short. It does not really
tell us very reliably what the long term emissions are. One thing we know is
that they cannot be any larger than what is in the product in the first
place. This is another piece of information that is valuable to have, but
somewhat difficult to determine, especially in the case of the floor product
where the formaldehyde may be a reaction product formed during curing
(drying) rather than a component of the product itself. Formaldehyde is
used, however, in some paints, as a biocide, replacing mercury since its
withdrawal from paint formulations. 

The curve fits at the end of the report allow a better albeit imperfect
understanding of the emissions profiles over time. They show air
concentrations as measured by a direct-reading instrument. The concentration
drops very rapidly after its initial peak and then decays exponentially,
approaching a line parallel to the x-axis (time). Most of the decay in
chamber concentrations (from which emission rates are calculated) occurs in
the first 4 to 6 hours after the peak. This is important information: it
tells us that ventilation really is important during and after application
of this product. Since elevated chamber air concentrations inhibit emissions
(due to air to source vapor pressure ratios), some of the decay early in the
profile is a function of the ventilation rate chosen. Under a higher
ventilation rate, the emission rate would be higher although the air
concentration would be lower. Another confounding factor is the "loading" of
the chamber walls during the initial burst of emissions. Finally, with the
wet-applied products, some significant quantity is absorbed by the matrix
(wood, particle board, etc.) and will come out more slowly but over a much
longer period of time.

The published study also reports data on TOTAL formaldehyde (HCHO) emissions
- implicitly, during the test period of 15 to 22 hours. This information is
useful, since, in the end, a mass balance is the most reliable "first
principles" approach to understanding the relationships between important

We know from many years and tens of thousands of measurements that HCHO
emissions from composite wood products tend to extend over a very long
period of time - many years. We want to know the emission rates so we can
calculate concentrations under various ventilation rates. But the total
emissions can never exceed what was available from the outset and will
approach that eventually during a long service life typical of composite
wood products.

Hal Levin	  <hlevin@cruzio.com>
Hal Levin & Associates         
2548 Empire Grade, Santa Cruz, CA 95060-9748
408.425.3946  fax 408.426.6522  

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