In December 2007 and January 2008, the Centers for Disease Control and Prevention (CDC) measured formaldehyde levels in a stratified (strata based on type of trailer) random sample of 519 FEMA-supplied trailers. CDC’s final report was issued on 2 July 2008. The geometric mean level of formaldehyde in sampled trailers was 77 parts-per-billion (ppb). The range encountered was 3-590 ppb.
The good news is that this mean level is lower than 100 ppb, generally considered to be the point at which sensitive individuals report symptoms. By comparison, nearly all people experience some irritation at 800 ppb, and 750 ppb is the OSHA 8-hour time-weighted average allowable exposure level for formaldehyde.
We offer our comments on the CDC report…
The agency utilized NIOSH Method 2016, a form of wet chemical analysis that required sample to be taken via a special pump for one hour at one select location in the trailer. We do not believe that this was the best way to accomplish the formaldehyde measurements. For one thing, the method has poor accuracy: ± 19%. For another, the result is simply an integrated average “single number,” that could be affected by ventilation and smoking habits of the occupant. Moreover, since the final analysis of the samples was not done on site, they had to be sent, via overnight courier packaged in ice, to the testing lab’s facility in Michigan.
Method 2016 yields formaldehyde concentration data in milligrams per cubic meter (mg/m3), but CDC reported the results in ppb. As such, a conversion must be made, and temperature and barometric pressure must be taken into account. Experience has shown, though, that this may not be done in practice. Instead, a conversion factor is stated—albeit at “normal temperature and pressure” (20° C, 760 torr)—that is often regarded as a static number applicable under all conditions.
Note that the formaldehyde testing was done in a temperature range of 41° F – 91° F. As no barometric pressure data was given, we are unable to consider this parameter.
Let’s convert the above-stated temperature range to Celsius: 5° C – 32.8° C. 77 ppb at the first temperature would be 0.101 mg/m3, and at the second temperature would be 0.092 mg/m3. This represents a variance of almost 9 percent. Although temperature data was recorded for each trailer formaldehyde measurement, and temperature was part of the mulitvariate statistical analysis, it is unclear if the actual formaldehyde concentration measurements were corrected for temperature variation.
A direct reading instrument (such as Interscan’s) would have allowed sampling at various locations in the trailer, and far more data could have been obtained in 10 minutes that way, than by using Method 2016 for one hour. Additionally, the instrument would have been much more accurate (± 2% of reading ± 1 ppb). The results would have been immediate, allowing for further field protocol adjustments, if necessary. For example, it may have been discovered—quite inadvertently—that a particular fixture common to many trailers (such as certain cabinetry) was a significant point source of formaldehyde emissions.
Such a finding could have immediately influenced additional testing within all trailers.
It is well known that cigarette smoke contains formaldehyde, and a trailer occupied by a smoker would have confounded the results. While the CDC study included questions about smoking on its questionnaire, I am uncomfortable with their finding that 66% of the subjects occupied trailers in which no one had smoked for the previous two weeks. It would have been far better to analyze the trailer air for some marker of cigarette smoke.
In any event, simply prohibiting smoking for the one hour period of the sample collection (as was their protocol) does nothing for the smoke-contaminated air already present!
Finally, even though this entire study was driven by media horror stories of all sorts of supposedly drastic health effects, there was not a single health question on the interviewers’ questionnaires. The CDC papers over this by stating that “it was not a health effects study.”
But, that is beside the point. It would surely have been valuable to correlate measured concentrations with reported symptoms, even in the most generic manner. A golden opportunity was missed here, and I have a feeling it was deliberate.