1

Decay or the Decrease in Formaldehyde Concentrations or Emissions over

Time and UF-bonded Wood Panel Products

William J. Groah

December 21, 2005

________________________________________________________________________

Abstract

 Decay is the decrease in formaldehyde concentrations in homes or the decrease in

emissions from formaldehyde containing products over time. The decrease in

formaldehyde concentrations over time (decay) in home studies is typically determined

by associating formaldehyde concentrations by home age. The average half life in such

studies is highly variable, varying from about 1 year to more than 20 years, depending on

the nature of the home population under study and other factors. Home age/concentration

studies generally show that formaldehyde concentrations are higher in new homes than

older homes of the same type. These types of studies have limitations as a means of

assessing product emission decay profiles. The introduction of additional sources of

formaldehyde as the homes age tends to cloud interpretations that seek to relate

concentration change over time with emission decay of the original formaldehyde

containing products in the home. Laboratory studies provide a better understanding of

decay from specific products. A shorter half life, from less than a month to a little over a

year, is demonstrated in laboratory experiments. Limited laboratory information

indicates a 1 to 2 year half life for multiple tested UF-bonded wood products, which is

longer than the half life of a UF-bonded product tested singly. Decay profiles from

laboratory studies, however, are not necessarily reflective of home exposures. Controlled

studies in unoccupied homes, while limited, suggest a reduction of 25 to 40% in

formaldehyde concentration during the first 4 to 8 weeks, and a half life of 18 to 24

months.

________________________________________________________________________

The author is a consultant and formerly Technical Director of the Hardwood Plywood and Veneer

Association. Home address: 11233 S. Shore Road, Reston, VA 20190-4400, wgroah@hotmail.com.

This project was supported by the Composite Panel Association, Formaldehyde Council Inc., Hardwood

Plywood and Veneer Association, and the Kitchen Cabinet Manufacturers Association.________________ 

 

 The persistence of formaldehyde has been an important question in the study of

formaldehyde concentrations in buildings and the study of emissions of formaldehyde

from product sources. Concurrent with the concern about formaldehyde indoor levels in

North America in the late 1970s and early 1980s, questions arose about how long

formaldehyde would be emitted from sources and what could be learned about the

formaldehyde concentration time profile in buildings. It became the lexicon of the

technical community to label this aspect of the study of formaldehyde as "decay" and to

measure decay by the half life of formaldehyde concentrations. The half life is the time

required for formaldehyde concentration to reach half the magnitude of the first

determined or original concentration.
2

 Decay is examined from three perspectives. First formaldehyde decay levels by home

age in field studies are reviewed. These studies have included both occupied and

unoccupied homes; however, the vast majority of homes were occupied. Second is the

study of formaldehyde emissions over time from specific products or groups of products

in laboratory tests in dynamic chambers at controlled conditions approximating

conditions in living spaces. Third is a discussion of a small amount of short-term decay

data from controlled studies in unoccupied homes. Decay rates of formaldehyde are very

different in these three perspectives. While the technical community generally

understands these differences there remains confusion among some administrators,

regulators, the popular press, and the public.

Formaldehyde concentrations and home age

Home studies

 Home age concentration data has only been reported in some formaldehyde studies

conducted during the past 25 to 30 years. Concentration by home age was one aspect of

the SRI International review report on exposures to formaldehyde inside residences

prepared for the U. S. Environmental Protection Agency (EPA) (Suta 1980).

Formaldehyde concentrations were plotted by home age from 5 studies, 2 of which were

European. It was found, in four studies for which decay formulas were computed, that

the relationship fit exponential equation models indicating that half life ranged from 1 to

5 3/4 years. Suta recognized that half life did not necessarily represent the change in

formaldehyde over time from the original formaldehyde sources by stating that the

"differences between the half-lives that are derived from test data and home monitoring

may partly result from the particleboard being added to older homes for repair and

improvement."

 A later EPA sponsored review, Formaldehyde Exposures in Residential Settings:

Sources, Levels, and Effectiveness of Control Options (Versar 1988), included summaries

of 37 studies: 25 in conventional homes and 12 in manufactured homes. Nine studies

referenced in the report appendix contained data on decay. Versar used decay

information reported by the original authors, calculated decay from a constant, or

calculated decay based on home age data in determining half life. Information on 4

studies cited by Suta (1980) and 9 by Versar (1988) are included in Table 1. Data in

these 13 studies show that half life varied from 1 year to 21.4 years.

 In addition to the home studies in the decay analyses of Suda (1980) and Versar (1988),

Syrotynski (1985) provided a table of formaldehyde concentration by home age data cells

(1 to 12 months, 13 to 24 months, etc) in 148 complaint manufactured homes (study

number 14 in Table 1). The data for 102 homes less than 84 months in age were plotted

with the average concentration value for each age cell considered at the cell mid-points: 6

months, 18 months, etc. The 46 homes older than 84 months were placed in a single age

cell category and were not included in this analysis. The exponential model provided the

best fit of the averages in each data cell among linear, power and logarithmic models and

predicted a half life of approximate 3.5 years.
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 The exponential has been the typical mathematical model used in relating

formaldehyde concentration to home age. Where reported, data correlation R2s varied

from 0.07 to 0.991 with more than 50% of the R2 values below 0.50 as noted in Table 1.

Versar (1986) selected an aggregate of the Clayton and Wisconsin non-complaint

manufactured home data as the best representation for decay for wood panel products in

homes. The exponential model described by Equation [1] was the best fit of the

combined data and resulted in a half life of 2.92 years. This decay value was used by

Versar (1986) as an input in their formaldehyde exposure model for predicting

formaldehyde concentration profiles in homes.

y = 0.504 e - 0.00065x [1]

where:

y is formaldehyde concentration (C) in ppm, and

x is home age in days.

 Versar (1986) reported that the correlation coefficient (R) for the equation is 0.59 and

the R2 value is 0.35, implying that home age determines approximately 35% of the home

formaldehyde level, while all other factors determine the other 65% of variability.

Half life in home studies is influenced by the nature of the home population under

study

 Three home studies identified in Table 1 had average or median concentrations under

0.10 ppm, yet the half life of formaldehyde in homes in these studies varied between 3.8

and 21.4 years: Reiland et al. (1985) at 3.8 years, Sexton et al. (1986) at 15.5 years, and

Stock and Mendez (1985) at 21.4 years. The following suggests that the large disparity

in observed half life is influenced by the differences in experimental design and the

nature of the homes in the study.

 Manufactured homes in the early to mid 1980s typically contained large quantities of

particleboard decking and hardwood plywood paneling interior finish on most of the

walls. In the California manufactured home study reported by Sexton et al. (1986),

formaldehyde was collected for 1 week using Lawrence Berkeley Laboratory (LBL)

designed passive monitors, available from Air Quality Research, with analysis by the

chromotropic acid method. Versar (1988) provided a more detailed breakout of the

number of home age cells than described by Sexton et al. (1986). Only 0.64% of the

homes cited in Versar were less than one year old. The half life of formaldehyde

concentration was 15.5 years. The weighted average concentration for the summer and

winter measurements in the homes, at 0.075 ppm, was relatively low compared to other

studies in manufactured homes during the period. This study was primarily a study of

older homes containing high loading rates of UF-bonded wood panel building products.

 1

 The 0.99 R2 was only for homes 3 years or less in age in the Reiland et al. (1985) study. Homes over the

full spectrum of age had much lower R2 correlations.
4

 The 0.07 ppm average formaldehyde concentration in the Texas study of 78 homes

(Stock and Mendez 1985) was determined from data by collecting formaldehyde in a

sampling train of two impingers, each containing 15 ml of deonized water, with analysis

by chromotropic acid. No manufactured homes were included in a study that contained

five categories of dwellings: conventional houses, energy efficient houses, apartments,

condominiums, and energy efficient condominiums. There was no breakdown on the

number of homes less than 1 year old, however, 14% of the homes were less than 2 years

old. While there was a definite relationship between average formaldehyde concentration

and home age, there were only small differences after homes reached 5 years in age. The

reported formaldehyde half life was 21.4 years. No information was provided concerning

the presence of formaldehyde containing building materials or components in furnishings

or the loading rates of these possible sources. In the analysis of questionnaire responses

only one significant factor was noted: residences with good kitchen ventilation,

characterized as homes having an exhaust fan to the outside. Formaldehyde levels in

homes with these fans were significantly lower than dwellings with lesser ventilation

capacity. It is almost certain that the homes, in general, contained much lower loading

rates of UF-bonded building products than the mobile homes evaluated by Sexton et al.

(1986). Based on the type of dwellings in the study, it is anticipated that few homes

contained hardwood plywood paneling.

 The Bonneville Power Administration study (Reiland et al. 1985) was in electrically

heated homes: 182 homes with energy efficient designs were compared with 348 homes

with conventional designs. Formaldehyde concentrations were determined using LBL

developed passive monitors with analysis by chromotropic acid. The median

formaldehyde concentration was 0.092 ppm with energy efficient homes having slightly

higher concentrations (11%) than control homes. This was attributed primarily to home

age: the median age of energy efficient homes was 1 year while the median age of control

homes was 3 years. About 5% of the homes were described as 0 years old and 40% were

1 year old. The average half life of formaldehyde concentrations as reported by Versar

(1988) was 3.8 years. The shorter half life observed was, no doubt, influenced by the

high percentage of newer homes included in the study as compared with the age profile

of homes in the Sexton et al. (1986) and Stock and Mendez (1985) studies.

 An example of the likelihood of a multi-phase process in the formaldehyde

concentration decay profile is illustrated by the incompleteness of Versar's

characterization of the Bonneville study (# 11 on Table 1) as having a correlation R2 of

0.99 using the exponential model and comments by the authors of the Bonneville study

(Reiland et al. 1985):

"The fit was poor when all years were considered, and when just years four to ten

were considered separately (R2 = 0.54 and 0.14, respectively). The fit was much

closer (R2 =0.99) when the first 3 years were considered separately, yielding a time

constant of 5.5 years . . . The first 3 years could represent decay of a strong, shorttime constant source (such as cabinets or furniture) as observed in other studies . . .

and the later years the decay of other slower sources (such as subflooring)."
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 The description of possible decay stages appears to be an over simplification of what

occurs in homes. The effects of interactions of formaldehyde sources and sinks such as

gypsum wall board and details on possible formaldehyde release mechanisms are not

addressed in the Bonneville characterization.

Controlled laboratory and field studies

Dynamic chamber decay studies on UF-bonded wood products

 There have been few designed laboratory decay studies on UF-bonded wood products.

Several practical considerations act to prevent performing such projects. The ideal way

of conducting these experiments is to keep formaldehyde source samples in dynamic

chambers at some established conditions similar to what would occur in the field, and

periodically extracting air for formaldehyde determinations during the life of the study. It

is not practical in intermediate and long-term experiments to dedicate the use of a

dynamic chamber, particularly a large chamber, for a study of decay that could take

months, if not years. Moreover, the results could become irrelevant when there are

advances in UF resin, or other technologies during the course of a long-term experiment

that could affect decay. What generally has occurred is a potpourri of single or a few

data points described by a relatively small number of authors. These data points are

available where decay information was not the primary study objective. Notable

exceptions are the decay studies described by Zinn, Cline, and Lehmann (1990);

Baumann (2000); and the slow and fast decay project by Oak Ridge National Laboratory.

 A project sponsored by the Composite Panel Association (CPA) consisted of large

chamber tests performed at four laboratory sites: the CPA laboratory and at three

particleboard manufacturer's laboratories (Zinn, Cline, and Lehmann 1990). The initial

and subsequent formaldehyde emissions from the products were determined by testing

particleboard at standard conditions of loading at 0.43 m2/m3 (0.13 ft.2/ft.3), 25o C (77o F),

50% RH and 0.5 air changes per hour (ASTM 1996, ANSI 1999) from formaldehyde

collected in an aqueous solution of 1% sodium bisulfite in impingers with analysis by

chromotropic acid. The average initial concentration of the 16 products in the study was

0.21 ppm, somewhat higher than the 0.15 to 0.16 ppm reported for particleboard as an

average by CPA for the 1998-2000 period (CPA 2001). Data analysis consisted of

comparing the fit of formaldehyde emissions over time with logarithmic, power, and

exponential models. It was found that the logarithmic, Equation [2], provided the best fit.

The correlation of the data to the logarithmic model is good with an overall average R2 of

0.88 and a range of R2s from 0.65 to 0.98 for the 16 products as shown on Table 2.

y =m · (ln t) + b [2]

where

y is the formaldehyde concentration in ppm,

t is the natural log (ln) function of time, and

b is a natural log function (ln) constant.
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 The average half life of the 16 products was 0.59 years (216 days) with a range of 0.225

to 1.02 years (82 to 371 days). Decay was more rapid during the earlier part of the

experiment as half the reduction in average emissions between the initial concentration

and the half life concentration occurred in only 0.104 years (38 days). This time period

was referred to as the 3/4 life.

 Initial formaldehyde concentration plotted by half life of formaldehyde for the products

in the Zinn, Cline and Lehmann survey are shown in Figure 1. The logarithmic model

provided a better fit of the data than either of the linear, power or exponential models

with a correlation R2 of 0.7099. The data clearly shows that there is a moderately strong

influence of initial formaldehyde emissions on half life: generally, the higher the initial

concentration the more rapid the half life. The data suggests that the half life of

particleboard with an initial concentration of 0.15 ppm, typical of current product (CPA

2001), is about 9 months.

 Baumann (2000) described formaldehyde decay for 12 particleboard and MDF products

in a study of VOCs. Formaldehyde air samples were collected in an aqueous solution of

1% sodium bisulfite in impingers with analysis by chromotropic acid. Extrapolation

between the data points was required for an estimate of half life. Information on these

findings is shown in Table 3. Except for four tests (4B, 5B, 9B, and 11B), the half life

was less than 1 month. Some of the conditions of test may have contributed to the shorter

half life than that reported by other observers. Testing was performed in small 0.053 m3

(1.87 ft3) stainless steel dynamic chambers. A desirable experimental feature was that

samples were housed in the test chambers for the course of the testing: ~ 6 weeks or less.

The surface area of the samples was 0.021 m2 (0.226 ft2) providing for a loading rate of

0.40 m2/m3 (0.12 ft.2/ft.3), only slightly lower than the standard 0.43 m2/m3 (0.13 ft.2/ft.3)

for particleboard (ANSI 1999), but higher than the standard 0.26 m2/m3 (0.08 ft.2/ft.3)

loading rate for MDF (ANSI 2002). Temperature at 23o C (73.4o F) and relative humidity

at 45 ± 5% are consistent with typical indoor conditions. The edges of the samples were

sealed with two coats of a saturated solution of sodium silicate, minimizing the likelihood

of increased emissions from the edges and ends of samples that could accelerate decay.

The 1.13 air change per hour rate used in these experiments is greater than the more

common 0.50 AC/hour standard large chamber rate (ASTM 1996).

 Information on other laboratory experiments describing formaldehyde concentrations

over time is shown in Table 4. Some data that appeared in the Versar (1988) review

included preliminary information (Zinn 2005) from Zinn, Cline, and Lehmann (1990).

To avoid duplication none of the data that could have appeared in the 1990 paper are

shown in the table. Experiments that contained less than three concentration/time points

are also not included in Table 4. Experiments were performed under a variety of loading

rates and conditions as described in the footnotes to the table. Except for data on

multiple product tests (number 11 and 15), the average half life of the 7 particleboard

products was about 1 year, slightly longer than the findings of Zinn, Cline, and Lehmann

(1990). The average half life of the 5 MDF products was also about 1 year.
7

 In an experiment performed after the Versar (1988) review was published, Sundin and

Roffael (1989) found in a dynamic chamber experiment that formaldehyde emissions of

UF-bonded particleboard decreased by 50% in 1 year with testing at three-month

intervals. The particleboard tested contained a formaldehyde-capturing agent or

scavenger, Kenosize FR 4514. Since the samples were wrapped in polyethylene foil

between tests during the course of the study, the reported 1 year half life was likely

longer than would have been observed if the samples had been exposed to air during the

study period.

 Two test series in Table 4 involved multiple products tested over time. Test number 11

combined particleboard, hardwood plywood paneling and MDF with an observed half life

of 1.52 years, much greater than the half life of any of the three products tested singly,

with a range 0.62 to 1.08 years (Matthews et al. reported by Versar 1988). The air

change rate of the tests on the single products was different than that of the three products

tested together making the single product and multiple product comparison problematic.

A separate study by other observers (Groah and Gramp 1988) indicates a half life of 2.10

years for three products tested together (test number 15). The half life for these products

tested singly– particleboard, hardwood plywood paneling and MDF– ranged from 1.07

to 1.40 years. The half life values in this series are conservative: samples of each product

were dead stacked ~8 weeks between the initial and second chamber test, thus, the half

life would likely be less than that stated.

Fast decay and slow decay

 A series of Oak Ridge National Laboratory (ORNL) laboratory and field experiments

investigated the persistence of formaldehyde (Gammage and Matthews 1988). The "fast"

decay procedure, performed at 23o C (73.4o F) and 50% RH, was designed to modify the

air change rate to maintain formaldehyde levels in a laboratory test room at ~0.1 ppm

(0.05 - 0.11 ppm). This procedure was designed to determine the assumed inherent decay

characteristics of the product. Formaldehyde surface emission monitors (FSEM) were

used to sample emissions from 5 MDF, 7 particleboard, and 4 hardwood plywood

products. A half-life of 21 months for MDF, 15 months for particleboard, and 11 months

for hardwood plywood were determined.

 The "slow" decay concept was designed to "simulate a potential indoor compartment

with large quantities of pressed-wood products and moderate exchange with outdoor air."

Testing was in a large 117 m3 (4132 ft3) chamber at 0.40 ± 0.03 air changes per hour and

at a total loading rate of 2.7 m2/m3 (0.82 ft.2/ft.3) with formaldehyde collected on a

molecular sieve with pararosaniline analysis. Initially the weaker emitters among various

MDF, particleboard, and hardwood plywood products were anticipated to suppress

emissions from the stronger emitters resulting in a prolonged decay period. A half life

for the three combined products of 28 ± 2 months was observed after correcting

concentrations for 23o C (73.4o F), 50% RH, and 0.4 air changes per hour.

 These studies were augmented by experiments in four unoccupied research homes in

Karns, Tennessee (Gammage and Matthews 1988). Formaldehyde concentration data in
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these homes were normalized to 23o C (73.4o F), 50% RH, and 0.2 air changes per hour.

An exponential decay model indicated a half life of 19 ± 4 months, which was less than

that observed in the "slow" decay laboratory study. Primary formaldehyde sources in the

homes were carpet covered particleboard underlayment and kitchen cabinets containing

industrial particleboard components. The experimental homes were not otherwise

furnished. The total loading rate of the formaldehyde sources was 0.29 m2/m3 (0.09

ft.2/ft.3), much lower than the very high loading of 2.7 m2/m3 (0.82 ft.2/ft.3) in the "slow"

decay study.

Discussion - concentration/home age and controlled laboratory studies

 Formaldehyde concentration by home age studies clearly demonstrates that newer

homes with new building products and other new formaldehyde sources have higher

formaldehyde levels than older homes within the same home type. There are, however,

limitations on valid extensions that can be made from this data, and to what extent

mathematical models derived from such data can be used to predict decay profiles over

time for products, or for general populations of homes. Findings from formaldehyde

concentration by home age studies reveal little if anything about the decay characteristics

of a single product because most homes have multiple sources. Moreover, newer sources

of formaldehyde are continually being brought into homes as they age. This distorts the

shape of concentration/home age decay curves, sometimes presumed to represent decay

characteristics of the original formaldehyde sources. Thus, points on the decay curve can

be elevated in older homes and artificially low in newer homes because the introduced

products are not present.

 In a study for the Formaldehyde Institute, Whippie (1986) describes some

interpretational difficulties of using home age/formaldehyde data as a means of

approximating formaldehyde emission decay from wood products:

• Most home age studies have little or no information about product loading rates,

source strength of formaldehyde emitters, air change rates, and other information

important in making product decay rate assessments.

• Most home age studies contain data generated weeks or months after homes are

completed and thus bypass the first phase, or most of the first phase in the decay

process.

• In home age studies conducted during the 1980s, formaldehyde concentrations in

older homes were likely higher because higher emitting wood based panels were

used. This tends to flatten the formaldehyde decay curve when older homes are

compared to newer homes.

• Home age/concentration studies generally make no allowance for the introduction

of new formaldehyde emitters in the home, such as could occur with the purchase

of furniture after the homes are finished. During the life of the home, sources
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from projects such as remodeling kitchens or adding a paneled room can also be

important as the home ages.

 Factors such as the use of unvented gas fuel appliances and cigarette smoking result in

the episodic release of formaldehyde. Formaldehyde from these types of sources does

not change in a consistent way with time, but can influence the shape of the

formaldehyde concentration decay curve. Homes in certain urban areas can be subject to

higher levels of outside ambient formaldehyde than homes in rural areas. Outside

ambient levels can also be influenced by seasonal changes in meteorological patterns and

are typically higher in the winter than summer and higher in the daytime than at night

(CARB 1992). Thus, the times during the day and year when air samples are taken can

influence the observed formaldehyde concentration profile during the study.

 In a critique of relating formaldehyde concentrations to home age and the interpretation

of such data, Groah and Zinn (1991) stated "the low correlation coefficients of fitted

equations derived from examining home age/formaldehyde concentration data are

accompanied by tortuous efforts to fit simple exponential and power curve models to a

complex process." Information in Table 1 is used to illustrate the possible aberrations in

fitting simple mathematical model curves to average concentration and half life data by

using the ten studies in the table containing sufficient half life information (studies #1, 2,

3, 5, 6, 7, 9, 11, 13, and 14). Among linear, logarithmic, exponential and power models,

the two models exhibiting the best correlation to this 10 study data set were the

exponential and power models. The data was slightly better correlated with the power

model with a R2 of 0.6112 as compared to the R2 of 0.5561 for the exponential model as

demonstrated in Figure 2. As a predictor, the power model suggests a half life of about 5

years from year 2.5, whereas the exponential model indicates a half life of about 10 years

from year 2.52.

 Groah and Zinn (1991) suggested a three-phase formaldehyde decay process. A rapid

flash-off during the first weeks after construction or installation of the formaldehyde

products represents the first phase. Test procedures and emission guidelines sometimes

anticipated this early emission rate phase as being uncharacteristic of concentrations to

which occupants of spaces are exposed. For example, conditioning periods of 7 days for

samples were established for North American test methods for determining formaldehyde

concentrations from wood products (ASTM 1994, ASTM 1996).

 The first decay phase is followed by a less steep decline that occurs from a few months

to perhaps a year or more and includes release of some free formaldehyde but is probably

dominated by weak-bonded formaldehyde to constituents in wood, including additional

mechanisms related to the cured glue bond. The last and probably final phase or

continuum of phases is more gradual and is probably influenced by complex interactions

related to the cured urea-formaldehyde glue bond, the wood itself, and wood moisture all

related to home seasonal humidity factors, loading rates, and background levels in the

home.

 2

 Year 2.5 is near the shortest average half life of 2.33 years of any study appearing in Table 1.
10

 Laboratory studies have sometimes been characterized as unrealistic because they

establish decay profiles within a pristine environment and do not reflect the home where

other emitters may be present. As previously stated, it is generally not practical to retain

UF-bonded wood product samples in large chambers for the duration of intermediate to

long term decay experiments in laboratories. Samples, however, are typically stored in

indoor locations where there are background levels of formaldehyde. Zinn, Cline, and

Lehmann (1990) reported that the average background formaldehyde levels in two of the

four laboratory testing sites were 0.08 ppm (site A) and 0.06 ppm (site C) where samples

were stored between large chambers tests. It is likely that formaldehyde levels at all four

storage sites were higher than would be anticipated at many home construction sites.

Formaldehyde concentrations during storage were all probably greater than home

background levels when only minor formaldehyde sources are present. The Consumer

Products Safety Commission (1997) has suggested that "formaldehyde is normally

present at low levels, usually less than 0.03 ppm, in both outdoor and indoor air."

Short-term control studies in unoccupied homes

 Two experiments in manufactured homes were conducted in the early 1980s, each over

an approximate two-month period as described by Groah, Gramp, Garrison, and Walcott

(1985). A joint HPVA/CPA team tested two homes in 1980 with air sampling using

impingers containing an aqueous solution of 1% sodium bisulfite. Formaldehyde was

determined using the chromotropic acid procedure. The four 1981 homes were also

described in the U. S. Department of Housing and Urban Development sponsored study

(Singh et al. 1982). Both chromotropic acid and pararosaniline were used in analyzing

air samples in these 4 homes. Formaldehyde levels in the six homes were somewhat

erratic over the first several weeks as emissions from formaldehyde sources became in

equilibrium with the sinks and weaker emitters that tended to initially suppress emissions

from the stronger sources. The average of the first three-week sampling period was used

as the initial concentration period to allow for some equilibrium adjustment. The average

formaldehyde concentrations during weeks 6, 7 and 8 (homes 1 and 2) and weeks 7, 8,

and 9 (homes 3 - 6) represented the comparison period as shown in Table 5. All

concentrations were adjusted for a temperature of 25o C (77o F) using the technique

described by Berge et al. (1980). The average decrease in formaldehyde concentration

over this period– effectively about 5 - 6 weeks– was 40% with a range of 35 to 48%. All

of the homes contained particleboard decking and hardwood plywood wall paneling on

most of the interior walls.

 The EPA sponsored pilot home study (Hare et al. 1996, Koontz et al. 1996) consisted of

one "medium" (run 7 in Table 5) and two "high" (runs 8 and 9) loading configurations in

a single conventional home. Four products– particleboard underlayment, hardwood

plywood wall paneling, kitchen and vanity cabinets, and partition doors– were the

primary formaldehyde sources. Loading rates of the UF-bonded wood panel building

products and components in cabinets and doors in this study are probably typical of

products found in homes in 2005 when the aggregate of the four wood based sources are

present. Formaldehyde concentrations at day 7 and day 33 are displayed and compared

in Table 5 as a measure of short-term decay. The decrease in formaldehyde
11

concentration for runs 8 and 9 were fairly consistent with a 25% and 33% decline,

respectively. There was an increase in formaldehyde concentration in run 7 at 29%;

however, this was likely a data aberration. The surface area of the gypsum board on the

walls and ceiling in this experimental home was greater than the total surface areas of the

formaldehyde sources combined and was identified as an important sink (Hare et al.

1996, Koontz et al. 1996). During the first loading (run 7 on Table 5) the gypsum wall

and ceiling finish was a net absorber of formaldehyde over the initial period of the test

thus depressing apparent emissions from the combined emitters during the first weeks of

the study. During the latter days of experiment # 7, the gypsum board likely became

bulked or partially bulked with absorbed formaldehyde, and perhaps also became an

emitter. These interactions probably skewed the concentration over the short one-month

time period within which data was collected, thus inverting the decay curve. The gypsum

wallboard was not replaced between the three runs (7, 8, and 9). In runs 8 and 9 gypsum

wallboard already had been bulked with formaldehyde from previous runs. Results from

runs 8 and 9 were likely more reflective of decay from the original sources of

formaldehyde.

Conclusions

 Analysis of formaldehyde by home age confirms that newer homes generally have

higher levels of formaldehyde. In such studies, decay is more rapid when the home

population contains homes in all age classes, including a reasonable number of new

homes.

 In general, the higher the average formaldehyde concentration in home age studies the

more rapid the decay. In controlled laboratory studies the higher the initial emission the

more rapid the decay.

 Concentration by home age studies provides useful information about exposures to

occupants in homes. Inherent limitations of such studies generally make them unsuitable

for interpreting changes in formaldehyde emissions over time from the original UFbonded wood products and other product sources.

 The Karns, Tennessee experimental homes project indicated a half life of about 19

months at moderate loading rates of formaldehyde sources. This study in unoccupied

homes was not confounded by the introduction of additional formaldehyde sources

during the study period.

 In controlled laboratory studies the half life of formaldehyde concentration varies from

less than 1 month to about 1 year for particleboard. A large chamber laboratory study

performed at four test sites on 16 particleboard products suggest that the half life of

current typical particleboard with ~0.15 ppm formaldehyde concentration at standard test

conditions is about 0.75 years (9 months).

 There is limited data on formaldehyde decay rates from hardwood plywood and MDF.

The data available suggests the half life in hardwood plywood is probably slightly more
12

rapid than particleboard. Data for MDF indicates that the half life is probably slightly

less rapid than particleboard.

 Very limited laboratory data on decay profiles of multiple UF-bonded wood products

show half life periods of about 18 to 24 months for the decay of particleboard, hardwood

plywood, and MDF tested together.

 Short-term decay information is available from a few controlled studies in unoccupied

homes. These studies generally indicate a reduction of formaldehyde concentration of

about 25 to 40% over the first several months. Caution is advised in interpretational

extensions from these studies: most available data is from earlier manufactured homes

containing uncharacteristically high loading rates of UF-bonded formaldehyde sources,

compared with current loading rates in both manufactured and conventional homes.

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______. 2005. Personal communication from T. Zinn of the Kitchen Cabinet

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