INDOOR AIR POLLUTION:
AN EVALUATION OF THREE AGENTS

Introduction

Environmental Tobacco Smoke

Formaldehyde

Combustion Gases

Formaldehyde

Characteristics
Formaldehyde is an organic chemical that is very prevalent in our environment. It has colorless gas with a pungent odor from a family of gases called aldehydes. Commonly known as a preservative in medical laboratories and mortuaries, formaldehyde is also found in other products such as chemicals, particle board, household products, glues, permanent press fabrics, paper product coatings, fiberboard and plywood. It is also widely used as an industrial fungicide, germicide, and disinfectant (1).

It is a sensitizing agent that can cause an immune system response upon initial exposure. It is also a suspected human carcinogen that is linked to nasal cancer and lung cancer. Formaldehyde exposure is most common through gas-phase inhalation. Airborne concentrations of formaldehyde above 0.1ppm can cause irritation of the respiratory tract (2).

Sources
Sources of formaldehyde in the home include building and insulating materials, smoking, household products, and the use of un-vented, fuel-burning appliances, like gas stoves or kerosene space heaters.

Table1 Formaldehyde Uses and Potential Indoor Sources (3)

Products Examples
Paper Products Grocery bags, sax paper, facial tissues, paper towels, disposable sanitary products
Stiffeners, wrinkle resisters and water repellents Floor covering(rugs linoleum, varnishes, plastics), carpet adhesive binder, fire retardants, permanent press clothes
Insulation Urea formaldehyde foam insulation (UFFI)
Combustion Devices Natural gas, kerosene, tobacco smoke
Pressed-wood products Pressed-wood products Plywood, particle board, decorative paneling
Other Cosmetics, deodorants, shampoos, fabric dyes, disinfectants,

Even though many products have the potential for releasing formaldehyde into indoor air, relatively few are responsible for causing significant levels of contamination. Pressed wood products and UFFI (Urea Formaldehyde Foam Insulation) can release formaldehyde at greater rates than other products.

In homes, the most significant sources of formaldehyde are likely to be pressed wood products made using adhesives that contain urea-formaldehyde (UF) resins. Pressed wood products made for indoor use include: particleboard (used as sub flooring and shelving and in cabinetry and furniture); hardwood plywood paneling (used for decorative wall covering and used in cabinets and furniture); and medium density fiberboard (used for drawer fronts, cabinets, and furniture tops). Medium density fiberboard contains a higher resin-to-wood ratio than any other UF pressed wood product and is generally recognized as being the highest formaldehyde-emitting pressed wood product (4).

a. Particleboard, www.warehouserack.com/ temp/partic7.jpg

b. Medium-Density fiberboard (MDF), www.wii.com/images/mdf.GIF

c. Hardwood plywood paneling, www.columbiaforestproducts.com/ images/m-4.jpg

Figure1. Several types of wood composite materials
Other pressed wood products, such as softwood plywood and flake or oriented strand board, are produced for exterior construction use and contain the dark or red/black-colored phenol-formaldehyde (PF) resin. Although formaldehyde is present in both types of resins, pressed woods that contain PF resin generally emit formaldehyde at considerably lower rates than those containing UF resin. Emission potential for various construction materials, furnishing etc are summarized in table 2.

Table 2 Formaldehyde Emissions from a Variety of Construction Materials, Furnishings, and Consumer Products (5)

The rate at which products like pressed wood or textiles release formaldehyde can change. Formaldehyde emissions will generally decrease as products age (Figure 2).

Figure 2 Time-dependent changes in formaldehyde levels associated with 6 grades of particleboards (5).

During the 1970s, many homeowners had urea-formaldehyde foam insulation (UFFI) installed in the wall cavities of their homes as an energy conservation measure. However, many of these homes were found to have relatively high indoor concentrations of formaldehyde soon after the UFFI installation. Few homes are now being insulated with this product. Studies show that formaldehyde emissions from UFFI decline with time; therefore, homes in which UFFI was installed many years ago are unlikely to have high levels of formaldehyde now (4).

When other materials in indoor such as carpets, gypsum boards etc, have adsorbed formaldehyde, these products may also start releasing it into the air and be secondary sources (2).

References
(2) An Update on Formaldehyde. U.S. EPA (1997 - Revised)
http://www.epa.gov/iaq/pubs/formald2.html
(3) Hines A. L. etc, Indoor Air Quality (1993)
(4) EPA, “Indoor Air Pollution: An Introduction for Health Professional”
http://www.epa.gov/iaq/pubs/hpguide.html
(5) Godish T, “Indoor air Pollution Control” (1989)

Exposure Level in Indoor Air
The World Health Organization guideline for indoor air formaldehyde concentration is 0.08 ppm (0.1mg/m3). The California Air Resources Board recommends an “action level” of 0.1 ppm and a “target level” of 0.05 ppm or lower for homes.

Formaldehyde is normally present at low levels, usually less than 0.03 ppm in both outdoor and indoor air. The out door air in rural area ha lower concentrations while urban areas have higher concentrations. Residences or offices that contain products that release formaldehyde to the air can have formaldehyde levels of greater than 0.03 ppm (2).

Average concentrations in older houses with UFFI are generally well below 0.1 ppm. In homes with significant amounts of new pleased wood products, levels can be greater than 0.3 ppm (6). Table 3 is the summary of the formaldehyde levels in residential environments.

Table 3 Formaldehyde Levels in Residential Environments (5)

Highest average concentrations are reported for mobile homes. The high concentrations of formaldehyde in mobile homes are primarily caused by the large quantity of the decking, decorative hardwood plywood wall covering, particleboard shelving, and cabinetry made form a variety of pressed wood products. With few exceptions, average formaldehyde levels in UFFI houses are typically in the range of 0.5-0.06 ppm.

References
(2) An Update on Formaldehyde. U.S. EPA (1997 - Revised)
http://www.epa.gov/iaq/pubs/formald2.html
(5) Godish T, “Indoor air Pollution Control” (1989)
(6) EPA, Reference guide to major indoor air pollutants in the home
http://www.epa.gov/iaq/pubs/insidest.html#ref8

Measurement Methods
There are numerous methods for determining the concentration of formaldehyde in indoor air. Air testing for formaldehyde can be conducted using either passive or active sampling techniques. The former are relatively inexpensive and are useful when the homeowner wants, in the interests of saving money, to do air beyond a screening function, interpretation of results is often difficult for experts and almost impossible for lay individuals. It is most desirable to conduct air testing by using an active sampling method, such as the NIOSH chromotropic acid method.

In cases where accuracy of results is important, only trained professionals should measure formaldehyde because of the difficulty of obtaining good data and interpreting the results. Do-it-yourself formaldehyde measuring devices are available. The results should be interpreted with caution, however, because weather conditions, ventilation rates, and other factors can affect the results. Such devices should be used according to the instructions (2).
The following is a brief summary of some of the methods.

Table 4 Formaldehyde Analytical Methods

Method ID Sampling Method Purpose of Sample
OSHA 52
OSHA ID-205
IP-6A
IP-6C
Detector Tubes
Miran 1A
NIOSH 3500
Coated XAD-2 tube
Passive dosimeter
DNPH-treated silica gel sorbent
DNPH treated passive monitor
Colorimetric (length-of-stain)
Non-dispersive infra-red
Chromoprotic method (Filter + impingers with 1%sodium bisulfide solution)
TWA or STEL
TWA
TWA
TWA
Grab
STEL
TWA

* TWA = time-weighted average (usually 8 hours)
STEL = Short Term Exposure Limit (15 minutes), Grab = short or instantaneous sample.

References
(2) An Update on Formaldehyde. U.S. EPA (1997 - Revised)
http://www.epa.gov/iaq/pubs/formald2.html
(7) K. Hess-Kosa, “Indoor air quality – sampling methodologies”, (2002)
(8) NIOSH Manual of Analytical Methods http://www.cdc.gov/niosh/nmam/pdfs/3500.pdf

Control and Steps to Reduce Exposure
A. Source control
l Purchasing pressed wood products labeled as low-emitting or products made from PF such as oriented strand board or soft wood plywood (figure 3).

a. Strand board http://www.homehardware.com/html/forest1.htm
b. Softwood plywood, http://www.tables4sale.com/ Tables_008a.jpg

Figure 3 Lower-emitting wood composite materials

  • Using alternate products such as lumber, metal, or solid wood furniture.
  • Avoiding the use of foamed-in-place insulation containing formaldehyde, especially UF foam insulation.
  • Enclosing unfinished pressed-wood surfaces of furniture, cabinets, or shelving with laminate or water based sealant
  • Washing durable-press fabrics before use.
  • Ensuring combustion sources are properly adjusted.
  • Avoiding smoking indoors.

B. Climate control

  • A good approach to controlling levels of formaldehyde is to control environmental factors such as temperature and relative humidity (RH)
  • Maintaining moderate temperatures and low relative humidity levels (30~50%) (table 4)

Reducing temperature from 30 to 20 ‘C alone resulted in a reduction of the levels of 70%: a 40% reduction was observed when reducing RH from 70% to 40% (5).

Table 4 Effect of temperature and RH on formaldehyde levels in a mobile home under controlled conditions of indoor climate (5)

C. Ventilation Improvement
Bring large amounts of fresh air into the home. Increasing ventilation by opening doors and windows and installing an exhaust fans.

Increase ventilation; particularly after bring new sources of formaldehyde into the home.

References
(2) An Update on Formaldehyde. U.S. EPA (1997 - Revised)
http://www.epa.gov/iaq/pubs/formald2.html
(9) IFAS, Indoor air quality in Florida: Formaldehyde http://edis.ifas.ufl.edu/pdffiles/HE/HE35300.pdf
(10) EPA, Source of Indoor Air Pollution-Formaldehyde, http://www.epa.gov/iaq/formalde.html