Formaldehyde Gas HCHO Exposure Limits

Formaldehyde Gas (Formalin Gas) Exposure
Standards & Limits in Buildings

Definitions of Common Exposure Limit Acronyms: EPERG, STEL, LC₅₀, IDLH, REL, STEL, PEL

The following list of definitions of common exposure limit recommendations is excerpted from US EPA: Formaldehyde Hazard Summary. Notice that these are generally industrial or workplace environment measures.

• AIHA ERPG  - American Industrial Hygiene Association's Emergency Response Planning Guidelines.
  • ERPG 1 is the maximum airborne concentration below which it is believed nearly all individuals could be exposed up to one hour without experiencing other than mild transient adverse health effects or perceiving a clearly defined objectionable odor;
  • ERPG 2 is the maximum airborne concentration below which it is believed nearly all individuals could be exposed up to one hour without experiencing or developing irreversible or other serious health effects that could impair their abilities to take protective action.
• ACGIH STEL - American Conference of Governmental and Industrial Hygienists' Short-Term Exposure Limit expressed as a time-weighted average exposure; the concentration of a substance which should not be exceeded at any time during a workday.
• LC₅₀ (Lethal Concentration50) - A calculated concentration of a chemical in air to which exposure for a specific length of time is expected to cause death in 50% of a defined experimental animal population.
• NIOSH IDLH - National Institute of Occupational Safety and Health's Immediately Dangerous to Life or Health limit; NIOSH recommended exposure limit to ensure that a worker can escape from an exposure condition that is likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from the environment.
• NIOSH REL - NIOSH's Recommended Exposure Limit; NIOSH recommended exposure limit for an 8- or 10-h time-weighted average exposure and/or ceiling.
• OSHA PEL - Occupational Safety and Health Administration's Permissible Exposure Limit expressed as a time-weighted average; the concentration of a substance to which most workers can be exposed without adverse effect averaged over a normal 8-h workday or a 40-h workweek.
• OEHHA REL - Reference Exposure Levels: RELs are intended to protect the most-sensitive individuals and include the provision of a safety margin.

Formaldehyde HCHO Limits / Recommendations in the European Union E.U.

In the E.U. formaldehyde use in household products and chemical outgassing from wood products has been more closely regulated since 2003 (Germany) or 2006 (elsewhere), and as The Times pointed out, in Japan it is home builders who are required to limit the overall formaldehyde levels in new construction. - op. cit. 3/11

Formaldehyde release from products is regulated in the E.U. for panel products such as un-faced cement-bonded particleboards, wet-processed un-faced fibreboard (when no formaldehyde emitting resin was added to the process) and for un-faced, coated or overlaid wood based panels (which might include laminate flooring) when glued with resins that emit either no formaldehyde or only negligible amounts of formaldehyde after production. The authors (Schwab et als) cite the use of isocyanate or phenolic glues as examples.

There are two formaldehyde outgassing level certification indicators used on products in the E.U.

1. Germany, through the German Association of Producers of Fabricated Houses (BDF), specifies 0.03 ppm panel boards asserted as equivalent to Japan's formaldehyde emission class F
2. "Blue Angel" labels indicate that the board has a formaldehyde outgas rate of 0.05 ppm (with changes or diminution over what lifetime is not stated)

In Europe there is one reference method and there are three or four derived methods for testing the level of formaldehyde in a building or in a material:

Reference Formaldehyde Testing Method: The E.U. Formaldehyde Testing Chamber method EN 717-1 with three different volume options.

The chamber method used in the E.U. involves a large-enough chamber that it can contain multiple structures of cabinetry or shelving or sheet goods. This method is illustrated and discussed by Schwab et als. (un-dated). Tested components are sealed in the test chamber for up to 28 days, permitting formaldehyde emission level measurements in ppm or mg/m³.

Derived Formaldehyde Testing Methods in the E.U.:

• Dessicator method for formaldehyde testing # ISO/DIS 12460-4 or JISD A 1460 / JAS 233 (possibly). This testing method uses a dessicator in a container of material and is used for testing the formaldehyde release from both coated or un-coated particleboard or medium density fiberboard, but using quite small physical samples.
• Flask method for formaldehyde testing # EN 717-3. This method determines the level of release of formaldehyde in mg/kg and according to Schwab et als is suitable only for internal production control of wood based panels by fabricators, presumably because there is no published official limit value.
• Gas Analysis method for formaldehyde testing # EN 717-2. This approach is used for coated particle board, for either coated or un-coated plywood, and determines the formaldehyde content in mg/M² xh
• Perforator method for formaldehyde testing # EN 120 permits determination of formaldehyde content in mg/100 g of substance using a toluene extraction method. This approach is used with particleboard (PB), medium density fiberboard (MDF), and oriented strand board (OSB).

Formaldehyde Emission Limits for the E.U. were published by Schwab et als (cited below) and vary depending on the testing method used. The authors we cite provide a helpful chart from which we excerpt and adapt below. Please see the original for complete details.

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• Using EN 120 for un faced particleboard, OSB or MDF, the formaldehyde content is limited to <= 8mg/100g of oven-dried board with moisture content specification depending on the panel or board type.
  
  Watch out: moisture content is a key factor in testing these products against formaldehyde emission standards, and if the moisture content is not within specification the test results will not be valid.
• Using ENV 717-1 for initial type testing of established products the limit is a formaldehyde release of <= 0.124 mg/m³ of air for all types of panel or board products including particleboard, plywood, OSB, MDF, solid wood, etc.
• Using ENV 717-2 the limit depends on whether the tested material is faced or coated or not

Australia & New Zealand Formaldehyde HCHO Emission Standards, Limits & Regulations

• NICNAS Priority Existing Chemical Assessment Report No. 28 – Formaldehyde. Sydney, NICNAS (2006), available at: www.nicnas.gov.au
• AS/NZS 1859.1:2004: Reconstituted wood-based panels – Specifications – Particleboard
• AS/NZS 1859.2:2004: Reconstituted wood-based panels – Specifications – Dry-processed Fibreboard
• AS/NZS 1860.1:2002: Particleboard flooring – Specifications
• AS/NZS2269.0: 2008: Plywood – Structural Part 0 Specifications1
• AS/NZS 2270:2006: Plywood and blockboard for interior use1
• AS/NZS 2271:2004: Plywood and blockboard for exterior use1
• AS/NZS 2272: 2006: Plywood-Marine1
• See http://www.ewp.asn.au/library/standards.html for direct links to these standards

Australian Standards, labelling and product certification, are available at Engineered Wood Products Association of Australasia website at: www.paa.asn.au

Australian, E.U. & U.S. Formaldehyde Emission Standards & Testing References:

• Australian Competition & Consumer Commission, "Product Safety in Australia, Formaldehyde in Consumer Products", retrieved 29 March 2015, original source: https://www.productsafety.gov.au/content/index.phtml/itemId/973697
• Australian Government Department of Health, "Formaldehyde in Pressed Wood Products Safety Fact Sheet, CAS No. 50-00-0", National Industrial Chemicals Notification and Assessment Scheme, retrieved 29 March 2015, original source: http://www.nicnas.gov.au/communications/
  publications/information-sheets/existing-chemical-info-sheets/formaldehyde-in-pressed-wood-products-safety-factsheet
• Binetti, Roberto, Francesca Marina Costamagna, and Ida Marcello. "Development of carcinogenicity classifications and evaluations: the case of formaldehyde." ANNALI-ISTITUTO SUPERIORE DI SANITA 42, no. 2 (2006): 132.
• Brelih, Nejc, and Olli Seppänen. "Ventilation rates and IAQ in European standards and national regulations." In The proceedings of the 32nd AIVC conference and 1st TightVent conference in Brussels, pp. 12-13. 2011.
• Bruynzeel, Derk P., Klaus E. Andersen, José G. Camarasa, Jean‐Marie Lachapelle, Torkil Menné, and Ian R. White. "The European standard series." Contact Dermatitis 33, no. 3 (1995): 145-148.
• Brown, S. K. "Chamber Assessment of Formaldehyde and VOC Emissions from Wood‐Based Panels." Indoor air 9, no. 3 (1999): 209-215.
• European Chemicals Agency (ECHA), "Response to comments document (RCOM) to the Opinion proposing harmonised classification and labelling at EU level of
  Formaldehyde", Committee for Risk Assessment (RAC) of the ECHA, (2012), retrieved 29 March 2015, original source: http://echa.europa.eu/documents/10162/e38c0fba-6104-4646-b787-116ed63deb9d
• Harald Schwab, Rainer Marutzky, Bettina Meyer, "European Regulations for Formaldehyde", [PDF] Fraunhofer Institute for Wood Research Wilhelm-Klauditz-Institut
  Braunschweig / Germany, Retrieved 29 March 2015, original source http://owic.oregonstate.edu/sites/default/files/pubs/Schwab.pdf
• Groah, William J., John Bradfield, Gary Gramp, Rob Rudzinski, and Gary Heroux. "Comparative response of reconstituted wood products to European and North American test methods for determining formaldehyde emissions." Environmental Science & Technology 25, no. 1 (1991): 117-122.
• Kim, Sumin, Jin-A. Kim, Hyun-Joong Kim, and Shin Do Kim. "Determination of formaldehyde and TVOC emission factor from wood-based composites by small chamber method." Polymer Testing 25, no. 5 (2006): 605-614.
• Kim, Sumin, and Hyun-Joong Kim. "Comparison of standard methods and gas chromatography method in determination of formaldehyde emission from MDF bonded with formaldehyde-based resins." Bioresource Technology 96, no. 13 (2005): 1457-1464.
• Lund, Kirsten H., and Jens Højslev Petersen. "Migration of formaldehyde and melamine monomers from kitchen-and tableware made of melamine plastic." Food additives and contaminants 23, no. 9 (2006): 948-955.
• Salthammer, Tunga, Sibel Mentese, and Rainer Marutzky. "Formaldehyde in the indoor environment." Chemical Reviews 110, no. 4 (2010): 2536-2572.
• Tang, Xiaojiang, Yang Bai, Anh Duong, Martyn T. Smith, Laiyu Li, and Luoping Zhang. "Formaldehyde in China: Production, consumption, exposure levels, and health effects." Environment international 35, no. 8 (2009): 1210-1224.

Canadian Formaldehyde Exposure Standards

"The risk of developing cancer from formaldehyde levels found in Canadian homes ... is essentially zero" - Health Canada

• Health Canada, "Formaldehyde in Indoor Air", Health Canada . Sante Canada, retrieved 29 March 2015, original source: http://www.hc-sc.gc.ca/ewh-semt/pubs/air/formaldehyde/fact-info-eng.php
  
  Excerpt:
  Although formaldehyde is a known carcinogen, the risk of developing cancer from formaldehyde exposure at concentrations found in most Canadian homes is essentially zero.
  
  Formaldehyde can be found in the air of most, if not all, homes.
  
  It is, however, generally below the levels recommended by Health Canada. Formaldehyde may be a concern for people with respiratory problems (such as children with asthma) following new home construction or renovations, when levels are generally at their highest.
  
  Health Canada's Residential Indoor Air Quality Guideline for formaldehyde recommends maximum exposure limits of;
  • Short-term Formaldehyde exposure: 123 µg/m³ (100 ppb) based on a 1-hour average to protect against irritation of the eyes, nose or throat.
  • Long-term Formaldehyde exposure: 50 µg/m³ (or 40 ppb) based on a minimum 8-hour average, to protect against respiratory symptoms in children with asthma.

  Health Canada's recommended short-term exposure limit is 1/10th of the lowest level at which symptoms have been observed, in order to protect more sensitive individuals. In direct exposure studies, formaldehyde has been shown to cause irritation of the eyes, nose and throat at 1230 µg/m³ (1000 ppb). However, people may vary in their sensitivity to formaldehyde and some may experience symptoms at lower levels.
  
  Health Canada's recommended long-term exposure limit is set to protect children with asthma, who may be more sensitive to the effects of formaldehyde. Long-term exposure to formaldehyde in indoor air has been associated with increased allergic sensitivity, airway inflammation and physician-diagnosed asthma.
  
  Health Canada's recommended levels also protect against the potential cancer risk from formaldehyde. Formaldehyde is classified as "carcinogenic to humans" by the International Agency for Research on Cancer (IARC). Industrial workers exposed to high levels of formaldehyde as part of their jobs have shown a higher risk of developing rare forms of cancer that affect the upper respiratory systems. The risk of developing cancer from formaldehyde levels found in Canadian homes, however, is essentially zero.

Table of Formaldehyde Exposure Recommendations, World Wide

The following table is excerpted from Salthammer, Tunga, Sibel Mentese, and Rainer Marutzky. "Formaldehyde in the indoor environment." Chemical Reviews 110, no. 4 (2010): 2536-2572. More work by these authors is cited atReferences or Citations .

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In comparing the recommended exposure limits for formaldehyde in various countries around the world as given in the table below note that the conversions from ppm are given in micrograms: ug per m^-3 NOT milligrams: mg/m³ (micrograms per cc rather than milligrams per cubic meter).

Calculate Conversions Between PPM and mg/m³

How & When to Convert Exposure Limits in ppm to mg/m³ for Formaldehyde or other Substances

Concentrations of chemicals in air are typically measured in units of the mass of chemical (milligrams, micrograms, nanograms, or picograms) per volume of air (cubic meter or cubic feet). However, concentrations may also be expressed as parts per million (ppm) or parts per billion (ppb) by using a conversion factor. The conversion factor is based on the molecular weight of the chemical and is different for each chemical. Also, atmospheric temperature and pressure affect the calculation. - Boguski (2006)

Only concentrations of substances that exist as a gas or vapor in air at "normal" room temperatures and pressures can be expressed as parts per million. In order to be able to express exposure limits in a consistent manner across a variety of materials, including metals, salts or other substances that are not airborne as vapors, occupational exposure limits are typically given as milligrams per cubic meter of air or mg/m³ of a substance in air. Still other substances such as airborne asbestos or fiberglass fibers may be expressed as fibers / cc but we warn that "fibers" needs to be more carefully defined since the size of particles of these materials can vary significantly and as health implications may also vary by particle size.

The Canadian Centre for Occupational Health and Safety (CCOHS) (www.ccohs.ca) and the ACGIH ("Threshold Limit Values TLVs™) discuss both threshold limit values (TLVs™) and Biological Exposure Indices (BEIs™) and give formulas for TLVs in both ppm and in mg/m³ assuming that these measurements are made at 25C and 1 atmosphere of pressure (1 ATM = 760 torr = 760 mm Hg = 406.64355 inches of water).

One Gram Molecular Weight or GMW or "mole" can be defined as the quantity of a substance whose weight in grams is equal to the molecular weight of that substance

Moles or molecular weights of any substance are calculated as

Atomic Weight of a Substance (from the periodic chart of its comprising elements expressed in atomic mass units) x number of atoms of each element present = the formula weight of the substance.

So any GMW or mole calculations for any substance require that you know the atomic weight of its individual comprising atoms as well as the number of atoms making up substance. The atomic weights of elements are found in a periodic table or in tables maintained by NIST.

Formulas for Converting Concentration of a Substance Between ppm and mg/M³

Assuming a pressure of 1 ATM and a temperature of 25C, we can write equations to convert between concentrations of a substance in parts per million (ppm) to concentration of the same substance in mg/M³ as follows: - Boguski (2006)

To convert ppm to mg/m³

Concentration of X (mg/m³) = 0.0409 x concentration of X (ppm) x molecular weight of X

To convert mg/m³ to ppm

Concentration (ppm) = 24.45 x concentration (mg/m³) ÷ molecular weight of X

Formaldehyde's atomic weight is 30.02598

To avoid confusion between milligrams per cubic meter and micrograms per cubic meter: 1.0 mg/m³ = 1000.0 ug/m³

Notes to the Table Above

Use these formulas to convert between ppm and mg/m³ assuming that the measurement is made at 1 ATM and 25°C (These numbers will be incorrect at other temperatures or pressures. )

0.0409 x concentration of Formaldehyde (in ppm) x molecular weight of Formaldehyde = Concentration of Formaldehyde in (mg/m³)

Example#1: convert 3 ppm of formaldehyde to mg/m³

0.0409 x 3ppm HCHO x 30.02598-HCHO = 3.68418775 mg/m³

Using the molecular weight of formaldehyde = 30.02598

Example #2: convert 400 mg/m³ of formaldehyde to ppm

24.45 x concentration 400 (mg/m³) ÷ 30.02598 molecular weight of Formaldehyde = 325.7179283 Concentration (ppm)

If you are working in micrograms per cubic meter (ug/m3) instead of milligrams per cubic meter (mg/m³) you can use these same equations to obtain parts per billion (ppb) instead of parts per million (ppm).

If you are working in concentrations of chemical substances in water the usual measurements are in mg/L or ug/L.

Just to keep our decimal places straight, if you are converting between ppm and ppb, 1 ppm = 1,000 ppb. A milligram is 1/1000 of a gram or 0.001 grams; a nanogram is 1/1,000,000,000 grams or a billionth of a gram, or 0.000000001 grams.

Definition & Composition of the molecular mass (popularly "weight") of Formaldehyde

The molecular mass of any substance is the sum of the mass of its constituent atoms. To have a useful meaning, all atomic mass units are expressed relative to the isotope ¹²C which is defined to have a mass of 12. Formaldehyde has an atomic weight expressed in atomic mass units or molar mass of 30.02598 computed as follows:

What is the atomic mass of Formaldehyde?

A molecule of formaldehyde is made up of a combination of atomic elements written as CH₂O (or HCHO)

Atomic mass of H, Hydrogen = 1.00794

Atomic mass of C, Carbon = 12.0107

Atomic mass of O, Oxygen = 15.9994

These atomic mass units or popularly, "atomic weights"are given in the atomic table. Adding these for CH₂O = (H + H + C + O) = (1.00794+1.00794+12.0107+15.9994) = 30.02598

What is one gram molecular weight of Formaldehyde? What is one mole of Formaldehyde?

One gram Molecular Weight (GMW) of any substance is defined as the amount of the substance whose weight in grams is numerically identical to the molecular weight of that substance.

One gram molecular weight (1 GMW) of formaldehyde = 30.02598 grams.

How many grams of formaldehyde are in one mole of that substance? The same. The term "mole" is a synonym for "gram molecular weight". One mole of CH₂O = 30.02598 grams.

Or inversely, one gram of formaldehyde = 0.0333044916436 moles.

How Gram Molecular Weight is used in TLV (Threshold Limit Value) calculations

Threshold limit values (TLVs), if we know the GMW of a substance, can let us easily convert between ppm and mg/m³ with the warning that the measurements assume that environment where the measurement is made is at 1ATM of pressure (sea level) and at 25°C. At other pressures and temperatures more adjustments need to be made to the simplified calculations shown below.

Any TLV expressed in mg/m³ = (gram molecular weight of substance) x (TLV in ppm) / 24.45

Any TLV expressed in ppm = 24.45 x (TLV in mg/m³) / (gram molecular weight of substance)

where 24.5 is a constant that equals the volume in liters of one mole (or one GMW) of a gas or vapor at 1 ATM of pressure at a temperature of 25C. For other temperatures the molecular weight must be re-calculated using the gas laws: V=(RT/P) where V=volume, R is the ideal gas constant, T is temperature in Kelvins, P is pressure in mm of hg.

Background about Gram Molecular Weight, Moles, Avogrado's Constant, and Fork Union Military Academy's Captain Peterson

In high school chemistry at Fork Union Military Academy Captain Peterson (ca 1959-1960) taught us that

Avogrado's number, 6.0221413 x 10²³

is defined as the mass of one mole (one gram molecular weight) of any substance. He also used as an equivalent term "gram molecule" or "gram molecular weight" for "mole" but Peterson is long retired and gram-molecule has lost popularity to a somewhat different term "gram atom".

One gram-atom or "gat.", a somewhat different idea, is the quantity of any substance that contains Avogrado's number of atoms.

Peterson, when he, along with the science teacher, was not busy building a still in the top floor chemistry lab, was an exciting teacher who was inclined put a little more lycopodium powder into a can with a candle (bigger boom) or to cut a little larger piece of raw sodium metal to toss into the Fork Union sewer drain (which was tremendously exciting).

When a spider was slowly spinning its way down over his desk, Peterson calmly opened a cylinder of raw chlorine gas that he had handy - just a little squirt, that's all. The spider turned white and the students, choking on chlorine, all jumped out of the classroom windows.

Online calculator converts among μg/L, μg/m3, ppmV and % concentrations

The U.S. EPA provides "EPA On-Line Tools for Site Assessment Calculation" at http://www.epa.gov/athens/learn2model/part-two/onsite/ia_unit_conversion.html including a calculator that converts measurements among various scales such as μg/L, μg/m3, ppmV and %.

However regrettably formaldehyde is not among the gases included in the EPA's calculator. We have asked that the EPA add that substance.

• "Boguski, Terrie K., "Understanding Units of Measurement", Center for Hazardous Substance Research, Kansas State University, (October 2006), Terrie K. Boguski, P.E., is the Assistant Technical Director of the CHSR at Kansas State University (tboguski@ksu.edu). - retrieved 18 April 2015, original source https://www.ksutab.org/?ResponseView=TABResourceDownloadView&id=9

Formaldehyde Outgassing from Clothing & Soft goods: Exposure Limits

According to the New York Times, the most stringent (but voluntary) industry standards for exposure to formaldehyde were established in Japan, as follows:

• 20 ppm or less (down to "undetectable") for products that touch the skin of children under three years of age
• 75 ppm for products that touch the skin of people other than children under 3 year old
• 300 ppm for products that do not touch the skin (such as outerwear)
• FORMALDEHYDE in TEXTILES, U.S. G.A.O. report to Congress. While [formaldehyde] levels in clothing generally appear to be low, allergic contact dermatitis is a health issue for some people, GAO-10-875, August 2010, retrieved 12/13/2010, original source: http://www.gao.gov/new.items/d10875.pdf
  
  OPINION - DF: We liked this report as exemplary in thoroughness, clarity, and impartiality on the subject of formaldehyde exposure from textiles.
  
  According to the NY Times article cited above, some critics complained that the U.S. government study should have included a wider arrange of textiles such as draperies and upholstery, and we agree, but add that upholstered furniture may in some products outgas more formaldehyde from foam used in the product than from its covering fabric. Similarly, carpeting could have been considered.
  
  But the focus of the study was textiles that are likely to be in prolonged (rather than incidental) contact with human skin. Under the aegis of contact with human skin and recognizing the very low limit set in Japan for fabrics in contact with the skin of children under three, one can but wonder about the possibility of concerns for skin contact of infants and small children placed on carpeting.

References:

• European Commission Joint Research Centre, "European Survey on the Release of FOrmaldehyde from Textiles", EC JRC (2007), European Commission Directorate-General Joint Research Centre Institute for Health and Consumer Protection Contact information Address: via E. Fermi 1, 21020 Ispra (VA), Italy E-mail: paola.piccinini@jrc.it Tel.: 0039-0332-789124 EUR 22710 EN ISBN 978-92-79-05215-6 ISSN 1018-5593 Luxembourg: Office for Official Publications of the European Communities,
  
  Website: http://www.jrc.cec.eu.int/pce http://www.jrc.cec.eu.int , retrieved 29 march 2015, original source: http://publications.jrc.ec.europa.eu/repository/bitstream
  /111111111/5233/1/6150%20-%20HCHO_survey_final_report.pdf

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Report on inadequate indoor gas testing, deaths, illnesse, worries about competent gas testing

My wife and I were exposed to carbon monoxide (and I'm assuming other combustible gases) for well over a year without knowing. We lived on a ground floor of an apartment and holes were drilled through the floor for plumbing and elec. but were never covered. They insurance company had Pinchin Engineering do a test on the place. and we were shown a basic 1 page sheet of CO and CO2 levels both in and around the house.

The readings from our detector that we finally bought a year later were at times almost 300. there readings were 20.

however the CO2 levels were 859.

Does this mean that combustion was happening because of both the readings and if so wouldn't tests be done for other combustible gases that may be present?

We lost a baby, dog died 2 years later, heart and kidney failure. wife has heart and joint issues. and I have a list as well. They settled out of court for $300Gs but I feel like we didn't receive ALL the disclosure from the air quality test. - Matt 11/30/11

Reply:

Matt,

Of course we are so sorry about the tragic losses you described, and I understand the tragedy of losing a child. When we suffer a tragic loss it is so difficult to endure that the look for a cause and blame is understandable, though sometimes we can be led astray in such a search.

In attempting to relate an illness or fatality to a building or environmental condition, a good place to start is with the physicians involved - ask about possible relationships between the illness or death and environmental factors.

About varying gas levels in buildings, our field experience confirms that small changes in a building (a window open or shut, or a door, or a bird building a nest in a chimney, or seasonal sooting in an oil fired appliance) and similar events can make an enormous difference in the measured result of indoor gases, airborne mold, other contaminants. For that reason, it is no surprise that a year later an individual measurement of gases indoors might find a very different level.

Only if the source of an indoor hazard can be clearly traced to a condition that was present, recogniziable by general home inspection standards and procedures, and visible at the time of the original inspection would one suspect the original inspector or test company of negligence.

• For CO₂ (carbon dioxide) typical indoor levels see TYPICAL CO₂ LEVELS.

• For CO (carbon monoxide) information see CARBON MONOXIDE - CO

• For examples of the sorts of conditions that an inspector should be able to observe and report
  see CARBON MONOXIDE INSPECTION

• Lastly, when considering a report from any building investigator, make certain that s/he is financially and ethicallyi completely independent from the person or company recommending or arranging for that service or inspection. Conflicts of interest in such matters are intolerable and even dangerous. And of course, provding more than one version of any building investigation report, say different versions to different parties, smells bad to me too.

...

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