Smell test last step (C) Daniel FriedmanSmell Patch Test - How to Track Down a Building Odor to a Specific Material or Source

  • SMELL PATCH TEST to FIND ODOR SOURCE - CONTENTS: How to find the source of an odor or smell in a building. Simple, photo-illustrated step by step procedure assists in tracking down building odors or smells to a specific surface or material. Using ozone in buildings to "purify air" or to "kill mold" can produce persistent "chemical" odors whose source needs to be identified and removed. Building smell or odor source identification using a smell patch test
  • POST a QUESTION or READ FAQs about using simple methods to track down the source of a building odor or smell

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Smell patch test procedure tracks down odor sources: how to use paper towels, aluminum foil, and tape to perform a simple but effective odor source test of building surfaces and materials.

This article describes a simple procedure using paper towels and aluminum foil wrap to track down odors in buildings, such as but not limited to tracking down mold smells, sewer smells, plastic smells, chemical odors, animal odors, and even new smells that occur after excessive indoor use of ozone in buildings to try to "kill" mold or remove other indoor odors (skunks or smoke).

Our page top photo shows the last step in the smell-source test procedure, though we recommend that this step be conducted outdoors in fresh air.

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How can I Track an Indoor Odor to its Source?

Smell test setup (C) Daniel FriedmanThe procedure we describe here is easy, inexpensive, and fast - you'll need a day or so, plus some common household materials to track down an indoor smell to the surface or material that is its most likely source.

Depending on what caused the material to smell in the first place, disposal may be the only option. In other cases, amateur or professional cleaning or use of sealant paints may be effective. If you've already tried using an ozone generator to kill an indoor odor, you may have used the equipment improperly.

Ozone or O3 is a highly reactive oxygen molecule that can cause oxidation of materials that it touches. This oxidation, especially of some rubbers and plastics, can leave a horrible smell in the treated building.

Before getting into the details of how to perform the smell patch test, note that there are at least the following odor investigation approaches:

Odor Diagnosis Strategies:

You can start tracking down the cause or source of an odor in one or more of several ways:

  1. ODOR DIAGNOSIS SIX STEPS - taking an orderly approach to odor source tracking
  2. ODOR DIAGNOSIS CHECKLIST - an easy checklist of stuff to examine or test
  3. ODORS GASES SMELLS, DIAGNOSIS & CURE - includes a catalog of places to look when tracking down an odor source
  4. SMELL PATCH TEST to FIND ODOR SOURCE - procedure for testing specific surfaces or items to see if an odor souirce of if they have absorbed and are re-emitting an odor - this article

Using Ozone to Get Rid of Skunk or Mold Smells?

This quote from a reader's email pretty well sums up what happens if you overdo it when using an ozone generator indoors to try to "kill off" odors:

It's a long story, but I used a high powered ozone generator in our house, to get rid of skunk smell. Now I can't get rid of the left over nitric oxide, or whatever odor or gases, that linger in our house. I have been leaving the windows open every day, with running the heat on high (85 degrees) at night, to try to force off-gas the odors/gases.

We have investigated a number of cases of misapplication of ozone generating machines both to "kill mold" (no good, you're leaving toxic or allergenic particles, and you haven't corrected the reason for mold growth in the first place). We have also investigated several cases of excessive ozone-use to try to remove odors from buildings, including fire or fireplace smells, mold smells, pet or animal smells, skunk odors, smoking odors, etc.

Using an Ozone Generator Has Left a Smell in our Home - How do I Get Rid of It?

If you have aired out the building and days or more have passed and you still smell a "new" chemical or plastic or other odor that was not there before you tried using your ozone generator, you'll need to determine just what materials were oxidized by the high levels of ozone in the building.

It's been our experience that once you identify and dispose of the new-smelly material you'll probably be fine. Here are some examples of material we've found giving off horrible smells after misuse of an ozone generator. (Misuse means using the ozone generator to try to kill mold, or running an ozone generator too long at too high a setting in too small a space - overdoing it).

  • Carpets, especially synthetic carpets
  • Carpet padding
  • Foam cushions
  • Other plastic furnishings or furniture covers
  • Rubber pads, padding

Try the Smell Capture Patch Test to Pin Down a Specific Indoor Odor Source

Smell test setup on carpeting (C) Daniel Friedman

Our friend Jeff May suggested this procedure for pinning down a specific odor test in buildings - it has worked remarkably well for us where ozone had caused an indoor smell that could not be tracked down.

Our photo (left) shows the supplies you need as well as a test set up on the surface of wall to wall carpeting. We have added to, elaborated, and provided details of just how this smell patch test works - below.

  • Purchase these indoor odor track-down supplies if you don't already have them
    • A roll of new clean odor-free paper towels (not something that has a perfume in it)
    • A roll of new clean foil wrap
    • A roll of blue easy-to-remove masking tape or painter's tape
  • Close up the building - windows, and doors

Smell test setup (C) Daniel Friedman Smell test setup (C) Daniel Friedman
  • Prepare and apply odor collecting test patches on the surface of each suspected material such as carpeting, carpet padding wall surfaces, trim surfaces, furniture surfaces
    • Fold a paper towel into quarters and place or hold it on the surface to be tested.
    • Tear off a sheet of foil wrap that is several inches larger than the folded paper towel
    • Place the folded paper towel on the surface to be tested (Photo above left shows this smell locator test set up on wall to wall carpeting - we would also recommend a separate test of the carpet padding below the carpeting)
    • Place the foil wrap over the paper towel
    • Tape the foil wrap in place using the blue painter's tape (Photo above right)

Odor test patch on wall surface (C) Daniel Friedman

  • Prepare and apply additional odor-collecting test patches on all other building surfaces to be tested as an odor source. Typically these include:
    • Rug or wall to wall carpet surface in most-suspect area
    • Rug or carpet under-padding
    • Painted wall surfaces (Photo at left)
    • Plastic or vinyl windows, trim, blinds, curtains
    • Surfaces of furniture suspected as an odor source, especially couches and chairs stuffed with foam padding if odor problems followed use of an ozone generation machine
  • Prepare additional control test patches (optional) - we apply multiple samples to the same surface as a test control described below
  • Wait 24 hours or longer - you are allowing odors and gases under the paper towel to impregnate and be absorbed into the paper towel.

    Do not disturb the foil covering the paper towel during this time. The foil covering assures that what's being absorbed into the paper towel is emanating just from the surface being tested. The aluminum foil will also be used to quickly wrap and trap gases in the odor-filled paper towel at the end of the test period.
  • Station your test subject person outdoors in fresh air out of the wind - select someone with a good sense of smell, or best, the person who has already complained of a specific odor in the building.

    This outdoor stationing of the person who is to perform the "sniff test" is very important because people who are exposed to a smell for a period of time tend to lose their ability to detect that odor. Actually some odor or chemical exposures can increase sensitivity (Rabin 1986) while in many if not most cases odor sensitivity diminishes (Dalton 1996, Zufall 1997).

    Bottom line: the "sniffer" person selected to detect the building odor whose source is being sought should be someone who already reports being familiar with the odor but who has been stationed in fresh air so as not to be de-sensitized to the smell. (Details are at REFERENCES.)
Test patch being removed (C) Daniel Friedman Test patch being removed (C) Daniel Friedman
  • Test each smell patch as follows:
    • Lift a corner of the masking taped foil-covered paper towel test patch (Photo at above left, peeling-off is in process. Don't stop to take a photo like this or you may lose some of the odor absorbed in the paper towel.)
    • Quickly fold the paper towel patch inside of the foil that was used to cover it - do this quickly so you don't contaminate the patch of paper towel with other indoor air or gases (Photo at above right shows that we have sealed the paper towel completely inside of the foil covering)
    • Take the smell test package outside into fresh air in a non-windy location: Quickly carry the paper towel patch, now folded in foil, outside and present it to your test person
    • Conduct the smell test: The test person opens the foil wrap and sticks his/her nose into the paper towel and sniffs, reporting when s/he smells the offending odor that was previously the complaint in the building.
Smell test container opened for sniffing (C) Daniel Friedman Smell test last step (C) Daniel Friedman

Test your control smell patches as follows:

  • Present smell test and smell test control patches to the smell-test person, without telling him/her the surface from which it was taken nor which sample is which - odor or control.
  • Tear open a corner of the foil covering the smell-absorbing paper towel - just large enough to get the test person's nose inside of the foil. (Photo, above left)
  • The smell test person sniffs the paper towel and reports their observations. (Photo, above right)

If a smell test is definitive, the test person will usually report very accurately which patches are from a given smell or surface area.

We have had very good results with this procedure when used to narrow down odor sources in an ozone-treated building, and we had up to 95% repeatability when we used additional smell test patches.


Continue reading at ODOR DIAGNOSIS CHECKLIST, PROCEDURE or select a topic from the More Reading links shown below.

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SMELL PATCH TEST to FIND ODOR SOURCE at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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