Odor — from where?

Finding the source of an odor

Ask about the odor — where? when?

• Is the odor constant, or when does it get stronger?
• before or after ventilation equipment startup? or shutdown?
• on sunny, hot days (from heating a wall cavity)?
• when using exhaust fans (drawing in air from elsewhere)?
• with a certain wind direction? (coming from inside a windward wall?)
• also noticed outdoors? from a certain wind direction?

Sniff out the source of an odor

• Detect the odor: the human nose and our sense of smell is the fastest, most sensitive, smartest identification tool we can get. Really!
• Decide if the odor suggests a certain source, like new carpet, paint, gasoline, solvent, smoke, rotten, damp, earthy, moldy, urine, sewage, or dead.
• Sniff around indoors to find and localize where the odor is strongest: the specific floor, area, room, corner, carpet, desk, cabinet, furniture, or air supply.
• Sniff at possible entry pathways (penetrations such as electrical outlets and cracks in walls, floors, around windows) coming from (and pointing toward) a hidden source, and there you will find it.
• Concentrate the odor from a surface by isolating suspect areas (wall, floor), like making a tent with plastic sheet held a foot away in the middle, to sniff later.
• Find the outdoor source if the odor was ever noticed outside the building: Check near the building: dead animal? bark mulch? spill on the ground?
• Circle the perimeter to find it strongest, then zig-zag out farther upwind to find the source.
• If fleeting and peripatetic, you may need many tries before you catch it.

Sniff out a hidden source of an odor

• Do a “depressurize and sniff” test, as follows:
• Depressurize the space using the building’s exhaust fans (and clothes dryer), with doors and windows closed, to force all pathways to leak inwards. (Caution: first turn OFF and close or isolate combustion appliances like fireplaces, stoves, furnaces, gas dryers to avoid back-drafting).
• Sniff penetrations when all pathways are leaking inwards, from inside walls, under floors, above ceiling lights.  You have the best chance of finding the odor immediately after depressurizing, when it should be strongest.
• Decide if the odor leaking in is any stronger than at the surface.  For example, is the stink of old fuel oil in the basement coming mostly from the floor tiles, or from under the floor?
• Sniff on different hours or days (if not found initially), or different wind directions.
• Or use a small suction fan on individual wall outlets. (That’s how I found Nancy’s dead rat.)

Confirm the source

• Cover the suspect source or pathway to find if the odor stops.
• Do a “sniff test” of the odor emissions from individual suspect materials:
  1. Sample flooring system components (carpet, pad, spot, adhesive, clear finish), or fabric, wallpaper, paint, insulation, etc.
  2. Place samples inside sealed wide-mouth glass jars.
  3. Let jars sit for a day at room temperature.
  4. Open, sniff briefly, and re-close:  Do you notice any odors yet, or react to any of them?
  5. Leave jars a few days more to concentrate the emissions.
  6. Sniff again to see if you notice a more definite odor.
  7. Decide if one jar is worse, or different.
  8. Sniff again after jars kept warmer and longer, if not much odor notices so far.

Characterize the source

After suspect sources have been found, only then might you test the air to find out what VOCs are emanating.

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