Jeff May

A: I was called into a law office to figure out why for months no one had been able to sit in the conference room for lunch without getting a headache. There was a slight unpleasant odor that was affecting the occupants. I spent an hour looking around but finally settled on the large oval conference table, the top of which reeked like a dirty sponge. There was a telephone book on the table that had not been moved for months, and I had one of the employees sniff it: first the top, which had no odor, and then the bottom, which stunk from the table surface. She shrieked and confirmed that the odor on the bottom of the book was the same as the room odor. Dirty sponge odor is caused by butyric acid (and has the odor of vomit) from bacterial degradation of fat. The acid can be neutralized by a base like ammonia. I wiped the table with an ammonia-containing window cleaner, and the next day the employees were able to enjoy lunch in the conference room again. Based on this experience I developed the aluminum foil/paper towel test to identify surface odor sources; just fold an odorless full sheet of paper towel in half twice, place it on a surface and cover it with aluminum foil held in place by removable blue painter’s tape. Remove the test after a day or two, fold it up as quickly as possible, enclosing the paper in the foil. Then partially open the packet outdoors and sniff the paper. Tests on several surfaces can be done, labeled and compared to each other.

In another case of an odor problem, a building owner recognized the odor detected by new tenants in their rental as the body odor of prior tenants. The odor from people is also due in part to fatty acids. I recommended fumigating the heating system with ammonia to neutralize the odor.

Another interesting project that I was not directly involved in was one brought to my attention by a former student. He was trying to help the owner of a convenience store into which no one could enter without experiencing eye and throat irritation. It was soon discovered that an employee in an attempt to clean the HVAC vents had sprayed them with an oven cleaner containing sodium (or potassium) hydroxide, a powerful base used to eliminate grease. Irritating particulate residues from the cleaner were being distributed through the HVAC system. Both the manufacturer of the cleaner and I suggested fumigating or fogging the store with vinegar, an acid that would neutralize the irritating base. After the fumigation, the store reopened without a problem.

A: The biggest misstep is not identifying the source before beginning remediation. We have had clients replace boilers and re-line chimneys when only simple repair was needed. Some companies are claiming that fogging in a room with some chemicals such as enzymes can eliminate odors caused by mold from within closed-wall cavities. This is not true. The musty-odor molecules can diffuse through wall materials and make a room stink, but the fog droplets are too large to enter a closed wall cavity.

A: Ozone (when properly used) is great for removal of some odors. I had a skunk in my garage and the space reeked. Skunk odor is caused by butenyl mercaptan, a sulfur-containing molecule readily oxidized by ozone. After 10 minutes of treatment, the odor was gone. Unfortunately, other odor molecules (including those from some species of mold growth) are not affected by ozone.

One very simple way to identify some hidden odor sources is to place a window box fan on exhaust; assuming other air sources such as doors and windows are closed, the exhaust reduces the air pressure in a room and causes odor infiltration to increase. Then all cracks and openings (especially at electric boxes) can be sniffed to locate the odor source. If the temperature in the space is different from the surrounding spaces, an infrared camera can be used to locate air-infiltration openings. I used this technique to find a pencil-sized hole in a floor/wall joint that forced a mother to move her son into another bedroom. The powerful odor that made the room uninhabitable was coming from a nest full of dead and decomposing bees discovered in the small roof of a bay window in an exterior wall of the dining room directly beneath the son’s bedroom.