Shared Attic and a Clearance Reading That Will Not Drop
A pest control company contracts to fumigate a two-story townhouse with 18,000 ft³ of treated space for drywood termites using sulfuryl fluoride at the label's 1X rate for a 24-hour exposure. The unit shares a common wall and a continuous attic with the attached unit; the firebreak drywall stops about 18 inches below the roof deck. The company plans to tarp only the treated unit and has told the neighbor to 'stay out for a day.' After aeration, a clearance reading in the living room is 1.4 ppm; the label clearance level is 1 ppm. The crew wants to sign off because the difference is small and the owner is waiting. The neighbor reports a headache and asks to re-enter her unit to get medication.
1. What is wrong with tarping only the treated unit given the attic construction, and what should have been done before the job?
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The continuous attic is a shared airspace. A firebreak drywall that stops 18 inches below the roof deck does not create an airtight barrier; gas will move over the top of the wall into the neighbor's attic and likely into the neighbor's living space. Tarping only the target unit cannot contain the fumigant, so the adjacent unit is effectively part of the fumigation zone without having been assessed, sealed, noticed, or cleared.
Before the job, the fumigator should have inspected the common wall and attic and chosen one of two lawful approaches. One option is to install and verify an airtight seal at the common wall and roof line so the treated volume is truly isolated. The other is to treat both units as a single fumigation, with both occupants notified and relocated and both units cleared before re-entry. Telling the neighbor to 'stay out for a day' is not a substitute for a proper notice and a coordinated clearance. The dose calculation should also reflect the actual treated volume and any attic space included.
2. The living room reads 1.4 ppm. Can the crew clear the unit? What should they do next?
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No. The label clearance level is 1 ppm, and 1.4 ppm is above that level. A clearance threshold is not a trend to be averaged or rounded down; it is a pass/fail limit. The fact that the owner is waiting does not change the legal or health requirement.
The crew should continue aeration and investigate why the reading is elevated. Given the shared attic, the likely explanation is that gas migrated into or out of the attic and is re-entering the living space, or that the living room is not yet fully ventilated. The fumigator should check the attic, the common wall, and other potential communication paths, use a calibrated instrument, and re-test in multiple locations, including the neighbor's unit if it was exposed. The unit should remain posted and unoccupied until a clear reading at or below 1 ppm is documented. The original reading and the corrective actions should be recorded.
3. The neighbor reports a headache and asks to re-enter her unit. What is the correct response?
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The neighbor should not be allowed to re-enter until her unit has been tested and cleared. Her headache may be unrelated, but with a known fumigant release in a connected structure it must be treated as a possible exposure. She should be moved to fresh air, kept calm, and evaluated by medical personnel if symptoms persist or worsen. Emergency medical services or poison control should be contacted as appropriate.
The fumigator should notify the supervisor, document the complaint and the actions taken, and expand clearance testing to the neighbor's unit. If gas is detected there, the unit must be aerated and cleared before occupancy. The company should also review why the shared attic was missed during site assessment and correct the isolation plan before any future fumigation in the building. A headache is not specific proof of exposure, but the conservative response is required because sulfuryl fluoride is an odorless gas and the neighbor had no warning.