The Homeowner in the Driveway and a 4 ppm Closet
A 7,500 ft3 condominium was fumigated with sulfuryl fluoride; the label clearance level for an occupied dwelling is 1 ppm. Aeration started at 6:00 a.m., the tarp came off at 9:30 a.m., and blowers have run at the front door and in the hallway since then. At 3:00 p.m. an unlicensed technician using the company detector records: kitchen 1 ppm, living room 1 ppm, master bedroom 2 ppm, hall closet 4 ppm, bathroom 2 ppm, crawlspace access 3 ppm. The homeowner is parked in the driveway with children aged 3 and 6 and says her pediatrician's office told her 'sulfuryl fluoride clears fast, it's fine.' The detector's calibration sticker reads 14 months old; the manufacturer's interval is 12 months.
1. Can the unit be cleared at 3:00 p.m.? Give the decision and the specific reasons behind it.
Read the worked answer
No. Three independent reasons, any one of which is sufficient:
- The closet reads 4 ppm against a 1 ppm clearance level. Clearance is not an average; every sampled location must be at or below the level. A closet is a dead-air space that will hold gas long after the open rooms read clean.
- The crawlspace access reads 3 ppm. Sulfuryl fluoride is roughly 3.5 times as dense as air and pools low. A clean living room does not mean a clean crawlspace or subarea.
- The instrument's calibration is expired (14 months against a 12-month manufacturer interval). The numbers cannot be relied on for a clearance decision in either direction -- they neither clear the unit nor prove it unsafe; they are informational only.
Actions: continue aeration with targeted ventilation into the dead-air spaces (open closet doors and the crawlspace access, direct a blower), obtain a calibrated instrument, re-sample, and do not re-enter for occupancy. Tell the homeowner a realistic window rather than a promised time. A physician's general statement about the product does not substitute for a clearance test, and the technician is not authorized to clear the structure.
2. Describe a defensible clearance sampling procedure -- where, at what height, and under what conditions -- and explain the desorption issue.
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Instrument: calibrated within the manufacturer's interval, with the calibration record and instrument ID recorded; zeroed in clean outdoor air before sampling.
Locations: every enclosed space and every dead-air space on every level -- closets, cabinets, the subarea/crawlspace, the attic if it was inside the envelope, the garage if attached. Multiple points per floor rather than one representative point.
Heights: breathing zone, roughly 4-6 ft, plus low points (floor level, crawlspace) because sulfuryl fluoride is heavy and stratifies.
Conditions -- the step most crews skip: after active aeration, close the structure and let it stand for a defined equilibration period before the final readings. Sulfuryl fluoride desorbs from porous materials -- wood framing, upholstery, carpet, stored goods -- and will rebound after the blowers stop. A reading taken with the doors open and air moving can look clean while the closed-up structure is not. The final clearance reading should be taken on a closed-up structure.
Sequence: aerate, close up, equilibrate, sample all points, and if any point fails, ventilate that space and repeat.
3. What must be documented and who is authorized to sign the clearance, and how does the notification to the homeowner fit into the record?
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Documented: tarp removal time; aeration start and method; each reading with time, location, height, and instrument ID; the calibration certificate; the equilibration period; any re-ventilation and re-test; the identity and license number of the person who made the clearance decision; and the occupant notification -- when the family was told the structure was clear and by whom.
Signature authority: clearance for occupancy is a licensed act. In California structural fumigation it is made by the Branch 3 licensee (field representative/operator) in charge -- not by an unlicensed technician, an office employee, or the homeowner signing 'I accept.' An unlicensed person may collect readings; the licensee certifies them.
Homeowner communication: the clearance notice, entry instructions, and any odor/irritation caveat go in writing, with a copy in the job file. If the family re-enters against advice or before clearance, note it.
Record value: if there is any later complaint or exposure claim, the file must let a third party reconstruct the timeline minute by minute. A stack of undated strip-chart readings with no instrument ID reconstructs nothing, and an expired calibration turns every reading into an admission.