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Fumigant monitoring and clearance

Quick answerVerified September 26, 2026

What is fumigant monitoring and clearance?

Measuring fumigant gas during and after a fumigation to protect people and document the job. For sulfuryl fluoride, a clearance device must read 1 ppm or less in each room's breathing zone before re-entry. Phosphine labels require a written fumigation management plan, monitoring, and aeration to 0.3 ppm. A clearance reading describes the air, not every void.

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Where it fits

Residential sulfuryl fluoride clearance. EPA requires the level inside the structure to be under 1 ppm, confirmed by a reading of 1 ppm or less in the breathing zone of each room. The certified operator posts clearance notices at every entry point and tells the resident. The device must tell concentrations apart at 0.5 ppm steps at minimum and be calibrated within the manufacturer's re-calibration interval.
A written record of each residential fumigation. EPA's site-specific structural fumigation log, required on residential sulfuryl fluoride labels in states without their own specifications, records dosing conditions, fumigant release time, who started aeration and when, the date and time final clearance testing was completed, and the clearance device model used.
Phosphine fumigations of any kind. Labels require a fumigation management plan written before every treatment, including a monitoring plan showing that nearby workers, bystanders and residents are not exposed above allowed limits. EPA's 2024 interim decision adds instructions to monitor phosphine inside the enclosure before aeration and record it in the plan, to decide whether an aeration buffer zone is needed. The plan and monitoring records must be kept on site during the job and for at least two years.
Knowing when people can go back in after phosphine. Fumigated structures must be aerated to 0.3 ppm or less before re-entry unless approved respiratory protection is worn. Labels allow no more than 0.3 ppm as an 8-hour average, or 1.0 ppm over 15 minutes, without respiratory protection. A self-contained breathing apparatus is required when levels are unknown or above that short-term limit.
Continuous readings in bins and other long fumigations. In farm-bin trials, wireless phosphine sensors tracked hand-held meter readings as levels changed and showed swings tied to the recirculation fan that manual sampling missed.

Where it does not

This is the part the brochure leaves out, so it is the part worth reading.

Treating clearance as the end of exposure. In California from 2003 to 2014, there were 59 reported sulfuryl fluoride illness incidents after structural fumigation, seven of them fatal. Over half involved people exposed after the structure had been cleared, though none of the deaths did. Wall voids, sockets, crawl spaces and cabinets can trap gas, and household materials absorb and release it. In one home, 11 breathing-zone samples were clear while the air cells of a mattress held 2.4 ppm weeks after fumigation.
Any gas analyser that happens to read sulfuryl fluoride. EPA tested five clearance device models and found two ineffective. Its performance bar is a false-negative rate (reading 0 ppm on a test standard) under 30%, and more than 70% of readings on a 1 ppm standard actually showing 1 ppm. In one serious poisoning case the operator had no working clearance device. An uncalibrated or unlisted meter gives a number, not a clearance.
Phosphine anywhere people live. The model fumigation management plan language prohibits use on single- and multi-family homes, nursing homes, schools, daycare facilities and hospitals. The exception that lets occupants stay in a building inside an aeration buffer zone, with continuous real-time monitoring at 0.3 ppm or less, applies only to occupational workers, never to homes, apartments, schools or hospitals.
Reading 0.3 ppm phosphine as a safe level. It is the label re-entry level and matches the OSHA and NIOSH 8-hour limits, and the label is the law. EPA's own review also notes that ACGIH recommends a lower threshold of 0.05 ppm as an 8-hour average and 0.15 ppm short term. Those are recommendations only, but they are the reason to keep exposure well under the legal figure, not up to it.
One sensor as proof the whole commodity was treated. The same bin study found concentration can vary considerably with depth in the grain, so a single sensor cannot show the fumigant reached everywhere it needed to.

Sources

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