9.4 Category 11: Structural & Non-Soil Fumigation
Key Takeaways
- Nebraska Category 11 covers solid or gaseous restricted-use fumigation of buildings, chambers, vaults, tents, vehicles, and vessels, and expressly excludes liquid insecticides and rodenticides used in grain storage facilities - those are Category 08 or private/commercial ground work.
- Fumigation is one of only four activities that 40 C.F.R. 171.103(c)(7)(ii) flags as requiring certification beyond the base category, alongside aerial application, sodium cyanide, and sodium fluoroacetate.
- A written Fumigant Management Plan must be in effect before the application begins, must be on site during the fumigation, must be available to handlers and responders, and is paired with a post-application summary completed after the fumigation ends.
- Aluminum and magnesium phosphide react with atmospheric moisture to release phosphine gas, which is why water must never be used on a phosphide spill and why unused product is deactivated by controlled wet deactivation outdoors, never sealed in a container.
- Phosphine has a permissible exposure limit of 0.3 ppm as an 8-hour time-weighted average, and its garlic or decaying-fish odor is unreliable as a warning property, so air monitoring with a calibrated detector - not smell - governs when respirators come off and when a structure is cleared.
9.4 Category 11: Structural & Non-Soil Fumigation
Category Scope: NDA defines Category 11 as the use of solid or gaseous restricted-use pesticides to fumigate buildings, chambers, vaults, tents, vehicles, or vessels, whether to protect food from insect, vertebrate, or disease pests or to control wood-infesting or imported pests inside structures, tents, vaults, vehicles, or vessels. NDA adds one boundary that is frequently tested: the category does not include the use of liquid insecticides or rodenticides in grain storage facilities. Spraying a bin wall with a residual liquid is not fumigation. Category 08W explicitly excludes fumigants, so tenting a house for termites is Category 11, not 08W, and soil fumigation is the separate sub-category 01A.
Additional Certification: The federal core standard at 40 C.F.R. 171.103(c)(7)(ii) requires every certified applicator - in any category - to know that use of a fumigant, aerial application, sodium cyanide, or sodium fluoroacetate requires additional certification. Fumigation is never something you do "under" another category.
The Eight Competency Areas
Nebraska adopts the federal non-soil fumigation standard at 40 C.F.R. 171.103(d)(14), which is organized into eight areas. Use them as your study checklist.
| Area | Core Question It Asks |
|---|---|
| (i) Label and labeling comprehension | What labeling requirements are specific to non-soil fumigants? |
| (ii) Safety | How do people get exposed, what are the signs, when do respirators go on, what is first aid? |
| (iii) Fumigant chemical characteristics | How does the material become a gas, how does it disperse, what does it corrode? |
| (iv) Application | Methods, equipment, timing, sealing, dosage calculation, calibration, air monitoring |
| (v) Pest factors | Which pests are controlled, how pest density relates to rate, why rate and timing matter |
| (vi) Personal protective equipment | Which respirator, fit testing, medical evaluation, cartridge replacement, recordkeeping |
| (vii) Fumigant Management Plans | When required, contents, where kept, who may see it, and the post-application summary |
| (viii) Posting | Who may be in the area, labeling-required posting versus treated-area posting, sign placement |
Fumigant Chemistry
Aluminum and Magnesium Phosphide
Supplied as tablets, pellets, sachets, plates, or bags. The solid reacts with atmospheric moisture to release phosphine (PH3) gas:
- The reaction is driven by humidity and temperature. Below roughly 40 degrees Fahrenheit the release is so slow that the fumigation may fail; high humidity accelerates it sharply.
- Phosphine is slightly heavier than air but diffuses well through grain.
- Never add water to phosphide. Water contact produces a violently rapid gas release that can ignite; phosphine is flammable above about 1.8 percent in air.
- The spent residue is a gray-white ash of aluminum or magnesium hydroxide that still contains unreacted material. It is deactivated by slow, controlled wet deactivation outdoors in a labeled procedure, never by sealing it in a drum, never by dumping it in water indoors.
- Odor is not a warning property you may rely on. Phosphine is described as smelling of garlic, carbide, or decaying fish, but the odor comes from impurities, is not reliably detected at hazardous concentrations, and olfactory fatigue sets in. The OSHA permissible exposure limit is 0.3 ppm as an 8-hour time-weighted average, well below a dependable odor threshold.
- Phosphine is severely corrosive to copper, brass, silver, and gold. Remove or protect electronics, copper wiring, motors, and precious metals before fumigating.
Sulfuryl Fluoride
A colorless, odorless gas used for structural tent fumigation and some commodity work. Because it has no odor and no irritant warning properties at all, a warning agent such as chloropicrin is introduced first to drive occupants out and to deter entry. Sulfuryl fluoride does not control most insect eggs well, which is why dosage is expressed in concentration-time products and why label dosage tables adjust for temperature and target life stage.
Concentration and Time
All fumigation is governed by the product of concentration and exposure time (Ct). Halving the concentration roughly doubles the required time. That is why a leaky structure fails: gas that escapes lowers concentration, and the Ct product never reaches the lethal threshold even though the clock ran the full period.
Sealing and Dosage
Sealing Is the Whole Job
A fumigation is only as good as its seal. In stored-grain work that means closing and taping aeration fans and ducts, sealing manways and inspection hatches, taping seams and the roof-to-wall joint, and covering the bin roof with a tarp where the label directs. In structural tent work it means a gas-tight tarp with clamped and sand-snaked seams, all utilities shut off, and refrigerators, medications, and unsealed foods removed or double-bagged in the approved barrier bags.
Dosage Calculation
Dosage is by volume, not area. For a cylindrical grain bin the fumigated volume is the cross-sectional area times the grain depth: multiply pi by the radius squared, then by depth in feet, to get cubic feet. A bin 30 feet in diameter holding grain 20 feet deep contains 3.1416 times 15 squared times 20, which is 3.1416 times 225 times 20, or 14,137 cubic feet. If the label calls for 1 tablet per 1,000 cubic feet, that bin needs about 14 tablets. Structural fumigation uses the same logic on rectangular volumes - length times width times height - with the label dosage table converting volume, temperature, exposure time, and target pest into pounds of fumigant.
Exam Tip: A calculation item in this category almost always tests whether you used volume rather than floor area, and whether you converted the diameter to a radius before squaring.
Fumigant Management Plans and Post-Application Summaries
The FMP is a written, site-specific plan that must be in effect before the application begins. It stays on site during the application, is available to handlers and to emergency responders, and is retained per the label - commonly two years under federal soil-fumigant rules, while Nebraska record retention under Title 25 NAC Chapter 2 Section 006 runs three years, so keep to the longer period.
A complete FMP addresses:
- Applicator, handler, and business identification, including certification numbers and training verification.
- A description and diagram of the site, structure, or bin, including dimensions and the calculated volume.
- The fumigant, dosage calculation, application method, and planned exposure period.
- The sealing method and how the seal will be verified.
- Monitoring: which detector, where samples are taken, at what intervals, and the action levels.
- Personal protective equipment and respiratory protection, including cartridge or canister limits and the switch point to supplied air.
- The buffer or clearance area, posting plan, and who is authorized to enter.
- Emergency response: nearest hospital and route, local fire and law enforcement notification, and a 24-hour contact.
- Aeration and clearance procedure, including the clearance concentration and who takes the reading.
After the fumigation ends, a post-application summary records what actually happened - actual dosage, actual exposure period, monitoring results, any incidents or deviations, and the clearance readings - and identifies who prepared it and when.
Safety, Monitoring, and Aeration
- Never fumigate alone. Standard practice and most labels require at least two trained handlers present whenever the fumigant is being introduced or the structure is entered.
- Monitor with an instrument. Colorimetric detector tubes or an electronic phosphine monitor, used at label-specified locations and intervals, decide when respirators are required and when the site is clear. Smell decides nothing.
- Respirators. Air-purifying respirators have limited or no approval for phosphine at high concentrations; entry at or above label thresholds requires a self-contained breathing apparatus or supplied-air respirator. Respirator use brings the full program with it: medical evaluation, fit testing, training, cartridge change schedules, and records.
- Placarding. Warning signs go at every entrance and likely access point before the fumigant is introduced. They carry the skull and crossbones, the signal word DANGER / PELIGRO, the words "Area under fumigation, DO NOT ENTER / NO ENTRE," the fumigant name, the date and time of fumigation, and the certified applicator name with a 24-hour contact number. Signs stay up until aeration is complete and the clearance reading is taken.
- Aeration and clearance. Open the structure in the sequence the label prescribes, run fans where applicable, and take clearance readings at the locations the label names. Only the certified applicator - or a trained handler under that applicator - removes the placards, and only after the reading is at or below the label clearance concentration.
- Neighbors and responders. Notify local fire and emergency services before a structural fumigation. In an attached-structure situation, adjacent units must be evacuated and monitored.
Exam Trap: Two answers frequently appear together - "the odor of garlic told the applicator the gas had dissipated" and "the applicator waited the full label exposure period, so entry was safe." Both are wrong. Clearance is established by a calibrated instrument reading, never by odor and never by elapsed time alone.
A Nebraska applicator finishes a phosphine fumigation of a farm grain bin. The label exposure period has elapsed, the fans have run overnight, and the applicator no longer detects the garlic odor at the manway. What must happen before the placards come down?
Which activity falls OUTSIDE Nebraska Commercial Category 11 as NDA defines it?
A grain bin measures 30 feet in diameter and holds wheat to a depth of 20 feet. The phosphide label calls for one tablet per 1,000 cubic feet. Approximately how many tablets are required?