Hot spot in Godown 3: fumigate, aerate or clear out?
On 12 July the depot officer at a north Indian depot reviews Godown 3, which holds 2,400 MT of wheat procured in April, packed in 60 kg jute bags and stacked ten bags high. Ambient temperature is 33 °C and relative humidity has stayed above 70% for a week. A probe pushed 1.2 m into the stack reads 38.5 °C, while two adjacent probes read 33-34 °C. A bag opened at the hot spot shows live Sitophilus adults, a few bored grains and a faint musty smell, but no visible mould. The laboratory reports 13.2% moisture against the 12.0% specification. The godown has fixed ventilation grills but no gas-proof sheeting. The departmental fumigation crew is on another district and cannot arrive before 16 July. A rake allotment requires 800 MT to be loaded and dispatched by 18 July. Depot staff propose opening the stack, spraying the bags with insecticide and clearing the grain out quickly.
1. State what the readings actually indicate, and set out the actions you would authorise in the next 72 hours in priority order. Say explicitly why the staff proposal is inadequate.
Read the worked answer
What the readings mean. A single probe reading 38.5 °C against 33-34 °C at adjacent points, with ambient at 33 °C, is a localised hot spot, not normal seasonal warming. Live adults, bored grains and a faint musty smell without visible mould indicate an active, early-stage infestation. The laboratory figure of 13.2% is above the 12.0% safe-storage level, so the grain is also carrying more moisture than it should going into the monsoon. This is a curative case, not a prophylactic one.
Actions, in order.
- Quarantine and re-grade. Mark the godown and stop issue or dispatch from the suspect block. Draw fresh samples at three depths (0-1 m, 1-2 m, 2-3 m) for moisture, insect-damage percentage and, because the musty smell persists, a mould/aflatoxin screen.
- Break the hot spot. De-stack the affected portion, spread it on a clean floor with dunnage, aerate and re-stack only after it has cooled, at reduced height and with cross-ventilation. Re-stacking warm grain simply rebuilds the hot spot.
- Protect the 800 MT commitment. Load it from an unaffected block or another godown. Never load suspect stock against a PDS indent before re-grading.
- Structural treatment. Spray the godown structure, dunnage and empty bag stacks with the approved contact insecticide. This is a hygiene measure, not a cure.
- Book the crew for 16 July and prepare sealing material in the meantime.
Why the staff proposal fails. A surface spray does not penetrate a jute bag and does not touch insects inside the grain; it treats the symptom and leaves the infestation. Rapid clearance simply ships infested grain to the receiving depot, where it becomes that depot's rejection problem, while the remaining 1,600 MT stays untreated through the wettest weeks of the year.
2. Work out the fumigation requirement at the standard dose and state the conditions that must be satisfied before the sheets go on. Then decide how the 800 MT dispatch and the fumigation are to be sequenced.
Read the worked answer
Dose and quantity. The standard schedule for bagged grain in a godown is 3 aluminium phosphide tablets of 3 g per tonne, that is 9 g of formulation per tonne. For the 1,600 MT that will remain after the dispatch: 1,600 × 3 = 4,800 tablets, or 14.4 kg of formulation. If the whole 2,400 MT were treated, the figure would be 7,200 tablets, or 21.6 kg.
Conditions before sealing.
- The enclosure must be gas-tight: grills, doors, cracks and the junction of wall and roof sealed, sheeting intact, no gaps at the floor.
- Grain temperature must be above about 15 °C; below that phosphine is released too slowly and the kill is unreliable.
- Grain moisture must be within the safe limit for sealed storage. At 13.2% the grain must first be aerated or dried towards 12%, otherwise moisture migrates to the cooler surface during a seven-day seal and condenses, producing mould in a godown that had none.
- A licensed applicator, warning boards, exclusion of all personnel, respirators and first-aid arrangements must be in place before the first tablet goes in.
Sequencing. Dispatch the 800 MT first, from the unaffected block, and complete the de-stacking, aeration and cooling. Only then seal and fumigate the residual 1,600 MT, keeping the godown shut for the full exposure period. Fumigating first and then opening the doors for a rake loading would release the gas and waste both the chemical and the seven days. The practical consequence is that the treated stock is unavailable until roughly 23-25 July; that revised availability should be notified to the regional office in writing rather than concealed by breaking the seal.
3. Three weeks later the laboratory reports 14.1% moisture and visible Aspergillus on about 60 bags of the same lot. What is your decision, and what do you record?
Read the worked answer
That is a quality failure, not a storage-management problem, and it must be handled as such.
Do not fumigate again to 'fix' it. Phosphine kills insects; it does not destroy mould or mycotoxins, and fumigating damp grain in a sealed godown adds a safety hazard without curing anything. Re-fumigation here would also disguise the real cause and delay the loss report.
Actions.
- Isolate the affected bags and the bags immediately above and below them, since mould spreads through moisture migration rather than staying put.
- Draw a composite sample and have it tested for aflatoxin before any decision on use.
- Reject the affected quantity for PDS issue. Route it to disposal at depreciated value on the competent authority's order, with the loss booked in the stock register and the loss statement supported by the laboratory report.
- Re-assay the rest of the lot; if the moisture is within limits and there is no mould, it can be retained under intensified watching.
Root cause to record. The lot was accepted at 13.2%, was never dried, and sat through a humid week before treatment. The loss was predictable at the moment of receipt, and the note on file should say so, because the same failure will recur in every godown that accepts grain above 12.0% and relies on fumigation alone.