C‑DRONE
Tiled rooftops seen from above during a drone inspection

C-DRONE GUIDE · 25 AUGUST 2026

Sugar Beet Factory Drone Inspection: Roof, Sugar Silos and Settling Ponds, Method and Price

A plant that runs seven days a week, twenty-four hours a day for about a hundred days, then goes dark for six months : the sugar beet factory is one of the few industrial sites whose entire maintenance calendar fits into a single window, the inter-season. The trade-offs made there — redo the waterproofing on a beet-washing hall roof or wait another year, dredge a soil settling pond or gamble on its remaining capacity — are usually decided on gut feel, for want of a recent survey of the envelope and the stockpiles. A drone can produce that survey in a short flight campaign, before the works schedule is locked, with no scaffolding and no cherry picker. Here is what it documents on a sugar factory and its attached distillery, what it does not do, and 2026 prices.

Published on 25 August 2026, reviewed on 25 August 2026 — regulations in force as of August 2026.

A classified installation that only produces three to four months a year

Mainland France has just under twenty beet sugar factories, concentrated across some thirty departments north of the Loire — chiefly the Hauts-de-France and Champagne regions, with sites in Normandy, the Centre-Val de Loire and the Paris region. All run on the same rhythm : the beet campaign starts between mid-September and early October, lasts around a hundred days, and runs seven days a week, twenty-four hours a day, because a lifted beet loses sugar every day it spends in a clamp. The rest of the year, the plant is shut down.

That rhythm shows up in the classified-installation nomenclature itself. The former heading 2225 ("sugar factories, sugar refineries, maltings"), which placed these sites under authorisation, was repealed on 24 November 2017 by decree n° 2017-1595. Sugar factories now fall, for the most part, under heading 3642 of the "IED" activities — treatment and processing of plant raw materials for the manufacture of food products — whose threshold is set at 300 tonnes of finished product per day, but raised to 600 tonnes per day where the installation operates for a maximum of 90 consecutive days in a year : a derogation written for seasonal industries, of which the sugar factory is the archetype. Falling under the IED means being subject to authorisation, to the best available techniques of the food, drink and milk BREF, and to periodic review of the file once new BAT conclusions are published.

On top of that main heading, almost every site also carries heading 2160 for silos and bulk storage of organic products giving off flammable dust (declaration with periodic inspection from 5,000 m³ of storage volume, registration or authorisation above 15,000 m³ depending on whether the silo is flat or vertical), heading 2910 for the boiler house or cogeneration combustion plant, heading 2921 for evaporative cooling circuits dispersing water into an air flow, and — where a distillery adjoins the plant — heading 2250 for the production of agricultural alcohol by distillation, plus the headings covering flammable liquid or potable alcohol storage (4755). The drone plays no part in any of these obligations : it documents the outer condition of the structures that carry them, as it does for a dairy or cheese plant.

The inter-season, the only window for works: why inspect beforehand

During the campaign, the plant never stops. An unplanned shutdown means a stream of beet still arriving at the gate with nowhere to go, clamps heating up, sugar lost. The consequence for maintenance is blunt : everything happens in the inter-season, between the end of the campaign and start-up — boiler refractory repairs, turbine and evaporator overhauls, cladding replacement, waterproofing works, pond dredging, refurbishment of the reception areas. Six months, comfortable on paper, that fill up fast once you add tendering lead times, contractor availability and holidays.

Hence a common-sense rule that is rarely applied : the envelope survey must come before the works decisions, not after them. Deciding in December, on aerial imagery a week old, that a beet-washing hall roof will hold for one more campaign is not the same exercise as deciding it in February from the memory of a leak. A one- to two-day flight campaign is enough to cover all the roofs, chimneys, silos and ponds on a site, and to deliver a report before the works planning meeting.

The mission is prepared like any intervention on a classified industrial site : prevention plan, safety briefing, defined take-off zones and no-go routes — a subject covered in our guide on how to host a drone mission on an industrial site. What differs here is the calendar : the useful window is short, and it closes exactly when the maintenance department needs the data most.

Roof and envelope: constant steam, corrosion and chimneys

A sugar factory is a steam plant before it is a sugar plant. Juice extraction by diffusion, lime-carbonation purification, multiple-effect evaporation and syrup boiling create, under the roofs, a hot atmosphere close to saturation. The consequences are familiar but fast : condensation on the underside of steel decking, corrosion of fixings and edge trims, degraded rooflights and extractors, flat-roof insulation soaking up water and losing its performance with nothing visible from the ground. A thermal pass, flown at the right time of day, maps those wet-insulation areas and the standing-water points ; the high-resolution orthophoto documents in parallel the condition of the cladding, the rainwater downpipes and the lagging on the steam mains running across the roof.

The high points deserve separate treatment. The boiler house or cogeneration chimney — often the tallest structure on site, visible for miles across flat country — normally only gets a close inspection when expensive scaffolding goes up ; the drone documents its shaft, liner rings, cage ladders, aviation markings and expansion joints from the outside, on the same principle as our dedicated guide to industrial chimney and silo inspection. Nearby, the cooling towers and condensers that reject heat from the juices throw off a permanent steam plume during the campaign : it accelerates corrosion on downwind roofs, and it is a genuine flight constraint, which argues for flying outside the campaign or upwind of the plume. Where these units work by dispersing water into an air flow, they fall under heading 2921 and the legionella monitoring described in our guide to cooling tower drone inspection — monitoring that remains a matter of sampling and laboratory analysis, never of a camera.

Sugar silos, beet clamps and pulp: measuring stockpiles on the ground

The sugar silo is the emblematic structure of a sugar factory : a concrete tower tens of metres high, where crystallised sugar is kept under conditioned air to prevent moisture pick-up and caking. From the ground, its wall is never examined other than through binoculars. The drone circles it in hover and documents what nobody looks at : micro-cracking and crazing of the concrete, spalling, infiltration streaks under the dome, condition of vents and pressure relief, corrosion of walkways, guardrails and the overhead conveyors linking the silo to the packing hall. The same photographs serve as a dated baseline when a crack is reported two years later : you then know whether it is new or whether it has moved.

On the ground, the factory handles considerable volumes of bulk material : beet waiting on the reception aprons during the campaign, pressed pulp and dried pulp destined for animal feed, limestone for the kiln, and carbonation lime. A photogrammetric flight reconstructs the volume of each pile to within a few percent, following the method described in our guide to stockpile volume measurement. The benefit is twofold : reconciling material accounting between two inventories, and checking before the campaign that the planned areas really offer the stated capacity, particularly where residual stock from the previous year has not been fully cleared.

Soil settling ponds and wastewater basins: the remaining capacity

This is probably where the drone delivers the most measurable value. Beet arrives at the factory loaded with soil, stones, leaves and crowns : this soil tare represents, according to the French sugar manufacturers' union, 7 to 20 % of the weight of the washed beet, heavily dependent on rainfall at harvest and reduced by field-side cleaning. Set against the tonnages a factory processes in a campaign, that washed-off soil runs into tens of thousands of tonnes, directed into settling ponds that often cover several hectares on the edge of the site. Add to that the wastewater basins, the polishing lagoons and, on many sites, a dedicated pond for carbonation lime, which settles there for several months before growers take it away as an agricultural liming material.

The question asked every summer is always the same : is there enough capacity left to absorb the next campaign, or does it need dredging? A photogrammetric survey produces a digital model of the emerged part ; compared with the previous year's survey, it yields the volume accumulated over one campaign, the volume actually removed during dredging, and the freeboard available below the dyke crest. The same pass documents the condition of the dykes and outlet structures : bank erosion, woody vegetation established on a crest, seepage traces, a blocked outfall — a reading close to the one described in our guide to retention pond siltation monitoring.

The approach is backed by the technical literature : Zhi, Zhu, Jang, Wang, Chiang, Su, Liang, Li and Yuan, in a 2023 paper in Sustainability, describe a method for analysing storage capacity change and dam failure risk on a tailings pond using drone oblique photogrammetry, validated on a real pond (see the study on Google Scholar). One limit must be stated up front, though : photogrammetry does not see underwater. The submerged volume calls for echo-sounder bathymetry, and drone data remains a measurement of the emerged part — valuable for comparative monitoring over time, insufficient on its own for a full hydraulic balance.

Sugar dust and confined spaces: what the drone does not do

Crystallised sugar is a combustible dust. Under mechanical stress — conveying, screening, bagging, free fall into a silo — it generates fines which, suspended in a confined volume, form an explosive atmosphere. A study by Liang, Li, Jiang, Zhong, Sun, Jiang and Yang, published in 2023 in Processes, characterised the explosion parameters of sucrose dust in a 20-litre sphere — minimum explosible concentration, maximum explosion pressure and rate of pressure rise — and analysed the ignition mechanism from the thermal behaviour of the crystals (see the study on Google Scholar). Accident records confirm the stakes : the dust explosion of 7 February 2008 at the Imperial Sugar refinery in Port Wentworth, Georgia, which started in a conveyor beneath the sugar silos, killed fourteen people and injured dozens, and remains the benchmark case in combustible dust investigations.

That reality defines the mission's boundary by contrast. The drone does not enter a silo, a hopper or a conveyor enclosure : these are confined spaces under ATEX zoning, whose access is governed by dedicated entry procedures. It measures no atmosphere — not dust loading, not oxygen, not stored-product temperature. It does not replace periodic cleaning of dust-laden surfaces, nor the inspection of explosion vents, nor the checking of electrical installations in classified zones, all obligations resting on the operator under the silo regulations and its prefectural order. Our guide to drone thermography of grain silos sets out the same division of roles for grain storage : the camera works on the outside, product metrology stays with the operator's probes.

Put positively : the drone documents the envelope, what is reachable from above and what is measurable from an image. Roof, cladding, chimney, silo wall, stockpile, pond, dyke. That is already most of what escapes ground rounds, and it is exactly what an inter-season works decision needs.

Method, flight framework and prices

A sugar factory is almost always set in open country, in the middle of its beet-growing area, which simplifies the flight framework : the mission is generally flown in the open category, below 120 metres above the take-off point, in a lightly populated or unpopulated environment — subject to checking local restrictions, any nearby aerodrome or military zone, and handling chimney height, which may call for a specific arrangement. The real constraint is not regulatory but operational : during the campaign, the plant yard is a merry-go-round of lorries, tipper trailers and reclaim machinery, with flows that never stop. Hence the working principle : fly outside the campaign where possible, otherwise a detailed prevention plan, take-off zones well clear of the traffic circuits, and no overflight of active unloading points.

A typical run takes one to two days : reconnaissance and briefing with the maintenance or HSE manager, gridded photogrammetric flight over the built footprint for the orthophoto and 3D model, close manual passes on the chimneys, the sugar silo and the roof's critical details, a thermal pass over the roofs and lagged pipework, and finally a photogrammetric survey of the ponds and storage areas. Deliverables : georeferenced orthophoto, annotated photo report structure by structure with defects located, thermal map, volume notes per pond and per stockpile, and a prioritisation table usable in the works planning meeting.

2026 prices (excl. VAT) : €1,200 to €2,500 for the envelope campaign of a typically sized factory (roofs, cladding, chimney, sugar silo, with a thermal pass) ; €3,000 to €4,500 for a full campaign including volume surveys of the settling ponds and of the pulp and beet stockpiles ; €500 to €1,100 for a short volume-only pass over one or two ponds, for instance as a post-dredging check. A follow-up campaign repeated each year on the same flight plan typically costs 20 to 30 % less than the initial one, and it is the identical repetition that gives year-on-year comparison its value. Our drone thermography page presents the service ; request a quote stating the site's processing capacity, whether a distillery is attached and the period targeted (end of campaign, inter-season, pre-start-up check).

Frequently asked questions

When in the year should the mission be scheduled?

Ideally at the very end of the campaign or in the first weeks of the inter-season, before the works schedule and the contracts with outside firms are finalised. An inspection carried out in March, once the orders are placed, is only documentation for the following year. A short second pass at the end of the inter-season is useful to check that the works and the pond dredging were completed before start-up.

Can the drone go inside a sugar silo or the drying tower?

No. A sugar silo is a confined volume that may hold an explosive dust atmosphere; the inside falls under ATEX zoning, confined-space entry procedures and specialised equipment, not an external inspection drone. Our mission documents the outside of the structures — walls, dome, vents, walkways — and stops at the door.

Does a settling-pond volume survey replace a topographic survey?

It is an independent, repeatable measurement of the emerged part, usable to track filling from one campaign to the next and to size a dredging job. It does not capture the submerged part, which requires bathymetry, and it does not replace a chartered surveyor's work where a regulatory file or a transaction calls for legally binding data.

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