From the Middle Ages until well into the 20th century, windmills, watermills and ship mills shaped the landscapes and riverbanks of Germany. The basic principle of grinding, crushing and separating has not changed, but milling operations have developed into state-of-the-art food companies. Mill operations comprise a wide variety of different businesses that grind, crush or process raw materials such as grain, seeds, oilseeds or animal feed. They play a central role in the food, animal feed and agricultural industries.

From a property insurance perspective, milling operations are among the most exposed industrial facilities, as the processing of grain and other free-flowing goods produces flours and dust which, in combination with ignition sources, create a significant risk of fire and explosion. The conditions for a dust explosion – the so‑called dust explosion triangle – are:

• Combustible dust (e.g. wheat, corn or rye dust)
• Oxygen (in the ambient air)
• An ignition spark (e.g. from hot bearings, electrostatic discharges or mechanical friction).

The consequences of such explosions are usually serious. This article provides a brief description of typical mill operation types and a general description of processing methods, followed by a discussion of potential hazards and possible fire and explosion protection measures. Finally, tips for underwriting property insurance are provided.

Typical Types of Mills

In general, a mill is defined as a facility in which raw material is ground into a fine or very fine-grained end product. Mills can be classified according to the type of product ground:

• Food processing mills: grain, rice, oat, corn and sugar mills, as well as mills for the production of special flours (e.g. gluten-free or functional flours)
• Feed mills for the production of feed for farm animals
• Oil mills and seed processors for the extraction of vegetable oils
• Speciality mills: e.g. malt, spice, sugar and starch mills

or differentiated according to the grinding principle used to crush the material:

• Stone mills: millstones (e.g. grinding, friction / shearing)
• Steel roller mills: rollers (friction / shearing), typical for industrial mills
• Hammer mills: impact / impact, comminution by fast impact mechanisms
• Colloid mills: very fine grinding, friction/shearing

There are also other classifications for mills, including those based on drive technology (e.g. water, wind, capstan and machine mills) or size (e.g. hand, industrial and special mills).

General Process

The basic process steps in the milling industry vary depending on the type of product, but largely follow a typical sequence. The process is described in broad terms below using the example of a grain mill (e.g. for wheat, rye, corn, rice).

1. Delivery and Acceptation – The grain to be processed is delivered by truck, train or ship, and random samples are taken for quality control, e.g. to determine moisture or protein content.
2. Rough Cleaning – Stones, straw, dust, insects and foreign objects are removed. Typical equipment for this purpose includes pre-cleaners for the coarse separation of foreign matter; magnetic separators for the removal of magnetizable components; trieur and screening systems for the shape and size selection of the delivered grain; and aspirator systems for the extraction of light components.
3. Drying – Grain with increased residual moisture is often dried using oil- or gas-fired dryers before being transported to silos or bunkers via pneumatic or mechanical conveyor systems for temporary storage.
4. Conditioning (Moistening) – To prevent the husk from splintering too much during the grinding process and to reduce the grinding energy at the same time, the grain moisture content is increased (e.g. to 16% to 18% residual moisture) before the grain is fed into the grinding equipment.
5. Grinding – Hammer mills, vertical mills and roller mills are particularly used in food production. The shredding principle selected depends on the product. For example, in flour milling grain kernels are broken or crushed between two steel rollers in the roller mill, and the flour core is separated from the husk and crushed. In the plansifter, particles of different sizes (flour and husk particles) are separated from each other using stacked sieves with increasingly smaller mesh sizes.
   In further grinding steps, the last flour particles are separated from the husk and ground to a fine flour. Each grinding process produces grain particles of different sizes. The sequence of grinding and sieving is called a passage. It is repeated until the planned degree of separation of husk and flour particles is achieved. This produces the various milled products: grist, semolina, fine semolina and flour.
6. Flour Mixture – Depending on requirements, flours from different stages are mixed and enriched, followed by quality control to determine moisture content, mineral content, etc.
7. Filling and Storage – The different milled products are stored in flour silos according to quality and, depending on their intended use, filled into sacks, big bags or loose into silos. Until they are sold, the finished products are stored temporarily and continuously checked for moisture, temperature and pests.
8. Shipping – The finished goods are shipped by truck, rail or ship. Most of the flour is usually transported to customers in bulk in silo trucks or packaged for retail sale, e.g. in 1kg small packs, in sacks of up to 25kg, or in bags which can hold up to 1 tonne of goods.

Infographic of a Modern Grain Mill

Graphic: Infographic of a modern grain mill, © Verband Deutscher Mühlen 2026, https://www.muehlen.org/fileadmin/Dateien/8_Presse_Service/2_Fotos_Infografiken/Muehlen-Produktionsablauf_englisch_2016_01082016.pdf

Nowadays, all processes – from grain reception to filling – are controlled and monitored in industrial milling plants from a computer-based control centre.

Ancillary and auxiliary operations of a mill include:

• Silos for storing bulk goods (e.g. grain, pellets). Silos are usually filled from above through the silo roof and emptied solely by gravity in the discharge hopper area. Conveyor systems (e.g. elevators, Redler conveyors, etc.) or pneumatic conveyor lines are required for filling.
• Conveyor systems are used to transport products from silos or warehouses to the production areas or within the production facility. There are pneumatic conveyor systems for bulk / powdery products and mechanical conveyor systems (e.g. belt conveyors, chain conveyors, bucket elevators, screw conveyors for larger items).
• Maintenance and maintenance departments (e.g. electrical workshops, laboratories).

Special mills, e.g. oil or feed mills, sometimes require different or more extensive processing steps.

Past Claims (Examples)

Fires and explosions have often occurred in mills around the world, resulting in considerable damage to insured property and subsequent business interruptions.¹

In the U.S., there have been 86 explosions in feed, grain and rice mills, among other places, over the last 10 years. The blog titled “Grain Fires and Explosions: Yearly Trends, Causes, and Prevention” provides a good overview of this.² Around 44% of all dust explosion incidents worldwide occur in agricultural and food production facilities.³ Statistics from Canada show similar results.⁴

According to press and media reports on the internet, an average of seven fires / explosions occur in grain mills in Germany each year, with the amount of damage per year varying greatly. A major fire (leading to losses of approximately EUR 50 million) occurred in an oatmeal mill in 2025.⁵

Existing reliable statistical data on fires and explosions in mills is generally not accessible to the general public.

Hazards and Possible Fire and Explosion Protection Measures

The greatest hazard is posed by combustible dusts that ignite when stirred up. The finer the dust, the longer the dust-air mixture remains when stirred up, and the greater the maximum explosion pressure and the maximum time-explosion pressure increase. At the same time, the minimum ignition energy required to ignite a combustible dust-air mixture decreases. If finely distributed combustible dust settles on machines, pipes and surfaces, it can be ignited by hot surfaces; sparks (e.g. from foreign objects); or hot bearings or machine parts (e.g. motors); or overloaded or defective electrical systems and devices. If the air concentration is sufficient, a deflagration or an explosion (known as a primary explosion) can occur in silos, filters or mills.

If the ignition and deflagration of a limited flour dust-air mixture causes further dust to be stirred up from surfaces by the pressure wave, this results in a particular hazard: the additional dust that is stirred up can explode, often with devastating consequences (known as a secondary explosion). Filter systems and conveyor lines are particularly important in this regard, as the pressure wave can be transmitted to neighbouring systems and buildings if protective measures are not in place.

Since dust-air mixtures are practically never homogeneous, the corresponding explosion limits for dust do not have the same safety significance as for gas-air mixtures.⁶

Another danger in milling operations that should not be underestimated is the possible self-heating of materials due to moist grain or flour, which can heat up on their own during prolonged storage due to microbial processes and, in extreme cases, ignite.

The following section describes possible hazards and corresponding protective measures for each individual processing step. It should be noted that, depending on the operating process, further measures may be necessary from an official or insurance perspective.

Fire Protection Measures

Particular attention should be paid to the use of suitable electrical equipment and operating materials. In addition to the relevant regulations for the installation and operation of electrical systems and equipment in fire-prone workplaces, the relevant provisions for installation and operation in potentially explosive workplaces should also be applied, e.g. DIN VDE, DGUV. According to these guidelines, only appropriately tested and suitable explosion-proof systems and equipment may be operated in rooms where explosive dust-air mixtures are likely to occur.

In addition, the usual structural, operational, technical and organisational preventive fire protection measures apply to mill operations, e.g. fire-resistant or non-combustible construction; taking into account explosion protection measures for mill buildings and silos; a risk assessment; appointment of a fire safety officer; good order and cleanliness; avoidance or regular cleaning of dust accumulations; smoking ban; welding permit; fire brigade plan with sufficient space for the fire brigade to set up; regular drills on the mill premises with the fire brigade – to name just a few measures.

Information and Recommendations from a Property Insurance Perspective

Due to the type of operation and the variety of technologies used in a mill, it is advisable to have an insurance engineer inspect the operation before accepting an insurance contract in order to obtain the necessary information for a risk assessment and the calculation of an adequate insurance premium. In addition to the typical insurance-related issues (scope of insurance; sums insured; deductibles; maximum compensation), this article addresses in particular the risk factors relevant to the type of operation:

Mills are usually very compact operations with tall buildings. They often represent a contiguous insurance complex, so that the maximum possible fire / explosion loss (PML/MFL) should often be assumed to be 100%. Some parts of mill buildings are made of combustible materials, such as wood. Since wood offers significantly less resistance to explosion pressure than reinforced concrete or steel, it is often used in roof constructions, e.g. to create appropriate pressure relief openings in the event of an explosion by forming a lightweight roof. Due to the different processes involved and the sometimes unavoidable increased risk of fire and explosion, a detailed risk analysis and assessment of the existing fire and explosion protection measures is necessary for an adequate risk assessment of mills in order to be able to provide a tailor-made insurance offer.

When evaluating actuarial visit and inspection reports prepared for the underwriting of mill operations, it is noticeable that, in addition to a detailed description of the process and any fire protection measures in place, explosion risks and existing explosion protection measures are considered rather briefly or not at all, even though the risk of explosion represents a significant exposure in mill operations. Furthermore, the economic impact of fire or explosion damage on the continued operation of the mill is usually dealt with only briefly. However, in addition to fire protection, it is advisable to pay special attention to the explosion risk, the existing explosion protection measures and the economic consequences of a damaging event in order to be able to make a reliable risk assessment and underwriting decision.

In addition, inspections of mill operations should be repeated regularly, e.g. at least every three years, in order to ensure insurability at attractive rates in the future. Inspection reports should contain meaningful information such as:

• Documentation of grain mill (location, neighbourhood)
• Type of mill and equipment used
• Type of construction and building materials used (silo, building)
• Fire protection/explosion protection separations between silo/milling/storage building (spatial or structural separations)
• Presence and functionality of existing explosion protection measures, e.g. silo, conveyor systems, grinding systems, explosion protection concept, zone classification according to ATEX or European Directive 2014/34/EU and 1999/92/EC, ignition source prevention and the conformity of electrical and mechanical equipment in accordance with ATEX. Measures against electrostatic charging (e.g. grounding) and lightning protection should also be in place. This also includes measures taken for explosion pressure relief and decoupling devices (e.g. bursting discs, non-return valves, quick-acting valves), in silos, filters, and elevators
• Monitoring measures (silo: temperature, monitoring of carbon monoxide; conveyor systems: storage temperatures, slip control, speed control and automatic shutdown; grinding systems: temperature monitoring of the grinding chamber with limit value shutdown)
• Certified, regularly maintained systems for early fire detection, in particular also measures for temperature monitoring and fire detection in the silo area
• Existing firefighting equipment and inerting systems such as spark extinguishing systems on pneumatic conveyor lines and elevators; sprinklers: automatic carbon dioxide or water spray extinguishing systems for hazardous areas such as mill rooms, presses, filter systems, silos, risers

Information on the organisational measures taken to prevent or minimise the risk of fire or explosion events should also be included:

• Cleaning plans: complete documentation of cleaning, especially areas that are difficult (e.g. under conveyor belts, in silo chambers)
• Temperature monitoring: continuous monitoring of bearings, motors, and conveyor belts for overheating
• Hot work regulations: strict approval processes (including permits, fire watch) for welding, cut-off grinders, etc.
• Regularly scheduled maintenance and servicing
• Training of employees through regular fire and explosion protection instruction for employees
• Up-to-date explosion protection document (pursuant to § 6 GefStoffV / ATEX 137) for documenting the explosion protection measures taken
• Fire safety regulations
• Test reports for electrical systems, extinguishing systems, pressure relief devices
• Maintenance and cleaning records
• Fire safety inspections, proactive risk analyses, and regular audits for continuous improvement by external and specialists (e.g. VdS, TÜV, DGUV)
• After near misses or minor fire / explosion incidents, results of root cause analysis with recommendations for necessary improvements and their implementation
• Regular drills with the fire department (including existing fire department plan)
• Consequences of fire/explosion damage for the continuation of operations the affected company, including expected reconstruction times for buildings and facilities that are important for operations, as well as information about possible alternatives and redundancies
• Existence and currency of a business continuity plan

The following points are also relevant for risk assessment and underwriting:

• Damage history with specification of the cause of damage and extent of damage
• Retroactive / impact damage (raw materials, customers), including existing purchase obligations for raw materials and possible interactions with other locations
• Required operating permits
• Additional insurance-related questions, such as possible maximum loss with a description of the underlying scenario
• Coverage concept (named perils / all-risk coverage)
• Definition of insurance sums and compensation (replacement value, current value, fair market value)
• Agreed deductible and maximum compensation
• Agreed first risk positions
• Regular review of insurance coverage, especially in the event of modernisation or production changes
• Early involvement of the insurer in construction projects or conversions

Summary

From a technological perspective, milling is a diverse industry that requires a great deal of specialist knowledge and experience in underwriting in order to identify and adequately assess potential risks. From a property insurance perspective, milling operations are caught between production-related risks and the need for extensive protective measures. The explosion of a dust-air mixture or the outbreak of a fire can not only cause damage that threatens the very existence of the business, but also jeopardise its insurability as a whole. It is particularly striking that, in the event of a claim, in addition to damage to property, there is also significant consequential damage covered by business interruption insurance.

Close cooperation with the insurer, consistent risk prevention and regular reviews are therefore essential for long-term affordable insurance cover.

Mill operations are insurable, but they require careful underwriting and the setting of an insurance premium that is sufficient and adequate in relation to the existing exposure. In addition to appropriate protective measures, the existing exposure of a mill operation can be kept within responsible limits by setting an appropriate deductible and maximum compensation.

All internet links cited in the text of the article were accessed on 24 March 2026.