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A silo (from the
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
σιρός – ''siros'', "pit for holding grain") is a structure for storing
bulk materials Bulk cargo is commodity cargo that is transported packaging, unpackaged in large quantities. Description Bulk cargo refers to material in either liquid or granular, particulate form, as a mass of relatively small solids, such as petroleum/ ...
. Silos are used in
agriculture Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people to ...
to store fermented feed known as
silage Silage () is a type of fodder made from green foliage crops which have been preserved by fermentation to the point of acidification. It can be fed to cattle, sheep and other such ruminants (cud-chewing animals). The fermentation and storage p ...
, not to be confused with a grain bin, which is used to store grains. Silos are commonly used for bulk storage of grain,
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when dea ...
,
cement A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel ( aggregate) together. Cement mix ...
,
carbon black Carbon black (subtypes are acetylene black, channel black, furnace black, lamp black and thermal black) is a material produced by the incomplete combustion of coal and coal tar, vegetable matter, or petroleum products, including fuel oil, fluid ...
,
woodchips Woodchips are small- to medium-sized pieces of wood formed by cutting or chipping larger pieces of wood such as trees, branches, logging residues, stumps, roots, and wood waste. Woodchips may be used as a biomass solid fuel and are raw material ...
, food products and
sawdust Sawdust (or wood dust) is a by-product or waste product of woodworking operations such as sawing, sanding, milling, planing, and routing. It is composed of small chippings of wood. These operations can be performed by woodworking machinery, ...
. Three types of silos are in widespread use today: tower silos, bunker silos, and bag silos.


Types of silos


Tower silo

Storage silos are cylindrical structures, typically 10 to 90 ft (3 to 27 m) in diameter and 30 to 275 ft (10 to 90 m) in height with the
slipform Slip forming, continuous poured, continuously formed, or slipform construction is a construction method in which concrete is poured into a continuously moving form.Nawy, ''Concrete Construction Engineering Handbook,'' 2008, p. 10—33. Slip formi ...
and Jumpform concrete silos being the larger diameter and taller silos. They can be made of many materials. Wood staves, concrete staves, cast concrete, and steel panels have all been used, and have varying cost, durability, and airtightness tradeoffs. Silos storing grain, cement and woodchips are typically unloaded with air slides or augers. Silos can be unloaded into rail cars, trucks or conveyors. Tower silos containing silage are usually unloaded from the top of the pile, originally by hand using a silage fork—which has many more tines than the common pitchfork; 12 vs 4—and in modern times using mechanical unloaders. Bottom silo unloaders are utilized at times, but have problems with difficulty of repair. An advantage of tower silos is that the silage tends to pack well due to its own weight, except in the top few feet. However, this may be a disadvantage for items like chopped wood. The tower silo was invented by
Franklin Hiram King Franklin Hiram King (8 June 1848 – 4 August 1911) was an American agricultural scientist who was born on a farm near Whitewater, Wisconsin, attended country schools, and received his professional training first at Whitewater State Normal Scho ...
. In
Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
,
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
and the United States, many country towns or the larger farmers in grain-growing areas have groups of wooden or concrete tower silos, known as
grain elevator A grain elevator is a facility designed to stockpile or store grain. In the grain trade, the term "grain elevator" also describes a tower containing a bucket elevator or a pneumatic conveyor, which scoops up grain from a lower level and deposits ...
s, to collect grain from the surrounding towns and store and protect the grain for transport by train, truck or barge to a processor or to an export port. In bumper crop times, the excess grain is stored in piles without silos or bins, causing considerable losses.


Concrete stave silos

Concrete stave silos are constructed from small precast concrete blocks with ridged grooves along each edge that lock them together into a high strength shell. Concrete is much stronger in
compression Compression may refer to: Physical science *Compression (physics), size reduction due to forces *Compression member, a structural element such as a column *Compressibility, susceptibility to compression *Gas compression *Compression ratio, of a c ...
than
tension Tension may refer to: Science * Psychological stress * Tension (physics), a force related to the stretching of an object (the opposite of compression) * Tension (geology), a stress which stretches rocks in two opposite directions * Voltage or el ...
, so the silo is reinforced with steel hoops encircling the tower and compressing the staves into a tight ring. The vertical stacks are held together by intermeshing of the ends of the staves by a short distance around the perimeter of each layer, and hoops which are tightened directly across the stave edges. The static pressure of the material inside the silo pressing outward on the staves increases towards the bottom of the silo, so the hoops can be spaced wide apart near the top but become progressively more closely spaced towards the bottom to prevent seams from opening and the contents leaking out. Concrete stave silos are built from common components designed for high strength and long life. They have the flexibility to have their height increased according to the needs of the farm and purchasing power of the farmer, or to be completely disassembled and reinstalled somewhere else if no longer needed.


Low-oxygen tower silos

Low-oxygen silos are designed to keep the contents in a low-oxygen atmosphere at all times, to keep the fermented contents in a high quality state, and to prevent mold and decay, as may occur in the top layers of a stave silo or bunker. Low-oxygen silos are only opened directly to the atmosphere during the initial forage loading, and even the unloader chute is sealed against air infiltration. It would be expensive to design such a large structure that is immune to atmospheric pressure changes over time. Instead, the silo structure is open to the atmosphere but outside air is separated from internal air by large impermeable bags sealed to the silo breather openings. In the warmth of the day when the silo is heated by the sun, the gas trapped inside the silo expands and the bags "breathe out" and collapse. At night the silo cools, the air inside contracts and the bags "breathe in" and expand again. While the iconic blue Harvestore low-oxygen silos were once very common, the speed of its unloader mechanism was not able to match the output rates of modern bunker silos, and this type of silo went into decline. Unloader repair expenses also severely hurt the Harvestore reputation, because the unloader feed mechanism is located in the bottom of the silo under tons of silage. In the event of cutter chain breakage, it can cost up to US$10,000 to perform repairs. The silo may need to be partially or completely emptied by alternate means, to unbury the broken unloader and retrieve broken components lost in the silage at the bottom of the structure. In 2005 the Harvestore company recognized these issues and worked to develop new unloaders with double the flow rate of previous models to stay competitive with bunkers, and with far greater unloader chain strength. They are now also using load sensing soft-start
variable frequency drive A variable-frequency drive (VFD) is a type of motor drive used in electro-mechanical drive systems to control AC motor speed and torque by varying motor input frequency and, depending on topology, to control associated voltage or current variat ...
motor controllers to reduce the likelihood of mechanism breakage, and to control the feeder sweep arm movement.


Bunker silos

Bunker silos are trenches, usually with concrete walls, that are filled and packed using tractors and loaders. The filled trench is covered with a plastic tarp to make it airtight. These silos are usually unloaded with a tractor and loader. They are inexpensive and especially well suited to very large operations.


Bag silos

Bag silos are heavy plastic tubes, usually around 8 to 12 ft (2.4 to 3.6 m) in diameter, and of variable length as required for the amount of material to be stored. They are packed using a machine made for the purpose, and sealed on both ends. They are unloaded using a tractor and loader or
skid-steer loader A skid loader, skid-steer loader, SSLs or skidsteer is a small, rigid-frame, engine-powered machine with lift arms that can attach to a wide variety of buckets and other labor-saving tools or attachments. Skid-steer loaders are typically four-whee ...
. The bag is discarded in sections as it is torn off. Bag silos require little capital investment. They can be used as a temporary measure when growth or harvest conditions require more space, though some farms use them every year.


Bins

A bin is typically much shorter than a silo, and is typically used for holding dry matter such as cement or grain. Grain is often dried in a grain dryer before being stored in the bin. Bins may be round or square, but round bins tend to empty more easily due to a lack of corners for the stored material to become wedged and encrusted. The stored material may be powdered, as seed kernels, or as cob corn. Due to the dry nature of the stored material, it tends to be lighter than silage and can be more easily handled by under-floor grain unloaders. To facilitate drying after harvesting, some grain bins contain a hollow perforated or screened central shaft to permit easier air infiltration into the stored grain.


Cement storage silos

There are different types of cement silos such as the low-level mobile silo and the static upright cement silo, which are used to hold and discharge cement and other powder materials such as PFA (
Pulverised Fuel Ash Fly ash, flue ash, coal ash, or pulverised fuel ash (in the UK) plurale tantum: coal combustion residuals (CCRs)is a coal combustion product that is composed of the particulates (fine particles of burned fuel) that are driven out of coal-fired b ...
). The low-level silos are fully mobile with capacities from 100 to 750 tons. They are simple to transport and are easy to set up on site. These mobile silos generally come equipped with an electronic weighing system with digital display and printer. This allows any quantity of cement or powder discharged from the silo to be controlled and also provides an accurate indication of what remains inside the silo. The static upright silos have capacities from 200 to 800 tons. These are considered a low-maintenance option for the storage of cement or other powders. Cement silos can be used in conjunction with bin-fed batching plants.


Sand and salt silos

Sand and salt for winter road maintenance are stored in conical dome-shaped (clear truss roof) silos. These are more common in
North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
, namely in
Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
and the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
. The shaped is based on natural shape formed when piling solids. The dome is made of prefabricated wood panels with singles installed on a circular reinforced concrete base. Open canopy entrance allows for front end loaders to fill and retrieve easily. These are usually found along major highway or key primary roads.


Plastic Silos

Plastic silos, also known as hopper bottom tanks, are manufactured through various processes such as: injection molding, rotational molding, and blow molding. They are constructed using a wide variety of polyethylene plastics. The silos are light weight and make for great small scale storage for farmers with livestock and grain operations. The light weight design and cost effective materials make plastic silos a great alternative to traditional steel bins. Unlike fabric silos, which "tend to be prone to grain rot and pests which have left many farmers frustrated", plastic silos are more safe and secure, keeping grain fresh and unspoiled. They can be designed to be stationary hopper bottom bins or portable pallet bins.


Fabric silos

Fabric silos are constructed of a fabric bag suspended within a rigid, structural frame.
Polyester Polyester is a category of polymers that contain the ester functional group in every repeat unit of their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include natural ...
based fabrics are often used for fabrication of the bag material, with specific attention given to fabric pore size. Upper areas of silo fabric are often manufactured with slightly larger pore size, with the design intent of acting as a vent filter during silo filling. Some designs include metal thread within the fabric, providing a static conductive path from the surface of the fabric to ground. The frame of a fabric silo is typically constructed of
steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
. Fabric silos are an attractive option because of their relative low cost compared to conventional silos. However, when fabric silos are used to store granular or particulate combustible materials, conventional practices prescribed by established industry consensus standards addressing combustible dust hazards can not be applied without a considerable engineering analysis of the system.


History

The 5th millennium BC site of
Tel Tsaf Tel Tsaf ( he, תל צף) is an archaeological site located in the central Jordan Valley, south-east of Beit She'an. It was first tested in 1978–1980 by Ram Gophna of Tel Aviv University. In 2004–2007 a large excavation project was conducted a ...
in the southern
Levant The Levant () is an approximate historical geographical term referring to a large area in the Eastern Mediterranean region of Western Asia. In its narrowest sense, which is in use today in archaeology and other cultural contexts, it is eq ...
contain the earliest known silos. Archaeological ruins and ancient texts show that silos were used in
ancient Greece Ancient Greece ( el, Ἑλλάς, Hellás) was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity ( AD 600), that comprised a loose collection of cult ...
as far back as the late 8th century BC; the term ''silo'' is derived from the
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
σιρός (''siros''), "pit for holding grain". The silo pit, as it has been termed, has been a favorite way of storing grain from time immemorial in Asia. In Turkey and Persia,
insurance Insurance is a means of protection from financial loss in which, in exchange for a fee, a party agrees to compensate another party in the event of a certain loss, damage, or injury. It is a form of risk management, primarily used to hedge ...
agents bought stores of
wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...
or
barley Barley (''Hordeum vulgare''), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains, particularly in Eurasia as early as 10,000 years ago. Globally 70% of barley pr ...
whilst comparatively cheap, and store it in hidden pits against seasons of dearth. In
Malta Malta ( , , ), officially the Republic of Malta ( mt, Repubblika ta' Malta ), is an island country in the Mediterranean Sea. It consists of an archipelago, between Italy and Libya, and is often considered a part of Southern Europe. It lies ...
a relatively large stock of wheat was preserved in some hundreds of pits (silos) cut in the rock. A single silo stored from 60 to 80 tons of wheat, which, with proper precautions, kept in good condition for four years or more. The first modern silo, a wooden and upright one filled with
grain A grain is a small, hard, dry fruit (caryopsis) – with or without an attached hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and legum ...
, was invented and built in 1873 by Fred Hatch of
McHenry County, Illinois McHenry County is a county located in the U.S. state of Illinois. According to the 2020 Census, it had a population of 310,229, making it the sixth-most populous county in Illinois. Its county seat is Woodstock. McHenry County is one of the f ...
, USA.


Forage silo usage


Forage harvesting

Forage silo filling is performed using a
forage harvester A forage harvesteralso known as a silage harvester, forager or chopperis a farm implement that harvests forage plants to make silage. Silage is grass, corn or hay, which has been chopped into small pieces, and compacted together in a storage silo ...
which may either be self-propelled with an engine and driver's cab, or towed behind a
tractor A tractor is an engineering vehicle specifically designed to deliver a high tractive effort (or torque) at slow speeds, for the purposes of hauling a trailer or machinery such as that used in agriculture, mining or construction. Most common ...
that supplies power through a PTO. The harvester contains a drum-shaped series of cutting knives which shear the fibrous plant material into small pieces no more than an inch long, to facilitate mechanized blowing and transport via augers. The finely chopped plant material is then blown by the harvester into a forage wagon which contains an automatic unloading system.


Tower filling

Tower forage filling is typically performed with a
silo blower A silo (from the Greek σιρός – ''siros'', "pit for holding grain") is a structure for storing bulk materials. Silos are used in agriculture to store fermented feed known as silage, not to be confused with a grain bin, which is used ...
which is a very large fan with paddle-shaped blades. Material is fed into a vibrating
hopper Hopper or hoppers may refer to: Places *Hopper, Illinois * Hopper, West Virginia * Hopper, a mountain and valley in the Hunza–Nagar District of Pakistan * Hopper (crater), a crater on Mercury People with the name * Hopper (surname) * Grace H ...
and is pushed into the blower using a spinning spiral
auger Auger may refer to: Engineering * Wood auger, a drill for making holes in wood (or in the ground) ** Auger bit, a drill bit * Auger conveyor, a device for moving material by means of a rotating helical flighting * Auger (platform), the world's f ...
. There is commonly a water connection on the blower to add moisture to the plant matter being blown into the silo. The blower may be driven by an electric motor but it is more common to use a spare
tractor A tractor is an engineering vehicle specifically designed to deliver a high tractive effort (or torque) at slow speeds, for the purposes of hauling a trailer or machinery such as that used in agriculture, mining or construction. Most common ...
instead. A large slow-moving conveyor chain underneath the silage in the forage wagon moves the pile towards the front, where rows of rotating teeth break up the pile and drop it onto a high-speed transverse conveyor that pours the silage out the side of the wagon into the blower hopper.


Bag filling

Silo bags are filled using a traveling sled driven from the PTO of a tractor left in neutral and which is gradually pushed forward as the bag is filled. The steering of the tractor controls the direction of bag placement as it fills, but bags are normally laid in a straight line. The bag is loaded using the same forage harvesting methods as the tower, but the forage wagon must be moved progressively forward with the bag loader. The loader uses an array of rotating cam-shaped spiraled teeth associated with a large
comb A comb is a tool consisting of a shaft that holds a row of teeth for pulling through the hair to clean, untangle, or style it. Combs have been used since prehistoric times, having been discovered in very refined forms from settlements dating ba ...
-shaped tines to push forage into the bag. The forage is pushed in through a large opening, and as the teeth rotate back out, they pass between the comb tines. The cam-shaped auger teeth essentially wipe the forage off using the steel tines, keeping the forage in the bag. Before filling begins, the entire bag is placed onto the loader as a bunched-up tube folded back on itself in many layers to form a thick pile of plastic. Because the plastic is minimally elastic, the loader mechanism filling chute is slightly smaller than the final size of the bag, to accommodate this stack of plastic around the mouth of the loader. The plastic slowly unfurls itself around the edges of the loader as the tube is filled. The contents of the silo bag are under pressure as it is filled, with the pressure controlled by a large brake shoe pressure regulator, holding back two large winch drums on either side of the loader. Cables from the drum extend to the rear of the bag where a large mesh basket holds the rear end of the bag shut. To prevent molding and to assure an airtight seal during fermentation, the ends of the silo bag tube are gathered, folded, and tied shut to prevent oxygen from entering the bag. Removal of the bag loader can be hazardous to bystanders since the pressure must be released and the rear end allowed to collapse onto the ground.


Tower unloading

A ''silo unloader'' specifically refers to a special cylindrical rotating
forage Forage is a plant material (mainly plant leaves and stems) eaten by grazing livestock. Historically, the term ''forage'' has meant only plants eaten by the animals directly as pasture, crop residue, or immature cereal crops, but it is also used m ...
pickup device used inside a single tower silo. The main operating component of the silo unloader is suspended in the silo from a steel cable on a
pulley A pulley is a wheel on an axle or shaft that is designed to support movement and change of direction of a taut cable or belt, or transfer of power between the shaft and cable or belt. In the case of a pulley supported by a frame or shell that ...
that is mounted in the top-center of the roof of the silo. The vertical positioning of the unloader is controlled by an electric
winch A winch is a mechanical device that is used to pull in (wind up) or let out (wind out) or otherwise adjust the tension of a rope or wire rope (also called "cable" or "wire cable"). In its simplest form, it consists of a spool (or drum) attache ...
on the exterior of the silo. For the summer filling of a tower silo, the unloader is winched as high as possible to the top of the silo and put into a parking position. The silo is filled with a
silo blower A silo (from the Greek σιρός – ''siros'', "pit for holding grain") is a structure for storing bulk materials. Silos are used in agriculture to store fermented feed known as silage, not to be confused with a grain bin, which is used ...
, which is literally a very large fan that blows a large volume of pressurized air up a 10-inch tube on the side of the silo. A small amount of water is introduced into the air stream during filling to help lubricate the filling tube. A small adjustable nozzle at the top, controlled by a handle at the base of the silo directs the silage to fall into the silo on the near, middle, or far side, to facilitate evenly layered loading. Once completely filled, the top of the exposed silage pile is covered with a large heavy sheet of
silo plastic A silo (from the Greek σιρός – ''siros'', "pit for holding grain") is a structure for storing bulk materials. Silos are used in agriculture to store fermented feed known as silage, not to be confused with a grain bin, which is used t ...
which seals out oxygen and permits the entire pile to begin to
ferment Fermentation is a metabolism, metabolic process that produces chemical changes in organic Substrate (chemistry), substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in ...
in the autumn. In the winter when animals must be kept indoors, the silo plastic is removed, the unloader is lowered down onto the top of the silage pile, and a hinged door is opened on the side of the silo to permit the silage to be blown out. There is an array of these access doors arranged vertically up the side of the silo, with an unloading tube next to the doors that has a series of removable covers down the side of the tube. The unloader tube and access doors are normally covered with a large U-shaped shield mounted on the silo, to protect the farmer from wind, snow, and rain while working on the silo. The silo unloader mechanism consists of a pair of counter-rotating toothed augers which rip up the surface of the silage and pull it towards the center of the unloader. The toothed augers rotate in a circle around the center hub, evenly chewing the silage off the surface of the pile. In the center, a large blower assembly picks up the silage and blows it out the silo door, where the silage falls by gravity down the unloader tube to the bottom of the silo, typically into an automated
conveyor A conveyor system is a common piece of mechanical handling equipment that moves materials from one location to another. Conveyors are especially useful in applications involving the transport of heavy or bulky materials. Conveyor systems allow ...
system. The unloader is typically lowered only a half-inch or so at a time by the operator, and the unloader picks up only a small amount of material until the winch cable has become taut and the unloader is not picking up any more material. The operator then lowers the unloader another half-inch or so and the process repeats. If lowered too far, the unloader can pull up much more material than it can handle, which can overflow and plug up the blower, outlet spout, and the unloader tube, resulting in a time-wasting process of having to climb up the silo to clear the blockages. Once silage has entered the conveyor system, it can be handled by either manual or automatic distribution systems. The simplest manual distribution system uses a sliding metal platform under the pickup channel. When slid open, the forage drops through the open hole and down a chute into a wagon, wheelbarrow, or open pile. When closed, the forage continues past the opening and onward to other parts of the conveyor. Computer automation and a conveyor running the length of a feeding stall can permit the silage to be automatically dropped from above to each animal, with the amount dispensed customized for each location.


Safety

Silos are hazardous, and people are killed or injured every year in the process of filling and maintaining them. The machinery used is dangerous and with tower silos workers can fall from the silo's ladder or work platform. Several fires have occurred over the years.


Dangers of loading process

Filling a silo requires parking two tractors very close to each other, both running at full power and with live
PTO shaft PTO may stand for: Organisations * Patent and Trademark Office (disambiguation), a government office that handles the issuing of both patents and trademarks * Parent teacher organization, organization that consists of parents, teachers and schoo ...
s, one powering the silo blower and the other powering a
forage wagon A silo (from the Greek σιρός – ''siros'', "pit for holding grain") is a structure for storing bulk materials. Silos are used in agriculture to store fermented feed known as silage, not to be confused with a grain bin, which is used t ...
unloading fresh-cut forage into the blower. The farmer must continually move around in this highly hazardous environment of spinning shafts and high-speed conveyors to check material flows and adjust speeds, and to start and stop all the equipment between loads. Preparation for filling a silo requires winching the unloader to the top, and any remaining forage at the base that the unloader could not pick up must be removed from the floor of the silo. This job requires that the farmer work directly underneath a machine weighing several tons suspended fifty feet or more overhead from a small steel cable. Should the unloader fall, the farmer will likely be killed instantly.


Dangers of unloading process

Unloading also poses its own special hazards, due to the requirement that the farmer regularly climb the silo to close an upper door and open a lower door, moving the unloader chute from door to door in the process. The fermentation of the silage produces
methane gas Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...
which over time will outgas and displace the oxygen in the top of the silo. A farmer directly entering a silo without any other precautions can be
asphyxiated Asphyxia or asphyxiation is a condition of deficient supply of oxygen to the body which arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects primarily the tissues and organs. There are many circumstances that can i ...
by the methane, knocked unconscious, and silently suffocate to death before anyone else knows what has happened. It is either necessary to leave the silo blower attached to the silo at all times to use it when necessary to ventilate the silo with fresh air, or to have a dedicated electric fan system to blow fresh air into the silo, before anyone attempts to enter it. In the event that the unloader mechanism becomes plugged, the farmer must climb the silo and directly stand on the unloader, reaching into the blower spout to dig out the soft silage. After clearing a plug, the forage needs to be forked out into an even layer around the unloader so that the unloader does not immediately dig into the pile and plug itself again. All during this process the farmer is standing on or near a machine that could easily kill them in seconds if it were to accidentally start up. This could happen if someone in the barn were to unknowingly switch on the unloading mechanism while someone is in the silo working on the unloader. Often, when unloading grain from an auger or other opening at the bottom of the silo, another worker will be atop the grain "walking it down", to ensure an even flow of grain out of the silo. Sometimes unstable pockets in the grain will collapse beneath the worker doing the walking; this is called
grain entrapment Grain entrapment, or grain engulfment, occurs when a person becomes submerged in grain and cannot get out without assistance. It most frequently occurs in grain bins and other storage facilities such as silos or grain elevators, or in grain trans ...
as the worker can be completely sunk into the grain within seconds. Entrapment can also occur in moving grain, or when workers clear large clumps of grain that have become stuck on the side of the silo. This often results in death by
suffocation Asphyxia or asphyxiation is a condition of deficient supply of oxygen to the body which arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects primarily the tissues and organs. There are many circumstances that can i ...
.


Dry-material/bin hazards

There have also been many cases of bins and the associated ducts and buildings exploding. If the air inside becomes laden with finely granulated particles, such as grain dust, a spark can trigger an explosion powerful enough to blow a concrete silo and adjacent buildings apart, usually setting the adjacent grain and building on fire. Sparks are often caused by (metal) rubbing against metal ducts; or due to static electricity produced by dust moving along the ducts when extra dry. The two main problems which will necessitate
silo cleaning {{unreferenced, date=December 2007 Silo cleaning is a process to maximize the efficiency of storage silos that hold bulk powders or granules. In silos, material is fed through the top and removed from the bottom. Typical silo applications include ...
in bins are ''bridging'' and ''rat-holing''. Bridging occurs when the material interlaces over the unloading mechanism at the base of the bins and blocks the flow of stored material by gravity into the unloading system. Rat-holing occurs when the material starts to adhere to the side of the bin. This will reduce the operating capacity of a bin as well as leading to cross-contamination of newer material with older material. There are a number of ways to clean a bin and many of these carry their own risks. However, since the early 1990s acoustic cleaners have become available. These are non-invasive, have minimum risk, and can offer a very cost-effective way to keep a small particle bin clean.


Notable silos

*
Henninger Turm Henninger Turm (Henninger Tower) was a grain storage silo located in the Sachsenhausen (Frankfurt am Main), Sachsenhausen-Süd district of Frankfurt, Germany. It was built by Henninger Brewery (now part of the Dr. Oetker#Binding Brauerei, Binding ...
,
Frankfurt Frankfurt, officially Frankfurt am Main (; Hessian: , "Frank ford on the Main"), is the most populous city in the German state of Hesse. Its 791,000 inhabitants as of 2022 make it the fifth-most populous city in Germany. Located on its na ...
,
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
, before demolition in 2013, had an observation deck and 2 revolving restaurants, height: 120 metres * Swissmill Tower,
Zürich Zürich () is the list of cities in Switzerland, largest city in Switzerland and the capital of the canton of Zürich. It is located in north-central Switzerland, at the northwestern tip of Lake Zürich. As of January 2020, the municipality has 43 ...
,
Switzerland ). Swiss law does not designate a ''capital'' as such, but the federal parliament and government are installed in Bern, while other federal institutions, such as the federal courts, are in other cities (Bellinzona, Lausanne, Luzern, Neuchâtel ...
, height: 118 metres, the world highest silo in activity. * Schapfen-Mill-Tower,
Ulm Ulm () is a city in the German state of Baden-Württemberg, situated on the river Danube on the border with Bavaria. The city, which has an estimated population of more than 126,000 (2018), forms an urban district of its own (german: link=no, ...
,
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
, height: 115 metres *
Silo Tower Basel The Silo Tower of Basel is located in the Switzerland, Swiss city of Basel, in the Rhine harbour of Kleinhueningen, near the Dreiländereck (Basel), Dreiländereck. The silo tower was built in 1923 by a Swiss shipping company. Its viewing platfor ...
,
Basel , french: link=no, Bâlois(e), it, Basilese , neighboring_municipalities= Allschwil (BL), Hégenheim (FR-68), Binningen (BL), Birsfelden (BL), Bottmingen (BL), Huningue (FR-68), Münchenstein (BL), Muttenz (BL), Reinach (BL), Riehen (BS ...
,
Switzerland ). Swiss law does not designate a ''capital'' as such, but the federal parliament and government are installed in Bern, while other federal institutions, such as the federal courts, are in other cities (Bellinzona, Lausanne, Luzern, Neuchâtel ...
, has an observation deck, height: 52 metres *
Quaker Square Quaker Square was a shopping and dining complex located in downtown Akron, Ohio which is now used by the University of Akron. Quaker Square was the original Quaker Oats factory; the complex consists of the former mill, factory, and silos. The bui ...
,
Akron, Ohio Akron () is the fifth-largest city in the U.S. state of Ohio and is the county seat of Summit County, Ohio, Summit County. It is located on the western edge of the Glaciated Allegheny Plateau, about south of downtown Cleveland. As of the 2020 C ...
,
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
, is a former set of tower silos that is now a hotel, restaurants and shops * ''Dagon'',
Haifa Haifa ( he, חֵיפָה ' ; ar, حَيْفَا ') is the third-largest city in Israel—after Jerusalem and Tel Aviv—with a population of in . The city of Haifa forms part of the Haifa metropolitan area, the third-most populous metropol ...
, Israel - transformed into a museum of agriculture, a prominent local feature.


Silo art

"Silo art" is a recent and distinctly Australian art movement which began in
Northam, Western Australia Northam () is a town in the Australian state of Western Australia, situated at the confluence of the Avon and Mortlock Rivers, about east-northeast of Perth in the Avon Valley. At the 2016 census, Northam had a population of 6,548. Northa ...
in 2015. Silos are usually decorated with huge
mural A mural is any piece of graphic artwork that is painted or applied directly to a wall, ceiling or other permanent substrate. Mural techniques include fresco, mosaic, graffiti and marouflage. Word mural in art The word ''mural'' is a Spani ...
-type paintings with many themes. The Australian Silo Art Trail shows 35 examples of silo art , with numbers growing. there is an ongoing legal battle over the use of the term "silo art trail", with the Yarriambiack Shire Council in
Victoria Victoria most commonly refers to: * Victoria (Australia), a state of the Commonwealth of Australia * Victoria, British Columbia, provincial capital of British Columbia, Canada * Victoria (mythology), Roman goddess of Victory * Victoria, Seychelle ...
attempting to
trademark A trademark (also written trade mark or trade-mark) is a type of intellectual property consisting of a recognizable sign, design, or expression that identifies products or services from a particular source and distinguishes them from others ...
it in 2017, with GrainCorp, Australia's largest grains handler, opposing the move, saying that the term should be usable by many councils. Old
water tower A water tower is an elevated structure supporting a water tank constructed at a height sufficient to pressurize a water distribution system, distribution system for potable water, and to provide emergency storage for fire protection. Water towe ...
s have also been decorated in many regional centres. In
Melbourne Melbourne ( ; Boonwurrung/Woiwurrung: ''Narrm'' or ''Naarm'') is the capital and most populous city of the Australian state of Victoria, and the second-most populous city in both Australia and Oceania. Its name generally refers to a met ...
, a huge painting of New Zealand Prime Minister
Jacinda Ardern Jacinda Kate Laurell Ardern ( ; born 26 July 1980) is a New Zealand politician who has been serving as the 40th prime minister of New Zealand and leader of the Labour Party since 2017. A member of the Labour Party, she has been the member of ...
embracing a Muslim woman, an iconic image beamed around the world after the 2019 Christchurch mosque attacks, was painted on the Tinning Street silo in the suburb of Brunswick, after was raised in a day via
crowdfunding Crowdfunding is the practice of funding a project or venture by raising money from a large number of people, typically via the internet. Crowdfunding is a form of crowdsourcing and alternative finance. In 2015, over was raised worldwide by crow ...
. The town of
Monto Monto was the nickname for the one-time red light district in the northeast of Dublin, Ireland. The Monto was roughly the area bounded by Talbot Street, Amiens Street, Gardiner Street and Seán McDermott Street (formerly Gloucester Street) in ...
in the
North Burnett Region The North Burnett Region is a local government area in Queensland, Australia in the northern catchment of the Burnett River. Established in 2008, it was preceded by several previous local government areas with histories extending back to the ear ...
of
Queensland ) , nickname = Sunshine State , image_map = Queensland in Australia.svg , map_caption = Location of Queensland in Australia , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , established_ ...
has been put on the tourism map as the most northerly silo art installation in Australia. Its "Three Moons" silos depict several stories of the past, including the era of
gold mining Gold mining is the extraction of gold resources by mining. Historically, mining gold from alluvial deposits used manual separation processes, such as gold panning. However, with the expansion of gold mining to ores that are not on the surface ...
,
cattle mustering A muster (Au/NZ) or a roundup (US/Ca) is the process of gathering livestock. Musters usually involve cattle, sheep or horses, but may also include goats, camels, buffalo or other animals. Mustering may be conducted for a variety of reasons in ...
and
The Dreaming The Dreaming, also referred to as Dreamtime, is a term devised by early anthropologists to refer to a religio-cultural worldview attributed to Australian Aboriginal beliefs. It was originally used by Francis Gillen, quickly adopted by his co ...
. It also has a mural on an old
water tower A water tower is an elevated structure supporting a water tank constructed at a height sufficient to pressurize a water distribution system, distribution system for potable water, and to provide emergency storage for fire protection. Water towe ...
. File:AU-NSW-Bourke-Percy Hobson mural-2021.jpg, Percy Hobson Park water tower,
Bourke, New South Wales Bourke is a town in the north-west of New South Wales, Australia. The administrative centre and largest town in Bourke Shire, Bourke is approximately north-west of the state capital, Sydney, on the south bank of the Darling River. it is also ...
, Australia (2021). File:Thallon silo art - The Watering Hole, 2021, 03.jpg,
Thallon, Queensland Thallon is a town and a locality in the Shire of Balonne, Queensland, Australia. In the , Thallon had a population of 257 people. There is a second town within the locality, Nindigully. Geography Thallon is in South West Queensland, west of ...
, Australia (2021). File:Yelarbon silos IMG 20190607 114008.jpg,
Yelarbon Yelarbon is a rural town and locality in the Goondiwindi Region, Queensland, Australia. It is on the border of Queensland and New South Wales. In the , Yelarbon had a population of 364 people. Geography Yelarbon is in south-central Queensland on ...
, Queensland, Australia (2019). File:Coonalpyn Silo Art 004.jpg,
Coonalpyn, South Australia Coonalpyn is a town and a locality in the Australian state of South Australia located about south-east of the state capital of Adelaide and about south-east of the municipal seat in Tailem Bend. It is situated in the local government area of ...
, Australia (2018). File:MG 2268 Silo art-crop-1920px.jpg, Brim, Victoria, Australia (2015). File:Rosebery Silo Art 001.JPG,
Rosebery, Victoria Rosebery is a locality in western Victoria, Australia. The locality is in the Shire of Yarriambiack local government area, west north west of the state capital, Melbourne on the Henty Highway. At the , Rosebery had a population of 5. The town w ...
, Australia (2018). File:Tungamah Silo Art2.jpg,
Tungamah Tungamah is a town in the Goulburn Valley region of northern Victoria, Australia. The town is located in the Shire of Moira local government area, from the state capital, Melbourne. Tungamah is situated on the banks of Boosey Creek and at the ...
, Victoria, Australia (2019). File:Kantola biscuit factory silos with artwork.jpg, Kantola Biscuit Factory,
Hämeenlinna Hämeenlinna (; sv, Tavastehus; krl, Hämienlinna; la, Tavastum or ''Croneburgum'') is a city and municipality of about inhabitants in the heart of the historical province of Tavastia and the modern province of Kanta-Häme in the south of F ...
,
Finland Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of B ...
(2019).


See also

*
Granary A granary is a storehouse or room in a barn for threshed grain or animal feed. Ancient or primitive granaries are most often made of pottery. Granaries are often built above the ground to keep the stored food away from mice and other animal ...
*
Grain elevator A grain elevator is a facility designed to stockpile or store grain. In the grain trade, the term "grain elevator" also describes a tower containing a bucket elevator or a pneumatic conveyor, which scoops up grain from a lower level and deposits ...
* Silos & Smokestacks National Heritage Area


References


External links


International Silo Association


from the U.S. National Agricultural Safety Database * Beedle, Peggy Lee
"Silos: an agricultural success story"
University of Wisconsin-Extension: 2001, G3660-4. {{Authority control American inventions Agricultural buildings Containers Food storage containers Articles containing video clips Building types