Canadian Grain Commission
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Spoilage and heating of stored agricultural products

Chapter 7 – Safety

Education and training

Storage facilities operated by experienced managers and trained staff are generally safe places in which to work, but because of the existence of potential hazards, uninformed persons can put themselves and others at risk. It is of paramount importance that all persons working on either a full-time or a part-time basis or for contractors must be made aware of potential hazards existing on the plant or farm. Special attention must be given to children working on or visiting farms.

Full-time staff require training as teams to handle routine but potentially hazardous situations, to apply first-aid procedures, to handle emergencies with ambulance and local fire brigades, and to guide part-time staff and contractors in safety practices. Managers need to be aware of the latest safety methods and any new management practices affecting safety and should bring them to the attention of staff. They must issue safety guidelines for staff and contractors, particularly welders, and strictly enforce a no admittance policy for casual visitors, for example bargers waiting to unload their vessels. It is most important that the manager or superintendent is given advance notice of persons intending to enter the bins to work and is again notified when the work is completed and everyone is safely out (National Safety Council 1962). For more information on occupational safety in grain elevators and feed mills see National Institute for Occupational Safety and Health (1983).

Protective wear

Wear tight-fitting clothing to avoid being entrapped by machinery belts and augers or by bin projections. Wear strong, flexible boots to protect the feet from being crushed or penetrated. Always have various different types of masks and respirators available, plus additional filters. Use this respiratory equipment routinely, as dust, always present in grain and feed-handling facilities, can pose a serious hazard to health. Wilkins (1984) describes the main types of respirators used by animal producers to reduce their exposure to dust, and health problems, in dusty barns. Never enter a bin containing out-of-condition grain unless you are wearing proper respiratory gear, because bad grain can produce toxic gases. Never shovel molded grain out of a bin without wearing a mask. Take frequent rests in fresh air. Exposure to spores in moldy grain can have lasting effects on one’s health (Manfreda and Warren 1984). Keep up-to-date on the latest respiratory protection equipment available and use it. It will pay dividends in the long run.



In recent years the number of suffocations that have occurred in grain bins has increased in the USA for many reasons, such as larger on-farm facilities, increased mechanization, and lack of knowledge of grain movement and safety precautions (University of Kentucky 1984). Fifty-one suffocation deaths occurred in farm bins in Nebraska and Indiana between 1970 and 1979, and 33 out of 126 deaths in 105 selected incidents in grain-handling facilities in the USA between 1979 and 1981 (Table 9) were due to this cause (Cloe 1983).

Table 9 – Causes of fatalities in elevators, mills, and other grain-handling facilities in selected incidents (Cloe 1983)
Types of accidents Number of incidents Number of fatalities
* Selected cases reported to the Occupational Safety and Health Administration (OSHA), Washington, D.C., during the period 1977-1981.
Suffocation 32 33
Explosion/fire 18 37
Falls 19 19
Contact with electric current 12 13
Collapse of structures 7 7
Caught in augers/conveyors 6 6
Crushed between surfaces 4 4
Hazardous vapors 2 2
Caught in machinery 2 2
Drowning 2 2
Run over by grain truck 1 1
Totals 105* 126

Suffocations occur when persons within bins become engulfed by flowing grain during unloading operations by bottom auger or gravity feed methods. Some crops such as flaxseed or millet act like a quicksand and operators can quickly sink under their own weight; the situation is even worse with flowing stocks (National Safety Council 1962). Persons within wet holding bins emptying by gravity feed into automatic-batch grain dryers can easily be engulfed during reloading of the dryer with wet grain. Other instances of suffocation occur when operators fall into air spaces, which are often present beneath bridged grain (Fig. 15), are buried by falling steep piles of moist grain, or breathe noxious gases, for example carbon dioxide produced by out-of-condition grain (University of Kentucky 1984). Suffocation as a result of diaphragm collapse can occur from welding fumes within bins under repair (Broadhurst 1985).

Potential hazards created by bridging

Figure 15 – Potential hazards created by bridging: A, moldy grain causes bridge to form before unloading; B, air space is created as loading begins; C, air space remains after unloading stops (after University of Kentucky 1984).

Suffocations can be prevented by taking the following precautions:

  • Installing ladders inside bins.
  • Obtaining safety harnesses and ropes.
  • Obtaining long poles and rakes to break crusts and bridges.
  • Purchasing a self-contained breathing apparatus.
  • Learning how to lock-out electrical bin systems.
  • Setting up an action plan for supporting and rescuing persons from bins.
  • Never entering a hermetically sealed silo without flushing first with fresh air.
  • Never walking across binned flaxseed or millet.
  • Never entering a bin containing out-of-condition grain without wearing a self-contained breathing apparatus.
  • Never entering a bin without first shutting down the electrical power to bin systems.
  • Breaking crusts and bridges with a pole or rake, working from the outside of bins.
  • Breaking crusts and bridges with a remote-controlled whip device (see Fig. 12), working from the outside of bins.
  • Entering a bin only if attached to safety harness and rope and anchored to a second person, and having a third person on standby to assist in pulling you up or going for help (Fig. 16).
  • Moving to the wall immediately if grain starts to flow.
  • Closing any bin access areas that are at the top of empty bins.
  • Using the bosun’s chair apparatus safely by working only above hang-ups (see Fig. 12).

Investigation of a questionable bin, using three persons for maximum safety

Figure 16 – Investigation of a questionable bin, using three persons for maximum safety: A, the person inside the bin Is secured to the outside; B, the person on the roof calls out instructions and assists in lifting; C, the person on the ground assists In pulling and, if necessary, goes for help (after University of Kentucky 1984).

The following account illustrates the difficulty involved in pulling out a trapped person from a grain bin. A salvage operator in western Canada cut a 30-cm diameter hole in the side of a bin of heated cereals prior to unloading by auger. Shortly after, an inexperienced worker was reported missing and later found buried up to his shoulders in grain in the bin. The auger was immediately switched off and five men with shovels tried to dig out but were unsuccessful. As a last resort, a rope was put around the man’s waist and tied securely to the roof. The auger was switched on again to lower the grain level and eventually the man was pulled out (E. Dorge, per. Com. 1986).

Toxic gases

Exposure to toxic gases produced during the storage of agricultural products or by-products has resulted in many fatalities among farm families and their employees in recent years. Nitrogen dioxide (NO2), carbon monoxide (CO), and carbon dioxide (CO2) are the gases most likely to be encountered during handling of stored products, whereas hydrogen sulfide (H2S), ammonia (NH3, and CO2 occur during storage of liquid manures (Table 10) (Agriculture Canada 1979). Methane (CH4), which is highly flammable, is also produced (Broadhurst 1985). Hydrogen cyanide (HCN), generated during storage of moist flaxseed, is absorbed through the skin and can cause death (Western Producer 1977).

Table 10 – Toxic gases encountered in stored farm commodities (Agriculture Canada 1979)
Toxic gas Chemical symbol Specific gravity Toxicity Flammability (Percentage by volume in air) Description Source
Nitrogen dioxide (silage gas) NO2 1.58 (sinks in air) 5 ppm (extremely toxic) Reddish color in certain concentrations, bleach-like odor By-product of early stages of silo fermentation of forages
Carbon monoxide CO 0.96 50 ppm 12-72 % (very flammable) Clear, odorless By-product of incomplete combustion of carbonaceous material; occurs in heating materials and during fires
Carbon dioxide CO2 1.53 (sinks in air) 5000 ppm Colorless, odorless Product of respiration; occurs in grain and feed storage tanks, oxygen-limiting silos, liquid manure systems
Hydrogen sulfide H2S 1.19 10 ppm 4-50 % Clear, colorless pungent odor Formed in liquid manure systems; formed during uncontrolled anaerobic digestion of organic substances
Ammonia NH3 0.60 25 ppm 10-30 % Clear, colorless pungent odor Formed in manure as a by-product of putrification

Nitrogen dioxide is produced in silos under certain conditions by green material such as chopped corn silage. This gas is extremely toxic, and when present in high concentration has a characteristic reddish or yellow brown color, sometimes visible above the surface of the material. In low concentration it is colorless and odorless but just as lethal. NO2 can develop within 6 hours of placement of material in the silo, the most dangerous period being 12-60 hours after filling. Usually, the gas dissipates in 3-6 weeks, but without ventilation it can remain indefinitely (Jonas 1979). When inhaled it reacts with water in the respiratory tract to produce acids, which burn the mouth, nose, throat, and lungs. The first symptoms are often a burning sensation and coughing. Inhalation of NO2 may cause silo filler’s disease, or nitrogen dioxide pneumonia (Grayson 1957).

Carbon monoxide is almost as toxic as NO2, is colorless, therefore visually undetectable, and is produced during ensilage and incomplete combustion of materials, as in fires. CO has also been detected in sample grade flaxseed and heating soybeans (Ramstad and Geddes 1942). The following example illustrates the sudden danger that can be caused by CO during fire-fighting operations (Reanney 1969). A firefighter combating a fire in a ship’s hold went into an adjacent empty hold to examine the bulkheads. Because the empty hold was entirely free from smoke and heat he did not wear a breathing apparatus. While traversing the empty hold, he suddenly became ill but was quickly rescued. The cause was attributed to a pocket of CO, resulting from leakage through cracks from the fire-affected hold next door. Breathing apparatus must be worn by firefighters who are working in enclosed spaces close to fires because of the danger of CO and other toxic gases.

Carbon dioxide is colorless but is relatively less toxic than NO2 and CO at low concentrations, although it can be fatal at high concentrations. It is often produced during respiration of grains, molds, and insects in grain and feed bins and oxygen-limiting silos, and during ensilage of green materials.

Toxic gas poisonings can be prevented by taking the following precautions:

  • Monitoring the levels of NO2, CO2, and CO in storages by using a system of plastic tubing, hypodermic syringes, and Dräger tubes (see Fig. 9) (Wilkins 1985a).
  • Remembering never to enter oxygen-limiting silos or grain and feed tanks containing out-of-condition grain unless you are wearing a self-contained breathing apparatus and a safety harness, and have two trained persons in attendance.
  • Reminding family members and workers of the dangers of NO2 in silos each year at harvest time.
  • Remembering that NO2 sinks and that a door left open near the silage surface could allow the gas to move down the chute into the feed room. Livestock have died when a connecting door to the barn was left open, and workers have succumbed to silo gas as it sank down the chute when they climbed the chute ladder and opened a door above their heads. Therefore, always close the barn door to the feed room and open the doors and windows in the feed room to allow fresh air into the chute (Jonas 1979).
  • Ventilating thoroughly silos containing freshly harvested forages before entering.
  • Using a fan to flush the silo air free from toxic gases.

The following example illustrates the dangers of toxic gases on farms (Jonas 1979).

A 17-year-old youth on an Ontario farm entered a 12 x 3.6-m tower silo into which four loads of chopped corn silage containing high levels of nitrates had been placed 6 hours previously. After being in the silo for less than 5 min leveling the corn, he felt dizzy, went outside, began to feel weak and nauseated, and later became delirious, vomited, and complained of suffocation. Almost lethal levels of oxides of nitrogen were present in his blood, although he saw no gas and smelt nothing. One year after the accident, he was still suffering from after effects. He tired easily, and on damp days his lungs, nose, and throat burned. His sense of smell was beginning to return but he still could not taste anything. He had to avoid dusty areas, as he had no nasal hairs to filter dust particles, and he still choked easily when he ate. X-rays showed that his lungs were as black as those of a person who had smoked for 90 years. It was considered that because of his youth, the damage would probably repair itself in time.


In Canada, hydrogen phosphide (phosphine) evolved from aluminum and magnesium phosphides is used to control insect pests in storages. Methyl bromide is used as a fumigant of empty holds of ships and mills. Although fumigants are usually applied by licensed pest control operators, elevator managers and railcar, plant, and ship personnel should be aware of the toxic effects and behavior of fumigants used in their workplace, for example their reaction to water and penetration to adjacent spaces, and of appropriate first aid procedures in emergency situations. Poisonings have occurred in grain elevators after persons have entered pits or bins fumigated 1-2 weeks earlier. Poisonings have also occurred on ships after leakage of fumigants into passenger compartments from treated stocks. Davis and Barrett (1986) have summarized the development of the United States in-transit shipboard fumigation program and the safety procedures used. Normally, fumigated holds are aerated at port of discharge by opening all hatches. Fumigant gas concentrations are monitored 1 m above the grain surface every 30 min until the fumigant gas is at or below 0.3 ppm. The grain may then be safely removed, using pneumatic or grab-type equipment.

Fumigant poisonings can be prevented by taking the following precautions:

  • Remembering nearby human habitations that could be affected by gases and vapors.
  • Fumigating on a windless day.
  • Identifying fumigated premises or stocks by prominently displaying warning signs.
  • Working in pairs.
  • Wearing a self-contained breathing apparatus when opening hatches, doors, and windows after an area has been fumigated.
  • Changing the canister of a canister-type gas mask each time this type of breathing apparatus is used.
  • Monitoring levels of phosphine and methyl bromide by using Dräger tubes or other devices.
  • Avoiding the use of water on materials fumigated with phosphine, as more phosphine may be generated.

See Bond (1984) for a comprehensive description on control of insects by fumigation and recommended safe practices.

Fires and explosions

Fires and explosions can result not only in injury to plant personnel at the scene but also, through modification of the environment, to firefighters and salvage operators. To minimize risks, firefighters need to know the types of commodities they are dealing with in order to select the correct extinguishing medium, for example foam, water, sand, or carbon dioxide, and the correct breathing apparatus. They also need to know whether gas cylinders, chemicals, and other dangerous substances are on site. Salvage operators should be advised of any gas cylinders that may be in the ruins and of any weakened structures such as walls which, if disturbed, may suddenly release large volumes of hot material.

Fires and explosions are known to occur in vertical silos containing grass silage or haylage (Koegel and Bruhn 1971). Firefighters fighting such fires are at risk from explosions. Campbell (1973) describes the events leading to an explosion in a partially filled, bottom-unloading type silo that contained smoldering haylage and produced a mixture of carbon dioxide and flammable carbon monoxide. Following previously recommended fire-fighting procedures, firefighters went to the top of the affected silo, 18 m above ground level, opened the hatch, and directed water or foam onto the hot haylage, thereby injecting air into the silo. The ingredients for an explosion were then present — a flammable gas and oxygen — in a closed container, and a spark from a glowing ember touched off an explosion (CampbeIl 1973). Current recommended fire- fighting procedures are much safer (see section on vertical silage silos). Descriptions of the effects of explosions in silos containing silage are given by Campbell (1973) and Singley (1968). Boumans (1985) describes the effects of dust explosions in silos containing grains and grain products, and the methods of explosion prevention and protection. Aldis and Lai (1979) have reviewed the literature relating to engineering aspects of grain dust explosions. For information on the investigation of fires and explosions see next section.

An excellent summary of safety procedures to follow while working in grain and feed silos, tanks and bins, food product tank cars, and liquid storage tanks is given by the National Safety Council (1962).