Silos are increasingly being used to store grain world over, as it offers a lot of advantages over bag storage and other means of storage. It is considered as the most economical long term storage for grains. However, it also poses certain dangers which one should be aware of. Many people have suffered injuries in a grain storage complex due to various unsafe conditions. It is dangerous & life-threatening, and hence one should never enter a grain bin unless it is extremely essential. The leading cause of injuries or deaths in grain silo terminals is suffocation due to grain engulfment and entrapment. There are many unsafe conditions that exist inside grain silo, and one must be aware of all, before planning any entry inside grain silo. Some of these unsafe conditions are described below.
Buildup of Toxic Gases
In a grain silo, there are two gases that may be present in high concentration. One is Carbon Dioxide, and another is Nitrogen Dioxide. These gases are called silo gases and buildup inside silo due to fermentation or infestation of mainly chopped grain inside silo. Nitrogen dioxide is characterized by a yellow or reddish fog and a bleach-like odor is more harmful because it causes severe irritation to the nose and throat and may lead to inflammation of the lungs. Immediately within 2-3 days after the grain is harvested Nitrogen dioxide gas starts forming and within 2-3 days after harvesting, buildup to its peak inside the silo and thereafter begins to decrease rapidly in a well ventilated silo. It takes approximately 2 weeks after the harvest for nitrogen dioxide gas formation to stop completely, but still entry inside the silo is not safe as gas takes time to escape out of the silo. Exposure to high concentration of these gases may cause someone to collapse and die immediately within minutes of inhalation.
Traces of Phosphine Gas
Fumigation is essential activity in a grain storage silo complex. Fumigation is carried out with phosphine gas, and hence traces of Phosphine gas may be present inside a grain silo which is recently been fumigated. Although once the fumigation is over, the silo is de-sealed and aeration fans are operated to expel residual phosphine gas out of silo but still some ALP tablet residue may again generate phosphine gas and hence one must take proper care while entering inside silo.
Bridged Grain - Collapse of Grain Mass
Suffocation, which is the leading cause of death in grain storage silos, happens due to grain mass collapsing on the people due to infestation or excessive moisture.
Infestation happens inside a silo due to many reasons and this grain infestation that grow inside silo forms solid masses, crusts, horizontal grain bridges and vertical grain walls that can collapse. The most common is hard crust formation on the top surfaces of grain, which stays intact even when you unload the grain from below it. This crust or bridge is extremely dangerous and collapses under a person’s weight and the person gets submerged inside the grain within seconds.
Entering inside the silo when the gravity flow stops from the silo discharge gates also poses a great danger as. sometimes while unloading the grain a huge mass of grain or heap that gets stuck on the wall of silo falls on the people trying to break this grain mass from the silo wall and may injure or suffocate the people trying to break the heap.
Flowing Grain – Grain flowing downwards
One must never ever think to entering a grain silo when grain is being reclaimed or unloaded from the silo. Grain that is flowing downwards acts like a sand and anyone who enters inside silo to break the bridged grain or vertical pile of stored grain will get completely buried or engulfed in grain in only 7 to 20 secs, if it collapses unexpectedly. One must also understand that force required to pull out a man buried in grain mass to the waist is more than 500 kgs hence it is very difficult to pull out a man engulfed in the grain without trained assistance.
Grains have inherent tendency to generate dust whenever it is conveyed or transported from one place to another. This dust forms a dust cloud while silo is being filled or being emptied and whenever this grain dust cloud is in high enough concentration and get an ignition source it may result into dust explosion as suspended grain dust is highly combustible. Generally, people enter inside silo when sweep auger stop working and the silo is to be emptied manually. During this silo emptying process, there are always chances of dust cloud formation and hence care should be taken not to allow any ignition source like match box, lighter, lithium batteries, steel studded shoes, etc. inside silo.
Grain Silo Entry requirements
We must take following well accepted precautions which can minimize grain entry requirements and thus prevents accidents
We must not store wet grain inside Silo as it increases infestation and result in crust / bridge formation inside silo which necessitates the chances of man entry inside silo
Display grain entrapment warning signs near grain silo entry manholes
Lock all the access ladders / gates to go inside silo
No silo entry should be allowed without a valid work permit from facility manager
True zero entry sweep augers must be installed to ensure total clean out
However, even after taking all above precautions, there are still some more reasons that makes the silo entry unavoidable.
1. To collect sample from the silo
2. To break the crusts or horizontal bridge formed on the top of silo
3. To break vertical grain walls, and
4. To repair Sweep Auger
5. To repair humidity sensor
6. To fix / remove insect probes
Precautionary measures to Enter Inside Silo
Although one must not enter Grain Silo but in case grain bin entry is unavoidable, one must follow the complete silo entry procedure. Entering any grain silo is a process, and it requires planning and preparation. Only the trained people who are fully aware of all the unsafe conditions that they may encounter inside the Silo and are trained to enter inside the silo should be allowed to enter.
Nobody should be allowed silo entry without a trained supervisor and Personal Protective Equipment (like Helmet, Safety Belt, Safety Mask, safety goggle etc.).
Roof exhaust fans must be operated for at least 15 minutes before allowing people to go inside the silo to expel all residual gases. Phosphine gas ppm should be below 0.3 ppm to allow entry inside silo.
And finally, there should be a foolproof work permit system to record such silo entries and take precautionary measures.