Silo Filling Safety

Dennis J. Murphy, Distinguished Professor Pennsylvania State University

Few farming operations provide as many different opportunities for accidents to happen as filling the silo.

High powered equipment, working in close quarters, and the potential of silo gas formation combine to produce numerous injury incidents throughout the late summer and fall.


Preseason Preparations

First, review the operator’s manuals and follow maintenance guidelines for corn and hay harvesting equipment. It is important to review these instructions because operators may be less familiar with seasonal equipment and its potential risk for injuries. During the preseason, clean, lubricate, and replace worn parts to ensure that the equipment is performing optimally. Check to make sure that all guards are securely in place and replace guards if they are worn or damaged. All guards and shields must be in place before operating the equipment.

The initial preparation for filling the silo includes raising the distributor/unloader to the top of the structure. Choose a calm, dry day to complete this activity to decrease the potential risk of slips and falls. Carefully inspect all cables, wires, pulleys, and connections to make sure they are properly working and securely anchored. One person, at ground level, should raise the distributor/unloader while another person watches the process from the blower pipe platform, signaling if lines become tangled or other problems arise. Under no circumstances should anyone enter the silo while the distributor/unloader is being raised or attempt to crawl onto it when it is suspended because a raised distributor/unloader can easily crush a worker should it fall.


Machinery Guarding

One of the main risks involved in filling the silo stems from the operator being exposed to numerous moving machine parts in a relatively crowded work area. These mechanical hazards include pinch, wrap, shear, and crush points as well as freewheeling parts hazards. Operators overestimate their ability to react in a mechanical hazard incident which may quickly result in a life threatening situation. Unfortunately, only certain areas of a self-unloading forage wagon and silo blower can be guarded. Both are operated by power take-off (PTO) shafts that should be, but many times, are not properly guarded. Add unsafe practices like stepping over shafts or reaching into operating unloading wagons, and it is easy to see why injury incidents occur.

Hazards on self-unloading wagons include a combination of moving aprons, beaters, conveyors or augers, and an assortment of chains and sprockets. To prevent injury incidents, all protective machinery shields must be in place. Operators should wear comfortable and close-fitting clothing and under no circumstances should a person ever enter a wagon while the power is on. Nor should you reach into the unloading chute to help speed the unloading rate. If clogging occurs, first disengage the PTO, shut down the tractor and remove the keys from the ignition before removing the clogged area. PTO’s can unexpectedly slip into gear, particularly if poorly adjusted, or on older tractors, so shutting off the engine and locking out the equipment is important. Also, keep the unloading wagon’s emergency shut-off device in good working condition because it could be instrumental in saving your life.

As forage is unloaded from the wagon into the silo blower hopper, it is moved by auger or conveyor to the blower fan which forces it into the silo. The main hazards of the silo blower are the PTO shaft, the exposed conveyor or auger, and the blower fan blades. Like the forage wagon, silo blower injury incidents are more likely to occur when the machine becomes plugged up. When this happens, do not climb onto the hopper or use hands or feet to force forage into the blower blades. Before unplugging, disengage the power, shut down the tractor and remove the keys from the ignition before removing the clogged area and make sure the freewheeling blower fan blades have completely stopped turning.

Power Take-Off

Another danger point in the silo filling process is the PTO shaft which powers the unloading wagon and the silo blower. A PTO shaft rotates at either 9 (540 rpm) or 16 (1,000 rpm) times per second at full operating speed. At these speeds, a person’s arm can be pulled into and wrapped around the PTO stub or driveline shaft in less than a second. The main PTO hazards include the stub, driveline, and driveline separation. The first step in guarding against a PTO entanglement is proper shielding of the PTO master stub and the driveline. In addition to shielding, other ways to protect again a potential PTO incident is to wear close-fitting clothing and secure long hair under a hat when working around equipment. Always walk around tractors and wagons instead of stepping over shafts which can result in an entanglement. During silo filling, make sure that the unloading wagon and silo blower are securely fastened to the tractors’ drawbars; otherwise, the PTO could separate. If the PTO separates on the tractor powering the blower pipe, it could also vibrate the blower pipe down.

Children and Bystanders

The silo filling area should be restricted to only those people directly involved with completing this task. This is especially true for children and unneeded helpers or bystanders. Non-essential persons not only pose a threat to them, but also increase the hazard to the machine operator by interfering with their level of concentration. Children are often curious during silo filling time and they want to climb on wagons and tractors. Youngster may also want to help with silo filling without fully understanding the hazards associated with the machinery. Farmers should allow only those individuals necessary to participate in filling the silo to be in that area of the farm.

Tractor Usage

Tractors are used during the harvest season in varying capacities such as operating an unloader or transporting wagons. When choosing a tractor for use during harvest, choose a tractor that is equipped with a rollover protective structure (ROPS) and has the correct horsepower and braking power for the job that you need to complete. Field conditions during harvest can include ruts, uneven terrain, and muddy conditions that require the operator to be aware of the conditions and make adjustments if needed. If a tractor tire hits a stump or rut it could possibly throw the operator if they are not wearing a seatbelt or cause the tractor to overturn. Before entering a field on the tractor, examine the area for changes since last harvest such as debris, fallen limbs, or ditches.

Maintaining a slower speed in the fields can also reduce your risk of an incident especially when turning in the field. Another way to reduce your risk of an overturn incident is to use a non-front end loader equipped tractor because the loader can change the center of gravity on the tractor. The operator should plan their harvest so that they are traveling downhill on steep slopes with equipment to reduce the risk of an overturn incident.

Noise Exposure

Sound is measured in decibels (dB) and farm tractors are known to generate sound levels in a range of 74-112 decibels. The Occupational Safety and Health Administration (OSHA) recommends hearing protection when workers and bystanders are exposed to 85 decibels or more for an 8-hour work day. During silo filling, workers are exposed to high noise levels because there are typically two tractors with one operating an unloader wagon, and the other a silage blower simultaneously. Noise levels at, or over 100 dB, are common with this farming activity. Sound levels of 100 dB or more for even short periods of time, can result in permanent hearing loss. There are three ways workers in excessive noise work areas can be protected. Personal protective equipment (PPE) such as ear plugs or ear muffs can significantly reduce the noise level. Look for a NRR (noise reduction rating) on the packaging of new hearing protection devices of at least 25. This would reduce a sound level of, for example, of 100 dB to 75 dB if the ear muffs or plugs were properly maintained and fitted. Other interventions would include limiting the worker’s exposure by maintaining the tractors and machinery in good condition, and requiring that the workers rotate out of the high noise area after shorter work sessions of no more than 10-15 minutes for 100 dB levels. See fact sheet E48 Noise Induced Hearing Loss in Agriculture for more detailed information on noise-induced hearing loss.

Silo Gas

Machinery operation is not the only type hazard associated with silo filling. Be aware of the potential threat of silo gases which typically reach the highest concentrations levels between 12 and 72 hours after filling. If you must enter the silo during this time, protect yourself by wearing a self-contained breathing apparatus (SCBA). If you do not have access to a SCBA, you should stay out of the silo. Dangerous levels of silo gas may be present for an additional two to three weeks. To enter without a self-contained breathing apparatus during this first two to three week period, do the following: run the silo blower for 15 to 45 minutes prior to and during entry, maintain visual contact with a second person outside the silo, and wear a body harness attached to a lifeline and secure anchor point.


Remember, filling the silo is a complex operation which involves the hazards of raising heavy equipment; working in close quarters with PTO powered machinery; and exposure to deadly silo gases. While this may sound like a potential disaster area, a safe harvest can be completed if workers understand the dangers and following recommendations. Remember the key recommendations is to always disengage the PTO and shutdown the tractor before unplugging clogged areas on the equipment, walk around revolving shafts, keep children and others away from the worksite, and be alert for silo gas.