Tractor Stability

NH Tractor

NH Tractor

(Photo Source: Pennsylvania State University – Ag Safety and Health)

Use the following format to cite this article:

Tractor stability. (2014) Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice. Retrieved from http://articles.extension.org/pages/70338/tractor-stability.

The tractor is the most recognized piece of equipment on a farm or ranch, but it is also associated with incidents that can lead to serious injuries or death. There are various makes, models, and designs for tractors, but the basic components of tractor stability remain the same. By understanding tractor stability, you can reduce your potential for a tractor overturn incident.

Understanding Center of Gravity

The center of gravity for any object is the point on the object where all parts perfectly balance one another. For example, the point at which a pencil will balance on your finger is its center, and this center point is easily found by practicing balancing a pencil on the end of your finger. But finding the center point on larger objects is not always as simple. For example, the center of gravity on a two-wheel drive tractor is typically in the center of the tractor body as you look from right to left, but is about 10 inches above and 2 feet in front of the rear axle as you look from back to front. This center of gravity placement disperses the weight so that 30 percent of the tractor’s weight is on the front axle and 70 percent is on the rear axle.

The center of gravity must remain within the tractor’s stability baseline for the tractor to remain in an upright position. Stability baselines (shown below) are imaginary lines drawn between points where the tractor tires contact the ground.

Stability Baseline Image

(Photo Source: Canadian Centre for Occupational Health and Safety)

Compared to an automobile, the center of gravity is higher on a tractor because the tractor needs to be higher in order to complete operations over crops and rough terrain. Terrains, attachments, weights, and speeds can change the tractor’s resistance to turning over. The following examples describe situations in which the stability of a tractor can change:

  • Whenever mounted equipment is raised, the center of gravity is also raised, decreasing tractor stability.
  • Any changes in weight from an attachment—such as a front-end loader, bale fork, and so on—or load can shift the center of gravity toward the weight.
  • Implements that are side mounted shift the center of gravity toward the attachment.

Tractor Stability

In addition to the center of gravity, other factors important to tractor stability include centrifugal force, rear-axle torque, and drawbar leverage.  

Centrifugal Force

Centrifugal force is the outward force of objects moving in a circular path. In regards to a tractor, centrifugal force is the force that is trying to roll the tractor over when it is making a turn. As the radius of the turn decreases (in a sharp turn) the centrifugal force increases. There is a relationship between centrifugal force and speed, but it is not directly proportional (for example, when the tractor speed is tripled from 3 mph to 9 mph, the centrifugal force increases 9 times). Since centrifugal force increases when turning, it is often a factor in a side overturn. The effect of this centrifugal force on stability is even greater when operating a tractor on sloped terrain.

Rear-Axle Torque

Rear-axle torque is the transfer of energy between the engine and the rear axle of a two-wheel drive tractor. When the clutch is engaged on this type of tractor, it results in a twisting force, or torque, which should rotate the tires and move the tractor forward or backward. If the rear tires are stuck (as in mud) or blocked from rotating, the rear axle is unable to rotate properly, so the tractor chassis rotates about the axle. This results in the front end of the tractor lifting off the ground, which can cause the tractor’s center of gravity to move past the rear stability baseline. This type of incident is called a rear overturn, and the “point of no return” (shown below) can occur in less than a second, which is not enough time for the operator to react and try to stop the rearward motion. A rear overturn incident with a four-wheel drive tractor can occur, but it occurs less frequently than with a two-wheel drive tractor because more weight is carried on the front axle, and the center of gravity is closer to the front of the tractor. By design, the front tires of four-wheel drive or front-wheel assist tractors have more traction and will not rise off the ground as easily as the wheels of a tractor with two-wheel drive.

Point of No Return Rear Tractor Overturn

(Image Source:Safety Management for Landscapers, Grounds-care Business, and Golf Courses, John Deere Publishing, 2001. Illustration reproduced by permission. All rights reserved)

Drawbar Leverage

Drawbar leverage is another stability factor in a rear overturn incident. When a two-wheel drive tractor is pulling a load, there is a backward and downward pull that causes the rear tires to become a pivot point. An “angle of pull” is created between the ground’s surface and the attachment point on the tractor that acts as a force to tip the tractor rearward. The drawbar on a tractor is designed to counteract the rearward tipping potential of pulled loads; however, when a load is attached to the tractor at any point other than the drawbar, the drawbar design is no longer effective in preventing rear overturn incidents.

Tractors are commonly used to pull stumps out of the ground. A tractor is hitched safely when the log chain is wrapped around the tree stump and attached to the tractor drawbar. The log chain is properly attached to the tractor drawbar, providing a lower “angle of pull” and decreasing the leverage necessary to tip a tractor rearward. Unsafe hitching occurs when the load is attached to a point other than the drawbar. If the log chain is attached to the rear axle instead of the drawbar, the “angle of pull” and leverage do not decrease as the tractor’s front end rises. When hitching to something that is higher than the drawbar hitch point, such as the rear axle, there is increased pressure on the rear tires. This might prevent the tractor tires from slipping and cause the front end to lift. Click here to view videos of tractor stability and tractor overturn incident demonstrations.

 

Use the following format to cite this article:

Tractor stability. (2014) Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice. Retrieved from http://articles.extension.org/pages/70338/tractor-stability.

 

Sources

How can you maintain stability on various gradients? (2002) Canadian Centre for Occupational Health and Safety. Retrieved from http://www.ccohs.ca/oshanswers/safety_haz/tractors/stability.html.

Murphy, D. (2014) Tractor overturn hazards. Penn State College of Agricultural Sciences, Cooperative Extension. Retrieved from http://extension.psu.edu/business/ag-safety/vehicles-and-machinery/tract….

Tractor stability (2012) Canadian Centre for Occupational Health and Safety. Retrieved from http://www.ccohs.ca/oshanswers/safety_haz/tractors/stability.html.

 

Reviewed and Summarized by:
Linda M. Fetzer, Pennsylvania State University – lmf8@psu.edu
Andrew Merryweather, University of Utah – a.merryweather@utah.edu
Dennis J. Murphy, Pennsylvania State University – djm13@psu.edu
Charles V. Schwab, Iowa State University – cvschwab@iastate.edu
Aaron M. Yoder, University of Nebraska Medical Center – aaron.yoder@unmc.edu

Identifying and Correcting Hazards on Your Farm or Ranch

Tractor Safety Training

(Source: Penn State Ag Safety & Health)

Use the following format to cite this article:

Identifying and correcting hazards on your farm or ranch. (2013) Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice. Retrieved from http://articles.extension.org/pages/69135/identifying-and-correcting-haz….

 

The majority of serious farm incidents involve machinery and equipment, but many hazards can be found in all areas of farm operations. Many of these incidents can be prevented through an inspection and correction of the hazard. The challenge is that most agricultural producers do not know how to properly assess and correct hazards on their farm operation.  

The Farm/Agriculture/Rural/Management-Hazard Analysis Tool (FARM-HAT) was developed by the Pennsylvania State University and is the most comprehensive on-line tool for assessing and identifying ways to correct hazards in 11 major categories including, but not limited to, farm operations, dwellings, agritourism, and tractors. FARM-HAT can be used by farmers, extension educators, insurance agents and others that are interested in improving the safety of a farm operation, equipment or rural enterprise.  

Take the inspection of your farm operation very seriously and also recruit other farm family members to participate in the process. Inspections can be done at various times of the year. Consider inspecting yours tractors and machinery over the winter so that you have time to complete repairs before the spring when you are preparing for the planting season.

In addition to FARM-HAT, other resources are available for specialized inspections including barns, machinery and tractors. Listed below are links to checklists for farm operations.

Resource Links – Pick a Site and Start Your Farm Inspection:

  1. FARM-HAT (Penn State University)
  2. Evaluate Equipment for Dangers (Iowa State University)
  3. Your Personal Farm Safety Audit (Agricultural Safety and Health Network)

 

Use the following format to cite this article:

Identifying and correcting hazards on your farm or ranch. (2013) Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice. Retrieved from http://articles.extension.org/pages/69135/identifying-and-correcting-haz….

 

Citations:

Farm/Agricultural/Rural Management Hazard Analysis Tool. (2010) Penn State Agricultural Safety and Health. Retrieved from http://extension.psu.edu/business/ag-safety/farmhat.

Folsom, R. (2009) Barn and farm inspection checklist. Virginia Cooperative Extension. Retrieved from https://vtechworks.lib.vt.edu/bitstream/handle/10919/48862/VCE_Barn_Farm….

Hanna, M., Schwab, C., and Miller, L. (1998) Evaluate equipment for dangers. Iowa State University Extension and Outreach. Retrieved from http://nasdonline.org/2469/d002295/safe-farm-evaluate-equipment-for-dang….

Tractor Safety Checklist (n.d.). Canadian Agricultural Safety Association.  Retrieved from http://aghealth.usask.ca/resources/documents/TractorModulePDF.pdf.

 

Reviewed and Summarized by:
Linda M. Fetzer, Pennsylvania State University – lmf8@psu.edu
Dennis J. Murphy, Pennsylvania State University – djm13@psu.edu
Aaron M. Yoder, University of Nebraska Medical Center – aaron.yoder@unmc.edu

Preventing Tractor Runover Incidents


Use the following format to cite this article:

Preventing tractor runover incidents. (2013). Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice. Retrieved from http://www.extension.org/pages/67752/preventing-tractor-runover-incidents.

 

The main types of tractor incidents include rollovers, power-take off entanglements, and runovers. Runover incidents that occur can involve either the operator or a bystander. Tractor manufacturers have made changes (e.g., safety start system) to reduce the risk of certain types of runover incidents. However, all types of runover incidents can be prevented by understanding the hazard and following specific safety recommendations.

Runover of Extra Rider

A runover incident can occur when an extra person on the tractor falls off the tractor and is run over by the tractor or an attachment. There should never be an extra rider on a tractor. The only exception is that a few newer, larger tractor models with an enclosed rollover protective structure (ROPS) cab have a factory-installed extra seat for temporary instructional purposes only. Most tractors used on farms and ranches only have one seat and that is for the operator only. Runover incidents can occur to a person who rides on the tractor drawbar, axle housing, side links of the three-point hitch, rear-wheel fender, or other area around the operator’s seat. When standing or sitting on one of these areas, a person can lose his or her grip, be thrown from the tractor, and be run over by the tractor or an implement.

Prevention Step:

  • Never allow an extra rider on a tractor.

Runover of Operator

A tractor runover incident can occur to the operator if he or she falls from the moving tractor and is run over by the tractor tire or an attachment. This type of incident can occur if the operator does not buckle the seat belt on a tractor with a ROPS or if an older tractor does not have a ROPS. An operator can be knocked out of the tractor seat by a tree branch or another obstacle. The operator can also lose balance if the tractor hits a tree stump or encounters rough terrain. An operator can be run over if he or she tries to mount or dismount a moving tractor.

Prevention Steps:  

  • Never dismount or mount a tractor or machine while it is in motion.
  • Use tractors with a ROPS with seat belt, and fasten the seat belt every time you operate the tractor.  
  • Slow down when driving on rough terrain or where hidden obstacles may exist.
  • Before leaving the tractor seat, always shut off the tractor and set the brake or place the tractor in PARK.
  • Make sure that the tractor’s brakes and clutch are in properly working condition.
  • Replace old pan-type seats with seats that have back and arm rests.

Runover of Person Located on the Ground due to Bypass Starting

A person located on the ground near the tractor can be involved in a tractor runover incident. This type of runover can happen to the operator or a bystander if someone attempts to start the tractor from the ground (e.g., bypass starting) and the tractor is in gear.

Prevention Steps:

  • Always start the engine from the operator’s seat.
  • Add or leave the bypass shield on the starter terminals.
  • Keep the tractor’s electrical system in good working condition.
  • Do not disable or wire around the safety interlocks installed by the manufacturer.
  • Always visually check in all directions for people around the tractor before moving the tractor.
  • Reduce your speed when operating the tractor in an area where people are located.
  • Instruct everyone how to get the attention of a tractor operator before approaching the tractor.
  • Provide a safe play area for children to keep them away from farm or ranch work areas.
  • Make sure that all children at your farm or ranch are properly supervised at all times.

Runover of Person Located on the Ground near the Tractor

Bystanders and children are at risk of a tractor runover incident if the operator does not see them. This is especially a concern if they approach a moving vehicle while it is hauling a load in a bucket or using a bale spear attached to the front or rear of the tractor and are knocked down in its path. Bystanders do not always realize they cannot be seen by the operator. They can slip and fall under a wheel of the tractor or equipment.

Prevention Steps:

  • Always visually check in all directions for people around the tractor before moving the tractor.
  • Reduce your speed when operating your tractor in an area where people are located.
  • Instruct everyone how to get the attention of a tractor operator before approaching the tractor.
  • Bystanders should not approach a moving tractor until recognized and acknowledged by the operator.
  • Provide a safe play area for children to keep them away from farm or ranch work areas.
  • Make sure that all children at your farm or ranch are properly supervised at all times.
 

 

 

Use the following format to cite this article:

Preventing tractor runover incidents. (2013). Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice. Retrieved from http://www.extension.org/pages/67752/preventing-tractor-runover-incidents.

 

 

Sources:

Harshman, W., Yoder, A., Hilton, J., & Murphy, D. (2011) HOSTA task sheet 4.2: Tractor Hazards. Pennsylvania State University. National Safety Tractor and Machinery Operation Program. Retrieved from http://www.extension.org/sites/default/files/NSTMOP%20Task%20Sheets%20Se….

Miller, J. & Fragar, L. (2006) Farm machinery injury: Injury involving tractor run-over. Retrieved from https://sydney.edu.au/medicine/aghealth/uploaded/Research%20Reports/farm….

Smith, D. (2004) Safe tractor operation: Runover prevention. Texas A & M System AgriLIFE Extension. Retrieve from http://agsafety.tamu.edu/files/2011/06/SAFE-TRACTOR-OPERATION-RUNOVER2.pdf.

 

Reviewed and Summarized by:
Linda M. Fetzer, Pennsylvania State University – lmf8@psu.edu
Dee Jepsen, Ohio State University jepsen.4@osu.edu
Dennis J. Murphy, Pennsylvania State University (Has since retired)
Charles V. Schwab, Iowa State University cvschwab@iastate.edu
Aaron M. Yoder, University of Nebraska Medical Center – aaron.yoder@unmc.edu