Trip vs. Slip: A Biomechanic View

By Dr. Richard Baratta | January 30, 2012

Understanding the Legal and Financial Implications Between a ‘Trip’ and a ‘Slip’


The legal and financial ramifications of an accident on a business’ property balance precipitously on the analysis of a “slip and fall” versus a “trip and fall.” There is a critical distinction between slip hazards and trip hazards.

A slip is when there is insufficient friction between an individual’s footwear and the floor surface. The common phrase is, “If it slides, you have a slip.”

A trip is something fundamentally different. Rather than a loss of friction, something, possibly including too much friction, prevents the foot from coming fully through its normal swing phase of the walking motion. This can be caused by a tile that sticks up, an irregularity in a surface, broken or cracked sidewalks, the edge of a rug, building entry “walk off” mats, loose tiles, indoor or outdoor planter boxes, or various other problems.

The standards for a trip hazard will depend on the area, whether there is a transition between surfaces, or whether the area is a means of egress. And the standards may vary from a quarter inch to a half inch.

When a fall occurs, whether injuries are reported or not, the incident may carry consequences well into the future.

Different Injuries

Slips and trips present different sets of injuries, but a careful analysis of those injuries can lead a skilled biomechanical engineer to answers on how exactly the person fell. The injuries themselves — forearm fractures, shoulder dislocations, knee ligament damage or head injuries — are all part of cause-effect relationships that provide clues to what and how the fall happened. Where a person was before he or she fell, where he or she landed and how he or she was moving is critical to understanding the incident and its consequences.

By definition, biomechanics is applying principles of engineering mechanics to biology and medicine. In terms of injury-related accident analysis, there are two fundamentally different things that can come into play: first, an analysis of human motion (the forces and speeds that are involved in how people move) and second, the relationship between forces and injuries.

Biomechanists look at human tissues as an engineering material: What does it take to cause a failure? What is its tolerance? What are the mechanisms that are involved in causing a specific injury or failure to the tissue? And most importantly in the context of motion, what are the mechanisms that result from each type of fall?

Inspect and Analyze

Not surprisingly, the common culprits for slip hazards are wet floors, resulting in a reduction of the friction between foot and flooring. It is critical to have a civil engineer and/or a biomechanical engineer inspect and notate the condition of the area where the slip occurred as soon as possible, because floor covering and floor maintenance can affect the evidence. If there is any change in the flooring prior to inspection of the surface weeks or months down the line, there is a possibility the factors that could have provided critical information for establishing the cause and effect relations will be gone. Carpets get replaced, tiles are changed, and even something as innocuous as a change in cleaning contractors can affect the friction of the surface, effectively erasing important evidence.

The first step in analyzing an accident is to gain an overall understanding of what happened. Witness statements are always good to have, but even more effective “down the road” is the skillful analysis of an engineer with the ability to inspect the area and conduct modeling that captures the dynamics involved in the evolution of the accident. This information will be essential in recreating the incident months or years later, when eyewitness accounts and memories may prove unreliable under legal examination.

The second step of the analysis is to gain an understanding of the injuries the person sustained, or the injuries the person is claiming. A multi-disciplinary engineering approach can effectively ascertain not only the particular injuries, but also help to clarify the diagnosis in relation to the specific effects of the individual’s fall.

Step three is to gain an understanding of the relationship between the accident and the individual’s injuries, and then to identify all of the evidence that will lead to a proper assessment of whether it was a trip or a slip. That also will help to identify and correct the hazard or hazards that caused the incident. This critical step is often missed.

How Biomechanics Can Help

It is imperative to understand the biomechanics the person underwent during the accident. Was the person carrying something? What thing(s) did he or she strike? How did the person fall? Which parts of the body made contact with objects or surfaces? What kind of mechanisms were the person’s body tissues exposed to, and are those mechanisms causally related to the diagnosis by physicians?

Given that information, it is possible to distinguish what happened in the accident from what was happening immediately prior to the accident. Most importantly, it can be determined what has been scientifically proven to be unrelated.

When a fall occurs, whether injuries are reported or not, the incident may carry consequences well into the future. Biomechanical engineers can help when:

  • Documenting a scene after a reported incident, because injuries may not be claimed or reported until months or years afterward.
  • Questions arise about the type or severity of a person’s injuries that are inconsistent with what is claimed.
  • Investigation is needed to discern whether the property complies with all required codes or recommended standards.
  • It is not clear whether the incident was due to a slip or a trip hazard.

In all incidents involving injury-related accidents, the best strategy is to work with a firm that has forensic experts with the interdisciplinary experience and insight to assess the potential risks of exposure. It also may be beneficial to find a firm familiar with the legal and financial ramifications from a slip or trip accident that can take many different twists and turns.

About Dr. Richard Baratta

Dr. Baratta is vice president with Rimkus Consulting Group Inc. in Houston, where he provides consulting expertise on injury causation biomechanics, accident reconstruction, medical device failures and intellectual property. He also provides expertise in relation to modified, high-performance and racing automobiles, and high-performance vehicle occupant protection systems and injury analysis.

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