Tribometers and Coefficient of Friction
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People slip, trip, and fall on walkways, sidewalks, paths, parking lots, steps, and stairways for many reasons. Among the more common reasons are clumsiness, a slippery surface, not paying attention, and defects in the surface or steps where the person fell. Many people walk in places where there are defects, but not all slip, trip, and fall injuries occur because of negligence.
This is not a criticism of the concept of coefficient of friction measurements or a comment on their value when properly used. This discussion purely applies to the widespread misuse of coefficient of friction measurements in evaluating slip and fall incidents. This is not applicable to properly made slip resistance measurements used, for example, by flooring manufacturers.
Coefficient of friction is the ratio of the force of friction between two bodies and the force pressing them together. Static friction is the friction force when an object is not moving. Static friction is the force that prevents a block from sliding down an incline. Kinetic friction (Sometimes called dynamic friction) is the force when two objects are moving relative to each other. Generally, the kinetic coefficient of friction is less than the static coefficient of friction.
Coefficient of friction and slip resistance are often used interchangeable. Although they are related concepts, they are not identical. Slip resistance is what one is looking at in slip and fall incidents.
A slippery surface can cause a fall. Years ago, a block of a known weight was dragged across the surface to measure the static slip resistance. However, slip, trip, and fall incidents occur when people are walking, so the dynamic slip resistance appears to be more appropriate.
A tribometer is a device for measuring tribological quantities. Tribology is the science of the interaction between surfaces in motion relative to each other. Tribology includes the application of the principles of friction, lubrication, fluids and fluid flow, materials properties. In slip and fall incidents, human dynamics and human reaction to a perceived loss of friction also play a roll. Tribology includes mechanical engineering, materials science and engineering, fluid flow, physics, and chemistry. When analyzing slip and fall incidents using tribology, human factors must also be included.
Various methods of measuring dynamic slip resistance. have been devised and some have been accept by Courts. In many cases, these measurements are made by self-proclaimed safety experts with no Engineering background. The device used to make these measurements is often referred to as a tribometer (sometimes called a slipometer), although there are other trade names by which a tribometer is called. In some cases, Courts and Insurance companies have accepted these measurements blindly, and used them to decide negligence or pay a settlement.
Tribometers do not slip and fall. People slip and fall. It is important to remember this when looking at tribometer slip resistance measurements. There are many problems with blindly taken dynamic slip resistance measurements:
- There is no objective standard for measuring slip resistance on existing steps, paths, walkways, floors, driveways, etc. Standards exist for the measuring slip resistance of manufactured flooring, and these standards have been misapplied to existing construction.
- Many people do not know exactly where they fell, or where their foot was located at the moment before they fell. The measured slip resistance can be different at different points on a surface.
- The measuring devices often do not accurately reproduce the conditions when the person fell. The operator of the measurement device often cannot accurately reproduce the motion of the person's foot before the slip, trip, and fall incident.
- The slip resistance measurement can be influenced by the person taking the measurement. All surfaces have some deterioration. Based on irregularities in the surface, one can set up the tribometer to show a higher or lower slip resistance measurement. In a Court trial, there may be two experts who testify to significantly different slip resistance measurements on the same surface.
- The actual slip resistance depends on the person's footwear. Often, the measurement is taken with a generic material.
- Because of irregularities in the surface, the size of the contact area is critical. Someone's shoe may be contacting different sections of a surface with different slip resistance measurements.
- Many people slip on wet surfaces, so it has become a common practice to pour water on a surface and measure the coefficient of friction. The quantity of water and impurities in the water can influence slip resistance. Spilling a cup of water on a surface does not accurately reproduce the conditions that existed when a person fell. All that is often determined is that a wet surface is more slippery than a dry surface.
- The tribometer does not accurately measure the slip resistance on a wet surface even if the exact liquid and floor conditions can be reproduced. This is because the dynamics of the tribometer on a liquid surface are considerably different than the dynamics of a person's footwear.
- Slip resistance measurements do not take into account hydroplaning-type phenomenon. (Hydroplaning and aquaplaning are generally reserved for the behavior of rolling objects like tires). Hydroplaning occurs when a film of water builds up between a tire and the road, causing the tire to loose contact with the road. A similar phenomenon occurs when there is a layer of water between shoes and a floor.
- Slip resistance measurement ignores the fact that when a human being walks, it is a feedback process. The human gait is a closed-loop feedback system, where the brain makes adjustments based on expected conditions and conditions found. Measuring the dynamic slip resistance ignores the feedback part of a human's walk.
In some cases, measurement of slip resistance (often by non-Engineer self-proclaimed safety experts) has replaced an evaluation of the defects and cause of the slip, trip, and fall accident by a Professional Engineer. Just measuring the slip resistance, without determining why the person slipped and fell, is bad engineering.
The Harold Krongelb P.E. does not use questionable slip resistance measurements in evaluating the cause of a slip, trip, and fall injury. Rather, actual defects in the design or maintenance are reported. In many cases, these defects are code violations that provide objective evidence as to the cause of the slip, trip, and fall injury.
Harold Krongelb P.E.
Harold Krongelb P.E. performs all Engineering inspections where litigation or arbitration is being considered. Harold Krongelb P.E. is a State of New York Licensed Engineer with extensive experience in the preparation of reports, preparation of affidavits for summary judgment and other court motions, along with testimony experience.
Harold Krongelb P.E. has experience with slip, trip, and fall incidents, playground incidents, injuries caused by falling ceilings, injuries caused by other building defects, injuries caused by sports equipment, injuries caused by scalding hot water, analysis of the dynamics of vehicle accidents, and other Engineering-related analysis, reports, and testimony. Harold Krongelb P.E. also has experience with Building Codes, Engineering analysis when only photographs and depositions are available, assessment based on historical codes and images, computer systems, and other areas of Engineering.
Proximate cause is often defined as the immediate or closest cause. When examining a site or building where a personal injury accident occurred, it is important to determine the proximate cause of the accident. Some Engineers cite irrelevant deficiencies as the cause of an incident. For example, if a client fell at the top of a set of steps, hazards near the bottom of the steps are irrelevant.
There are many experts who look to find any defect or hazard and never determine if it is the proximate cause of the accident. We only include relevant defects, hazards, and codes in the reports. Engineering reports that include irrelevant information may look good, but these reports can be defeated in summary judgment.
Trivial or De Minimis Defects
Who decides if a defect is de minimis? Is it decided by the Attorneys, the law, or the Engineer? Engineers need to take into account whether a defect is de minimis in determining the proximate cause of an accident and subsequent injury. It a Professional Engineer determines that a defect is the proximate cause of an injury, then it is axiomatic that the defect is not de minimis.
Foreseeable Incidents and Reasonable Care
The cause of injury is often the defendant's failure to use reasonable care in the maintenance or repair of a building. Engineers need to look at the site conditions, and determine if the owners created a defect or hazard by failing to use reasonable care. It is also important to determine if it is foreseeable that the condition could cause an injury.
Engineer Experts or Hired Guns?
Some expert witnesses are "hired guns". These expert witnesses provide a report in favor of their client regardless of the facts or reality. We never exaggerate or embellish findings. If there is no defect, that is what you are told. There are Attorneys who will never use us because we do not embellish the reports in favor of their clients.
Embellishing a report or relying on a code reference that is not applicable may work if the insurance company settles based on an inaccurate report. In other cases, the expert's statements in the inaccurate report cannot stand up to summary judgment or under cross-examination in a Court of Law. We provide a professional opinion based on the reality that will hold up to summary judgment or under cross-examination.
Words are Important
It is important to know what not to say and how to phrase findings. Judges typically do not accept medical, psychological, legal, financial, etc. professional opinions from Engineers. Yet some Engineer routinely provide these opinions in their reports. These non-Engineering opinions often do not hold up under summary judgment.
It is important not to make statements that might be interpreted (or perhaps misinterpreted) as being a non-Engineering statement. Even an otherwise well written report can be thrown out in summary judgment if an otherwise accurate statement is misinterpreted.
Everything in our reports is designed to stand up to summary judgment and under cross-examination during trial. This has been tested during many court trials and summary judgment decisions.
"Old School" Engineers
After World War II, Engineering moved from war-related work to developing products for consumers and of national interest (such as the space program). There were few universally accepted standards other than building codes and mechanical standards (for example, screw sizes or wire sizes). Many Engineers who graduated before the mid-1970s created their own standards, possibly changing these standards from project to project.
Although organizations such as the American National Standards Institute (ANSI) began developing standards after World War I, many of these standards did not acquire the force of law or become well accepted practices until the 1960s. In addition, organizations such as the Environmental Protection Agency (EPA) and the National Highway Traffic Safety Administration (NHTSA) set and enforced standards. Organizations such as ANSI and the Consumer Product Safety Commission (CPSC) set standards that may not have the force of law, but are universally followed.
Some "Old School" Engineers retired from full-time employment to become consulting Engineers. These "Old School" Engineers approached accident investigations the same way they had worked their whole life. The result was reports that reflected the "Old School" Engineer's standards or the Engineer's interpretation of Building Codes without regard to the realities of how the Department of Buildings interprets codes or good and accepted practices.
An example of the difference between old self-created standards and newer standards can be seen in the change in automobile safety in the last 50 years. In the late 1950s, automobile manufacturers advertised how safe their cars were. The standards for safety were set by automobile manufacturers. In the late 1950s, General Motors stated their cars had a "safety X-frame" in advertising.
The Insurance Institute for Highway Safety released a video in 2009 that showed a frontal offset collision between a 1959 Chevrolet Impala and a 2009 Chevrolet Malibu. Analysis after the collision showed that the driver of the 1959 Impala would have died instantly, and the driver of the 2009 Chevrolet Malibu might have sustained a knee injury.
This video illustrates the difference between self-created standards and well developed and accepted standards. By the self-created standards of 1959, the Impala was "safe". By today's standards, the 1959 Impala offers little passenger protection.
When choosing a Professional Engineer, be careful of Engineers who define their own standards. While they may sound good, they will hold up no better under cross-examination based on today's standards than the 1959 Chevrolet Impala held up against the 2009 Chevrolet Malibu.
Accident or Incident
Accident has no clear meaning. An accident could be an injury caused by a property owner's negligence. An accident could be a mistake by the injured party. An accident could be caused by a contractor's negligence.
We evaluate incidents. Someone is injured, and that is the incident. It is only after the incident is evaluated that the cause and negligence can be established.
When an incident is evaluated, there is no pre-conceived notion of who is negligent or how the defect or hazard was created. The incident is evaluated from an unbiased point of view, including the application of Engineering principles. Only after all the facts related to the incident are determined can negligence and blame be determined.
Building Codes and
It is important to determine which building codes, regulations, and standards are applicable to a specific incident. When a building is constructed, it is constructed under the codes, regulations, and standards are in force at the time of construction. Heimer Engineering has an Extensive Library of Historical Building Codes, Heimer Engineering's searchable Building Code library includes:
City of New York Codes
- 1877 City of New York Building Code
- 1892 City of New York Building Code
- 1899 City of New York Building Code
- 1900 City of New York Building Code
- 1901 City of New York Building Code
- 1906 City of New York Building Code
- 1916 City of New York Building Code
- 1938 City of New York Building Code
- 1968 City of New York Building Code
- 2008 City of New York Building Code
- 2014 City of New York Building Code
State of New York Building Codes
- 1951 State of New York Building Code
- 1954 State of New York Building Code
- 1959 State of New York Building Code
- 1964 State of New York Building Code
- 1972 State of New York Building Code
- 1977 State of New York Building Code
- 1978 State of New York Building Code
- 1984 State of New York Building Code
- 2004 State of New York Building Code
- 2008 State of New York Building Code
- 1938 FHA Construction Standards
- 1915 Fire Underwriters Model Code
- State of New York Multiple Dwelling Law
- State of New York Tenement Law
- State of New York Department of Transportation Standards (roads, signs, traffic signals, etc.)
- Federal Transportation Standards (roads, signs, traffic signals, etc.)
- City of New York sidewalk regulations
- Electrical Codes
Most important is knowing which codes apply to which locations. If irrelevant codes are cited, the Professional Engineer's report is of little use.
Codes, regulations, and standards change over time and modifications are made to existing buildings and sites. It is important to examine available history of the building to determine what codes, standards, and regulations are applicable.
The term "grandfathered" is often applied to existing construction. Saying a building is "grandfathered" is often inaccurate. "Grandfathered" only applies to original unaltered construction. "Grandfathering" requires that no changes were made without required permits and approvals. Once a change is made to a building, newer building codes, standards, and municipal regulations become applicable. For example, making a change to the interior of a building might require that exterior steps be brought up to modern codes. Just because a building complied with the applicable codes at the time it was constructed does not mean that hazardous defects are permitted.
Even if the building or site is unaltered, it may not have complied with the codes, standards, and regulations in effect at the time the building was constructed. Many older codes, standards, and regulations are not as clearly written as their more modern counterparts.
The Engineer needs to consider both the wording and the correct application of the code, standard, or regulation. In addition, the injury may have been caused by faulty maintenance, which may be a violation under current codes.
Just because a building complied with the applicable codes at the time it was constructed does not mean hazardous defects are permitted. Failing to maintain a building or site in a safe condition is never "grandfathered".
Expert Witness Court Testimony
Clearly written reports help make it clear how defects and hazards at a site contributed to an accident and injury. Clearly written accurate reports can help you settle a case and avoid the time and expense of a trial.
If the case has to be litigated in a court of law, Harold Krongelb P.E. has served as expert witness and has qualified as and expert witness in United States Federal Courts and at all levels of State of New York Courts.
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Heimer Engineering℠ performs home inspections, building inspections, condo inspections, and co-op inspections in the State of New York. Expert witness services are provided regarding playground injuries, parking lot, walkway, and stairway slip, trip, and fall.
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