Expert Testimony in a Premises Liability Case

July 29, 2009

By: David K. Jaffe

Coefficient of Friction & Unsafe Design

In establishing whether a particular condition is unreasonably dangerous, many slip and fall litigants frequently call on a variety of expert witnesses to prove such things as the existence of a hazardous condition, constructive notice of such a condition, the improper application of wax and similar floor treatment products, unsafe designs, or methods of construction or operation. Once qualified, an expert witness can render an opinion as to the safety of the particular hazard at issue which often carries a significantly greater probative value than ordinary lay testimony. Such testimony must be within the scope of the original pleadings, and it always remains subject to the trial court's discretion concerning the witness' qualifications, as well as the relevancy and admissibility of their proffered testimony.[1]

Expert testimony, once admitted into evidence, is not binding on the trier of fact in slip and fall cases. Instead, the trier of facts is often called on to resolve conflicts even among experts. Moreover, even when expert testimony is allowed for purposes of establishing that a particular injury-causing condition on the premises was unreasonably dangerous, the plaintiff must still establish that the injury was in fact caused by such a condition.

Coefficient of Friction

Typical of the types of issues frequently addressed by expert witnesses in slip and fall cases are test results establishing the degree of slipperiness of particular substances and floor types.[2] Compared in terms of their "coefficients of friction," a figure which is obtained by dividing the drag necessary to move an object across any given surface by the weight of the object being pulled, generally those surfaces which have coefficients of friction of less than 0.5 are considered slippery and potentially unsafe.[3] Among the most commonly encountered floor types in slip and fall cases, marble and terrazzo floorings are normally considered to be more slippery than other types of flooring materials, such as asphalt and vinyl tile or even concrete.

Two other variables which can dramatically affect the coefficient of friction for virtually any type of flooring material are the type of shoes worn by the injured plaintiff and the amount of water or other moisture on the floor. Although some methods have been devised to determine coefficients of friction according to the type of shoe material involved,[4] practical procedures which account for the many variables relating to differences in shoe types or designs and the manner in which different persons apply and distribute weight to their feet while walking do not yet appear to have been successfully developed.[5] With respect to wet floors, virtually any floor type tends to become more slippery when wet. Because of this fact, coefficient of friction tests are most valid when applied to dry floors.

Unsafe Design

Expert witnesses are also used in many slip and fall cases to establish that particular floor and stairway designs are unsafe. In Carpenter v. Hartford Fire Ins. Co.,[6] the plaintiff tripped and fell as she attempted to step down onto an obliquely angled concrete platform leading away from the defendant's store. Conflicting testimony was presented from two different experts as to the design of the defendant's store entry. The plaintiff's expert concluded that the design was hazardous because, although the single step-down was only a few inches high, the oblique angle of the defendant's store front actually directed customer's attention away from the fact that they had exited onto a platform from which they were required to step down to leave the premises.

This condition, according to the plaintiff's design expert, coupled with the distractions caused by traffic from the adjacent street, produced a hazardous condition which should have been remedied by enlarging the exit platform or by the placement of handrails or right-angled planters to focus the direction of the customer's travel. Conversely, the defendant's expert emphasized the platform's compliance with existing building code requirements, and opined that the red carpet on the landing more than provided an adequate warning of the short step-down. The court held that such evidence clearly supported the conclusion that the design of the store exit presented an unreasonable risk to customer's exiting the premises.

Expert testimony is often given additional credibility based on a structure's non-compliance with applicable building or safety codes. Typically, such codes often specify a minimum height and width of risers and treads in steps designed for use by the public. Experts may also be used to establish the existence of other hazards typically associated with slip and fall injuries, such as those caused by inadequate lighting or improper design.


[1] See, e.g., Van Holt v. AMTRAK, 238 Ill App. 3d 62, 70, 218 Ill. Dec. 762, 669 N.E.2d 1288, 1295 (1966). The plaintiff, an employee of the defendant, was walking to her car when she slipped and fell on a "greasy, slimy slick spot" on the cobblestone surface of a taxi tunnel at the defendant's train station. In the plaintiff's action under the Federal Employers' Liability Act, the trial court did not abuse its discretion in allowing the plaintiff's expert to testify that the cobblestone surface was unsafe and that is should have been composed of a smooth, anti-slip concrete or asphalt surface to decrease the likelihood of slipping from the oil and grease that leaked from cars using the tunnel.

[2] See generally Attorney's Guide to Engineering (Matthew Bender), regarding engineering aspects of slip and fall cases.

[3] See Miller, Investigating Slips and Falls: The Complex Dynamics Behind Simple Accidents, 24 Trial 49, 52 (Dec. 1988).

[4] See Sigler, Geib & Boone, Measurement of the Slipperiness of Walkway Surfaces, Appendix to Ch. 26, American Trial Lawyers' Ass'n 1965 Convention, 701, Table 2. This Table also shows the differences in anti-slip test results obtained on a variety of different flooring surfaces using both a rubber heel and a leather heel.

[5] See Sigler, Geib & Boone, Measurement of the Slipperiness of Walkway Surfaces, Appendix to Ch. 26, American Trial Lawyers' Ass'n 1965 Convention, 693-694. In locomotion tests reported by the authors on both men's and women's walking strides, the angle of contact of the shoe heel ranged from 11 degrees to 32 degrees.

[6] 537 So. 2d 1283 (La. Ct. App. 1989).