Archive for February, 2008

Slip and Fall Claims

Thursday, February 7th, 2008

A large number of people are injured every year in the United States due to falls in public places.  The majority of these falls are classified as “Slip and Fall” accidents.

 

The determination of the cause of such accidents is a complex undertaking and involves a large number of variables. 

 

One of the variables is a property known as the coefficient of friction between two surfaces.  In the case of a person walking, this is the determination of the resistance to slipping between the shoe or other foot covering and the surface on which the person is walking. 

 

There are several methods of measuring the coefficient friction.  The methods range from simple friction sled methods to highly technical measuring devises to determine the static coefficient of friction (SCOF).  VCE uses both in investigations of slip and fall accidents.

 

 

The SCOF of a surface is generally reported as a value from 0.00 to 1.0, the slipperiest being at the low end of the scale, and the more slip free, near the 1.0 value.

 

In the case of sidewalks, floors or other walking surfaces, it is generally accepted that SCOF values of 0.50 and above do not present a slip and fall hazard and values below 0.50 are slip and fall hazards.  American’s With Disability Act requires that a level walking surface have a SCOF of 0.6 or greater and a handicap ramp has a SCOF of greater than 0.80.

 

Contamination of the walking surface or shoe soles is often the cause of Slip and Fall accidents.  Either type contamination can greatly reduce the effective coefficient of friction.  In the case of the walking surface, spills such as grease, water, etc. are usually quite apparent, however, contamination of a person’s shoes can be less obvious. 

 

It is important that the Adjuster determines, if possible, the actions of the fall victim immediately prior to the accident.  This Investigator has worked on cases where there was confusion as to whether the victim was actually entering or leaving a building or coming or going to a table in a restaurant when the fall occurred.  Obviously, the source of potential shoe contamination is important in the determination of fault.

 

Herb Stewart

 

The Skid Mark / Crush Factor Method

Thursday, February 7th, 2008

When investigating an accident a common question that arises is, “How fast were the vehicles going?” If the skid distance of the striking vehicle and the maximum crush depth of the target vehicle are known, a simple estimate of the speed of the striking vehicle can be made. This is done by determining the impact speed of the striking vehicle by measuring the maximum crush depth of the target vehicle and inputting the distance in the Crush Factor Formula.

The Minimum Speed Formula uses the pre-impact skid distance of the striking vehicle and the roadway drag factor.

Both the Crush Factor Formula and the Minimum Speed Formula are then combined in the following way to determine the Striking Vehicle Start of Skid Speed.

30 - Mathematical Constant in the formula

d1 - Striking Vehicle’s Pre-Impact Skid Distance (measured in feet). Note: Measure the skid marks from the start to the point of impact (offset in the mark) and then subtract the wheelbase (front to rear axle distance of the skidding vehicle) from the skid distance.

f - The adjusted drag factor of the vehicle leaving the skid marks on the roadway surface. Note: if the vehicle is a passenger car, van, SUV or pickup truck and all four wheels left skid marks and the roadway was level, the roadway coefficient of friction is the vehicles drag factor. For a dry traveled asphalt surface the coefficient of friction is usually within the range .6 to .8 g’s. If the roadway surface is wet or has gravel on it, the coefficient of friction can be significantly less.

d2 - The target vehicle’s maximum crush depth (measured in feet from the normal undamaged position to the maximum permanent crushed position) of either the side or rear surface. Note: this calculation can not be used for head on collisions. This may only be used for t-bone or rear end collisions.

cf - The crush factor of the target vehicle is vehicle specific, but the average crush factor for the side and rear surface is 27. The crush factor values are based upon statistical analysis of 1000 vehicles involved in accidents where the speeds of the vehicles were verified by independent means.

The following example illustrates how the combined speed formula works:

 

The striking vehicle left 59.5 feet of pre-impact skid marks and had a wheel base distance of 9.5 feet. Subtracting the wheelbase distance from the total skid mark distance gives a pre-impact skid distance of 50 feet. The skidding occurred on a roadway that was level, dry asphalt. The drag factor was measured to be .7 g’s. The vehicle impacted into the side of another car and left 18 inches (1.5 feet) of permanent crush damage.

The combined formula was used to determine the start of skid speed.

This formula works as an approximation of the start of skid speed for situations where one car, van, SUV or pickup truck impacts into the side or rear of another car, van, SUV or pickup truck. This is a relatively easy way to determine if the vehicle was traveling in excess of the speed limit and to decide whether or not a more detailed accident reconstruction would be helpful. This simple estimate of the striking vehicle speed and the speed of the target vehicle can be confirmed by the conservation of linear momentum method. In collisions that involve vehicles that impacted either head-on or head-on at an angle, this skid mark / crush factor method can not be used. In those cases either conservation of linear momentum or some other method needs to be used to determine the speed of the vehicles.

Todd Hutchison