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Catastrophic Stair Falls


January 1, 2011   by Richard Nellis and Bailey Gutkin, Kleinfeldt Consultants Limited


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Any stair fall has the potential to be catastrophic (resulting in a severe injury or fatality). Contributing factors can include design, construction, maintenance and user behaviour. The investigating forensic engineer focuses on site examinations, reported information and reviews of the injuries to determine the most likely fall scenario and contributing factors.
This article looks at various stair fall scenarios and identifies contributing factors in each. A specific case study demonstrates how these scenarios and contributing factors can be used to mitigate risk related to catastrophic stair falls (CSFs).

Stair Fall Scenarios

CSFs can be either witnessed or unwitnessed, resulting from a trip, slip or misstep. They can happen in ascent or descent. Each and every stair fall assessment requires an objective and consistent approach, although ultimately each individual stair fall scenario will determine the course of the investigation.

Witnessed vs. Unwitnessed

Typically a witnessed CSF has more information available from a number of sources to aid in the assessment.
Unwitnessed stair falls make up the majority of investigated cases. They can be difficult to investigate, since it is common for the injured party to have a limited recollection of the event.

It is crucial that all scenarios be considered and prudently accepted or rejected. Determining the most likely fall scenario requires considerable experience and knowledge in order to correlate the physical attributes of the stairs with the reported injuries.

Determining the fall method ultimately helps identify the cause and contributing factors and must be consistent with the injuries, physical attributes and reported information. A detailed methodology based on the engineer’s knowledge and experience, and which considers all aspects of the fall, lends credibility to the assessment.

Trips vs. Slips vs. Missteps

Literature defines a slip as “a sudden loss of footing, the result of an unforeseen, unexpected and out-of-control slide of the foot.”

A trip is defined as “a sudden loss of footing, the sequela of an interruption in the natural, rhythmic movement of the swinging leg.”1

A misstep is an inaccurate placement of the foot, causing loss of balance.

Slips on stairs are less likely than trips or missteps, because most momentum is in the vertical direction rather than the horizontal. A contaminant or lubricant reducing the slip resistance of the tread surface, such as ice or snow, will typically be a contributing factor for a slip.

Generally, a slip will cause the person’s feet to come out from under them, and they will fall backwards or to the side.
Trips on stairs can occur as a result of a variety of factors such as trip edges, loose carpeting and inconsistent riser/tread dimensions.

Contrary to a slip, a trip will generally cause a person to fall forward.

A misstep can occur when a person places their foot partially over the edge of a tread, or cannot identify where the stair begins or ends. This type of fall can be a result of inadequate stair geometry, unexpected stairs, confusing carpeting or user behaviour.  A misstep will often, but not necessarily, cause a person to fall forward, in the direction of their momentum.

Ascent vs. Descent

Understanding the differences in gait for ascending and descending stairs is essential to determining the causes and contributing factors in CSFs.

During ascent, the centre of gravity is held slightly forward with the leading foot landing with the ball of the foot in a horizontal position. The heel may or may not touch the tread, as the rear foot pushes back against the lower tread and pushes off. The rear foot will swing up and over the leading foot to land in a horizontal position on the tread above.

With very little horizontal or lateral movement, slips are unlikely. If a slip occurs in ascent, it is likely due to the presence of a lubricant. Trips in ascent are likely, since the rear foot lifts up onto the next tread. If the riser height is greater than expected, or if the toe catches on the nosing of the lower tread, a trip can occur. A misstep is also possible if the leading foot is placed inaccurately on the edge of the tread. The contributing factors for a misstep in ascent could include inconsistent or excessive riser heights, or visual deception.

A fall in ascent causing a person to fall backwards can result in injuries to the head, which can be serious or fatal. However, as the centre of gravity is held forward during ascent, it can be difficult to determine the fall origin, particularly if it is unwitnessed.

In descent, the centre of gravity is held back to maintain balance. The leading foot angles downward such that the ball of the foot will first contact the tread, allowing the foot and leg to absorb the impact.

Upon contact, the force is mostly vertical, making it unlikely that the foot will slip forward. If such a slip occurs, due to ice, for example, it will likely cause a person to land on their buttocks or back and bounce down the stairs. A misstep could occur if the ball of the foot lands on the nosing or over the edge of the stair. Inconsistent stair geometry or a visually confusing stair might cause this to happen. It is possible to trip in descent, if a trip edge is present, possibly caused by poor construction or maintenance practices.

Once the fall scenario is understood, it is necessary to identify the cause. This requires expertise relating to stair design, construction and maintenance, as well as a comprehensive understanding of building codes and bylaws, construction best practices, maintenance, industry standards and academic research.

The following case study illustrates the complexity of accurate determination of cause and contributing factors.

Case Study:
Unwitnessed Fall in Ascent

Background: A woman was found at the bottom of a stair in a restaurant where she was dining. Among other injuries, she was rendered a quadriplegic as a result of the fall.

Fall Scenario: The woman was found lying on her left side at the bottom of the stairs. Based on her injuries and her body position when found, it was determined the woman fell backwards while ascending the stairs.

It was difficult to assess whether the fall was a slip, trip or misstep because the incident was not witnessed. Further, the injuries did not imply one specific fall scenario.

For the purposes of this CSF assessment, biomechanical engineering experts were retained. They reported the injured party had fallen backwards while ascending, possibly due to a misstep. Her body likely rotated during her fall, such that she landed with considerable force on the bottom landing, against the wall.

Once this fall scenario was determined, our role as the investigating engineer was to determine the cause of her fall.
Origin of Cause: Many code violations were identified including  riser heights that exceeded the maximum in the building code. The tread depth was also below the minimum criteria, creating a steep stair.  Excessive, varied risers are unexpected and create trip hazards.

The handrail clearance was such that fingers could not maintain a continuous grasp of the handrail.
It was our opinion that the condition of the stair, specifically the excessive riser heights and variance of the risers and treads throughout the stair created an unsafe condition that contributed to the loss of balance and fall.

Assessment

A search of building permit records, building codes and bylaws was conducted to determine contributing factors and cause. We reported the following conclusions:

•     The stair dimensions did not comply with the building code in effect at the time of renovations.

•&
nbsp;    The renovation drawings provided insufficient information, but the municipality accepted and issued a permit for the proposed work.

•    A break in the hold of the handrail could result in loss of balance and
stabilization.

•    The building owners did not ensure the renovations conformed to safe building code standards.

•    The stairs did not comply with the municipal property standards bylaw.

•     The municipality should have identified construction deficiencies and building code compliance issues during the building permit approval and inspection process.

•    The Building Code Act required the municipality to conduct a competent inspection upon completion of the renovations. The municipality should have noted the deficiencies and taken appropriate action.

An objective and consistent approach is required in every CSF investigation so that the conclusions are consistent with the reported information, injuries, fall scenario, site observations and site history.

End Note

1 Alex Sacher, “The Application of Forensic Biomechanics to the Resolution of Unwitnessed Falling Accidents,” Journal of Forensic Sciences, 41, no. 5 (1996): 776-781.


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