Licensed Professional Engineers
FORENSIC CLUES # 28 - "Platform Lift Accidents" by John L. Ryan
A newsletter dedicated to keeping attorneys informed of the technical side of product liability cases.
Volume 28 July/August 2008
“Platform Lift Accidents”
By John L. Ryan
Platform lifts are used in numerous industries, for construction, maintenance, moving personnel, lifting heavy objects, stocking warehouses, pulling orders, and countless other applications. Fatalities occur every year when people fall from lifts, are crushed by lifts, get entangled in lift mechanisms, get electrocuted when a lift contacts power lines, and when a lift tips over. This issue of Forensic Clues will examine the different types of accidents, their causes, and designs that can prevent many of these accidents.
A common injury or fatality scenario occurs when a worker moves a mobile lift platform into power lines or other energized power source. Manufacturers like to point to user error and operators who haven’t read the operator’s manual.
Typical lift platform
While warnings and instructions are necessary, they should not be relied upon for safety purposes when a safer alternative is available. The National Safety Council’s hierarchy of design provides a step by step process to safeguard hazards. The first step is to use the most effective method, removing a hazard from a design. If this is not possible, as with inherently dangerous products, then the hazard should be safeguarded. Only when it is not possible to rely on safeguarding are warnings to be used as a primary safeguarding method. Further down the priority list is the less effective method of providing instructions.
The fact is that there are safeguarding and warning solutions to contacting electric lines. Power line proximity detection alarms can alert lift users of nearby electrical hazards by detecting the electrostatic field of any AC power line. It provides audible and visual warning signals to alert the operator and ground personnel when the boom or basket of a lift comes in proximity of an energized high voltage line. This device can prevent accidental collisions with a power line. The Department of Energy Technical Reference states “Proximity warning devices should be installed on all aerial devices where possible to warn of potential contact with overhead electrical wires…” OSHA 1926.550 (a)15 calls for a minimum clearance of 10 feet between linemen and power lines. Proximity alarms use technology to help accomplish this, relying less on operator preparedness and attentiveness than on safe design features.
Tip-overs are another common cause of serious injuries and fatalities associated with platform lifts. Tip-overs occur when the lift base cannot support the horizontal forces acting on the lift boom and platform. Simple engineering equations can be used to determine the forces required to tip lifts. Lift manufacturers can fail to account for various use situations such as lifting a heavy object with a lift platform without the object being centered on the lift. Lift manufacturers should design their lifts to safely handle loads to the lift’s rated capacity, regardless of positioning of the heavy load. Lift height should be limited to that which the lift base can support.
A poorly designed lift can topple when encountering potholes, a common cause of lift tip-overs. ANSI A92.6 calls for scissor lifts to successfully negotiate a four inch depression while remaining stabile. Any incident resulting from an obstacle or depression greater than this is often said to be the fault of the operator. It is uncertain how an operator is supposed to discern between an obstacle less than four inches from an obstacle greater than four inches. The fact is that lifts will encounter holes and obstacles greater than four inches and that these are foreseeable uses of a product. Some manufacturers are beginning to design and manufacture lifts that use pothole guards. These effectively reduce the ground clearance of the lift so that if a pothole is encountered, the lift will only fall until the lift rests on its pothole guards. These supporting structures will sometimes raise and lower as the lift is lowered and raised. These pothole guards are intended to provide safety without enlarging the footprint of the lift.
Outriggers are legs that extend out from the lift base to form a larger base area. This helps prevent tip-overs by providing a much more stable base. Outriggers can help provide stability for lifts, but can be a liability if the lift operator does not accurately extend the outriggers or fails to extend them.
Outrigger interlocks have been available for a number of years. Interlocks prevent movement of a lift when the outriggers are not extended. This ensures that the lift will be used as designed, with outriggers extended. Failsafe designs will prevent lift use in the event of interlock failure.
Another solution to tip-over accidents is using tilt sensors. These instruments detect the angle that the lift is positioned at. If the angle is too steep, the lift can prevent motion of the lift and/or elevation of the lift. A tilt sensor can also be interlocked so that if the ground angle is within certain parameters, the lift can still be used, but elevation limits as well as motion limits can be interlocked.
Outriggers help prevent tip-overs
Falls from Lifts
Falls from lifts frequently occur, and are a completely foreseeable result of providing a work platform that rises to dangerous heights. Simple precautionary measures can ensure that lift personnel do not fall. Harnesses and safety lines will prevent lift workers from falling. Standards require safety lines on some lifts but not others. Manufacturers who supply safety harnesses and lines will not have to rely on employers and operators to provide these items. Interlocking technology could help ensure that lift operators use their harnesses. Using properly designed handrails will also help prevent falls from lifts.
Mechanical Energy Hazards
Platform lifts often have numerous pinch points, especially scissor lifts. These pinch points must be guarded to prevent personnel from becoming crushed. Some lift manufacturers use a light curtain of sorts that protects the perimeter of the scissor lift. If anything crosses the light barrier under the platform into the profile of the lift, the lift will automatically stop moving. Other options include expandable guards that can cover the pinch points, yet allow the necessary range of motion.
Platform lifts have inherent hazards, and hazards that can often be removed at the design level. Manufacturers have been adding safety features over the years, creating a situation where the state-of-the-art can change rapidly in a few years, leaving some manufacturers with unsafe, inferior designs.
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