NIOSH Scissor Lift Tipover Study Details Updated

Brad Boehler, P.Eng., director of product safety at Skyjack, Inc., Guelph, Ontario, recently reported more details of the NIOSH Scissor Lift Tipover Study. To date, preliminary virtual model development, static tests, dynamic tests, and operator force tests have been conducted, while validation of the virtual model, applications of virtual environment, and field operator-lift stability tests will be performed in 2007.
 

Static and Dynamic Tests

Under the virtual model portion of the testing, a preliminary computer model of a 19-foot scissor lift was created, and NIOSH used the virtual model to validate the machine against both static and dynamic physical tests. Static tests performed included both horizontal and center of gravity tests, following ANSI A92.6-1999 • 4.7.1 static stability tests requirements (tilts for longitudinal and transverse axles).

For tilt about the longitudinal axis, the 19-foot scissor lift was tested at platform heights of 229, 180, 144, 108, and 72 inches. The study found that the scissor lift was stable at all heights up to at least 300 pounds of applied side force. For tilt about the transverse axis, the scissor lift was also tested at platform heights of 229, 180, 144, 108, and 72 inches and was found to be stable at all heights up to at least 150 pounds of applied side force.

Dynamic tests on the scissor lift included dynamic curb tests, depression tests, braking tests, and frequency analysis. Accelerations were measured at five locations and in three directions using a Kionix KXM52 tri-axial accelerometer.

During the curb tests, the scissor lift was driven at maximum forward and reverse speeds on a flat, level surface. The machine was tested at two different elevated heights • 7 and 19 feet • at the impact at the 4-inch curb was at two angles • 0 degrees and 30 degrees. Dynamic curb testing met ANSI A92.6-1999 • 4.7.4.1 requirements.

During the depression tests, the scissor lift was driven at the maximum speed and suddenly sunk into a pothole at one of the front wheels. All the tests were conducted on a flat, level surface . The machine was tested at both 7 and 19 feet, and the left and right front wheels were tested separately.
 

Operator Motion and Force Tests

Testing parameters for operator motion and force tests included three directions, two locations, three heights, and pushing and pulling tasks. NIOSH acquired information on the center of gravity of operators, acceleration and side force of the lift, and ground reaction forces. Operator motion and force tests included a standing location on the main platform, and standing directions included a stance perpendicular to the length of the lift, parallel with the length of the lift, and diagonally 45 degrees to the length of the lift. Platform heights were at 39, 56, and 72 inches, and the tasks included pulling, pushing, and upright standing.

NIOSH found that during the side-force testing that the height of the aerial lift did not affect the maximum side forces exerted by the operators; pushing tasks generated greater forces than pulling tasks; and greater forces were generated on the main platform only for pulling tasks. Standing direction also had a significant effect on maximum forces, and subjects exerted the greatest forces when standing parallel with the length of the lift.
 

Future Validation

In 2007, validation of the static and dynamic virtual models should be determined. Under the static virtual model validation, NIOSH will compare physical data observed with computer simulation • specifically data on the center of gravity • and it will identify stability margins from model predictions compared to both static and dynamic physical tests. Currently in progress are applications of the virtual environment, such as simulations of the use of scissor lifts in various working conditions as well as conditions that go beyond regulatory parameters or manufacturer's recommendations.

Additionally, NIOSH and Skyjack have proposed future study concepts. Three of the study components included biomechanical assessment of harness/lanyard uses and ingress/egress designs on aerial lift operators; establishment of lift stability margins and impacts on operators; and evaluation of fall hazards and relevant intervention effectiveness using virtual reality techniques.

Disclaimer: The findings and conclusions in this APS presentation have not been formally disseminated by the National Institute for Occupational Safety and Health and should not be construed to represent any agency determination or policy.