The effect of instructions on potential slide-out failures during portable extension ladder angular positioning

Abstract

Accidents involving portable ladders are a common cause of serious occupational and non-occupational injuries throughout the industrialized world. Many of these injuries could be prevented with better instruction on the proper usage of portable ladders. Research is reported that focused on both the human factors and engineering aspects of portable extension ladder usage based on common ladder setup procedures. Results of the human factors experiment revealed evidence of unsafe acts that could lead to catastrophic ladder slide-out accidents in real-life situations. Six different ladder setup methods were evaluated for safety and stability based on placement angles: the basic, 75 degree, stand–reach, L sticker, 4:1, and bubble level methods. Ideally, ladder users would set the ladder up at 75.5 degrees to achieve the consensus industry standard safest angle. Setup methods varied in complexity and nature of instruction. The level method produced the most accurate and the least variable results. The engineering analysis determined the coefficient of friction of a variety of clean and contaminated surfaces commonly used with ladders. This analysis determined the total number of slide-out failures that would likely have occurred in the data obtained in each of the ladder setup methods tested in the human factors experiment. Based on test participants’ setup angles, the average calculated ladder slide-out failure rate was 8.7 percent for ladders positioned on a surface with the lowest measured coefficient of friction. When broken down by ladder setup method, the 4:1 method had a failure rate of 18.8 percent, the 75 degree method had a failure rate of 15.2 percent, and the basic method had a failure rate of 9.8 percent. The stand–reach and L sticker methods had identical failure rates at 3.3 percent and the level method was best at 1.1 percent. The level method provided the lowest error, least variability, and setup closest to the target angle of 75.5 degrees. Analysis of the overall results revealed the need for additional user training and clearer instructions affixed to ladders. This research is unique in that it combines an analysis and comparison of human factors and engineering in the same study.