The Angle of Inclination of Extension Ladders

Abstract

For extension ladders and other non-self supporting ladders, setting the angle of inclination of the ladder is a critical step in the set up process. The angle of the ladder influences: 1) the potential for a ladder to slide out at the base, 2) the overall strength of the system, and 3) the biomechanics of the climber/user on the ladder. A field study was conducted where over 120 real world ladder installations were documented, including angle of inclination, site conditions, and use. The average angle of inclination in the field study was 67.7 ± 4.9 degrees. Research was further conducted to assess the effectiveness of existing ladder labels for setting the ladder at the instructed 75.5 degree angle of inclination. 45 participants set up extension ladders following the “anthropometric” label (appendices of current ANSI A14 ladder safety standards), and/or the backward “L” label (historic ANSI A14 label). The average set up angle for the “anthropometric” label was 74.1 ± 3.2 degrees. This is consistent with calculations of the expected angle of inclination using anthropometric data. The calculated angles ranged from 74.9 to 75.2 degrees. The average angle of inclination for the backward “L” label was 72.7 ± 2.7 degrees. These results indicate that the current “anthropometric” label resulted in a set up angle consistent with anthropometric calculations and significantly higher than documented in real world ladder use.