Tlv´s de la acgih

50
The ACGIH TLVw for Low Back Risk
50.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50.2 TLV Development Background . . . . . . . . . . . . . . . . 50-1 50-2 50-7
Spine Load Estimates † Load Tolerance † Studies of Lift Location † Repetition Modifiers

William S. Marras
The Ohio State University

Chris Hamrick
Ohio Bureau of Worker’s Compensation

50.3Using the Lifting TLV . . . . . . . . . . . . . . . . . . . . . . .
About the Lifting TLV † Instructions for Determining the Lifting TLV † If a Lifting Task Exceeds the TLV † Example 1 † Example 2

50.1

Overview

The Lifting TLV (threshold limit value) was the product of a team of scientists whose goal was to develop a lifting guideline that was accurate, used the latest scientificinformation, and easy to use. This group of scientists consisted of Lawrence J. Fine, Christopher Hamrick, W. Monroe Keyserling, William S. Marras, Robert Norman, Barbara Silverstein, and Thomas Waters with correspondence members consisting of Peter Buckle and John W. Frank. The product of this group’s work has been presented as an ACGIH 2005 TLV. This chapter is based upon the work of the committeeestablishing this NIE (notice of intent to establish) of which the two authors of this chapter were members. The scientific rationale for this TLV is based on the most recent biomechanical, psychophysical, and epidemiological studies, which together demonstrated a causal association between lifting activities and increase risk of low back disorders characterized by pain and the temporary or prolongedinability to perform normal occupational and nonoccupational activities. The model for the structure of this TLV was based upon the structure of the Finnish lifting guidelines and the 1995 Occupational Safety and Health Administration (OSHA) draft standard. These approaches were latter incorporated in the State of Washington Ergonomic Rule. The approach for these efforts was to define the vertical andhorizontal space relative to the base of the spine (L5/S1) of the material handler. Surveillance studies have shown that the single strongest indicator of risk for a lifting task was the load moment (weight of the object lifted times the distance from the spine) relative to L5/S1 (Marras et al., 1993). In addition, biomechanical studies have indicated that the vertical location of a load relativespine has profound biomechanical implications for spine loading and tolerance (Marras, Granata, Davis, Allread & Jorgensen, 1999). Therefore, a tool that identifies the origin location of the load to be lifted from a horizontal and vertical location perspective was a reasonable approach. Lift origins were divided into 12 horizontal and vertical zones relative within the sagittal plane of the body(Table 50.1). The lift height zones consisted of four regions: (1) the region from 30 cm above to 8 cm below shoulder height (reach limit), (2) knuckle height to below shoulder height, (3) middle shin height to knuckle height, and (4) floor to middle shin height. Horizontal location origins were divided

50-1

© 2006 by Taylor & Francis Group, LLC

50-2
TABLE 50.1
Anatomical LandmarksFundamentals and Assessment Tools for Occupational Ergonomics
Table with Cell Names
Start Height of Lift (Use of anatomical landmarks from column one is preferred) 132–183 cm Close Lifts: origin , 30 cm from mid-point between inner ankle bones Near Lifts: origin 30 –60 cm from mid-point between inner ankle bones Extend Lifts: origin ! 60–80 cm from mid-point between inner ankle bones

Fromoverhead reach limit to 8 cm below shoulder height [Ht] (Axilla) Knuckle Ht to below shoulder Ht Middle shin Ht to knuckle Ht Floor to middle shin Ht

Cell A

Cell B

No known safe limit for repetitive lifting

.82 to 132 cm .30 to 82 cm 0–30 cm

Cell C Cell F Cell I

Cell D Cell G No known safe limit for repetitive lifting

Cell E Cell H No known safe limit for repetitive lifting...