MODULE: INTRODUCTION TO ERGONOMICS

Considerations Relating to Proactive Ergonomics:

The workstation:

The workstation layout should comfortably fit a wide range of body sizes. The range of bench height, tool access and space clearance should accommodate all but the very tall or very short worker. An adjustable workstation should be able to accommodate the majority of works.

Some general guidelines include:

• Employees should be able to work in an upright and forward-facing position with the majority of tasks performed at or near waist height and within easy reach.
• Workstations should be adjustable and allow for flexibility of postures to accomplish work, preferably alternate seated and standing positions.
• Tools/material should not be placed above shoulder height.
• Frequently used tools should be stored in front of and close to the body.
• Items to be lifted should be kept between hand and shoulder height.
• Adjustable fixtures and rotating cutting tables.
• Mechanical assists to eliminate the use of extreme force.
• Suspension of heavy tools.
• The workbench is divided into primary and secondary task areas, the primary area is the space recommended for major activities and the secondary area for infrequent work activities..

Tool design:

Tools should be designed and selected to minimize the risk of WRULD, for example:

• Matching the tool to the task.
• Redesign of handles so as to reduce wrist bend.
• Select tools with minimum vibration.
• Tool handles should have textured grips in preference to grooves so as to allow for the distribution of pressure.

Manual material handling:

NIOSH developed an equation to rate lifting tasks in terms of whether the loads were excessive. Risk assessment of lifting tasks using the NIOSH equation can be found at http://www.cdc.gov/niosh/docs/94-110/.

Limitations of the NIOSH lifting equation:

• It only applies to two-handed manual lifting tasks, from a standing position.
• The calculations are based on the assumption that other manual material handing activities are minimal (less than about 10% of worker activity).
• It does not include factors to account for unpredicted conditions such as unexpectedly heavy or suddenly applied loads, unstable loads, slips, falls, traumatic incidents or unfavourable environmental conditions.

The formula takes into account the six different factors in defining a recommended weight limit (RWL) for lifting and lowering of loads.

• Horizontal location of the load relative to the body.
• Vertical location of the load relative to the floor.
• Vertical distance the load is moved.
• Frequency and duration of the lifting activity.
• Asymmetry (lifts requiring twisting or rotation of the trunk or body).
• Quality of the worker’s grip on the load.

The RWL (max) is equal to the maximum load under ideal conditions and is taken to be a load of 23 kg, lifted from a height of 75 cm above the floor and held 25 cm in front of the body. The load is to be lifted no more than 25 cm vertically, with good handgrips and the load is to be lifted only occasionally.

LC = load constant of 23 kg
HM = horizontal multiplier = 25/H
VM = vertical multiplier = 1 - (0.0003 |V-75|)
DM = distance multiplier = 0,82 + (4,5/D)
AM = asymmetric multiplier = 1 - 0.0032A
FM = frequency multiplier (from Table 1)
CM = coupling multiplier (from Table 2)

And

H = Horizontal distance of the hands at the midpoint of hand-grip from midpoint of the ankles
V = Vertical distance of the hands from the floor at the origin of the lift measured vertically from the floor to the mid-point between the hand grasps, as defined by the large middle knuckle
D = Distance through which the load is lifted, the distance between the origin and the destination of the lift
A = Angle of asymmetry is the angular displacement of the load (required pivot). The sagittal plane extends vertically from front to back in the body’s medium plane (dividing the body left and right). This angle is measured at the origin and the destination of the lifts (degrees). The asymmetrical angle is defined as the angle between the asymmetry line and the mid-sagittal line. The asymmetry angle is limited to the range from 0° to 135°. If A > 135° then AM is set equal to zero.
F = Frequency of lifting is determined from Table 1. For repetitive lifting tasks, FM is determined by:

• The number of lifts per minute over a 15 minute period.
• The amount of time engaged in the lifting activity.
• The vertical height of the lift from the floor.

For lifting tasks with a frequency < 0.2 lifts/minute, frequency is set = 0.2 lifts/minute.

The ratio between the load actually lifted and the RWL is known as the lifting index, (LI). The lifting index provides a relative estimate of the level of physical stress associated with a particular lifting task. It is defined by the relationship of the weight of load lifted (L) and the recommended weight limit (RWL). In an equation form this index is LI = L/RWL.

A lifting index < 1 is believed not to increase the risk of injury. An index of three or more indicates that many workers will be at increased risk and the task should be redesigned. The goal of NIOSH in developing the equation is to protect workers by setting limits on occupational lifting. The goal of the exercise is to apply the NIOSH lifting guidelines to this task and determine what factors would need to be changed to have this task meet the guidelines. To find the most appropriate solution for the job, look for the lowest number used to do the calculation.

See attachment for quick tool for assessing Safety and health requirements for handling of loads

General Introduction to Occupational Health: Occupational Hygiene, Epidemiology & Biostatistics by Prof Jonny Myers is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 South Africa License