Occupational Ergonomics E-Book

Theresa Stack

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 825

Veröffentlichungsjahr: 2023

Beschreibung

OCCUPATIONAL ERGONOMICS Develop a healthier connection between worker and work with this practical introduction The United States Bureau of Labor Statistics estimates that 34% of all workdays lost each year are the result of work-related musculoskeletal disorders (WMSDs). These disorders result from a mismatch between a worker, their working conditions, and the task they perform. Improperly designed tasks or equipment, insufficient downtime between shifts or tasks, or even simple sitting position can all produce WMSDs. The key insights into preventing these disorders are produced by ergonomics, the scientific study of human bodies as they relate to objects, systems, and environments, especially work environments. Occupational Ergonomics: A Practical Approach aims to supply an ergonomic toolkit for creating healthier relationships between workers' bodies and their work. Beginning with a set of foundational ergonomic principles, it then details multiple assessment techniques in ways easily adapted to specific workplace situations. This balance of theory and practice has made Occupational Ergonomics an essential reference concerning human beings and the work they do. Readers of the second edition will also find: * Up-to-date ergonomic research reflecting the latest clinical and workplace data * Entirely new chapters on Work Physiology, Total Worker Health, Return on Investment, and more * Major revisions to chapters on Elements of an Ergonomic Program, Workstation Design, Work-Related MSDs, How to Conduct an Assessments, and Office Ergonomics * Detailed and updated case studies applying ergonomic assessment techniques to common workplace scenarios Occupational Ergonomics is a must for workplace safety managers, safety coordinators, ergonomics program coordinators, facilities managers, and any professionals concerned with the work environment, and worker health and safety.

Leseprobe

Occupational Ergonomics

A Practical Approach

Second Edition

THERESA STACK

Sheridan, MT, USA

LEE T. OSTROM

Idaho Falls, ID, USA

Copyright © 2024 by John Wiley & Sons, Inc. All rights reserved.

Published by John Wiley & Sons, Inc., Hoboken, New Jersey.Published simultaneously in Canada.

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Library of Congress Cataloging‐in‐Publication Data

Names: Stack, Theresa, author. | Ostrom, Lee T., author.Title: Occupational ergonomics : a practical approach / Theresa Stack, Lee T. Ostrom.Description: Second edition. | Hoboken, New Jersey : Wiley, [2024] | Includes index.Identifiers: LCCN 2023040647 (print) | LCCN 2023040648 (ebook) | ISBN 9781119714255 (cloth) | ISBN 9781119714279 (adobe pdf) | ISBN 9781119714323 (epub)Subjects: LCSH: Human engineering. | Industrial safety.Classification: LCC TA166 .S725 2024 (print) | LCC TA166 (ebook) | DDC 658.3/82–dc23/eng/20230909LC record available at https://lccn.loc.gov/2023040647LC ebook record available at https://lccn.loc.gov/2023040648

Cover Design: WileyCover Image: McKenzie M. StackBackground: © sanchesnet1/Getty Images

This book is dedicated to all the practitioners, present and future, who desire to improve the working conditions of workers in the United States and around the world. Keep up the great work in ergonomics, safety, and health.

Preface

We first wish to thank everyone who purchased the first edition of this book and hope this edition meets your expectations as well. We have added considerably more material to this edition, with additional chapters on work physiology and total worker health. There are also additional case studies and more information in the chapters. The case studies are all real and, as the announcer from the old Dragnet show would say, “the names have been changed to protect the innocent.”

We are very passionate about ergonomics and safety and health. We have seen the results of poor ergonomics in our careers. They manifest in employees having back and other musculoskeletal injuries. These injuries usually do not go away on their own. They require medical intervention, and they require workplace redesign to ensure they do not recur.

This book is focused on providing the bases of ergonomics and the principles of workplace redesign. Since we started in our careers in ergonomics, we have seen the increased availability of ergonomic equipment and the reduction of cost of this equipment. In the 1990s a good, adjustable computer workstation could cost thousands of dollars. Now, an electrically driven, adjustable workstation can cost less than a couple hundred dollars.

The limitation now is not implementing ergonomic solutions to observed workplace challenges.

May 2023

Theresa Stack and Lee T. Ostrom

About the Companion Website

This book is accompanied by a companion website:

www.wiley.com/go/stack/occupergo2 

The website includes:

PowerPoint slides

Answer Key

Exam Questions

Syllabus

CHAPTER 1Book Organization

LEARNING OBJECTIVES

The goal of this module is to recognize the basic principles behind seated, standing, and leaning workstations. Common workstation solutions and how to apply workspace envelopes are presented. At the end of this module, the students will have the skills to evaluate workstations in the United States.

Introduction

A workstation is a location where a person performs one or more tasks that are required as part of his/her job. The design of the workstation can have a profound impact on the person's ability to safely and effectively perform the required tasks. Reach and strength capability, body size and shape, endurance, and visual capabilities are just a few of the factors that should be considered in work place design. The design guidelines to be discussed in this section include the following:

Accommodate people with a range of body sizes or anthropometric dimensions.

Permit several working positions/postures to promote better blood flow and muscle movement.

Design workstations from the working point of the hands. People work with their hands, so we want their working surface height to be relative to their hand height.

Place tools, controls, and materials between the shoulder and waist height, where they have the greatest mechanical advantage.

Provide higher work surfaces for precision work and lower work surfaces for heavy work.

Reduce compressive forces by rounding or padding work surface edges.

Provide well‐designed chairs in order to support the worker.

As each of the design guidelines are discussed, keep in mind that some of these principles may not be applicable to designs for individuals with special needs. Different tasks may also require different design guidelines, such as providing a brake pedal extension for a bus driver of less height (Figures 1.1 and 1.2).

FIGURE 1.1 Worker moves a 125‐lb tire manually, resulting in a poor lifting posture.

Source: Mohawk Lifts, LLC

FIGURE 1.2 A tire dolly, does much of the manual work and results in a safer task.

Source: Courtesy of Mohawk Lifts, LLC

Key Points

The design of the workstation can have a profound impact on the person's ability to safely and effectively perform the required tasks.

Reach capability, body size, muscle strength, and visual capabilities are just a few of the factors that should be considered in workstation design.

Review Questions

What anthropometric principle is used when selecting the placement of the pull cord on a safety shower?

If a person is 20th percentile in height, will they be 20th percentile in weight? Why?

What anthropometric design principle is used as a last resort? Why?

CHAPTER 2The Basics of Ergonomics

LEARNING OBJECTIVES

At the end of this module, students will be able to identify the basic principles of ergonomics, including a working definition of the term, and a brief history of the development of ergonomics and human factors. Students will also be able to recognize the physical workplace risk factors and other contributors to the development of work‐related musculoskeletal disorders (WMSDs) as well as potential resolutions to reduce or control workplace risk.

Introduction

Ergonomics is a field of study that involves the application of knowledge about physiological, psychological, and biomechanical capacities and limitations of people (Butterworth, 1974). This knowledge is applied in the planning, design, and evaluation of work environments, jobs, tools, and equipment to enhance worker performance, safety, and health. Ergonomics is essentially the science of work.

Defining Ergonomics

Wojciech Jastrzębowski, a Polish biologist, coined the word “ergonomics” as the science of work in an 1857 philosophical narrative “based upon the truths drawn from the Science of Nature.” The term ergonomics – er·go·nom·ics \ ûrg‐go‐’näm‐iks\ – is derived from two Greek words, Ergon meaning work and Nomos meaning principles or laws. Jasterzebowis understood the human and economic impacts of the Industrial Revolution during a time when a society of farmers traded in their hoes for 14‐hour days in factories, growing iron and steel in lieu of wheat and potatoes. Factories brought people, process, and power together like never before.

A more commonly used definition of ergonomics today, as defined by one of the fathers of modern ergonomics Étienne Grandjean, is “fitting the work to the worker.” Ergonomics is an applied science combining various disciplines that cater to the special needs of humans as they interact with their work environment. Ergonomics is a goal‐oriented science that seeks to reduce or eliminate injuries and disorders, increase productivity, and improve life quality.

Ergonomics, as defined by the Board of Certification for Professional Ergonomists (BCPE), “is a body of knowledge about human abilities, human limitations and human characteristics that are relevant to design. Ergonomic design is the application of this body of knowledge to the design of tools, machines, systems, tasks, jobs, and environments for safe, comfortable and effective human use” (Ergonomics, 2023). The profession has two major branches with considerable overlap. One area of the discipline referred to as “industrial ergonomics,” or “occupational biomechanics,” concentrates on the physical aspects of work and human capabilities such as force, posture, and repetition. The second branch, referred to as “human factors,” is oriented to the psychological aspects of work such as mental loading and decision‐making.

The History of Ergonomics

Disease and work have a long history; however, let us begin this story with Bernardino Ramazzini born in Carpi, Italy, in 1633. While he was still a medical student at Parma University, his attention was drawn to diseases suffered by workers. In 1682, when he was appointed chair of theory of medicine at the University of Modena, Ramazzini focused on workers’ health problems in a systematic and scholarly way (Brauer, 2005). He visited workplaces, observed workers’ activities, and discussed their illnesses with them. The medicine courses he taught were dedicated to the diseases of workers. Primarily, on the basis of this work, Ramazzini is called “the father of occupational medicine” (Report, 2012). Ramazzini systematized the existing knowledge and made a large personal contribution to the field by collecting his observations in De Morbis Artificum Diatriba (Diseases of Workers); the first edition was printed in Modena in 1700 and the second in Padua in 1713.

Each chapter of the De Morbis Artificum Diatriba contains a description of the disease associated with a particular work activity followed by a literature analysis, workplace description, questions for workers, disease description, remedies, and advice. Ramazzini regularly asked his patients about the kind of work they did and suggested that all physicians do the same, expanding on the list of questions by Hippocrates (Giluliano Franco, 2009).

Ramazzini realized that not all workers’ diseases were attributable to the working environment (chemical or physical agents): “The first and most potent is the harmful character of the material that they handle, for these emit noxious vapors and very fine particles … and induce particular diseases (in humans). The second cause I ascribe to certain violent and irregular motions and unnatural posture of the body, by reason of which the natural structure of the vital machine is so impaired that serious disease gradually develop …”

Ramazzini observed that a variety of common workers’ diseases appeared to be due to prolonged, violent, and irregular motions and prolonged postures. Such cumulative trauma and repetitive motion injuries have recently been called the occupational epidemic of the 1990s (Giluliano Franco, 2009) and have been linked to the 2010 opioid epidemic. Figure 2.1 displays the risk factors for housemaid’s knee or bursitis.

FIGURE 2.1 Housemaid’s’ knee as in bursitis.

Source: Library of Congress / Public Domain

Ergonomics and the Industrial Révolution

In the 19th century, Frederick Winslow Taylor pioneered the “scientific management” method, which proposed a way to find the optimum method of carrying out a given task by maximizing human performance. Occupational ergonomics today seeks to decrease injury while enhancing performance. Taylor found, for example, that you could triple the amount of coal workers shoveled by incrementally reducing the weight of coal or ore in shovels by increasing the shovel size and shape, Figure 2.2. Over time, he determined the fastest shovelings literally matching the task and tools to the worker. Frank and Lillian Gilbreth expanded Taylor’s methods with formal “time and motion study.” They aimed to improve the efficiency by eliminating unnecessary steps and actions. By applying this approach, Gilbreth et al. reduced the number of motions in bricklaying from 18 to 4.5, allowing bricklayers to increase their productivity from 120 to 350 bricks per hour. Industrial engineering, lean engineering, and Six sigma are built on the same underlying principles, Figure 2.3.

Prior to World War I (1914), the focus of aviation psychology or human factors was on the aviator, but the war shifted the focus onto the aircraft, in particular the design of controls and displays, adjustability of controls and seating, and the physical size of the aviator within the flight deck. The war witnessed the emergence of aeromedical research and the need for repeatable testing and measurement methods to ensure, as much as possible, that aviators cognitive and physical capacities were maximized but not exceeded.

Henry Ford’s (1920) efficiency of motion focused on decreasing the cost of manufacturing an automobile while increasing quality through consistency. In the modern production line, as Henry Ford stated, “…. the work must be brought to the man waist‐high, no worker must ever have to stoop to attach a wheel, a bolt, a screw or anything else to the moving chassis.” World War II (1940) marked the development of complex machines and new demands on operators’ cognition and physical capacity. In 1943, Alphonse Chapanis, a lieutenant in the U.S. Army, showed that this so‐called “pilot error” could be greatly reduced when more logical and differentiable controls replaced confusing designs in airplane cockpits. After the war, the Air Force published 19 volumes summarizing the research.

FIGURE 2.2 The size and shape of the shovel maximize use if matched to the task. A coal shovel, second from the right, is wide and flat. A gravel shovel, far right, is smaller because gravel weighs more than coal. A spade, first on the left, is used for digging, whereas it is impossible to dig a hole with.

Source: Angie from Sawara, Chiba‐ken, Japan/Wikimedia Commons

FIGURE 2.3 Staging the raw stock close to the work location is another method to reduce long reaches and unnecessary movements.

Source: kalpis/Adobe Stock

The Human Factors Society, the main professional organization for human factors and ergonomics practitioners in the United States, was formed in 1957, with approximately 90 people attending the first annual meeting. The name was changed to the Human Factors and Ergonomics Society in 1992. In 2021, the society had 3500 members (Society, 2021) and is the benchmark for an internationally recognized designation in the practice of ergonomics, the Certified Professional Ergonomist.

Ergonomics and Technology

Starting in the mid‐1960s, the discipline expanded into computer hardware (1960s); computer software (1970s); nuclear power plants and weapon systems (1980s); the Internet and automation (1990s); and adaptive technology (2000), just to name a few. Most recently, new areas of interest have emerged including neuro‐ergonomics and nano‐ergonomics. With the rapid advances in science and technology today, it is interesting to speculate on what newly discovered challenges human factors and ergonomics will be called upon to solve. Exoskeletons are being used to perform tasks and decrease the burden on the humans today but may increase mental workload. As they were at inception, human factors and ergonomics remain multidisciplinary professions.

Work‐Related Musculoskeletal Disorders

Ergonomics seeks to prevent WMSDs by applying principles to identify, evaluate, and control physical workplace risk factors. Musculoskeletal disorders (MSDs) involve damage to soft tissues; WMSDs are MSDs aggravated by working conditions. WMSDs are not typically caused by acute events but occur slowly over time due to repeated wear and tear or microtraumas to the tissue. For example, dental hygienists tend to develop hand‐related tendon damage due to repeated gripping of small diameter tools while applying force.

Micro‐trauma is a small, minor, limited area tissue damage or tear. Cumulative trauma occurs when rest or overnight sleep fails completely to heal the micro‐trauma, and the residual trauma carries over to the next day. Damage continues to proliferate if the exposure or dose remains unchanged (Labor, 1999).

WMSDs are also known as cumulative trauma disorders (CTDs), repetitive strain injuries (RSIs), repetitive motion trauma (RMT), or occupational overuse syndrome.

OSHA defines MSD as a disorder of the muscles, nerves, tendons, ligaments, joints, cartilage or spinal discs that was not caused by a slip, trip, fall, motor vehicle accident or similar accident (OSHA).

When present for sufficient duration, frequency, or magnitude, physical workplace risk factors may contribute to the development of WMSDs, Figure 2.4. In addition, personal risk factors, such as physical conditioning, existing health problems, gender, age, work technique, hobbies, and organizational factors (e.g., job autonomy, quotas, and deadlines), contribute to but do not cause the development of WMSDs. Applying ergonomic principles to reduce a worker’s exposure to the physical workplace risk factors decreases the chance of injury and illness.

FIGURE 2.4 Awkward posture of the back, high spinal forces, and hand compression are found with emergency transport

Physical Workplace Risk Factors – Overview

Physical workplace risk factors are those aspects of a job or task that impose biomechanical stress on a worker. Researchers have identified specific physical workplace risk factors that cause or contribute to the development of WMSDs. Ergonomic principles are commonly used to mitigate the exposure. The following will be covered in detail (Figure 2.4).

Postures – both awkward (nonneutral) and static

Forces – including heavy, frequent, or awkward lifting

Compression

Repetition and

Vibration.

Force, repetition, and awkward postures, especially when occurring at high levels or in combination, are most often associated with the occurrence of WMSDs. While exposure to one risk factor may be enough to cause injury, typically physical workplace risk factors act in combination. An example is the position of the wrist a server uses when carrying a tray (with hand bent back and the wrist at almost a 90° angle), Figure 2.5. This position causes severe hand extension and when combined with the gravitational force created by a heavy and long shift, multiple risk factors are present that place the employee at risk of injury, Posture + Force + Duration + Repetition. Dialing down or decreasing any single risk factor will ultimately decrease the risk of injury. Other workplace conditions can contribute to but do not cause WMSDs:

Duration

Intensity

Temperature

Workplace Stress

FIGURE 2.5 Server with poor wrist posture.

Source: Angel_a/Adobe Stock

Personal risk factors contribute to the development of WMSDs and can be mitigated with an industrial athlete or total worker health program:

Age

Gender

Hobbies

Previous injuries

Physical or medical conditions

Smoking

Fatigue.

Posture

The neutral posture is the optimal body position of each body joint to minimize stress and provide the greatest strength and control as seen in Figure 2.6. The neutral posture is the body position in which there is the least amount of tension or pressure on the nerves, tendons, muscles, joints, and spinal disks. It is also the position in which muscles are at their resting length, neither contracted nor stretched. Muscles at this length can develop and maintain maximum force most efficiently. The neutral posture in the workplace can be recognized by the proper alignment of body landmarks. Neck, shoulders, and arms should be relaxed with elbows by the sides. The elbow should be open at an angle that is no less than 90°. The ears are roughly over the shoulders, shoulders over hips, hips over knees, and knees over ankles and the spine with a slight S shape.

Awkward Postures 

Awkward postures or nonneutral postures are those outside of the neutral posture. Awkward or unsupported postures can stretch the body’s physical limits and can compress nerves and irritate tendons. Awkward postures are often significant contributors to MSDs because they increase the work and the muscle force required (OSHA, 1999). Examples of awkward postures include

FIGURE 2.6 Standing neutral posture

Raising hands above the head or elbows above the shoulders, a common awkward posture in manufacturing and manual material handling

Kneeling or squatting, found in maintenance operations and construction

Working with back, neck, and/or wrist bent, for example, when using a microscope

Sitting with feet unsupported, which can cause blood to pool in the feet and flatten the natural curve in the lumbar spine. This problem is common among laboratory technicians who work at high benches (

Figure 2.6

).

FIGURE 2.7 (a) Workers are exposed to long reaches above the shoulders and below the knees. (b) The automated storage and retrieval system delivers parts at elbow height reducing the repeated and frequent awkward postures

Awkward postures are generally more fatiguing than neutral ones because the muscles, tendons, and ligaments are actively working to maintain the posture; the greater the posture deviations from neutral, the higher the stress on the human and resultant risk of injury. As shown in Figure 2.7, before, the worker bends down and reaches up to gather parts for eyeglass assembly. Afterward, an automatic storage and retrieval system delivers parts at elbow height, reducing awkward postures and improving quality control through an automated inventory stem.

Static Postures 

Holding a posture for extended periods is known as a static posture, resulting in static muscle loading. Static postures limit blood flow and muscle recovery. These types of exertions put increased load or forces on the muscles or tendons, which contribute to fatigue (OSHA). Blood flow brings nutrients to the muscles and carries away waste products. Holding a muscle in contraction causes waste products to build up and leads to fatigue. Fatigue is considered a precursor to injury. For more information on fatigue, see the administrative chapter.

Examples of static postures include

Gripping tools that cannot be put down and holding arms out or up to perform tasks

Standing in one place for prolonged periods.

Repetition

Repetition is a physical risk factor that occurs when the same motion or group of motions is performed over and over again. Different tasks may still utilize the same muscle groups and, therefore, not allow the muscles to rest, leading to overuse. Repetition alone is not typically a problem, but when it occurs with other risk factors, it magnifies the exposure.

Force

Force refers to the amount of physical effort that is required to accomplish a task or motion. Tasks or motions that require application of higher force place mechanical loads on muscles, tendons, and joints (OSHA, 1999) and can quickly lead to fatigue. The force required to complete a movement increases when other risk factors are involved. For example, more physical effort may be needed to perform a task when speed is increased or vibration present. Performing forceful exertions requires the application of muscle contraction; the more force that must be applied, the more quickly the muscles fatigue. Excessive or prolonged exposure leads to overuse of the muscles and may result in muscle strain or damage.

Compression

Compression or contact stress is a concentrated force on a small surface area. Contact stress reduces blood flow and can cause tissue (e.g., tendon) irritation due to the constant pressure. One of the most common sources of compression is a sharp or hard desk edge creating a compressive force on the forearm or elbows as we rest to stabilize the joint. Nerves in the forearm are close to the skin surface; compression of the forearm impedes nerve conduction.

Vibration

There are two types of vibration, single point and whole body. More information can be found in Chapters 9 and 10.

Contributing Factors