85
Design of work areas, tools, and equipment
About the chapter
This chapter focuses on the space requirements of people performing jobs in factories, commercial facilities, and offices. Several space-related issues related to workplace design are addressed to varying degrees, for example, issues related to the design of work and traffic areas, workstations, work surfaces, work layout, seating, equipment used in workstations, and hand tools. Some of the topics addressed include clearance and reach requirements, accessibility, visibility, accommodation of disabled people, and the need for adjustability. The chapter begins with a brief discussion of the important role of anthro- pometric data in workplace design, before introducing methods of using anthropometric data, such as drafting templates and computer modeling techniques. The discussion then shifts to selected application areas. As emphasized in the chapter, the topics covered are traditional areas of industrial engineering and ergonomics, but significant changes in the regulatory environment and other factors have resulted in new needs and design constraints.
Introduction
A workplace is the place where one works, be it a workbench, an assembly-line station, or a desk. In all cases, tools, parts, equipment, and other devices must be located in eas- ily accessible locations, if people are to work productively in comfort and good health for protracted time periods. Tools and equipment must also be appropriately sized so that they fit the people using them. It does not take a lot of imagination to realize that seating, desks, hand tools, clothing, and personal protective equipment all pose potential problems if they do not fit the person using them. Workplace layout becomes especially important when workers are repetitively doing the same activity hour after hour. Part of the issue is that workers may need to maintain the same posture or a limited set of postures most of the time they spend working. The layout determines posture, and this determines a whole host of other factors, such as whether the job will be pleasant or unpleasant, fatiguing, or potentially harmful.
People must also have enough space to be able to easily move around work areas while they do their tasks. While the provision of adequate space does not guarantee proper per- formance, lack of it almost guarantees poor performance. A closely related issue is that traffic areas, such as aisles, passageways, doors, entrances, ramps, and stairs, must be properly designed to allow convenient, unimpeded ingress, egress, and movement around a physical facility. Inadequate or blocked passageways may impede ingress or egress from work areas or allow inadequate clearance for passing vehicles or people. At the very least, passageways must be adequate to allow quick egress under emergency egress conditions.
Unimpeded access of disabled workers to work areas is another concern that has been bumped up in priority by the passage of the Americans with Disabilities Act (ADA).
Visibility is another important issue. It is important that people of all sizes be able to enjoy unblocked vision of the things they need to see while doing their day to day tasks or jobs, and especially so under demanding conditions where the failure to see things has serious consequences.
Reflecting such concerns, practitioners have traditionally focused on creating work- places that fit the workers who use them. The designs that are specified must accommo- date the majority of users, typically those within a range from the 5th percentile to the 95th percentiles of the population. When the population is normally distributed in size, the interval corresponding to 95% of the users is defined as μ ± 1.96σ (where μ is the mean and σ is the standard deviation of a particular measure used to describe the fitted population).
Special people in the lower and upper 2.5% of the population need to be addressed as well, but not necessarily with the same design. An old rule of thumb is to design large enough for a large man and small enough for a small woman. However, it clearly does not follow that one size fits all. When it does not, a number of different sizes are needed. With more sizes, users are fit better but the design is usually more costly. Accordingly, some trade-off is needed. Current practice also focuses heavily on providing means of adjustability to accommodate wide variations in human size.
All of these approaches rely heavily on anthropometric measures of various types.*
Simply put, anthropometry provides a scientific basis for analyzing and designing ele- ments of the workplace so that they fit people of different sizes, as expanded in the follow- ing section.
Applied anthropometry
The field of applied anthropometry relates basic measures of human size, strength, and bodily motion to very helpful design criteria used by designers interested in creating things that fit or otherwise better match the size or other aspect of the human body. Some of these basic measures and design criteria are shown in Table 3.1. The table also gives examples of the many different things that might be designed (referred to as designed ele- ments in the table) to satisfy certain objectives or requirements associated with particular criteria and basic measures of the human body.
As quite apparent from the table, many different design criteria can be suggested.
The first criteria, fit, is especially appropriate for describing more intimate types of items, which are worn by a person such as clothing (see Box 3.1), ear plugs, gloves, or helmets. As such, fit requires body shape to be considered. Body shape is one of the most difficult items to get good information on. However, data collection systems are becoming available that allow the shape of a person’s foot, for example, to be scanned. This information can, in theory, then be sent to a manufacturer who will make a shoe or other clothing tailored to a specific person. This approach is rapidly becoming a reality.
Clearance requirements are often described in terms of the height and width of a rect- angular opening. The necessary clearance describes how much of safety margin needs to be provided between the latter measures and particular measures of the body to make it easy to pass through the opening or prevent collisions from occurring. Accessibility is a somewhat overlapping criterion that refers to how easy it is to reach something. This
*Chapter 2 covers the topics of anthropometry, human body movement, and biomechanics in some detail.
Table 3.1 Examples of Anthropometric Measures and Criteria Mapped to Design Elements and Objectives
Design
Criteria Anthropometric
Measure Designed Element Design Objective or Requirement Fit Body size and shape
Hand size and shape Foot size or shape Head size and shape Nose size and shape
Clothing Glove Shoe Helmet Glasses
Degree of looseness, tightness, comfort, etc.
Ear size and shape
Finger length Ear plug
Handle Ability to reach fingers around the handle
Clearance requirements
Body size and shape Door of car or building
Aisle or passageway Egress or ingress Clearance between users Standing height
Finger size or shape
Overhead objects Button or key on
keyboard
Collision avoidance (bumping head)
Foot size or shape Brake pedal Inadvertent activation of keys Inadvertent activation of gas
pedal
Accessibility Height Height of work surface Object within reach Length of arm Location on work surface
Length of finger Access hole on engine
Length of foot Location of brake pedal Pedal within reach Inaccessibility Diameter of finger
or hand
Diameter of child’s head
Guard
Distance between bars on baby crib
Prevent finger or hand from entering guard Openings into hazard zone
Length of arm or finger
Separation distance from hazard
Prevent head from entering though opening between bars Prevent hand or finger from
reaching the hazard zone Posture Standing height Height of work surface Reduce bending
Shoulder rotation Height of shelf Reduce extended reaches Wrist deviation Relative height of desk
to chair
Eliminate excessive deviation Visibility Standing eye height Location of sign Vision not blocked
Sitting eye height Height of seat in car Height of screen in
theater
Person can see over hood of car
Relative height of auditorium seats
Person can see over head of person sitting in front of them Mechanical
advantage Grip strength Handle length of scissors
or shears Person able to exert enough force to cut object
Finger length Handle diameter Person able to grasp handle tightly
Adjustability Variability of eye height
Variability of length of lower leg
Car seat Office seat
Adjust height of seat for shorter people
Adjust height of seat for shorter person or higher work surface
principle is especially important in deciding where to locate tools, parts, or items in a work area. It also applies to access openings, guides decisions on where to locate controls and input devices. It is especially important, for example, to be sure that emergency stops can be reached at the time they are needed.
Inaccessibility requirements refer to situations where it is important to make sure something is far enough away to make sure it might not be accidentally contacted. This principle is applied extensively in the design of guards and barriers. Postural criteria refer to the way particular combinations of design elements and human bodily measures inter- actively affect objectives such as the need to reduce bending, twisting, or awkward sus- tained postures. Visibility criteria are for the most part concerned with blockages of vision as a function of expected eye positions and the location of obstacles. Both of the latter factors can be controlled to some extent if necessary steps are taken, such as providing lower seating in the front rows of an auditorium. Mechanical advantage criteria describe how characteristics of particular design affect the forces people can exert. Longer han- dles on cutting shears, for example, make it easier for people to exert high cutting forces.
Adjustability criteria refer to how variability in particular bodily dimensions is accom- modated by particular design elements. Examples include adjustable height work tables, chairs, or stretchable gloves.
As mentioned in Chapter 2, anthropometric data is available for a number of target populations. While such data is helpful, it often requires quite a bit of interpretation before it can be applied. For example, simply knowing that most people have a body width measured in centimeters does not tell us how wide an aisle needs to be. Much effort has been spent over the years to make this leap in judgment, resulting in recom- mended dimensions for a wide variety of settings and tasks. Such sources include hand- books (e.g., Van Cott and Kincaide, 1972; Woodson, 1981) and standards published by governmental groups including the U.S. military (i.e., MILT 1452), NASA (STD-3000A and others), and OSHA (see CFR 1910). The Society of Automotive Engineers (SAE) also pub- lishes detailed recommendations for automobile interiors. It also should be mentioned that databases and scaled drafting templates are available from a variety of commercial institutions and consulting firms. Humanscale 1, 2, 3 is an example. Other commercially
BOX 3.1 BODY TYPE AND CLOTHING DESIGN
Clothing designers need to know something about the shape of the human body, before they can design clothing that fits (see Kemsley, 1957). Length dimensions, such as arm length and chest width, provide only an approximation of the human body’s shape. One of the earliest methods of body-type classification was developed by Sheldon who referred to a lean, slender, and fragile person as ectomorphic; a strong, sturdy, and muscular person as mesomorphic; and finally, the stocky, stout, and round person as endomorphic. Sheldon hypothesized that ectomorphs, meso- morphs, and endomorphs were fundamentally different in character. This approach turned out to be a dead end, as a psychological theory, but his distinction is defi- nitely relevant in anthropomorphic modeling. More recently, software developers have devised the categories of slim, athletic, regular, robust, corpulent, and extra corpulent. Most shoppers know that many clothing manufacturers produce different cuts of clothing for these different shapes of people.
available databases include the Architectural Graphic Standards* and Time-Saver Standards. Architectural Graphic Standards, as implied by the name, are primarily used to specify the dimensions of architectural details such as stairs, ramps, lavatories, and sinks. Some of the factors considered in various sources include the number of people occupying a space, the fire safety requirements of a space, or the building codes of a loca- tion.† Required dimensions to provide adequate access to facilities by disabled people are also available in most such sources.
Drafting templates
It might be argued that the most traditional ergonomic method for designing spaces for people to work, play, or live, has been to use scaled drawings and drafting templates.
Drafting templates are two-dimensional scaled models of the human body made of firm transparent plastic. The templates normally include pin joints that allow the body parts to be rotated into different positions, and come in different sizes. Figure 3.1 shows examples of articulated drafting templates providing scaled side views of 5th, 50th, and 95th percen- tile bodies. The first step of the process is to draw the side view of the design in the same scale used in the available templates. The templates then are overlaid onto the locations where people are expected to work. As part of this process, the different parts of the tem- plate can be moved in a way that duplicates how the people are expected to move.
Although such modeling helps determine, for instance, whether operators can reach all of the required objects and controls, use of drafting templates does not always pro- vide an accurate answer. These devices show quite accurately whether operators can touch
*The Architectural Graphic Standards, Ramsey and Sleeper (1932) are periodically updated. Also see Humanscale or other commercial sources for detailed information on this topic.
† The National Fire Protection Association (NFPA) publishes a collection of standards called the Life Safety Code, which addresses safety of occupants and safe egress. Other standards include model building codes and local codes.
reachMax
reachMax Funct
reach
Funct reach Drill 1/16 throughhole all pieces in line (TYP)
Figure 3.1 Drafting templates of human body shapes.
particular objects, but whether operators can grasp objects or activate control devices is not always certain. As a result, these graphic methods of assessing many of the ergonomic features are only considered as a first phase approximation of the design. Later tests are frequently made of actual equipment or full-scale mockups in order to be surer of ergo- nomic adequacy in the design.*
Design of work areas and stations
A work area may be thought of as the area within a building or other facility within which people do their tasks. A work area is likely to contain one or more workstations along with equipment or tools. In some cases, several people may be using the same work area, but normally will be at different workstations. Some work areas, and buildings in general, will also have traffic areas, such as passageways, aisles, corridors, or stairs, through which people pass as they perform their activities. The following discussion will provide some guidelines regarding the design and layout of work areas and workstations, illustrating some of the many ways anthropometric data can be used. The discussion will begin with a brief overview of some typical requirements for traffic areas, before moving on to several more specific topics, including recommended workplace dimensions, work layout, seating, and computer workstations.
Traffic areas
A lot of information is available from governmental sources such as MILT STD 1452, OSHA (see 29 CFR 1910), or the FAA (HF-STD-001) containing a variety of general requirements for stairs, aisles, ramps, floors, and other traffic areas. Some of the more typical require- ments found in such sources and elsewhere (also see Van Cott and Kincaide, 1972) are as follows:
1. Aisles and work areas should not occupy the same floor space to help prevent inter- ference and collisions.
2. Providing necessary pull-outs or turning space in aisles for passage of wheelchairs or material handling devices or equipment.
3. Ensuring that adequate space is marked out and allocated for placing materials in storage or marshalling areas, to eliminate interference with work or passage.
4. Appropriate markings of aisles and passageways.
5. Adequate clearance dimensions for aisles and passageways (Figure 3.2A and B).
6. Appropriate dimensions of stairs (Figure 3.3).
7. Appropriate flooring materials free of protruding objects that might create tripping hazards.
8. Eliminating obstacles that might be collided with.
9. Avoiding blind corners.
10. Making sure there is connected, accessible path, by which disabled users can reach most of the facility.
11. Ensuring that doors do not open into corridors.
12. Avoiding one-way traffic flow in aisles.
13. Special requirements for emergency doors and corridors.
*See Pheasant (1991) in the Evaluation of Human Work (Wilson & Corlett, editors).
One person non-egress (forward passage)
Two person passage
(A)
One door 1.67–1.83 m
(5.5–6.0 ft) Facing doors 2.13–2.34 m (7.0 –7.7 ft)
1.22–1.37 m (4.0–4.5 ft)
Minimum clearance: 510 mm (20 in.) Preferred clearance: 780 mm (30 in.)
4254 60
3036 36
76 27
36 36
40
6992 92
102 40
44102 112
48 123 130 51 9292
137152
18
31
1720 50 24 61
43
9696 96
244244 36 244
38 79
59 150
(B)
157 62
9297
22 20
2624 5061 66 32 815646
7375 78 198191185 107
cm in.
Figure 3.2 Clearance requirements in passageways. (From A: FAA HF-STD-001, 2003; B: Rigby, L.V. et al., Guide to integrated system design for maintainability, USAF, ASD, TR 61-424, 1961.)
Not all of these requirements are easily related to anthropometric qualities of the human body, but many of them are. For example, it is easy to see that the clearance requirements for passageways, as well as possible work locations (Figure 3.2A and B), are very much related to the width and orientation of the human body. The potential presence of wheel chairs, material handling carts, or other items is also a concern. Figure 3.4 shows some clearance dimensions for a traditional wheelchair. A quick comparison to the clearance dimensions in Figure 3.2A shows that wheelchairs require significantly more space to pass without risking a collision in a passageway than walking people do. Consequently, it may be necessary to provide turn around spaces or pull out areas for wheelchairs in corridors.
Stair dimensions such as appropriate tread depth, riser height, handrail height, handrail diameter, and overhead height are also related to body size in important ways.
Workplace dimensions and layout principles
People do many of their tasks while standing or sitting in front of tables, work benches, desks, conveyer belts, or other flat work surfaces. In some cases, as when people write on a piece of paper, the activity is performed on the surface itself. In others, much of the activity is performed immediately above the surface, as when people pick up an object and manipulate it in some way, before setting it down again. If we wanted to describe the spatial element of the particular task setting, or workplace, accurately, several workplace
Angle of rise
Minimum Maximum Best
30° 50°
24 cm (9.5 in.) 13 cm (5 in.) 2 cm (0.75 in.)
56 cm (22 in.) 122 cm (48 in.) 2.1 m (7 ft) 76 cm (30 in.) 4 cm (1.5 in.) 8 cm (3 in.)
86 cm (34 in.) 8 cm (3 in.)
8 cm (3 in.) 84 cm (33 in.) 56 cm (22 in.) 28–30 cm (11–12 in.) 17–18 cm (6.5–7 in.)
130 cm (51 in.) 2.1 m (7 ft) 4 cm (1.5 in.) 3 cm (1 in.)
4 cm (1.5 in.) 20 cm (8 in.)
30 cm (12 in.)
—
—
—
— A —
F H
D B G C
E A I
CB D E
F G H I
Tread depth Riser height Depth of nosing Width (handrail to handrail) One-way stairs Two-way stairs Minimum overhead clearance
Height of handrail Diameter of handrail Hand clearance
Figure 3.3 Recommended dimensions for stairs. (From FAA HF-STD-001, 2003.)