CHAPTER 14
DESIGN FOR USABILITY (HUMAN FACTORS)
1) Human factors refer to those characteristics that are associated with the human being that
must be considered in the design of systems where there are humans (i.e., operators and
maintainers) involved in the operation, maintenance, and/or support of the system.
Consideration must be given to the human’s anthropometric characteristics (i.e., human
physical dimensions – both static and dynamic), sensory factors (i.e., hearing, sight, feel,
smell, etc.), physiological factors (i.e., impact on the human from external environmental
forces such as temperature extremes, vibration, noise, radiation, toxicity), psychological
factors (i.e., human needs, expectations, motivation, attitude, etc.), and their
interrelationships. It is essential that the “human” be considered as a major element of the
system (along with hardware, software, facilities, data/information, elements of support),
and that these factors be addressed from the beginning in the early stages of conceptual
design. Referring to Figures 2.6 (page 38), 4.4 (page 107), 4.9 (page 116), and 5.3 (page
132), human factors and human system integration (HSI) requirements must be properly
integrated with other design requirements to include reliability (Chapter 12, page 362),
maintainability (Chapter 13, page 410), supportability (Chapter 15, page 497), and so on.
Reference: Figure 2.6 (page 38), Section 4.4 (page 112), and Section 14.1 (pages 469–481).
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14) Personnel quantities and skill–level requirements are defined through the OTA, OSD, and
MTA (for maintenance personnel). The OTA, with the support of “timeline” and
“workload” analyses, leads to the identification of operator personnel quantities and skills.
The requirements for each task/function are combined, integrated, and assigned to specific
“job positions” or “work stations,” leading to the total number of positions by skill level.
The MTA is used for the purposes of determining maintenance personnel quantities and
skills. Potential problem areas are noted when the quantity of personnel is high and/or
when high skill–levels are required to accomplish a task/function. Reference: Section
13.5.5 (page 446) and Section 14.4.1 (page 486).
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18) The effectiveness of a training program may be measured at the “output” stage in terms of
the number of functions/tasks completed, the number of individuals involved in the
process, and the number and type of errors made as a result. This type of information can
be acquired from an overall organizational standpoint. More specifically, the adequacy of
personnel training can be assessed through a personnel test and evaluation exercise (refer
to Section 6.2.3 on page 154 and Section 14.6 on page 494), an error analysis (Section
14.4.3, page 489), or some activity of an equivalent nature. Operator/maintenance
personnel, in accomplishing their assigned functions/tasks, are monitored in terms of their
level of performance; i.e., accuracy, timeliness, and the consumption of resources in the
performance of a task. In the event that errors are introduced in the process, the possible
“causes” for such will be investigated, and the results will be evaluated in terms of the
adequacy of the training program for the individuals involved. This may result in some
changes in training coverage and emphasis. Reference: Section 14.5 (page 492).
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