23-Ind-B5 Ergonomics · December 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — Dec. 2014 — 98-Ind-B5 Ergonomics. Three-hour, open-book exam (all notes, books and any non-communicating calculator permitted); the paper requires 4 of its 5 questions (Part A mandatory, any two of Part B's Questions 2–4, and Part C mandatory) — all five are solved below for completeness.
Reference texts: Sanders & McCormick, Human Factors in Engineering and Design (7th ed.) — controls/displays, anthropometry, workplace and computer-workstation design; Waters, Putz-Anderson & Garg, NIOSH Applications Manual for the Revised NIOSH Lifting Equation (1994) — the RWL/LI formula and multiplier tables reproduced on the exam's own pages 6–7; NIOSH, Elements of Ergonomics Programs (1997) and CSA Z1004 (Canada) — workplace musculoskeletal-disorder (MSD) prevention programs.
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
Computer workstation design is governed by three linked principles. First, neutral posture: the workstation should let the user maintain straight wrists, elbows near 90–100°, upper arms relaxed at the sides, a monitor top at or slightly below eye height so the neck stays near vertical, and feet fully supported, since sustained deviation from these neutral joint angles is the mechanism behind most computer-related MSDs. Second, adjustability: because no single fixed geometry can put every user's joints in a neutral posture simultaneously – users vary in stature, arm length, and seated eye height – every element that determines posture (seat height, work-surface height, monitor position, keyboard/mouse height) must be independently adjustable across the range needed to accommodate the working population (conventionally the 5th-percentile female to 95th-percentile male). Third, multi-task accommodation: since the same station must support both screen-based work and paper-based work, the layout must let the user switch between a keyboard/mouse task and a reading/writing task without repeatedly re-adjusting the whole station – achieved by giving the document holder and work surface their own independent positioning rather than sharing a single fixed height with the keyboard.
The station is built from six elements, each adjustable over the range needed to seat a 5th-percentile-female to 95th-percentile-male population:
Monitor (on an arm). Vertical range of roughly ±15 cm so the top of the screen can be set at or just below seated eye height for any user's eye height, viewing distance adjustable 50–100 cm, and tilt adjustable about ±20° to keep the screen perpendicular to the line of sight.
Document holder. Independently positionable and placed in-line with the monitor (same viewing distance/angle) rather than flat on the desk, so paper-based work does not force repeated neck flexion/rotation between screen and document – this is the element that specifically makes the station "multipurpose" rather than computer-only.
Keyboard/mouse tray. Height-adjustable independently of the main work surface (since a fixed desk height cannot simultaneously be correct for typing and for writing/reading), with a 0° to about −15° negative-tilt range so the wrists can stay straight regardless of elbow height, sized to keep elbow angle in the 90–100° neutral range.
Work surface (desk). Height-adjustable across roughly 56–84 cm (22–33 in), which spans seated use for the full percentile range and also permits sit-stand use – the widest single adjustability range on the station because it must accommodate both the shortest seated user and a standing posture.
Chair. Seat height adjustable roughly 38–53 cm (so feet remain flat or the footrest compensates), seat-pan depth adjustable to fit thigh length without pressing behind the knee, backrest height and recline adjustable with lumbar support positionable to the user's own lumbar curve, and armrests adjustable in height and width so the forearms can be supported without elevating the shoulders.
Footrest. Height- and angle-adjustable, provided as a compensating element for any user whose seat height (set for correct keyboard/elbow geometry) leaves their feet unsupported off the floor – without it, a shorter user is forced to choose between correct arm posture and correct leg posture.
