Rapid Office Strain Assessment (ROSA)
Quantifies ergonomic risk for computer workstation environments
Assessment Details
Assessment Reference Guide (How Scoring Works)
Click to expand
Click to collapse
The Core Logic: The ROSA tool works by asking you to observe the worker and answer simple setup questions. Your answers establish a "Base Score" for each body part. Additional checkboxes apply "Penalty Points" for risk factors like hard edges or lack of adjustability.
The Lookup Grids: You don't need to do the math. The tool automatically cross-references your Base + Penalty scores on official, empirical ROSA lookup grids. The Final ROSA Score (1 to 10) is the calculated intersection of the worker's Chair setup vs. their Peripherals (Monitor/Phone/Keyboard/Mouse) setup.
Risk isn't just posture; it's how long that posture is held. Modifiers are automatically applied based on your selections:
Note: The Chair and Computer Peripherals (Monitor, Mouse, Keyboard) use global duration modifiers based on overall time seated/working. The Telephone has an independent duration modifier to account for varying communication demands.
Seat Pan Height
Whether the knees sit at roughly 90 degrees with the feet flat on the floor. A neutral setup scores 1. A seat too low (knees above the hips) or too high (feet dangling) scores 2, and no foot contact at all scores 3. Add 1 point each for insufficient leg room under the desk and for a height that cannot be adjusted.
Seat Pan Depth
The clearance between the front edge of the seat and the back of the knee, ideally about 7.5 cm (3 inches). Neutral scores 1. A pan too long (less than 3 inches of clearance, pressure behind the knee) or too short (more than 3 inches, thighs unsupported) scores 2. Add 1 point if the depth cannot be adjusted.
Armrests
Elbows resting supported at about 90 degrees with relaxed shoulders. Neutral scores 1. Armrests too high (shoulders shrugged) or too low (elbows unsupported) score 2. Add 1 point each for armrests that are too wide, have a hard or damaged surface, or cannot be adjusted.
Back Support
Lumbar support fitting the small of the back, with the chair reclined about 95 to 110 degrees. Neutral scores 1. Missing or misaligned lumbar support, a recline past 110 degrees, or no back contact (leaning forward or perching on a stool) each score 2. Add 1 point if the desk is high enough to negate the back support, and 1 point if the backrest is non-adjustable.
Monitor
Top of the screen near eye level at about an arm's length. Neutral scores 1. A screen low enough to bend the neck down scores 2; a very low screen, or one high enough to tip the neck back, scores 3. Add 1 point each for a screen placed too far, a neck twist beyond 30 degrees to see it, glare on the screen, and paper documents used without a holder.
Telephone
A headset or one-handed hold with a neutral neck, handset within about 300 mm. Neutral scores 1. Reaching beyond 300 mm scores 2, and cradling the phone between the neck and shoulder scores 3. Add 1 point if no hands-free option is available. The telephone carries its own duration modifier, separate from the computer.
Mouse
In line with the shoulder, on the same surface and level as the keyboard. Neutral scores 1. Reaching outward or forward to the mouse scores 2. Add 2 points if the mouse and keyboard sit on different levels, 1 point for a pinch grip or undersized mouse, and 1 point for a palm rest that creates a pressure point in front of the mouse.
Keyboard
Wrists straight and shoulders relaxed. Neutral scores 1. Wrists extended beyond about 15 degrees score 2. Add 1 point each for side to side wrist deviation while typing, a keyboard high enough to shrug the shoulders, and reaching out or overhead to type.
How the Sections Combine
Each component score, with its duration modifier, is paired with its partner on a lookup grid: seat height and depth versus armrests and back support give the Chair score; monitor versus telephone give Section B; mouse versus keyboard give Section C. Section B and C combine into a Peripherals score, which is then read against the Chair score on the final grid to give the ROSA score from 1 to 10.
- ▸Office computer work only: ROSA was developed and validated for seated computer workstations using the CSA Z412 office guidelines. It does not apply to standing desks, laptop-only setups without peripherals, industrial or manual tasks, or non-computer office activities.
- ▸Equipment setup, not measured angles: Unlike RULA or REBA, ROSA scores equipment position and broad posture categories rather than measured joint angles. A workstation can score low while the worker still adopts awkward wrist or neck postures the checklist does not capture. Pair it with RULA for a detailed upper-limb posture assessment.
- ▸Single observation snapshot: A score reflects the setup and postures seen during one brief observation. It does not capture how posture shifts across the day, nor the protective effect of movement and micro-breaks.
- ▸Duration is self-reported: The duration modifiers depend on the worker's estimate of continuous and daily use, which is often inaccurate. Confirm against software usage logs or direct observation where it matters.
- ▸Chair scoring is the least reliable part: In the validation study the final, mouse and keyboard, and monitor scores showed excellent inter-observer reliability, but the chair score was only moderate (ICC 0.51). Chair scoring benefits most from assessor training and calibration.
- ▸Moderate discomfort correlation: ROSA final scores correlate with reported discomfort at about R = 0.38. A low score lowers but does not eliminate risk, and personal factors such as prior injury, stress, and fitness are not modelled.
The final score is driven by whichever is higher, the Chair score or the Peripherals score. Improving the lower side will not change the final score, so always target the dominant section first.
- 1.Treat 5 as the action level: A final score of 5 or higher is the validated action level, where reported discomfort rises sharply. Prioritise any workstation scoring 5 or above for change, and use lower scores to screen out setups that need no immediate action.
- 2.Fix the chair first: The chair section showed the largest improvement after intervention in field studies. Provide an adjustable chair and set it to neutral (knees at 90 degrees, feet flat, lumbar support in the small of the back, armrests at elbow height) before investing in other equipment.
- 3.Cut reach and neck load: Bring the mouse in line with the shoulder on the keyboard surface, raise the monitor to eye level at arm's length, and supply a headset to eliminate phone cradling. These directly lower the Section B and C scores.
- 4.Lower the duration modifier: Where continuous or daily use is long, build in task variation, micro-breaks, and short standing or walking breaks. Dropping a section from the over 4 hours band to the 1 to 4 hours band removes a full point from that section.
- 5.Train, then re-score: The most durable gains come from giving workers adjustable equipment and training them to set it up, rather than either step alone. Re-score after the change with the same tool to confirm the final score has dropped.
Chair Evaluation
Total time the worker spends seated in this chair.
Monitor & Telephone
Mouse & Keyboard
Applies globally to Monitor, Mouse, and Keyboard.
ROSA Final Score
Calculated Intersection
Room for improvement. Minor adjustments recommended.