CIH Ergonomics Reference
In the order the exam works: risk factors and the body, recognize the disorders, evaluate with the tools, then control and manage, plus office setup, lighting and a self-test. The fact an exam question most often leans on is in red.
How to use this page
BGC treats ergonomics as one of the technical subject areasBGC, and the exam reaches it three ways: recognizing ergonomic hazards, measuring ergonomic risk factors in a survey, and applying ergonomic controls. This page follows that path.
- Red text is the recognition cue; yellow cards are memory tricks and worked examples.
- Original wording, not a copy of any course text, BGC material or OSHA publication. Sources are on the CIH references page.
01 What Ergonomics Is, and What Drives Risk
The definition, the difference from human factors, and the six risk factors every disorder traces back to.
Ergonomics fits the job to the person, not the person to the job. BGC defines the subject as anthropometry, human factors, biomechanics and work physiology applied to workplace designBGC. The aim is to keep the demands of a task inside what people can sustain, so fatigue and injury stay low and performance stays high.
| Term | What it focuses on |
|---|---|
| Ergonomics | The body’s physiological response to work demands. Keep the task within human capacity so fatigue stays manageable |
| Human factors | The worker–machine interface: how people interact with controls and displays, and how to reduce human error |
| Anthropometry | Body dimensions, used to size workspaces, reaches and clearances |
| Biomechanics | Mechanical forces on the body: moments, compression and the stress they put on muscles and joints |
| Work physiology | The energy cost of work, fatigue, and the balance of work and recovery |
The six risk factors
| Risk factor | What it looks like on the job |
|---|---|
| Force | Heavy lifting, a hard grip, a strong pinch, pushing or pulling a loaded cart |
| Awkward posture | Elbows above mid-torso, hands above the shoulders, a wrist bent or twisted, a held static position |
| Repetition | The same motion at a high rate with little variation |
| Vibration | Hand-arm vibration from power tools, whole-body vibration from vehicles and heavy machinery |
| Inadequate rest | No chance for tissue to recover between efforts or between shifts |
| Extreme environment | Cold, heat, noise or poor lighting that raises grip force or forces a poor posture |
Hard edges pressing on the skin (contact stress) are often counted as a seventh factor. Risk comes from combinations: force plus repetition plus an awkward posture is far worse than any one alone. OSHA has no general ergonomics standard, so musculoskeletal hazards are enforced under the General Duty ClauseOSHA.
02 The Body: Anthropometry and Biomechanics
Whose body you design for, and how a load held away from the spine multiplies the force on it.
Anthropometry: whose body you design for
A percentile says how many people are smaller than a given size: the 5th percentile means 5% are smaller, the 95th means 95% are smaller. Designing for one narrow group, such as healthy young men, leaves much of the workforce out.
| Principle | Use it when | Example |
|---|---|---|
| Design for the extreme | One end of the range decides whether the design works at all | Clearance (doors, headroom) for the largest user; reach to a control for the smallest user |
| Design for adjustability | People differ widely and the item can move | Chair height, monitor height, a sit-stand desk, spanning roughly the 5th percentile woman to the 95th percentile man |
| Design for the average | Rarely, and only where being off the average harms no one | A fixed item no one needs to fit closely |
Biomechanics: moments and compression
A moment is force times perpendicular distance. The farther a load is from the spine, the bigger the turning effect the back muscles must resist.
| Concept | What to remember |
|---|---|
| Moment = force × distance | Double the distance and the moment doubles. This is why keeping a load close to the body matters more than almost any other lifting tip |
| Compression | The back muscles pull from a short lever arm close to the spine, so they pull much harder than the load itself. The disc takes the sum, several times the weight in the hands |
| NIOSH 1981 action limit | 3,400 N of compression at the L5/S1 disc, the benchmark the original NIOSH lifting guide usedNIOSH |
03 Recognize: The Disorders
Sorted by what is damaged: nerves, tendons, the lower body, and bursa, joint and muscle.
Cumulative trauma disorders build from repeated small injuries rather than one event. Sort them by what is being damaged, then match the body part to the work factor.
Nerves and blood vessels
| Disorder | What is affected | Typical work factors |
|---|---|---|
| Carpal tunnel syndrome | Median nerve at the wrist: thumb, index, middle and half the ring finger | Repetitive forceful gripping, bent-wrist work, long keyboard or scanning work |
| Cubital tunnel syndrome | Ulnar nerve at the elbow: little finger and half the ring finger | Leaning on the elbow, holding the elbow sharply bent |
| Guyon’s canal syndrome | Ulnar nerve at the base of the palm | Sustained pressure on the heel of the hand, such as handlebars or a tool base |
| Radial tunnel syndrome | Radial nerve branch in the forearm: pain over the top of the forearm | Repeated forearm rotation, wrist extension and a heavy grip |
| Thoracic outlet syndrome | Nerves and vessels between the neck and shoulder | Overhead reaching, a slouched shoulder girdle, carrying heavy loads |
| Hand-arm vibration syndrome (vibration white finger) | Blood vessels and nerves of the fingers; a secondary Raynaud’s phenomenon | Chronic use of vibrating hand tools: jackhammers, chainsaws, grinders |
Tendons and sheaths
| Disorder | What is affected | Typical work factors |
|---|---|---|
| Tennis elbow (lateral epicondylitis) | Extensor tendons at the outer elbow | Repeated wrist extension, forceful forearm twisting, heavy grip |
| Golfer’s elbow (medial epicondylitis) | Flexor tendons at the inner elbow | Repeated wrist flexion, pulling, tight clenching |
| De Quervain’s syndrome | Thumb tendon sheaths at the wrist | Constant thumb pinching, wringing, repeated hand twisting |
| Trigger finger | Finger flexor tendon in its sheath | Repetitive gripping, tools with hard edges pressing the palm |
| Ganglion cyst | A fluid-filled swelling near a wrist or hand joint | Associated with repetitive wrist work |
Lower body
| Disorder | What is affected | Typical work factors |
|---|---|---|
| Meralgia paresthetica | Lateral femoral cutaneous nerve: numbness on the outer thigh, sensory only | A heavy tool or duty belt, tight clothing or body armor |
| Sciatica | Sciatic nerve, with pain running down one leg | Whole-body vibration from driving, heavy lifting, repeated twisting of the spine |
| Tarsal tunnel syndrome | Tibial nerve at the ankle and sole of the foot | Prolonged standing, repetitive foot or ankle work |
Bursa, joint and muscle
| Disorder | What is affected | Typical work factors |
|---|---|---|
| Bursitis | The fluid-filled sacs that cushion joints | Repeated friction or pressure: kneeling, resting an elbow on a hard surface |
| Work-related osteoarthritis | Joint cartilage in the knees and spine | Years of heavy lifting, joint impact and kneeling |
| Myofascial pain syndrome | Skeletal muscle of the neck and back | Static postures, long sitting, constant muscle tension |
| Plantar fasciitis | The connective tissue of the foot arch | Standing for long periods on hard floors |
04 Evaluate: ACGIH Tools, the NIOSH Lifting Equation and Work Physiology
How the hands, the back and the whole body are measured against a limit.
Recognizing a disorder says where the damage is. Evaluation says how much exposure is too much. Each tool targets a different body regionACGIH.
| Tool | Target | What you measure |
|---|---|---|
| ACGIH Hand Activity Level (HAL) | Hands, wrists, forearms | Average hand activity (0–10) and peak hand force. Applies to mono-task hand work done four or more hours a day |
| ACGIH Lifting TLV | Low back, shoulders | Weight limits read from tables by lift frequency, daily duration, horizontal distance and lift height. The best-case limit is about 32 kg (70 lb) |
| ACGIH Upper Limb Localized Fatigue | Upper limbs, shoulders | Duty cycle against relative force (% of maximum): the more of the time a muscle works, the less force it can sustain |
| NIOSH lifting equation | Low back | Recommended weight limit (RWL) and lifting index (LI)NIOSH |
| Work physiology | Whole body | Energy expenditure or heart rate against what the worker can sustain over a shift |
Hand Activity Level: the two equations
| Quantity | Equation |
|---|---|
| HAL | A 0–10 rating of repetition: 0 is idle, 10 is the greatest repetition imaginable or continuous exertion |
| TLV for peak force (NPF) | NPFTLV = 0.56 × (10 − HAL) |
| Action Limit | NPFAL = NPFTLV − 2 |
NIOSH lifting equation
The equation starts from a best-case load and cuts it for every way the lift departs from ideal: RWL = LC × HM × VM × DM × AM × FM × CM. Metric form, with distances in centimetres.
| Term | Meaning | Value |
|---|---|---|
| LC | Load constant | 23 kg |
| HM | Horizontal multiplier (H = hands to the midpoint between the ankles) | 25 ÷ H |
| VM | Vertical multiplier (V = hand height at the start of the lift) | 1 − 0.003 × |V − 75| |
| DM | Distance multiplier (D = vertical travel) | 0.82 + 4.5 ÷ D |
| AM | Asymmetric multiplier (A = twist angle in degrees) | 1 − 0.0032 × A |
| FM, CM | Frequency and coupling (grip quality) multipliers | Read from tables |
| Lifting index | LI = load ÷ RWL | Above 1: increased risk. Above 3: substantial risk, redesign |
Equation cards: NIOSH recommended weight limit (RWL) · Lifting index (LI).
Work physiology and what a job analysis looks at
| Idea | What to remember |
|---|---|
| Sustained work limit | Over an eight-hour day, energy expenditure should stay near one third of maximum aerobic capacity, roughly 5 kcal per minute for a fit workerNIOSH |
| Heart rate | Heart rate and oxygen uptake both rise with work intensity, so either can estimate energy cost |
| Effort level | Light, moderate or heavy work, judged by intensity, duration and frequency together |
| Fatigue management | Work and recovery cycles, machine pacing and shift planning |
| Job analysis dimension | What it covers |
|---|---|
| Physical and motion | Mass handled, repetition rate, working heights, postures, reaches, task duration |
| Environmental | Temperature, noise, illumination, long hours, PPE that restricts movement |
| Mental and perceptual | Information handling, decision complexity, visual and auditory demands, external pacing |
05 Control: From Symptom to Fix
Engineering before administrative, and the best first fix for each complaint.
Ergonomic controls follow the usual order: change the job first, then change how people do it. Gloves and braces are a weak last resort, not a fix.
| Level | Examples |
|---|---|
| Engineering | Adjustable workstations, lift assists, fixtures and jigs, redesigned tool handles, vibration isolation |
| Administrative | Job rotation, extra breaks, pacing, training in body mechanics |
| PPE | Anti-vibration gloves, knee pads: a supplement, never the main answer |
Symptom to fix
| Area | Complaint and clue | Likely root cause | Best first engineering control |
|---|---|---|---|
| Any muscle group | Deep burning ache, cramping, fatigue | A held static posture: continuous contraction squeezes the blood supply | Jigs, fixtures or adjustable supports so no one has to hold the position |
| Wrist and hand | Tingling in the thumb, index and middle fingers | Bent wrist plus repetition (carpal tunnel) | Adjustable keyboard or mouse tray, curved or angled tool handles to keep the wrist neutral |
| Forearm and back of hand | Aching or stabbing over the top of the forearm | Wrist extension, forearm rotation and a heavy grip (radial tunnel) | Change tool angle or work height so the forearm stays in a neutral plane |
| Elbow and little finger | Tingling in the little finger | Pressure on the elbow or palm (cubital tunnel, Guyon’s canal) | Rounded, padded forearm or palm rests |
| Neck and upper back | Sore neck, tension headaches | A screen too low or too high | Adjustable monitor arm: top of the screen at or slightly below eye level |
| Shoulders | Dull ache, tight rotator cuff | Long reaches, elbows above shoulder height | Re-lay the work so tools sit close to the body, between hip and chest height |
| Lower back (sitting) | Dull ache and stiffness after sitting | No lumbar support | A fully adjustable chair with lumbar support |
| Lower back (lifting) | Back pain after lifts | Loads held far from the body, lifts from the floor | Lift assists, raise the work to waist height, keep loads close |
| Outer thigh | Numbness only, no weakness | A heavy tool belt or tight gear (meralgia paresthetica) | Take the weight off the waist: suspenders or a load-bearing vest |
| Knees | Pain and swelling from kneeling | Work done at floor level | Lift tables or hoists to bring the work to waist height |
| Feet and legs | Burning arches, heel stiffness | Standing on hard concrete all shift | Anti-fatigue mats, a sit-stand stool |
| Whole body | Low back pain, leg pain | Whole-body vibration from forklifts and heavy machinery | Air-ride suspension seats, vibration-isolation mounts |
Lifting and posture rules
| Rule | Why |
|---|---|
| Keep the load close, lift smoothly near waist height, avoid twisting, use aids | Distance multiplies the moment on the spine; a jerk or a twist adds force the back is not built to take |
| Avoid work with elbows above mid-torso or hands above the shoulders | Overhead and high work loads the shoulder and cuts blood flow |
| Avoid extreme wrist positions and strong pinch grips | Flexion, extension and side-to-side deviation squeeze the carpal tunnel and strain the tendons |
06 The Ergonomics Program
The six elements that turn one-off fixes into a program that keeps working.
One fix solves one job. A program finds the next problem early and keeps fixes in place.
| Element | What it involves | Why it matters |
|---|---|---|
| 1. Management commitment and employee involvement | Workers help find hazards and propose fixes; management supplies budget, resources and authority | Keeps the program proactive and uses the hands-on knowledge of the people doing the job |
| 2. Problem identification | Review injury logs, workers’ compensation claims and absences; give workers an easy way to report early symptoms | Catches micro-trauma before it becomes a chronic disorder |
| 3. Job hazard analysis | Formal task assessment with tools such as the HAL TLV or the lifting equation; measure force, repetition, posture and vibration | Pins down which tasks are doing the damage |
| 4. Hazard prevention and control | Engineering fixes first, then administrative ones such as rotation and breaks | Changes the job to fit the person |
| 5. Training and education | Body mechanics for workers; hazard recognition for managers and engineers | Helps people keep safe habits and spot risk early |
| 6. Medical management | Early evaluation, therapy and restricted-duty options | Returns people to full capacity without re-injury |
07 Workstations and the Office
Sit, stand or both; which display fits which job; and a computer desk set up correctly.
| Layout | Best for |
|---|---|
| Sitting | Fine assembly or writing, with no heavy items and no large forces |
| Standing | Handling heavy items, or tasks needing long reaches |
| Sit/stand | Repetitive operations with frequent reaches: the worker can change position |
Displays: match the readout to the question
| Display | Best for |
|---|---|
| Annunciator light | Reporting a major event or a deviation |
| Digital readout | An exact number: quantitative reading or gauging |
| Dial readout | A quick check-reading: is it in the normal band? |
| Graphical readout | Watching a trend over time |
The computer desk
| Item | Setup |
|---|---|
| Chair height and seat | Feet flat on the floor, knees near 90°, thighs supported with a little clearance behind the kneesOSHA |
| Backrest and armrests | Lumbar support, a hip angle of 90° or a little more, armrests set so the shoulders stay relaxed and do not shrug |
| Monitor | Top of the screen at or slightly below eye level, about an arm’s length away |
| Keyboard and mouse | Close to the body with the wrists neutral; split or curved keyboards and vertical mice help some people |
| Habit | Common guidance |
|---|---|
| Move through the day | Long unbroken sitting carries health risk beyond posture. Alternating sitting and standing about every 30 minutes is the usual advice |
| Micro-breaks | Short breaks and stretching about every 30 minutes |
| Rest the eyes | The 20-20-20 habit: every 20 minutes look at something 20 feet away for 20 seconds |
The 30-minute and 20-20-20 figures are widely repeated good-practice guidance, not regulatory limits. Do not present them as OSHA or ACGIH requirements.
08 Illumination
Light units, the inverse-square law, and how much light each kind of task needs.
| Quantity | What it describes | Unit |
|---|---|---|
| Luminous flux | Total light a source emits | lumen (lm) |
| Illuminance | Light arriving on a surface | lux (lm/m²) or foot-candle (lm/ft²); 1 fc = 10.76 lux |
| Luminous intensity | Light a source sends in one direction | candela (cd) |
| Luminance | How bright a surface looks to the eye | cd/m² |
How much light does the task need?
| Zone | Typical tasks | IES categories | Lux | Foot-candles (approx.) |
|---|---|---|---|---|
| Safety and transit | Parking lots, entryways, stairways, inactive storage, occasional tasks | A–C | 20–200 | 2–20 |
| Standard work | Office screen work, reading print, large or high-contrast tasks | D | 200–500 | 20–50 |
| Precision work | Small or low-contrast tasks, vehicle repair, difficult assembly and inspection | E–F | 500–2,000 | 50–200 |
| Exacting work | Very small, low-contrast tasks done for long periods, such as fine inspection | G–H | 2,000–10,000 | 200–1,000 |
Construction-site minimums are far below recommended levels
| Construction area (29 CFR 1926.56) | Minimum |
|---|---|
| General construction areas, concrete placement, excavation, accessways, loading platforms | 3 foot-candles |
| General construction area lighting; indoor warehouses, corridors, hallways, exitways; tunnels and shafts (10 foot-candles at tunnel headings during drilling, mucking and scaling) | 5 foot-candles |
| General construction plant and shops: equipment rooms, carpenter shops, active store rooms, mess halls | 10 foot-candles |
| First-aid stations, infirmaries and offices | 30 foot-candles |
These are minimums for construction workOSHA. Recommended task levels in the table above are far higher. Glare also matters: direct glare from a bright source and reflected glare from a glossy surface both cut visibility, and older workers need more light for the same task.
09 Self-Test
Original scenarios. Cover the answer, decide, then open it.
1A packaging operator repeats a forceful pinch grip all shift and reports night-time numbness in the thumb, index and middle fingers. Which nerve and which condition?
The median nerve at the wrist: carpal tunnel syndrome. Neutral wrist positions and curved or angled tool handles are the first engineering response.
2A painter repeatedly extends the wrist while gripping a roller and has tenderness on the outside of the elbow. Which condition, and which tendons?
Lateral epicondylitis, tennis elbow. It involves the extensor tendons at the outer elbow.
3A hand-intensive job is rated HAL 5. What are the TLV and Action Limit for peak force, and what does an observed peak force of 2.5 mean?
TLV = 0.56 × (10 − 5) = 2.80. Action Limit = 2.80 − 2 = 0.80. A force of 2.5 is under the TLV but well above the Action Limit, so controls are warranted.
4A worker lifts a 15 kg box with H = 40 cm, V = 50 cm, D = 40 cm and no twist. FM and CM are both 1.00. What are the RWL and the lifting index, and what do they say?
HM = 0.63, VM = 0.93, DM = 0.93. RWL = 23 × 0.63 × 0.93 × 0.93 ≈ 12.4 kg. LI = 15 ÷ 12.4 ≈ 1.21. Above 1 means increased risk, so the lift should be redesigned, starting by bringing the load closer.
5A designer must set the headroom of a machine-room doorway and the reach distance to an emergency stop. Which body size sets each?
Headroom (a clearance) is set by the largest user, for example a 95th percentile man or taller. Reach to the stop is set by the smallest user, for example a 5th percentile woman.
6A worker holds a 10 kg load 20 cm from the spine and then 40 cm from it. What happens to the moment about the spine?
It doubles, from about 19.6 N·m to about 39.2 N·m. Moment is force times distance, so doubling the distance doubles the moment.
7A job requires about 7 kcal per minute for a full eight-hour shift. What is the concern, and what are the options?
It is well above the roughly 5 kcal per minute (about one third of aerobic capacity) usually sustainable over a day. Reduce the load with mechanical aids, add rest, rotate the work or share it.
8A single bulb has an intensity of 2,000 cd. What is the illuminance on a facing surface 2 m away, and 4 m away?
E = I ÷ d²: 2,000 ÷ 4 = 500 lux at 2 m, and 2,000 ÷ 16 = 125 lux at 4 m. Doubling the distance cuts it to a quarter.
9A carpenter wearing a loaded tool belt has numbness on the outer thigh but no weakness. Which condition, and what is the first fix?
Meralgia paresthetica, compression of the lateral femoral cutaneous nerve, which is sensory only. Take the weight off the waist with suspenders or a load-bearing vest.
These are original practice scenarios written for this page. They are not BGC questions and do not predict exam content.