Lecture 4: Office Ergonomics PDF

# Lecture 4 ## Recommendations to improve sitting workstations - The Use of **ergonomic** (**well-designed**) chair; a chair becomes ergonomic only when it specifically suits a worker's body dimensions (anthropometry), their particular workstation, and the work tasks. - The average office los...

# Lecture 4 ## Recommendations to improve sitting workstations - The Use of **ergonomic** (**well-designed**) chair; a chair becomes ergonomic only when it specifically suits a worker's body dimensions (anthropometry), their particular workstation, and the work tasks. - The average office loses over $7500 per employee per year in poor productivity and medical and workers’ compensation claims (the bureau of labor statistics). - LBP comprises 50% of these cases. - A survey conducted 1996 on 670 full-time computer users showed that their back complaints are related to poor ergonomic furniture, including the chair. - Another survey conducted 2002 on 170 women typists working at computers, mismatch between chair height and desk height and poor furniture. ## Chair components and dimensions - **Headrest** - **Lumbar Support System** - **Arm Pads** - **Arms** - **Seat Pad/Pan** - **Chair Mechanism** - **Footring** - **Chair Cylinder** - **Cylinder Cover** - **Chair Base** - **Casters** The image shows a chair with the above components. The chair is also labelled with the dimensions listed below. - **seat width** - **back width** - **seat depth** - **chair height** - **back height** - **seat height (min & max)** ## Chair dimensions vs sitting anthropometry | Seat Dimension | Anthropometric Measurement | |---|---| | Cushion Width | Seated Hip Breadth | | Cushion Length | Buttock-to-Popliteal Length | | Seat Height | Popliteal Height | | Backrest Width | Chest Breadth | | Backrest Height | Shoulder Height | The image then shows a person sitting in a chair with the below anthropometric measurements labelled. 1. Sitting Height 2. Eye Height 3. Shoulder Height 4. Elbow Rest Height 5. Thigh Clearance 6. Popliteal Height (Stool Height) 7. Knee Height 8. Buttock-Popliteal Length 9. Hip Breadth 10. Knee-to-Knee Breadth ## Is this description correct? The image shows a white leather chair with the following labelled dimensions. - 46cm - 12cm - 72cm - 50-60cm - 53cm - 116-126cm - 25cm - 26cm - 60 cm - 70cm ## What are the features of a good chair? ### Seat Height - Seat height should be pneumatically adjusted while seated. - A range of 16-20.5 inches off the floor should accommodate most users. - Thighs should be horizontal, lower legs vertical. - Feet flat on the floor or on a footrest, range 347 to 525 mm. ### Seat Depth - It is measured from the front edge of the seat to the lumbar support region of the backrest. - If the seat depth is excessive, small people will not be able to sit back far enough to get the benefit of the backrest. - A seat width of 17-20 inches suffices for most people and should be deep enough to permit the back to contact the lumbar backrest without cutting into the backs of knees. - The front edge should be rounded and padded - "A WATERFALL EDGE". - Bucket-type seats must be avoided. The seat should swivel easily. - Minimum width of 450mm is required. This gives a little extra space above the 97.5th percentile hip width for Indian women of 445mm. The 97.5th percentile hip width for Indian males is less than this (417mm). RANGE: 380 to 480 mm. ### Seat Slope - Provision for forward slope of the seat, up to a maximum of 10 degrees, is useful to reduce pressure on the thighs when working while leaning forward. - But for general purposes, a chair with the seat angle fixed and horizontal is probably best. The seat slant should be adjustable (0 to 10 degrees). ### Head Rest - Purpose: to provide comfort and safety. - Headrest-height adjustable cushioned for comfort. - Effect: relaxed posture that helps relieve the pressure on your postural muscles which can decrease fatigue and increase comfort. ### Backrest - The backrest should be large enough to cover the entire width of the back. A minimum of 12" is recommended for width. - Seat back height preference varies dramatically from user to user. Lumbar support, these commonly range from 6" to 10" in height. In that case, the lumbar support should be centered at L 3-4 vertebrae. - A lumbar support should also have at least 4" of adjustability to allow centering in the back. - In full-length designs, backrests should be contoured to fit the "S" shaped curves of the spine, not entirely flat or straight. - Backrest-Seat Pan Angle - The angle between the seat pan and chair back should be adjustable when the user is seated with thighs parallel to the floor and legs properly supported vertically. This angle permits the user to sit slightly forward, straight up or recline back depending on the type of computing performed, support needed, and comfort desired. ### Seat Material: - **LEATHER** - **CUSHION** A chair seat and back should be padded enough to allow comfortable circulation. - If a seat is too soft, the muscles must always adjust to maintain a steady posture, causing strain and fatigue. - The seat fabric should "breathe" to allow air circulation through clothes to the skin. - **WIRE MESH** - **LEATHER** ### Foot Rest - Adjustable - Does not restrict leg movement - Easily removed - As wide as your hips - Large enough for the soles of both feet - Has a nonskid surface - Made of anti-skidding, anti-fatigue material ### Arm Rest - Ergonomic armrests are optional features. - Armrest users report enhanced performance including less fatigue, increased comfort, and better endurance with sustained computing. - Armrests should be placed at least 18.5" apart and made of soft or padded material. - An ergonomically designed armrest should be adjustable vertically and not impair circulation due to direct pressure to contact areas but distribute that load over broad areas comfortably. Armrests should adjust between 2" and 4" vertically to accommodate user's preference. ### BASE - An ergonomically designed chair has a solid, safe, and stable 5-post chair base. It should be made of strong materials to support up to five times the body weight. - The chair base should also be equipped with quality casters to permit easy maneuvering on office floor surfaces. ## The working desk ### Height - 66-71 cm Sitting elbow height - 50-60 cm - 40-45° - 90-100° Sitting knee height + foot rest + knee clearance ### Depth & width - (W) WIDTH - (D) DEPTH - (H) HEIGHT - MR - NR - Edge of work height - Forward arm reach with elbow extended - Maximum work area - Occasional work - Normal work area - Usual work - Forward arm reach with elbow flexed 90 deg. ## Sitting workstations ## Health problems associated with sitting posture 1. When sitting, the 2/3 of the body weight falls on to the two small “sit bone” or ischial tuberosities. 2. Increased compressive stresses exerted on areas of buttocks (soft tissues) covering the tuberosities. 3. When we sit, the hamstring muscles pull on and rotate our pelvis posteriorly, which flattens the lumbar spine. 4. Sitting with the straight spine puts additional pressure on the spinal disks and creates additional strain on ligaments. 5. Disc pressure is greater during sitting than standing especially in the slouched seated postures. 6. Sitting requires the muscles to hold the HAT in a fixed position. This squeezes the blood vessels in the muscles, reducing the blood supply which accelerates fatigue and makes the muscles prone to injury. 7. Pressure on the underside of the thighs from a seat that is too high can sciatic nerve compression syndrome. 8. There is also less demand on the circulatory system due to the limited mobility while sitting. As a result the heart activity and the blood flow slow down. ## THE SILENT KILLER The image shows three people sitting in various postures demonstrating the potential health issues associated with prolonged sitting. ## Different types of sitting posture - Erect, Middle Sitting - Relaxed, Arms Supported Feet supported - Relaxed, Feet Unsupported Arms Unsupported - Sitting Relaxed Feet Supported Arms Unsupported - Posterior Sitting Slouching with hip extension - Anterior Sitting, Straight Lumbars - Anterior Sitting with Kyphosis Slouching with hip flexion ## Recommendations to improve sitting workstations - The Use of **ergonomic** (**well-designed**) chair; a chair becomes ergonomic only when it specifically suits a worker's body dimensions (anthropometry), their particular workstation, and the work tasks. - The average office loses over $7500 per employee per year in poor productivity and medical and workers’ compensation claims (the bureau of labor statistics). - LBP comprises 50% of these cases. - A survey conducted 1996 on 670 full-time computer users showed that their back complaints are related to poor ergonomic furniture, including the chair. - Another survey conducted 2002 on 170 women typists working at computers, mismatch between chair height and desk height and poor furniture. ## Chair components and dimensions - **Headrest** - **Lumbar Support System** - **Arm Pads** - **Arms** - **Seat Pad/Pan** - **Chair Mechanism** - **Footring** - **Chair Cylinder** - **Cylinder Cover** - **Chair Base** - **Casters** The image shows a chair with the above components. The chair is also labelled with the dimensions listed below. - **seat width** - **back width** - **seat depth** - **chair height** - **back height** - **seat height (min & max)** ## Chair dimensions vs sitting anthropometry | Seat Dimension | Anthropometric Measurement | |---|---| | Cushion Width | Seated Hip Breadth | | Cushion Length | Buttock-to-Popliteal Length | | Seat Height | Popliteal Height | | Backrest Width | Chest Breadth | | Backrest Height | Shoulder Height | The image then shows a person sitting in a chair with the below anthropometric measurements labelled. 1. Sitting Height 2. Eye Height 3. Shoulder Height 4. Elbow Rest Height 5. Thigh Clearance 6. Popliteal Height (Stool Height) 7. Knee Height 8. Buttock-Popliteal Length 9. Hip Breadth 10. Knee-to-Knee Breadth ## Is this description correct? The image shows a white leather chair with the following labelled dimensions. - 46cm - 12cm - 72cm - 50-60cm - 53cm - 116-126cm - 25cm - 26cm - 60 cm - 70cm ## What are the features of a good chair? ### Seat Height - Seat height should be pneumatically adjusted while seated. - A range of 16-20.5 inches off the floor should accommodate most users. - Thighs should be horizontal, lower legs vertical. - Feet flat on the floor or on a footrest, range 347 to 525 mm. ### Seat Depth - It is measured from the front edge of the seat to the lumbar support region of the backrest. - If the seat depth is excessive, small people will not be able to sit back far enough to get the benefit of the backrest. - A seat width of 17-20 inches suffices for most people and should be deep enough to permit the back to contact the lumbar backrest without cutting into the backs of knees. - The front edge should be rounded and padded - "A WATERFALL EDGE". - Bucket-type seats must be avoided. The seat should swivel easily. - Minimum width of 450mm is required. This gives a little extra space above the 97.5th percentile hip width for Indian women of 445mm. The 97.5th percentile hip width for Indian males is less than this (417mm). RANGE: 380 to 480 mm. ### Seat Slope - Provision for forward slope of the seat, up to a maximum of 10 degrees, is useful to reduce pressure on the thighs when working while leaning forward. - But for general purposes, a chair with the seat angle fixed and horizontal is probably best. The seat slant should be adjustable (0 to 10 degrees). ### Head Rest - Purpose: to provide comfort and safety. - Headrest-height adjustable cushioned for comfort. - Effect: relaxed posture that helps relieve the pressure on your postural muscles which can decrease fatigue and increase comfort. ### Backrest - The backrest should be large enough to cover the entire width of the back. A minimum of 12" is recommended for width. - Seat back height preference varies dramatically from user to user. Lumbar support, these commonly range from 6" to 10" in height. In that case, the lumbar support should be centered at L 3-4 vertebrae. - A lumbar support should also have at least 4" of adjustability to allow centering in the back. - In full-length designs, backrests should be contoured to fit the "S" shaped curves of the spine, not entirely flat or straight. - Backrest-Seat Pan Angle - The angle between the seat pan and chair back should be adjustable when the user is seated with thighs parallel to the floor and legs properly supported vertically. This angle permits the user to sit slightly forward, straight up or recline back depending on the type of computing performed, support needed, and comfort desired. ### Seat Material: - **LEATHER** - **CUSHION** A chair seat and back should be padded enough to allow comfortable circulation. - If a seat is too soft, the muscles must always adjust to maintain a steady posture, causing strain and fatigue. - The seat fabric should "breathe" to allow air circulation through clothes to the skin. - **WIRE MESH** - **LEATHER** ### Foot Rest - Adjustable - Does not restrict leg movement - Easily removed - As wide as your hips - Large enough for the soles of both feet - Has a nonskid surface - Made of anti-skidding, anti-fatigue material ### Arm Rest - Ergonomic armrests are optional features. - Armrest users report enhanced performance including less fatigue, increased comfort, and better endurance with sustained computing. - Armrests should be placed at least 18.5" apart and made of soft or padded material. - An ergonomically designed armrest should be adjustable vertically and not impair circulation due to direct pressure to contact areas but distribute that load over broad areas comfortably. Armrests should adjust between 2" and 4" vertically to accommodate user's preference. ### BASE - An ergonomically designed chair has a solid, safe, and stable 5-post chair base. It should be made of strong materials to support up to five times the body weight. - The chair base should also be equipped with quality casters to permit easy maneuvering on office floor surfaces. ## The working desk ### Height - 66-71 cm Sitting elbow height - 50-60 cm - 40-45° - 90-100° Sitting knee height + foot rest + knee clearance ### Depth & width - (W) WIDTH - (D) DEPTH - (H) HEIGHT - MR - NR - Edge of work height - Forward arm reach with elbow extended - Maximum work area - Occasional work - Normal work area - Usual work - Forward arm reach with elbow flexed 90 deg. ## Sitting workstations ## Health problems associated with sitting posture 1. When sitting, the 2/3 of the body weight falls on to the two small “sit bone” or ischial tuberosities. 2. Increased compressive stresses exerted on areas of buttocks (soft tissues) covering the tuberosities. 3. When we sit, the hamstring muscles pull on and rotate our pelvis posteriorly, which flattens the lumbar spine. 4. Sitting with the straight spine puts additional pressure on the spinal disks and creates additional strain on ligaments. 5. Disc pressure is greater during sitting than standing especially in the slouched seated postures. 6. Sitting requires the muscles to hold the HAT in a fixed position. This squeezes the blood vessels in the muscles, reducing the blood supply which accelerates fatigue and makes the muscles prone to injury. 7. Pressure on the underside of the thighs from a seat that is too high can sciatic nerve compression syndrome. 8. There is also less demand on the circulatory system due to the limited mobility while sitting. As a result the heart activity and the blood flow slow down. ## THE SILENT KILLER The image shows three people sitting in various postures demonstrating the potential health issues associated with prolonged sitting. ## Different types of sitting posture - Erect, Middle Sitting - Relaxed, Arms Supported Feet supported - Relaxed, Feet Unsupported Arms Unsupported - Sitting Relaxed Feet Supported Arms Unsupported - Posterior Sitting Slouching with hip extension - Anterior Sitting, Straight Lumbars - Anterior Sitting with Kyphosis Slouching with hip flexion ## Office Ergonomics - **Chair** - **Working surface (desk)** - **Footrests** - **Monitor (Visual Display Unit-VDU)** - **Document holders** - **Keyboard (Keyboard trays)** - **Mouse** - **Wrist pads** - **Glare (Eye strain)** - **Laptop** ## Scalloped desks There is growing evidence that, compared with a straight edged desk for computer-based work, a scalloped desk (which has a curve cut out at the center provides - More opportunities for forearm support - Greater desktop space within acceptable reach zones - Better work postures when using multiple screens - Persons with large waist circumference The image shows different types of scalloped desks. - 90 degrees desktop with cut out - 120 degrees desktop with cut out - straight edge desktop with cut out ## The area under the desk should be clear The image shows a variety of suggestions for keeping the area under the desk clear and organised. ## When to use a footrest? A footrest should be used if the user's feet cannot be placed flat on the floor. The correct height of the footrest is the distance the feet are off the floor after adjusting the seat height. A footrest should - Have a non-slip surface large enough for both feet to rest comfortably. - Have an adjustable slope (10-20 degrees) to allow a comfortable ankle position. - Be stable enough so it does not slide. ## Monitor (Visual Display Unit-VDU) - **Screen height**: the top of the screen should be set at eye level, tilted 10-20° backward. - **Viewing distance**: position the screen about one arm length away. - This may reduce visual fatigue (eye strain) ## Viewing Distance - 40-74 cm Horizontal - Line-of-Sight 15° - 30° The image shows a person sitting looking at a monitor with these viewing distances labelled. ## How To Increase The Monitor Height - Using a monitor stand or arm The image shows a monitor stand and a monitor arm. ## Multiple computer monitors - Should have separate monitor arms - If one monitor is used more frequently than the other: place the primary monitor straight ahead to avoid twisting the body, move the chair when using secondary monitors to avoid bending or twisting to see the display. ## If using multiple monitors with equal frequency - then: position the screens right next to each other (an arc) with both screens at equal viewing distance from the user. ## If using a combination of computers e.g. a desktop monitor and a laptop computer: - Place the laptop on a stand so that the laptop display is at the same height as the desktop monitor, place the laptop and desktop monitors at an equal viewing distance. ## Document holder - In the middle in front of the user or near the screen at about the same height and angle. The image shows two examples of document holders. ## The keyboard - Position the keyboard straight in front of the user to avoid twisting the neck or body. - Use a keyboard without a numeric key pad to reduce the width of the keyboard. this allows the mouse to be positioned closer to the body. - Adjust the angle and height of the keyboard by folding or unfolding the small legs under the keyboard. - Elbow is 90-100°. - Wrist joint should be in neutral position. ## To Have Forearm Support, Position The Keyboard And Mouse Away From The Front Edge Of The Desk. - The majority of the forearm is supported on the desk with the fingers sitting comfortably on the middle row of the keys with both wrists in neutral position IS GOOD. The image shows examples of good and bad positioning of the keyboard in relation to the users wrist. - PERFECT - BAD - BAD ## The Pencil Test For Neutral Hand Position - Place a pencil across the back of the hand. - The pencil should be able to lie nearly flat across the back of the hand. - The pencil will also help you see if you have the hand turned out or inward. ## When to Use The Keyboard Tray? - With the touch or floating typists, the work surface is just below the elbows. The image shows two examples of keyboard trays in use. ## The mouse - The device to be kept at the same height and as close to the keyboard as possible. - The mouse should fit comfortably in the hand to minimize any undue pressure on the wrist and forearm. - Consider operating the device with the non-dominant hand. Change this operating preference on the computer settings. - Have enough space and a flat smooth surface so that the wrist can be kept straight. - Take hands off the keyboard and mouse when not in use. This assists in reducing muscle fatigue from hovering over the equipment. ## Wrist pads - Wrist pad is good only if it promotes proper and neutral typing hand posture. If the wrist pad changes the hand posture from the neutral, then it is not recommended. Address overall sitting posture to promote better alignment when working on the computer before using the wrist pad. The image shows a person using a wrist rest in an incorrect position. ## The phone - To be kept in the normal working zone on the non-dominant side to keep the dominant hand free to function. - Telephone headsets should be used when there is sustained phone use. ## Organizing the working surface - Primary work zone - Secondary work zone The image shows a person seated at a desk demonstrating primary and secondary work zones. ## Keying priority ## Mouse priority ## Non Comp priority ## Phone and writing priority The image shows four different examples of desk set up in relation to the users priority. - Keying priority - Mouse priority - Non Comp priority - Phone and writing priority ## Head - Head back, chin tucked. Ears, shoulder, hips aligned. ## Neck - Use headphones. Do not cradle phone between head and shoulder! ## Elbows - At sides—slightly more than 90 degree bend. ## Chair - Fully adjustable with lumbar support in small of the back. ## Eyes - Level with top 1/3 of screen. 18-24” ## Document Holder - Adjacent to and at same height as monitor. ## Keyboard - Same height as elbow with wrists slightly bent. Keystroke gently! ## Mouse - Adjacent to and at the same height as keyboard. ## Chair Height - Hips slightly more than 90 degrees, feet flat on the floor. ## Take breaks every 30 minutes! ## Laptop computers - Laptop computers are designed for short-term use only. They are very convenient but can challenge good working postures and not suitable for standing workstations. - When using a laptop for significant periods, or when being used as a desk top replacement, use separate components that allow for better posture and can be independently adjusted. - Components include docking stations, external monitors, external keyboard and mouse, laptop stands. ## Lighting - Glare is probably the frequent problem with lighting in a work area causing visual fatigue or eye strain. - Glare can be reduced through: - Repositioning the display screen can eliminate glare. - Properly adjusted window treatments (blinds, curtains) Can reduce glare. - Dimmer switches can control man-made light. - An anti-glare screen may be placed on the display. ## Sometimes too little light - May be the problem. Use a task lamp to supplement lighting for detailed work, or writing. The image shows a person seated at a desk with light coming from a window and creating glare on the monitor. ## Thank you.