BIFMA G1-2002 ERGONOMICS GUIDELINE FOR VDT (Visual Display Terminal) FURNITURE FURNITURE USED IN OFF

BIFMA G1-2002ERGONOMICS GUIDELINE FOR VDT (Visual Display Terminal)FURNITURE USED IN OFFICE WORK SPACESBIFMA InternationalDate: 28/FEB/2002© Copyright“Portions of material in this BIFMA publication are copyrighted by the International Organization for Standardization (‘ISO’) and are being reproduced from ISO 9241-5:1998 with permission of the American National Standards Institute on behalf of ISO. No part of this material may be copied or reproduced in any form, electronic retrieval system or otherwise or made available on the Internet, a public network, by satellite or otherwise without the prior written consent of the American National Standards Institure, 11 West 42nd Street, New York, NY 10036.”BIFMA G1-2002 ERGONOMICS GUIDELINE FOR VDT (Visual Display Terminal) FURNITUREUSED IN OFFICE WORK SPACESBIFMA InternationalDate: 28/FEB/2002© CopyrightTable of Contents Page FIGURES (3)TABLES (4)1FOREWORD (5)2SCOPE (6)3CONFORMANCE CRITERIA (6)4LIMITATIONS (7)5DEFINITIONS (8)6GENERAL CONSIDERATIONS (9)7THE WORK CHAIR (13)7.1S EAT H EIGHT (13)7.2S EAT D EPTH (16)7.3S EAT W IDTH (18)7.4S EAT P AN A NGLE (20)7.5B ACK S UPPORT (21)7.5.1Seat Backrest Height (21)7.5.2Backrest Width (22)7.5.3Lumbar Support (23)7.6M OVEMENTS OF THE S EAT P AN AND B ACK S UPPORT (25)7.7A RM S UPPORT (26)7.7.1Armrest Height (26)7.7.2Armrest Length (29)7.7.3Inside Distance Between Armrests (30)8WORK SURFACES (33)8.1C LEARANCES U NDER W ORK S URFACES FOR S EATED W ORK (34)8.1.1Height Clearance for Legs - Sitting (34)8.1.2Depth Clearance for Knees - Sitting (38)8.1.3Width Clearance for Thighs - Sitting (40)8.1.4Height Clearance at Foot Level - Sitting (42)8.1.5Depth Clearance at Foot Level - Sitting (44)8.2C LEARANCES U NDER W ORK S URFACES FOR S TANDING W ORK (48)8.2.1Height Clearance at Foot Level - Standing (48)8.2.2Depth Clearance at Foot Level - Standing (50)8.2.3Width Clearance at Foot Level - Standing (51)8.3S UPPORT S URFACE H EIGHTS FOR I NPUT D EVICES AND VDT S (54)8.3.1Support Surface Height for Input Devices - Sitting (54)8.3.2Support Surface Height for VDT - Sitting (59)8.3.3Support Surface Height for Input Devices - Standing (64)8.3.4Support Surface Height for VDT – Standing (66)8.4S UPPORT S URFACE D EPTH FOR VDT – S ITTING OR S TANDING (70)9ADDITIONAL RELEVANT INFORMATION (72)O THER R ELEVANT P RINCIPLES FROM ISO 9241-5 (72)R ELEVANT NATICK/TR-89/044 A NTHROPOMETRIC M EASUREMENTS (74)S UMMARY OF G UIDELINE FOR F URNITURE USED IN VDT W ORKSTATIONS – D IMENSIONS AND R ANGES (75)10RECOMMENDED READING (77)FiguresPage Figure 1 – CMD (BIFMA - Chair Measuring Device) (11)Figure 2 – Typical Working Postures (12)Figure 3 – Popliteal Height (14)Figure 4 – Buttock-Popliteal Length (16)Figure 5 – Hip Breadth, Sitting (18)Figure 6 – Waist Breadth (22)Figure 7 – Elbow Rest Height (27)Figure 8 – Hip Breadth, Sitting (31)Figure 9 – Thigh Clearance (34)Figure 10 – Popliteal Height (35)Figure 11 – Knee Height (35)Figure 12 – Buttock-Knee Length (38)Figure 13 – Abdominal Extension Depth (39)Figure 14 – Hip Breadth, Sitting (41)Figure 15 – Lateral Malleolus Height (43)Figure 16 – Buttock-Popliteal Length (45)Figure 17 – Foot Length (45)Figure 18 – Abdominal Extension Depth (46)Figure 19 – Seated Clearance Envelope Based on 95th Percentile Male Dimensions (48)Figure 20 – Lateral Malleolus Height (49)Figure 21 – Hip Breadth, Sitting (52)Figure 22 – Foot Clearance Envelope -- Standing Based on 95th Percentile Male Dimensions (53)Figure 23 – Thigh Clearance (55)Figure 24 – Popliteal Height (55)Figure 25 – Elbow Rest Height (56)Figure 26 – Forearm to Thigh Space (58)Figure 27 – Seated Viewing Angles (60)Figure 28 – Eye Height, Sitting (60)Figure 29 – Popliteal Height (61)Figure 30 – The ISO-Allowable Extremes for VDT Placement, and Variations of Monitor Size and User Dimensions - Sitting , Make a Recommendation for VDT Support Surface HeightImpractical (63)Figure 31 – Elbow Rest Height, Standing (64)Figure 32 – Standing Viewing Angles (67)Figure 33 – Eye Height, Standing (67)Figure 34 – The ISO-Allowable Extremes for VDT Placement, and Variations of Monitor Size and User Dimensions - Standing, Make a Recommendation for VDT Support Surface HeightImpractical (69)TablesPage Table 1Popliteal Height (14)Table 2Buttock-Popliteal Length (17)Table 3Hip Breadth, Sitting (19)Table 4Waist Breadth (23)Table 5Elbow Rest Height, Sitting (27)Table 6Hip Breadth, Sitting (31)Table 7Height Clearance for Thighs and Lower Legs (36)Table 8Height Clearance for Knees (36)Table 9Buttock-Knee Length Minus Abdominal Extension Depth (39)Table 10 Width Clearance for Thighs (41)Table 11Height Clearance at Foot Level (43)Table 12Depth Clearance at Foot Level (46)Table 13Height Clearance at Foot Level (49)Table 14Hip Breadth, Sitting (52)Table 15Calculated Input Device Support Surface Height (56)Table 16Elbow to Thigh Clearance (57)Table 17Eye Height, Sitting (From Floor) (61)Table 18Support Surface Height for Standing Work (65)Table 19Eye Height, Standing (68)Table 20Relevant NATICK/TR-89/044 Measurements (74)Table 21Summary of Guideline for Furniture used in VDT Workstations – Dimensions and Ranges (75)1ForewordThe Ergonomics Guideline for VDT (Visual Display Terminal) Furniture used in Office Work Spaces,referred to throughout this document as “the Guideline”,quotes the measurable ergonomics guiding principles and design requirements of the international standards published by the International Organization for Standardization, (ISO) 9241 Ergonomic Requirements for Office Work, Part 3: Visual Display Requirements (1992) and (ISO) 9241 Work Station Layout and Postural Requirements, Part 5 (1998).ISO 9241-3 and 9241-5 represent accepted principles for office ergonomics. They also provide guidance for evaluating workstation furniture that conforms to the body sizes of the working population. Because body sizes vary widely in different parts of the world, ISO 9241-3 and ISO 9241-5 do not provide specific dimensions for workstation components such as chairs and work surfaces.This Guideline also considered the dimensions and adjustment ranges as they appear in ANSI/HFS 100 (1988), CAN/CSA Z412 (2000) and CAN/CGSB 44-232 (1997) and 44-227 (1997). Where reference information is incomplete, conflicting or impractical, this Guideline suggests commonly used industry practices.The application of the concept of Fit, as defined by ISO 9241-5, 4.3, is the primary consideration of this Guideline:“Selection and design of furniture and equipment requires a fit to be achievedbetween a range of task requirements and the needs of users. The concept offit concerns the extent to which furniture and equipment (work chairs, worksurfaces, visual display units, input devices, etc.) can accommodate individualusers’ needs.Good fit is needed for the intended user population including users sharingworkstations and users with special needs, e.g. handicapped persons. Fit canbe accomplished by furniture built for a specified use (or user), or be providedin a range of sizes and forms or by adjustability and combinations thereof.Since, except under special circumstances, workstations cannot be custom-made for individual users, some alternative forms of ensuring a good fit arerequired. The extent to which the workstation provides a good fit between therequirements of users and their work should be of primary consideration.”2ScopeThe purpose of this Guideline is to provide guidance in applying some of the relevant measurable ergonomic principles and design requirements found in ISO 9241-3 and 9241-5 to the dimensions and adjustment ranges of components used in the design of work spaces utilized specifically for intensive VDT1 use in North America, using the anthropometric data provided in Natick/TR-89/044. Other tasks may require considerations not addressed in this Guideline.Proper application of ISO’s principles will enhance the performance and comfort of VDT users. The more intensive the VDT usage, the more important adherence to these principles becomes.This Guideline is intended for use by:•BIFMA Members, Furniture Dealers and their clients•Interior Designers/Architects/Specifiers/Industrial Designers•Facility and Material Managers•Purchasing Managers•Ergonomists•Testing Facilities•Other professionals involved in the design, manufacturing, specifying, qualifying, and purchasing of office furniture for VDT work spaces3Conformance CriteriaDesigning products to fit the 5th percentile female body dimensions to the 95th percentile male body dimensions will accommodate a large number of users. This Guideline attempts to achieve that objective.It is important, however, to realize that purchasing/designing furniture for the above range will not accommodate at least 5 percent of the users for any particular dimension. In order to accommodate users outside the 5th to 95th percentile ranges, it will most likely be necessary to purchase components that are not within that range. The practice of ergonomics requires fitting the work environment to the user. A furniture component that fits a particular user conforms to ISO and the recommendations in this Guideline, even if it does not conform to certain numerical ranges.1See definition of VDT work space.•The individual workspace dimensions recommended in this document are based on a single anthropometric database, Natick. The workspace dimensions are based on meeting the requirements of the relevant 5th percentile female through 95th percentile male body dimensions in an upright posture. Alternate postures may result in different dimensional requirements.•If the anthropometric dimensions of a particular user population can be estimated, it is preferable to utilize those dimensions to accommodate thatpopulation.•The application of ergonomic principles is broader than anthropometry, and workstation design should consider other aspects such as lighting, acoustics, heating and ventilation, and psycho-social aspects.•The application of ISO principles to specific user/workspace combinations may result in dimensional conflicts. The final criteria for determining whether anindividual user has been accommodated are the parameters given in theUltimate Test for Fit. Multiple product solutions may be required in order toaccommodate the entire user population.Note:Merriam-Webster dictionary definitions are used for terms in this Guideline unless otherwise defined in this section.armrests: “Support for the lower arms” (ISO 9241-5). For the purpose of this Guideline, armrests are attached to the chair.BIFMA International: Business and Institutional Furniture Manufacturer’s Association, a not-for-profit trade association of furniture manufacturers and suppliers.CGSB: Canadian General Standards Board, a Canadian governmental agency that produces voluntary standards in a wide range of subject areas through standards committees and the consensus process.CMD: The BIFMA Chair Measuring Device used for the measurement of seating products.CMD-1 Chair Measurement Procedure: A universal procedure for the BIFMA Chair Measuring Device.CSA: Canadian Standards Association, also known as CSA International, a voluntary membership association engaged in standards development and certification activities.HFES: Human Factors and Ergonomics Society, the principal association of ergonomists in the United States.input device:“User controlled device that transmits information to a system” (ISO 9241-9).ISO: International Organization for Standardization, a worldwide federation of national standards bodies.Natick report: The 1987-88 anthropometric survey of Army personnel prepared for the United States Army Natick Research, Development and Engineering Center in Natick, Massachusetts. (Technical Report Natick/TR-89/044)support surface: See “work surface”.VDT (Visual Display Terminal): For the purposes of this Guideline, a VDT may include a central processor unit, display, and/or input devices. This does not include the category of portable computers typically referred to as “lap top” computers with the display and input device integral to the same unit.VDT work space: The portion of a workstation dedicated to intensive VDT use. Typically, these work spaces are comprised of seating, VDT support surfaces, input device support surfaces, etc. VDT intensive use may include tasks such as CAD design, word processing, graphic design, data entry and telemarketing.workstation: A group of furniture items and components where a person performs work.work surface: Surface on which equipment and task materials are used.(Defined in ISO 9241-5 as “worksurface”.)6General ConsiderationsAnthropometric Data SourceData relating to body sizes of the user population are taken from the standard and derived measurements published in Technical Report Natick/TR-89/044 by the United States Army Natick Research Development and Engineering Center (Natick). Copies of the Natick report may be obtained from the National Technical Information Service using accession number AD A225 094.All Natick data, quoted text and relevant body dimensions (measurements and diagrams) used throughout this Guideline, unless otherwise noted, are from the following Natick source:Claire C. Gordon, Thomas Churchill, Charles E. Clauser, BruceBradtmiller, John T. McConville, Ilse Tebbetts and Robert A. Walker(1989). 1988 Anthropometic Survey of US Army Personnel:Methods and Summary Statistics. NATICK/TR-89/044. Natick, MA:US Army Natick Research, Development, and Engineering Center.(AD A225 094)While the population measured by Natick does not precisely reflect the actual office working population of North America, it is the most encompassing set of measurements available at this time. The measurements are consistent with the anthropometric measurements described in ISO 7250: Basic Human Body Measurements for Technological Design. If another database is available, or has been developed for a particular population, the user of this Guideline is encouraged to apply such information. The Ultimate Test(s) for Fit suggested by this Guideline can be applied universally.The posture and measurement diagrams used throughout this document are for anthropometric measurements and illustrative purposes only. They are not necessarily meant to represent preferred or recommended postures.Some dimensions used in this document were derived by adding and/or subtracting anthropometric dimensions within subjects. That procedure adds and/or subtracts anthropometric dimensions for each subject contained in the Natick data base, and then calculates a mean for the new dimension. Percentiles are calculated using the means and standard deviations for the derived dimensions. That method produces more accurate dimensions than simply adding and/or subtracting percentile dimensions in the published Natick tables, which is between subject groups.Guideline LayoutThe sections of this Guideline pertaining to the ergonomic recommendations are presented in the following format:•Section Title•ISO Related Quote and Reference*•Relevant Body Dimension- What is it and how is it measured**- Relevant NATICK/TR-89/044 Data•Why is Parameter “x” (for example, Seat Height) Important•Discussion•Recommended Dimensions/Ranges•Ultimate Test for Fit for the Individual User* All ISO 9241 text quoted throughout this Guideline is italicized.** NATICK/TR-89/044 references used are in quotation marks only.Chair MeasurementThe chair dimensions provided in this Guideline are obtained using the BIFMA Chair Measuring Device (CMD)® BIFMA/CMD-1 (see Figure 1) and the Universal Measurement Procedure©. . The definitions used in the BIFMA Universal Measurement Procedure relating to product dimensions and adjustment ranges are applicable throughout this Guideline.Figure 1 – CMD (BIFMA - Chair Measuring Device)The BIFMA CMD ©has a weight of 45.5 kg (100 lb.).There are other similar devices that are used to determine such measurements. These devices have many differences, including the use of different weights, which may cause differences in the measurements. Therefore, these devices cannot be used in the application of this guideline.Work Surface Measurement ToleranceTolerance, unless otherwise specified, shall be:•Linear measurements, ± 1.5 mm (1/16 in.),Working PosturesWhile the Natick body dimensions are generally taken from upright postures, there is no uniquely correct working posture that would fit any user for an extended period of time and/or accommodate every personal working habit. The dimensions given in this Guideline consider these generally upright postures only. Other dimensions may be acceptable if other postures are assumed.Figure 2 – Typical Working PosturesSome typical working postures (based on seat pan angle) include:−Rearward Tilt (positive seat pan angle)−Upright (near horizontal seat pan)−Forward Tilt (negative seat pan angle)−Standing−Alternating between sitting and standingAll of these working postures are acceptable as long as the concept of fit is given proper consideration. ISO principles suggest that movement within and among these and other postures be encouraged.7The Work ChairSitting Postures (ISO 9241-5, 5.2.2)“The purpose of well-designed seating is to provide stable support which allowsmovement, comfort, and task accomplishment.”General Considerations (ISO 9241-5, 5.5.1)“The purpose of good seating is to provide stable body support in a dynamicposture which is comfortable over a period of time, physiologically satisfactory and appropriate to the task or activity which is to be performed.”7.1Seat HeightSeat Height (ISO 9241-5, 5.5.2.2)“The appropriate seat height for a user for sitting in the upright position is thepopliteal height plus the thickness of footwear. Work chairs designed toaccommodate a specified user population shall achieve fit for the range suitablefor the intended user population. This range can be covered by applying theconcept of fit.”“Within a selected range of adjustability, the seat height shall be user adjustable.”Relevant Body Dimension: Popliteal HeightWhat is Popliteal Height and How is it Measured?Popliteal Height is “the vertical distance from a footrest surface to the back of the right knee (the dorsal juncture of the right calf and thigh), [and] is measured withan anthropometer. The subject sits with the thighs parallel, the feet in line with the thighs, and the knees flexed 90 degrees.”Figure 3 – Popliteal HeightNATICK/TR-89/044 Supporting Information:Table 1 Popliteal HeightFemale Malecm inches cm inches 5th Percentile Popliteal Height35.1313.8339.4615.53Plus Shoe Allowance* 3.00 1.18 3.00 1.18Resulting Height38.1315.0142.4616.7195th Percentile Popliteal Height42.9416.9147.6318.75Plus Shoe Allowance* 3.00 1.18 3.00 1.18Resulting Height45.9418.0950.6319.93*No Natick guidance is available for shoe allowance. ISO 9241-5, Table A1suggests 30 mm (1.2 in.).Why is Seat Height Important?Proper seat height(s) ensure the comfort of the lower limbs by avoiding pressure on the underside of the thigh caused by a seat pan that is too high, or decreased thigh-to-torso angle if the seat pan is too low. Seat height is also important insetting the hand position and, given that it dictates sitting eye height, is a criticalfactor in determining the line of sight.DiscussionTable 1 indicates that a 12.5 cm (4.9 in.) adjustment range from 38.1 cm (15.0 in.) to 50.6 cm (19.9 in.) will accommodate from the 5th percentile female to the 95thpercentile male popliteal height.Mechanical restrictions in the design of height adjustment mechanisms oftenmake the 12.5 cm (4.9 in.) range difficult to achieve. When attempting to fit alarge group of users, it may be necessary to consider multiple chairs, therebyproviding more than one range of height adjustability.For example:−One chair with a 6.9 cm (2.7 in.) seat height adjustment range from 38.1 cm (15.0 in.) to 45.0 cm (17.7 in.) will accommodate the 5th through the 90thpercentile female and up to the 30th percentile male popliteal heights.− A second chair with a range of 9.0 cm (3.5 in.) from 41.6 cm (16.4 in.) to50.6 cm (19.9 in.) will accommodate the 45th percentile female through the95th percentile male popliteal heights.−When combined, those two chair height adjustment ranges accommodate the 5th percentile female to the 95th percentile male popliteal heights.The range of seat height adjustment needs to cater to the intended userpopulation. Allowances should be made for footwear and variations in sittingpostures. A footrest is necessary in cases where the work chair height is to be set in a position which does not allow a VDT user’s feet to rest flat on the floor. (ISO9241-5, 5.6.2) The use of a footrest may restrict postural changes. Recommendation for Seat HeightA chair, or combination of chairs, with a minimum seat height range from 38.1 cm(15.0 in.) to 50.6 cm (19.9 in.) is recommended.Ultimate Test for Fit for the Individual UserUsers should be able to sit with their feet comfortably on the floor or footrestwithout undue pressure on the underside of the thighs. The thigh-to-torso angleshould not be less than 90°.7.2Seat DepthSeat Depth (ISO 9241-5, 5.5.2.3)“The fit for seat depth is achieved if the depth is less than the buttock-popliteallength of the user. Work chairs designed to accommodate a specified userpopulation can achieve fit by either adjustability or by using different sizes of theseat pan for the range suitable for the intended user population.”“Adjustable seat depth can be achieved either by adjusting the back rest inrelation to the seat or by moving the seat pan in relation to the back rest. If theseat depth is fixed, priority should be given to proper back support since properback support is more important than the support of the whole length of the thighs.”Relevant Body Dimension:Buttock-Popliteal LengthWhat is Buttock-Popliteal Length and How is it Measured?Buttock-Popliteal Length is “the horizontal distance between a buttock plateplaced at the most posterior point on either buttock and the back of the right knee (the popliteal fossa at the dorsal juncture of the calf and thigh) [and] is measured with an anthropometer. The subject sits erect. The thighs are parallel and theknees flexed 90 degrees with the feet in line with the thighs.”Figure 4 – Buttock-Popliteal LengthNATICK/TR-89/044 Supporting Information:Table 2 Buttock-Popliteal LengthFemale Malecm inches cm inches 5th Percentile Buttock-Popliteal44.0017.3245.8118.04LengthMinus Clearance Allowance*-1.00-0.39-1.00-0.39Resulting Length43.0016.9344.8117.6595th Percentile Buttock-Popliteal52.7720.7854.5521.48LengthMinus Clearance Allowance*-1.00-0.39-1.00-0.39Resulting Length51.7720.3953.5521.09* See DiscussionWhy is Seat Depth Important?An adequate seat depth supports the thighs and allows the user to sit back farenough to use the lower portion of the backrest without creating pressure on the back of the knees.DiscussionTable 2 indicates that after applying a clearance allowance of 1.0 cm (0.4 in.) to prevent the back of the knees from contacting the seat, a seat no deeper than43.0 cm (16.9 in.) will fit the 5th percentile female and all users with a longerbuttock-popliteal length. While that dimension will provide full thigh support for smaller users, users with long thighs may prefer a deeper seat. This isacceptable; however, if the seat depth is greater than 43.0 cm (16.9 in.), onlyusers with longer thighs will be able to properly utilize the back support. Oneshould keep in mind that “back support is more important than the support of the whole length of the thighs” (ISO 5.5.2.3). A seat cushion with a waterfall front or declining front edge will significantly reduce compression on the back of theknees.Recommendation for Seat DepthFor chairs with fixed seat depth, the depth should not be deeper than 43.0 cm(16.9 in.) to accommodate the 5th percentile female buttock-popliteal length.For adjustable seat depth chairs, the adjustment range should include a seatdepth of 43.0 cm (16.9 in.) or less.Ultimate Test for Fit for the Individual UserUsers should be able to sit in the chair without undue pressure against the back of the knees, with their back properly supported by the backrest and with adequate buttock and thigh support.7.3Seat WidthSeat Width (ISO 9241-5, 5.5.2.4)“For seat width, fit is achieved when the seat width is wider than the width of thehips.”Relevant Body Dimension: Hip Breadth, SittingWhat is Hip Breadth, Sitting and How is it Measured?Hip Breadth, Sitting is “the distance between the lateral points of the hips or thighs (whichever are broader) [and] is measured with a beam caliper. The subject sits erect with the feet and knees together.”Figure 5 – Hip Breadth, SittingNATICK/TR-89/044 Supporting Information:Table 3 Hip Breadth, SittingFemale Malecm inches cm inches 5th Percentile34.2513.4832.8712.94Hip Breadth, SittingPlus Clothing Allowance* 2.500.98 2.500.98Resulting Breadth36.7514.4635.3713.9295th Percentile43.2217.0241.1616.20Hip Breadth, SittingPlus Clothing Allowance* 2.500.98 2.500.98Resulting Breadth45.7218.0043.6617.18* See DiscussionWhy is Seat Width Important?Adequate seat width allows users to adjust their posture. If the seat pan is toonarrow, undue pressure to the thighs will occur which can restrict blood flow andcause discomfort.DiscussionTable 3 indicates that when an allowance of 2.5 cm (1.0 in.) for clothing is added to the actual Hip Breadth measurement, a seat cushion of no less than 45.7 cm(18.0 in.) should fit all users to the 95th percentile female hip breadth (which iswider than the 95th percentile male hip breadth). Generally, seats wider than the user’s hip breadth are desirable. Seats narrower than the user’s hip breadth may not provide an adequate support surface and, if the chair has armrests, willcompromise getting into and out of the chair. The 45.7 cm (18.0 in.) seat widthwill not allow as much movement for 95th percentile hip breadths as it will for users with narrower hip breadths.Recommendation for Seat WidthSeat widths should be no less than 45.7 cm (18.0 in.).Ultimate Test for Fit for the Individual UserThe seat should be wider than the hip breadth of the user to allow space formovement and clothing. The seat width should not limit the ability to comfortablyuse the armrests (see section 7.7.3 Inside Distance Between Armrests).7.4Seat Pan AngleSeat Angle (ISO 9241-5, 5.5.3.2 )“The seat angle should allow users to vary their posture forward and backward.”“Seats may be designed with a fixed or adjustable seat angle. Adjustable seatpans may incorporate a forward as well as a rearward tilt.”Relevant Body Dimension: Not applicableNATICK/TR-89/044 Supporting Information:None availableWhy is Seat Pan Angle Important?Appropriate seat pan angles provide the user with adequate support in variousseated working postures.DiscussionExcessive forward seat pan angle may cause users to slide out of the seat, orshift too much weight to their feet resulting in prolonged static loading of legmuscles. If rearward tilting of the seat is accompanied by an excessive rise in its front edge, it may not allow users to keep their feet firmly on the floor or footrest.Without the ability to keep their feet firmly on the floor, the user may experienceexcessive pressure under the thighs.Recommendation for Seat Pan AngleIndustry practice suggests that the seat pan angle, if fixed, should fall within arange from 0° (horizontal) to 4° rearward. If adjustable rearward, forward or both, the seat pan angle adjustment should include some part of the range from 0°(horizontal) to 4° rearward.Ultimate Test for Fit for the Individual UserThe angle of the seat pan should allow the user to support their feet on the floor or footrest. Seat pan angles should not cause the user’s torso-to-thigh angle to beless than 90°. Forward seat pan angles should not cause users to shift excessive weight to their feet or experience the sensation of sliding out of the chair.。