Evaluation of Work Chairs according to European Community Standards Authorities (CEN) and German DIN 4551 and Italian UNI 7498.

1. MS.c of Industrial hygiene (Tehran, Iran)

2.  The purpose of this chapter is to illustrate an
organized approach for objectively evaluating the
ergonomic features of a work chair
 BASIC ERGONOMIC REQUIREMENTS FOR
WORK CHAIRS(the principal requirements that a
work chair should meet to be defined as ergonomic:)

3. Safety: the chair should never be the cause or the means of
accidents.
Adaptability: the chair and its components should have
dimensions or be adjustable to meet the anthropometric
needs of a wide range of users, and of at least 90% of the
population.
Comfort: the chair and its components (i.e. especially the
seat and the backrest) should be upholstered, body
contoured and reciprocally adjustable so as to meet the
physiological needs and characteristics of many different
“body shapes, curves and sizes.”

4. Practicality : Adjusting the various chair components
should be made as easy as possible for the user.
Solidity:The sturdiness and resistance to wear of the seat
and its components
Suitability for the intended use:
every workplace has its peculiarities and special needs from an
ergonomic standpoint.

5. Safety:
 Stability of the chair: the chair-to-ground projection of vertical force
application points, placed 5 cm apart
 Chair components should be made of non-flammable material
 The chair should come in a choice of castors for different types of
floors;
 Absence of sharp edges.
 Armrests should never pinch

6. Adaptability:
 Height of the seat, “popliteal height.”
adjustable(5th percentile in women 95th
percentile in men).
 width of the seat plane“hip breadth” (95th
percentile in women)
 Depth of the seat “buttock–popliteal length.”
5th percentile subjects. A : SEAT HEIGHT
B : SEAT DEPTH
C : BACKREST SEAT PLANE HEIGHT
D : BACKREST HEIGHT

7.  Backrest height: support the trunk,
correspondent values of the 95th percentile
in men
from low back curvature(L5–S1)
up to maximum thoracic kyphosis.
 Backrest width:
(corresponding to the 95th percentile in men)
maximum lumbar lordosis and maximum
thoracic kyphosis.
B : BACKREST WIDTH (LUMBAR LEVEL)
C : BACKREST WIDTH (THORACIC
LEVEL)
Frontal view

8.  Height, depth and width of the armrests:
Height: supporting upper limbs,keeping balance
“elbow–seat plane height”, 5th to 50th percentile
Depth: recommended depth of the armrest: “elbow-to-wrist length”
in the 95th percentile of men.
Width: width of 4 cm or more arerecommended.

10. COMFORT:
 Inclination of the backrest:
Backrests equipped with an
inclination ranging between 90
and 115º (with respect to the
horizontal plane) are preferable
(120º for high backrests).

11.  Contours of the seat plane:
To avoid compressing the neurovascular structures at the popliteal
level, the front edge of the seat should be rounded and possibly
made of non-rigid material,
A slope ranging between 3 and 10º
The center concavity, 10 cm of the most protruding point of the
lumbar support
A : LUMBAR SUPPORT HEIGHT (FROM SEAT PLANE)
B : DEPTH OF LUMBAR SUPPORT
C : EXTENTION OF LUMBAR SUPPORT ALONG BACKREST
D : SPACE FOR BUTTOCKS (FROM BACKREST)
E : SEAT PLANE AREA FOR MEASURING INCLINATION
VS. HORIZONTAL
F : ROUNDED FRONT EDGE

12. Lumbar support:
Height of maximum protrusion:defined “lumbar lordosis–seat plane
height.” maximum protrusion is fixed between 20 and 24 cm(not
adjustable backrest)
Depth: according to anthropometry data of low back curvature.
If it is not adjustable, set between 2 and 4 cm.
Length:
determined by using anthropometric parameters such as: “distance
between 1º sacral vertebra and 1º lumbar vertebra” and “distance
between 1º sacral and maximum thoracic kyphosis ”

13. Padding:
providing an appropriate distribution of body pressure,
Chairs should be manufactured using semi-rigid upholstery (with a
deformation due to the weight of a person 2.0–2.5 cm),
Covering materials:
 surface that comes in contact with the user should not create any
thermal undesirable sensation.
 seats and backrests should be made of porous material

15.  PRACTICALITY:
The covering material of the chair should also be washable in order to
guarantee the minimum hygienic require ments. This aspect is
particularly important in industrial or in very dirty environments,
or in cases where the chair is intended for multiple users.
 SOLIDITY:
The sturdiness and resistance of the seat and its components can be
evaluated using the specific tests and interpretation criteria
developed by National Standards Authorities,

16.  SUITABILITY FOR THE WORKPLACE AND
INTENDED USE:
 Covering materials and padding crowded areas, or areas with
flames and sparks, both materials should be flameproof.
 type of floor used (smooth, carpeting, etc.). Chairs with castors
for carpeting should not be used on smooth surfaces.

21.  Disc pressures are lower in standing than in sitting and lower still
when lying down. In standing, the load is shared between the facet
joint. In sitting, the discs bear more of the load (Adams and Dolan,
1995)
 Rohlmann et al. (2001) found that disc pressure was lower in
relaxed sitting than in standing, but higher when subjects
attempted to extend the spine to sit erect.
 Both Nachemson (1966) and Rohlmann et al. report lower disc
pressures when subjects recline against a backrest. This implies that
seated workers should be able to adopt relaxed postures.