A chair is a piece of (Furnishings that make a room or other
area ready for occupancy) furniture consisting of a seat,
legs, back, and sometimes arm rests, for use by one person.
Without back and arm rests it is called a stool. A chair for
more than one person is a (A narrow bed on which a patient
lies during psychiatric or psychoanalytic treatment) couch,
sofa, settee, loveseat or bench. A footrest for a chair is
known as an (Thick cushion used as a seat) ottoman, hassock
or (Offensive terms for an openly homosexual man) poof. A
chair mounted in a vehicle or in a theatre is simply called
a seat.
The back often does not extend all the way to the seat to
allow for ventilation. Likewise, the back and sometimes the
seat are made of porous materials or have holes drilled in
them for decoration and ventilation.
The back may extend above the height of the head. There may
be separate headrests. Headrests for seats in vehicles are
important for preventing (An injury to the neck (the cervical
vertebrae) resulting from rapid acceleration or deceleration
(as in an automobile accident)) whiplash injuries to the neck
when the vehicle is involved in a rear-end collision.
See (Click link for more info and facts about history of
the chair) history of the chair for an extended look at chairs
from antiquity to the modern day.
Design and ergonomicsChair design considers intended usage,
(Click link for more info and facts about ergonomic) ergonomics
(how comfortable it is for the occupant), as well as non-ergonomic
functional requirements such as size, stackability, foldability,
weight, durability, stain resistance and artistic design.
Intended usage determines the desired seating position. "Task
chairs", or any chair intended for people to work at
a desk or table, including dining chairs, can only recline
very slightly; otherwise the occupant is too far away from
the desk or table. Dental chairs are necessarily reclined.
Easy chairs for watching television or movies are somewhere
in between depending on the height of the screen.
Ergonomic designs distributes the weight of the occupant
to various parts of the body. A seat that is higher results
in dangling feet and increased pressure on the underside of
the knees ("popliteal fold"). It may also result
in no weight on the feet which means more weight elsewhere.
A lower seat may shift too much weight to the "seat bones"
("ischial tuberosities").
A reclining seat and back will shift weight to the occupant's
back. This may be more comfortable for some in reducing weight
on the seat area, but may be problematic for others who have
bad backs. In general, if the occupant is suppose to sit for
a long time, weight needs to be taken off the seat area and
thus "easy" chairs intended for long periods of
sitting are generally at least slightly reclined. However,
reclining may not be suitable for chairs intended for work
or eating at table.
The back of the chair will support some of the weight of
the occupant, reducing the weight on other parts of the body.
In general, backrests come in three heights: Lower back backrests
support only the lumbar region. Shoulder height backrests
support the entire back and shoulders. Headrests support the
head as well and are important in vehicles for preventing
"whiplash" neck injuries in rear-end collisions
where the head is jerked back suddenly. Reclining chairs typically
have at least shoulder height backrests to shift weight to
the shoulders instead of just the lower back.
Armrests will also support part of the body weight through
the arms. They further have the function of making entry and
exit from the chair easier. Armrests should support the forearm
and not the sensitive elbow area. Hence in some chair designs,
the armrest is not continuous to the chair back, but is missing
in the elbow area.
A kneeling chair adds an additional body part, the knees,
to support the weight of the body. A sit-stand chair distributes
most of the weight of the occupant to the feet.
Padding will not shift the weight to different parts of the
body (unless the chair is so soft that the shape is altered).
However, padding does distribute the weight by increasing
the area of contact between the chair and the body. A hard
wood chair feels hard because the contact point between the
occupant and the chair is small. The same body weight over
a smaller area means greater pressure on that area. Spreading
the area reduces the pressure at any given point. In lieu
of padding, flexible materials, such as wicker, may be used
instead with similar effects of distributing the weight. Since
most of the body weight is supported in the back of the seat,
padding there should be firmer than the front of the seat
which only has the weight of the legs to support. Chairs that
have padding that is the same density front and back will
feel soft in the back area and hard to the underside of the
knees.
There may be cases where padding is not desirable. For example,
in hot climates, padding with fabric or plastic covers is
often uncomfortable against the skin. Where padding is not
desirable, contouring may be used instead. A contoured seat
pan attempts to distribute weight without padding. By matching
the shape of the occupant's buttocks, weight is distributed
and pressure at any given point is reduced.
Actual chair dimensions are determined by measurements of
the human body or (Click link for more info and facts about
anthropometric) anthropometric measurements. Individuals may
be measured for a custom chair. Anthropometric statistics
may be gathered for mass produced chairs. The two most relevant
anthropometric measurement for chair design is the popliteal
height and buttock popliteal length.
For someone seated, the popliteal height is the distance
from the underside of the foot to the underside of the thigh
at the knees. It is sometimes called the "stool height".
(The term "sitting height" is reserved for the height
to the top of the head when seated.) For American men, the
median popliteal height is 16.3 inches and for American women
it is 15.0 inches(*). The popliteal height, after adjusting
for heels, clothing and other issues is used to determine
the height of the chair seat. Mass produced chairs are typically
17 inches high.
For someone seated, the buttock popliteal length is the horizontal
distance from the back most part of the buttocks to the back
of the lower leg. This anthropometric measurement is used
to determine the seat depth. Mass produced chairs are typically
38-43 cm deep.
Additional anthropometric measurements may be relevant to
designing a chair. Hip breadth is used for chair width and
armrest width. Elbow rest height is used to determine the
height of the armrests. The buttock-knee length is used to
determine "leg room" between rows of chairs. "Seat
pitch" is the distance between rows of seats. In some
airplanes and stadiums the seat pitch is so small that there
is sometimes there is no leg room for the average person.
For adjustable chairs, the aforementioned principles are
applied in adjusting the chair to the individual occupant.
Chair seatsChair seats vary widely in construction and may
or may not match construction of the chair's back. Some systems
include:
Solid center seats where a solid material forms the chair
seat.
Solid wood, may or may not be shaped to human contours.
Wood slats, often seen on outdoor chairs
Padded leather, generally a flat wood base covered in padding
and contained in soft leather
Stuffed fabric, similar to padded leather
Metal seats of solid or open design
Molded plastic
Stone, often (A small ball of glass that is used in various
games) marble
Open center seats where a soft material is attached to the
tops of chair legs or between stretchers to form the seat.
Wicker, woven to provide a surface with give to it
Leather, may be tooled with a design
Fabric, simple covering without support
Tape, wide fabric tape woven into seat, seen in lawn chairs
and some old chairs
(Work made of interlaced slender branches (especially willow
branches)) Caning, woven from (Grasslike plants growing in
wet places and having cylindrical often hollow stems) rush,
(Tall woody perennial grasses with hollow slender stems especially
of the genera Arundo and Phragmites) reed, (Untanned hide
especially of cattle; cut in strips it is used for whips and
ropes) rawhide, heavy paper, strong grasses, (Tall erect herbs
with sword-shaped leaves; cosmopolitan in fresh and salt marshes)
cattails to form the seat, often in elaborate patterns
Splint, (Any of various deciduous pinnate-leaved ornamental
or timber trees of the genus Fraxinus) ash, (A deciduous tree
of the genus Quercus; has acorns and lobed leaves) oak or
(American hardwood tree bearing edible nuts) hickory strips
are woven
Metal, Metal mesh or wire woven to form seat
Standards and specificationsDesign considerations for chairs
have been codified into standards. (Click link for more info
and facts about ISO) ISO 9241-5:1988(*), "Ergonomic requirements
for office work with visual display terminals (VDTs) -- Part
5: Workstation layout and postural requirements
" is the most common one for modern chair design.
There are multiple specific standards for different types
of chairs. Dental chairs are specified by ISO 6875. Bean bag
chairs are specified by (Click link for more info and facts
about ANSI) ANSI standard ASTM F1912-98(*). ISO 7174 specifies
stability of rocking and tilting chairs. ASTM F1858-98 specifies
lawn chairs. ASTM E1822-02b defines the combustibility of
chairs when they are stacked.
The Business and Institutional Furniture Manufacturer's Association
(BIFMA) defines BIFMA X5.1 for testing of commercial-grade
chairs. It specifies things like(*):
chair backstrength of 150 pounds (68 kg)
chair stability if weight is transferred completely to the
front or back legs
leg strength of 75 pounds (34 kg) applied one inch (25 mm)
from the bottom of the leg
seat strength of 225 pounds (102 kg) dropped from six inches
(150 mm) above the seat
seat cycle strength of 100,000 repititions of 125 pounds (57
kg) dropped from 2 inches (50 mm) above the seat
The specification further defines heavier "proof"
loads that chairs must withstand. Under these higher loads,
the chair may be damaged, but it must not fail catastrophically.
Large institutions that make bulk purchases will reference
these standards within their own even more detailed criteria
for purchase
(*). Governments will often issue standards for purchases
by government agencies (e.g. Canada's Canadian General Standards
Board CAN/CGSB 44.15M (*) on "Straight Stacking Chair,
Steel").
AccessoriesIn place of a built-in footrest, some chairs come
with a matching ottoman. An ottoman is a short stool to be
used as a footrest but can sometimes be used as a stool. If
matched to a glider, the ottoman may be mounted on swing arms
so that the ottoman rocks back and forth with the main glider.
A chair cover is a temporary fabric cover for a side chair.
They are typically rented for formal events such as wedding
receptions to increase the attractiveness of the chairs and
decor. The chair covers may come with decorative chair ties,
a ribbon to be tied as a bow behind the chair. Covers for
sofas and couches are also available for homes with small
children and pets. In the second half of (Click link for more
info and facts about 20th century) 20th century, some people
used custom clear plastic covers for expensive sofas and chairs
to protect them.
Chair pads are cushions for chairs. Some are decorative.
In cars, they may be used to increase the height of the driver.
Orthopedic backrests provide support for the back. Obus Forme
is a major brand in this category and helped develop this
market niche. Car seats sometimes have built-in and adjustable
lumbar supports.
Chair mats are plastic mats meant to cover carpet. This allows
chairs on wheels to roll easily over the carpet and it protects
the carpet. They come in various shapes, some specifically
sized to fit partially under a desk.
Remote control bags can be draped over the arm of easy chairs
or sofas and used to hold remote controls. They are counter-weighted
so as to not slide off the arms under the weight of the remote
control.
English phrases relating to chairsA movie or a story is said
to keep you on the edge of your chair, if it is suspensful
and engaging.
If you nearly fell off your chair, it was because you were
very surprised
Office
Chair Related information 
