Design
What is the correct ergonomic height for my desk, computer monitor and office chair?
Correct height settings for sitting and standing at work
If you have a larger build and need a high-back chair, most standard task chairs will not be suitable for you. To complicate matters, if you have a back-related ailment, you face an additional hurdle. Not only do you require a heavy duty office chair, but also an orthopaedic one that will provide the correct support for your back.
Many retailers claim to sell “heavy duty” chairs, but most of these do not qualify as being “heavy duty”. The same argument applies to “orthopaedic” chairs.
Unfortunately, there are not many office chairs available in South Africa that combine both the heavy duty and orthopaedic attributes.
The Heathrow and OrthoGrande XXL are the exceptions - they are true heavy duty orthopaedic chairs.
What makes a chair “Heavy Duty and Orthopaedic”?
1. What makes a chair “Heavy Duty”?
To make a chair that is stronger and more durable, its overall design needs to take the higher performance requirements into account. This means that the combination and strength of 5 of its 6 major components, is vital.
6 Major components of an office chair
For a ‘heavy-duty’ office chair, there are 5 components that must be strengthened to withstand the additional load. The 6th component (headrest), is optional.
Note: Not all heavy duty chairs need a headrest.
1.1 The Base Set
a. Castors or Wheels
This is where the rubber meets the road!
For a heavy duty office chair, it is better to have large diameter castors. Larger wheels result in a higher carrying capacity. 60mm diameter castors have a higher carrying capacity than 50mm ones and are more manoeuvrable.
If the chair is used on a hard surface such as a tiled floor, soft rimmed castors roll better and won’t damage the floor. Hard castors work fine on a carpeted floor.
b. The 5-Star Base
The 5-Star base can be manufactured from aluminium, glass reinforced nylon, or formed steel tubing.
Aluminium bases have a very high weight carrying capacity and so are often used on heavy duty office chairs. They are often the most expensive option.
Bases made from nylon with glass fibre reinforcing have become extremely popular. With the correct design structure and 30% glass fibre reinforcement, nylon bases are a good choice for heavy duty office chairs.
Nylon bases provide excellent strength and are flexible enough to move easily over slightly uneven floors. They are less expensive than their aluminium counterparts.
Bases made from steel tubing are welded together and have been known to fail along weld lines. Although they can be very strong, the integrity of the base is highly dependent on the quality of the weld. These bases are the least preferred option for heavy duty chairs.
c. The Gas Lifter
The gas lifter enables you to lift or lower the seat height of the chair. It also acts as a ‘damper’ to cushion the impact when you first sit down.
Gas lifters should be manufactured in accordance with an international design standard, for example DIN EN 16955-2017. If they are, they will carry the applicable mark or logo as well as a Class Rating.
For heavy duty chairs, a Class 4 gas lifter is preferred because it has a higher load rating than the standard Class 3.
1.2. The Mechanism on a Heavy-Duty Orthopaedic Chair
For a heavy duty office chair, the strength of it’s mechanism is vital.
To ensure that the mechanism is suitable for heavy duty use, it should be strength tested.
Organisations such as SABS or BIFMA will conduct tests in accordance with the relevant Product Performance Standards.
The mechanism enables you to adjust the movement of the seat and backrest. Adjustments include:
1.3. The Seat
The chair seat is made up of 3 basic components, namely the seat base, the foam cushion and the upholstery material. Seats for heavy duty chairs need to be strengthened to “carry the load”. Normal or standard office chair seats are not designed for a heavy duty application.
a. The Seat Base
Common materials used for the seat base are plywood, polypropylene or nylon. A seat suitable for a heavy duty chair needs thicker plywood with more laminations for greater strength. For example, the Heathrow has a 12 lamination (18mm), plywood seat shell. Heavy duty seats made from polypropylene or nylon require additional structural webs, or steel reinforcement.
b. The Foam Cushion
Flexible Polyurethane foam is used on nearly all office chair seats, and may be either block cut or moulded. Moulded foam, like that used for a car seat, is more resilient and will last longer. Good quality, high density moulded foam is essential for all heavy duty office chairs.
c. Upholstery Material
Select an upholstery material that suits the operating environment. Polyester, acrylic or nylon weaves are breathable but more difficult to clean than vinyl or leather. What is the best upholstery fabric for office chairs?
1.4. The Backrest on a Heavy-Duty Orthopaedic Chair
The chair backrest consists of 3 major components:
a. The Support Structure
For any office chair, the backrest support structure is not as heavily stressed as the seat. Upholstered plywood backrests do not normally require additional reinforcement, while polypropylene shells typically have standard web reinforcements. If the chair has a mesh backrest, the supporting frame should be made of aluminium or a good quality, glass fibre reinforced nylon. Other plastics are simply not strong enough for a heavy duty application.
b. Backrest Foam
The foam on upholstered office chair backrests is not highly stressed, even in a heavy duty environment. The use of softer, block cut foam is usually adequate.
c. Mesh Backrest
A good quality mesh will easily have a lifespan of 10+ years. An inferior mesh quickly becomes “saggy” and no longer provides the correct ergonomic support for your back. Advantages of mesh back chairs.
d. Lumbar Support
Some backrests, like the Heathrow, inherently offer good lumbar support, while others like the Alya and Firefly, have an additional lumbar support adjustment feature.
In 24/7 environments where multiple people use the same office chair, you often find that different users don’t re-adjust the lumbar support at start of their shift. This negates the benefit of the additional lumbar adjustment function.
Under such circumstances, a control room chair like the Heathrow 24/7 orthopedic chair is worth considering.
1.5. The Armrests
Height adjustable armrests are an ergonomic essential for all office chairs used in a 24/7 control room or call centre. What are the best armrests for my office chair?
Depending on the work performed, height adjustable armrests can add to the ergonomic benefit. Some chairs have multi-functional armrests. These are height and width adjustable, and may also allow the arm pads to be moved forwards, backwards and swivel inwards and outwards.
Stratos armrests on the Heathrow are ideal for Big & Tall users
Armrests for Big and Tall executive office chairs should be of a strong construction as they are often used as a support aid to get into and out of the chair. A good example is the Stratos armrest available on the Heathrow.
The Ultimate Heavy Duty Orthopaedic Office Chair
The Heathrow was specifically designed by Karo to meet the highly demanding 24 hour, 7 days a week work environment. All the components used in this heavy duty chair have been designed to out-perform and out-last any conventional task chair.
Buy Heathrow Orthopaedic Office Chair2. What makes a Heavy Duty Office Chair an Orthopaedic one?
A Heavy Duty Orthopaedic Office Chair must have both a Free-Float Swivel Mechanism.
Free-Float Mechanism
Orthopedic chairs use a free-float swivel mechanism that allows separate, or independent control of the seat and backrest. The seat and backrest do not need to be locked in a certain position, but can float forward and back in unison with your body. This prevents excessive lower spine pressure when leaning forward. This is not possible on a chair fitted with either a synchronous, or permanent contact mechanism.
Free-Float Mechanism
By independently controlling the angles between the backrest and the seat, orthopaedic chairs may alleviate, and even rehabilitate, certain medical preconditions, specifically musculoskeletal issues of the spine. Medical professionals often endorse orthopaedic office chairs.
The mechanism on the Heathrow Heavy Duty Orthopaedic Chair allows you to independently adjust the:
- Backrest angle
- Seat Tilt angle
- Seat Depth.
A Free-Float mechanism allows you to independently adjust the backrest and seat of the chair. This enables you to customise the exact angle of the seat and backrest to create your optimal sitting posture.
All orthopedic office chair use a Free-Float mechanism.
Conclusion
24/7 call centres, control rooms, and Big and Tall people need a heavy duty chair. A standard office chair will usually not be able to ‘carry the load’ and won’t last as long as one would expect. Many people that need a heavy duty chair, also have back ailments, and so require a chair with orthopaedic adjustability. There are not many office chairs available that combine both the heavy duty and orthopaedic attributes. The Heathrow is a good example of a chair which does and is therefore a heavy duty orthopaedic office chair.
By the same author:
Design
What is the best foam for an office chair?
At Karo, we improve the comfort of our chairs by including moulded foam in the design of all our seats.
FAQ's
What is Dynamic Sitting?
Office chairs fitted with either a Free-Float or Synchronous mechanism encourage Dynamic Sitting which is crucial for improved ergonomic comfort.
