Correct posture at the video terminal (VDT)

 

Feet completely resting on the floor. Thighs horizontal and legs vertical. The knees shall be able to bend from 90° to 120° and the ankles from 0° to 10°. Vertical arm and horizontal forearm (the elbow must form an angle of approximately 90°). Elbows at work surface height. The wrist should remain straight and without extension. It is important not to have twists in the torso.

 

 

 

 

Ergonomics of the VDT: Desk and Chair (UNI EN 527-1 and ISO 11064-4)

To maintain the correct posture, you need to have:

1) a desk designed according to the ergonomic requirements currently in force (UNI EN 527-1 and ISO 11064-4). As a general principle, an ergonomic desk must:

• be able to adapt to the physical characteristics of the operator;
• facilitate the movement of the operator and be adjustable in height to be able to alternate between sitting and standing position.

To learn about the characteristics of an ergonomic desk you can read the article dedicated to the Ergonomic design of control centers: dimensions of workstations.

2) an ergonomic chair according to ISO 9241-5 which must be robust and stable for 24/7 continuos work, with simple height adjustment functions that support the natural movement of the body.

 

 

 

 

Where to position the VDT display: height and inclination (UNI EN ISO 9241-5 and ISO 11064-4)

To determine the height at which displays should be placed, the following factors must be considered:

1. the height of the eyes, which depends on the physical characteristics and posture of the user while carrying out his task;
2. the line of vision that depends on point 1).

UNI EN ISO 9241-5 determines the ergonomic requirements for the main monitor of a VDT considering the upright sitting position.

 

The line of vision in the sitting erect position (with the head relaxed) is inclined approximately 35° below the horizontal. In the standing position, the inclination of the line of vision is approximately 30°. The optimal position of the most important video unit is between ±15° in the vertical and horizontal directions from the line of vision.

 

 

 

 

 

Where to position the VDT display: viewing distance (UNI EN ISO 9241-5 and ISO 11064-4)

The viewing distance must be chosen taking into account:

• Eye strain

• The viewing angle (angle formed by the line of vision and the line perpendicular to the surface of the video at the point where the line of vision intersects the image on the surface of the video itself).

• The task performed

General recommendations:

• For VDTs, the recommended height for latin characters is around 0.3°. Approximately, the following formula should be used. 

Maximum viewing distance = 215 x height of latin characters

• The viewing distance for identifying characters and symbols should be >500 mm, as many users may have difficulty adapting their vision to shorter distances.
• To minimize eye strain the viewing distance should be at least 700 mm.
• Displays that require frequent or critical monitoring (e.g. an operator's work screen) must be positioned in front of the operator in the primary monitor area.
• The primary monitor zone: in the vertical plane, extends at an angle of 40° above and below the natural line of vision; in the horizontal plane, it extends at an angle of 35° to the right and left of the natural line of vision.

The ideal viewing distance for office work in a sitting position is 600 mm. However, some users may feel more comfortable with distances ranging between 450mm and 750mm. Viewing distances within this range require character heights of 20' to 22' (approximately 0.3°).