Ergonomic study of office workplaces involving multiple display screens or large screens

Status:

completed 03/2016

Aims:

The traditional VDU workplace with a single (19") display screen is increasingly being replaced by multi-screen workplaces. The possible effects of these workplaces upon their users have been the subject of little study to date.

For this reason, the German Social Accident Insurance Institution for the administrative sector (VBG) tasked the Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA) with conducting a laboratory study.

In this study, a typical VDU workplace with a single screen (22") was compared with two variants of a dual-screen workplace (two 22" screens, in one arrangement horizontal + horizontal and in the other horizontal + vertical).

The purpose of the studies was to identify indications of possible hazards and in turn to identify any need for additions to the existing recommendations for prevention.

Activities/Methods:

The available international literature on the subject of work at VDU workplaces involving multiple display screens or large screens was first examined and assessed.

The laboratory studies were then planned based upon the results of this preparatory work. Three different screen combinations (single 22" screen; two 22" screens arranged horizontally; two 22" screens, one arranged horizontally and one vertically) were selected, and a number of standardized office tasks (copying texts, comparing texts, sorting data) were then performed on them. For qualitative and quantitative measurement of physiological parameters, methods were specified, in some cases with modification, for the measurement of body posture, movement and position (CUELA body posture measurement system), muscular activity in the shoulder and neck region (surface electromyography, sEMG), eye-blink frequency (eye tracking), visual acuity (Landolt C by means of a smartphone), and screen distance (pattern detection software). The test subjects' subjective perception was recorded in parallel by means of questionnaires (NASA-TLX and in-house). Studies were conducted of the test subjects' qualitative and quantitative performance. The ethics commission of the University of Greifswald approved the use of the methods described.

Ten test subjects (five male, five female, healthy, members of the DGUV's staff) took part in the laboratory study, which took the form of a comparative cross-sectional study. Participation by the test subjects was conditional upon completion beforehand of an eye test (performed by the occupational medical service) and a medical consultation on stresses/disorders of the musculoskeletal system. The test subjects completed the three different standardized tasks on different days, employing all screen combinations for the purpose. The results were interpreted by statistical tests of the measurement parameters for the tested screen combinations.

Results:

The results showed that upper-body movement activity was not pronounced and did not differ significantly across all screen combinations studied.

The majority of movements were performed with the head (rotation and inclination) or eyes, according to the screen combination. Rotary movements of the office chair occurred on only a very minor scale for all screen combinations. A significant change in muscle activity in the shoulder/neck area was detected as a function of the type of task, but not of the screen combination.

The eye-blink rate also appeared to be influenced substantially more by the task type than by the screen combination used. Work with the two-screen setup was however associated with a minor increase in the eye-blink rate compared to the single-screen setup; owing to the greater wetting of the ocular surface, this can be regarded as positive.

A change in the test subjects' visual acuity (pre- vs. post-test) was not demonstrated by the methods used, nor was a relationship between the distance adopted from the screen and the screen combination.

A majority of test subjects preferred the use of two screens arranged horizontally.

Assessment of the performance delivered with the screen combinations studied revealed differences, in some cases significant, in its quality and quantity, the two-screen setups proving superior in this respect.

Altogether, the performance of the test subjects in this study and their preferences favour the use of a multi-screen setup.

The results of the measurements yielded no significant evidence of physiologically limiting factors at the VDU workplaces studied. Major changes to the existing prevention recommendations for the use of VDUs at office workplaces appear unnecessary for the time being in consideration of these study results.

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