Ergonomic guidelines for using notebook personal computers. Technical Committee on Human-Computer Interaction, International Ergonomics Association.

In the 1980's, the visual display terminal (VDT) was introduced in workplaces of many countries. Soon thereafter, an upsurge in reported cases of related health problems, such as musculoskeletal disorders and eyestrain, was seen. Recently, the flat panel display or notebook personal computer (PC) became the most remarkable feature in modern workplaces with VDTs and even in homes. A proactive approach must be taken to avert foreseeable ergonomic and occupational health problems from the use of this new technology. Because of its distinct physical and optical characteristics, the ergonomic requirements for notebook PCs in terms of machine layout, workstation design, lighting conditions, among others, should be different from the CRT-based computers. The Japan Ergonomics Society (JES) technical committee came up with a set of guidelines for notebook PC use following exploratory discussions that dwelt on its ergonomic aspects. To keep in stride with this development, the Technical Committee on Human-Computer Interaction under the auspices of the International Ergonomics Association worked towards the international issuance of the guidelines. This paper unveils the result of this collaborative effort.

Ergonomic aspects of portable personal computers with flat panel displays (PC-FPDs): evaluation of posture, muscle activities, discomfort and performance.

The advent of compact and lightweight portable personal computers has offered its users mobility. Various sizes of PC-FPDs can now be seen in the occupational setting as an alternative to the desktop computers. However, the increasing popularity of this relatively new technology may not be without any accompanying problems. The present study was designed to evaluate the use of PC-FPDs in terms of postural changes, muscle load, subjective complaints and performance of the subjects. Ten subjects, 5 males and 5 females, were asked to perform a text-entry task for 5 minutes using each of the 5 types of personal computers--1 desktop and 4 PC-FPDs of various sizes. Results showed that the posture assumed by the subjects while using the PC-FPDs was significantly more constrained than that assumed during work with the desktop computer. Viewing and neck angles progressively lowered and the trunk became more forward inclined. The EMG results also revealed that the activities of the neck extensor in PC-FPDs were significantly higher than in the desktop computers. Trends of increasing discomfort and difficulty of keying with the use of smaller PC-FPDs were noted. Performance was significantly lower for smaller PC-FPDs. This study shows that PC-FPDs have ergonomic attributes different from the desktop computer. An ergonomic guideline specific for PC-FPDs users is needed to prevent the surge in health disorders previously seen among desktop computer users.

Noise levels and hearing ability of female workers in a textile factory in Vietnam.

Noise and hearing ability profiles were determined in a textile factory in Vietnam. Noise mapping done in the weaving section showed that the noise levels exceeded the Vietnamese standard of 90 dBA by as much as 9 dBA in some areas. Audiometric tests performed on 69 female workers from the weaving section revealed that workers with more than 10 years of noise exposure had the worst hearing threshold levels at 1,000 and 4,000 Hz. Similar findings were observed for workers greater than 35 years old. The 4,000 Hz notch, suggestive of exposure to intense noise, was noted in the audiograms of 26 subjects.

Sitting posture and neck and shoulder muscle activities at different screen height settings of the visual display terminal.

The effects of the VDT screen height on working posture and electromyographic (EMG) activities of the neck and shoulder muscles were determined in 10 healthy subjects. The subjects performed a mouse-driven interactive task at the screen height settings of 80, 100 and 120 cm. Changes in body positions were measured by video image and frame analysis. Surface EMG recordings were done on the neck extensor muscle and the descending part of the trapezius muscle, both on the right side. The results of the postural analysis showed that at higher screen height settings, the neck became significantly more erect. The subjects also assumed a more backward-leaning trunk position at higher screen heights. The EMG activities of the neck and shoulder muscles were related to the neck angle and trunk inclination, respectively. A more flexed neck produced significantly higher neck extensor muscle activities. A backward-leaning trunk was also noted to decrease trapezius muscle activity in some subjects.

[Correlation analysis between visual acuity and sitting postural parameters of young students].

The relationship between failing eyesight and the sitting posture of young students while studying was studied quantitatively. Among the 19 students who participated in this study, 9 were classified as emmetropic and 10 were myopic. The mean age was 13.2 +/- 2.2 (mean +/- standard deviation) years. Viewing distance, neck angle, viewing angle, vertical gaze direction, and ocular surface area while studying were measured from the lateral and frontal view images of video recordings of the posture. Viewing distance, accommodative power, neck angle, viewing angle, near point, and log transformed visual acuity showed significant differences between these two groups (p < 0.001). Viewing distance of myopes (15.0 +/- 1.9 cm) (mean +/- standard desviation) is shorter than that of emmetropes (30.2 +/- 4.1 cm). Accommodative power of myopes was lower than that of emmetropes. Correlation analysis revealed that the viewing distance of students significantly correlates to neck angle, viewing angle, accommodative power, near point, and visual acuity (p < 0.01). It can be surmised that the failing eyesight of young students results from postural problems such as shortness of viewing distance and increased neck flexion.

The effect of a back belt on torso motion--survey in an express package delivery company.

According to the Labor Standard Bureau of Japan, accidental back injuries accounted for about 60% of all occupational injuries and diseases in the last decade. The Ministry of Labor issued guidelines to prevent low back injuries in 1994 to address the problem. The use of back belts is recommended for some special working conditions but details on its proper use were not given. This study was planned to evaluate a newly developed back belt and was done at an express package delivery company where the incidence of low back injury was high. The BackTracker was used to evaluate the effect of the back belt on the range and velocity of torso motion. The results indicated that there were no significant differences in the range of motion (ROM) during flexion/extension, lateral bending, and rotation between with and without the belt. The maximum angular velocity (MAV) of flexion decreased significantly (average decrease: 30 +/- 28.3 degrees/sec) when the back belt was worn. The MAV of extension with belt showed a decreasing tendency though not significant. No notable trends were observed in the MAV, during lateral bending and rotation of the subjects while wearing and not wearing the belt. The results also indicated that the back belt affected differently the torso motion of each subject. This study suggested that this back belt could be useful for tasks with high velocity of flexion/extension and that proper instruction on the use of the back belt is needed for each worker.

Adjustments of posture and viewing parameters of the eye to changes in the screen height of the visual display terminal.

To understand the motions caused by the interaction among the different body parts, adjustments of both eye position and body posture to screen height settings of 80, 90, 100, 110 and 120 cm were determined in 10 subjects. The subjects engaged in a non-keyboard, interactive computer game requiring constant visual monitoring. Changes in body positions were determined by video image analysis for the posture parameters and by video frame analysis for the eye parameters. Analysis of variance and correlation analysis showed that neck angle, thoracic bending and vertical eye position were significantly affected by changes in the screen height of the VDT. The study of the interrelationship of eye position and body posture suggested that changes in body positions served to complement the eye position in attaining a better view of the visual target. Viewing angle was observed to be decided mainly by inclination of the neck and the eye. Thoracic bending was also noted to contribute in setting the viewing angle, although to a lesser extent. On the other hand, viewing distance and trunk inclination showed significant correlation.

Analysis of ocular surface area for comfortable VDT workstation layout.

This paper proposes a comfortable visual display terminal (VDT) workstation layout based on an analysis of ocular surface area (OSA). A large OSA induces eye irritation and eye fatigue because the eye surface is highly sensitive to various stimuli. The authors considered that OSA must be one of the useful indices of visual ergonomics and applied it to evaluate VDT workstation layout. Each subject was asked to perform a word processing task using four different VDT workstation layouts. It was found that the main factor affecting OSA was not cathode ray tube (CRT) height itself but the distance between the CRT and keyboard. Thus the following workstation layout is recommended to realize comfortable VDT operation: (1) the desk height should be adjusted to the user's height; and (2) the CRT display should be set closer to the keyboard to provide a smaller OSA.

Toxic effects of hexane derivatives on cultured rat Schwann cells.

The cytotoxic effects of the following five hexane-related compounds were examined on Schwann cell DNA synthesis: 2,5-hexanedione (2,5-HD), 2-hexanol (2-OH), 2-hexanone (MnBK), 2,5-dimethylfuran (DF) and gamma-valerolactone (VL). Schwann cells were isolated from the sciatic nerves of neonatal Sprague-Dawley rats and cultured. [(3)H]-thymidine incorporation into Schwann cell nuclei was measured by scintillation spectrometry and autoradiography when hexane derivatives were added to the culture medium. All of the hexane-related compounds suppressed [(3)H]-thymidine incorporation in a concentration-dependent manner. DF was the most cytotoxic for the inhibition of Schwann cell DNA synthesis among the compounds. The finding suggests that DF-mediated cytotoxicity should be taken into account as a possible additional mechanism of hexane intoxication, especially in the impairment of mitotic cells.

Cytokine profile of human peripheral blood mononuclear cells exposed to 50 Hz EMF.

The effect of 50 Hz electromagnetic fields on the immune system was assessed by measuring the cytokine production of the peripheral blood mononuclear cells (h-PBMCs) of a healthy individual. The h-PBMCs were exposed in vitro to varying magnetic flux densities of 1, 3, 10, and 30 milli Tesla for 3 days. Changes in cytokine production of IL-1 beta, IL-2, IL-6, IL-10, IFN-gamma, and TNF-alpha were studied using the ELISA method. Significant reduction in TNF-alpha production by the EMF-exposed h-PBMCs, in comparison with the non-exposed cells, was detected at all exposure levels (p < 0.05, p < 0.01). Significant increase in IL-1 beta production and decrease in IFN-gamma production were also detected at some exposure strength. No significant differences were detected between the control and the EMF-exposed cells in the production of the other cytokines.

Effects of earplugs on catecholamine and cortisol excretion in noise-exposed textile workers.

To investigate physiological and psychological effects of industrial noise, a survey was performed on 50 female workers exposed to machinery noise [93-100 dB(A)] (noise group) and 25 female workers in less-noisy environments [71-75 dB(A)] (control group) in a textile factory in Vietnam. Urine was collected for analysis of catecholamines and cortisol. The subjects were also asked to fill out a questionnaire. Each subject was examined over 2 working days. The workers in the noise group were asked to put earplugs in their ears during the working hours of the 2nd day. On the 1st day without earplugs, urinary excretion of catecholamines in the noise group were greater than those in the control group. Cortisol in urine showed a similar tendency. Differences in catecholamine excretion between the noise group and the control group decreased on the 2nd day when the earplugs were used for attenuation of noise level in the noise group. Frequency of subjective fatigue symptoms was lower on the 2nd day than that on the 1st day in noise group, while the control group showed almost no day-difference. The results indicate that the catecholamine response to noise in workers was reduced through the use of earplugs.

Ocular surface area as an informative index of visual ergonomics.

A large ocular surface area (OSA) is thought to be one of the causes of eye irritation and eye fatigue. Because ocular surface is very sensitive to various irritants such as dust, heat, dryness, air flow, etc., a large OSA increases the possibility of eye surface exposure to such irritants. Thus, OSA is one of the most important indices of visual ergonomics. This paper aims at making OSA an exact and practical index by first describing an accurate method of measuring it, and then clarifying the relationship between OSA, the width of the palpebral fissure, and vertical gaze direction, all of which are thought to be strongly correlated with each other. We derived the following equations: 1) y = 0.039x1 + 3.36, r = 0.99, 2) y = 3.05x2 - 0.39, r = 0.97, 3) x1 = 72.7x2 - 91.4, r = 0.97, where x1 = vertical gaze direction (degrees), x2 = width or the palpebral fissure (cm), y = OSA (cm2). Finally, this paper also introduces the practical applications of OSA measurement, and notes the differences between OSA when VDT work (word processing using a keyboard and drawing a picture using a mouse) is performed and when traditional office work without a VDT (reading, drawing, and writing) is performed.

[Medical examination of workers exposed to lead in the Philippines].

The medical examination of workers exposed to lead was conducted as part of the activity of the Occupational Safety and Health Center (OSHC) Project in the Philippines (JICA Project). The subjects of the medical examination were 21 male and 193 female workers of a semi-conductor plant (abbreviated A company), 59 male and 6 female workers of a refrigerator manufacture (B company); 199 male workers of a storage battery manufacturer (C company); and 107 male and 6 female workers of a lead smelter (D company). Among the examination items were questions regarding occupational history, subjective complaints and objective signs, determination of blood lead levels, urine delta aminolevulinic acid levels, and examination for anemia. The survey was conducted from June to September in 1990. The following results were obtained: 1) The mean age of the workers ranged from 21.8 to 33.8 years. Those of companies A and B were younger than those of companies C and D. The mean employment duration of males at C company was 10.7 yr, and the longest among the four companies. That in both sexes for A company was 1.8 yr and the shortest among the above mentioned companies. 2) The blood lead geometric mean levels of companies C and D showed the highest concentration. The level in males of C company was 64.5 micrograms/dl and that of D company was 80.8 micrograms/dl. The level in females of A company was 9.9 micrograms/dl and the lowest in concentration. The urine delta aminolevulinic acid geometric mean levels were less than 6.0 mg/l in the four companies. There was no company having hemoglobin mean values less than 14.0 g/dl in males or less than 12.0 g/dl in females. 3) The proportion of blood lead levels of 60 micrograms/dl or more was 67.3% in males of C company, and 89.7% in males and 16.7% in females of D company. The proportion of urine delta aminolevulinic acid levels of 6 mg/l or more was 1.0% in females of A company, 20.1% in males of C company, and 43.0% in males of D company. The proportion of hemoglobin values less than 14.0 g/dl in males or less than 12.0 g/dl in females was 4.7% in females of A company, 1.7% in males of B company, 3.5% in males of C company, and 12.1% in males of D company.(ABSTRACT TRUNCATED AT 400 WORDS)

Dietary sources and background levels of hippuric acid in urine: comparison of Philippine and Japanese levels.

Levels of sodium benzoate in processed food from the Philippines and Japan were analyzed by high performance liquid chromatography. Results showed that of the 44 samples from the Philippines, 31 (70%) contained the compound. The samples with sodium benzoate included 19 juice, 6 softdrink and 6 soy sauce varieties. As for the Japanese products, only 8 (26%) out of 31 food items tested positive for sodium benzoate. The values of the compound in the Philippine samples ranged from 20 micrograms/ml to more than 2,000 micrograms/ml; the Japanese products showed a range of 50 to 200 micrograms/ml. Background urinary hippuric acid levels in 43 male Filipinos and 34 male Japanese with no occupational exposure to toluene were also measured using a high performance liquid chromatograph. Hippuric acid levels expressed as geometric means (SD) were 0.11 g/g creatinine (0.41) for the Filipino subjects and 0.09 g/g creatinine (0.39) for the Japanese subjects. No statistically significant difference in hippuric acid values in the 2 groups was noted. Possible explanations for the lack of any difference in background urinary hippuric acid levels between Filipino and Japanese subjects were discussed.

Urinary metabolite levels and symptoms in Filipino workers using organic solvents.

To compare symptoms with urinary metabolite levels, 900 workers from 7 organic solvent-using industries were studied. Urinary metabolites were determined using a high performance liquid chromatograph. Urinary hippuric acid concentrations exceeding the reference value (2.5 g/g creatinine) were found in 78 (8.7%) workers. However, only 3 (0.3%) and 1 (0.1%) of the participants exceeded the reference value for mandelic (0.8 g/g creatinine) and total methylhippuric acid (1.5 g/g creatinine), respectively. The sum of the values of the ratio of measured urinary metabolite concentration to the corresponding ACGIH's biological exposure indices (BEI) [(HA/BEI of HA + MHA/BEI of MHA + MA/BEI of MA)] exceeded 1.0 in 166 (18.4%) workers. Majority of them were from the footwear manufacturing industry (63/129 or 49.2%). Questionnaire interviews were also administered to determine the prevalence of symptoms while at work (acute symptoms) or within the past 6 months (chronic symptoms). Urinary metabolite levels of individual and mixed solvents were compared with the symptoms of all workers. Analysis using Spearman's rank correlation showed in workers whose urinary hippuric acid exceeded 3.75 g/g creatine (1.5 x BEI), significant correlation between their hippuric acid levels and subjective complaints. Workers whose sum of the values of the ratio of measured urinary metabolite concentration to corresponding BEI exceeded 1.5 were selected and comparing this level with their symptoms, significant correlation was also noted in some complaints.