Abstract of Special Research Report (SRR-No.22)

National Institute of Occupational Safety and Health, Japan

Ergonomic Studies on Analyzing the Risk of Accidental Falls in High-Rise Construction Works


Yoshimasa KAWAJIRI, Yoshimi SUZUKI and Hisao NAGATA

: Many accidents, caused by falls, are occurring in many workplaces. Especially in the construction industries, accidents caused by falls reckoned for more than 30% of casualties and 40% of fatal accidents in 1998.
    To date, although many countermeasures to prevent accidental falls have been brought into effect by the construction industries and administrative authorities concerned, there has been no remarkable decrease in the number of accidental falls over the last few decades. As one of conceivable reasons, conventional countermeasures to prevent accidental falls seem to be mainly put much emphasis upon strength and durability of hardware, such as scaffolds, guardrails, ladders, roofs, etc. Accidental falls are considered to be caused by various factors, not only physical factors, but also human factors. An approach from the aspects of human related methods, so-called software methods should be taken to decrease accidental falls. From these aspects, the following survey and three experimental studies have been carried out:
  (1) A questionnaire survey to construction workers to seek relevant human factors to cause accidental falls.
  (2) An analysis of physiological and psychological workloads of workers during scaffolding work.
  (3) Working limits and safety limits in regards to accidental falls due to wind-induced vibration during high-rise construction work.
  (4) Study on sliding properties on pitched roofing surfaces.
    Latent human factors, which cause accidental falls, were analyzed from 817 questionnaires in the first study. Experimental data of human factors during scaffolding work were generated from 10 skilled workers and 7 non-skilled workers. Stability of standing posture was analyzed for low frequency sway by using non-skilled 15 males, 15 females and 5 skilled welding workers, and working limits in regard to safety and work efficiency especially for welding works were obtained. In stead of actual workers, a dummy on various pitched roofing surfaces was employed to study sliding speed, dynamic slip resistance of clothes or footwear on wet and dry surfaces.
    A lot of data were generated from these studies. These data and the ergonomic approach can be expected to give new information and to initiate studies to prevent accidental falls.

A Questionnaire Survey to Construction Workers on Human Factors Concerning Falling-Accident

Yoshimi SUZUKI, Shin-nosuke USUI, Yoshiyuki EGAWA and Takuro SHOJI

: In order to establish the ergonomic countermeasures against falling-accidents in construction works, a questionnaire survey to construction workers was carried out. To approach the latent factors concerning falling accident in construction work sites, the questionnaire was focused on the following three points; non-taking or non-using safety belt, opening/handrail and insufficient information. Statistical analyses were made on 817 subjects which were obtained by this questionnaire survey.
    Summary results are as follows:
  (1) Concerning questions about non-taking or non-using safety-belt, three factors, i.e. daily non-using factor, task-efficiency factor and hurry/fatigue factor were extracted from the factor analysis.
  (2) Depending on the occupation or age of worker, there were some remarkable differences in answer patterns for someitems of questionnaire. For example, item choice patterns of scaffold workers concerning reason of taking/non-taking safety belt were different from those of the other workers.
  (3) Some uneven tendencies in free descriptive answers among occupations of worker were also extracted from the statistical quantification analysis.

An Analysis of Physiological and Psychological Workload for Workmen on Scaffolding

Yoshiyuki EGAWA and Shin-nosuke USUI

: In Japan, the number of deaths in construction work is reckoned 794 victims in 1999 and 37% of these victims were caused by falling from high elevated work place like scaffoldings. So, in order to establish the ergonomic countermeasures against these falling accidents in construction work, an analysis of physiological and psychological workload for workmen on scaffolding was carried out.
    Main results of these experiments were as follows:
  (1) Walking speeds of unprofessional persons were 1.0 m/sec. on the ground and 0.6 m/sec on the scaffoldings (the height of 10.8 m). However, the walking speed of professional worker was 0.9 m/sec both on the ground and the high place of 10.8 m.
  (2) In the walking situation (at the height of 10.8 m) for the difference of walking plate width, walking speeds were investigated. Unprofessional persons' speeds were 0.6 m/sec on the plate width of 50 cm and 0.3 m/sec on the width of 24 cm. Professional workmen's speed like spider-man was 0.9 m/sec on both walking plates' width.
  (3) Mental workload in walking at the height of 10.8 m was examined by dual task method. Mental workload of unprofessional persons increased on high elevated place, but no increase was indicated in the results from professional workmen.
  (4) For stable walking posture and less-load to the foot, walking plate width of wider than 40 cm was necessary.
  (5) In walking on the scaffolding, footprint angles of 30 degrees or more were observed for several spider men. It was cleared that this walking style was very strong against impulsive side force.
  (6) Since the scaffolding frame height was 1.7 m, forward-bent walking postures were observed in walking on the scaffolding. The workmen of 1.75 m or more in stature walked with 30 - 45 angles of forward-bent postures.
  (7) It was answered that the professional workmen preferred cross type handrail to that of parallel type.

Working Limits and Safety Limits in Regards to Accidental Falls for Wind-Induced Vibration during High-Rise Construction Work

Katsutoshi OHDO and Hisao NAGATA

: During the construction of high-rise structures, weather has a strong influence on work efficiency and safety. Especially, bridge pylons under construction are likely to vibrate due to winds even less than 10 m/s, which is a widely used criterion for suspension of construction work in Japan. In fact, at a site workers, who were welding, felt it difficult to work due to wind-induced vibration and construction work had to be interrupted. Although these problems are recognized there are no construction work efficiency standards or even safety standards for working in wind-induced low-frequency motion, particularly in regards to accidental falls.
    Therefore, criteria of construction work efficiency and safety regarding falls under wind-induced vibration were experimentally investigated by an originally designed linear accelerator. In this study, limits of welding work were assumed to be criteria of construction work efficiency, and limits to keep an upright posture were assumed to be safety limits regarding falls during wind-induced vibration. In the experiments, low-frequency sine-wave acceleration was transmitted to each subject by the accelerator. The critical acceleration was investigated while straight line drawing, simulated welding tasks, and the critical limits to keep an upright posture were being conducted. Thirty young males and females, and five welders participated in a series of experiments.
    From the results obtained, it was found that the critical acceleration for an upright posture for the male subjects was larger than the female subjects. Subjects were more likely to lose balance due to backward forces. The critical acceleration for an upright posture increased in proportion to frequencies, which ranged from 0.5 to 2.0 Hz, but under 0.5 Hz the critical acceleration tended to keep constant. On the other hand, the relations between the critical acceleration during straight line drawing tasks and for welding tasks showed similar tendencies and they were almost at the same levels. Both critical accelerations increased in proportion to frequencies increases between 0.5 to 2.0 Hz. However they were in inverse proportion to frequencies under 0.5 Hz. These results are different from the international standards of ISO 6897, which are used to evaluate the response on occupants on offshore structures to low-frequency horizontal motion.
    As the result of this study, standards for construction work efficiency and safety standards, particularly for falls are proposed to be in the range of 0.1 to 2.0 Hz. Using these results for wind frequencies, it was found that construction work efficiency was negatively affected during the construction of the Hakucho Bridge or the Rainbow Bridge. Therefore, in case where vibration in the range from 0.25 to 2.0 Hz is expected and welding work is scheduled, the critical point at which the vibration control system is activated, should be lowered from 10 cm/s2, which was used on the Hakucho Bridge or Rainbow Bridge, to the critical point of 5 cm/s2.

Sliding Properties on Pitched Roofing Surfaces

Hisao NAGATA, Seiji TAKANASHI and Yoshimasa KAWAJIRI

: A lot of occupational accidents caused by falls are occurring especially in the construction industries. According to statistics of occupational accidents of the year 1998, 43% of fatal accidents in the construction industries in Japan are caused by falls from roofs, scaffolding, ladders, eaves, girders etc. The ratio of fatal falls has been gradually increasing year by year. The wooden house construction sectors have more accidents than other sectors.
    In order to obtain safety data for preventing fatal falls from pitched roofs of wooden houses, sliding properties on various roofing materials are being studied by utilizing a suitably dressed dummy, shoes, tools and building materials on an adjustable pitched experimental roof. The five roofing materials are tested for sliding properties such as zinc galvanized steel sheet, plywood, Japanese tiled roof, slate shingle roof and bitumen felt. Sliding properties are three kinds of footwear such as sneaker, safety shoes and Japanese split-toes socks with rubber sole (jikatabi).
    The results of experiments are summarized as follows:
  (1) There are no distinct differences among measured values of coefficient of dynamic sliding resistance of the dummy at different degrees of inclination of a roof.
  (2) When the dummy is sliding on a roof, the most slippery roof is covered with zinc galvanized steel sheet.
  (3) As for footwear, coefficients of dynamic sliding resistance between dry and wet surfaces show remarkably large differences.
  (4) The coefficient of sliding resistance of jikatabi largely decreases on wet surfaces of zinc galvanized steel sheet.
  (5) The coefficient of dynamic sliding resistance of jikatabi on wet surfaces shows 72% lower than one on dry surfaces. When it rains while working on a roof, the coefficient of sliding resistance can suddenly decrease and sometimes can trigger fatal accidents.
  (6) Sneakers show relatively higher frictional properties on wet surfaces than the other footwear such as safety shoes and jikatabi.

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