Abstract of Special Research Report (SRR-87)

National Institute of Occupational Safety and Health, Japan

Study on Preventing Occupational Accidents Due to Falling Construction Works for Elderly Workers



: At present, the number of aged workers has been increasing year by year due to the rapid aging of population in Japan. The back ground that stimulates the increase of elderly workers can be explained in many ways such as aging of population, needs for maintaining daily life, etc.
    In accordance with the increase of the number of elderly workers, it becomes necessary to accomplish more efficient safety countermeasures for elderly workers whose physiological and mental function are relatively weak.
    In this paper, for the purpose of preventing occupational accidents due to falling, in construction work, particularly of elderly workers, research areas on which emphasis should be place are briefly outlined. They include the improvements of working conditions and environment as well as the improvements of equipment and facilities of work places. Among them, specific research works shown below were carried out :
  1) An analysis of occupational accidents of elderly workers in construction industry.
  2) Experimental study for critical forces causing accidental falling of elderly workers.
  3) Study on simple method to evaluate human balance of field workers.
  4) Safety of lifeline employed in the work on the sloped roof.

An Analysis of Occupational Accidents of Elderly Workers in Construction Industry


: The population aged over 55 is gradually increasing year by year in Japan. In the year of 2000, about one fourth of the total workers will be over the age of 55. Particularly in construction industry, the proportion of elderly workers is much more rapidly increasing than that in other industries. As aged population grows, the number of occupational accidents of elderly workers proportionally increases.
    In this paper, it was aimed to obtain the analysis data of occupational accidents, which can be used to establish future safety countermeasures for elderly workers in construction industry. For the purpose of the analysis, the existing papers such as Outdoor Employee's Wage Survey (1963-1985), Statistics on Industrial Injuries under Workmen's Accident Compensation Insurance (1975-1984), Survey on Industrial Injuries (1981, 1984) etc. were investigated. In addition, we computed and analyzed accidents by the raw coding data of the Special Survey of Occupational Accidents in the Construction Industry based on the casualties reports submitted to the Labour Standard Inspection Offices during the years 1981 and 1984, of which average sampling rate was 1/6.
    Workers such as navvies and labours become aged year by year. Nowadays more than half of them are over 50 years of age. The peak of distribution curve of labours population ratio in 1965, was between 30 and 40 years of age, but in 1985 it was shifted between 50 and 60 years of age. Technical workers such as carpenters, plasters, painters, etc. were gradually ageing, but the peak of age distribution still exists between 30 and 40 years in 1985.
    According to the results of analysis, the accident ratio in most occupations in the construction industry is increasing among the workers under the age of 20 or over the age of 60. It is clearly shown that falling accidents on the surface are apt to happen on aged workers. The clear increasing trend like falling accidents on the surface, which come from ageing effects, could not be found among other accident types.

Experimental Study on Critical Forces Causing Accidental Falls of Elderly Workers


: According to the results of the analyses of occupational accidents, elderly workers are apt to fall on the surface. These accidents come mainly from the physical degeneracy of standing ability. In this report, it was aimed to research the critical forces causing accidental falls of elderly workers in various actual standing postures.
    When a worker slips or trips on the floor, the cause is considered to be by a sudden change of body balance. To justify this, a new test device was set up by use of the principle of catapult so as to give a sudden dynamic movement to the subject's body. On the other hand it was considered to give the subject a very slow static movement. In this report, the other test devise was made in order to compare the characteristics between the dynamic and the static forces.
 For the subjects five elderly males (mean age: 64) and five young workers (mean age: 22.6) were tested in the experiments. Critical forces to cause a fall were examined from 16 directions around a standing subject. Various standing postures on the footing boards, on stairs and on floors were implemented. At the first stage of the experiments, analyses were carried out by using the simple theory of leg-mechanics and observations on contacts of foot-sole just when falling through a pedo-scope.
    According to the results of the dynamic experiments, critical forces of elderly workers were lower than these of young workers by about 30 to 50 %. Especially for elderly workers, thumbs and other fingers of feet could not sufficiently play the role of supporting their bodies against sudden movements. In the case of the static experiments, the large difference between the groups of younger and elder workers could not be found, that is, elderly workers also could follow the changes of forces produced by slow movements of body. New technique and devise for measuring the critical dynamic forces of human standing postures can also be applied to evaluate suitable dimensions of hand rail, heel heights of shoes, etc. in regard to preventing them from falling.

Study on Simple Methods to Evaluate Human Balance of Field Workers


: A stabilometry system is widely used in the field of neurology, orthopedics and athletics to register the excursions of the centre of gravity of the body in standing posture and to estimate human balance. But it needs expensive costs for setting up a measure-system including a computer, force plate, recorder, etc., and also needs special measuring skills to manage a stabilometer. Individual data of the gravity movements of human body obtained from a stabilometer, that is, electrogravitiograph (EGG) can be analyzed by highly mathematical techniques such as frequency analysis, etc., but results of analyses are characterized by the deviations coming from wide shifts of individual raw data. Therefore it is not always efficient to adopt the system as an expedient method to evaluate human balance of field workers because of complicated measuring technique, and its insufficient reliability not corresponding with economical costs of the system.
    Various kinds of balancing tests such as ramp test, walking test, and standing test are considered and employed in Japan. One singled standing test with closed eyes is recently popular in the field of industrial safety. It is very convenient to quantify the level of ability of human balance of field workers without any expensive instruments. In this report one singled standing test with closed eyes was modified into two methods, that is, one (method A) was very similar to the ordinary test method, and the other (method B) was a newly devised method carried out by standing on the board of 9 cm width with tiptoe of a single leg with closed eyes. 646 male adults were examined by these two methods. In order to evaluate the measured value of these two balancing tests, the average death ratio of slipping, tripping or stumbling accidents on the surface during past 36 years from the year of 1950 to 1985, were calculated using the data of the vital statistics of Japan in this report.
    The results obtained from measurements of human balance and the evaluations on the basis of death ratio were as follows :
  1) Individual difference of measured values of standing time were not so small as the results of other methods as shown in Fig.5 or 6.
  2) Values of method A were about ten times as large as those of method B, but distribution trends with ages were very similar.
  3) The death ratio of falls on the surface was rapidly increasing with measured values by method A, which showed below 7 seconds, but by method B, those were 2 seconds as shown in Fig.7.
  4) The evaluation table by correspondent ages, estimated death ratio and category ranks of human balance are described in Table 2. Therefore the measured values of standing time can be evaluated the table.

On the Safety of Lifeline Employed in the Workers on the Sloped Roof

Katsunori OGAWA and Katsuya NAKAYASHIKI

: Every year heavy casualties take place in construction industry. In particular, fall accidents represent about 40% of the fatality in construction industry. Among them, the wooden house construction sector has a higher accident frequency rate than the other construction sectors.
 While the lifeline has been used for the prevention of fall accidents in the construction site, the specification of it is yet to be standardized.
    This report investigates experimentally into the dynamic characteristics of lifeline employed in the work on the sloped roof.
    The experiments were carried out by dropping a dummy connected to lifeline along the roof.
 Experimental condition are as follows :
  1) Lifeline; φ 5 and φ 9 mm wire ropes and φ 10, φ 12 and φ 16 mm nylon ropes
  2) Length of lifeline; 3, 5 and 7 m.
  3) Length of horizontal lifeline; 2, 3 and 5 m.
  4) Angle of sloped roof; 20-45 degrees.
  5) Weight of dummy; 75.8 kg.
    The results of the experiments are summarized as follows :
  1) The impact load of the dummy is not influenced by the length and diameter of lifeline on condition that the descent distance is the same.
  2) For the lifeline of wire, the more the stiffness of the parts suspending the lifeline is increased, the larger the impact load of the dummy becomes.
  3) For the lifeline of nylon, the impact load of the dummy is not influenced by the stiffness of its parts.
  4) For the horizontal lifeline of nylon, the impact load of the dummy is 1.0 - 1.7 times as large as that for the vertical lifeline.
  5) For the horizontal lifeline of wire, the impact load of the dummy is 2.5 - 3.5 times, as large as that for the vertical lifeline. With respect of the impact load of the dummy, the empirical expression is shown in chapter 3.

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