Abstract of Special Research Report (SRR-No.13)

National Institute of Occupational Safety and Health, Japan

Development of Devices and Working Systems for Promoting Safety of Aged Workers (First Report)


Shigeo UMEZAKI and Kiyoshi FUKAYA

: As the aged society is coming true in Japan, the expansion of the field of work and the promoting safety for aged workers has become a matter of great concern. Therefore, the specific research of the "Development of Micro-Electronics for Promoting the Working Life of Aged Workers" was conducted from 1986 to 1989. That research aimed mainly at promoting safety of aged workers in regular or usual operations.
    On the other hand, in recent Japanese industries, accidents in irregular or unusual operations such as trouble-shooting, repairing and maintenance are regarded as important while the ratio of accident in regular or usual operations to irregular or unusual operations has relatively decreased. The specific research of the "Development of Devices and Working Systems for Promoting Safety of Aged Workers" is conducted from 1990 to 1994 in order to secure the safety in irregular or unusual operations for aged workers.
    In this report, the following researches from a viewpoint of human factors were executed to provide safety facilities and to improve work environments in above situations as a part of this specific research.
(1) Improvement of environmental conditions for aged workers.
    The abilities of preventing falling accidents and preventing errors under noisy conditions were evaluated.
(2) Evaluation of abilities of aged workers to predict and avoid accidents.
    The abilities of predicting risks and danger perception of aged workers were investigated experimentally.
(3) Improvement of operating equipments for aged workers.
    The equipment for start operations adapted to aged workers were developed.
(4) Ensuring safe works in warehouses for aged workers.
    Safety facilities for operation in warehouses are being developed and evaluated.
(5) Development of supporting equipments for heavy goods handling.
    The equipments which help aged workers in heavy goods handling are under development.
This report contains the above 4 researches ((1)-(4)) which have finished by 1992.

Falling Accidents and Evaluation of Potential Risk of Fatal Falls of Elderly People


: As the population of the elderly in Japan is gradually increasing year by year, and at the same time the birth rate is declining, Japanese employees are tending to work until a more advanced age. Accidental falls are causing a large number of deaths and disabilities, and importantly the elderly are more liable to lose their balance, and to suffer fatal injuries by falls than the younger.
    Balancing ability is considered to be closely related to the occurrence of accidental falls. There are many methods to measure the balancing ability of the elderly. For example, postural activities have been observed as the displacement of the projection of body center of gravity, and stabilographic methods are widely used to measure human balancing ability in the standing posture. However, it is costly to set up the measuring system, including a computer, force plate and recorder. It is not always efficient to use stabilographic methods system for evaluating the balancing ability of the elderly, because the system is not effective enough to justify its high cost, and necessary technical competence. The results of these tests are always shown to the elderly in terms of physical test scores such as time, length, or force, which the elderly find difficult to relate to, and the physical test scores are therefore not persuasive. Thus reasonable and acceptable evaluation methods are required for job assignments, especially for elderly employees who do not wish to change their jobs, even if their jobs are comparatively dangerous and subject to falls; such as roofing, demolishing and steel erection. Further it is very important in evaluating human ability to explain what the measured scores mean, otherwise employees will not understand why they have new job assignments.
    A fundamental method for evaluating risk of fatal falls for the effects of aging was presented in a previous reports (Nagata, 1988). The objective of this study is to refine that method, namely, the method of cross matching of personal physical scores with the relative probable risk of a fatal fall, for new safer job assignments. As single leg standing tests with eyes closed are very simple, and currently popular in the field of occupational safety in Japan. This paper adopts this kind of test, and an evaluation scale for the probable risk of a fatal fall is constructed. As the ankle joint contributes greatly to stabilize during standing, a leg standing test with eyes closed is originally devised where the subject stands with only the toe of his shoe on a flat beam. A jump step test, which shows the application of the above mentioned cross matching method is discussed in this paper.
    I suggest the cross matching method which highlight the relationship between these equations for fatality rates and physical scores. It can be concluded that the elderly who can stand for less than 2 seconds in a single leg standing test on a flat beam with eyes closed, for less than 8 seconds on a floor with eyes closed and jump less than 10 times in a jump step test must be very cautious when they are engaged in dangerous jobs where they are liable to fall.

Effects of Noise in Work-Place on Performance of Elderly Workers

Yoshiyuki EGAWA

: Since the knowledge of the effect of noise on task performance is limited and is generally inconclusive, the effect of noise on the performance of data processing task was investigated. In this experiment, three aged subjects and four controlled subjects were used, and the comparison was made between the aged group and the controlled group. During the experimental procedure, these subjects were exposed to six kinds of noises which were impulsive noise with high frequency, steady-state noise with high frequency, impulsive noise with low frequency, steady-state noise with low frequency, fractal noise and resonance noise. These experiments with the six environments were compared with an environment of non-noise condition. Each subject performed the experimental task for 30 minutes under the noise intensity of 85dB(A). The procedure of experimental task was as follows;
  (1) Two random numbers in significant three figures were presented on the screen of the personal computer.
  (2) Subjects memorized these numbers in significant two figures by rounding up the three digits
  (3) On the next screen, they selected a scale including the number in their memory. And they adjusted a cursor to the memorized number on the selected scale.
  (4) The sequence of this task was repeated for 30 minutes.
    The experiments were carried out on the subjects in the two different task types. One is "the man oriented task type" and the other is "the machine paced task type". The man oriented task type means that each subject is able to perform the task by the pace of himself. However, it is difficult for the machine paced task type to perform the task by the pace of each subject, because the two random numbers presented on the screen are erased automatically. These two types of task were performed by each subject under the above environmental conditions.
    As the results, the two effects on the task performance were observed. One effect was that repetition time of the tasks was suddenly prolonged in the man oriented task type, while in the machine paced task type the increase of the overlooking of the presented number on the screen was observed. These effects of task performance were obtained under the environment of the resonance noise. To investigate the reason for the increase of the overlooking, the interview was conducted for the subjects. As the result of the interview, it was clarified that this type of noise disturbed the subject's concentration on the experimental task. Because the resonance noise was audible like an onomatopoeic word. This may be a main reason why the prolongation of the repetition time and the overlooking of the presented number have occurred in each subject.
    Further, the questionnaires of fatigue symptom were carried out to investigate the fatigue of the subjects due to the exposure noise. As the result of this questionnaires, the difficulty in concentration on the task designated the high rates of the complaints in the noise exposure experiment.

An Experimental Study on Risk Perception of Aged People

Shinnosuke USUI

: This study was aimed to clarify some characteristics of aged people regarding their ability of risk perception. In this experiment, the risk perceptions for respective 32 aged (56-77 years old) and younger ( 18-26 years old) subjects in each group were evaluated by using twenty videotaped scenes which consist of four situations; daily work, working in a factory, driving and cycling.
    The following three different scores concerning the risk of accident involved were used to compare the ability of risk perception for aged people with that for younger people:
  a) Risk sensibility score; degree of feeling of overall risks in the scene
  b) Risk cognition score; degree of awareness of hazards in the scene
  c) Behavioral preparation score; skillfulness to cope with hazardous situation
    The main results obtained in this study can be summarized as follows:
  1) Analyses of the mean scores revealed that risk sensibility score of aged people was significantly higher than that of younger people, but significant differences were not found for risk cognition score and behavioral preparation score.
  2) In daily work situation, every score of aged people was significantly higher than that of younger people. This result could be due to being more careful to slipping or falling accidents for aged people than younger people. However, scores of risk cognition and behavioral preparation of younger people were significantly higher in driving situation.
  3) Two-factor (age and situation) analyses of variance showed the interaction of these two factors in every score. This means the ability of risk perception depended not on age, but on their own knowledge or experience as to the specific situations.
  4) Factor analysis extracted five factors contributing to evaluation of risk perception: traffic in crowded situation, working in factory, slipping or falling, traffic in simple situation, and so on.
  5) Mean factor scores computed in each factor indicated that younger people are superior in the ability of risk perception to aged people in traffic situation, but in slipping or falling situations aged people were superior to younger people.
  6) Applying signal detection theory to the results of risk cognition score revealed that aged people were more difficult to discriminate the hazards and judged them more carefully than younger people.

Evaluation of Danger Perception Ability by Tactile Sense of the Aged

Kiyoshi FUKAYA

: In this report "danger perception" implies "danger avoidance", because the concept of "danger" implies the concept of "prediction" and "avoidance"
    Such works as trouble shooting and maintenance for machinery need that a worker approaches the dangerous zone and he has a danger perception ability. In general, the abilities of the aged tend to decrease with getting old. Therefore it is feared that danger perception ability of the aged also decreases and it is difficult for the aged to avoid danger.
    In this study, the ergonomic experiments were performed to measure the danger perception ability of the aged and the young. In the experiments, the subject was indicated to take a task in the movable range of an industrial robot. In addition to that, he was indicated to push an emergency stop button in case of sudden start of robot operation, which was the danger. Response time of pushing the button was measured in several conditions, that is, by changing the direction of robot motion, the sense organ to detect the sudden start of robot operation and the work load of additional task. The period between start of trial and sudden start of operation was determined by random number.
    The response time was shorter in the tactile perception than in the visual perception. In the perception by vision, a worker needs to share his attention positively not only to the work but also to the movement of robot. On the other hand, in the perception by tactile impression, the motion of the robot can interrupt a worker's operation and compel him to draw attention to the robot. Therefore, a worker can share more attention to the work itself in the tactile sense than in the vision.
    The auditory perception was difficult, because the start of robot operation does not generate special sound.
    The mean response time of the aged was longer than that of the young, and the deviation was larger in the aged than in the young. That means the danger perception ability of some aged persons were lower than that of the young, and they can not avoid the danger in some works which require quick response. Therefore, a supplementing device is necessary for safe work.

Improvement of Operation Devices Suitable for Aged Workers

Kiyoshi FUKAYA, Hiroyasu IKEDA, Shigeo UMEZAKI and Shoken SHIMIZU

: The most important requirement for an operation of aged workers was the realization of safety of work near the dangerous movable parts of machinery. In the present situation, when many aged workers are engaged in such work, they are forced to use complicated or highly computerized operation devices, and they feel difficulty and anxiety for this operation. Therefore improvement of operation devices which is suitable for aged workers should be required.
    The following proposals were submitted to satisfy above mentioned requirements.
  1) An operation device is needed to have a "confirmation function for intention" to confirm starting operation by aged workers.
  2) This confirmation system generates a permission signal for motion of machinery only when an operation signal and a confirmation signal are surely generated.
  3) Confirmation signal can be generated by methods of "window level judgement", "multiplication" or "key operation".
  4) Fail-safe control circuit is necessitated to avoid sudden movement of automated machinery.
    Several types of operation devices which have above mentioned characteristics were developed or improved so that aged workers can work safely near the dangerous movable parts of machinery.
    Devices developed or improved in this research are described as follows;
  [A] "ON delay switch" generates the ON signal (permission signal) only when aged workers have kept on pushing it over a certain period.
  [B] "OFF triggered start switch" generates the ON signal only when aged workers release it after they have kept on pushing it over a certain period.
  [C] "Three position switch" generates the ON signal only when aged workers push it with their appropriate force, that is, the stroke should not be too short nor too long.
  [D] "Both hands control system" generates the ON signal only when aged workers push two buttons by both hands at the same time. Strictly speaking, time difference of both hands operation were examined to be under allowable time difference (0.1 sec) by the fail-safe simultaneity discrimination circuit.

Safety Evaluation of Prevention System for Crushing in Warehouse

Shigeo UMEZAKI and Shoken SHIMIZU

: The operation in warehouses which many aged workers are engaged in can be characterized by the fact that they are forced to work near many dangerous moving machines such as stacker crane, automatic guided vehicle and motor-drived door of cold warehouse. For this reason, some rules of stopping machines when they operate or approach machines are usually established in industries, but actually there are many other operations without stopping machines, so that many serious accidents have sometimes occurred during the execution of these dangerous operations.
    In this report, a new type of prevention systems for crushing which can be adaptable to these operations is proposed. The authors made use of a kind of touch sensor "safety edge"; that is, detect the human presence directly, which is one of effective safety means for these operations.
    The conventional "safety edge" has already applied to a motor-drived door for cold warehouses. Nevertheless, many serious accidents due to doors have been caused in warehouses by inappropriateness of safety edges, because the crushing force of doors with safety edge is in large excess or safety edges have not fail-safe characteristics. In addition, the method of deciding human tolerance for crushing and the appropriate design for "safety edge" were also discussed to solve these problems.
    The results of this research are summarized as follows:
  (1) A method of deciding human tolerance for crushing with taking no consideration of safety factor was proposed. This method uses the feeling of pain caused by crushing between human and safety edge. If this feeling can be substituted for the physical characteristics of human body, it may be possible to predict real crushing accidents by using this physical characteristics objectively.
  (2) The means of controlling the crushing force with human tolerance was proposed by using the "compliant safety edge" which consists of soft elastic bodies or plate spring. The latter safety edge can suppress the crushing force within about 3 kgf when it is applied to the motor-drived door of cold warehouses.
  (3) The characteristics of fail-safe safety edge is clarified. The output voltage of it decreases according to the distance between the machine movable part and human is coming close.

Summary and Subject of Future Studies


: The aim of this research was promoting safety of aged workers engaged in irregular or unusual operations. For that purpose, various characteristics of the agd were studied, and several safety measures were proposed. The results of these studies are summarized as follows.
(1) Improvement of environmental conditions for aged workers.
    The cross matching method to detect the risk of degenerating ability to stand up right was suggested to prevent accidental falls.
    The effect of noise on the performance of data processing task was investigated to prevent errors under noisy conditions.
(2) Evaluation of abilities of aged workers to predict accidents.
    The ability of long range perception or prediction before action was evaluated. Its ability depends not on age but on their own knowledge or experience.
(3) Improvement of operating equipments for aged workers.
    An inquiry about operation revealed the necessity of automatic stop device and check function for start operations. For that reason, start buttons with check function were developed.
(4) Ensure works in warehouses.
    The characteristics of finger under crushing force was investigated for crushing prevention systems. The limitation of allowable crushing force was proposed on the basis of the result.
    The subject of future studies are summarized as follows.
[A] Establishment of the method for selecting subjects of aged workers.
[B] Establishment of the methodology to decide the allowable limitation of aged workers.
[C] Research from the stand point of considering skills and sense of responsibility of the aged.

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