JNIOSH

Abstract of Special Research Report (RR-29)

National Institute of Occupational Safety and Health, Japan

Quantification of Sigularity by Using Expextation Probability and an Example in Pursuit Tracking Task (1st report)

RR-29-1
Kiyoshi FUKAYA, Noboru SUGIMOTO and Taiji KONDO

: The method of quantifying the singularity of phenomena or events such as emergency were discussed. The singular event is defined as "The event which surprises man" and the singularity is evaluated by the "surprisal" which the event gives to the man. The largeness of "surprisal" (S for short) is the function of the following three factor.
  (1) D; the difference between expectation and the event which really happens
  (2) W; the degree of importance of the event to the man
  (3) U; the degree of urgency of the event or emergency,
and defined as S = D·W·exp U.
    In this paper the first factor was mainly discussed The expectation is supposed to be expressed as ( Ei, Pi ), where Ei is the event which is thought to be able
to happen and Pi is subject probability that Ei will happen. And suppose Ej which is among (Ei) really happens. At this time the difference between expectation and the event, i.e. D, is defined as
    -log Pj + Σk Pk log Pk.
    To confirm the effectiveness of the theory, we tried a few experiment where second and third factors are considered not to change. The experiment was of pursuit tracking. The expectation related to the position of the target point on the monitor scope were examined, and the probability was measured. By using them, the "surprisal" were calculated and compared with the score of tracking task which was described by mean square error. An sufficient result was obtained.

Accident Prevention on Walkways and Stairways (Third Repoet) --Psychological Assessment to Stair Dimensions--

RR-29-2
Hisao NAGATA

: The previous report: an experimental study of human motion on stairs, was carried out based on the statistical research on stair accidents, and then the characteristics of the following fundamental factors of stair accidents, that is, slipping, stumbling and miss-footing came to light. But no distinct relations between dimensions of tread and rise with those fundamental factors of stair accidents could be shown, because human motion changes on stairs to various stair dimensions, were smaller than individual differences and variations of walking speed.
    This report was studied not by objective observations of human motion, but by psychological method on subjects' estimations. Many optimum dimensions of tread and rise are recommended from past studies. However, the study connected with psychological pressure -- which were dealt with in this report -- for many combinations of tread and rise could not be found, and those studies put stress not on a safety walk in descent, but mainly on a comfort walk in ascent.
    Each of twenty students and aged men estimated 42 combinations of tread and rise for four items, namely, height of rise, width of tread, hardness to walk and instability to walk on verbal category judgement, and some of them also evaluated walking velocity and handrail height. The students group only assessed various dimensions of nonskid edge of tread by the Scheffé-Nakaya's paired comparison method. Furthermore easy terms to express the psychological magnitude or degree and psychological numerical relations among Japanese terms were investigated on the preference questionnaries of 50 persons of different sexes antecedently to the psychological experiments.
    Main results obtained are as follows:
  1) Optimum dimensions for tread and rise exist in a definite combination; tread -- 28 cm and rise -- 18.5 cm for students, 30 cm and 18 cm for aged men. Psychological pressure increases as measurements deviate from this combination.
  2) Descent average time for one stride in neutral on verbal scale is 1.11 sec. for students and 1.41 sec. for aged men. Linear relations between terms on verbal scale and the stride times are clearly shown.
  3) General handrail height is recommended between 80 cm and 90 cm. Suitable handrail height will be changed depending on stature and the usage of the handrail.
  4) A longer width of nonskid edge is better and the rise from the floor of a tread to the top of nonskid edge is recommended within 4 mm.

Composition Limits of Detonability in Fuel-Air Mixtures

RR-29-3
Hidenori MATSUI

: On the view point of prevention of accidental explosions, it is important to clarify the criteria of propagation of a detonation wave in fuel-air mixtures. These-criteria are called limits of detonability such as limit of composition, limit of tube diameter and limit .of initial pressure. These three limits are related each other. One of the fundamental properties of an explosive gas mixture is the composition limit of detonability at atmospheric pressure in a certain tube diameter. It is known that the composition limits obtained experimentally are strongly influenced by initiation methods and the size of the testing vessels. At the present time no standard operational definition for the detonability limits based on. experiments has been established.
    In this study influence of the initiation methods, tube diameters and existence of an obstacle in the tube on the composition limits of detonability was investigated using the detonation tubes. Detonation parameters have been determined in fuel (hydrogen, methane, ethylene and propane)-air mixtures for ambient pressure and temperature in 1 in. (2.8 cm) and 2 in. (5.4 cm) diameter tube, with self-initiating by flame acceleration with spiral wire and with direct-initiating impact from driver detonations of stoichiometric oxy-hydrogen mixture and equimolar oxy-acetylene mixture.
    It is found that the detonable composition rage of fuel-air mixtures which is obtained with direct-initiating impact from driver detonation depends on the strength (i.e., wave velocity ) of blast wave from the driver at the end of the testing tube measured in non-reactive medium (i.e., air or nitrogen). Thus, the stronger the initiation source, the shorter and wider the testing tube are, the measured composition limits of detonability result in wider range. It was suggested that the most of the data of composition limit obtained in laboratory scale vessel using strong initiator were not for self-sustained but for overdriven detonation waves.

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