Abstract of Technical Note (TN-84)

National Institute of Occupational Safety and Health, Japan

Ergonomic Investigation on Installed Steps with Brace of Steel Tubular Scaffolding

TN-84-1

Hisao NAGATA and Yoshiyuki EGAWA

: Vertical fixed ladders are commonly employed in single pole scaffoldings which are generally put up in small construction site. But most of them are not utilized to the fullest, because construction workers are apt to climb up or down by use of brace, ledger and pole. It is therefore considered that, if small steps are welded on the brace, they will much more safely climb up/down.
    In this study, differences between a vertical fixed ladder and the brace with steps were investigated in respect of climbing, through human motion analysis and subjective evaluation of dimensions. Nine subjects were adopted in human motion analysis, and three of them were actual construction workers.
They climbed up and down several times, and their motions were photographed by a 35 mm still camera and a video camera. The motion of the subjects was analysed by the video pictures taken at each time of 1/100 sec.
    Variables from the motion time was characterized by the factor analysis method. The method of multiple image photography was adopted, using a rotary shutter camera to superimpose a number of image of the body on a single frame of a 35 mm film.
    As a result, it was concluded that the brace with steps was superior to the vertical fixed ladder as a means of climbing a single pole scaffolding. It was particularly noted that the shift time into/from planking was shorter than that of the vertical fixed ladder according to the factor analysis. Preferences of dimensions of the brace with steps were examined by 111 subjects and the most preferable tread of the installed step is 21 cm. Its range from 18 cm to 24 cm is recommended. In case of setting the brace at 45 degree against a horizontal line, the horizontal length (or rise) of step intervals is 40 cm, and its range from 35 to 45 cm is recommended.

Ultraviolet Degradation of Rubber Insulating Gloves for Use in High Voltage Electrical Working

TN-84-2

Kenji ICHIKAWA

: Rubber gloves for use in high voltage electrical working are degraded with various degradation factors in service. As the various degradation factors, voltage, sunshine (ultraviolet), heat, air, injury, tensile force, bending etc. are well known. It is also said that rubber materials are degraded with oxidization resulting from the absorption of ultraviolet ray or from ozone generated by ultraviolet and oxygen in air. This report describes the results of degradation of electrical and mechanical properties of rubber gloves or rubber materials, when ultraviolet is irradiated on them.
    Summaries of the experimental results are as follows :
  (1) Partial discharges or sudden increase of current (a phenomenon that the leakage current increases suddenly at a certain applied voltage) was not observed on these rubber gloves. Furthermore, it was found that the rubber material of gloves has no defects such as voids in it.
  (2) The dielectric loss tangent of rubber gloves was about 1.0 - 1.1%, showing that it is larger than that of natural rubber material. This is caused by the fact that water electrodes have been used in this measurement. On the other hand, capacitance of rubber gloves is usually about 1000 pF, and it increases as the irradiated volume of ultraviolet increases.
  (3) Properties such as leakage current, surface resistivity, tensile strength, elongation and contact angle showed the degradation in the range of about 2000 hours of irradiation of ultraviolet, but the degradation halts over the duration. Properties such as volume resistivity and electrical breakdown voltage did not affect the degradation irrespective of the amount of ultraviolet. As the result, the degradation due to ultraviolet occurred only on the surface of rubber material, and not developed inside of it.
  (4) The correlative relations exist between electrical and mechanical properties. Thus, the measurement of electrical properties makes the estimation of the degradation of mechanical properties possible to some extent.
  (5) The degradation due to ozone causes the numerous cracks on the surface. These cracks become wider and deeper as the irradiated times of ultraviolet are increased.
  (6) Electrical breakdown paths on rubber gloves do not develop straight forward between the water electrodes, and carbonized particles adhere to the inside wall of the paths.
  (7) In this experiment, much more ultraviolet was irradiated on rubber gloves from short distance than that irradiated in service, but the gloves were not degraded greatly. Actually the degradation will be influence not only by ultraviolet, but also by other factors such as injury, tensile force, bending etc., leading to faster degradation.

The Buckling Strength of Frame-Type Scaffold with One-Sided Cross Braces

TN-84-3

Katsunori OGAWA

: The frame-type scaffold is usually made up of vertical frames, cross braces on both sides and horizontal frames. However, a cross brace on one side is often neglected in construction sites, which might cause the reduction of the buckling strength of frame-type scaffold (comparing with those on both sides). In order to clarify this problem a series of loading test was performed to investigate the buckling strength of such various types of scaffold as of 5 stages 1 span, 10 stages 1 span and 5 stages 5 spans. The height of vertical frame and the span length in each test are 1.8 m and 1.7 m, and the widths of vertical frame are 600 mm, 900 mm and 1,200 mm, respectively.
    The results obtained from the experiment are summarized as follows :
  1) The buckling strength of frame-type scaffold with one-sided cross braces becomes smaller, comparing with both-sided cross braces the decrease of buckling strength of frame-type scaffold having 900 mm or 1,200 mm width of vertical frame is more noticeable than those of 600 mm width.
  2) The buckling strength of frame-type scaffold without horizontal frame decreases extremely.
  3) The buckling strength of frame-type scaffold decreases as the width of horizontal frame becomes smaller.
  4) When a horizontal frame is placed on every stage, the buckling strength of frame-type scaffold decreases with the number of span without cross brace on one side.
  5) When a horizontal frame is placed on every stage and cross braces on one side are removed through out the whole stages, the buckling strength of this type scaffold was reduced by 10% for 600 mm width vertical frame and by 20-40% for 900 mm or 1,200 mm width, respectively, comparing with those attached cross braces on both sides.
  6) The buckling strength of frame-type scaffold connected to a tie on the wall on every 5 stage is almost same as that of 5 stage 1 span frame-type scaffold.
  7) When horizontal frames are consecutively fixed throughout several spans, the decrease of buckling strength of frame-type scaffold is small, comparing with those of 1 span frame-type scaffold, and the buckling strength is reduced by 10% comparing with frame-type scaffold with cross braces on both sides.

Standardization of Machine Guards with reference to Anthropometric Study of Selected Japanese

TN-84-4

Noboru SUGIMOTO and Kiyoshi FUKAYA

: Safeguards have to be standardized on the basis of as many anthropometric data of the worker as possible. For example, BS5304, DIN31001 etc. are specified on anthropometric data of each country's workers. Also in Japan, the necessity of such standard on safeguards became pressing lately, and the collection of anthropometric data, or the measurement of physical size of selected people was carried out.
Items of measurement were divided into two groups; the first group consisted of 17 general items related to body dimension, namely, stature, weight, length of forearm, etc., which were measured with Martin's anthropometer, and the second group, of 5 items, each of which was directly related to the requirement of the standard. They were "reach over barriers", "reach through openings", "finger or hand admittable minimum opening size", etc. These five items were measured with photo-technique ; for in stance, by taking photograph of locus of finger tip over model barrier.
The subjects were grouped into 5 ; the male workers of machinery, the male college students, the female high school students, the male business clerks and the female business clerks. In standardizing each requirement of safeguard, the most unfavorable group, which is connected with the severest case on guard design, was chosen out of the five, and the anthropometric data of the group was used as the basis of the standardization.