Abstract of Technical Note (TN-78)

National Institute of Occupational Safety and Health, Japan

Analysis of the Fatal Accidents caused by Slope-Failure and Rock-Fall in the Cutting Work Sites

It is well known that the accidents caused by slope-failure and rock-fall have occurred frequently in construction sites, and the need of decreasing these accidents is regarded as of major importance nowadays.
    Especially, the works on natural ground are influenced by geological, geographical and weather conditions. In addition there are various difficult problems with the behavior about the cutting slopes which have not been clarified.
    So there are many causes for slope-failure and rock-fall accidents and the reliable prevention against these accidents have not been established.
    In order to establish effective countermeasures of accidents caused by slope-failure and rock-fall in the cutting work sites, as first step, it is necessary for investigation of the actual conditions (workers, environment, geology, etc.) of these accidents.
    In this report we studied some classification of various factors of 142 examples of available accident data which were reported by Labour Standard Offices during the period 1973-1976.
    The outlines of this investigation are as follows ;
  1) The largest number of accidents caused by slope-failure and rock-fall in the cutting works were that of road-construction works which were ordered by the local public entities.
  2) A great number of accidents occurred in the small scale cutting works.
  3) The average age of fatal workers in the cutting work sites are high in general. This is a reflected fact that the ages of workers in the construction works have been increasing.
  4) A great number of failures occurred at the slope of low height and steep grade.
  5) From the geological point of view, there were a few typical lithologic-character and typical geological-time concerning the localities where the accidents caused by slope-failure and rock-fall involved.
  6) In these accidents there were a few typical failure patterns.
  7) The data of failure caused by natural phenomenon such as land-slides may be useful for establishing countermeasures of the accidents caused by slope-failure and rock-fall in the cutting work sites.

TN-78-1

Ikuo MAE, Yoshimi SUZUKI and Noriyuki HORII

Research on Flame and Detonation-Arresters (4th Report) --Detonation-Arrester Model Based on Decaying of Detonation by Sudden Enlargement of Pipe--

TN-78-2

Hidenori MATSUI and Toshihiro HAYASHI

: Detonation arresters are safety devices used in a pipe line for preventing a propagation of a detonation wave through out the pipe layout in which detonable gas mixture might be formed. However very few detonation arresters with low flow resistance have been commercially available. In the present work, an arrester with simple structure was designed based on the principle that a detonation decays into combustion wave when the primary pipe diameter is suddenly enlarged under the condition that the diameter is smaller than a certain critical value which is defined by the composition and initial pressure of the mixture. The arrester was set and tested in 1 inch pipe line. A layer of 100 mesh stainless steel wire gauges was used as a quenching element.
It was found that the arrester was effective for quenching the detonation of acetylene-air and hydrogen-air mixtures. The mixture of 10% acetylene in air was found to be the strongest composition from the view point of detonation quenching. At least twelve gauges were required to quench the detonation of the above composition at one atmosphere. Using the 0.1 mm thick aluminum rupture disk, the critical number of gauges was reduced to seven for quenching the same detonation. For hydrogen-air mixtures, the critical number of wire gauges for quenching the strongest detonation which corresponds to the composition of 30% hydrogen in air was ten. But for pipe enlargement, it should require at least thirty wire gauges to quench the detonation of stoichiometric composition of both acetylene and hydrogen-air mixtures.
When a mixture was flowing, after stopping a detonation, burner flame on the gauze surface was held unless supply of fuel-air mixture was cut off, and some tens of minutes later such a burner flame caused a flash back through the arrester into the other side of the pipe line. Therefore it is necessary to shut off the mixture supply by some means soon after the occurrence of burner flame.

Fractography of Wires and its Application to Accident Analysis

TN-78-3

Masazumi TANAKA and Taiji KONDO

: Important informations about fracture are often left on the fracture surfaces. Fractography, or fracture analysis mainly with electronmicroscope, therefore, has become an influential method studying fracture mechanisms and analyzing fracture accidents. This technic, so far, has been used mostly for slightly wrought (rolled or forged) materials, for example, those for airplane, ship and pressure vessel structure and for various machine parts, but it has scarcely been for wire materials. Such materials, however, are classified in one category, and characterized by excellent mechanical properties and extremely elongated structure owing to severe drawing.
    Therefore, it seems very important to analyze fractographically steel wires as a representative of them, in order to get more knowledge of fracture phenomena and data for accident analysis.
    In this report, first, fractographic features of eutectoid steel wires are fundamentally investigated using scanning electronmicroscope, as to tensile, torsion, impact bending and fatigue fracture modes.
    All modes show basically similar fracture surface morphology of wires to usual wrongest steel. But some differences that seems to characterize the material of this kinds are also found.
    For example, elongated dimples in the shear lip often have parallel ridge fairly long, and river pattern on cleavage facets is less clear, and striations are less frequent and definable.
    Secondly, using the fractography as a main measure, the wire rope that had fractured and caused a serious accident is investigated precisely. In this case, the above preliminary analysis was referred to beneficially. The rope has been used as the lift wire of a derrick crane on a cargo ship. From the precise analysis of failure state of the rope around the fractured portion and some tests to confirm its strength, the following conclusions concerning to the cause of rope fracture were obtained ;
  (1) Wires in rope fractured portion were subjected to marked one-side wear and fair fatigue failure. Outlayer wires were worn so hard that most of them fractured and had no practical loading capacity. Innerlayer wires were fairly worn too, and more than 21 of them had broken or had no loading capacity.
  (2) The structure in which an end block of left guy tackle is not appropriate, and accelerated wear and fatigue failure mentioned above.
  (3) Marked wear was caused because the rope had been rubbed with the side plate of block, through unsuitable design of mast block and/or topping rope.
  (4) Fatigue failure was accelerated by a number of microcracks previously formed in zinc-plated layer of wires, and also helped by rather small block diameter.
  (5) The strength of the topping rope at fractured portion had been lowered to about 4 ton before the accident, because of the failure described above.
  (6) It is assumed that cargo collapsing during unloading operation, caused dynamic load corresponding to 4 ton and broke down the rope.
    At last, through experience on empirical and practical fracture analysis, the importance of them are emphasized.

JNIOSH

Abstract of Technical Note (TN-78)

National Institute of Occupational Safety and Health, Japan

Analysis of the Fatal Accidents caused by Slope-Failure and Rock-Fall in the Cutting Work Sites

Research on Flame and Detonation-Arresters (4th Report) --Detonation-Arrester Model Based on Decaying of Detonation by Sudden Enlargement of Pipe--

Fractography of Wires and its Application to Accident Analysis

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