National Institute of Occupational Safety and Health, Japan
The Failure of the Earth Supporting in the Excavation Job Site
SH-1961-2-1
I.MAE
: This paper is the investigation report on the accident occurred at the site of drainage cannal construction under the ground.
The scale of the open cut was 80 meters in length, 17.5 - 21 meters in width and 7.3 meters in depth, and excavated soil was loose sands whose water content was 85 - 115 percent.
The continuous sheet piling was employed in making excavation, and the horizontal wales and struts were installed at intervals of 2.6 meters in the vertical direction.
The accident occurred when the excavating work was almost finished.
Suddenly the bracing system was broken, sheet piles fell inside and then surrounding muds flowed into the excavated pit. Consequently two men were killed and two men were injured.
The causes of the accident were conjectured as following.
a) the heaving phenomena at the bottom of the excavated pit.
b) the structural defects of the bracing system.
c) the executive faults of the bracing system.
d) lack of strength of the bracing materials.
Above mentioned causes were investigated in some aspects.
Consequently it seemed that this accident was due to the unstability of the supporting system and lack of the strength of the bracing members.
In order to prevent this sort of accident, it is important for an engineer to try to design pertinently, to execute the plan carefully and to inspect frequently even if it is temporary work such as excavation.
On the Points of Safety Practices on Oil-Extraction Plants
SH-1961-2-2
M.MISHIRO
: Oil-extraction industry is one of the chemical industries that especially have the high explosion hazard. From 1949 to 1959, 30 explosions occurred. In these explosions, 43 persons were killed and 89 were injured, and the damage amounted approximately to \380,000,000.
These explosions were mostly caused by the solvents that leak out by the accident or beak-down of extractor or distiller.
Most of Ignition sources were fires or electrical faults in the oil-extraction department or its neighborhood.
The writer investigated 70 oil-extraction plants to study safety measures in these plants and, in conclusion, pointed out the followings.
1. Generally there were the faults in fire protection of buildings and these buildings were insufficiently isolated.
2. In extractor or distiller, measures for preventing the abnormal pressure development resulting from mis-operation of the processes were imperfect.
3. Considerations for elimination of ignition sources were not satisfactory. Especially, explosion-proof electrical equipments and non-sparking tools were not used completely.
4. Safety rules in inspection and repair were not established.
Oxygen Hazard and Accident Preventive Measures
SH-1961-2-3
K.KOMAMIYA
: With the rise of consumption of oxygen in the industrial working places, accidents due to oxygen are increasing. These accidents can be classified into the following three categories, among which Item 1 is giving rise to fatal injuries every year.
1. Rapid inflammation of working suits owing to superfluous oxygen.
2. Explosion of pressurised oxygen added with organic compounds such as oil. etc.
3. Explosion of liquefied oxygen added with organic compounds.
Many of these accidents occurred because the persons handling oxygen were not aware of hazards of oxygen. The writer tried to illustrate the hazards of oxygen by describing the behavior of oxygen including the heightening of combustion speed, lowering of ignition temperature, and lengthening of flame length.
Furthermore, he explained explosion hazard of oxygen with the enlarging of explosion range, minimizing of ignition energy and the like.
Thus, he gave a warning against the careless handling of oxygen. He illustrated the field measurement of oxygen concentration and the fire-retardant working suits as the measures to prevent oxygen accidents.
