National Institute of Occupational Safety and Health, Japan
Studies on the Missfireing of Electric Detonaters Caused by the Leakage of Blasting Current, and its Prevention
SH-1957-1-1
S.KOUZUKI, M.TERAZAWA and K.SAKANUSHI
: In general, electric leakage from blasting circuit in series causes the difference of firing current among detonaters, and this slight difference causes the misfire of detonaters.
The authors express the relation of electric leakage of blasting circuit in series, the electric characteristics of each detonater and the numbers of detonaters. In the typical blasting series circuit, these relations are shown as follows.
Ks = 1 / [ cosh( N/2 ) √( r / rg) ] ........ (1)
where Ks ..... ratio of the minimum value to the maximum value of firing current among all detonaters in series
N ..... numbers of detonaters in series
r ..... mean electric resistance of each detonater including one joint between detonaters
rg ..... mean insulating resistance of each detonater including one joint between detonaters.
From this equation, the insulating resistance of detonater can be calculated as follows.
rg = N2r / [ 4 { cosh-1( 1/ Ks)}2 ] ....... (2)
Then for successful explosion in series blasting circuit, the required insulating resistance of detonaters should be increased in proportional to square of numbers of detonaters in series.
The authors measured the insulating resistance of typical detonater leg wires and its protected joints inserted into water, sand or hot damp atmosphere. From these measurements, it is shown that polyvinyl or polyethylene insulated wires and polyvinyl or polyethylene protective tubs for joints should be used for successful explosion in a series blasting cirnit of detonaters.
Experimental Study on Properties of Sand
SH-1957-1-2
Gisei MORI and Ikuo MAE
: In order to study of sand in the bin, some experiments were performed by the penetrometer and the vibrator which generates a horizontal vibration.
This experiment is the first step study on soil mechanics, and the final purpose is to solve the problem about trolley road-bed compaction, and slope failure of cuts and embankments.
As the results, effect of horizontal vibratory condition to compaction of sand in the bin was recognized.
The degree of compaction was discriminated by penetration resistance, and the following experimental formula of the relation of penetration resistance to void ratio of sand in the bin was obtained.
P = ah (e0 - e)
where
P = Penetration resistance
a = Experimental constant
h = Depth of Penetration
e0 = Void ratio of the sand in the loosest possible state
e = Void ratio of the sand
Stress Test of Broken Cast Iron T Pipe
SH-1957-1-3
T.ANDO, K.ISHIBASHI and T.SATO
: Two workers died, when they changed a pipe of the apparatus in a certain sulfuric acid plant, owing to brake adjacent cast iron T pipe and they were spurted and by fuming sulfuric acid.
In this care, we measured stress of this T pipe under various, loads presumed external stress which T pipe were broken and pointed out counter measures from the standpoint of safety about these repairing works.
