R. Meyer J. Köhler A. Homburg Explosives

365 Water Stemming
cut off at one end, and the cartridge is tested for detonation and
transmission with the aid of a No. 6 blasting cap. The criterion for the
water resistance of the explosive is the time of exposure to water, after
which it still retains its capacity to detonate the cartridge in three trials,
without leaving any non-detonated residual explosive behind.
There is no generally accepted quality classification. Nevertheless,
water resistance of an explosive is considered to be satisfactory,
acceptable, or poor if the cartridge can still be detonated after 24, 8, or
2 hours respectively.
In Germany, the following method for testing the water resistance of
powder-form permissibles has been laid down at the Test Station at
Dortmund-Derne.
A train of four cartridges is fixed in a file on a wooden board; the first of
the four cartridges is equipped with a detonator No. 8. Five longitudinal,
2 cm long notches, uniformly distributed over the circumference,
are cut into each cartridge. The train is immersed for 5 hours in water,
in a horizontal position, 20 cm under the water surface, after which
they are detonated. The train must detonate in its entirety.
This method, including some additions regarding the preparation of
the test sample is standardized as EN 13631-5 as a so-called Harmonized
European Standard. The water resistance of partly water –
soluble, powder-form explosives (e.g. ammonium nitrate explosives or
blasting agents) can be improved by the addition of hydrophobic or
gelling agents. If e.g. W Guar Gum is added, the water entering immediately
forms a gel which blocks the penetration of more water.
Water-resistant Detonator
Unterwasserzünder; détonateur pour tir sous l’eau
Such detonators differ from conventional detonators in being watertight;
water cannot penetrate into the detonator even under increased
water pressure (W Bridgewire Detonator).
Water Stemming
Wasserbesatz; bourrage à l’eau
Water stemming of explosive-blasted boreholes consists of waterfilled
cartridges made of plastic material, which give some protection
against firedamp and coal dust explosions.