Safety and safety planning - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 314

Explosive residues in the muck pile. There is also a risk that explosives are not detonated
but are ejected from the hole and end up in the muck pile. This risk can be regarded as low
in the case of cut and stoping blasts, even if some holes are not loaded with charges. The
risk becomes real in the case of contour holes, in which the small-calibre cartridges cannot
be tamped unless the holes are provided with stemming.
Particularly dangerous is the extremely rare case that a detonator does not detonate de-
spite having received the correct impulse (defect in the delay connector) and the priming
cartridge is thrown out into the muck. In this case, mechanical damage to the priming
cartridge when the muck is loaded can result in a detonation.
Loading charges before the completion of drilling. Above all when large-diameter tun-
nels are excavated and when blasters are waiting and not engaged in drilling, the tempta-
tion can be great to save time by starting to load the charges before the completion of
drilling work. In this case, there is a danger that a drill enters a hole that has already been
charged and the charge detonates.
Firedamp. Another specific danger in tunnelling is the occurrence of firedamp, which is
flammable air with methane content. Since methane mixed at concentrations of 5 to 15 %
in air forms an explosive mixture, there is a danger that a spark could ignite the explosive
air or that the firedamp could detonate together with the explosives and produce an unin-
tended reinforcement of the blasting effect.
Stray currents. Particularly when explosives are transported by rail with an electric lo-
comotive, there is a danger of stray currents, which in some circumstances could have
enough energy to cause an unintended early detonation of an electric detonator.
Lightning. A thunder strike could also lead to unintended early detonation of an electric
detonator, unless the tunnel is already sufficiently deep underground.
Working from both ends. When the two tunnel drives are sufficiently close, a blast on
one side could lead to a danger situation on the other (falling rock pieces etc.).
Protection measures. In order to expose the miners to the least possible extent to the
health dangers from nitroglycerine, carbon monoxide and nitrous gases - according to the
basic principle of the EU guideline to combat dangers at their source and reduce dangerous
moments - explosives should be used, which lead to the lowest possible concentrations
of harmful agents. This is a very clear argument for the use of emulsion blasting agents.
Nitroglycerine. When emulsion blasting agents are used, which do not contain any explo-
sive oils such as nitroglycerine, there can be no ingestion of nitroglycol or nitroglycerine
through the skin or inhalation. Headaches are often suffered by miners when loading gela-
tin explosives, but cannot occur when emulsion blasting agents are used. If nonetheless
gelatin explosives are used, any contact of the bare hands with the explosive should be
avoided (protective gloves should be worn).
Fumes. If emulsion blasting agents are used, the explosion only produces a fraction of the
hazardous content in the fumes, specifically about half the carbon monoxide and a third of
the nitrous gases compared to gelatin explosives.
In order to further minimise the formation of hazardous substances in the fumes, cares
should be taken that the explosion is initiated by the appropriate detonators (danger of ex-
cessively weak detonation). Suitable, fresh, unimpaired explosives with the least possible