# Blasting - how to calculate the charge concentration Ib (kg/m)?

I posted this question in physics, but they advise me to post it here so here I am.

I was looking for the formula to calculate the burden in bench blasting and I found this document. The problem is I have to calculate the concentration of the charge first with the unit kg/m. I know that some materials are given but I need the formula to calculate other materials in which I have their energetic values calories/g calories/cm3 ..

• This document might be interesting: Explosive Engineer's Guide.
– Fred
Commented Nov 9, 2023 at 6:19
• My understanding is the charge concentration, I$_b$ is the mass of explosive divided by the length of hole that contains explosive.
– Fred
Commented Nov 9, 2023 at 6:23
• This seems to be a units issue, not an engineering issue. Commented Nov 9, 2023 at 6:42
• @SolarMike: For those who don't know anything about explosives engineering & blasting, it's not a units issue. If anything, it's more of a terminology issue. The units at the end of the text are not important to what is being asked.
– Fred
Commented Nov 9, 2023 at 9:05
• @Fred sure it is terminology issue no doubte on that, so since it is mass per distance can it be the velocity or pressure? Commented Nov 9, 2023 at 16:28

The charge concentration, in kilograms per meter of drill hole, serves two purposes. The first is being able to determine the amount of explosives needed to blast a given amount of rock. This is needed when ordering explosives from the supplier or when taking out enough explosives from the magazine.

$$M_{Explosives} \ = \ I_b \cdot N \cdot (L_H \ - \ L_S)$$

Where:

• $$M_{Explosives}$$ is the mass of explosives required [kg]
• $$I_b$$ is the charge concentration [kg/m]
• $$L_H$$ is the length of the drill holes [m]
• $$L_S$$ is the length of the stemming [m]
• $$N$$ is the number of drill holes

The other purpose of the charge length is, if one knows the energy equivalent of each type of explosive [J/kg], for its given density of explosive, it becomes possible to calculate the amount of energy expended in the blast by the explosives used.

• first thank you for the time you have gived to answer my question i apreciate that, so lets say the material is TNT it has 1.65 g/cm3 and 4.184 MJ/kg can you please add that as an example in your answer thank you again. Commented Nov 9, 2023 at 21:30
• When you say "The charge concentration, in kilograms per meter of drill hole" you mean X kilograms multipied by numbers of meters deep of the hole? For example if the charge concentration is0.3kg/m TNT and a drilled hole is 7 meters deep stemming excluded this gonna equal to 0.3×7 = ~ 2.1 kgs total per one hole. Commented Nov 10, 2023 at 14:13
• @Tintin: Regarding your last question with a charge concentration of 0.3 kg/m & a 7 m long hole, yes the mass of explosive in the hole would be 2.1 kg.
– Fred
Commented Nov 10, 2023 at 19:14
• @Tintin: TNT is not a good example of an explosive to consider. It's basically a military explosive & rarely used for civil or mining purposes. It is mixed with other explosives as a compound, but I'm unaware of it being available as sticks. For surface mining & quarries ANFO or emulsion explosives are more likely to be used.
– Fred
Commented Nov 10, 2023 at 19:21
• Thank you very much Fred that was very informative. Commented Nov 10, 2023 at 19:40