Explosion Protection of Buildings

Transcription

1 1 Exlosion Protection of Buildings Author: Miroslav Mynarz

2 2 Exlosion Protection of Buildings Exlosion of a Condensed Exlosive and Calculation of Blast Wave Parameters

3 Theory of exlosion of condensed exlosive Condensed exlosive: The exlosive means a substance that is able indeendently on surrounding to release large volumes of energy by very fast chemical reaction under defined conditions. A hrase very fast chemical reaction means a big value of equilibrium constant of irreversible reaction and very short lasting of this reaction (even icoseconds). At condensed exlosives, blast wave is generated as a result of release of chemical energy at reaction of the exlosive.

4 4 Theory of exlosion of condensed exlosive Condensed exlosive: In most cases, it reresents decomosition of solids with more comlex structure to substances or roducts with simler structure (articularly a gas state of matter) at release of heat energy. Then this heat energy warms the exanding ambient atmoshere and together with exanding gases they articiate on generating blast wave sreading from the exlosion. Beside decomosition reactions, also oxidation reactions can be considered when two agents react together; one of them is in a caacity of fuel, the other acts as an oxidant.

5 5 Theory of exlosion of condensed exlosive Blast/shock wave: Blast wave is a fast-growing wave of condensed air in the atmoshere characterized by gradual change of ressure, density and temerature on its front. Trajectory of exansion of this wave leads from the eicentre of the exlosion. If it is moving through continuous surroundings its velocity is the same in all directions. Figure was created thanks to articiation on the 12th Conference on Structures Under Shock and Imact organized by Wessex Institute of Technology, Southamton.

6 6 Theory of exlosion of condensed exlosive Blast/shock wave: When the charge exlodes in an oen sace, the imact of the blast wave on the obstructer in our case a building, deends on object s osition, relating to the exlosion centre. With some simlification, calculation of the exlosion in oen sace can be used also for the exlosion inside the building. For calculation uroses, the whole henomenon of shock wave imacting is simlified by many assumtions enabling the use of emirical formulas. That means the calculations of the structures submitted to shock wave effects are influenced by these inaccuracies of inut quantities as well. eliability of calculations is growing with increasing the distance from the exlosion centre.

7 7 Theory of exlosion of condensed exlosive Calculation of exlosion arameters: Calculation rocedures are based on the so-called reduced and dimensionless characteristics. Main reason for converting various units and arameters to dimensionless and reduced ones is ractical use. With the hel of known and roved relationshis between arameters, various shock waves can be assessed without laborious and demanding measurements. The cube root law became a base for it; it says that two charges of the same exlosive and the same geometry but different weight detonating in the same atmoshere roduce very similar shock waves in the same reduced distances.

8 8 Theory of exlosion of condensed exlosive TNT equivalence method: It is assumed that energy released in exlosion is roortional to a mass of the exlosive; the solution lies in imlementation of reference exlosive known as TNT (trinitrotoluene) was chosen. Therefore, mass of various exlosives is exressed using the so-called TNT equivalent (k TNT ). This equivalent can be calculated easily if not found in secialized literature. Several rocedures exist; for illustration, two simle rocedures are chosen.

9 9 Theory of exlosion of condensed exlosive TNT equivalence method: If condition 2 Q v (MJ.kg -1 ) 5 is met then: or k k TNT TNT 0, Q 0, 2 Q Q v TNT v where k TNT is a ressure TNT equivalent of the exlosive (for TNT it is equal to 1), Q v is calculated or measured heat of exlosion (MJ.kg -1 ), Q TNT is heat of exlosion of TNT (4.2 MJ.kg -1 ).

10 10 Theory of exlosion of condensed exlosive Equivalent weight of the exlosive: W W N k TNT k E k G where W is TNT-equivalent weight of the exlosive (in kg of TNT), W N is the weight of the actual (used) exlosive (kg), k E is a coefficient of seal of the exlosive and k G is a coefficient of geometry of shock wave roagation in sace. Coefficient of seal of the exlosive: k E k B

11 11 Theory of exlosion of condensed exlosive Ballistic ratio: weight of k B weight of enveloe exlosive kg kg Coefficient of geometry of shock wave roagation: For the coefficient k G, following is valid: k G = 5 for detonation in free air sace; k G = 1 for detonation on (earth) surface (it results from assumtion that energy is roagating in the shae of a hemishere with total surface reflection).

12 12 Theory of exlosion of condensed exlosive educed distance: For determination of overressure at the face of air shock wave roagating from the exlosion to the surrounding, calculation results from reduced distance: W where is reduced distance from the eicentre of the exlosion (m.kg -1/ ), is the distance from the eicentre of the exlosion (m), W is the equivalent weight of the exlosive (kg TNT).

13 1 Exlosion arameters of the exlosive Basic exlosion arameters: + - overressure at the face of shock wave (MPa), - - underressure in the negative hase of the exlosion (MPa), - reduced sacing distance (m.kg -1/ ), - distance from the eicentre of the exlosion (m), W - equivalent weight of the exlosive (kg), τ + - duration of the ositive hase (s), τ - - duration of the negative hase (s).

14 14 Exlosion arameters of the exlosive ussian sources: Surface exlosion Above-ground exlosion τ W 0 τ Surface and above-ground exlosion τ 016 W 6 W

15 15 Exlosion arameters of the exlosive M. A. Sadovskij: Formulas are derived for the exlosion in the air; for surface exlosion, double of a real weight should be ut into the formula instead of a weight of the exlosive W for for 1 15

16 16 Exlosion arameters of the exlosive J. Henrych: for for for 1 10

17 17 Exlosion arameters of the exlosive D. Makovička: Formulas are derived for the exlosion in the air; for surface exlosion, double of a real weight should be ut into the formula instead of a weight of the exlosive W τ 16, 10 6 W for 1 for 1 15 τ 0, 016 W

18 18 No. TNT equivalents of chosen exlosives Exlosive Combustible/Exlosion heat Q v (kj/kg) Pressure TNT equivalent k TNT 1 Trinitrotoluene Dynamite Cotton owder Black owder Semtex Nitroglycerine Nitroglycol DX (hexogen) Penthrite Tetryl Dinitronahtalene Picric acid Lead azide Mercury fulminate

19 19 Thank you for your attention.