c.m. lownds and b.w. wallace- the performance testing of permitted explosives for coal mines

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J. S. A t,. In st. M in . M eta l/., vol. 86, no. 10.O ct. 1986. pp. 415-423.

The performance testing of perm itted explosives

for coal m ines* by C.M . LOWNDSt and B.W . WALLACE*

SYNOPSIS

Permitted explosives in South Africa are those explosives approved by the relevant State authority for use infiery coal m ines. The main tests that an explosive must pass for this approval are the gallery tests derived from

the Buxton (U .K.) classification. These tests are described briefly.

In addition, the safety of perm itted explosives is affected by their ability to deflagrate, and to produce a naked

flame after blasting, rather than to detonate fully. Tests done on this phenomenon are discussed.

A further potential hazard of explosives is after-blast fume. The testing and behaviour of several perm itted ex-plosives in this respect are covered, both in the laboratory and in the fie ld. Performance testing of perm itted ex-

plosives, specifically the double-pipe, underw ater, and ballistic m ortar tests, and their relationship to fie ld use, are

considered in som e detail. The application of traditional and new tests to perm itted explosives leads to guidelines

for the safe and efficient formulation and use of these products.

S AM EV A TT IN G

Ve roo rloo fde sp rin gsto ww e in Su id-Afrika is die sp ring sto ww e w at d eu r d ie b etrokke sta atsow erh eid go edg eke ur

is vir gebruik in brandgassteenkoolm yne. D ie vernaam ste toets wat 'n sp rin gsto f vir h ierd ie g oe dke uring m oa t d eu r-

staan, is die galerytoetse w at van die Buxton-klassifikasie (V.K.) afgelei is. Hierdie toetse word kortliks beskryf.

Verder word die veiligheid van veroorloofde springstowwe geraak deur hul vermoti om snel te verbrand en na

d ie on tp lof fi ng 'n oap vlam af te gee in plaas van volledig te detoneer. Toetse wat in verband met hierdie verskynsel

u itge vo er is, w ord be sp ree k.No g 'n potensitile gevaar van springstow we is die dam pe na die ontploffing. Die toetsing en gedrag van verskeie

v ero orlo ofd e p lo fs to ww e in h ie rd ie ve rb an d, in B Ow el d ie la bo ra to rium a s in d ie v eld , w ord g ed ek. W erkv errig tin gs to ets eop veroorloofde springstoww e, spesifiek die dubbelpyp-, onderw ater- en ballistiese m ortiertoetse, en hul verband

m et veldgebruik, word uitvoerig bespreek. Die toepassing van tradisionele en nuw e toetse op veroorloofde spring-stowwe lei tot rig lyne vir die veilige en doeltreffende formulering en gebruik van hierdie produkte.

IntroductionCoal is won in South Africa by the common methods

of m ining: undergrou nd bord-and-pillar, und erground(m echanized) longw all, opencast strip, and opencast

bench m ining. D espite the recent grow th of opencast an dmechan ized mining , the long- es tabl ished bord- and-pi ll ar

m ethod still produces over 40 per cent of South A frica'scoal. In the long term , the com petitiveness of this typeof m ining depends upon continuing improvements insa fety a nd e ffic ie ncy . T he o ptim um fo rmula tio n, c ho ic e,

and use of explosives and accessories for the blasting ofcoal are som e of the m ore im portant technical require-m ents for successful bo rd-and-p illar m ining.This paper deals with the main factors affecting the

safety and results of blasting in collieries. O ver m anyyears, as know ledge of the relevance and im portance of

various features of perm itted explosives has increased,new tests have been d evised for the ch aracterization andcom parison of explosives and their m ethods of use.T he p ro pe rties o f p erm itted e xp lo siv es th at a ffe ct th eir

. Presented at the Colloquium on Recent M ining and Metallurgical

Dev elo pmen ts in th e E as te rn T ra ns va al, w hic h w as h eld b y The Sou thA fr ic an I ns titu te o f M in in g a nd Me ta llu rg y in W itb an k in S ep tembe r1985.

t Product M anager, Packaged Explosives.

t Senior Research O fficer.

B oth th e a bo ve o f A EC I E xp lo siv es & C hemic als L im ite d, P .O . B ox

1 12 2, J oh an ne sb urg 2 00 0.@ The South A frican Institute of M ining and M etallurgy, 1985. SAIS SN 0 038 -2 23X /S 3.00 + 0.0 0.

safety in use are as follow s:

(a) incendivity, Le. the likelihood that m ixtures of

methane and air, or of coal dust and air, w ill beignited by the action of blasting;

(b) deflagration, Le. a naked flame after blasting as a

result of the explosives burning rather than deto-nating, w hich is extrem ely undesirable in an under-ground coal m ine;

(c) im pact and friction sensitivity; and(d ) a fter-b la st fume s.

The designing and conducting of tests aimed at thepotential hazards of explosives is difficult ow ing to thevery low probability of an event in practice. It is im pos-

s ib le to d isc ov er from c on tro lled lab ora to ry o r fie ld te stsw hat the actual probability of a hazardous event is. In-stead, hazards have to be inferred from tests done underextrem e conditions, w here the m agnitudes of the poten-tial causes are grossly exaggerated. O n the other hand,these p otential causes are often easy to identify, and teststhat exaggerate them can usually be set up. In this w ay,useful com parative data can be gathered and, w ith tim e,test results can be correlated with the statistics of un-desirable ev ents from the user industry.The problem s in the designing and conducting of per-

form ance tests for explosives are som ew hat different.There is a variety of tests, w hich in them selves are wellunderstood. In fact, m ore test procedures for explosives

JO URNA L O F TH E SOUTH AFR IC AN IN STITU TE O F M ININ G AND METALLU RGY OCTOBER 1986 415



are described in the literature than the explosives andm in in g in du strie s c an h an dle . E qu ally , th e d esire d re su lts

of blasting-fragm entation, heave, advance, etc.-caneas ily b e s pecif ied. Howeve r, t he r ela ti on sh ip b etween oneor more param eters o f exp losives m easured in the labor-atory and their likely perform ance in blasting is alm ost

a lw ay s p oo rly u nd ersto od . B la stin g is a c omple x p ro ce ss,not only because of the heterogeneity of m ost rocks andm inerals, but because of stro ng interactio ns betw een the

energies available for fragm entation an d for heave, e.g.b etw ee n th e e xp lo sio n p ro du ct g ase s a nd th e ta rg et mate r-ials.

For these reason s, the m ain thrust of the p erfo rm ancetests described here has been towards the quality ofdetonation. Detonation in a borehole is not a simplego-no go situation. Tests designed to m im ic the condi-tions of use as far as possible show that the detonationb eh av io ur o f c ommerc ia l e xp lo siv es c an v ary w id ely . Theapproach has therefore been to use laboratory tests to

ensure good-quality detonation in a borehole by the im -p ro ve d fo rmula tio n a nd u se o f e xp lo siv es. T he fre qu en cyand consistency of blasting in bord-and-pillar m iningm ean that explosives can be com pared in term s of prac-tical b lasting results fairly easily and accurately.

P erm itte d Exp lo siv es S tu die dThe fo llowin g c ommerc ia l a nd e xp erimen ta l c ompo si-

tions w ere exam in ed , all the explo sives bein g prod ucedby A EC I E xplosives & C hem icals Lim ited:

An amm on gelatine dynam ite (or,gelignite')Wa te rp ro of p owde r, n itro gly ce rin -

basedWa te rg el, se nsitiz ed b y p ain t-g ra de

aluminiumE nergex 140/150 W atergels, sensitized by m ono-

me thylamine n itr ate .

Ajax

Coalex 1

S in ex 9 05

S afety T estin g of P erm itted E xp losivesAt present, the only testing gallery in South Africa

belongs to AECI Explosives & Chem icals Lim ited andis situated at Modderfontein. Before explosives aresched uled as perm itted ex plosiv es in Sou th A frica, theym ust pass the incendivity tests on this gallery or the onefrom which it is co pied, the B ritish g allery at B ux ton. (Indue course, the testing of perm itted explosives w ill be-

com e the responsibility of the South A frican Bureau ofStandards.)

B ritish standards specify six classes of perm itted ex-plosives: PI, P2, P3, P4, PS, andP4/5. In South Africa,only PI is used. B rief definitions and descriptions of the

tests for PI explosives are given below.

Definitions

Me th an e-A ir M ix tu re . The m ixture into w hich a test shotis fired shall contain com bustibles equivalent to 9,0 :t0,25 per cent of m ethane in air. A m ethane-air mixture

is most sensitive in these pro portion s.

C oal D ust. Wankie Coal ground to such a degree offineness that 85 per cent by mass will pass through a0,066 mm sieve.

41 6 OCTOBER 1 98 6 JOURNA L O F TH E SOU TH A FR IC AN IN ST ITU TE O F M IN ING AND META llU RGY

Cannon. A cy lin der o f sp ecia l steel w ith a d iame ter o f457 mm or m ore and having an axial bore that, w hen new ,is 55 mm in diameter and 120 cm long.

Cartridges. Waxed paper shells 36,5 to 37,5 mm in dia-meter.

Priming. B y m eans of a C arrick detonator inserted flushwith the end of the prim er cartridge.

L oad ing a nd Stemmin g. A dry fireclay plug is insertedin to th e cylinde r fi rs t. When inve rs e in it ia tio n i s s pecif ied,the prim er cartridge is inserted w ith the detonator to theback, followed by the remainder of the charge. W hendirect initiation is specified, the prim er cartridge is in-serted last w ith the detonator to the front. W hen stem-m in g is sp ec ifie d, a sin gle d ry fire cla y p lu g is p ush ed o nto

the charge but not with such force as to distort the cart-ridges. The plugs are m ade of unfired fireclay, and are51 mm in diameter and 25 mm in length.

Coal- du st Tes ts . A steel platform 305 mm wide by 3,0 mlong is placed in the gallery with one end t<m ching the

end plate through which the shot is fired, and with itssurface 1 2,5 mm below the b ore o f the cann on. A cco rdingto the laid-down rules, 2,27 kg of coal dust is scatteredonto the table.

T ests for PI E xplosives

Series (i) 26 shots, each 140 g , inversely initiated,without stemming, into m ethane-air m ix.

Series (H) 5 shots, each 800 g, directly initiated, w ithstemming, into m ethane-air m ix.

Series (H i) 5 shots, each 800 g directly initiated, w ithstemming, over coal dust.

To pass the PI test, the explosive must. result in not more than 13 ignitions in series (i), and. result in no ignitions in series (H ) and (iii), and. d isp la y sa tisfa cto ry d eto na tio n th ro ug ho ut th e te sts.

Dej/agration

U nder certain circum stances, explosives can fail tod eto na te c omple te ly in a b ore ho le . T he re sid ua l e xp lo siv ecan b e ig nited by being subjected to gases at high pressureand tem perature from the part of the charge that deto-nated. This phenomenon has been known around thew orld for m any years!. D eflagration is m ost likely, and

has occurred in South Africa on a few occasions, withn itrogly ce rin -b as ed powde r exp lo siv es.

T here are tw o approaches to the testin g o f an explo sivefor po ssib le deflagration in use. Firstly, tests can be co n-ducted to show the aspects of form ulation or the condi-tions of use that can cause partial m isfires. S eco ndly , thepropensity of an explosive cartridge to be ignited, and

to sustain com bustion at atm ospheric pressure, can bein ve stig ate d in id ea liz ed la bo ra to ry te sts.

V arious experim ental 'set-ups have been used in dif-ferent laboratories to study th e b urn ing characteristicsof explosives1.2. These studies have concluded that thep robabili ty o f igni tio n and s us ta in ed burn ing is in cr ea sed

w hen the explosive is a nitrog lycerin-based powder, andthere is excessive wax on the end of the cartridge.

A t A EC I, the ease w ith w hich a nitroglycerin pow der



Diameter

mm

Test x Cartridging CO NOx

no . Explosive m ass, g materials Vkg Vkg

Ajax 29 x 200 Pos t-waxed pap er 32,8 2,2

2. Ajax 29 x 200 Pos t-waxed pap er 31,4 1,1

3t Ajax 29 x 200 P os t-wa xe d p ap er 23,3 1,7

4t Ajax 29 x 200 P ost-w axe d p ape r p lu s

c oa rs e c oa l 27,1 1,7

5t Ajax 29 x 200 P ost-w axe d p ape r p lu s

f in e c oa l 32,4 1,4

6 Ajax 29 x 200 P re -waxed pap er 10,2 2,5

7 Coalex 1 32 x 200 Pos t-waxed pap er 22,9 2,3

8 Coal ex 1 29 x 160 Pos t-waxed pap er 30,2 2,2

TABLE I

DEFLAGRATION TESTS ON COALEX US ING SLOW IGNITERCORD

Test no. E xp erim en ta l a rra ng em en t Result

~ No ign it io n

W rapped. w ith incendiary cord

2 !]JJJJ]]JJJ)J No ign it io n

W rapped. w ith incendiary cord-

c ar tri dg e w ra pp er remo ve d

3 A I D J J J I D J J J I 1 No ign it io n

Dou bly w rap ped . w ith in ce ndia ry

co rd -cartrid ge w ra pp er remove d

. Completely encased in a tightly wound spiral

(Coalex 1) could be ignited was exam ined in a series of

tests that w ere conducted on a single, unconfined cart-rid ge o f e xp lo siv e. The ig nitio n so urc e w as a n in ce nd ia ry

cord (Slow Ignitercord). These sim ple tests, w hich aresummariz ed in T ab le I, sh ow ed that, u nde r atm osp hericpressure, C oalex is difficult to ignite, even w ith a fierce

h ea t so urc e. Mo re so ph istic ate d te sts a re b ein g e xamin edfor use in the further study of this behaviour.

A llied to ease of ignition, partial m isfire of a colum nof explosive is a necessary cause of deflagration. Teststo identify causes of m isfires fall into the broad class oftests on the quality of detonation, and are dealt withbelow. The conclusions about which m ethods give them ost reliable detonation are sim ilar to those reached

elsewhere! .

F um e Te stin gA ll e xp losives p ro du ce a sm all amo un t o f no xio us fume

on being detonated. The m ajor species are carbon m on-oxide (CO) and oxides of nitrogen (NOx). The com-m onest international test for fum es from explosives in-volves the Bichel Gauge, which is a small chamber inw hich a sing le stick of ex plosiv e is fired u ncQ nfin ed. T heh eav y, sea led app aratu s c ompletely co ntain s all the gases

produced by the detonation, w hich are then analysed.The experimental set-up in the AECI laboratory is

sim ilar to the 'Large Cham ber' operated by the United

States Bureau of M ines3. It consists of a steel mortarsituated in a 17 m 3 slightly vented cubicle (Fig. 1). Theshot is fired in the confinement of the mortar, and the

TABLE II

EVALUATION OF FUM E BY PERM ITTED EXPLOSIVES FROM

LABORATORY MEASUREMENTS

Notes:. T he a ve ra ge of 3 m easu reme nts

t On cartridges from a single batch. The free space around the cart-ridge in the cannon borehole w as filled w ith coal dust as indicated

product gases fill the cubicle. E xcess pressure after the

shot is allow ed to vent, the rem aining gases are allow edto mix, and samples are withdrawn for analysis. Thereadings are reduced to litres of gas per kilogram of ex-plosive, selections of which are shown in Table 11.

For com parison, a series of tests was conducted in abord-and-pillar coal m ine, w here m easurem ents of theCO an d NOx con cen trations w ere tak en at in terv als afterproduction blasts of 1, 2, or 3 ends at a tim e. The results

are given in Table Ill.

A com parison betw een laboratory and fum e m easure-m en ts sh ow s the fo llowing :

(a) the lab orato ry tests correlate w ell w ith th e real situa-

tion,(b) the amount of fume generated does not increase in

proportion to the mass of explosive used,(c) ev en w ith the be st exp lo siv~ g oo d v entilatio n is essen -

tial to create hygienic working conditions afterblasting,

(d) significant quantities of fume are trapped in the

broken coal and released during loading,(e) elim ination of post-w axing of A jax cartridges signi-

ficantly reduces the am ount of carbon m onoxide

lib era ted , an d(f) Energex 140 produced the lowest concentration of

fume.

M ost of these findings are confirm ed by m ore extensivestu die s d on e e lsewh ere 4.

A s a result of this w ork, the post-waxing of commer-cial A jax and Coalex 1 has been discontinued.

Im pa ct a nd F riction Sen sitivity

T he standard tests for im pact and friction sensitivityconducted in the A EC I laboratory are the traditional 5 kgfall-h ammer an d to rp edo -frictio n testss. A sk etch o f the

latter is given in Fig. 2. These tests are valuable duringth e fo rmu la tio n o f e xp lo siv e c ompositio ns. F or e xamp le ,they can show w hether a change in form ulation has m ade

JOURNA L O F THE SOU TH A FR IC AN IN ST IT UT E O F M IN ING AND MET ALLURGY OCTOBER 1986 41 7



2 , 7 2 m

= = = 1

Volume ca 17 m3 2,78 m

.....-

To analysis

Fig. 1-Cham ber and m ortarfor the testing of fum e

Hole diameter

38 mm

jCI,

II

II

I II

I II II IU

450 mm

Testing the Q uality of D etonation

Two test procedures are used to indicate the qualityof the detonation: the double-pipe test6 and the under-wa te r (bubble ) tese.

In th e IlfS t, th e e xp lo siv e c artrid ge s a re p la ce d in a m ild -"'steel pipe with an internal diameter of 40 mm, which isthe borehole diam eter in m ost South A frican bord-and-p illa r c ollie rie s. T he c artrid ge s a re a rra ng ed , fo r e xa mp le

w ith coal dust betw een them , to represent as far as pos-sible realistic conditions of use. The test pipe is placedon top of a witness pipe at firing; the depth of dent in

the w itness pipe correlates w ith the peak pressure gene-rated by the test charge8.

In the underwater test, the charge of permitted ex-plosive, protected from w ater p enetra tio n, is fired un de r

6 m of water. The bubble energy of the explosive? isderived from the resulting oscillation of the bubble ofproduct gas. A second charge (of Pentolite) can con-veniently be used to generate precursor shocks in thew ater to show the effect of precom pression on the energyyield of the test charge.

( )

210 mm

the com position m ore or less sensitive, how a new com -position ranks against older ones of w ell-know n sensi-tivity, an d w hether factors like th e pa rticle size s of solid

ingredients or the presence of grit adversely affect thesensitivity.

The rating of explosive com positions by fall ham meror torped o friction d oes n ot h av e a direc t bearin g on th eirsa fe ty in u se . In g en era l, n itro gly ce rin -b ase d e xp lo siv es

react more readily in these tests than water-based ex-plosives. The latter are very dependent upon the specialconditions of the test, e.g. the kind of grit present.

P re ssu re D ese nsitiza tio n T ests

T wo m ajo r form s of pressu re d esen sitization a ffect the

p erfo rm an ce o f c artrid ge d e xp lo siv es, in clu din g p erm it-ted explosives: the channel effecf, and dynamic de-sensitization from a preceding adjacent shot.

41 8 OCTOBER 1 98 6 JO URNA L O F TH E SOU TH A FR IC AN IN STIT UT E O F M IN IN G AND META LLU RGY



Distance Air velocity CO, ppm NOx, ppm

in from in last after after

l as t t hr ough through

Blast Mass road road 2 15 30 2 15 30

no . Explosive. kg m mIs mill mill mill mill m ill m ill Remarks

1 Ajax 16 13 0,75 300 250 150 90 10 -

2 Ajax 16 12 0,6 16 0 100 220 50 Tr - 3 rd r eadi ngdur in g l oadi ng

3 Ajax 16 13,5 0,6 310 200 200 100 20 -

14 Ajax 16 16 0,86 350 17 0 100 60 20 -

10 Ajax 16 19,5 1,0 500 190 100 100 30 -

11 Ajax 16 11 1,0 280 160 100 70 Tr -

12 Ajax 16 12 1,0 290 90 90 60 6 -

13 Ajax 32 15 0,86 300 230 120 90 20 - 2 fa ces

4 Ajax 48 16,5 1,0 300 130 280 110 20 - 3 rd r eadi ng

dur in g l oadi ng

31 Mod. Ajax 16 15 0,5 280 100 50 lOO 5 Tr

32 Mod. Ajax 18 13 0,8 220 50 20 80 Tr Tr Stone bands

33 Mod. Ajax 17 100,8

240 40 40 70 Tr - S to ne b an ds34 Mod. Ajax 16 12 0,8 200 80 60 80 Tr -

35 Mod. Ajax 16 10 1,0 100 40 20 40 Tr -

29 Mod. Ajax 16 18 1,0 80 20 Tr 60 Tr -

30 M od. A jax 44 18 1,65 500 200 200 300 20 Tr 3rd reading

dur in g l oadi ng

8 Sinex 905 16 20 1,0 120 110 50 90 Tr -

9 Sinex 905 16 20 1,0 100 10 - 50 Tr - F ac e h ole d

through

5 Sinex 905 16 15 0,86 120 40 30 80 Tr -6 Sinex 905 16 15 0,86 lOO 50 10 80 Tr -

16 S in ex 9 05 16 20 1,2 160 80 10 70 10 -

17 S in ex 9 05 16 19 1,2 150 60 10 60 10-18 S in ex 9 05 16 14 1,2 110 70 10 60 Tr -

15 S in ex 9 05 32 17 1,2 90 20 Tr 60 Tr - 2 fa ces

7 S in ex 9 05 48 18 1,0 160 90 10 80 20 - 3 fa ces

21 E nerg ex 1 40 16 18 1,0 200 15 Tr 50 Tr -

19 E nerg ex 1 40 16 16 1,0 80 30 Tr 50 10 -

22 E nerg ex 1 40 16 20 1,2 60 10 Tr 30 Tr -23 E nerg ex 1 40 16 16 1,2 120 30 Tr 40 Tr -

24 E ne rg ex 1 40 16 14 1,2 100 10 Tr 30 Tr -

25 E ne rg ex 1 40 16 11 1,8 lOO 60 20 40 Tr -

26 E ne rg ex 1 40 16,8 8 1,0 80 20 Tr 30 Tr - S to ne b an ds

27 E nerg ex 1 40 16 20 1,0 20 Tr , 6 20 10 -

28 E nerg ex 1 40 32 18 1,0 lOO 60 10 40 Tr -20 E ne rg ex 1 40 32 17 1,0 210 180 50 80 20 - 2 face s

TA BLE III

MEASUREMENTSBY ORAGER TUBE OF FUME IN A BORD-AND-P ILLARCOLLIERY

.Mod. Ajax = Ajax without post waxing

Tr = Trace

T he channel effect occurs w hen a colum n of explosivecartridges of sm aller diam eter than the borehole is notpressed hom e to fill the cross-section of the hole. Thesp ace betw een th e ex plosive and the bo reh ole w all fo rm s

a channel in w hich an air shock is created during detona-tion. The air shock runs ahead of the detonation in thecharge, pre-com pressing the explosive and altering its

mod e o f d eto na tio n. R esu lts o f c ha nn el-e ffe ct te sts u sin gthe double-pipe technique are shown in Figs. 3 to 6.A ll the perm itted explosives tested suffer from the

c han nel effect. T he pea k b oreh ole p re ssu re (as m easu redby the depth of dent) declines along the length of the

charge as the precursor air shock becom es established.

N ot surprisingly, the m agnitude of the channel effect iserratic, but the phenomenon is none the less real. Thedent profiles of Figs. 7 and 8 show that consolidation ofthe test charge in the pipe elim inates the channel effect.

(E ven relatively m ild consolidation of cartridges, so asto buckle rather than squash them , has been found toe ffe ctiv ely e lim in ate th e c ha nn el e ffe ct.)

JOURNA L O F THE SOU TH A FR IC AN IN ST ITU TE O F M IN ING AND MET ALLURGY OCTOBER 1986 419



Slide

Anvil

ClampRubber-lined base

F ig . 2 - T orpe do-friction a ppa ra tu s use d In te stin g th e frictionsens it iv it y o f explos ives

III(I)

Top Primed + S~.mmin9 one end

'" :::.::.:.:::;

2111ON...:z11 1

0" ,u."0

:I:

till111"0

'"

111111

Fig. 3- The results of channel-effect tests on Coalex 32 x 200w ith top prim ing and stem ming one end

IIITop Ini~iohon + S~ in9 bo~h ende

III ;:>:;:~~, .:,';:.:-;,,~.:

2111i5N...:z11 1

0" ,u. "0

:I:

till111"0

'"

1111114 1 1 1 1 1 1 6111111 BIIIIII 1111111111 12111111 14111111

D IST"N CE "L ON G PIPE (MM)

Fig. 4- T he results of channel-effect tests on Coalex 32 x 200w ith top initiation and stemming both ends

'"I)

"'

'> :

~re...n.

~"'...-:z~111'"n. -a:

"'

'"I!J 41!J1!J 61!J1!J BI!JI!J 11!J1!J1!J 121!J1!J 141!J1!J 161!J1!J 181!J1!J 21!J1!J1!J

DIST"NCE " L O N G PIPE (MM)

21!J1!J

Fig. 5- The results of channel-effect tests on A/ax 29 x 200

15 1(I)

. . E NE RG EX 1 51 11 U n~ om ped

t~:I:N...11 ;

cU I

..."ff i0111151n."a:

'"

8 688 B8111 1 1 1 1 8 1 1 1 128111 14111111 16ft 1BIIIIII 211188

DIST"NCE "LONG PIPE (MM)

2111111 48111

Fig. 6- The results of channel-effect tests on Energex 15032 x 200

42 0 O CTO BER 1986 JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY



15 1III

I!J

* *5B Cooldu." pook.". b."..." .ooh oo,,",.1dg.

C."",.. 1"1"101:.10" + SI: 1"g bol:.h ."d.

~

~151<vN~Z

!,Ijl/]

u."0

::t:

1;:151

Ill"C

I/]

I5IB2BB 4BB 61i1B 8BB llilBB 12BB 14BB 16BB leBB 2BIiIB

DISTANCEALDNGPIPE (MM)

Fig. 10-Effects of coal-dust gaps on Coalex 32 x 200

15 1III

I/]N

. . AJAX 29 .. 21 i11 i !g 25 .. Coaldu ... pook... .

* *AJAX 29 .. 21 i11 i! g75 .. . Caaldu .. . pook .. ..

2~151::t:N~

"-IIcl/]

~"ZIIIC

111151

~"

"-

Fig. 11-Effects of coal-dust gaps on Ajax 29 x 200

III

I!J . .ENERGEX1~ wl...h 7s.. oooldun pookn.

. . ENERGEXSI1 w Hh SILo. o ooldun pookn.- . l.dp, .I .. .d

!E!R )

~I!I."

~"II!~a:

."

. 2IiIIi! 4ft I5U 8Ii!II 111. 12l1li 141i!1I 16. 18111i121i11111

DISTANCE A LD NG P IP EC MM )

Fig. 12-Effects of coal-dust gaps on Energex 15032 x 200

42 2 OCTOBER 1 98 6 JO URNA L O F T HE SOU TH A FR IC AN IN ST ITU TE O F M IN IN G AND MET ALLU RGY

TABLE IV

CRIT ICAL S IZE OF COAL-DUSTGAPS

Explosive

Size of gap

mm

Ajax

Coalex

E nerge x 1 50

> 7550 to 75

> 75

Per fo rmance Paramet ersB lasting in bo rd -an d-pillar m ining is a sse sse d largely

in term s o f adv ance p er ro und , b ut fragm en tation is ofte nimportant as well. For explosives to 'pull the round

drilled', the coal m ust be fractured and then rem ovedfrom the face for easy loading. The authors regard thee ffe ctiv e fie ld p erfo rman ce in de x o f p erm itte d e xp lo siv esas a com bination of a fragm entation index and a heaveindex. Good fragm entation w ithout adequate heave ordisplacem ent of the broken coal is not m uch use, and vice

versa.

N o single laboratory param eter of explosive perfor-man ce a de qu ate ly re fle cts th is re qu irement. T he mea su re sof perform ance that are applied in the A EC I laboratoryand their m eaning are sum marized in Table V , and fiveperm itted explosives are rated in Table VI. The data inthis table illustrate the com plexity of the situation: theranking of the explosives depends on w hich test is used.

One method of using the available data is in some wayto combin e the vario us param eters o f perfo rm ance y ield-

ed by th e d iffe ren t te sts to giv e an empirical field p erfor-m ance index (FPI) that conform s to practical blastingexperience.

T he d erivatio n o f reliab le empirical m eth od s of rating

the blasting potential of perm itted and other explosivesis a challenge for the future. In addition, AECI and as-so cia te d la bo ra to rie s a re work in g o n way s o f c alc ula tin gth e en ergy de liv ered from non -ide al, sm all-diam eter ex -plosives.

ConclusionsT he testin g proce dures discussed represen t a compre-

he nsiv e set of te chn iqu es aim ed at op tim izin g th e p erfor-m ance of perm itted explosives in term s of safety, quali-ty of detonation, and blasting potential. They are used

in the AEC I laboratory m ore or less routinely in the for-

m ulation of guidelines and in the derivation of recom -mend ation s for the best m etho ds o f use of the exp lo sives.T his ap proach is empirical a nd p rac tica l, b ut g iv es u se fu lin sig ht in to h ow p erm itte d e xp lo siv es b eh av e in fie ld u se ,

and w hich features of these explosives are im portant incon tr olli ng t he ir p er fo rmance.

Am ong the tests applied to perm itted explosives, thegallery test has been extremely valuable in ensuring a

rang e o f e xplosives w ith a v ery go od safety record in fiery

m ines. The double-pipe test is a m ore recent introduc-tion , bu t it h as g iv en valuab le dep th to o ur u nd erstand in gof the complex m an ner of ex plosive be hav io ur un der real-ist ic condi tions .

Further application of the tests described should leadto continued im provem ents in the safety and efficiencyof perm itted explosives in South A frica.



Ballistic Maximum*

Calculated Bubble mortar dent

ASV energy value depth

Explosive MJ/kg MJ/kg 0"/0BG t mm

Ajax 3,11 1,90 59 8

Coalex I 3,34 1,98 66 6

Sinex 905 3,32 1,96 66 15

E ne rg ex 1 40 2,75 1,92 58 15

E ne rg ex 1 50 3,37 1,98 73 15

TABLE V

MEASURESOF PERFORMANCE OF EXPLOSIVES

Performance

measure Property of explosive reflected Gen er al r ele va nc e to b la sti ng

Ab so lu te s tr engt h

v alu e (ASV)

T he A SV indicates the idea1ized potential of the explosive,

all else being equal. In practice, many different factors

intrude, particularly non-ideal quality of detonation of

explosives, so that A SV is not a useful measure of blasting

performance

Indicates broadly the fragm entation ability of the explo-

sive. The peak pressure gives no indication of how well

fractured material will be displaced or heaved

Theoretical (calculated) maximum amount of energy an

explosive can deliver to its surroundings

Maxim um dent depth,

d oubl e- pi pe t es t

Effective peak borehole pressure

Und erwate r b ub bleenergy

The timescale of energy release in the under-water test

is sim ilar to that of the early (fragmentation) stage in

blasting. T his param eter show s w hether potential energy,

shown by the ASV, can be released quickly enough in

practice

G ives no indication of peak pressures. This param eter cor-

relates most closely w ith the heave potential of the ex-

plosives

Residual energy in explosion product gases after the ex-

plosive has created and released a shock w ave in the w ater

Ballistic mortar energy Amount of energy the explosion product gases can deliver

to a projectile in the Iow-pressure regime

TABLE VI

PERFORMANCE PARAMETERS OF PERMITTED EXPLOSIVES

*See Fig. 13

t BG = B la stin g g ela tin

15 1I)

InN

. . SINEX 91115

+ + ENERGEX 15111. COAL-EX

e .. AJAXop 1 "1 \1 0\ 1. ., ,

111 2111111 4111111 el1ll1l

D IS TANC E ALONG P IP E(MM )

eBI1I

F ig. 13-P eak borehole pressures w hen all the charges are fullyc ou ple d b y tampin g (th e w itn es s p ip es u se d In t he se d ou ble -p ip etests w ere thicker and stronger than those used In all the other

tests reported In this paper)

Acknowledgements

The authors thank the m anagement of AECI Explo-sives & Chem ica ls L im ited for p erm issio n to p ub lish th isw ork, the M anagem ent and Ventilation D epartm ent ofG reenside C olliery for assistance w ith the fum e experi-ments, and colleagues M r N.W . Munro and Mr A.B.Ma rtin fo r th eir c on trib utio ns.

References

I. GALADZHII, F.M . Causes of deflagration of perm itted explosives

and measures to reduce its hazard in shot firing operations. 11th

International Meeting of D irectors of Safety in Mines Research,

W arsaw , 1963.

2. TAMCHYNA, V ., and MOSTAK, P. A method for determ ining the

deflagration behaviour of explosives. P ro pe lla nts a nd E xp lo siv es ,

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3. U .S. BUREAU OF MINES. A large chamber test for the laboratory

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8. LowNDs, c.M ., and Du PLESSIS, M .P. The double pipe test for

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Institutes, France, 1963.

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JOURNA L O F THE SOU TH A FR IC AN IN ST IT UTE O F M IN ING AND META LL URGY OCTOBER 1 98 6 42 3

c.m. lownds and b.w. wallace- the performance testing of permitted explosives for coal mines

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