Fift h E FEE World Co nference o n Explos iv es and B last ing (Bu dap est C onf er ence Pr oceedings 2 009, P. Mos er et a l, © 200 9 Eur op ea n F eder ation o f Explos ives E ngineer s, UK, ISBN 978- 0-9550 290-2-8 )

Blasting demolition of structures in power plants and urban areas: guidelines for a proper risks analysis S. Scaini Dexplo S.r.l., Parma, Italy ABST RACT : T he ana lys is of mor e t han 100 blasting demolit ion yar ds accomp lis hed since 1994, statistically conf ir ms t hat the ma in Saf et y pr ob lem p er ceived fr om T echnica l sup er vis or s and P er sons in char ge is du e t o the pr es ence its elf of H igh exp los ives on the field. T his wr ong way t o evaluat e t he r eal Saf et y pr ob lems in situat ions like b lasting demolit ions of str uctur es in act ive p ower p lants or in thickly built -up ur ban ar eas, is oft en b ecaus e of a wide t echnical u npr epar edness of p eop le delegat ed t o ma nage a nd contr ol our activities on the f ield. T his is why it ’s ver y imp or tant , for the gr owt h of all pr of ess iona ls, to f ocus our attent ion on t he r eal r is ks involved, t o tr ace help fu l gu idelines f or a cor r ect assess ment a nd analys is of r is ks; t he a war eness and knowledge of diff er ent or der s of r is ks, the ef f ective appr oaches f or their mit igation a nd the ma in f eatur es of mat er ia ls and H igh exp los ives, might to b e inclu ded in t he t echnica l cu ltur e of thos e pr of ess ionals delegat ed t o pla n and ma na ge Saf et y pr ob lems. As t he ma in output of t heir activit y is t he calculat ion of S af et y dista nces f or p eop le and s ensit ive str uctur es a nd pla nts, the only ma nner t o evaluat e t hem eff ect ively is t o assess and analyze r is ks a nd pr ocedur es in a pr op er wa y. 1) RISKS AN AL YS IS OF BL AST ING DEMOLI T ION OF ST RUCT URES T he activit ies of blasting demolit ion ins ide of industr ia l wor king s it es, active p ower pla nts (Figur e 1) and cr owded ur ban ar eas (Figur es 2, 4 and 5), hide a lot of cr it ical aspects not dir ect ly connect ed t o the pr es ence its elf of H igh exp los ives on t he field, as p er ceived b y t he most, but dep ending pr incip ally on t he scener y’s char acter ist ics (f or exa mp le, in cas e of u nder wat er blasting in tanks, docks and da ms or blasting us ing r op es and climb ing t echniqu es in chimn eys, boiler s and fur naces ) and on t he var ious ef f ects caus ed by t he b last (such as dust, f lying fr agments, vibr ations a nd air -b last). Figur e 1. Decommiss ioning in a ct ive p ower p lant. Figur e 2. Demolit ion of bu ilding in ur ban ar ea . For a cor r ect ass ess ment and a pr op er analysis of Saf et y pr ob lems, it ’s basic t o def ine f our diff er ent cat egor ies of r is ks : dir ect, indir ect, induced a nd connect ed r is ks. 1.1 Dir ect r is ks T his cat egor y is r elat ed to t he ha ndling of H igh exp los ives b y author ized p er s onnel on the field, that is t o say to t he dir ect int er act ion b et ween wor ker s and H igh ex plosives.

As a matt er of fact, the int er act ion b y inhalat ion and t ou ch, esp ecia lly dur ing indoor op er ations, is the caus e of a lot of r ever s ib le sympt oms as wea kness, str ong hea dache a nd sickness; as r ever s ib le s igns they ca n b e ef f ectively pr event ed or mit igat ed b y wear ing pr op er light Saf et y mas ks and nitr ile S af et y gloves. 1.2 I ndir ect r is ks T hey ar e clos ely r elat ed t o the char acter ist ics of t he scenar io in which we us e H igh exp los ives; f or exa mp le, in cas es like u nder wat er blasting in tanks, da ms (Figur e 3) and docks or blast ing op er ations us ing r op es and climb ing t echniqu es on chimn eys and ins ide boiler s and b last-fur naces. T his cat egor y of r is ks, not r elat ed to t he us e its elf of H igh exp los ives, ca n b e eff ect ively mit igated b y t he us e of sp ecif ic equip ments and pr op er t echniqu es of int er vent ion. Figur e 3. Under wat er blasting in da m. 1.3 I nduced r is ks T he induced r is ks ar e clos ely r elat ed to t he eff ects of the det onat ion of H igh exp los ives ; cons equ ent ly, they ar e str ict ly dep ending on the f eatur es a nd condit ions of mat er ials (concr et e, br ic k, ir on, pig, slack), as well as on t he f eatur es of t he H igh exp los ives us ed. Exclu ding cir cu mstances caus ed b y inex p er tness and inatt ent ion, b ecaus e of the highly skilled t echnicia ns involved on t he f ield, as well as events r elat ed to t er r or is m a nd sabotage acts, the induced par t of r is ks in su ch blasting demolit ions comes out fr om t he over - output of p henomena like:   

r ising of dust ( incidenta l obstr uct ion of su ction and abs or bing f ilt er s); flying fr agments ( incidental hea vy injur y/ da ma ge t o p eop le and pr op er t ies ) ; air -blast ( incidental br eaka ge of glass es and diap hr agms );

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vibr ations ( incidental da ma ges t o wea k str uctur es, pla nts and pr ecis ion equ ip ments).

1.4 Connect ed r is ks T his class r ef er s to pr ob lems connect ed t o a failur e of t he b lasting demolit ion pr ocess. T hes e r is ks, like t he indir ect ones, ar e not r elated t o the us e its elf of H igh ex plos ives, but imp ly a wide r ange of Saf et y pr ob lems (Figur e 6) t o assess a nd evaluat e ver y car efu lly like, f or exa mp le:  

da nger of su dden collaps e of t he bu ilding; incidental r ecover y of High exp los ives a nd det onat or s in t he r ubble t o cr ush wit h exca vator s or mob ile cr usher s.

Figur e 4. School bu ilding in t hickly p opu lat ed ar ea. Figur e 5. Blast ing demolit ion of school bu ild ing in thickly popu lated ar ea.

Figur e 6. Demolit ion failur e: da nger f or the demolit ion cr ew. 2) PASSI VE/ ACT I VE MIT IG AT ION APPRO ACHES Focus ing on t he cat egor y of induced r is ks, we ha ve t wo dif f er ent kinds of appr oach available t o mit igat e an incidenta l over - outp ut of t he b lasting eff ects : t he passive pr ot ect ion appr oach a nd the act ive one. 2.1 Passive pr ot ect ion appr oach As passive pr ot ect ion appr oach, we mea n t he whole Saf et y pr ocedur es we ca n pr epar e t o mit igate a n over - output of t he b lasting eff ect s soon aft er war ds the det onation of H igh exp los ives in the blast ing demolit ion pr ocess . It is p oss ib le t o car r y int o ef f ect pr actices like, f or exa mp le:  

to us e wat er f og nozzles; to wr ap pilla r s wit h st eel mes h a nd t ext ile (F igur e 7);

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to cr eat e pr ot ect ive ba nks wit h activit ies of gr ou nd exca vation (Figur e 8); to st op pr odu ction cycles; to evacuat e neighb our s.

It’s ob vious ly tr ue t hat all t hes e Saf et y pr ocedur es will incr eas e decidedly t he gener a l Safet y level of the pr ocess, but it’s not the r ight wa y to pur su e our pur pos e! Figur e 7. Wr apping of concr et e p illar s with s teel mes h and t ext ile. Figur e 8. Cr eation of pr ot ect ive ba nks. T he aim we all must attain is t o accomp lis h b lasting demolit ions in s ens it ive cont exts wit hout us ing passive pr ot ect ion pr ocedur es or , at least, r educing t hem as mu ch as poss ib le, ans wer ing f or top levels of Saf et y b y t he car efu l exa mina t ion of t he pr oject phas e of t he b lasting demolit ion pr ocess. 2.2 Act ive pr ot ection appr oach T he active pr ot ect ion appr oach is t he r ight way we all might f ollow t o guar ant ee t op Safet y levels, thr ou gh t he deep knowledg e of the char act er ist ics of ma t er ials b y stu dies and t ests on-s it e and off-s it e a nd t he knowled ge of the ma in f eatur es of the H igh exp los ives ava ilable on t he mar ket . T o accomp lis h an eff ect ive mit igation of bot h induced and connect ed r is ks , it ’s poss ib le to exa mine car efu lly t he ma in char act er ist ics of t he mat er ials ob jects of t he act ion of High exp losives b y using pr act ices like:  

geo-r adar techniqu es t o invest igat e the quant it y and qualit y of concr et e a nd its r einf or cements (F igur es 9 and 10); test b lasts to t est the har dness and t he matt er typ e of str uctur al st eelwor k and r einf or ced concr et e;

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on-sit e schler omet er t ests (F igur e 11) t o study t he scr atch har dness of concr et e and on-s it e u ltr asonic t ests (F igur e 12) t o investigat e t he degr a dation level of mat er ials;

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analys is of air -b last/acoust ic exp ect ed va lu es using soft war e t ools (F igur e 13).

Figur e 9. On-s it e a nalys is us ing geo-r adar techniqu es. Figur e 10. Outputs of t he geo-r adar analysis. Figur e 11. Schler omet er f or on-s it e t ests. Figur e 12. Equ ip ment f or ultr asonic on-s it e t ests. Figur e 13. Analys is of air -blast/acoust ic exp ect ed va lu es. T he addit ional st ep t o t he exa minat ion of t he ma in char acter ist ics of mat er ials , t o comp let e an eff ect ive wa y t o mit igat e t he induced par t of r is ks, is t he st u dy of t he ma in f eatur es of H igh exp los ives; t hos e f eatur es t hat state their eff ect iveness and, r elating t o the mat er ia ls, their ef ficiency. 3) EFFECT IVENESS OF HIGH EXPLOSI VES T he p er f or ma nce p ot ent ial of H igh ex plosives cannot b e expr ess ed b y mea ns of a single char acter ist ic par amet er . It is det er mined b y:  the a mou nt of gas lib er at ed p er u nit weight, th e ener gy evolved in t he pr ocess;  the pr opagat ion r ate of t he ener get ic mat er ial. T he ma in par amet er s and t heir r esu lt ing pr op er t ies of H igh explosives, str aight “per f or ma nce indicator s” t hat inf lu ence ver y much t he output eff ects of b lasting, in connect ion to t he mat er ials sub ject of t he fr agmentat ion, ar e basica lly:   

D et onation velocit y; D et onation pr essur e; H eat of explosion;

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Br isa nce; Str engt h.

A nu mb er of convent ional t ests and calcu lation met hods ex ist f or det er mining t he compar ative p er f or ma nce of dif f er ent ex plosives ; the det er minat ions of t he det onat ion r ate and dens it y do not r equ ir e convent ions, since t hey ar e b ot h sp ecif ic p hys ical par amet er s. 3.1 Det onat ion velocit y T he det onation velocit y is the r at e of pr opa gation of a det onation in an ex plosive.

If the dens it y of t he exp los ive is as its maximu m va lu e, and if t he exp los ive is char ged int o colu mns which ar e cons ider ably wider t han the cr it ica l dia met er , the det onation velocit y is a char acter ist ic of each individual exp los ive a nd is not inf lu enced b y ext er nal factor s; it decr eas es wit h decr eas ing dens it y of packing in t he colu mn. 3.2 Det onat ion pr essur e T he det onation pr essur e in the wa ve fr ont is pr op or tiona l to t he pr oduct of t he densit y, the det onation r ate, and t he fu me velocit y or , since t he fu me velocit y is pr op or tional t o the det onation r ate, to t he s quar e of the det onati on r ate. For a given exp los ive, t he det onat ion velocit y r is es wit h incr eas ing dens it y; t he det onat ion pr essur e incr eas es ver y cons ider ably if t he initia l dens it y of t he exp los ive ca n b e r ais ed to its max imu m valu e (b y cast ing or pr essing) or if the dens it y of t he exp los ive is intr ins ica lly high (T NT , RDX, HMX). High dens ity of the exp los ive is imp or tant if high Br isance is needed, wher eas the blasting p er f or ma nce is less aff ect ed b y it. 3.3 Heat of exp losion T he heat of exp los ion of an exp los ive mat er ial is t he heat lib er at ed dur ing its exp los ive decomp os it ion. Its magnitu de dep ends on the t her mo - dyna mi c state of t he decomp os it ion pr odu cts; the data used in pr actica l calcu lations usually ha ve wat er ( which is a pr oduct of t he exp los ion) in the f or m of vap or as the r ef er ence comp ou nd. T he heat of exp los ion ma y b e b ot h theor et ica lly calcu lat ed and exp er imentally det er min ed: t he calcu lat ed va lu e is t he dif f er ence b et ween t he ener gies of f or mat ion of the exp los ive comp onents ( or of the exp los ive its elf if chemica lly homogen eous) a nd the ener gies of f or mat ion of t he exp los ion pr odu cts. 3.4 Br isance Br isa nce is t he destr uct ive fr agmentation ef f ect of a char ge on its immediat e vicinit y. T he r eleva nt par amet er s ar e the det onation r ate a nd the loa ding dens it y ( compact ness ) of the exp los ive, as well as the gas yield a nd t he heat of ex plosion. T he higher t he loa ding dens it y of t he exp los ive is ( molding or pr ess ing dens it y), t he higher its p er f or mance concentr ation is p er unit of volu me; als o, the fast er the r eact ion r ate is, the str onger the impact eff ect of t he det onat ion is. Mor eover , an incr eas e in dens it y is accompa nied b y an incr eas e in t he det onat ion r ate of the exp los ive, while t he s hock wa ve pr essur e in the det onation fr ont var ies wit h the squar e of the det onation r at e. T hus it’s ver y imp or tant t o ha ve t he loa ding dens it y as high as poss ib le. 3.5 Str enght If an exp los ives is t o b e det onat ed in a bor ehole, t he r eleva nt par amet er is its “str engt h”. H er e the cr it er ion of t he p er f or ma nce is not so much a hig h det onat ion r ate as a high gas yield a nd a high heat of exp los ion; if, on t he ot her hand, a str ong dis int egr ation eff ect in the near est vicinit y of t he det onat ion is r equ ir ed, the most imp or tant par amet er s ar e the det onat ion r ate and t he dens it y.

4) CONCLUS I ONS T o su m up all pr evious consider at ions , the r ight wa y f or a pr op er and ef f ect ive r is ks analys is in s ens itive activit ies like t he us e of High exp los ives f or blasting demolit ion in ur ban ar eas and active industr ial s it es, might pr oceed along t he f ollowing st eps : a. to ident if y t he str uctur es and p lants r eally t o b e pr ot ect ed; b. to char act er ize car efu lly the mat er ials ob ject s of t he act ion of H igh exp los ives by on-sit e t ests and stu dies; c. to b e a war e of t he ma in char act er ist ic f eatur es of t he H igh exp los ives t o b e us ed; d. to ca lcu lat e t heor et ica lly the exp ect ed a ir blas t/acoust ic valu es ; e. to exp ect, only if necessar y, to equ ip passive pr ot ect ions ma de of st eel mes h and text ile. T he ma in output of this way t o pr oceed might be t he r ight ca lcu lat ion of Saf et y dista nces and ar eas (Figur e 14), that is t o say imp or tant valu es that ar e ver y oft en wr ongly over estimat ed. Figur e 14. Cor r ect ( ???) ass ess ment of Saf et y distances and ar eas. REFERENCES Meyer R., Kӧhler J. & Homburg A. 2002. Explosives. Wiley-VCH (ed.): 42, 83-84, 90, 161, 300.