Shielding of Facilities for Work with Explosive Materials - ACS

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Toxic Chemical and Explosives Facilities Downloaded from pubs.acs.org by UNIV OF MICHIGAN ANN ARBOR on 11/07/17. For personal use only.

Shielding of Facilities for Work with Explosive Materials D A V I D J.

KATSANIS

Chemical Systems Laboratory, Aberdeen Proving Ground, M D

21010

A r e l a t i v e l y new concept c a l l e d suppressive s h i e l d s i s o f f e r e d to provide p r o t e c t i o n to the area surrounding hazardous work with pyrotechnic and e x p l o s i v e m a t e r i a l . At present, these operations are e i t h e r l i m i t e d to small q u a n t i t i e s , widely d i s persed, or segregated by b a r r i c a d e s . Suppressive s h i e l d s provide an a l t e r n a t i v e i n the form of a vented s t e e l enclosure. Figure 1 illustrates the concept of a suppressive s h i e l d . The enclosure u s u a l l y c o n s i s t s of a s t r u c t u r a l s t e e l framework with b u i l t - u p panels of s t e e l angles, I-beams, p e r f o r a t e d p l a t e , or louvered panel. The space between panel components allows gaseous products of combustion to pass through while suppressing flame and, i n case of a detonation, reducing b l a s t overpressure to a safe l e v e l . There i s no d i r e c t path through the panel f o r fragments to escape. All fragmentation e f f e c t s are confined w i t h i n the enclosure. The s h i e l d s can be any s i z e . They can be small t r a n s p o r t able l a b o r a t o r y s h i e l d s or l a r g e s t r u c t u r e s i n a b u i l d i n g s i m i l a r to the concrete b a r r i c a d e s sometimes used ( 1 ) . T y p i c a l r e i n f o r c e d concrete b a r r i c a d e s are shown i n Figure 2. The b a r r i c a d e s are designed as c u b i c l e s with three w a l l s to withstand d i r e c t b l a s t pressure and to prevent propagation of a detonation from one area to the next [2). They do not prevent hazardous run-up r e a c t i o n s where a fire can s t a r t i n one c u b i c l e and through pyrotechnic dust i n the air or accumulation on equipment, spread from one c u b i c l e to another until the e n t i r e facility i s i n flames. In the event a detonation occurs, the c u b i c l e s do not prevent wide d i s p e r s a l of damaging primary and secondary fragments, nor do they prevent b l a s t overpressure leakage beyond the open edges. The b l a s t overpressure from the open edges of the c u b i c l e can spread over the outside of the b u i l d i n g w a l l and sometimes i s large enough to c o l l a p s e the frame f r o n t w a l l and r o o f or the masonary end and back w a l l . A s p e c i a l r e i n f o r c e d b u i l d i n g design can prevent t h i s , but adds c o n s i d e r a b l y to b u i l d i n g c o s t s . Since suppressive s h i e l d s are full enclosures, they perform This chapter not subject to U.S. copyright. Published 1979 American Chemical Society


36 TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

Figure 2.

Typical concrete cubicles


2.

KATSANIS

Work with Explosive

Material

37

i n a d i f f e r e n t way from these c u b i c l e s . Suppressive s h i e l d s w i l l : - Confine a l l fragments from a detonation. - Attenuate b l a s t pressure to a safe l e v e l i n a l l directions. - Reduce f i r e b a l l diameter s u f f i c i e n t l y to prevent spreading of the f i r e beyond the l o c a l area. Another p a r t i c u l a r l y a t t r a c t i v e feature of suppressive s h i e l d s i s that they are modular i n design f o r quick e r e c t i o n and m o d i f i c a t i o n to provide maximum p r o t e c t i o n and f l e x i b i l i t y . Several general c l a s s e s of s h i e l d designs have been conceived. As shown i n Figure 3, some have c y l i n d r i c a l or s p h e r i c a l c o n f i g u r a t i o n while others are rectangular frame and panel designs. Generally the c o n f i g u r a t i o n i s governed by the dominant hazard, i . e . , b l a s t , fragment, or flame. I f b l a s t pressures are the f a c t o r s which are most important i n design of the s t r u c t u r e , the s h i e l d w i l l u s u a l l y have a c y l i n d r i c a l or s p h e r i c a l shape. The rectangular frame and panel s t r u c t u r e s are t y p i c a l l y used where the dominant hazard i s flame. In t h i s paper, the Group 6 and the Group 5 S h i e l d w i l l be discussed to i l l u s t r a t e d e t a i l s of two t y p i c a l a p p l i c a t i o n s . The Group 6 S h i e l d i l l u s t r a t e s a unique s p h e r i c a l design which i s small and portable f o r use with l a b o r a t o r y q u a n t i t i e s of p r i mary e x p l o s i v e s . The Group 5 S h i e l d demonstrates the modular design concept that makes suppressive s h i e l d s an a t t r a c t i v e a l t e r n a t i v e to i n f l e x i b l e concrete b a r r i c a d e s . Discussion

of Group 6 and Group 5 S h i e l d Designs

Group 6 S h i e l d . The Group 6 S h i e l d i s s p h e r i c a l . The requirement f o r t h i s s h i e l d i s that an operator be capable of t r a n s p o r t i n g on a push c a r t small q u a n t i t i e s of extremely hazardous primary explosive m a t e r i a l . I t i s not f e a s i b l e to vent t h i s s h i e l d because of the hazardous m a t e r i a l involved and the close proximity of the operator. The two foot diameter s p h e r i c a l s t e e l s h e l l shown i n Figure M- i s l A inch t h i c k and weighs about 165 pounds. A rectangular t r a y i s used i n s i d e the s h i e l d to carry 10 cups of primary explosive material. Each cup contains 70 grams of lead azide i n a t y p i c a l a p p l i c a t i o n . T o t a l weight of explosive i s l i m i t e d to 700 grams lead azide or equivalent (1, 3). One i n t e r e s t i n g use of t h i s s h i e l d w i l l be i l l u s t r a t e d . Although i t i s not a l a b o r a t o r y a p p l i c a t i o n , i t i s i n t e r e s t i n g because i t shows how q u a n t i t i e s of i n i t i a t i n g or primary exp l o s i v e s can be handled i n detonator production without exposing operating personnel to explosive hazards. Use of the s h i e l d and c a r t shown i n Figure 5 w i l l r e s u l t i n about 3 m i l l i o n d o l l a r s savings i n modernization of- the detonator production l i n e at Iowa Army Ammunition Plant. C o s t l y automated


TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

GROUP 5

Figure 3.

General configuration of suppressive shield groups

Figure 4.

Group 6 suppressive shield

KATSANIS

Work

with

Explosive

Material

DESIGN FEATURES •

VERY HIGH PRESSURE APPLICATIONS

•

MINIMAL FRAGMENT THREAT

•

PERSONNEL CLOSE BY

•

CART TO TRANSPORT PRIMER MIX FROM PROCESS BUILDING TO DETONATOR ASSEMBLY BUILDING (DETONATOR BACKLINE - IOWA AAP)


(500 - 2000 PSI)

TYPICAL

APPLICATION

Figure 5.

Group 6 suppressive shield cart


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TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

conveyors are replaced by a manual system which makes use of the Group 6 Suppressive S h i e l d mounted on a c a r t as shown. The r i n g at the f r o n t mates with an opening i n a storage b a r r i c a d e . A f i x t u r e f o r mechanical f u n c t i o n t e s t i n g i s photographed i n Figure 6 . I t i l l u s t r a t e s the attachment of the s h i e l d to the b a r r i c a d e . The operator r o l l s the c a r t up to the b a r r i c a d e where a clamp i s c l o s e d and the s h i e l d i s locked to the b a r r i c a d e . Transport mechanisms shown behind the b a r r i c a d e remove the t r a y with e x p l o s i v e m a t e r i a l from the s h i e l d . At no time i s the operator exposed to e x p l o s i v e hazards. A s e r i e s of t e s t s were conducted to v e r i f y the adequacy of the design. Figure 7 i s a photograph of the set up f o r proof t e s t of the system. The Group 6 t e s t s h i e l d i s supported by a wooden frame and i s attached to the storage b a r r i c a d e i n the middle of the photograph. Summary data from proof t e s t s , tabulated i n Table I, show that the Group 6 S h i e l d and the storage b a r r i c a d e s are adequately designed. The system contained a l l e f f e c t s from b l a s t of s e r v i c e charge with a sound l e v e l of lk6 db outside the s h i e l d . One hundred f o r t y - s i x d e c i b l e s i s roughly the noise l e v e l from f i r i n g a s e r v i c e r i f l e such as the M - l 6 r i f l e . Ear p r o t e c t i o n i s d e s i r able but a s i n g l e exposure w i l l often produce no ear damage. This i n d i c a t e s a safe environment f o r the operator. A charge weight of 307 grams C-4- [31% above the design s e r v i c e charge) was r e q u i r e d to rupture the s h i e l d . The proof charge which i s 25% above s e r v i c e charge caused a bulge i n the bottom of the s h i e l d but no rupture. Group 5 S h i e l d . The Group 5 Suppressive S h i e l d i s designed f o r use with pyrotechnic m a t e r i a l ( 4 ) . Although the example discussed here i s a l a r g e f i x t u r e , these s h i e l d s can be s c a l e d down i n s i z e f o r l a b o r a t o r y use or modified to meet s p e c i a l requirements. One of the features that adds to suppressive s h i e l d u t i l i t y i s the modular design i l l u s t r a t e d i n F i g u r e 8 . The panels f o r the Group 5 S h i e l d are l a i d out by the foundation ready f o r assembly. Each panel i s about 9 f e e t long and 5 f e e t wide. When erected they form a cube about 1 0 f e e t long on each side and about 9 f e e t h i g h . As i l l u s t r a t e d by the Group 5 panel s e c t i o n shown i n Figure 9 , each panel i s a composite s t r u c t u r e with a double row of i n t e r l o c k i n g s t r u c t u r a l s t e e l angle beams arranged as shown i n the photograph. There are three p e r f o r a t e d p l a t e s , one on the i n s i d e and two on the outside. Wire screening was added between the panel l a y e r s f o r a d d i t i o n a l flame suppression, but i t proved i n e f f e c t i v e . Tests demonstrated that there was s u f f i c i e n t exposed metal surface to suppress flames e f f e c t i v e l y without the a d d i t i o n of metal screens. The photograph i n Figure 1 0 shows the panels being moved


KATSANIS Work with Explosive

Figure 6.

Figure 7.

Material

Mechanical function test fixture

Proof test fixture

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Shielding of Facilities for Work with Explosive Materials - ACS

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