232...232 committee on dust explosion hazards de-1 repor~ of committee on dust ~:xplosion hazards c....

232 C O M M I T T E E ON D U S T E X P L O S I O N HAZARDS DE-1

Repor~ of Committee on Dust ~:xplosion Hazards

C. G. G i b s o n , Chairman, O n t a r i o D e p a r t m e n t o f L a b o u r . 8 Y o r k St . . T o r o n t o 1, .On t . , C a n a d a (rep.

C a n a d i a n Assn . of A d m i n i s t r a t o r s of L a b o u r L e g i s l a t i o n )

R. W. A n d r e w s , J r . , A m e r i c a n Soci- e t y of M e c h a n i c a l E n g i n e e r s .

D a v i d W . B i x b y , T h e S u l p h u r I n - s t i t u t e .

C. M. B lae s i , N F P A C o m m i t t e e o n B l o w e r S y s t e m s .

J . J . B u r k e , A m e r i c a n Societ3~ of H e a t i n g , R e f r i g e r a t i n g & Ai r Con- d i t i o n i n g E n g i n e e r s . Inc .

Dean M. C l a r k , G r a i n E l e v a t o r a n d P r o c e s s i n g S u p e r i n t e n d e n t s .

D. P . C o n g d o n , F a c t o r y I n s u r a n c e Assn .

R . E. D u f o u r , U n d e r w r i t e r s ' L a b o r a - to r i e s , Inc .

Douglas L . H a l l , Mi l l e r s ' N a t i o n a l F e d e r a t i o n .

S. F . H e n d e r s o n , N a t i o n a l E l e c t r i c a l . Manufacturers Assn.

J . A. H o u g h t o n ~ A m e r i c a n F o u n d r y - ~men ' s Soc ie ty .

David H. Hunt , T h e S p e n c e r T u r b i n e Co.

G u y I s e n b e ' r g , M a n t f f a c t u r i n g C h e m - i s t s ' Assn .

G e o r g e L . K i t c h e n t T e r m i n a l E l e v a t o r G r a i n M e r c h a n t s " Assn .

G. C. K o t h , F a c t o r y M u t u a l E n g i - n e e r i n g C o r p o r a t i o n .

J . R . M c C a n n , N a t i o n a l S a f e t y C o u n - " cil.

Reynar Meadoweroft, C ° r n I n d u s t r i e s F o u n d a t i o n .

Dr . E. G. M e l t e r . A m e r i c a n I n d u s - t r i a l H y g i e n e A s s n .

J o h n N a g y , U. S. Dept , o f t he In - t e r i o r .

Don O. Noel, " M e t a l P o w d e r P r o - d u c e r s A s s n . of t h e M e t a l POWder

• I n d u s t r i e s F e d e r a t i o n . J o h n P. O!Neil l ; U. S. D e p a r t m e n t of

L a b o r . T h o m a s A. Oraveez , I n t e r n a t i o n a l

Assn . of G o v e r n m e n t a l L a b o r Of- ficials.

J . A. P e l o u b e t , T h e D o w Meta l P r o d - u c t s Co.

]P rank E. R a d e m a c h e r , F a c t o r y In - s u r a n c e Assn . '

J . M. R o b i n s o n , A m e r i c a n I n s u r a n c e Assn .

W . A. R o e s s l e r , Assn . of Mill & Ele- v a t o r M u t u a l Ins . Cos.

A r t h u r C. Seh r l e r , N a t i o n a l Confec- t i o n e r s ' Assn. "

• T..T. Singer, Western Actuarial Bu- reau.

George H. Steel, American Society of Safety Engineers.

J. Karel Sundermeyer, Society of the Plastics Industry, Inc.

P a u l J . T u r n e r , G r e a t N o r t h e r n Ra i l - w a y .

H . L . W a l k e r , E d i s o n E l e c t r i c I n s t i - tu te .

James B. W a l k e r , J r . , A m e r i c a n B o i l e r Mfrs . Assn .

J . A. W o o d , N a t i o n a l A u t o m a t i c S p r i n k l e r & F i r e C o n t r o l Assn .

G. M. W o o d s , J r . , . K e m p e r I n s u r a n c e C o m p a n y .

A l t e r n a t e s . G. Walker Daubenspeck, U. S." De-

p a r t m e n t of L a b o r . ( A l t e r n a t e t o . J o h n P. O 'Ne i l l . )

J o h n F . H e n n e s s e y , N a t i o n a l Confec - t i o n e r s ' A s s n . ( A l t e r n a t e to A r t h u r C. S c h r i e r . )

J . M. J e n s e n , C o r n I n d u s t r i e s F o u n - d a t i o n . ( A l t e r n a t e to R e y n a r M e a d o w c r o f t . )

Frank Juno Mi l l e r s ' N a t i o n a l F e d e r a - t ion . ( A l t e r n a t e to D o u g l a s L. H a i l . )

H a r r y G. L a e e y , I n t e r n a t i o n a l Assn . of G o v e r n m e n t a l L a b o r Officials. ( A l t e r n a t e to T h o m a s A. Oravecz . )

Gordon A. Olson , E d i s o n E l e c t r i c I n - s t i t u t e . ( A l t e r n a t e to H. L. W a l k e r . )

G. D. P e r k i n s , A s s o c i a t i o n of Mil l & E l e v a t o r M u t u a l I n s u r a n c e Cos, ( A l t e r n a t e to W . A. R o e s s l e r . )

R . F . S c h w a b , F a c t o r y I n s u r a n c e Assn . ( A l t e r n a t e to D. P . C o n g d o n a n d F r a n k E. R a d e m a c h e r . )

L. S. Shook , W e s t e r n A c t u a r i a l Bu- r eau . ( A l t e r n a t e to T. T. S i n g e r . )

M a x S p e n c e r , G r a i n E l e v a t o r & P r o - c e s s i n g S u p e r i n t e n d e n t s . ( A l t e r n a t e to D e a n M. C l a r k . )

E. J . W i l l i a m s , A m e r i c a n Soc i e ty of H e a t i n g , R e f r i g e r a t i n g & Ai r Con- d i t i o n i n g E n g i n e e r s , Inc . (Al te r - n a t e to J . J . B u r k e . )

ScoPz: T h e p r e v e n t i o n of d u s t e x p l o s i o n s in "connec t ion w i t h p r o c e s s e s a n d i n d u s t r i e s p r o d u c i n g c o m b u s t i b l e o r exp los ive d u s t s , i n c l u d i n g m e a s u r e s for t h e p r e v e n t i o n of i g n i t i o n , r e s t r i c t i o n of p o t e n t i a l d a m a g e b y p r o p e r c o n s t r u c - t i on a n d a r r a n g e m e n t of b u i l d i n g s , r e s t r i c t i o n o f t he p r o d u c t i o n a n d escape of d u s t t h r o u g h t h e c o n t r o l of d u s t - p r o d u c i n g p r o c e s z e s a n d e q u i p m e n t , ex- t i n g u i s h i n g m e t h o d s , a n d r e l a t e d f e a t u r e s . F i r e p r e v e n t i o n a n d e x t i n g u i s h i n g a r e i n c l u d e d , s ince d u s t e x p l o s i o n s m a y r e s u l t f r o m fire.

DE-2 233

C O M M I T T E E ON D U S T E X P L O S I O N HAZARDS

S e c t i o n a l C o m m i t t e e o n G r a i n a n d F o o d

C. ~ Blaesi De~l M. Clark IL. ~ Dufour C. 6 Gibson (ex-officio)

las L. Hai l F. H e n n e s s e y ernate to Ar thu r C.

Sc ier) ,I. ,~ '" Jensen

~ ternate to Reyna r ~dowcroft)

F ~ ~k Jun .& ternate to Douglas L. Hail)

P r o c e s s i n g D u s t s

Thomas T. Singer, Chairman George L. Kitchen R . F . Schwab G. C. Koth (al ternate to F r a n k E.

Rademacher ) J. ~ . MeCann L, S. Shook Reynar Meadowcrof t (al ternate to T. T. E. G. Meiter Singer) G. D. P e r k i n s Max Spencer

(al ternate to W .A. (al ternate to Dean l ~ e s s l e r ) M. Clark)

Frank E. Rademacher George It[. Steel J. M. Rob inson Paul J. Turner W. A. Roessler J . A . W o o d Arthur C. Schrler " G.M. Woods, Jr .

S e c t i o n a l C o m m i t t e e o n M e t a l D u s t s

R. W. Andrews, Jr . , Chairman D F. Congdon G . C . Koth 'Thomas A. Oravecz G" Walker D a u b e n s p e c k ' H a r r y G. Lacey J . A . Pe loubet

'(alternate to John P. (al ternate to J . M . Kobinson o'Neill) Thomas A. Oravecz) It. F. Schwab

C G. Gibson (ex-offlcio) Don O. Noel (al ternate to D. P. J~ A. Houghton John P. O'Nei l l Congdon)

T h e r e p o r t o f t h e C o m m i t t e e o n D u s t E x p l o s i o n H a z a r d s is in

three p a r t s : . ,

Part I, prepared by the Sectional Committee on Grain and Food Processing Dusts, recommends Reconfirmation of the NFPA S t a n d a r d f o r t h e P r e v e n t i o n o f D u s t E x p l o s i o n s in . t h e P r o d u c t i o n , P a c k a g i n g a n d H a n d l i n g o f P u l v e r i i e d S u g a r a n d C o c o a ( N o . 6 2 -

1959).

Part I has been submitted to ballot 'o[ the Sectional Committee on Grain and Food Processing Dusts, which consists of 19 members, of whom all have voted a~rmatively.

Part I has also been submitted to ballot o[ the. Committee on Dust Explosion Hazards which consists o[ 35 members, o[~ whom 34 have voted a~rmatively. Mr.. Walker is recorded as "not voting." . " *

Part II, prepare d by" the Sectional Committee on Grain and Food Processing Dusts, recommends Reconfirmation of the NFPA Code for the Prevention of Dust Explosions in Confectionery Manu- facturing Plants (No. 657-1959).

Part I I has been submitted to ballot of the Sectional Committee on Grain and Food Processing Dusts, which consists o[ 19 members, of whom all have voted a~rmatively.

Part I I has also been submitted to ballot o[ the Committee on Oust Explosion Hazards which consists of 35 members, o[ whom

234 COMMITTEE ON D U S T EXPLOSION HAZARDS I ) ]~ .3

34 have voted affirmatively. Mr. Walker is recorded as "not voting."

Part III, prepared by the Sectional Committee on Metal Dust~ proposes adoption of extensive amendments of the Code for the

Prevention of Dust Explosions in the Manufacture of Aluminum Powder, NFPA No. 651-1963. Changes are proposed throughout, including a complete revision of Chapter 3, Conveying Powder; j complete revision of Chapter 10, Fire Fighting Methods; and addio tion of a new Chapter 9, Wet Milling of Aluminum Powder.

Part I I I has been submitted to ballot of the Sectional Committee on Metal Dusts, which consists o[.9 members, of.whom all have. t/oted affirmatively

J

Part H I has also been submitted to [~allot of the Committee on Dust Explosion Hazards, which consists of 35 members, of whom 34 have voted affirmatively. Mr. Clark is recorded as "not voting."

Part I • . L

The Committee recommendsRecont~rmafion*of the NFPA Stan. dard for the Prevention of Dust Explosions in the Production, Packaging'and Handling of Pulverized Sugar and Cocoa (No. 62- 1959) incompliance with Paragraph 91 of the NFPA Regulations Governing Technical Committees., No changes in technical content are proposed. If.favorable action is taken, a few. editorial changes' will be made in the text to up-date references. Copies of the 1959 edition of NFPA No. 62 are available from the Association.for any.' one interested in the contents. " :~ t

Part II . . . . , .

• The Committee recohamends Reconfirmation ofl the NFPA Code' for the Prevention of Dust Explosions in Confecfionery"M~inufac.

tur ing Plants '(No. 657-1959). in compliance withParagraph 91 oI the NFPA Regulations Governing Technical Committees. Ne! changes in. technical content are proposed.• If favorable action taken, a few editorial changes will'be made in the "t~xt to updat~ references. Copies of the 1959 edition of NFPA No.. 657 are avail. able from the Association for anyone interested in the contents.

C O N T E N T S 235

6 5 1 - 3

PaN. III

STANDARD, FOR THE PREVENTION OF DUST EXPLOSIONS IN THE

MANUFACTURE OF ALUMINUM POWDER

NFPA No. 6 5 1 - 1967

Contents

1. I n t r o d u c t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 651~- 4

2. L o c a t i o n a n d B u i l d i n g s o f A l u m i n u m P o w d e r - m a k i n g P l a n t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~ . . . . . . . . . . . . . . . . . . . . . . . . . . ~ . . . . . . . . . . . . . . . . 6 5 1 - 5

3. C o n v e y i n g Po~vder ' " 6 5 1 - 9

4. E l e c t r i c i t y f o r L i g h t a n d P o w e r .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , 6 5 1 - 1 2

5. C o n t r o l o f S t a t i c E l e c t r i c i t y , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . 651 ' -13

6. P r e v e n t i o n o f A c c u m u l a t i o n o f A l u m i n u m P o w d e r o r D u s t ...... .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~. .. . . . . . . . . 6 5 1 - 1 4

7. P r e v e n t i o n o f I g n i t i o n o f A l u m i n u m P o w d e r ... . . . . . . . . . 6 5 1 - 1 5

8. A l u m i n t ~ m l~ owde r S t o r a g e " • 651 -1 ,9

9. W e t M i l l i n g o f A l u m i n u m P o w d e r ... . . . . . . . . . . . ~..... . . . . . . . . . . . 6 5 1 - 1 9

10. F i r e F i g h t i n g M e t h o d s ' 651- :20

11. S a f e t y P r o v i s i o n s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5 1 - 2 3

236 651-4 ALUMINUM POWDER

CHAPTER 1. INTRODUCTION.

11. The objective of this s tandard is to reduce the hazards of ig. nition and explosions i n t h e manufacture of aluminum flake powder, or paste and atomized aluminum granular particles, and/ or the dust of any aluminum alloy "that is explosive in an environ. mental gas, as determined by test.

12. Where theStandard has reference to plant location or con- ',' struction, or the installation of radically'new types of equipment, the specifications are not retroactive in application.

13. All new installations should be under the supervision of engineers qualified by experience in the design, construction and operation of equipment for the purpose.

14. This Standard is not intended to apply to situations where waste dust is produced by operations such as grinding, buffing and polishing of aluminum castings. Prevention of fires and explosions in ir/dustries where aluminum arid aluminum alloys are subject to processing or finishing operations in which a fine metallic dust or , powder is liberated is covered in NFPA No. 65, C o d e for the Processing and Finishing of Aluminum.

15. Definitions. In this Standard th~ following words are' used as defined below:- . . . . . . . . "

SHALL is intended to: indicate requirements.. SHOULD is intended to indicate recommendations, or that which

is advised but not required. " APPROVED refers to approval by'the authority having jurisdiction

in the enforcement of standards.

LOCATION AND BUILDINGS 237

651-5

CHAPTER 2. L O C A T I O N A N D BUILDINGS OF ALUMINUM POWDER-MAKING PLANT.

21. Location of the Plant.

211. The plant should be located on a tract of land large enough so that the buildings in which the powder is manfactured shall be at least 300 feet distant from occupied structures such as public buildings, dwellings, stores or manufacturing establishments other than those whii;h are a part of the powder manufacturer's plant. The premises in which are located the powder-making buildings should be sun'ounded by high strong fencing with suitable entrance gates under charge of a guard to the property and should be well floodlighted at night for safety.

22. Location of Operations.

221. Different operations in the manufacture of aluminum powder should be located in separate buildings further subdivided into as many small units as practicable by substantial brick or reinforced concrete division walls without openings. Separate buildings (other than the small-units of a major process section) should preferably be separated by not less than 50 feet of space and in no case shall they be less than 2 5 feet apart, unless barricades, similar to those used in explosives manufacturing plants, are built between the buildings. Where two buildings are less than 50 feet apart, only one of those shall have windows or doors in the wall facing the other building

222. For new construction, in addition to designing to fulfill minimum statutory requirements, the insurance carrier involved or one of the major insurance engineering organizations should be consulted for counsel regarding specifc installations.

23. Electric or Steam Power Generators."

231. Electric or steam power generators shall be in a separate building or buildings which should be at least 100 feet from the dust-making building.

24. Building Construction.. ~-

241. All buildings used for the manufacture, packing or loading for shipment of aluminum powder shall conform, with the following requirements:


a. CHARACTER OF BUILDINGS: They shall, where practical, be I of one-story type, with no basements , and constructed of noncom. bustible materials throughout, and the buildings shall be designed so that every internal surface is readily accessible to facilitate cleaning. In all building walls of rooms where dust may be produced, which are not of monolithic construction, all masonry joints shall be thoroughly slushed with mortar and troweled smooth so as to leave no interior or exterior voids for the infiltration and accumulation of aluminum powder. Where elevated floors, plat- forms or balconies are required, as possibly for tanks or collector~ or for other process masons, the same. principles shall apply. Floor Covering and railings shall be of minimum sparking metal construction and all internal metal structures shall be adequatelygrounded. Suitable emergency exits shall be provided from all areas, including from balconies.

b. CONSTRUCTION WITH REFERENCE TO POSITION OF BUILD- INGS: Where two buildings are less than 50 feet apart, one of the facing walls shall be blast resistant - - either reinforced concrete or brick construction without openings (preferably reinforced concrete) ; the other facing wall may he of "daylight type" construction.

C. COMMUNICATIONS BETWEEN BUILDINGS: Buildings separated by not less than 50 feet of space (or small units of one major process section) may communicate ~hrough enclosed passageways of noncombustible construction, provided that such enclosed passageways from production or storage areas are specially designed for the release of internal pressures and all openings to such passageways are protected by self-closing fire doors approved for the protection of openings in fire division wails.' An exit door for escape from enclosed passageways to outdoors should be provided (see Section 241d following).

d. FRAMES oFDooRs AND WINDOWS should be Of metal; the doors shall be approved self-closing fire doors. There should be adequate window areas both for l ight add in case of an explosion to afford relief of pressure by. automatically opening; windows which may be opened should be hinged at the top, Open outward and, if fastened with catches, these should release on moderate pressure-from the inside. See the Guide for Explosion Venting, NFPA No. 68, for suggested vent ratios in specified room volumes. Each room should have at least two widely separated exits to corridors or to the outside. All exit doors to the outside for escape purposes shall be of the emergency type, opening outward wi th pressure .bar latch. See 5-216, Panic Hardware; of the Code fo~ Safety to Life from Fire in Buildings and Structures, NFPA No. 101.

LOCATION A N D B U I L D I N G S

239 651-7

e. FLOORS OF BUILDINGS: H a r d surfaced nonslip floors should be installed in a manner that avoids joints which might catch and collect dust.

The use of electrically conducting floor material is recommended although it is recognized that it is difficult to maintain conductance over a period of time using materials now available. Careful ex- amination of the details of t h i sS tanda rd will disclose the logic of the employment of conducting floor materials.

The surface of a conductive floor should provide a path of moderate electrical conductivi tybetween all persons and portable equipment making contact with the floor to prevent the accumulation of dangerous electrostatic charges. Fixed machinery and equipment shall be individually grounded as indicated in the ap- propriate paragraph of this Standard. .

The maximum resistance of the conductive floor should be less than 1,000,000 ohms~ as measured between two electrodes placed 3 feet apart at any points on the floor.,

The minimum resistance of the conductive floor should be more than 25,000 ohms, as measured between a ground, connection and an electrode placed at any location on the floor. This minimum resistance value' is recommended .tO provide protection for personnel against the hazard of electrical shocks.

Resistance values should be checked' at regular intervals. The following equipment and methods are recommended:

(1) Each electrode shall weigh 5 pounds and shall have a dry, flat, circular contact area 2I~ inches in diameter, which shall comprise a surface of aluminum foil 0.0005 to 0.001 inches' thick,. backed by a layer, of rubber .~ inch thick find measuring 40 to 60 durometer hardness as determined by a Shore Type A durometer or equivalent.*

(2) Resistance shall be measured with a suitably calibrated ohmmeter, which shall operate on a nominal open-circuit output voltage of 500 volts DC and a short circuit current of 2.5 to 10 milliamperes (showing units of resistance).

(3) Measurements** shall be made At five or more locations m each room and the results ayeraged.

(a) For compliance with maximum resistance the average shall be less than 1,000,000 ohms, and

*American Society for Testing Materials Tentative Method of Test for In- dentation of Rubber by Means of a Durometer, ASTM Designation D-676- 59T, obtainable from ASTM, 1916 Race St., Philadelphia, Pa. 19103.

**NOTE: If the resistance changes appreciably with time during a measurement, the value observed after the voltage has been applied for about five seconds shall be considered to be the measured value.

[ 651-8 ALUMINUM POWDER,

( b ) For compliance with minimum resistance no location shall have a resistance less than 10,000 ohms and the average of not less than five locations shall be greater than 25,000 ohms. Where resistance to ground is measured, two measure. ments shall be made at each location, with the test leads inter. changed at the .instrument between measurements, with the average to be taken as the resistance to ground at that loca. tion. All readings may be taken wit h the electrode or elec. trodes more than 3 feet from any ground connection or " grounded object resting on the floor.

In certain manufacturing areas any use of water must be avoided. Where it is possible to use water for washing down without danger of leaving damppowder in dust-catching joints and without danger of water lodging in equipment, this method of cleaning may be used. This method of cleaning shall be confined to floors, walls and structural elements that can be washed down comple te ly ' leaving n o powder residue and without water coming in contact with any powder processing equipment. In such areas the floor shall be pitched to water drains in the floor leading to an isolated area from which the collected' powder can be transferred to a safe disposal location. Sanitary or sewage disposal systems shall not be used for this purpose.

f. RooFs oF BUILDINGS in which there are dust-making operations shall be supported on girders so designed as to minimize the area of surfaces on which dust may collect. Where these surfaces are unavoidably present, and on other more or less horizontal places, such as wide girder flanges and window ledges, they shall be covered by a smooth, steeply sloping concrete or plaster filling having a minimum angle of 55 degrees with the horizontal. The roof coveriflg shall be as light as practicable, but fire resistant, and shall be so arranged that it will be easily blown off by an internal explosion. Any sheet metal used in the roof covering shall be well cemented to prevent leakage and be well painted with aluminum~ paint, or else shall be galvanized and well maintained to prevent: corrosion, which might cause leakage.

g. GROUNDING AND'LIGHTNING PROTECTION" All steel work should be well grounded to a suitable ground outside the building in accordance with the Lightning Protection Code, NFPA No. 78.~ Lightning rods should be provided for all boiler house stacks or chimneys and high points on buildings. The power lines should I be adequately protected against lightning. A lightn.ing arrestor system should be provided around or within the building area, of such a capacity as to fully protect all buildings in that area from lightning.

CONVEYING POWDER

C H A P T E R 3. C O N V E Y I N G POWDER.

31. Construction and Grounding of Dust-Making Machines.

311. All dust-making machines and conveyors shall be so constructed as to minimize the escape of dust into the rooms in which they are located. All parts of the machinery and conveyors shall be thoroughly bonded and grounded to minimize static discharges (see Chapter 5, Control of Static Electricity).

32. Conveying of Aluminum Powder.

321. MOVABLE CONTAINERS : Movable containers for transport- ing powder shall be constructed throughout of nonferrous, minimum sparking material or nonmagnetic, minimum sparking stainless steel. These containers shall be provided with wheels or casters with nonsparking conductive tires. If rails are used for placing containers, locking type swivel casters should be provided to eliminate heat of friction at the time container's motion is reversed. If the floor is a conducting material and it is desired to establish an electrical ground through the Wheels or casters, the wheels or casters may be made Of aluminum, b r o n z e or other minimum sparking conductive materials. To obtain positive grounding, it is necessary to provide positive bonding either through or around the lubricating film in ' t he bearings. When charging or discharging the container, the container shall be positively grounded by a conducting cable from the container to a suitable ground connection. When these containers have to be transported in the open, they shall be protected from the weather by minimum sparking metallic covers. Covers are also advisable for all storage conditions.

322. PNEUMATIC CONVEYING: Pneumatic conveying is a com- mon method of transferring the dust.from place to place in a building or to an adjacent building. Conveyor ducts shall be fabricated from nonferrous, minimum sparking, metal or nonmagnetic minimum sparking stainless steel. The ducts shall be electrically bonded and grounded.. Plastic or other nonconductive liners shall not he used. Preferably an inert gas should be used instead of air in such a system wherever the concentration of powder will possibly come within the explosive range. The inert gas should be a nitrogen type with an oxygen content of 3 per cent to 5 per cent. I t should contain no carbon monoxide and must have a dew point sufficiently low as to insure that n o free moisture can condense ou t and accumulate at any point in the system.


323. INERT ATMOSPHERE: Aluminum and aluminum alloy powders are produced by various mechanical means of particle size degradation. These processes, as well as certain finishing and trans- porting operations, have a tendency to expose a continuously in- creasing area of new metal surface. Aluminum, and in fact most metals, immediately experience a surface reaction with available atmospheric oxygen to form a protective oxide coating which then serves as an impervious layer to inhibit further oxidation. This reaction is exothermic, producing sensible heat. If a fine or thin lightweight particle having a large area of new surface is Suddenly exposed to the atmosphere, enough heat will be generated to raise its temperature to the ignition point. Completely inert gas should not be used as an envelope to promote operational safety or for transport of aluminum powder in a pneumatic or fluidized trans- fer device. This would be a very unsafe practice because some- where in the process of manufacture, packaging, or ultimate use the powder will eventually be exposed to the atmosphere where the unreacted surfaces will react suddenly with available oxygen to produce enough heat to cause either a fire or an explosion. To provide maximum safety, a means for the controlled oxidation of newly exposed surfaces sh.ould b e provided as soon as they are exposed. Tests conducted by the U. S. Bureau of Mines and others have disclosed that an inert gas as described in 'Section 322 is ,effective for this purpose., This mixture serves to control the rate of oxidation and at the same time provides an environment which materially reduces the fire and explosion hazard.

324. Am CONVEYING: If the conveying gas is air, the aluminum dust-air ratio throughout the conveying system shall be held below the minimum explosive concentration of aluminum as determined by the Bureau of Mines and reported in Bureau of Mines Report of Investigations 6516, "Explosibility of Metal Pow- ders." Although the aluminum dust-air suspension may be held below an explosive concentration in the conveying system, the suspension necessarily will pass through the explosive range in the collector at the end of the conveying system unless the dust is collected in a liquid - - such as a spray tower. Any such liquid shall

b e nonflammable, nonreactive with the aluminum dust or react at a controllable minimal rate and the liquid in the product should be compatible with subsequent processing requirements. In an air conveying system, any dry collector must be considered as an explosion hazard, containing a dust-air mixture in~ the explosive range, and should be constructed of nonferrous, nOnsparking material -or nonmagnetic, nonsparking stainless steel. The entire system and particularly the collector shall be thoroughly and completely bonded

C O N V E Y I N G P O W D E R

243 651-11

and grounded and the entire ground system Checked with an olmaeter to show less than 5 ohms (2 ohms, if possible) resistance (see Chapter 5, Control of Static Electricity). A high efficiency cyclone-type collector presents less hazard than a bag-type collector and except for extremely fine powders will. usually operate with acceptable dust losses. Unless such losses are prohibitive, the cyclone type collector should be used and, in this case, the exhaust fan shall discharge to atmosphere away from other operations. If a bag type collector is used, the shaking system or dust discharge system shall either be of the pneumatic type with no moving parts, o'r shall be of nonferrous, nonsparking components or nonmagfietic, nonsparking stainless steel and the bags shall be positively grounded to the baghouse framework (see grounding systems for bags in Chapter 5, Article 51). If bags are used, an alarm should be added to be actuated by a build-up in pressure across the bags, beyond prescribed limits. The collector, in all cases, shall be located at least 50 feet from any other building or operation, shall be isolated by rk fence or other barrier and persoflnel shall not be permitted within 50 feet of the collector during operation or shaking (see Chapter 2, Article 22). Blowout patches or explosion vents should be built into the system in accordance with recommendations in the Explosion Venting Guide, NFPA No. 68.

a. Where the conveying duct is exposed to weather or moisture, it shall be moisturetight, as any moisture entering the system can react with the aluminum, dust, generating heat and serving as a potential source of ignition. Sufficient velocity 5,500 feet per minute minimum) shall be provided throughout the conveying system to prevent accumulation of dust at any point and to pick up any powder that might drop out during an unscheduled system stoppage. If the conveying gas is inducted into the system in a relatively warm environment and the~.duct work and collectors then are subjected to a relatively cold environment, at such cold locations, temperatures may drop below the dew point of the conveying gas. In such cases, the duct and collector shall be suitably insulated to maintain the temperature of the conveying gas above the dew point to prevent moisture from condensing inside the system.

33. Relief Vents of Conveyor Ducts.

331. Wherever, in the ducts, it is practicable to have relief vents of sufficient area with antiflash-back swing valves extending to the outside of the building, these shall be provided. Care shall be taken to limit the inertia of swing valves to the minimum required.

244 651-12 A L U M I N U M POWDER

332. WORKING PRESSURE STRENGTH OF DUCTS: Wherever damage may result from the rupture of a duct, in case the relief vent does not offer sufficient relief, the duct should be designed for a working pressure of at least 100 pounds per square inch. Where so located that no damage will result from its bursting, it should be of the lightest construction possible.

34. Fan Construction and Arrangements.

341. Blades and housing of fans that are used to move the air or inert gas in conveying ducts should be constructed of nonspark. ing material such as bronze or aluminum. The arrangements should be such that intercepting dust collectors, suitably grounded (see Chapter 5, Article 51), or the design of the ducts, will prevent aluminum dust from passing into the fan; in all cases, however, it is advisable that the fan blades or propellors and the fan housing be made of nonsparking material in case of a temporary bag leak, etc. In no case sh~/ll the design be such that the dust is drawn through the fan before entering the final collector. Per- sonnel shall not be permitted within 50 feet of the fan during operation. This means that the fan and associated equipment shall be shut down for oiling, inspection or preventive maintenance. If the area must be approached during operation for pressure test or other technical reasons, it must only be done under the direct supervision of competent technical pe.rsonnel and with the knowl- edge and approval of the operating management. Any fans into which dust may accidentally enter shall be placed-outside of the dust-making building and outside of buildings .where powder is drummed, screened, stored or otherwise handled in quantity. Fan bearings should be equipped with suitable instruments for recording the temperature therein and With an indicating device to give warning when a dangerous degree of heating is reached. When the fan is belt driven, a vibration-sensitive device may be, attached to the outside end of the fan drive shaft, with an indicating device to give warning when a dangerous degree of. vibration.is reached.

CHAPTER 4. ELECTRICITY F O R L I G H T AND POWER.

41. Electrical Wiring and Equipment.

411. All electrical wiring and equipment shall conform to the National Electrical Code, NFPA No. 70, o r to the Canadian Elec- trical Code, whichever is applicable. A l l parts of manufacturing buildings shall be considered Class II, Division 1 locations under Articles 500 and 502 of the National Electrical C/)de (Section 18

ELECTRICITY FOR L I G H T AND POWER

245 651-13

of the Canadian Electrical Code) except offi.ces and similar loca- tionS so occupied and segregated as to be reasonably free from dust, and so classed by the authority having jurisdiction.

42. Requirements of National Electrical Code.

421. Attention should be specifically directed to the require- r~°-ts of the National Electi'ical Code, NFPA No. 70, or of the Canadian Electrtcal Code for the location of transformers, type and location of motors, generators and their control equipment, cables, fuses, circuit breakers, conduits and lights of all types.

43. Special Provisions.

431. Provision should be made for remote control of the electrical circuits so that light and power in any dust-making building may be cut off by switches outside of the building at a distance of at least 4 feet from the nearest doorway. It should also be arranged that the power of the whole plant can be cut off by switches located at one or more central points, such as the office, watchman's booth, etc.. All electrical equipment shall be inspected and cleaned periodically. Where flashlights or storage battery lamps are used, they should be of a type approved for the purpose.

CHAPTER 5. CONTROL OF STATIC ELECTRICITY.

51. Grounding Machinery to Remove Static Electricity.

511. Grounding machinery to remove static electricity produced in dust making and collecting is vital for safety. It should be thoroughly done according to Recommended Practice on Static Elec- tricity, NFPA No. 77, not only for stamp mortars or other mills, fans and conveyors in all parts of the plant where dust is made or handled, but also for all dust screens, cyclone collectors, bag collectors, and screen-cloth collectors. These several kinds of cloth collectors and screens, if .not themselves metallic, should have fine noninsulated,-nonferrous wire enmeshed or woven with the cloth or otherwise, securely fastened into it a.t suitable intervals, and should be grounded.

246 651-14

a ° A L U M I N U M P O W D E R

CHAPTER 6. PREVENTION OF ACCUMULATION OF ALUMINUM POWDER OR DUST.

61. Cleaning Methods and Systems.

611. Dust shall not be permitted to accumulate. Good house. keeping is a factor of utmost importance. To this end an adequate vacuum sweeping system is recommended, although" soft push .~ brooms may be used. If 'portable vacuum cleaners are used, they should employ a highly efficient wet collecting system ahead of the vacuum exhauster. If dry collectors are used, they shall be located outdoors and a'#ay from all working areas and personnel. In all cases, the entire vacuum system shall be thoroughly grounded electrically, the hose shall be conductive and the pickup nozzle shall be of metallic, minimum sparking material. Each time the stamps or other dust-making machines are charged and/or discharged. all dust and other material spilled on open surfaces of the machinery or t he floor of the building shall be promptly and thoroughly removed. When vacuum cleaners are emplo3/ed, bulk accumulation of powder and material shall be removed by soft push brooms and nonsparking scoops before the vacuum sweeping equipment is used. Care shall be taken to avoid sucking water into the vacuum pickup nozzle to avoid caking of damp aluminum in the hose, etc. The electrical system shall be suitable for use in Class II, Group E atmospheres, that is, the electrical system shall be aluminum dust-ignition proof.

62. Cleaning Frequency.

621. Competent supervision and periodic cleaning should always be maintained, and the foremen should be alert to prevent the accumulation of excessive dust on any portions of buildings or machinery which are not regularly cleaned in daily operations. Reg- ular periodic cleaning, with all machinery idle and power off, should be carried out a s often as local conditions require it to maintain safety, but in any case at least once a week.

63. Location of Discharge Receptacles of Dust Collectors.

• 631. The dust collected by vacuum cleaner nozzles or brushes or otherwise and drawn through an evacuating pipe equipped with antiflash-back valves and explosion vents located outside the build, ing shall be discharged into a suitable receptacle located outside the dust-making building. Each piece or group of such equipment shall be surrounded with a tight, strong, steel shield, preferabl~

I i

P R E V E N T I O N . O F I G N I T I O N

247 651-15

cylindrical, open at the top and closed at the bottom and designed to withstand an' instantaneous shock pressure of 200 pounds per sauare inch, so that, if an explosion should occur in dust-collecting r~ceptacles, its full force and flame would be diverted upward..

64. Fans and Other Air Moving Equipment.

641. Fans and other equipment for moving the air shall be so placed that the entrance of dust is minimized, or else enclosed as above specified. They should have ball o r roller bearings, and, when used for pneumatic 'conveying of dust froni a machine or group of machines, they should b~ electrically interlocked with the vower supply for such machines so that, in case the fan stops, the m' achine will stop making dust.

CHAPTER 7. PREVENTION OF IGNITION OF ALUMINUM POWDER.

71. General Precautions.

711. In the operation of the plant every precaution shall be taken to avoid the production of sparks from electrical faults or from. either static electricity or sparks caused by impact, such as that of steel or iron articles or stones Upon each': other or upon, concrete. The leakage of water in or into any building where it can come into contact with any aluminu m powder shall be pre- vented to avoid spontaneous heating and ignition therefrom. The electrical heating to a high temperature of any wire .or resistance dement in a dusty or dust-producing building and the develop- ment of serious local heating in machinery, due to friction, should likewise' be pre~bnted. The installation of thermostats connected by relays with bell or 6tiler ifidicat0rs m~y be advisable in some parts o f thd pl~int. A l l electrical components of'thermost'ats, relays, etc., shall either be suitable for use in Class II, Group E atmospheres, that is,' the components shall be aluminum dust-ignition proof, or shall be located outside of 'the buildings in dust-free a r e a s . . .

72. Removal of Tramp Metal and Stray Pebbles.

721. Approved magnetic separators of the permanent magnet or self-cleaning electromagnetic types or approved pneumatic separators or screens should be installed in an approved manner ahead of all mills, stamps or pulverizers to remove tramp metal from the pieces of aluminum" going to the mills or stamps, and these pieces

A L U M I N U M POWDER

should also be carefully examined to remove pebbles or other foreign material which might, in subsequent operations, produce frictional sparks of sufficient intensity to ignite the aluminum powder. Any electro-magnets shall be suitable for use in Class II, Group E atmospheres, that is, the magnets shall be aluminum dust-ignition proof.

73. Bearings. 731. Ball or roller bearings properly sealed against dust shall "

be used generally for line shafts or other high-speed equipment, instead of plain bearings, becauge of the difficulty of maintaining proper lubrication of the latter for preventing their heating. Any open bearings which have to be used should be protected as thoroughly as possible against the ingress of aluminum dust and, on high speed equipment, should be equipped with automatic hot journal alarms. Bearings should be of the outboard type, protected by dust seals or packing glands lubricated or packed with permanently lubricated packing. A 5 per cent oxygen-bearin~ nitrogen or a compatible liquid may be continuously forced through the packing gland if necessary. In any case, before opening up seals or packing glands they shall be thoroughly "wetted down" with a high flash solvent or oil to prevent rapid oxidation of any accumulated aluminum with fresh unoxidized surfaces, which without such protection will ignite violently.

732. Internal machine clearances shall be maintained to insure against jamming against the walls of any material which may enter the equipment.

733. Slurry or solvent pumps should be installed with proper controls to make sure they will be shut down if they run dry. They should also be protected against the possibility of sucking in air from empty tanks or from leaky suction lines.

734. Electrostatic grounding shall include grounding across the lubricating film (by use of current collector brushes or "jumpers") for all bearings. All alarms and actuating equipment shall be suitable for use in Class II, Group E atmospheres, that is, alarms and actuating equipment shall be aluminum dust-ignition proof, or be located outside the building in a dust-free area.

74. High Temperature Warning. 741. Cyclone and bag collectors should be equipped with suit.

able instruments for recording the temperature therein and with an indicating device to give warning when a dangerous degree ot heating is reached. The temperature limit may he set by the igni. tion temperature of the collector material (i.e., well below cloth

PREVENTION OF I G N I T I O N 249

651-17

ignition temperature of cloth bags) or may be limited to stay well below the ignition temperature of the aluminum dust-air mixture as in the case of cyclone type collectors. Synthetic fibers which tend to accumulate high static charges shall not be used to con- struct bags. Polishing equipment should also be equipped with temperature recording instn~ments, to indicate to the operators any tendency toward excessive heating. All such temperature recording instruments should preferably give their indications and make their record at easily observed central locations so the men in responsible charge may receive warning and take action to remedy the hazardous conditions. AI1 alarms and actuating equipment shall be suitable for use in Class II, Group E atmospheres, that is, alarms and actuating equipment shall be aluminum dust-ignition proof, or be located outside the building in a dust-free area.

75. Open Flames, Cutting and Welding Equipment, Powder-Op- erated Tools.

751. No open flames or electric or gas cutting or welding equipment shall be permitted within the buildings housing the powder- producing or handling machinery during operation. If it becomes absolutely necessary to use such equipment for making repairs, all machinery in the room or section of the building where the repairs are to be made shall be shut down and the entire room or section with its machinery shall be thoroughly cleaned to remove all accumulations of aluminum powder. Operators of cutting or welding torches should be required to obtain a permit from the safety or fire protection officer of the plant before using their equipment under any condition around aluminum powder plants. Attention is called to the hazardous conditions that may exist either inside or outside of the plant if cutting torches are used in dismantling dust collectors or powder-producing machinery before all dust accumulations have been removed.

752. POWDER-OPERATED TOOLS: Gun-type tools using powder or cartridges for driving pegs or pins into concrete, brick, steel, etc., shall not be used where flammable dust or dust clouds are present. When the use of this type of equipment becomes necessary, all dust-producing machinery in the area shall be shut down; all equipment, floors and walls shall be carefully cleaned; and all dust accumulations shall be removed. A careful check shall be made to be sure that no cartridges or charges are left on the premises where they could enter equipment or be accidentally discharged after operation of the dust-producing or handling machinery is resumed.

250 651-18 • A L U M I N U M P O W D E R

76. Spark.Producing Tools.

761. Aluminum, copper or bronze metal tools, including shovels, and not iron or other spark-producing tools, should be used in any dust-making building except when that part of the plant is stopped, and then only after thorough removal of dust accumulation. This rule shall also be followed in dismantling either inside or outside of the plant any discarded, powder-producing equipment. : that may_ contain dust accumulations. Not even nonsparkmg tools or other hard objects should be allowed to strike any other hard surface in a dusty atmosphere as the energy so dissipated, if applied to only a few grains of powder, can raise the powder temperatures to the ignition poinf. . . .

77. Heating and Drying. ' "

771. Heating and drying should be done"only by-hot air, the air to be heated by steam or hot water coils in a small offset to the building. In buildings which may have aluminum dust in them, the heating and drying should be forced by blower fans into each respective building through a heating unit. In the case of dusty buildings, the fans should draw in their air supply from the outside in order that no explosive dust accumulates in the heating cham. ber. Air used in the process shall have a dew point sufficiently low to insure that no 'free moisture can form at any point in the process.

78. Sweepings.

781. , Powder or dust sweepings and other materia.ls swept from the floor, machines,' or other locations must be .carefully screened to remove foreign matter before being placed in any machine for additional fabrication.

79. Starting Machinery after Shutdown.

791. All machines should be thoroughly cleaned and be absolutely dry before they are charged with metal and placed in operation.

P O W D E R S T O R A G E - - W E T M I L L I N G 251

651-19

CHAPTER 8. ALUMINUM POWDER STORAGE.

81. Packing and Storage.

811. The aluminum powder product, the conveyance of which is referred to in Article 32, and the collection of which is to be in a separate building from the dust-making building, should be packed into steel drums as soon as possible, and these drums tightly sealed and stored in a dry location until they are ready to be shipped from the plant or repacked. Open bin storage is dangerous unless the bin is purged and maintained with a gas atmosphere of the character described in Article 322.

cHAPTER 9. WET MILLING OF ALUMINUM POWDER.

91. Prevention of Ignition.

911. SPONTANEOUS HEATING: When aluminum is milled or otherwise comminuted in the presence of a liquid which is inert chemically to the metal, the air-dust explosion hazard is eliminated. When the resulting product is subsequently exposed to air such as in filtering or drying, any unoxidized new surface produced during comminution will react and may generate sufficient heat to. cause spontaneous ignition. To prevent this, it is imperative to have sufficient oxygen present in the milling or other comminuting operation, or i n slurries ahead of tilters and blenders, to at all tunes oxidize the new surface as it is formed. Addition of a milling agent, such as stearic acid, does not eliminate the necessity of maintaining an adequate supply of oxygen to prevent the subsequent spontaneous ignition hazard. During milling, where fresh surface is being developed rapidly, the oxygen content should be maintained at no less than 8 per cent. In slurries and blenders and other equipment, where new surface is not being developed rapidly, the oxygen content can be reduced to a minimum of 4 per cent. If the oxygen is supplied as a constituent of air, the dew point of the air must be maintained substantially below that which could introduce a free moisture problem.

912. STATIC SPARKS: Mill bearings shall be grounded across the lubricating film by use of current collector brushes to provide for continuous grounding from the mill through to mill supports, piping, etc.

913. FLAMMABLE VAPORS: Adequate ventilation, forced or otherwise, shall be maintained in all rooms handling solvents to reduce vapor hazards from accidental spillage.

252 651-20 A L U M I N U M P O W D E R : "

C H A P T E R 10. FIRE F I G H T I N G METHODS.

101. Categories, Aluminum Fires.

1101. Aluminum fires should be considered in two separate cate. gories:

1. Those where the aluminum is in a paste or slurry with an organic solvent.

2. Those where the aluminum is in d ry powder form.

102. Fires in Aluminum Pastes o r Slurries.

1021. A fire in an aluminum paste or slurry in' an organic solvent is, for all practical purposes,.a, solvent fire until most of the solvent has burned off to expose dry aluminum. The "first attack on this type of fire should be with carbon:dioxide which, if available in sufficient quantity, will adequately control and plat the fire out; Automatic carbon dioxide systems with outlets designed to adequately cover all vulnerable areas are recommended. An adequate supply of back-up carbon dioxide cylinders and portable carbon dioxide extinguishers is also recommended. If the fire such as could develop in a paste or filter cake gives evidence of having started through spontaneous ignition, the carbon dioxide may temporarily put the fire out, but subsequent contact with a i r would cause re-ignition. To prevent this, the aluminum paste or cake should be immediately completely covered with dry sand or an acceptable proprietary dry extinguishing material. * The covered material shall I~ left unmoved until the temperature of "the whole mass has dropped to ambient. W h e n the temperature throughout the entire m~iss is no t above ambient and no "hot spots" can be found, the covered material should be removed very carefully and in small unit quantities (i.e., no more than three gallons 0f material in a five gallon pail). Throughout the removal operation great care is necessary to avoid creating any dust-air mixture; the aluminum cake must be kept covered at all times and again covered after it is transferred to the conveying pails. An aml~le supply of dry extinguishing material shall be kept immediately available to re-cover the aluminum cake if any heating reaction is started.

1022. • Water should be used on a solvent-aluminum fire only as a last resort, when the methods above have' failed and the fire shows evidence of going out of control. In such case, the water

~NoTE :" Several such proprietary materials are on the market.. Tests should be conducted to determine acceptability of any particular extinguishing material.

253 FIRE FIGHTING 6 5 1 - 2 1

shall be supplied through low velocity spray or fog nozzles and in great vOlume to cool down the fire area while being careful not to stir up a cloud of semidry aluminum dust which would create a serious explosion. Only trained personnel should be allowed to direct this operation. Once water has been Used on" the fire area, it shall be continued until the fire is out and the temperature has dropped to that "of the water. At this stage the aluminum sludge, while being kept flooded with water, shall be completely and carefully removed to a "fire safe area." Any wet aluminum left in the working area will reignite through exothermic reaction between the water and aluminum - - necessitating complete clean-up of all areas and equipment subjected to water. Good drainage to a "fire safe area" should be planned on for all units subject to this fire fighting method. Good ventilation shall be maintained during and after such water treatment to insure against developing pockets of hydrogen gas.

1023. Sprinklers may be used in certain .areas to protect the building structure only. This protection should be in the form of an empty pipe system with sealed sprinklers, the-supply valve for which can be turned to the "on" position should the fire become so great as to .threaten the building structure. Sprinklers are not recommended as first-line protection over equipment or storage areas. It is considered preferable to have low velocity fog nozzle stations (at accessible strategic locations), which can be manually directed to those specific areas which may require this last resort treatment. Sufficient volume of water shall be available at that location to insure doing the job correctly and completely. Where possible to do so, it is recommended to direct all waste water - - by means of dams and trenches - - into an outside "fire safe area."

103. Fires in Dry Aluminum Powder. 1031. In a dry aluminum fire the procedures given in Article

102 would be dangerous. Aluminum powder in bulk is ignitable only with great difficulty. 'However, once suspended in a dust-air cloud it is readily ignited and ver'y explosive.

1032. The use of fine dry sand, preferably that screened through a 20-mesh sieve, or use of an acceptable proprietary dry extinguishing material,* is a t present the best known method of fighting incipient fires of'aluminum powder. Water streams or liquid sprays of various kinds that vaporize quickly are highly dangerous, as shown in many instances, since the dust is thrown into the air and

~NoTE: Several such proprietary materials are on the market. Tests should be conducted to determine acceptability of any particular extinguishing material.


the ignited particles instantly cause a violent explosion of the dust. For the same reason, any mechanical agitation or disturbance of the burning powder or that adjacent thereto must be avoided. An ample supply of dry fine-screened sand or other approved powder should be kept in covered bins or covered receptacles, each containing about a cubic yard. These receptacles should be placed at a sufficient number of suitable points at or in each building, convenient to reach quickly. The receptacles should be covered and arranged so that the sand can be quickly scooped up by bucket or shovel. These implements shall be made of aluminum or other nonferrous material.

1033. In fighting an aluminum powder fire avoid stirring it. All electric power should be first shut off, then if the aluminum powder is burning quietly in a place where it can be safely isolated, the sand should be carefully ringed around but not dropped on the burning powder, great care being taken to avoid fanning the dust into the air. The powder, when burning quietly, forms a crust which excludes oxygen and .gradually extinguishes itself. As soon as the isolation of the fire has been accomplished, the room should be closed, the windows shut, the bottoms of the doors sealed with sand, and the fire allowed to burn itself out.

1034. Water and other extinguishers shall not be used: All liquid, carbon dioxide or foam type extinguishers shall be rigidly excluded from the operating plant area to prevent their being used by excited and inexperienced persons during an emergency.

1035. FIRE FIGHTING ORGANIZATION: The operating crew should consist in part of men trained to combat the fires of the type encountered in these processes, and only these men should be permitted near the area involved by fire. It is preferable that one individual on this crew be responsible for directing fire fighting operations until more senior personnel arrive on the scene. Local town or city firemen, who might be called to the plant in case of fire, shall be thoroughly instructed in the dangers of using jets of carbon dioxide, water, carbon tetrachloride or other liquids in an aluminum powder fire. They should receive positive orders from their superiors, by prior arrangement with the respective officials, forbidding such use in combating any fire in the aluminum powder plant.

255 SAFETY PROVISIONS 651-23

C H A P T E R 11. SAFETY PROVISIONS.

111. Protective Clothing for Workmen.

1111. Outer clothing should be clean, fire resistant, nonstatic enerating and easily removable. Tightly woven smooth fabrics

ated with fire ~esistant chemicals and preferably fastened with ,nonmetallic snap or slide fasteners should be used. These clothes should have no pockets. Safety shoes with conductive soles, resistant to embedding particles (and petroleum solvents if they will be in contact 'with such.), sewed or pegged on, should be used. Safety toe caps must be covered with a scuff-resistant coating. No :nails, metal cleats or plates in the heels or soles can be permitted and the design should ~ be made for. quick and easy removal. Per- Sonnel working On electrical equipment shall not use conductive soles, but all other conditions outlined above shall be followed for them.

112. Smoking and Match6s.

1121. Smoking materials and matches are forbidden on the premises except in the official "change-house" at entrance. They should not be carried nor used by employees or visitors about the premises adjacent to or in any building in which explosive dust is made or loaded for shipment. This is not intended to preclude the bringing of tobacco by employees in their street clothes into the "change" or "wash-house." This building should be of fire- resistive construction, located at or near the entrance to the premises, and should be surrounded by a fence. In this building the employees should leave their street clothes and put on the fire re- sisting clothing without pockets. Nor does this provision preclude smoking in a recreational room in the "change-house" which may be provided by the company for the purpose, nor in the office. It is desirable that a fixed tobacco lighter be furnished in such room to avoid accidental carrying of matches into the plant grounds and buildings. Maintenance and furnace operators shall be provided with safe ignition tools of the flint and file type for lighting torches and furnace burners under approved conditions and provision shall be made to make sure such ignition tools are not carried away by such employees absentmindedly or otherwise.

113. Employee Instruction.

1131. All employees in the aluminum powder or paste manufacturing plant shall be carefully and thoroughly instructed by their foremen as to their behavior and procedure in case of fire or ex-


plosion, the location of electrical switches, first-aid and safety equip. ment, permissible methods used for incipient paste fires and per. missible methods used in the isolation of aluminum powder fires, the hazard of raising a dust cloud, and the hazard of throwing liquids on an incipient fire of aluminum powder.

114..Periodic Inspection. . . . .

1141. Strict discipline and good housel~eeping are essential at all ~imes. A thorough systematic inspection should be made regularly at periods not exceeding one month by two or more competent persons, and the records of such an inspection should be made and entered in a book kept at the office of the plant and be available to the operating head responsible for the c0ndi't!ons found and for the authorization of such changes as may be recommended. This inspection should cover general safe'cy precautions, fire fighting methods, first aid, good hofisekeeping, electrical and mechaniea' equipment. Indicating and recording instruments and alarm de- vices should be checked daily and a regular program of instrument calibration at periods not exceeding six months should be im. plemented.:

115. Deluge Showers.

1151. Deluge showers, actuated by a hinged floor valve, should be installed at strategic poinfs immediately outside" of critical working areas to immediately douse any employee's clothing fire.

232...232 committee on dust explosion hazards de-1 repor~ of committee on dust ~:xplosion hazards c....

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