205 R E P O R T OF C O M M I T T E E ON C O M B U S T I B L E M E T A L S CM-1

Report of Committee on Combustible Metals

Richard B. S m i t h , Chairman, U. S. Atomic Energy. Commission, Washington, D. C. 20545

S, g. Auck, Underwriters' Laboratories, Inc. Victor O. Bohn, American Insurance Assn. John A. H a w t h o r n e , Titanium Metals In-

dustry. IL J- K a u t z m a n , Aluminum Company of

America. Robert J. Kr.leger, Titanium Metals Cor-

poration o! America. R. B. Lawrence, Factory Mutual Engineer-

ing Corporation. John A. Peloubet , Dow Chemical Co. A. F. Ratzer , Chemical Concentrates Corp. Joe B. R o s e n b a u m , U. S. Dept. of the

Interior.

I l e r m a n H. Spaeth , Pacific Fire Rating Bureau.

D. C. T lmbe r l a ke , Fire Equipment Manu- facturers' Assn. Ins.

d. E. T r o u t m a n , Factory Insurance Assn. T. H. Wright , Ohio Inspection Bureau.

Alternates, R. P. Day, Factory Insurance Assn. (Alter-

nate to J. E. Troutman.) J , A. Slevert , Fire Equipment Manufae-

tursre' Assn., Inc. (Alternate to D. C. Timberlake.)

~COPE: To obtain and correlate information on fire hazards, methods of 8 to r t e , handling ~nd use, and fire protection of magnesium and other combustible metals, and to develop ,tandards for the safe storage, handling and manufacture of these metals. Measures for the prevention or control of metal dust explosions are under the jurisdiction of the Committee on i~nst Explosion Hazards.

This report has been submitted to ballot of "the Committee, which consists 14 voting members, of whom all have voted affirmatively.

The Committee on Combustible Metals presents for official adoption amendments to the Standard for the Storage, Handling and Processing of Magnesium NFPA No. 48-1961. NFPA No. 48 s published in the National Fire Codes, Vol. 3, and in separate jamphlet form.

The proposed amendments include a reorganization of the ~tandard by segregation of information on scrap disposal, storage, md fire protection in separate chapters. Other proposals pertain o heat treating furnaces (233, 235, 236), machinery (31), incinera- ion of dust collector sludge (411), handling scrap (43), storage of heet and extrusions (537), shipment and storage of pure mag- lesium chips (538), scrap storage (542), smelting (543), extinguish- ng agents (611, 622, 623), and automatic sprinkler protection 625(d)).

206 INTRODUCTION

STANDARD FOR THE STORAGE, HANDLING AND PROCESSING OF MAGNESIUM

NFPA No. 48 - - 1967

CHAPTER 1. I N T R O D U C T I O N

11. Purpose and Scope

111. The purp9se of this standard is to call attention to the fire and explosion hazards in the stoi'age, handling and processing of magnesium or magriesium alloys marketed under different trade names but commonly referred to as magnesium, and. to emphasize the measures that can be adopted for the control of such hazards. This standard covers magfiesifiha foundries, magnesium processing plants and commercial s'torage of magnesium. Primary production of magnesium is not included, and the hazards inherent in plants manufacturing magnesium powder ,are covered in the Code for Explosion and Fire Protection in Plants Producing or Handling Magnesium Powder or Dust, NFPA No. 652. The recommenda- tions and requirements in this standard are based ori conclusions drawn from available reports or data on magnesium fire tests and actual magnesium fire experience. ,

12. Definitions . . . . . . .

MAGNESIUM is the term used in this standard to refer to either the pure metal or alloys having the generally recognized properties of magnesium, marketed under different trade names. ~

SHALL is intended to indicate requirements.' " '

' . SHOULD is intended to indicate recomihendations or tha which is advised but not required.- ' " ~ • . . . . " :

• A~PROVED refers to approval by theauthori ty having)urisdiction.

The terms PROPERLY, SAFELY and ADEQUATE shall be interpreted as conditions subject to determination by the authority having jurisdiction. " - " : - ' "

15. Propert ies and :Characteristics' of Magnesium

131. Magnesium, .a silvery white metal with an atomic weight of 24.32 and specific gravi ty of 1..74, is sometimes described as the lightest known, structural metal possessing properties of permanence and stability. The melting point of naagnesium, is 1202 ° F. (650 ° C.) and the ignition temperature is generally considered to be very

MAGNESIUM

207

close to the melting point but ignitions of magnesium in certain forms may occur at air temperatures below the temperature given as the melting point. Magnesium riSbon and fine magnesium shavings can be ignited under certain conditions at air temperatures of about 950 ° F. and very finely divided 'magnesium powder has been ignited at air temperatures below 900 ° F.

132. Commercially pure magnesium may contain traces of aluminum, copper, iron, manganese, nickel and silicon, but these contaminants in typical analyses generally total less than 0.2 per- cent. Metal marketed under different trade names and commonly referred to as magnesium may be one of a large number of dif- ferent alloys containing widely different percentages of magnesium, aluminum, zinc and manganese~ Some of these alloys may have ignition temperatures cofisiderably lower than the figure determined for pure magnesium .and i n some cases it may be necessary to consider the eutectic melting point of certain alloys of these metals which may be as low as 800 ° F. because the metal will ignite if it is held at this lower temperature for some time.

1 ~ . RADIOACTIVE ALLOYS:

(a) There are several magnesium alloys produced which con- rain thorium. These alloys are used primarily where it is essential that the metal retain good mechanical properties at elevated tem- peratures. Thorium, which is a low level radioactive material, is used in these alloys up to a nominal concentration of 3 percent. While it is possible with a sensitive radiation survey meter to detect the radiation from such alloys, the level of external gamma radi- ation is so low that there is no hazard to personnel. The level seldom goes much above one or two milliroentgens per hour at the surface and on small masses is less than one.

(b) The natural decay or daughter products of thorium are locked up in the alloy until such time as the metal is melted, burned or chemically disintegrated. Under fire conditions these decay products are normally within visible fumes and are diluted .as the visible fumes dissipate into the air. These elements could be in- haled with possible excessive irradiation of the lung tissue and deposition in the bone structure. Maximum permissible air-borne concentrations of such radioactive materials have been set up through the Atomic Energy Commission and are based on con- tinuous exposure for a normal 40-hour work week. (See Article 44.)

154. I t is clesirable to know the specific properties and character- istics of products being stored or handled when provision is made for fire protection, and such information on the composition of metal or alloys purchased from producers or distributors is gen- erally readily available. "

208 I N T R O D U C T I O N

T"

14. Spot Tests for Magnesium

141. In the construction or assembling of certain machinery or equipment, magnesium or one of its alloys having similar properties may have been used for 0nly a few of the comPonent parts and where finished or painted products are being stored or handled it may be difficult to determine what percentage consists of naag. nesmm. Investigation has shown that silver nitrate, vinegar or acetic acid can be used to distinguish between parts composed of ' magnesium and those composed of aluminum. T h e portion of • metal to be tested is first cleaned of grease, dirt, oxide, etc., by abrading with sandpaper or steel wool. After the test area has been prepared a drop of the test solution is placed on it.. ,

(a) SILVER NXTRATE TEST. The test solution is prepared by dis- solving about 5 grains of silver nitrate (AgNO3) in one liter of ' distilled water. A black coloration is iinmediately produced on magnesium or magnesium alloy. (This coloration is essentially reduced silver.) No coloration is noted on aluminum and its alloys, or most other metals. Zinc and cadmium will show a similar black coloration but are much heavier.

(b) VINEGAR OR ACETIC Aeto TEST. Ordinary vinegar or a weak solution of acetic acid will give a bubbling reaction in con- tact with magnesium while other common metals are. not affected.

15. Combustibiiity and Explosibility 151. The ease of ignition of /magnes ium depends to a large

extent upon the size and shape of~the material as well as the size or intensity of the source of ignition. In the form of ribbon, shavings or chips with thin feather-like edges or ' grinding dust a spark or the flame of a match may be sufficient to start the material burn- " ing. Heavier pieces such as ingots and thick-vCall castings are dif- ficult to ignite because heat is conducted rapidly away from the source of ignition. If the entire 'piece of metal can be raised to the ignition temperature (about 1200 ° F. for pure magnesium and many of the alloys) self-sustained burning will occur.

• 152. The combustibility of magnesium, the ineffectiveness of : ordinary types of extinguishing agents on magnesium fires, and the fact that under certain conditions the application of some of these agents intensifies the burning and may .release hydrogen to form an explosive gas-air ,mixture, all combine to create serious fire and explosion hazards.

153. Magnesium, in its solid form, melts as it burns and may form puddles of molten magnesium which, in the presence of sufo

M A G N E S I U M

209

ficient moisture, may present explosion hazards similar to those as- sociated with other molten metals.

16. Extent of Hazard

161. Magnesium is widely used in the construction Of household avpliances, furniture, office equipment, portable tools, luggage, a~t'omobiles, buildings, machine parts and engines and structural members oI airplanes. A s a result of this general usage, the fire hazarOs associated with this material are of interest to fire-fighting and fire-prevention organizations.

210 M I L L S A N D F O U N D R I E S

CHAPTER 2. MAGNESIUM M I L L A N D FOUNDRY OPERATIONS

21. Melting and Casting. 211. It is good practice to locate melting operations in buildings

of noncombustible construction preferably with a high roof and adequate ventilation. Floors shall be noncombustible. Melt rooms should have easy and adequate access to facilitate fire control.

212. Moisture and foreign material are dangero~us, where any molten metal is present, and all metal added to melting pots should be thoroughly predried. Floors around melting units ~hould be of hard burned or vitreous paving block, cast iron or steel plate laid in concrete, kept clean and free of moisture. Fuel supply lines should have remote valve controls.

213. Furnace settings must be kept dry and free from iron scale. Leaking pots and crucibles that allow molten metal to contact concrete or hot iron scale are dangerous. Pots and crucibles should be inspected regularly and discarded as soon as there is any evi- dence of possible failure. Safety runoff containers should be pro- vided for melting pots and crucibles.

214. Ladles, skimmers and sludge pans must be thoroughly predried and hot before contacting molten metal.

215. Extreme care should be exercised in pouring magnesium castings to avoid spillage where moisture on floors or other surfaces may cause explosions. Permanent molds should be thoroughly preheated before pouring. It is considered good practice to purge all permanent molds with sulfur dioxide gas prior to use and be- tween pourings.

216. Flame-resistant clothing, high foundry shoes, and ade- quate face protection should be used by operators.

22. Rough Finishing of Castings

221. Provision shall be made for the proper removal of dust as it is produced at grinders and for the immediate quenching o f sparks that may be produced by such equipment. Flash fires in fine dust may be dangerous to the operator. The chance of flash fires igniting castings is remote but fires in accumulated dust may ignite castings. Cuttings from band saws should be swept up at regular intervals to prevent excessive accumulation in the work area.

222. Good housekeeping is essential.

M A G N E S I U M

211

223. Electrical equipment, including motors, shall be of the type approved for use in Class II , Group E atmospheres and in- stalled in accordance with the requirements of Article 502 of the National Electrical'Code, NFPA No. 70: All other possible sources of dust ignitions shot/ld be eliminated from the area.

224. Work.benches and o ther lequipment should be noncom- bustible. If wood table tops or other fixtures of wood or combustible material are considered necessa~Ty they should be treated to render them fire retardant and should be free from cracks or recesses in which magnesium dust can accumulate.

225. Operators should wear .caps and hard finished or flame- resistarit outer clothing .without pockets or cuffs.

25. Heat Treating 231. Fire may occur in furnaces or ovens when magnesium is

being heat treated if there is a lack of proper temperature control or if the surface of the work is not free from dust or fine particles of. metal. Failure to provide for proper circulation of the heated air in the furnace may, result in overheating or higher temperatures in certain zones than that indicated by the thermocouples that op- erate the temperature control devices.

232. A standard procedure for checking the uniformity of tem- perature at various points in heat treating furnaces should be estab- lished. Furnaces should be tested initially and at regular intervals to locate undesirable high temperature areas.

233. Furnaces should be properly and tightly constructed. Gas- or oil-fired furnaces should be provided with combustion safety controls. All furnaces should have two sets of temperature con- trois operating independently. One maintains the desired tem- perature while the second set should be a high temperature limit control. The high temperature limit control should be adjusted to operate at a temperature slightly above the controller so that in case the latter fails, the limit switch will cut off the power pre- venting ignition of the magnesium. To retard the ignition of mag- nesium, the provision of a dilute sulfur dioxide or carbon dioxide atmosphere is advisable on heat treating furnaces set to operate above 750 ° F.

234. Magnesium parts to be put in a heat treating furnace should be carefully freed of magnesium turnings, chips and sawdust.

235. Magnesium billets, castings and wrought products must not be placed in a heat treating furnace with wood spacers or pallets. The ignition temperature of the wood is below normal

212 M I L L S A N D F O U N D R I E S 48---~

heat treating ranges, and the burning wood ignites the hot mag. nesium. : ' :

236." Aluminum parts, sheets or separators must not be inc'luded in a furnace load of magnesium. Direct, coniact between a luminura and magnesium at heat treating temperatures promotes diffusion and formation of a low melting, readily ignited haagnesium-alu. minum compound. T h e high ' temperature flame of the burning compound can ignite the heated magnesium.

237. There should be strict adherence to the heat treating tern. perature cycle recommended by the alloy manufacturer.

238. Molten salt baths containing nitrates and/;or nitrites are not recommended for heat treating magnesium alloys. Special salt fluxes can be safely used for the dip brazing of magnesium. Certain commonly used molten mixtures of nitrates and nitrites can i'eact explosively with magnesium alloys immersed in them. The possibility of accidental immersion of magnesium alloys in salt baths used for aluminum, where both metals are being processed. in the same area, is ever present. Every effort should be made to keep these metals segregated and easily identified.

L ! " . . . . . " f

J

I

i - 5

~ - 1 0 M A G N E S I U M

213

CHAPTER 3. MAGNESIUM MACHINING' AND FABRICATION

51. Machining Magnesium 311. Machifiing includes sawing, turning, chipping, drilling,

routing, reaming, tappir/g, milling and shaping.

312. Magnesium can usually be machined at the maximum speeds ob'tainable:on modern machine tools. The low power re- quired permits heavy depths o f cut and high rates of feed as may be consistent with good workmanship. The thick chips seldom ig- nite due to their large heat capacity. The tool should never be allowed to ride On the ~ metal without cutting as the frictional heat may ignite the fine metal that is scraped off, For the same reason, the tool should be backed off as soon as the cut is finished. Tools should be kept sharp and ground with sufficient clearance to pre- vent rubbing on the end and sides of the tool.

$13. W.he'n deep holes are being drilled in magnesium (depth greater than •five times drill diameter) the use of a high helix drill (45 ° ) will prevent packing of chips with resultant, frictional heating and possible flash fire'in the fines.' Such'a drill is also recommended when drilling deep holes through composite or sandwich type sections. :,, . . . . ~'

314. Grooving or parting operations:frequently'result in flashing since the tool tends to rub on th_e.sides of the groove while cutting on the eiid. Adequaterelief.on the sides (5 °) and on the.end (10-20") minimizes the generatio n of fine ldus..t, and excessive heat.

315. If flashing of chips during machining becomes a problem it can be minimized by: "-

(a) keeping surface speed below 300 or above 2200 feet per minute,- ..

(b) increasing feed rate tO 0.008 to 0.010 'inches per revolutioh, (c) reducing the relative humidi ty of the.air to 45 percent or

lower, . . . . (d) using an alloy containing a low amount of aluminum (3 per-

cent) and zinc (1 percent), (e)-using high aluminum (9 percent) zinc (2-3 percent)-mag-.

nesium alloys in the. solution heat treated condition (T4), (f) replacing high speed steel tools with carbide, (g) "applying a coolant.

316. Magnesium is normally machined without a coolant. If

214 MACHINING AND FABRICATION

some lubrication is needed as in tapping or where extremely fine or grooving cuts require cooling, a high flash point neutral mineral oil should be used. Water," water-soluble oils and oils containing more than 0.2 percent fatty acids may generate flammable hydro. gen gas. Scrap wet with animal or vegetable oils may ignite SpOn. taneously. Where compressed air is used as a coolant, special pre- cautions should be taken to keep the air dry.

317. Machines should be provided with a pan to catch the chips or turnings. The pail should be such that it can be readily with- . drawn from under the machine in case of fire. It should be accessible for chip removal, and for application of extinguishing powder to control a fire. :In case of fire in the chips the pan should be with. drawn f rom under the machine but not picked up or carried away before the fire is extinguished.

32. Grinding, Butting and Wir e Brushing

321. Dust COLLECTION: (a) Dust shaU be collected by means of suitable hoods or en-

closures at each operation, such enclosures to be connected to a liquid precipitation type of separator, and the suction unit in such a way that the dust shall be converted to sludge without contact, in a dry state, with any high-speed moving parts. Figure 1 and Figure 2 show typical liquid washed dust collectors servicing fixed and portable grinding units. Water in large volume normally is the medium used as the precipitating liquid.

(b) Connecting ducts or suction tubes shall be completely grounded and as short as possible, with no unnecessary bends. Ducts shall b~e carefully fabr ica tedand assembled, with a smooth interior and with internal lap joints pointing in the direction of air flow, and without unused capped side outlets, pockets or other dead-end spaces which might allow an accumulation of dust.

(c) Each machine shall be equipped with its individual dust separating unit, except that with multiunit machines not more than two dust-producing units may be served b.y one separator. Not more than four portable dust-producing umts in a single enclosure or stand may be served by one separator unit.

(d) The power supply to dust producing machines shall be interlocked with the motor driving the exhaust blower and the liquid level Controller of the wet collector in such a wa~, that im- proper functioning of the dust collecting system will shut down the machine it serves.. A time delay switch or equivalent device shall be provided on the dust producing machine to prevent the starting of its motor drive until the wet collector is in complete operation and several changes of air have swept out any residual hydrogen.

MAGNESIUM 215

EyJ.IAUSTI[R WITH I"OTAL,LT ENCLOSED M O T O R ~ f SELF-OPENING

INSPECTION & \ " ~ [ [ / out ooo. \ X--"-. /

\ ,-. ~ h l v ' UQuIo \ - I ~ III ][ ELIMINATOR \ I ~ I • I ~ L.U U / P L A T E S

-poss~,o---- \ \ ~ 0 ~ - ~ I / -~-/- .J/ LIQUIOLEVEL \ ' ' \ ~1 [ /t , .1,/1 CONTROL' & \ \11 I . [ 7 % > 1 /INTERLOCK

• WET '

(.D)\ \ DUST

~ 1 ~ 2 N p ~ . _ _ . t . _ _ . E 2 _ E ~ - - ~ - / [ SLUDGE UNOER '~,,~"~"1" I STAND I I ~ - , , ~ , . - J ~ LIQUID .

- a L

Figure 'i

No'rB: This drawing is schematic and intended only to indicate some of the features which should be incorporated in the design of a collector. The volume of all dust-laden air spaces should be as small as possible.

322. CLEANING: Systematic cleaning of-the entire area involved, including roof members, pipes, conduits, etc., should be conducted

; daily or as often as conditions warrant , (1) by use of soft brushes and nonsparking scoops and containers, or (2) by means of a fixed suction pipe and outlet vacuum cleaning system, provided the separator unit is of the l iquid-precipitation type and provided also that the suction piping system is of s tandard ,nild steel pipe and standard recessed drainage fittings, with a check valve installed at each outlet. Implements and hose used in connection with sta-

~ tionary vacuum systems should be completely grounded. A rup- ture d iaphragm shall be provided in" the piping at its connect ion to the inlet side of the separator in such a way that a possible explosion in the piping may be safely vented to atmosphere.

323. ELECTRICAL EQUIPMENT: (a) Electric motors, lighting fixtures, control equipment and

wiring within a few feet of or a t tached to dust-producing machines, including that used in connection with separator equipment , shall

216 MACHINING AND FABRICATION 4s--

be of a type approved for use in Class II, Group E atmospheres and installed in accordance with the provisions of Article 502 of the National Electrical Code.

(b) All electrical equipment shall be inspected and cleaned periodically.

(c) Where flashlights or storage battery lamps are used, they should be of a type approved for the purpose.

324. GROUNDINO OF EQUIPMENT: All equipment shall be securely grounded by permanent ground wires to prevent the accumula. tion of static e l e c t r i c i t y . .

LIQUID ELIMINATOR

PLATES CLEAN OUT

DOOR

LIQU ID LEVEL CONTROL & INTERLOCK , , ~

DUST PRECIPITATING

ELEMENT SLUDGE UNDER

LIQUID

f ,,..,..~"~VET COLLECTS,

a ~

• t | i i l I I | l I I . I 1 - - I

I I i , - , ~ - - J °

Figure 2

BURRING BENGH GRILLED TOP NON $PARI~tNG MATERIAL

4~14 MAGNESIUM 217

$25. SAFETY PRECAUTIONS: (a) Special clothing for machine operators is recommended.

Employees' clothing should be easily removable, kept clean and free from dust. Leather or other smooth clothing, from which the dust can be brushed off readily may be worn. Smooth canvas or denim suits can be made flame-resistant by treatment with chemi -~ cals. Clothing should be made with nonferrous snap fasteners and without pockets or cuffs. Wearing of Woolen, silk or fuzzy outer clothing or shoes with exposed steel parts should be prohibited.

(b) Machinery and equipment described in Section 321 shall not be used for processing ferrous metals unless the entire grinder and collecting system is thoroughly cleaned. The grinding wheel o r belt shall be replaced prior to changing metals.

(c) No open flames or. electric or gas cutting.or welding equip- ment shall be permitted in' the section of the building where mag- nesium dust is produced or handled, while the equipment is in operation. If it becomes absolutely necessary to use such equip- ment for making repairs, all machinery in the section where the work is to be done shall be shut down and the section shall be thoroughly cleaned to remove all accumulations of magnesium dust. All internal sections of grinding equipment, ducts and dust col- lectors must be completely free from moist or dry magnesium dust and all hydrogen must be flushed out.

(d) Special precautions are necessary to prevent ignitions while dressing wheels used for grinding magnesium castings. Hot metal thrown off by the dressing tool may ignite dust or magnesium de- posits in the hood or duct. If it is not feasible to remove wheels to a safer location for dressing, hoods should be thoroughly cleaned or removed entirely before wheel dressing operations are started and all deposits of dust on and around the wheel should be removed before, during and after dressing.

(e) Nonsparking tools are recommended when making repairs or adjustments around grinding wheels, hoods or collector units where magnesium dust may. be present.

(f) Dust collection equipment shall not have filters or other ob- structions that will allow accumulation of dust.

(g) Sludge pits shall be arranged so as to be well ventilated at all times.

(h) In the grinding of chrome-pickled magnesium surfaces, special precautions should be taken to guard against accumulations of dust or formation of explosive concentrations of dust and air within range of the sparks which may be produced.

218 MACHINING AND FABRICATION 48-15

33. Drawing, Spinning and Stamping 331. The heating of magnesium for drawing or spinning should

provide for reliable means to prevent overheating.

3:$2. Clippings and trimmings should be collected at frequent intervals and placed in clean, dry, steel or other noncombustible containers. Fine particles should be handled in accordance with Article 42.

34. Welding :$41. The molten ma nesium forming the bead during welding

would oxidize heavily o g ignite if allowed to contact the air. This bead is protected by a flow of argon or helium gas that sweeps the air away until the metal temperature drops below the melting point. Proper welding procedures prevent ignition.

~--16 MAGNESIUM 219

C H A P T E R 4. H A N D L I N G A N D D I S P O S A L O F S C R A P

41. Dust C o l l e c t o r Sludge

411. S ludge from dust separa tors and v a c u u m c lean ing uni t pre- cipitators should be removed da i ly or as often as condi t ions war ran t . Covered vented steel containers , p referab ly of not over fifty pounds capacity each, should be used to t r anspor t the collected sludge to a salve point for disposal by a p p r o v e d methods. An excess of wate r shall be m a i n t a i n e d a t all t imes.

NoTs 1: Sludge should be burned in a segregated area at a safe dis- tance from combustible material. The burning area may be a layer of fire brick or hard burned paving brick with sufficient slope to permit it to drain properly. The wet sludge should be spread in a layer three or four inches thick. Damp magnesium sludge is more flammable than dried sludge, therefore caution must be exercised in ignition. Ordinary burnable refuse is placed over the wet grinding sludge and ignited. The burning refuse supplies enough heat to ignite the top surface of the sludge and the entire pile burns rapidly.

NOTE 2: Sludge can be burned in an incinerator. A suitable type is shown in Figure 3. This size unit will handle up to a five gallon pail of wet sludge at a time. Excess water is drained offthe top of the can and

36 INCH D I A M E T E R ( , ~ P E N TOP

REFRACTORY - L I DOOR - 2 0 ~ VENTED

4 INCH REFRACTORY L I N I N G BOTTOM AND SIDES - PLIBRICO KL OR E Q U I V A L E N T

Figure 3

, 4 8 INCH HIGH I0 GAGE STEEL S H E L L

~ S L U G

EMOTE V A L V E

BLOCK MAXON T - 2 2 OR E Q U I V A L E N T

220 SCRAP HANDLING, DISPOSAL

in cold weather wood sawdust is added to absorb moisture before dump. ing into the incinerator. The gas burner is ignited" by remote control and is left on until the magnesium is consumed. The hot magnesium oxide residue should be removed after each batch is burned to prevent ,acci- dental preignition.

NOTE 3: Magnesium sludge may be rendered chemically inactive +, and noncombustible by reac,ting it with a 5 percent solution of ferrous

chloride (FeCI~'2HzO). The reaction takes place with the evolution of hydrogen, at such a rate that the magnesium fines'are changed in less than 24 hours to magnesium hydroxide and magnesium chloride to such an ex-

tent that the residue will not burn. Since hydrogen is generated by the re- action, the process should be carried out in an open container placed ,out- side in such a location that natural air movement will prevent dangerous accumulation of hydrogen. Open flames and smoking shouldbe prohibited in the immediate vicinity of the process. The amount of FeCI~'2H20 re- quired to carry out the decomposition is approximately 0.6 pound for each pound of magnesium fines (dry weight). The amount of water in the sludge should be considered in determining the weight of the magnesium fines., Exact concentrations should be determined on the b~is of the type of fines being handled. The cycle can be repeated daily in the same con- tainer until the amount of the brown, damp residue is such:that the container should be cleaned out. To be certain of complete reaction, a sample of the residue should be heated with a Bunsen burner or oxyacetylene torch to determine ff it can be ignited: While the method is simple, it should be operated under strict technical supervision to avoid disposal-on a dump of partially reacted magnesium.

NOTE 4: WA~L~O: It is essential that all drums or pails used to con- thin magnesium sludge wet with water be adequately vented. Vent holes in the cover will permit escape of hydrogen generated within the container, An excess of water shall be maintained at all times to keep the sludge from partially drying, resulting in spontaneous heating and increased reaction rate. This heat can lead to spontanesous ignition at a critical moisture level and possible exlblosion.

42. Chips, Turnings and Sawings

421. Chips, turnings and other magnes ium fines should be re- moved from the pans under machines and from any other places where they collect at such frequent intervals as may he needed to prevent the accumula t ion of any large amount , and a lways at the end of each day 's work.

424. Magnes ium fines should be placed in covered, plainly labeled, clean, d ry , steel or other noncombus t ib le :con ta iners and r emoved to a detached scrap storage bui ld ing or to a special scrap storage roiJm of fire-resistive construct ion for subsequent" 'salvage.

• I

423. Magnes ium fines which are not be ing salvaged Shouid be disposed of by bu rn ing in thin layers at a safe location where sur- round ing combust ible material will not be i g n i t e d . . ,

424. Magnes ium fines which are to be recovered sl~oulcl be kept free of all foreign matter except neut ra l mineral oils.

~ - ' 1 8 MAGNESIUM 221

425. If magnesium fines havebeen wet with coolants other than aeutral minei'al oils they should be handled with special care and stored preferably outdoors. ,

NOTE 1: Fines, .wet with water, water-soluble oils and oils containing more than 0.2 percent fatty acids may generate flammable hydrogen gas. Fines wet with animal or vegetable oils may ignite spontaneously.

426- Magnesium chips or turnings, wet or damp with water, present a definite fire and explosion hazard when attempts are made to melt or process them in foundry operations. If chips or turnings are included with scrap to be remelted, special precautions must be taken to insure that the mixture is free of moisture or water- oil emulsion. It is impractical to dry wet chips and turnings.

43. Clippings and Castings

431. Solid magnesium scrap such as clippings and castings can be readily salvaged by secondary metal smelters. Pending salvage, the scrap should not be contaminated with combustible materials as a fire in wood, heavy cardboard or flammable liquids could ignite thin sections of the solid metal.

432. Care should be taken to see that no pieces of scrap that are moist are thrown into a salvage pot containing molten metal. Such moisture may result from outdoor storage or by Collection of condensate during indoor storage. The scrap should be preheated prior to melting to prevent a metal-water explosion.

44. Radioactive Scrap

441. Some magnesiu/n scrap may be known to contain thorium. (See 133.) Tests have been run to determine the distribfition of the thorium arid decay products under actual fire conditions which exist in the burning of chips and turnings. The thorium remains essentially in the ashes. Decay products such as radium 224 and lead 212 have been detected only in the visible fumes and then only in concentrations below the current AEC limits for the air- borne material. One should not purposely breathe the fumes from such a fire continuously but some inhalation of the fumes 'up to normal limits of t ime for ordinary smoke intake could be tolerated by the fireman with no adverse effects from the low levels of the radioactive materials presenL

442. Since the thorium content of the ashes increases to about 10-20 percent as thorium dioxide, the ashes should be handled.as thorium waste in accordance with the AEC Standards for Protection Against Radiat ion 10CFR Part 20. This information is in the hands of all licensed users of thorium. One should not be concerned with

222 STORAGE 48-19

external radiation from the thorium in the ashes even though it is higher than that of the original alloy. The level is still low enough to permit simple removal of the ashes to a metal can using shovels or scoops. If it is necessary to sweep the area, it may be wet down with a water spray first to prevent the formation of a dust cloud.

CHAPTER 5. STORAGE OF MAGNESIUM

51. Storage of Pigs, Ingots and Billets

511. Magnesium pigs, ingots and billets are not easily ignited but if exposed to fire of sufficient intensity they will burn.

512. Good storage arrangement is important. The size of piles should be limited and aisle widths should be based on the height ot the piles.

513.. YARD STORAGE: In open or yard storage magnesium ingots should be carefully piled on firm and approximately level areas to- prevent tilting or toppling. Storage areas and yard pavements should be well drained and no combustible flooring or supports should be used under the piles. The area should be kept free of grass and weeds.

(a) The quantity stored in one pile should be kept to a minimum but in no event should the amount in one pile exceed 1,000,000 pounds. Aisle widths should be not less than one-half the height of piles; aisle widths equal to the height of piles are recommendecL Readily combustible material should not be stored within 10 fe~ of any pile of magnesium ingots and accumulations of trash should not be burned near the magnesium storage area. Ati open space equal to the height of piles plus 10 feet should be provided between the stored magnesium ingots and adjoining property lines where combustible material or buildings are exposed or where the ad- jacent occupancy may provide fire exposure to the magnesium.

~-~20 MAGNESIUM 223

~14. BUILDING STORAGE: Storage in noncombustible buildings is preferable. Floors of buildings used for magnesium ingot storage and supports used under piles of magnesium ingots should be non- cor~bust}ble. Floors should be well drained to prevent the accumu- lation ox any water in puddles or pools. Magnesium ingot storage shoUlO be restricted to the first or ground floor level and there should be no basement or depression below the magnesium storage into which water and molten metal may flow or fall during a fire. The quantity stored in one pile should be kept to a minimum but in no event should the amount in one pile exceed 500,000 pounds. The same recommendations for width of aisles given for yard storage are applicable to building storage. Where the building is com- bustible or the magnesium storage is exposed by other combustible mater al automatic sprinkler protection should be provided.

52. Storage of Castings

521. HEAVY CASTINGS: (a) Large castings (25 pounds or more) having walls of heavy

cross section (at least ~ inch) may be ignited after some delay when in contact with burning magnesium chips or when exposed to fires in ordinary combustible materials.

(b) Buildings used for the storage of magnesium castings should preferably be noncombustible, with particular attention given to the construction and maintenance of floors. Single-story storage buildings with well-drained noncombustible floors are recom- mended. There should be no basement or depression below the magnesium storage into which water and molten metal may flow or fall during a fire.

(c) It is desirable to inspect all magnesium castings prior to storage to see that they are clean and free from chips or fine par- ticles of magnesium.

(d) The size of storage piles of heavy magnesium castings either in cartons or crates or free of any packing material should be limited to 1,250 cubic feet. Proper aisles should be maintained to permit inspection and effective use of fire protection equipment. Aisle widths should be not less than one-half the height of the piles; aisle widths equal to the height of the piles are recommended.

(e) When the building in which magnesium castings are stored is of combustible construction or cartons, crates and other com- bustible packing material around the castings constitute a fire hazard, automatic sprinkler protection is recommended.

522. LIGHT CASTINGS: (a) Light castings, particularly in large quantities, should be

224 I STORAGE

stored in noncombustible buildings. Segregated storage is desirabl~- because a slow burning fire in nearby combustible material rna~ develop enough heat to ignite thin-section magnesium, producin~ a well-started magnesium fire before' the operation of automati~ sprinklers. Special importance attaches to prompt fire detectio~ and alarm service, prompt sprinkler operation, and the avoidance of obstructions to sprinkler distribution which would permit corn. bustible materials to continue to burn under sprinkler discharge and result in ignition of magnesium~ . . . . .

(b) Piles of stored light magnesium castingsceither in cartons or' crates or without packing, should be limited in size to 1,000 cubic feet. Light castings should be segregated from other combustible 'materials in so far as possible, and kept away from.flames or sources of heat capable of causing ignition.

(c) Recommendations for aisle widths and fire protection where'~ heavy castings are stored are generally applicable for light casting, storage.

53. Storage in •Mills, Warehouses and Processings Plants

' 531. Buildings used for storage of m~tgnesium should preferablt be nonconabustible, with particular attentiori given to constructio~ and maintenance of floors. Single-story storage buildings with well. drained noncombustible floors and without basements or depressior~ are recommended.

532. Magnesium should not be stored in a basement or simil~ subgrade space because of the difficulty of venting and relieving explosion pressure produced by contact of molten metal with watt. Storage over such spaces is likewise not advisable.

533. Stocks of magnesium should 'be stored separately fron ' storage of combustible materials.

534. The size of storage piles of heavy magnesium castin~ forgings, bars, rods and plates (25 pounds or more) should be limited to 1,250 cubic feet, and piles of light castings, structural shape, sheets and sub-assemblies to 1,000 cubic feet. Proper aisles should be maintained to permit inspection and effective use of fire protee. tion equipment. Aisle widths should be not less than one-half the height of piles; aisle widths equal to the height of piles are recoa. mended.

535. Combustible packing materials should be removed pile to stock storage whenever practicable.

536. When the storage area or preferably the whole buildinl is protected by automatic sprinklers the volume of vari6us fore

48-22 MAGNESIUM 225

of magnesium described in Section 534 may be increased to 4,000 cubic feet. Original shipping cartons, crates or skids need not be removed. Standard packaging of finished products is .permissible. Recommended aisle widths should be maintained. Clearance from sprinklers shall be as required for highly combustible material in the Standard for the Installation of Sprinkler Systems, NFPA No. 13.

537. WAREHOUSES: (a) In a metal distributor warehouse extruded shapes including

barS and rods are normally stored 'on long open metal racks with metal dividers t o facilitate order processing. These racks 'may ex- tend along a noncombustible wall at the rear with the length optionalprovided aisle space in front of the racks is equal to the height ol the piles. This aisle space should be kept clear. Com- bustible packaging such as dry or oiled paper .wrapping or card- board cartons should be removed prior to storage. When sheet and plate products are stored on similar racks, paper or cardboard wrapping should be removed but wood crates or skids and sheet separators may be left in place.

(b) Combustible rubbish, spare crate§ and separators should not be permitted to accumulate within the rack space. Separators and metal sheets should not be stacked on edge, leaning against the racks as they prevent heat from a small fire from reaching auto- matic sprinklers and act as shields if sprinklers are actuated.

(c) Aluminum sheets should not be stored in the piles of mag- nesium. Prolonged contact at heat treating temperatures resulting from an internal fire may yield a readily ignited magnesium- aluminum compound. .

538. Chips (a) Prime (commercially pure) magnesium chips and fines are

commonly used in large quantity in Grignard and other chemical reactions. These chips are completely free of contaminants such as oils and are not subject to spontaneous ignition. Shipping and storfige containers include fiberpaks, 4-ply paper bags and 15oly- ethylene bags.

(b) Where prime chips are produced, shipped (by carload) and stored for chemical or metallurgical process purposes the con- ditions of handling and storage are such that a fire is unlikely. All other combustibles should be excluded from the storage area. Warehouses should be of noncombustible construction.

(c) While water should not be applied to a large chip fire, auto- matic sprinklers would be valuable in confining or extinguishing an incipient fire in packaging and small amounts of chips provided detection and water release were rapid.

(d ) Prime chips are delivered in drum lots or truckload or car-

226 STORAGE 4~-~2~

load quantities. The amount to' be held in storage must be de. termined in individual cases based on purchase value and maxi. mum probable loss.

4 ,

54. Storage of Scrap

541. "MAGNESIUM FINES: (a) This section applies, to the storage of magnesium fines in

the form of chips, turnings or other fine particles. (b) Magnesium fines should be kept well separated from other

combustible materials. They should preferably be kept in covered steel ~or other noncombustible containers, and should always be kept in such manner or location.that they . will riot become wet.

(c) Storage in quantity.greater than 50 cubic feet of fine mag- • nesium scrap (six 55-gallon steel drums) should be separated from other occupancies by fire-resistive construction without window openings or by an open space of at least 50 feet. Such buildings should have explosion vents equivalen t to thin glass windows or skylights of area at least equal to one .square foot to each 15 cubic feet of room volume. " ~..

(d) Storage in quantity greater than 1,000, cubic feet should be separated from all buildings other than those used for magnesium scrap recovery operations by a distance of not less than 100 feet.

"' 542. SOLID SCRAP: (a) Solid magnesiumscrap such as clippings and castings should

be stored in noncombustible bins or containers pending salvage. The" storage building should be of noncombustible construction and automatic sprinklers are recommended. The danger of ignition of this solid scrap is virtually nil provided combustible materials are not-stored with it. Oily rags,, packing materials and similar com- bustibles should not be permitted in the storage bins.

543. SECONDARY SMELTING OPERATIONS: (a) Scrap magnesium is usually received by secondary smelters

in truck or carload quantities. Solid scrap may be shipped loose but chips and turnings are packed in multiply oil proof paper bags or covered steel drums. This scrap is commonly ̀ stored outdoors, in a paved area and is covered with tarpaulins to avoid contact with water. Such scrap is ordinarily processed quite promptly so there is no need for a storage building. Since the storage is in the open incipient fires can be readily observed and extinguished.

55. Storage of Finished Articles

531. This article applies to the storage in warehouses,:/vholesale

48-24 MAGNESIUM 227

and retail stores of magnesium in the form .of finished articles in which magnesium makes up the major portion of the article meas- ured volumetrically.

552. Storage in quantity greater than 50 cubic feet should be separated from storage of other materials that are either combustible

o or in combustible containers; by, aisles equal in width to not less than the height of the piles of magnesium parts.

553. Magnesium articles stored in quantity greater than 1,000 cubic feet shall be separated into piles each not larger than 1,000 cubic feet with aisles between equal in width to no~ less than the height of the piles.

554. Where storage in quantity greater than 1,000 cubic feet is in a building of combustible c'onstruction, or the magnesium is packed in combustible crates or cartons, or there is other com- bustible storage within 30 feet of the magnesium," the. storage area, and preferably the entire building, should be protected by auto- matic sprinklers.

CHAPTER 6. FIRE PROTECTION

61. Precautions

611. Fire protection should be provided in all areas where mag- nesium is melted, machined, fabricated or stored. Magnesium fires are easily extinguished if attacked with the proper agents during the early stages. Agents that accelerate the fire must be avoided. These include water (on chip fires), foam; carbon dioxide, vaporizing liquids, dry chemical and powders containing mono- or diammonium phosphate (ABC type).

612. The flame temperature of burning magnesium is approxi- mately 7200 ° F. Direct contact of clothing, shoes or skin must be avoided. However, the heat of combustion is only half that of petroleum products and unless abused, the fire can be approached closely during extinguishment. .

2,28 FIRE PROTECTION 48--25

62. Extinguishing Agents 621. EXTINGUISHING POWDERS"

• (a) A supply of approved extinguishing powder for magnesium fires should be kept within easy reach of every operator performing a machining, grinding or other operation on magnesium. The powder should be kept in substantial containers with easily re- movable covers and a hand scoop provided at each container for applying the powder. Approved extinguisher units designed for use with these powders may replace the scoop and container.

(b) The amount of extinguishing powder needed will depend on the amount of chips or turnings involved. An ample supply should be provided to control any possible fire situation. Where conditions may permit the development of a fire requiring a large quantity of powder it should be provided in suitable containers, and long-handled shovels provided for its application. Heat- resistant gloves and face guards Should be available for protection of the personnel applying the powder.

(c) Containers of extinguishing powder for magnesium fires should be plainly labeled.

(d) The recommended method oi applying powder is to make a ring around the fire with the powder to contain the fire and then to spread the powder evenly over the surface of the fire to a depth sufficient to smother the fire. Care should be taken to avoid scatter- ~ng the burning metal. If smoking continues in spots more powder may be added as required. Where the burning metal is on a com- bustible surface the fire should be first covered with powder, then a one- or two-inch layer of powder spread out nearby and the burning metal shoveled onto this layer, with more powder added as needed.

622. FOUNDRY FLUX: Fires in foundry melting rooms or pour- ing areas may develop from leaking pots in furnace settings or mold breakage. The most effective means of extinguishing the resulting molten magnesium fire is by application of the readily available foundry melting flux. The flux melts or crusts over the hot metal, excluding air from the burning surface.

623. CAST IRON CHIPS: Clean cast-iron borings'or turnings ap- plied over a magnesium chip fire cool the hot metal and smother the fire. Oxidized iron should not be used due to a possible thermite reaction with the burning magnesium. The cast-iron chips should also be free from moisture such as condensate.

624. WATER" (a) Small streams of water from portable" extinguishers will

violently accelerate a magnesium chip fire. Water should not be

~--26 MAGNESIUM 7;29

used on any large chip fire since it is impossible to provide enough coolant to handle the large area of burning metal. A few burning chips can be extinguished by dropping into a bucket of water and automatic sprinklers will extinguish a typical shop fire where quantities of chips are limited.

(b) Burning parts including castings; wrought products and fabricated structures can be cooled, a n d extinguished with coarse streams of water applied with standard fire hoses. A straight stream scatters the fire, but coarse drops produced by a fixed nozzle op- erating at a distance or by use of an adjustable nozzle, flow over and cool the unburned metal. The. hose .streams are then worked into the fire where some temporary acceleration takes place, fol- lowed by rapid extinguishment, as water application is continued. Well-advanced fires in several hundred pounds" of magnesium solid scrap have been extinguished in less than one minute with two 1N-inch fire hoses. Waterfog tends to accelerate such a fire more than cool it.

(c) Application of water to magnesium fires where quantities ~ molten metal are likely to be present should be "avoided. The steam formation and possible metalrwater reactions may be explosiue.

(d) With the exercise of care , to keep water from reaching molten metal, water spray applied with caution can be used safely to fight fires in combustible material in the vicinity of melting pots.

625. AuToMATIC SPRINKLERS: (a) When the building in whic h, magnesium castings are stored

or processed is of combustible construction, or cartons, crates or other combustible packing matel:ials around ,the castings constitute a fire hazard, automatic sprinkler protection is recommended.

(b) Special importance, attaches t o pi'ompt fire detection and alarm service, prompt sprinkler operation, and tile avoidance of obstructions to sprinkler distribution which would_ permit com- bustible materials to continue to burn under sprinkler discharge and result in ignition of magnesium.

(c) Substantially constructed tight tote boxes (,with or without covers) have considerable confining effect on the burriing of small magnesium parts therein. This confining effect makes the use of such tote boxes of definite value in the control of magnesium fires by sprinklers. Noncombustible tote boxes are prefei'red. Tote boxes should not be used as containers for chips or dust. Such material should be l~laced in covered steel or other nonc0mbustible-drums.

(d) In general, automatic sprinkler-installations are recom- mended in all buildings where magnesium is machined, fabricated or stored, particularly-if combustible solids, flammable liquids or gases are present-. Foundry. operations should also be protected

230 FIRE PROTECTION ~ 48--27

except that there should not be any sprinkler heads over melting pots, die casting machines or heat treating furnaces. Buildings housing such operations, however, should be of noncombustible or fire-resistive construction.

6 2 6 . HEAT TREATING FURNACES: ..

(a) Magnesium fires in heat treating furnaces can best be con- trolled with proprietary powders, melting fluxes or gases approved for use on such fires.

(b) If powder is used, burning metal should where feasible be removed from the furnace before application of the powder. Melt- ing fluxes may be successfully applied to the burning metal in the furnace, excluding air from the metal surface: • (c) If gas is to be used, entry ports should be provided in the furnace at a low point, preferably .down near the fl6or level. Ex- perience indicates that boron trifluoride gas (BFa) is an effective extinguishing agent for small magnesium fires in heat treating furnaces at conc6nti:ations as low as 0.04 percent in the presence of normal air. The cylinder or cylinders (containing about 60 pounds of BFs) may be permanently connected to the furnace or may be mounted on a suitable buggy for transportation to the furnace when needed. No heat is required to expel the gas from the cylinder. The tanks of BF3 may be equipped with Monel needle valves, flexible bronze or teflon hose for distribution and ¼-inch black iron pipe for insertion into the furnace. This system a t 30. psi will discharge about 2 pounds per minute.

(d) When a fire in "a heat ~ treating' furnace is discovered, the power, f u e l a n d sulfur dioxide feed lines should be shut off im- mediately and the BFs'cylinder connected to the entry port if the installation is not permanent. The valve on the BF~ c),linder is then,opened enough to supply about 2 pounds per minute (depend- ing upon the size of the furnace and number of cylinders employed). The furnace-circulating fans should be turned on for about one minute while the BFs is flowing into the furnace, providing good distribution of the gas. Subsequently, the gas flow should be main- tained until the temperature drops to about 700 ° F., indicating that the fire has been extinguished. All cylinders of BF~ installed for furnace fire protection should be weighed at intervals not ex- ceeding 6 months to check the contents.

(e) Tests of several years' duration in which animals were ex- posed to various concentrations of air-borne boron trifluoride have indicated no injury at or below 2-3 ppm. "The recommended in- dustrial hygiene standard based on these tests is 1 ppm for continuous exposure of personnel on a normal 40-hour work week. At these levels, the boron trifluoride has rather poor warning properties and

48-28 MAGNESIUM 23 :

detection must be made with air sampling devices. While higher concentrations (5-10 ppm) are experienced in the vicinity of the heat treating furnace during fire control, the time the operator or fire fighter is in the area is short enough to prevent overexposure. The operator should wear 'an acid or a Type N filter-canister mask or self-contained breathing apparatus to avoid the slight irritating effect of the vapors. Under the conditions of use and concentration in fire fighting, boron trifluoride gives good warning through the presence of a white cloud in the air. ,Contrary to expectations, hydrofluoric acid is not a breakdown product. '

(f) Boron trichloride gas (BCI3) has previously been used to sup- press magnesium fires in heat treating furnaces. How.ever, the re- quireo gas concentration- m air is about ten umes that ot t~oron trifluoride. To assure a.good flow of BCI3 gas, means must be pro- vided to heat the cylinder to a temperature above 54 ° F. and pref- erably to about 70°F . The suppliers of the gas do not approve of heating the cylinders. A special valve and gage is required to control the flow of gas ~from the cylinder. Flexible ~ - i n c h (internal diameter) neoprene hose may be used to conduct the gas from the cylinder to the connection at the entry port. Operations in han- dling a furnace fire ~ire similar to those described for boron tri- fluoride.

(g) Boron trichloride fume~ are irritating and considered similar to hydrochloric acid fumes as a health hazard. When using BCIa, adequate ventilation should be provided and suitable breathing equipment should be available.

(h) If the heat treating furnace fire includes more than several hundred pounds of magnesium parts, is well advanced prior to discovery, involves a large pool of molten metal on the floor of the furnace, or is in a furnace with excessive air leaks, these gases can- not be expected to extinguish the fire completely. However, both BFs and BCIs are valuable in slowing or suppressing the fireuntii it can be extinguished with melting flux . . . .

(i) Water m a y be used to fight fire in combustible material nearby but must not be used in fighting fi/'e in the furnaces.

(j) Where automatic sprinkler protection is provided, a de- flecting shield or hood shall be provided over the furnace or the sprinkler heads over the furnace shall be removed and the ceiling or roof construction modified to be either noncombustible or fire- resistive.