Hazardous Materials

Although elemental aluminum is stable in the form of foil and sheets, alu :, and powder are pyrophoric materials that pose the risk of fire and explosion ~~tun dust num burns violently in air with an intensely bright, white and orange flame · e alutni. mixture of aluminum oxide and aluminum nitride. producing a

4Al(s) + 30z(g) 2Al203(s) Alnminum Oxygen Aluminum oxide

2Al (s) + N2(g) 2AIN(s) Aluminum Nitrogen Aluminum nitride

These reactions may be initiated by the combustion of hydrogen, produced when th and powder react with atmospheric moisture. e dust

2Al(s) + 3H20(/) Al203(s) + 3H2(g) Aluminum Water Aluminum oxide

Hydrogen

Powdered aluminum burns spontaneously on contact with liquid oxygen. Ahunin oxide is the sole product of combustion. UJn

The reactivity of aluminum powder is put to use in the formulations of many fir _ ~arks, i~ whic~ the metal, when activated, burns to pro~uce a bri_lliant disp~ay of oran:e light. It is also mcorporated into certain paints and varmshes for its decorative and heat- reflective features; but consideration must be given to their use, because these coatings may behave as flammable solids once the paint solvent has evaporated. Aluminum pow- der is also a component of solid rocket fuels, in which it is mixed with ammonium nitrate and ammonium perchlorate. The mixture of powdered aluminum and ammonium nitrate is an explosive called ammonal.

The catastrophe of the German dirigible Hindenburg may have been linked with the combustion of aluminum powder. The exterior surface of the dirigible consisted. of a cloth cover impregnated with a doping mixture of aluminum powder and ferric oxide. The presence of aluminum powder provided a surface having high reflectivity. The cover was intended to serve an important purpose: The aluminum particles reflected heat off the vessel and prevented the hydrogen from expanding. The prevail- ing theory is that the aluminum powder first caught fire at an isolated location, per- haps triggered by static electricity or lightning. Once initiated, the fire then rapidly spread across the entire covering, ultimately igniting the reserves of hydrogen. The resulting inferno consumed the vessel.

In circumstances where the temperature is substantially elevated compared with the norm, even bulk aluminum acts as a fast-burning fuel. The skin of shuttle aircraft, for example, must be armored with heat shielding to protect the shuttle when it reen· ters Earth's atmosphere from outer space, experiencing temperatures in excess of 3000°F (1650°C). If this shielding is pierced in any way, the underlying aluminum becomes superheated. Aluminum melts at 1220°F (660°C) and vaporizes at 4221°F (2327°C). At these temperatures, aluminum fires occur when oxygen is available to support the combustion.

In 2003, the space shuttle Columbia disintegrated on reentry into Earth's atmosphere, killing the seven astronauts onboard. The shuttle was covered with more than 20,000 interlocking ceramic tiles designed to protect the aluminum alloy shell from the heat

0 ~

reentry. Experts who examined debris from the accident wreckage observed droplets 0

aluminum and stainless steel. This observation suggests that the cause of the accident w~s linked with the loss of the thermal protective system on the left wing, especially alo~g its leading edge. Without its protective covering, the underlying aluminum alloy most likelY burned, ultimately destroying the entire shuttle.

322 Chapter 9 Chemistry of Some Water- and Air-Reactive Substances

E IVIETALLIC ZINC 9 3· d · ·1 b • -

5 produce pnman Y Y means of the following two-step thermal process·

z;inC I . . .

11 First, the zinc sulfide ore sphaler,te, or zinc blende, is roasted in air to produce zinc oxide.

2ZnS(s) + 302(g) - 2ZnO(s) + 2S02(g) Zinc sulfide Oxygen Zinc oxide Sulfur dioxide

11 Then, the oxide is reduced with carbon monoxide.

ZnO(s) + CO(g) - Zn (g) + C02(g) Zinc oxide Carbon monoxide Zinc Carbon dioxide

The zinc vapor _produced by the reaction is then distilled, condensed, and cast into ingots. The zinc depos~ts on the walls of the distillation apparatus as a gray, finely divided pow-

d known as zmc dust. er uf . The zinc man acturmg process is complicated by the presence of the metal impuri- ties silver, lead, copper, arsenic, antimony, and manganese, all of which occur naturally in sphalerite. These ~etals are rem?ved by a combination of chemical processes. The manu- facturing process 1s also complicated by the simultaneous production of the pollutant sulfur dioxide (Section 10.12), which must be scrubbed from the off-gas plume generated during the roasting process.

Metallic zinc is used for several purposes. The metal is coated on iron products to protect them from corrosion by the air. This zinc-coated iron is said to be galvanized. Zinc is also used as a component of several alloys; for example, zinc and copper are com- bined in the molten state to produce brass. Metallic zinc is also used in the manufacture of dry-cell batteries and a variety of structural materials. Zinc dust is a component of certain primers and rust-resistant paints.

Zinc is hazardous only as its dust. Especially when it is hot, zinc dust is a pyrophoric material that poses a fire and explosion hazard. It ignites spontaneously in air with a green flame, producing zinc oxide as the sole combustion product.

2Zn(s) + 02(g) 2Zn0(s) Zinc Oxygen Zinc oxide

The reaction may be initiated by the combustion of hydrogen, produced when the dust reacts with atmospheric moisture.

Zn(s) + H20(/) ZnO(s) + H2(g) Zinc Water Zinc oxide Hydrogen

9.3-F TRANSPORTING COMBUSTIBLE METALS When shippers offer a combustible metal for transportation, DOT requires them to iden- tify the appropriate material on the accompanying shipping paper. Some examples for several representative combustible metals are listed in Table 9.5. DOT also requires ship- pers and carriers to comply with all labeling, marking, and placarding requirements.

When molten aluminum is transported in bulk packaging by highway or rail, DOT requires carriers at 49 C.F.R. § 172.325 to mark the packaging with the expression MOLTEN ALUMINUM and the identification number 9260 on orange panels, white square-on-point diamonds, or HOT markings. The following examples illustrate the nature of these markings:

Zinc metal powder/dust

galvanize The process of coating a metal with a protective layer of elemental zinc

Chapter 9 Chemistry of Some Water- and Air-Reactive Substances 323

TABLE 9.5

COMBUSTIBLE METALS SHIPPING DESCRIPTION Aluminum, molten NA9260, Aluminum, molten, 9, PG I

Aluminum powder UN1309, Aluminum powder, coated, 4.1, PG 11 or UN1396, Aluminum powder, uncoated, 4.3, PG 11 (Dan

Magnesium (with more than 50% magnesium in pellets turnings, or ribbons) '

UN1869, Magnesium, 4.1, PG Ill

Magnesium alloys (with more than 50% magnesium in UN1869, Magnesium alloys, 4.1, PG Ill pellets, turnings, or ribbons)

Magnesium granules (particle size not less than 149 microns) UN2950, Magnesium granules, coated, 4.3, PG Ill (Dan When Wet) Qerous

Magnesium powder UN1418, Magnesium powder, 4.3, (4.2), PG I (Dangerous When Wet) or UN1418, Magnesium powder, 4.3, (4.2), PG 11 (Dangerous When Wet) or UN1418, Magnesium powder, 4.3, (4.2), PG 111 (Dangerous When Wet) -Titanium powder UN2546, Titanium powder, dry, 4.2, PG I

Titanium (powder), wetted with not less than 25% water UN1352, Titanium powder, wetted, 4.1, PG II (a visible excess of water must be present) (a) mechanically produced, particle size less than 53 microns; (b) chemically produced, particle size less than 840 microns

Titanium sponge granules UN2878, Titanium sponge granules, 4.1, PG Ill

Titanium sponge powders UN2878, Titanium sponge powders, 4.1, PG Ill

Zinc dust UN1436, Zinc dust, 4.3, (4.2), PG I (Dangerous When Wet)

Zinc powder UN1436, Zinc powder 4.3, (4.2), PG I (Dangerous When Wet)

Zirconium, dry (finished sheets, strip, or coil wire) UN2008, Zirconium, dry, 4.1 PG Ill

Zirconium powder, wetted with not more than 25% water UN1358, Zirconium powder, wetted, 4.1, PG II [(a visible excess of water must be present) (a) mechanically produced, particle size less than 53 microns; (b) chemically

· m'crons produced, particle size less than 840 1

9.4 ALUMINUM ALKYL COMPOUNDS AND THEIR DERIVATIVES

aluminum alkyl • A compound whose molecules are composed of an aluminum atom covalently bonded to three carbon atoms, each of which is a component of an

Organometallic substances are compounds whose molecules have one or more metal atoms covalently bonded directly to a nonmetal atom. Examples of organometallic sub· stances include the aluminum alkyls, whose molecules have an aluminum atom covalently bonded to three carbon atoms. An example of an aluminum alkyl compound is triethyl- aluminum, whose chemical formula is Al(CH2CH3)J, or Al(C2H5)).

alkyl group

CH2CH3 I

CH3CH2 - Al-CH2CH3 Triethylaluminum

(TEA)

324 Chapter 9 Chemistry of Some Water- and Air-Reactive Substances

is instance, the ~lkyl grou~ is na~ed ethyl, which has the formula -CH2CH3. In the Jo th ical industr~, tnethY1alummum is often designated as TEA. Its properties are repre- chern ·ve of aluminum alkyl compounds. eorau · I r ps of I · lk I I h I'd s rwo specia g ou . a ummum a yl compounds are the aluminum a ky a es

JUJllinum alkyl hydrides. These compounds are the halide and hydride derivatives aod t JJJinum alkyl compounds, respectively, in which one or two halide or hydrogen of au substitute for an alkyl group. Examples of these derivatives are diethylaluminum at0~:de and diisobutylaluminum hydride, whose formulas are (C2H5 )zAICI and chi~ ) cHCH2]zAIH, respectively. [(CP 3 2

Cl H I I

CH3CH2-Al - CH2CH3 (CH3)zCHCH2-AI - CH2CH(CH3h Diethylaluminum chloride Diisobutylaluminum hydride

(DEAC) (DIBAH)

The alkyl group having the formula _(CH3)zCHCH2- is named isobutyl. In the che1?ical . dustrY, these compou?ds are sometimes designated as DEAC and DIBAH, respectively. ;~ this section, we consider them as representative of the halide and hydride derivatives of all aluminum alkyl ~ompounds. . .

Table 9.6 provides some physical properties of triethylaluminum, diethylalununum hloride, and diisobutylaluminum hydride. Chemical manufacturers display the flame

;icrogram on la_bel~ affixed to containers holding the aluminum alkyls and their halide and hydride derivatives.

g,4-A COMMERCIAL USES OF THE ALUMINUM ALKYL COMPOUNDS AND THEIR DERIVATIVES

The aluminum alkyls are used by the chemical industry primarily as polymerization cata- lysts, one of which is a mixture of titanium(IV) chloride and an aluminum alkyl. It is called a Ziegler-Natta catalyst, after Karl Ziegler and Giulio Natta, the chemists who first discovered its catalytic capability. Aluminum alkyl halides and aluminum alkyl hydrides are also primarily used as catalysts in the chemical industry.

Aluminum alkyl compounds have also been used by the military, albeit rarely, as incendiary agents. For example, triethylaluminum has been used as the active component in flamethrowers. Trimethylaluminum has also been used to produce luminous trails in the upper atmosphere for tracking the location of rockets.

Physical Properties of an Aluminum Alkyl Compound TABLE 9.G and Two Metal Alkyl Derivatives

Melting point Boiling point

Specific gravity Vapor pressure Flashpoint

Autoignition temperature 'At 3 mmHg (0.3 kPa). bAt 68'F (20'C). 'At 77'F (25'C).

TRIETHYLALUMINUM

-62°F (-52°C)

367°F (186°C)

0.837b

0.0147 mmHgb

-63°F (-53°C)

Spontaneously flammable in air

DIETHYLALUMINUM DIISOBUTYLALUMINUM CHLORIDE HYDRIDE

-121 °F (-85°C) -112°F (-80°C)

417°F (214°C) 237°F (114°C)a

0.961' 0.798'

0.17 mmHg'

-9.4°F (-23°C)

Spontaneously Spontaneously flammable in air flammable in air

Triethyl- aluminum

Ziegler-Natta catalyst Any of a group of

compounds produced from titanium tetrachloride and an aluminum alkyl compound that is used mainly as a catalyst

Chapter 9 Chemistry of Some Water- and Air-Reactive Substances 325

I /I : I

I I I I I I/ I I Ill

i I I I

111 I I

I I

9 .4-B PROPERTIES OF THE ALUMINUM ALKYL COMPOUNos A THEIR DERIVATIVES "'~[)

The aluminum alkyl compounds and their derivatives are spontaneous! b_le, pyrophoric, violently water-reactive, and highly toxic liquids. They y cornbllsr cially available as individual compounds and solutions in which they are~~ comm/ organic solvents. When triethylaluminum, diethylaluminum chloride, and ~~~0 lved t' aluminum hydride spontaneously ignite, their combustion reactions are re lisobllty~ as follows: Presented

2(C2H5)3Al(l) + 2102(g) Al203(s) + 12C02(g) + 15H20(g) Triethylalurninum (TEA) Oxygen Aluminum oxide Carbon dioxide Water

2(C2HshAICl(l) + 1402(g) Al203(s) + 8C02(g) + 9H20(g) + 2BC!(g) Diethylaluminurn chloride (DEAC) Oxygen Aluminum oxide Carbon dioxide Water Hydrogen chloride

2 [(CH3)iCHCH2hAIH(s) + 2702(g) Al203(s) + · I6C02(g) + 19H20 (g) Diisobutylaluminum hydride (DlBAH) Oxygen Al uminum oxide Carbon dioxide Water

When triethylaluminum and diethylaluminum chlor~de react with water, the fl mable gas ethane (Section 12.2) is produced as a hydrolysis product. a111•

Triethylaluminum (TEA) Water Aluminum hydroxide Ethane

Diethylaluminum chloride (DEAC) Water Aluminum hydroxide Ethane Hydrogen chloride

Diisobutylaluminum hydride, however, is a reducing agent. When it reacts with water, the flammable gases isobutene and hydrogen are produced.

Diisobutylaluminum hydride (DIBAH) Oxygen Aluminum hydroxide Isobutene Hydrogen

When water is applied to these reactive substances, the gaseous hydrolysis prod- ucts immediately burst into flame as they are generated. The considerable heat evolved to the environment often triggers secondary fires. Bulk quantities of aluminum alkyl compounds burn so vigorously and persistently that they pose an especially dangerous risk of fire and explosion. The heat of combustion that evolves necessitates that fire- fighters wear special protective gear like the silvers shown in Figure 9.4 when combat· ing these fires. .

To prevent their accidental ignition, the aluminum alkyl compounds and their halide and hydride derivatives often are stored within electrically grounded containers under an atmosphere of nitrogen in a cool, well-ventilated area.

9.4-C TRANSPORTING ALUMINUM ALKYL COMPOUNDS AND THEIR DERIVATIVES

When shippers offer an aluminum alkyl compound or a halide or hydride derivative for tr:· portation, DOT requires them_ to id~ntify it with the proper shipping ~ame, "organomet F.R~ substance," on the accompanymg shipper paper. The Hazardous Materials Table at 49 C. . §172.101 lists several shipping names for organometallic substances. Because triethylal~: num is both water- and air-reactive, its most appropriate shipping description is the followmg.

UN3394, Organometallic substance, liquid, pyrophoric, water-reactive (triethyl- aluminum), 4.2, (4.3), PG I (Dangerous When Wet).

326 Chapter 9 Chemistry of Some Water- and Air-Reactive Substances

FIGURE 9 .4 When responding to fires involving aluminum alkyl compounds and their halide and . hydride derivatives, firefighters should wear special protective clothing such as alum1nized suits tha: reflect heat and provide protection against bodily contact with the reactive substances as they burn . (Courtesy of Lakeland Industries, Inc., Ronkonkoma, New York; Image © 2012, All Rights Reserved.)

FIGURE 9.5 When a carrier transports an alumi- num alkyl compound or its halide or hydride deriva- tive in an amount exceeding 1001 pounds (454 kg), DOT requires SPONTANEOUSLY COMBUSTIBLE and DANGEROUS WHEN WET placards to be displayed on the transport vehicle . AKZX is the reporting mark of AKZO Nobel Chemicals, Inc., Chicago, Illi - nois, a distributor of triethylaluminum and other class 4 compounds.

When transporting aluminum alkyl compounds or their halide or hydride derivatives, shippers and carriers must also comply with all applicable labeling, marking, and placard- ing requirements. Figure 9 .5 illustrates that DOT requires carriers to display DANGER- OUS WHEN WET placards on the bulk packaging used for shipment regardless of the amount transported.

When 387 gallons (829 L) of liquid diisobutylaluminum hydride is transported in a 400-gallon (857-L) portable tank by highway:

(a) What sh ipping description does DOT require the shipper to enter on the accompanying shipping paper? (b) How does DOT require the carrier to placard and mark the tank?

Solution:

(a) There are two regulations in Table 6.2 that are pertinent to preparing the shipping description . First, when a hazardous material is described with a generic description in the Hazardous Materials Table shippers must include the name of the substance in parentheses in the shipping description . Second: when a hazardous material, by chemical interact ion with water, is liable to become spontaneously

Chapter 9 Chemistry of Some Water- and Air-Reactive Substances 327

ionic A compound composed of a metallic ion and a simple or complex hydride ion

Sodium hydride

flammable or give off flammable gases in dangerous quantities, the _w~rds "Dangerous Wh must be included with the shipping description. Consequently, the shipping description of d" en 'Net• luminum hydride is entered on a shipping paper as follows: iisobu~la.

SHIPPING DESCRIPTION (IDENTIFICATION NUMBER, PROPER SHIPPING NAME, PRIMARY HAZARD CLASS OR DIVISION, SUBSIDIARY VOLU••,

_ _:_U::_N.::_IT:_:S:_--1-_.:_H::.:M~___:_::HAZ~ A_R_D_C_LA_S_S_O_R_D-:-IV_I_SI_O--::N,_A-:-:N_D_P_A-;-C-:K_IN_G_G_R_O_UP...:...)-+- (gal)' 1 portable tank x UN3394, Organometallic substance, liquid, pyrophoric, water-reactive 387 (diisobutylaluminum hydride), 4.2, (4.3), PG I (Dangerous When Wet)

(b) Since the amount transported exceeds 1001 pounds, DOT requires carriers to display side b . SPONTANEOUSLY COMBUSTIBLE and a DANGEROUS WHEN WET placard on each side and eac~ side a the cargo tank. Because the tank has a capacity of less than 1 OOO ~allo~s (3785 L), DOT requires t~: ~: mark the tank with the identification number 3394 on two opposing si?es on orange panels, across the center area of the SPONTANEOUSLY COMBUSTIBLE placards, or on white square-on-point diamond I ,

9.5 IONIC HYDRIDES Approximately ten ionic hydrides are encountered commerciall!. T_hey are compounds consisting of metallic ions bonded to simple or complex hydnde ions. Some metallic hydrides are not ionic hydrides. For example, although tin(IV) hydride is a metallic hydride, ·it is composed of molecules. Each molecule consists of a tin atom covalently bonded to four hydrogen atoms. Its chemical formula is S~. ·

Ionic hydrides are used as powerful reducing agents by the chemical industry. They can be classified according to their general chemical composition as simple ionic hydrides, ionic borohydrides, and ionic aluminum hydrides.

9.5-A SIMPLE IONIC HYDRIDES Simple ionic hydrides are compounds consisting of metallic ions bonded to hydride ions (H-). They are lithium hydride, sodium hydride, calcium hydride, magnesium hydride, and aluminum hydride, whose chemical formulas are LiH, NaH, CaH2, MgH2, and AlH3, respectively. They are produced by reactions between the corresponding metal and hydro- gen. For example, sodium hydride is a simple ionic hydride produced by the union of sodium metal and hydrogen.

2Na(s) + H2(g) 2NaH(s) Sodium Hydrogen Sodium hydride

9.5-B IONIC BOROHYDRIDES Ionic borohydrides are ionic hydrides in which metallic ions are bonded to borohydride ions (BH4). The commercially important ionic borohydrides are lithium borohydride, sodium borohydride, and aluminum borohydride, whose chemical formulas are LiBl-Li, NaBH4, and Al(B~ h, respectively. The ionic borohydrides are produced by relatively complex chemical reactions.

9.5-C IONIC ALUMINUM HYDRIDES Ionic alu~inu?1 hydrides are ionic hydrides in which metallic ions are bonded to ahuni· num hydnde ions (A1H4 ). Two commercially import t · · 1 • h drides are 1. h' 1 · h d 'd . an tome a ummum y it mm a ummum y n e and sodium aluminum h d 'd h h . 1 f ulas are . . Y n e, w ose c emica orm . L1Al:I4 and NaAlH4, respe~tlvely. They are produced by reacting the relevant ionic hydnde and anhydrous aluminum chloride (Section 9.S-A).

328 Chapter 9 Chemistry of Some Water- and Air-Reactive Substances

,NATER REACTIVITY OF THE IONIC HYDRIDES 9,S·D h the ionic hydrides are relatively stable compounds they possess several com- I houg f Of . I · ' At hazardous eatures. specia interest here is the fact that they react with water to

f!l00 flammable hydrogen. oduce h . . h . d . pr '[o prevent t e1~ contact wit atmosphenc moisture, all ionic hydrides are store . m

. hrlY sealed containers. When enc?untered commercially, they are often covered with ng I um oil. The presence of the 011 lends an element of safety when handling and stor- etrO e h d h . P them- Howeve~, t _ese compoun s_ are also encountered as ethereal solutions; t _at 1s,

ing are dissolved m diethyl ether, a highly flammable liquid. The combination of diethyl and an io~ic hydri~e po~es the risk of fire and explosion. . . .

'[he following equations illustrate the water reactivity of several representative 1omc hydrides:

LiH(s) + H20 (/) - LiOH(aq) + H2(g) Lithium hydride Water Lithium hydroxide Hydrogen 3NaBH4(s) + 6H20(I) - 3NaB02(aq) + l 2H2(g) Sodium borohydride Water Sodium borate Hydrogen LiAIHi s) + 4H20(l) - Al(OH)3(s) + LiOH(aq) + 4H2(g) Lithium aluminum hydride Water Alumi num hydroxide Lithium hydroxide Hydrogen

Al(BH4)3(s) + 12H20( I) - Al(OH)3(s) + 3H3B03(aq) + 12H2(g) Aluminum borohydride Water Aluminum hydroxide Boric acid Hydrogen As these ionic hydrides react with water, the evolved hydrogen absorbs the heat of reaction and spontaneously bursts into flame.

Because the ionic hydrides are water-reactive substances, precautions should be exer- cised to avoid exposing them to humid air or other potential sources of water. Experts recommend that firefighters use water as a fire extinguisher only when they encounter small spills of these substances.

9.5-E TRANSPORTING IONIC HYDRIDES When shippers offer an ionic hydride for transportation, DOT requires them to provide the appropriate shipping description on the accompanying shipping paper. Table 9.7 provides

TABLE 9.7 Shipping Descriptions of Some Representative Ionic Hydrides

IONIC HYDRIDE SHIPPING DESCRIPTION Aluminum borohydride UN2870, Aluminum borohydride, 4.2, (4.3), PG I (Dangerous When Wet)

or UN2870, Aluminum borohydride in devices, 4.2, (4.3), PG I (Dangerous When Wet)

Calcium hydride UN1404, Calcium hydride, 4.3, PG I (Dangerous When Wet) Lithium aluminum hydride UN1410, Lithium aluminum hydride, 4.3, PG I (Dangerous When Wet) Lithium aluminum hydride dissolved in ether

UN1411, Lithium aluminum hydride, ethereal, 4.3, (3), PG I (Dangerous When Wet)

Lithium borohydride UN1413, Lithium borohydride, 4.3, PG I (Dangerous When Wet) Lithium hydride UN1414, Lithium hydride, 4.3, PG I (Dangerous When Wet) Sodium aluminum hydride UN2835, Sodium aluminum hydride, 4.3, PG II (Dangerous When Wet) Sodium borohydride UN1426, Sodium borohydride, 4.3, PG I (Dangerous When Wet) Sod ium hydride UN1427, Sodium h dride, 4.3, PG I (Dan erous When Wet y g

Sodium borohydride

Lithium aluminum hydride

Chapter 9 Chemistry of Some Wate r- and Air-Reactive Substances 329

metallic phosphide • An inorganic compound composed of metallic and phosphide ions

Calcium phosphide

some representative examples. When the shipping description is not listed at 49 C § 172.101, DOT requires them to identify the commodity generically and include th •P.R. of the specific compound parenthetically. DOT also requires shippers and carriers t: nallle ply with all applicable labeling, marking, and placarding requirements. coll).

9.6 METALLIC PHOSPHIDES Metallic phosphides are produced by combination reactions in which a given metal u . with elemental phosphorus. Calcium phosphide, for example, is formed by heatingnitels . d h h ca. c1um an p osp orus.

Calcium Phosphorus Calcium phosphide

These compounds once were popular fumigants used on grain and other postharve crops, but in the United States, their use is not nearly as po~ular ?ow as it was in the pas:'.

The metallic phosphides function as fumigants by reacting with atmospheric moisture to produce the toxic gas phosphine.

Ca3P2(s) + 6H20(l) 3Ca(OH)2(s) + 2PH3(g) Calcium phosphide Water Calcium hydroxide Phosphine

When calcium phosphide is applied within an enclosure used for the storage of crops, it~ the phosphine produced by hydrolysis that actually kills mice and other unwanted pests.

9.6-A TRANSPORTING METALLIC PHOSPHIDES When shippers offer a metallic phosphide for transportation, DOT requires them to iden- tify the appropriate material on the accompanying shipping paper. Some examples of the shipping descriptions for several representative metallic phosphides are listed in Table 9.8. DOT also requires shippers and carriers to comply with all applicable labeling, marking, ' and placarding requirements.

SOLVED EXERCISE 9.3 What is the most likely reason that DOT requires shippers to affix DANGEROUS WHEN WET and POISON labels to packages of stannic phosphide? Solution: DOT assigns two hazard codes, 4.3 and 6.1, to stannic phosphide because the properties of this sub- stance comply with the defining criteria for both a dangerous-when-wet substance and a poisonous material (Sec· tion 10.1-C). Stannic phosphide is a solid compound that reacts with water to produce phosphine, a flammable and toxic gas.

Stannic phosphide Water Stannic hydroxide Phosphine

When shippers affix DANGEROUS WHEN WET and POISON labels to packages of stannic phosphide, these hazard warning labels quickly inform emergency responders that the substance is simultaneously water-reactive and toxic.

,...,...~ __ ,,,....,,,._,___...,....--!'!l"."!""~ ........ .......... ~~~_,_/

9.6-B PHOSPHINE As noted previously, phosphine is generated when metallic phosphides react with water. This substance possesses the following hazardous features:

Phosphine is a poisonous gas. Toxicity is its primary haz:,ird. The gas may be detected by its exceptionally offensive odor, which has been described as a mixture of garlic and rotten fish. The odor threshold for phosphine is only 0.15 part per million,

Chapter 9 Chemistry of Some Water- and Air-Reactive Substances

rASLE 9.8 Shippi~g Descriptions of Some Representative Metallic Phosphides

MffA LLIC PHOSPHIDE SHIPPING DESCRIPTION • urn phosphide UN1397, Aluminum phosphide, 4.3, (6.1), PG I (Dangerous

,Alurnin When Wet) (Poison) ---.-:---.--:-:--:--t--_:_:_::..::...::._..:.:='.:!._ _ _______ _ . urn phosphide (pesticides) UN3048, Aluminum phosphide pesticides, 6.1, PG I (Poison) ,Alulllln~.:._s~ ------+ - :....::._.:::...:...=:==.:.:.'....!:'.'..~~~~~~~'..'....:...::...:....'.:...::=-..::.-

calciUrTl phosphide UN1360, Calcium phosphide, 4.3, (6.1), PG I (Dangerous When Wet) (Poison)

Magnesium phosphide UN2011, Magnesium phosphide, 4.3, (6.1), PG I (Dangerous When Wet) (Poison)

potassium phosphide

sodiurn phosphide

UN2012, Potassium phosphide, 4.3, (6.1 ), PG I (Dangerous When Wet) (Poison) UN1432, Sodium phosphide, 4.3, (6.1), PG I (Dangerous When Wet) (Poison)

When inhaled, it primarily attacks the cardiovascular and respiratory systems, causing pulmonary edema (Section 7.3-B) and massive destruction of the lung tissues. Long-term exposure to lesser concentrations causes the bones to soften. Exposure to a concentration of 50 parts per million is immediately dangerous to an individual's life and health.

I Phosphine is also a spontaneously flammable gas. Flammability is considered its secondary risk. Its autoignition temperature is only 100°F (37.8°C), a value readily at- rained in most environments. Phosphine burns in air to produce a dense white cloud of retraphosphorus decoxide and water vapor.

Phosphine Oxygen Tetraphosphorus decoxide Water

We examine the methods recommended for extinguishing fires involving gases that are simultaneously flammable and poisonous in Chapter 10.

9.6-C WORKPLACE REGULATIONS INVOLVING PHOSPHINE When phosphine is present in the workplace, OSHA requires employers to limit employee exposure to a concentration of 0.3 part per million, averaged over the 8-hour workday.

9.6-D TRANSPORTING PHOSPHINE When shippers offer phosphine for transportation, DOT requires them to identify the gas on the accompanying shipping paper as follows:

UN2199, Phosphine, 2.3, (2.1) (Poison - Inhalation Hazard, Zone A)

DOT also requires shippers and carriers to comply with all applicable labeling, marking, and placarding requirements.

9.7 METALLIC CARBIDES Metals bond with carbon to form compounds having either ionic or covalent units. Our concern here is solely with the compounds composed of metallic ions and carbon ions that exist as ct or c4-. They are called metallic carbides. There are only two commer- cially important metallic carbides: aluminum carbide and calcium carbide. Both are water- reactive substances. ·

Phosphine

metallic carbide An inorganic compound composed of metallic and carbide ions

Chapter 9 Chemistry of Some Water- and Air-Reactive Substances 331

I I

Aluminum carbide

Calcium carbide

Anhydrous aluminum chloride

TABLE 9.9 Shipping Descriptions of Metallic Carbides

METALLIC CARBIDE SHIPPING DESCRIPTION

Aluminum carbide Calcium carbide

UN1394, Aluminum carbide, 4.3, PG 11 (Dangerous When Wet) UN1402, Calcium carbide, 4.3, PG I (Dangerous When Wet)

9. 7-A ALUMINUM CARBIDE Aluminum carbide is prepared by heating aluminum oxide wit~ coke in ~n electric fur. nace. It is used as a catalyst by the chemical industry._When alummum carbide reactswitn water, flammable methane is produced as a hydrolysis product.

AJ 4 C

3 (s) + J 2Hz0(/) --+ 4Al(OH)3(s) + 3CH4(g)

Aluminum carbide Water Aluminum hydroxide Methane

Aluminum carbide that has been exposed to humid air poses a flammable and explosive hazard.

9.7-B CALCIUM CARBIDE Calcium carbide is manufactured by heating a mixture of coke and lime at an elevated temperature in an electric furnace.

CaO(s) + 3C(s) - CaC2(s) + CO(g) [t > 3600°F ( l 982°C)] Calcium oxide Carbon Calcium carbide Carbon monoxide

The production process is very energy-intensive. Calcium carbide formerly was used as a raw material for the production of industrial-

grade acetylene.

CaC2(s) + 2Hz0({) - Ca(OH)z(s) + C2H2(g) Calcium carbide Water Calcium hydroxide Acetylene

Today, this method of producing and manufacturing acetylene is used to a very limited extent because it produces a huge amount of calcium hydroxide slag. Although some of this slag is incorporated into cement, acetylene manufacturers often choose to avoid deal· ing with the negative environmental impact altogether.

Because of its water-reactive nature, calcium carbide that has been exposed to humid air poses a flammable and explosive hazard. For this reason, it must be stored and ban· died in a dry environment that is free of ignition sources.

9.7-C TRANSPORTING METALLIC CARBIDES When shippers offer aluminum carbide or calcium carbide for transportation, DOT requires them to identify it as shown in Table 9.9 on the accompanying shipping papet DOT also requires shippers and carriers to comply with all applicable labeling, markmg, and placarding requirements.

9.8 WATER-REACTIVE SUBSTANCES THAT PRODUCE HYDROGEN CHLORIDE

Certain substances react with water to produce hydrogen chloride vapor or hydrochloric acid as products of their hydrolysis. When they are encountered these substances rou· tinely have the suffocating, pungent odor of hydrogen chloride ~hich fumes in air aflcl limits visibility. As first noted in Chapter 8, hydrogen chloride 'is a toxic, irritating gas,

332 Chapter 9 Chemistry of Some Water- and Air-Reactive Substances

d hydr ochloric acid is a corrosive liqui·d. I h" · h h d 1 · d · n t 1s section, t e y ro ys1s pro uct 1s

d~noted solely as hydrogen chloride vapor.

s-A ALUMINUM CHLORIDE, ANHYDROUS 9' 1 . hl "d · Anhydrous a umu~um _c on e is a wh!te-to-yellow solid whose chemical formula is AICl3• In the chemical

1_ndustry su~stantial quantities are used as catalysts and as a raw cerial for the production of aluminum alkyl compounds and lithium aluminum hydride.

(Ila d d . · . also use to pro uce ant1persp1rants. JtlS dr 1 . hl "d AnhY ous a Uffilnum c on e reacts violently with water to produce hydrogen chloride.

2AICl3(s) + 3H20(l) - Ai 20 3(s) + 6HCl(g) Aluminum chloride Water Aluminum oxide Hydrogen chloride

for this reason, the manufacturers and distributors of this substance caution potential users that it irritates the skin, eyes, and respiratory tract.

g,S-8 PHOSPHORUS OXYCHLORIDE Phosphorus oxychloride, also called phosphory/ chloride, is a colorless, fuming liquid whose chemical formula is POCl3. It is used primarily by the chemical industry as a chlo- rinating agent.

Phosphorus oxychloride reacts violently with water to produce hydrogen chloride.

POCl3(l) + 3H20(l) - H 3P04(aq) + 3HCl(g) Phosphorus oxychloride Water Phosphoric acid Hydrogen chloride

9.8-C PHOSPHORUS PENTACHLORIDE This substance is a yellow-to-green solid whose chemical formula is PCl5. It is primarily used as a chlorinating and dehydrating agent by the chemical industry.

Phosphorus pentachloride is decomposed by water in a multistep process, summa- rized in the following equation:

PC15(s) + 4H20(l) H3P04(aq) + 5HCl(g) Phosphorus pentachloride Water Phosphoric acid Hydrogen chloride

9.8-D PHOSPHORUS TRICHLORIDE This substance is a colorless, fuming liquid whose chemical formula is PCl3. It is used in the chemical industry as a chlorinating agent and catalyst. Phosphorus trichloride is used, for example, as a raw material for producing acetyl chloride (Section 9.9-C).

Phosphorus trichloride reacts with water to form phosphorous acid and hydrogen chloride.

Phosphorus trichloride Water Phosphorous acid Hydrogen chloride

9.8-E SILICON TETRACHLORIDE Silicon tetrachloride is a colorless, fuming liquid whose chemical formula is SiC14• It is used as a raw material to manufacture liquid or semisolid silicon-containing polymers known as silicones, substances widely used in electrical insulation. Silicon tetrachloride is also used in the semiconductor manufacturing industry.

Silicon tetrachloride reacts vigorously with water to form silicic acid and hydrogen chloride.

Silicon tetrachloride Water Silicic acid Hydrogen chloride

Phosphorus oxychloride

Phosphorus pentachloride

Chapter 9 Chemistry of Some Water- and Air-Reactive Substances 333

I '

Ii

Phosphorus trichloride

Silicon tetrachloride

silane An organic compound whose molecules are composed of silicon and hydrogen atoms

chlorosilane A chlorinated derivative of silane (SiH4)

9.8-F SULFURYL CHLORIDE Sulfuryl chloride also called su/lony/ chloride, is a colorless liquid whose chemic 1 ' '' · · h h · 1 · d a fo mula is SO?Cl2. Sulfuryl chloride is used mamly mt e c erruca m UStry as a chlorin . r-- a~ and dehydrating agent. . . g

Sulfuryl chloride reacts slowly with water to form sulfuric acid and hyd chloride. rogen

S0 2Ci 2(l) + 2Hz0(/) ---? H2S04Caq) + 2HCl(g) Sulfuryl chloride Water Sulfu ric acid Hydrogen chloride

9.8-G THIONYL CHLORIDE Thionyl chloride is a red-to-yellow liquid whose chemical formula is SOCl2, Thionyl chlo. ride is used mainly within the chemical industry.

Thionyl chloride reacts vigorously with water to form sulfurous acid and hydrogen chloride.

SOCI2(l) + 2H20(l) ---? H2S03(aq) + 2HCl(g) Thionyl chloride Water Sulfurous acid Hydrogen chloride

9.8-H TIN(IV) CHLORIDE, ANHYDROUS Tin(IV) chloride, also known as stannic tetrachloride, is a colorless, fuming liquid whose chemical formula is SnC14. It is used to manufacture blueprint and similarly sensitized types of pa per.

Anhydrous tin(IV) chloride reacts slowly with water to form tin(IV) oxide and hydro- gen chloride.

SnCl4(/) + 2H20(l) ---? Sn02(s) + 4HCl(g) Tin(TV) chloride Water Tin(IV) oxide Hydrogen chloride

9.8-1 TITANIUM(IV) CHLORIDE, ANHYDROUS Titanium(IV) chloride, also called titanium tetrachloride, is a colorless, volatile liquid whose chemical formula is TiCl4. Titanium(IV) chloride is the intermediate compound produced during the production of metallic titanium and the white paint pigment tita- nium dioxide. The mixture of titanium(IV) chloride and an aluminum alkyl compound is an important polymerization catalyst (Section 9.4).

Titanium(IV) chloride reacts slowly with water to produce titanium(IV) dioxide and hydrogen chloride.

TiCl4(/) + 2H20(/) Ti02(s) + 4HCl (g) Titanium(IV) chloride Water Titanium(IV) oxide Hydrogen chloride

9.8-J CHLOROSILANES The hydrides of silicon are called silanes. They consist of a class of compounds having the chemical formula SinH2n+2, where n is a nonzero integer. The simplest silane, itself called si/ane, is a substance having the formula Si~. When one or more of the hydrogen atoms in a silane molecule is replaced with a chlorine atom, the resulting substances are called chlorosilanes. All chlorosilanes are water-reactive substances.

The chlorosilanes are used predominantly in the polymer industry. For example, tri· chlorosilane is used to manufacture the polysilicon employed for the production of solar cells and solar wafers. Some of its physical properties are noted in Table 9.10. It is a water-reactive, flammable, and corrosive liquid having the chemical formula SiHCJ3.

334 O.apter 9 Chemist,y of Some Water- and Air-Reactive Substances ......oil

1ASLE 9.10 Physical Properties of Some Chlorosilanes

METHYLDICHLOROSILANE METHYLTRICHLOROSILANE

r,,elting point -135°F ( 93°C) -130°F (-90°cJ

soiling point 106°F (41 °C) 149°F (66.4°C) ·fc gravity at 68°F (20 °C) 1.1 1.27 5peCI I .

density (air= 1) 3.97 5.2 vapor pressure at 68°F (20°C) 321 mmHg 134 mmHg vapor

Flashpoint -18°F (-28°c) 14°F(-10°C)

Autoign ition point 471 °F (244°C) 759°F (404°C)

LOW er flammable lim it 3.4% by volume 3.4% by volume r flammable limit 55% by volume >55% b volume y

Trichlorosilane reacts violently with water, producing choking vapors of hydrogen chlo- ride and crihydroxysilane.

H- SiCl3(/) + 3H20(I) - H- Si(OH)3(s) + 3HCl(g) Trichlorosilane Water Trihydroxysilane Hydrogen chloride

Other chlorosilanes, including methyldichlorosilane and methyltrichlorosilane, possess similar hazardous properties. Their physical properties are included in Table 9.10.

9,8-K TRANSPORTING SUBSTANCES THAT REACT WITH WATER TO PRODUCE HYDROGEN CHLORIDE VAPOR

When shippers transport any substance noted in this section, DOT requires them to provide the relevant shipping description shown in Table 9.11 on the accompanying shipping paper. DOT also requires shippers and carriers to comply with all applicable labeling, marking, and placarding requirements.

TRICHLOROSILANE

-196°F (-127°C)

89°F (32°C)

1 .33

4.7

500 mm Hg

7°F (-14°C)

219 °F (104°C)

1 .2% by volume

90.5% by volume

Sulfuryl chloride

TABLE 9.11 I

Shipping Descriptions of Substances That Produce Hydrogen Chloride Upon Reacting with Water

WATER-REACTIVE SUBSTANCE SHIPPING DESCRIPTION

Aluminum chloride, anhydrous UN1726, Aluminum chloride, anhydrous, 8, PG II

Methyldichlorosilane UN1242, Methyldichlorosilane, 4.3, (8), (3), PG I (Dangerous When Wet)

Methyltrichlorosilane UN 1250, Methyltrichlorosilane, 3, (8), PG I

Phosphorus oxychloride UN1810, Phosphorus oxychloride, 6. 1, (8), PG II (Poison - Inhalation Hazard, Zone B)

Phosphorus pentachloride UN1806, Phosphorus pentachloride, 8, PG II

Phosphorus trichloride UN1809, Phosphorus trichloride, 6.1, (8), PG I (Poison - Inhalation Hazard, Zone B)

Silicon tetrachloride UN1818, Silicon tetrachloride, 8, PG II

Stannic chloride, anhydrous UN 1827, Stannic chloride, anhydrous, 8, PG II

Sulfuryl chloride UN1834, Sulfuryl chloride, 6.1, (8), PG I (Poison - Inhalation Hazard, Zone A)

Thionyl chloride UN1836, Thionyl chloride, 8, PG I

Titanium tetrachloride, anhydrous UN1838, Titanium tetrachloride, 6.1, (8), PG II (Poison - Inhalation Hazard, Zone B)

Trichlorosilane UN1295, Trichlorosilane, 4.3, (8), (3), PG I (Dan erous When Wet g

Chapter 9 Chemistry of Some Water- and Air-Reactive Substances 335

SOLVED EXERCISE 9.4

Thionyl chloride

Anhydrous Tin(IV) chloride

Why should emergency responders use protective gear including self-contained breathing apparatu tigating a transportation mishap involving a massive spill of liquid methyldichlorosilane?

5 When inves.

Solution: k, indicated by the shipping description in Ta?le 9.11.' methyldichlorosilane is a "."ater-reactive, fl and corrosive liquid. When it reacts with water, methyld1chloros1\ane forms hydrogen chloride vapor. Tab\ arnrnable that the inhalation of this vapor causes exposed individuals to experience a variety of adverse health effe~·

9 sh~

hydrogen chloride poses a health hazard by inhalation, the use of self-contained breathing apparatus . · Becaose when emergency responders are investigating a transportation mishap involving methyldichlorosilane. Js essential

DOT requires carriers to display DANGEROUS WHEN WET placards on the hulk aging or transport vehicle used to transport trichlorosilane, and when transporting an :ck. exceeding 1001 pounds (454 kg), to display FLAMMABLE and CORROSIVE placards as~: 9.9 WATER-REACTIVE COMPOUNDS THAT

PRODUCE ACETIC ACID VAPOR When acetic acid is formed as a product of a chemical reaction, its highly irritating and pungent odor is immediately evident. This can pose serious consequences, as the inhalatio of acetic acid vapor is suffocating, and exposure to the eyes an~ nose is severely irritatint

We briefly note here two organic compounds that react with water to produce acetic acid vapor: acetic anhydride and acetyl chloride. Some physical properties of these com- pounds are provided in Table 9.12.

Acetic anhydride causes severe burns on contact with the skin or eyes. Inhalation of its vapor is suffocating and causes irritation of the respiratory tract. Before the advent of the GHS, chemical manufacturers often marked acetic anhydride containers as follows to warn users of these potential hazards:

DANGER: CORROSIVE CAUSES BURNS TO ANY AREA OF CONTACT

FLAMMABLE LIQUID AND VAPOR WATER REACTIVE HARMFUL IF SWALLOWED OR INHALED

VAPOR CAUSES RESPIRATORY TRACT IRRITATION AND SEVERE EYE IRRITATION

9.9-A ACETIC ANHYDRIDE Acetic anhydride is a colorless, fuming liquid whose condensed chemical formula is (CH3CO)iO. Acetic anhydride is used principally by the chemical, pharmaceutical, and polymer industries for the manufacture of aspirin, cellulose acetate (Section 14.5-A), and related products.

When acetic anhydride combines with water, the sole product produced is acetic acid.

0 II

CH3 - C \ O(l) + H20(l) I

CH3-C i 0

Acetic anhydride Water

0 //

2CH3-C(g) \ OH

Acetic acid

336 Chapter 9 Chemistry of Some Water- and Air-Reactive Substances

rASLE 9.12 Physical Propert· f . . 1es o Two Water-Reactive Organic Compounds

ACETIC ANHYDRIDE ACETYL CHLORIDE

Melting point -99°F (-73°C) -170°F (-112°C)

soiling point 284°F c14o•ci 124°F cs1°ci

•fie gravity at 68°F (20°C) 1.08 1.10 specI vapor density (air= 1) 3.52 2.7

vapor pressure at 68°F (20°C) 4mmHg 249 mmHg

Flashpoint 130°F (54 °C) 40°F (4.44°C)

Autoignition point 734°F (390°c) 734°F (390°c)

Lower flammable limit 2.7% by volume 7.3% by volume

u PP er flammable limit 10.3% b y volume 19% b volume y

g,9-B WORKPLACE REGULATIONS INVOLVING ACETIC ANHYDRIDE

When acetic anhydride is used in the workplace, OSHA requires employers to limit employee exposure to a concentration of 5 parts per million, averaged over the 8-hour workday.

9.9-C ACETVL CHLORIDE p Acetyl chloride is a colorless, fuming liquid with the chemical formula CH3-C . Acetyl

\ Cl

chloride is used principally in the chemical industry. It is produced by various means, one of which involves the reaction between phosphorus trichloride and acetic acid.

0 0 II II

PCl3(/) + 3CH3 - C(/) -----? 3CH3 - C(/) + H3PO3(/) \ \ OH Cl

Phosphorus trichloride Acetic acid Acetyl chloride Phosphorous acid

On contact with water, acetyl chloride reacts violently, producing acetic acid and hydro- chloric acid vapor. This vapor poses the risk of inhalation toxicity.

0 0 II II

CH3 - C(/) + H2O(/) -----? CH3 -C(g) + HCl(g) \ \ Cl OH

Acetyl chloride Water Acetic acid Hydrogen chloride

Table 9.12 reveals that acetyl chloride has a relatively low flashpoint. Consequently, acetyl chloride also poses a dangerous risk of fire and explosion.

9.9-D TRANSPORTING ACETIC ANHYDRIDE AND ACETYL CHLORIDE

When shippers offer either acetic anhydride or acetyl chloride for transportation, DOT requires them to identify it as shown in Table 9.13 on the accompanying shipping paper. DOT also requires shippers and carriers to comply with all applicable labeling, marking, and placarding requirements.

Anhydrous titanium(IV) chloride

Methyldichloro- silane

Methyltrichloro- silane

Chapter 9 Chemistry of Some Water- and Air-Reactive Substances 337

338

Trichloro- silane

Acetic anhydride

TABLE 9.13 Shipping Descriptions of Organic Compounds That Produce Acetic Acid Vapor Upon Reacting With Water

WATER-REACTIVE COMPOUND SHIPPING DESCRIPTION

Acetic anhydride UN 1715, Acetic anhydride, 8, (3), PG II

Acetyl chloride UN1717, Acetyl chloride, 3, (8), PG 11

9.10 RESPONDING TO INCIDENTS INVOLVING THE RELEASE OF A MATERIAL IN HAZARD CLASSES 4.1, 4.2, AND 4.3

When a flammable solid, spontaneously combustible material, or water-reactive substance is involved in a transportation mishap, first-on-the-scene responders may readily identify it by noting the following, as relevant:

(a) A flammable solid The number 4.1 as a component of a shipping description of a hazardous material listed on a shipping paper The words FLAMMABLE SOLID and the number 4 printed on white-and-red- striped labels affixed to packaging The words FLAMMABLE SOLID and the number 4 printed on white-and-red- striped placards displayed on each side and each end of a transport vehicle contain- ing 1001 pounds (454 kg) or more of a flammable solid

(h) A spontaneously combustible material The number 4.2 as a component of a shipping description of a hazardous material listed on a shipping paper The words SPONTANEOUSLY COMBUSTIBLE and the number 4 printed on white-and-red labels affixed to packaging The words SPONTANEOUSLY COMBUSTIBLE and the number 4 printed on white-and-red placards displayed on each side and each end of a transport vehicle containing 1001 pounds (454 kg) or more of a spontaneously combustible material

(c) A water-reactive material The number 4.3 as a component of a shipping description of a hazardous material listed on a shipping paper The words DANGEROUS WHEN WET and the number 4 printed on blue labels affixed to their packages The words DANGEROUS WHEN WET and the number 4 printed on blue plac· ards displayed on each side and each end of the transport vehicle

Although it is always desirable to know the chemical identity of a hazardous material involved in any transportation mishap, this statement has special meaning to the firSC responders a~riving at scene involving a substance that could spontaneously burst int: flame or readily react with water. These responders are confronted with a unique challeng ' because the use of most common e~nguishers would exacerbate the ongoing emergencY: . The ~mergenc~ Response G~tdebook provides emergency responders with special mformauon regar_dmg th_e followmg hazardous materials: gases and volatile liquids that pose a hazard by mhalat10n toxicity· chemical warfar t d t 've rnare-. 1 h d • ' e agen s; an water-reac 1 na s t at pro uce toxic gases upon contact with t Th ERG 'd 'f' h se haz·

d · 1 b h • . . . wa er. e 1 entl 1es t e h

ar ous matena s y t eir DOT identification nu b d b h ' . h • in bot m ers an y green 1ghhg ung Chapter 9 Chemistry of Some Water- and Air-Reactive Substances

....illlll

UoW· and blue-bordered sections Th E 1be ye nt the following actio . · e RG further directs emergency responders ·Jllplerne ns. [O l • .

When there is no fire, go directly t h • b d name of th h d O t e gr~en-bordered pages, locate the identifica- cioll nu_rn er ~n di'stanc e azar ous material, and identify the initial isolation and

cove-action es. prote "''hen a fire is involved also co 1 h . . • w . f . h ' nsu t t e orange guide and, 1f applicable, apply the

Uation in ormation s own under PUBLIC SAFETY evac . oOT provides two entries in the green-bordered pages of the ERG one for land-based

spills and ~he 0ther for water-based ~pills. ~hen a -~ater-reactive mat:rial is not a hazard- ous rnatenal that poses a hazard by inhalation toxicity, and when it is not spilled in water, ernergency respo~ders should consult the safety distances in the orange-bordered pages.

Because s_pecial pro~edu~es are required when responding to fires involving the haz- ardous rnatenals noted m this chapter, we briefly note the recommended practices for the following groups of substances.

g,10-A ALKALI METALS Fires involving the alk_ali metals are extremely difficult to extinguish. When first-on-the- scene responders consider a response action involving an alkali metal fire, it is appropri- ate to recall that these elements react with two common fire extinguishers, water and carbon dioxide. Alkali metal fires cannot be extinguished with water, because the alkali metals displace flammable hydrogen from water. Furthermore, alkali metal fires cannot be extinguished with carbon dioxide, because the alkali metal reacts with it to produce carbon particulates.

4Na(s) + C02(g) - 2Na20(s) + C(s) Sodium Carbon dioxide Sodium oxide Carbon

Because this reaction is exothermic, the underlying metal usually erupts into flame as the carbon dioxide dissipates.

The use of a dry-chemical or dry-powder fire extinguisher frequently is recommended for extinguishing or controlling the spread of alkali metal fires. Nonetheless, caution needs to be exercised when using graphite-based dry powder to extinguish an alkali metal fire. Graphite effectively extinguishes the fire by a smothering action, thereby limiting the amount of atmospheric oxygen and moisture available to the metal. At the high tempera- tures accompanying alkali metal fires, however, the graphite may react with the metal to produce metallic carbides. As previously noted in Section 9.7, these compounds are water- reactive substances. Even the moisture in the air could cause the alkali metal to reignite.

When combating fires involving nonbulk quantities of lithium, two fire extinguishing agents are uniquely recommended for use: lithium chloride, a dry-chemical fire extinguisher; and LITH-X, the graphite-based dry-powder extinguisher illustrated in Figure 9.6. Both effectively function by their smothering action. The use of LITH-X is also recommended for extinguishing magnesium, sodium, potassium, and zirconium fires.

When primary lithium batteries are involved in a fire, large volumes of water can be used to consume the lithium, but experts consider the use of LITH-X to be preferable.

9.10-B COMBUSTIBLE METALS Firefighters frequently are warned against using water on combustible metal fires . Not- withstanding this generally sound advice, water effectively extinguishes combustible metal fires when the following two conditions are met: 1 The water is discharged in a volume that totally deluges the fire scene and cools the metal. 1 The water is discharged rapidly soon after the metal first ignites.

Acetyl chloride

Chapter 9 Chemistry of Some Water- and Air-Reactive Substances 339

FIGURE 9.6 LITH-X dry powder, a graphite-based fire extinguisher. Although it was initially developed to extinguish lithium fires LITH-X also extinguishes ' magnesium, sodium, potassium, and zirconium fires. (Courtesy of Tyco Fire Protection Products, Lansdale, Pennsylvania.)

Firefighters must consider not only whether enough water is available at the fire scene but also whether an appropriate means is available to rapidly apply it to the fire.

When a deluging volume of water is unavailable for extinguishing a combustible metal fire, experts recommend the use of dry sand, earth, dry-chemical extinguishers, or dry powders. The application of a special extinguishing agent is recommended for use on specific combustible metal fires. For example, the use of MET-L-X is recommended for extinguishing fires involving nonbulk quantities of metallic magnesium, titanium, zirco· nium, and aluminum.

The fire-extinguishing agent used in the MET-L-X extinguisher, shown in Figure 9.7, is primarily sodium chloride containing a plastic additive. The metal fire causes the plastic to melt, thereby forming a crust on the surface of the burning metal. This effectively pre· vents contact between the burning metal and atmospheric oxygen. It is the displacement of the oxygen that causes the fire to be smothered.

The application of carbon dioxide is not recommended for extinguishing combustible metal fires, because these hot metals react with carbon dioxide. Magnesium, for example, reacts with carbon dioxide to produce a sooty plume of carbon.

2Mg(s) + C02(g) - 2MgO(s) + C(s) Magnesium Carbon dioxide Magnesium oxide Carbon

Because this reaction is exothermic, the use of carbon dioxide does not cool the burning metal, and the magnesium fire is not extinguished.

340 Chapter 9 Chemistry of Some Water- and Air-Reactive Substances

The environment of a class D fire can be extremely caustic because of the formation of the corresponding metallic oxides, hydroxides, and carbonates. The particulates of such compounds are constituents of the smoke accompanying alkali metal and combus- tible metal fires. Their inhalation can cause adverse health effects ranging from minor irritation and congestion of the nose, throat, and bronchi to severe lung injury. Because combustible metal fires frequently burn with exceptionally brilliant flames, firefighters should be aware that the evolved radiant energy could damage the retinas of their eyes. They should also avoid breathing the smoke evolved during these fires, as it contains tiny particulates of caustic metallic oxides. When inhaled, exposure to these particulates causes considerable discomfort and localized injury to the respiratory tract and inflam- mation of the eyes. 1

9.10-C ALUMINUM ALKYL COMPOUNDS AND METALLIC HYDRIDES, PHOSPHIDES, AND CARBIDES

When first-on-the-scene responders encounter the release of an aluminum alkyl compound or a metallic hydride, phosphide, or carbide from its packaging, experts recommend the use of vermiculite, dry sand, or dry powder pressurized with nitrogen to extinguish fires.

1NFPA 484, Standard for Combustible Metals (Quincy, Massachusetts: National Fire Protection Association, 2012).

FIGURE 9.7 MET-L-X, a sodium chloride-based fire extinguisher intended for use on NFPA class D fires, especially magne- sium fires. (Courtesy of 7yco Fire Protection Products, Lansdale, Pennsylvania.)

Chapter 9 Chemistry of Some Water- and Air-Reactive Substances 341

FIGURE 9.8 This portion of the label affixed to containers of sodium hydride communicates hazard information that includes caution against exposing the contents to water.

SODIUM HYDRIDE

UN1427, Sodium hydride

DANGER In contact with water, releases flammable gases that may ignite spontaneously. Causes mild skin irritation. Causes serious eye irritation.

Keep away from possible contact with water because of violent reaction and possible flash fire. Handle under inert gas. Protect from moisture.

In case of fire: Use dry sand, dry chemical or alcohol-resistant foam for extinction. Store contents under inert gas.

FIRST-AID INSTRUCTIONS:

IF ON SKIN: Remove immediately all contaminated clothing. Rinse with water/shower.

IF IN EVES: Rinse cautiously with water for several minutes. Remove contact lenses, if present, and easy to do. Continue rinsing. Immediately call POISON CENTER or doctor.

Read Safety Data Sheet before use.

My Company My Street

My Town, My State 00000 Telephone (000) 000-0000

The container label in Figure 9.8 shows that caution should be exercised to avoid exposing sodium hydride to humid air or other potential sources of water. Experts recom· mend the use of water as a fire extinguisher only when they encounter very small spills of these substances.

9.10-D WATER-REACTIVE SUBSTANCES THAT GENERATE HYDROGEN CHLORIDE

When responding to a transportation mishap involving the release of any substance listed in Table 9.13, firefighters should use water only sparingly and cautiously. Du~t the corrosiveness of these products and their potential to form hydrogen chlo~i responders must wear fully-encapsulated protective clothing and use self-containe breathing apparatus.

9.10-E ACETIC ANHYDRIDE AND ACETYL CHLORIDE To extinguish fires involving acetic anhydride or acetyl chloride, experts recommend ~he of carbon dioxide or dry chemical. When emergency responders are called to a scene invo vd ing a release of acetic anhydride or acetyl chloride, they should wear fully-encapsulate f protective clothing, use self-contained breathing apparatus, and totally avoid rhe use

0

water as a fire extinguisher.

342 Chapter 9 Chemistry of Some Water- and Air-Reactive Substances