I
~ i n n e a ~ o l ' i Minn., s, 55455
V. Benzoyl Peroxide Requires Special Handling and Storage The CHICM study progranl, being used in hundrds of high school laboratories thmughont. the USA, inrludes itn experiment requiring oent.igrarn quantities of benmyl peroxide. The small quantity of hensayl peroxide per student (0.01 to 0.02 g) is not especially haoardous, hut the dispensing and storage can be, since 4.50 g is t,he minimum quantity normally sold by laboratory supply companies. The required use of benzrryl peroxide in the CHEM study program was reported by a high school chemistr,~teacher who experienred an explosion of the n ~ & terial in a. reagent bottle immediately after a small quantity had been removed during R. univer~itysummer class. Dr. Mark M. Chamberlain, Safety Officer of the Department of Chemistry a t Western Reserve University forwarded the information and requested the problem he brought to t,he attention of the profession. Theexperiment calling for use of bensoyl peroxide, shown on page 133 of Appendix 6 of "1,ahoratary Manual for Chemistry, an Experimental Science," W. H. Freeman Co., Ran Francisco, 1963, is described in part a s follows: "Part 111. The Depolymerisation of a Mebhyl Methacrylate Polymer and the
Subsequent P~,lvmerisstionijf the Monw
me^" "With the aid of an appropriate ratalyst this monomer can he repolymerised. "Cm~tion: Do not sttempt this erperimont without the appropriate equipment. U s e suitable preradons to avoid inhaling !.he vapors of the monomer lliethl,l m d h a . r r ~ late. (The italics w e thp Kditor'~.)
(a) . . . ( h ) T o repolymerize the methyl met,hnerylate, plate 10 ml uf the liquid in a small expendable glass rontainer (such as n bahy food jar) and add 0.01 to 0.0'' g vf henzyyl CaHsC-0-0-C-CsHi, 11
4
II
6
prroride ns the initiatnr. Cover it with 8, piece of aluminum foil, tucked in around the edges and held in place by a ruhher band. Place the jar in a hotwater bath and keep the temperature just below bailing for about 30 min or until polymerization is complete. "Allow the polymer tn roo1 and record
1
feature June Job
I ~ T O R 'NOTE: S The eutl i , f the arndemia year is an errellenl tiwe get rid of chemicals whirh have swui~utlatedin Iaharattt,rries and storage areas. Citemic d s whirh helong tn stall 01. students who have lefl or are leaving, should he disposed of or transfelxd. All unidentified and unlsheled rhpmirals s h d d he rollerled for rlispmal hy a[>proprinte and respcmsihle methcals. I'nhlems whirh are idetrtifird hefore July lllt,ll or so could he tmn~ght, tu the 1,aboratory Waste IXspusnl dis,.ussion a t the July 14th Lahorntmy Safely Workshop a t Rubgers TTniversiby. (See THE JOI-RNAL, 41, A 3 4 (1!)64) for details.) The end uf t,he arademir. year is nlso a good time to evaluate and inrprnve labeling and purchasing plwt,ir.es, to take steps t,oward dating individunl rontainers of rhemicals surh a8 the ethers which form perrwides, to minimize quant,ities of Hnmmnhle liquids in the lahurntnry, and tcl move trlwnrds laheling which conforms to the prar{.ires recommended in MC.4 Manual I.-] "Warning Lahels." Before s c l d starts again in the Fall we plan to present inforrnntion here on t,esting ethers for peroxides, and on mews of providing fire-prnterted &orage for ahemirsls.
VI. Use of Flammable Liquids William 5. Wood, Safety Engineer, Research & Development Division, Sun Oil Company, Marcus Hook, Pennsylvonia When handling of a. dangerous compound or mixture of compounds beromes routine or commonplace, normal care is relaxed and the way is open to accidents. The seriousness of the hazard is dependent upon the nature of the material handled. With flammable solvents, ordinary care is not enough. The term "flammable solvent" has come to mean many things besides hydrocarbons and derivatives. It mesns a. liquid whiah is sufficiently volatile even under severe ambient eonditionrr t,o form vapor mixtures that will burn. Combustion requires a sufficient eoncentration of fuel vapor in air to propagate the Hame from layer tn layer. As t,his minimum concentration is exceeded (lower flammable limit), energy release increases to a maximum near the stoichiometric proportions. Energy then decreases as concentration is further increased until there is not sufficient ziir or oxygen to support cambustian (upper Hammable limit).
These conditions exist for all of the eommody used eolvents and are a measure of the hazard in their handling. The liquid temperature a t which vapor eom:entrat,ion exceeds the lower Hammahle limit is defined as the flash point,. Although a. solvent may be handled with relative safety below the Hash point, mists can be ignited a t much lower temperrttures if a sufficient,quzntit,y of liquid is dispersed.
Ignition. An explosion or tire "lust be started. The temperature t o which a Hammable mixture must be raised to get things going is t,he ignition temperature. Organic solvents such as carbon disulfide and diethyl ether have dangerously low ignition temperatures and some of the more common solvents in the napt,ha, category
can be ignited well belr~wdiwemil~lered11888. Common sources of ignitim are often overlooked. Flames and hot gases aye (Continued on page .4448) Vol. 4 1 , N o . 6, June 1964
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a description of its properties in your notebook." Although we have questions about the meaning and meaningfulness of the cautions noted, we are not concerned about the use of small quantities of henaoyl peroxide. Our greatest concern is that dispensing be carried out by a fu1l.v responsible and informed person, and that storage of the hensnyl peroxide he in a cool, ventilated place away from all sources of heat and all eornhustihle materids. Rensoyl peroxide can decompose instantaneously and explosively-a fact whieh is demonstrated impressively in the film "Chemical Boohytmps," produced a t General Elertrir Research Laboratory in Scheneetadv, N. Y., hy Howard H. Fawcett. We had an opportunity recently t o witness the reaction of 1 lh of henzoyl peroxide exposed to the thermal radiation from a small fire, and the film does not exaggerate. MCA Chemical Safety Data Sheet SD81 describes the properties and essential information for the safe handling and use of hensayl peroxide. This sheet should he obtained and consulted before the chemical is purchased. A few of the stat,ements in SD-81 are: "When heated to just. ahove its melting point, 103-10.5T (217-222'F) henzoyl peroxide will decompose instantaneously and explosively. This deeomposit,ion caused by heat done will often proreed without flame. However, the dernmposit,ion vapors are flarnmahle and irrnit,ion may occur. Bensoyl peroxide will demmpose explosively when overheated under confinement,. While it remains st,ahle for yeal.8 a t ordinary temperaBlres (itmund 25'C), when held for long periods a t elevated temperatures, decomposibion may occur. The higher the temperat,ure, the shorter the time before deeompo~ition starts and the more rapid the decomposit,ion. "While it is not possible to give a.precise maximum temperature below whieh it is stahle, when henzayl peroxide is held for prolonged periods a t t,emperatures of 7Fr80°C (167-176T) decomposition may OCCUI.." "Heat, frict.ion, impact, or addition of chemicals can initiate explosive decomposit,inn." The Data Sheet says in part under
Hazards: "In its ease of ignition and strength when fired under confinement the reaction of hensoyl peroxide may he considered as resembling that of a low explosive hut it develops much leas explosive force. However, under certain conditions, i t is more easily ignited or initiated than some convention$ explosives." Discussing Heat and Other Sources o f Decomposition, the Data Sheet SD-81 "Common sources of heat, other than flames or fire, whieh may cause such decomposition are, steam radiator, steam pipes, hot metal surfaces of reactors, lights, and possihly exposure to direct or (Continued on pago A448)
Vol. 41, No. 6, June 1964
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reflerted sunlight. All surh sources of heat should be avoided. When benzayl peroxide has h, he mired with ot,her materials rare should he taken that the temperature of such materials is below 50°C (122°F). Considering the relation between the minimum purchase of 4.50 g m d 0.02 g per experiment, the cautions of Data Sheet 81)-81 under /??packaging. are impwtanl.: "Benmyl peroxide should not be repackaged in any type conbainer other t,hxn t,he original fiber carton or paper bag. TTnder no circumstances should metal or glass containers with screw type rlosures be used for benaoyl peroxide rontsinem. This is in order t o avoid t.he possibility of decomposition by frirtion or of deeomprrsit,ion under close confinement." The MCA D&n Sheet gives precautions for cleaning up spills of benaayl peroxide, and for disposing of spilled or rmtaminat,ed material. One method for safe destruetion of waste benaoyl pemside is to submerge Lhe nmterial in an excess of wat,erand to b r a t the s1urr.v with ten times its weight of 10% sodium hydnxide solut,ion. The Data Sheet specifies: "The peroxide should be i~dded gradually in small portions with sufficient agitation t o prevent settling or lump formation. The r e a h o n is only mildy exothermic when properly carried out so that cooling is unnecessary. If the mixture thickens so that stirring is diffimdt, i t should be diluted with water ss required. The final slurry of sodium benzoate inxy be flushed into the drain." Data Sheet SIX31 a180 prescribes xn alternative method of waste disposal which mtly be emier or more suited t o cert,ain situations. Bithme in "Fire Protect,ion for Chemicals" cit,ed in the January bibliography, THIS JOURNAL, 41, A36 (1964), discusses organic peroxides and the problems of fighting fires involving bensoyl peroxide. He recommends that no attempt be made t,o extinguish such fires with fire extinguishers after decomposit,ion has st,arted. Rahme suggests that benzoyl peroxide be handled and stored wet. Brigades which are going t o be trained t,o fight chemical fires in laboratory building8 will find Rahme's text invaluable. Every laboratory using or storing hensay1 peroxide should have z copy of MCA Chemical Safety Data Sheet SD-81, and should f d o w t,he recommended pravtioes to prevent serious ncridents.
VI.
Use of Flammable Liquids (Continued)
obvious sources. 1x8s common are steam lines (which will ignite carbon disulfide), electric coils, and other hot surfaces. Sparks from welding operations or hot metal chips from cutt.ing operations are equally dangerous. Electric sparks of sufficient energy to cause ignition occur in open motors, switches, m d other electrical equipment. (Continued on page A449)
A448
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Chemical Education
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Leakage current, static charges, and ,mechttnird friction are lesser but real ocm(Continued on page A460)
Equilibrium Temperatunes Corresponding lo Flammable Limits of Solvann Temperoture.
b 0
h 0
A
0
0
N
0
P
0
O 0
. 0
OF 4
-
~ 0
O
0
4
-
4
am 0
0
0
Safety
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bilities. Recent experinlents show tlmt in pumping or mining of petrnleum, suficient static charges can he generated t,oexplode the receiving t,ank. Not all fires or explosions are trared t,o a commonly accepted starting point through these sources of ignit,ir,n. Several new chemical compounds bring such phrases xs "oxidizing agents" and "sutoignibinn" into the pirture. Metal alkyls and hormes ignite spontaneously upon exposure to air a t ordinary temperatures. Peroxide formstion in ether or other solvents may render them hazardous when they are distilled or evaporated. This aobion e m be minimized by using copper wire or inhibitors in the distillabion ar evaporation flask. Because peroxides will also form on standing, storage time of solvents which have a tendency to fmnm peroxides should be kept short. The additional heanrd of toxirit,y should not be overlooked when handling flammable solvents such as an,m.ztirs. Kareosis, a state of stupor or drnwsiness, can be produced by amounts well below the lower flammable limit of ordinary hydrocarbons. Analysis. Combustion on the surface of hut wires has been used in curnmercisl instruments as z means of detecting rnmbust,ible concentrations. These meters may be portable for on-thudpot checking, ststionayy for monitoring a single point, {lr stat,ionery for monitoring many points. 1':xplosivity meters have proved their worth many times over, using the very conditions to detert the dangernus eondition that will and do cause serious arcidents-combust,ian, but under contnrlled conditions. Storage. Criterion for storage o i vdlrtile solvents is obvious-minimize the quantity. Should a fire occur under these rondit,ions, it will be small and easily controllable. Quantity permissible for stmage in a given ares. will vary, but in most, r:mes it is small. Storage containers themselves me a sore point in handling these flamm2~ble solvents. Expediency dictates that glass containers be used in the laboratory for convenient handling and to avoid contamination. Yet they are frequently the muse of serious accidents through rupture under pressure or dropping. When under refrigeration or when being used on the work table, these containers should be kept, in pans to catch leakage. Metal safety cans are preferred to glass containers where practical. A convenient and efficient one-gallon container is one that has a spring closing cap and a flame mester inside the spout. The arrester is simply a metal screen that cools the hot gases and stops the flame travel, should the e m ignit,e a t the pouring spout. Where large sample containers are used, such as drums, properly designed pumps are best far dispensing liquids. If spigots are used, flame arresters and a vent cap should replace the other bung. In making transfers irom one metal container t,o another, a grounding wire should be used to discharge static electricity generated
(Continued on page A4581
A450
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during pumping or pouring. .4 xire wit11 hulldog clips is often used, Imt clamps with hardened points are more reliable her.nuse t,hey srale and paint more eH'ec. uenebritle . tively. Expksion-pmof equipmenl slr
