mfety in the chemkol loborotory
edited by MALCOLM M. RENFREW University of Idaho Moscow, Idaho 83843
Chemical Laboratory Safety: The Academic Anomaly Leslie Eretherick Chemical Safety Matters, Bridport, Dorset DT6 6AE, England It would seem reasonable to assume that there should he s direct correlation between the level of intellectual attainment in a chemical research laboratory and the level of appreciation of the potential hazards associated with the work and the materials used in that laboratory. One would therefore expect to find in the laboratories of our leading centers of academic learning and chemical knowledge that there would he few, if any, examples of accidents arising from ignorance of the inherent properties and reactions of chemicals used in teaching and research. Experience suggests, however, that in many academic laboratories the converse annears to be true. Some entirely avoidable academic laboratory accidents are examined and speculations advnnced as to posaihie rtaJOnS for thrs anomaly.
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The Accidents Four accidents that appear to support this view are covered in same detail, all heing of fairly recent origin; none of the lahoratories involved are identified, for obvious reasons. The first accident concerns the preparation of a molten inorganic salt hath to beat a small metal reactor. Salt baths usually consist of potassium nitrate and sodium nitrite in the ratio 1:0.85 by weight. On this occasion a mixture of 3 lh of sodium nitrite and 1 Ih of potassium thiocyanate was used to make up the required volume for the hath. Why the thiocyanate (a reduciugagent) was used instead of the nitrate (an oxidant) and why the nitrite was used in excess was never explained, hut perhaps the storeroom was out of potassium nitrate, so "another potassium salt" was selected instead. Heating was then applied to the mixture, and when it began to melt, probably at around 170 T , there was a violent explosion, which embedded the fume hoodsashes in a wall 20 ft away and caused structural damage amounting to $0.2M. In the following approximate equation, an equivalent molar quantity af sodium thiocyanate has been substituted for the potassium salt to simplify the equation.
used for the hath was very close in composition to the 7228 mixture that gives the calculated maximum reaction heat of 3.51 kJ/g. Thus the hath mixture would give an instantaneous release of same 6.5 MJ of thermal energy, with an apparent damage potential of $41.13 per kilojoule released. The explosive nature of nitrite-thioeyanate reactions an heating had been known for well over 50 years. I t is, of course, an example of an energetic redox reaction-that is, a reaction between a reducing substance and an oxidizing suhstance that produces three fully oxidized solids, a large volume of gas, and a great deal of heat. I find it difficult to understand how anyone associated with scientific matters can he unaware of the hazard potential of such reactions, which are the source of the huge energies involved in the rocket propulsion systems used in the space program. The second accident concerns a reaction product of acetone and hydrogen peroxide, which was used to demonstrate the violent combustion of organic ~eroxides.I t was supposed that the solid was 2,2-his(hydroperaxy)propane, farmed by reaction of acetone with 2 mol of hydrogen peroxide.
H3C'
'OOH
peroxyacetone (actually a liquid) The solid, which was prepared, stored, and used occasionally for lecture demonstrations, was in fact trimeric acetaneperoxide, formed by self-condensation of the reaction product with 1mol of hydrogen peroxide, the hydrogen peroxide equivalent of a ketone hydrate.
\/ CMe2
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d C n a n l m y s ~ n h e a x m r C a I ~ ryl4ed 19861 ? i e t s a f e w d m R W a Sac* ol Chmw and s a *mty recqpued m n s b
When the surplus solid was being disposed of hy burning, it exploded violently. The demonstrator was an extremely lucky man because, when the explosive properties of the trimeric peroxide were first investigated in 1943, it was found that a small sample would perforate a steel plate on which it was heated. This violent decomposition has been encountered many times during the past 45 years because, whenever acetone, hydrogen peroxide, and traces of acid have been in contact, this nicely crystalline solid uaually appeared and often subsequently detonated after isolation. The third accident concerns a halogenated acetylene compound, 1,6-dichloro-2,4hexadiyne, CICH2=C-MCH&l, which has been known as a highly shock- and heatsensitive explosively unstable compound since 1972. It may, however, he carefully distilled at 55 W 0 . 5 tom from a carefully controlled heating hath. Recently a research student, supervised by a lecturer with 20 years experience in acetylene chemistry, made a larger than usual amount of the unstable material and then tried to distill it
H3cv00H
4.25NaN0, -Na?SO, + 2.6% NaN=C=S Na,CO, 0.6Na20 Fartuito&ly, the 75% mixture that was
( t a ~ i ~ s e r v l a , t o ~ i n d S a ~ l f a his "big bock? thlxxk of RBscdve L%mk-a M . 3 ed.. 1985). He spent 20
peroxide
(Continuedon page A I 5 ) Presentedat the 190th national meeting of ACS in Los Angeles in a symposium on "Topics in Academic Laboratory Safety."
from a flask in a heating mantle at atmospheric pressure, with an equivalent boiling point around 230 'C. In due course, it exploded violently, wrecking a fume h w d and iniurine the student. The wtential enerev reiease'has been assessed ai over 3 kJ/g, since the quantity of material involved has not heen revealed, the energy releasecannot be calculated. Apart from the technical interest, thisaccident is of considerable legal significance in the United Kingdom because it represents the first occasion on which an academic institution has been prosecuted by the Health and Safety Executive, and a substantial fine and costs were imposed. The final example involved another weUknown pair of reagents, hydrogen peroxide and acetic acid, which just cannot help forming peroxyacetic acid when in contact, and especially on warming, and which have been causing problems and explosions for well over 50 years.
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A sample of 100 mg of jute tibe1 waa to be bleached by treatment with hydmgen peroxide in acetic wid by heating in a water bath for several hours prior w cxaminatiun by a atandard forensictest.The specifiedquantitiesof 20 mL of r l a d acetic acid and m ml. of "m voL" (6%) &-de solution would have oroduced some i.7 g of the o r i d i i add as a 791solution in aqueous acetic acid. Unforwnately, b u s r the lahel on the hydrogen m x i d e was either misread or was not undemtwd, the much more concentrated "100 voL" (3096) peroxide solution waa used in error. 'I%is would pmduce 14.7 g of pemxyaeetc acid as a 34% solution, and after 4 h heating this erpkded violently, shattering the ceramic hotplate under the water bath. The energy of d e mmpitionof l4.lgofperoqvaeeticacidwoul be about 60 kJ.
Why Did lMse Acddents Happen? It is not easy at first sight to understand why any of t h e accidents happened at all, as the hauudous nature of the materials had been known and described in the open literature between l5and 75yemagaLetusnotforget that the literature of chemistrv is the best ommized of any of the scientific disEiplines. Manv academia who ewerience such a& dents&y aRenvardPin thei;owndefense that it is diicult to find such information: although thii may once have k n hue to some extent it is no longer so today. 1h e pa- 25 yean many chemist^ haw been involved in publicizing the potential ha& asroriated with reaetrve c h e m i d , and the number of books, bulktins,abatrads, and data sheets on the subjectof chemical safety is legion. Further., the maioritv of academia indved . .~ in thii kind of accident are usually mwientious and experiend wientists who are mnvinced that they are doing a good joh. I have concluded that there may he aome unsuspeaed fador that prevents people fmm maldng effec~~~~
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tive uae ofthe information resowhich are available to them. So what could this fador be? It appears to contain several possible comp" nents, starting perhaps with a touch of mgance ("You can't tell me anything about that!"), a streak of optimism ("%t couldn't happen to me!"), or a moment of wmplacenq ("That will have to do!"). Many concerned with safety have eritidzed the contentof p-tday cwkda, withoverempbasisoftheoreticalmae ters at the expense of descriptive chemical fa&. I wonder, tm,whether there might be some SF (SanFraneism) bloeksge in many of us, this being the factor that hm led those worthy dti~nstorefertothel906mturaldisastwas"the Great Fire," and to build some of their emergency s e h buil* astride the fault line. All this is perhape best s d up in a quotation fmm a Washington Post editorial d o c tober 31,1979,after the Kenney Cornmiasion's report on the Three Mile Island accident A p u p that set out b investigate a teehn o l w ended up tal!ubg about people. In the Commiapion's own words,"It became clear that the fundamental problems were peoplerelated prohlema"
Thereseemstabeaneedtafmdouthowto persuade academics, and of course others, tm, to make better use of the informationresawees that now surmund them.
