edited by
MALCOLM M.
RENFREW
University of ldaha MOSCOW, Idaho 83843
Reactive Chemical Hazards: Their Causes and Prevention L. Brelherlck, Research Project Leader
New Technology Division, The British Petroleum Company Limited, BP Research Centre, Sunbury-on-Thames, Middlesex, TW16 7LN.
The Background Safety in the use of chemicals is a topic which has had for nearly two centuries the active support of people concerned with preventing accidents involving chemicals in both industrial and academic situations. In 1802, E. I. Du Pont de Nemours designed his gunpowder factory a t Wilmington
on a safety basis, with the stout stone buildings equipped with blow-out wooden walls facing onto the Brandyvine river. Further, he insisted that his factory superintendents take a very direct personal interest in the safety system by living in houses just a few hundred feet away, where they would also be on call in emergency ( I ) . In 1815, Humphrey Davy (Continued on page A62)
ricultural, and other speciality ehemicals. After applying his organic chemical evoerience t o small-scale
Leslie Bretheriek received his BSc from the University of Liverpool and worked in the May andBaker laboratories from 1945-60 on research and development of pharmaceutical, ag-
tical chemical experience into several areas of chemical safety. A long-standing ambition to improve availability of chemical safety information t o fellow chemists and students led to publication in 1975 of the "Handbook of Reactive Chemical Hazards," a 1000-page volume eantaining brief information on some 5000 items far which details had been published. This work continuesand a second edition now contains over 7000 such items. He has also been involved in the detailed work of Safety Committees at B P Research Centre, in a variety of safety publications, and currently is Safety Adviser to the Home Experiment Kits group of the Open University, the British TVIRadio organisation for home-study degree courses.
Volume 56, Number 2,February 1979 1 A57
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stressed the need for great caution in preparing chlorine dioxide from potassium chlorate and sulfuric acid (2). Hans Eulenberg in Germany published a treatise on toxic gases in 1865 (31, and, in Paris the next year, Jean Thelmier's collected account of laboratory accidents appeared (4). During the next two decades, Ludwig Mand lived in a house adjacent to his factory a t Winnington, Cheshire, so that he could take personal charge if an accident happened a t night.
In 1896 the National Fire Protection Association published in Boston a handbook on fire protection, including data on chemicals as fire hazards, and the Chemical Section of the National Safety Council in Chicago was established in 1921 ( 1 ) .Even in 1925. Hein-
ratory safety information in this Journal in 1935. Warren Cook compiled the first TLV list in 1945, and Howard Faweett published his list of incompatible chemicals in 1952 ( 6 ) . Since then. a raoidlv inereasine number of
toxic hazards of chemicals
The outcome of all this activity has been a very large amount of detailed printed infarmation on many aspects of the hazardous nature of individual chemicals, but usually scattered across a wide range of publications. Further, much of the safety information published more than about 20 years ago cannot be traced via the usual indices because safety was not then considered as an indexing keyword. However, this situation has now dramatically improved; several retrospective compilations of such information have recently appeared (7-11); the keyword "Safety" bas been used by Chemical Abstracts since 1974; and their publication of a "Chemical Hazards" selection of abstracts now ensures ready availability of current printed information relevant to this subject. Those with computer terminal facilities now have the added advantage of rapid access to a continuously updated and increasing range of data-bases relevant to chemical hazards, including TaxlineIChemline as well as the CA and similar data-bases.
The Current Gap It has been apparent for many years that there is a gap between the usually adequateto-mod use of available information re" sources in many industrial laboratories and the often inadequate-to-bad use of the same resources in some academic laboratories. Attempts to improve this situation have been made steadily over many years by, for example, the ACS Committee on Chemical Safety, and of course the many contributors to this column since 1964. Yet speakers a t the 10th Biennial Education Conference in Cbicago last October (12) again highlighted various aspects of this continuing disparity between industrial and academic safety performance. From my own experience in abstracting safety literature, I know that it is likely to be in academic laboratories that well-known reactive hazards, such as those involved in distilline mixtures of acetic acid and hvdrogen perkide, will be rediseavered.with shattering results. The reason for this apparent failure to make effective use of available information resources for established chemicals is not a t all clear, because the underlying physicochemical principles (below) are simple and readily understandable. and the eamole-
above.
Underlying Principles All chemical reactions depend on and are accompanied by energy changes, and because most chemical reactions are exothermic, the energy usually is evolved as heat. According to the principles of chemical kinetics, the rate a t which a reaction goes is controlled by the temperature, the concentration of reagents, and other factors specific to the reaction. The temperature has a very significant effect on the rate of a reaction because temperature appears as an exponent in the Arrhenius equation. Practically, an increase of lO0C may double or treble the rate of many reac(Continued on page A66) A62 I Joumal of Chemical Education
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tians. The concentration of reagents will also have an important effect on reaction velocity, because there is minimally a direct relationship and sometimes an exponential relationship between them, according to the Law of Mass Action. Catalysts may also exert a profound effect upon reaction rate. The majority of chemical reactions are exothermic, and the size of the exotherm is specific for a particular reaction. Of greater importance than size is the rate of release of heat, which is of course related to the reaction velocity. The facts that most reactions are exothermic, and that moat reaction rates increase with temperature together imply that most reactions are potentially unstable, and will accelerate if the reaction heat is not effectively removed from the system to prevent undue rise in temperature. If the self-aecelerating tendency is unchecked, it may lead progressively t o violent boiling, pressure effects, ignition of flammable vapour or gas a t the auto-ignition temperature, and possibly explosion. If thermally unstable materials or products are involved, explosive deeamposition is likely to occur sooner than later. Explosion involves very fast chemical reactions which release heat energy a t so high a rate that destructive effects appear.
Control In very general terms, all reactive chemical hazards involve excessive rates of energy release, and in avoiding such hazards the key factor is the control of reaction rate. Such cuntrol is usually effected by adequate temperature control, and sueh factors as mixing and contact of reagents, rates of addition, and heating or cooling of both liquid and vapor phases in a vessel of ample capacity may need consideration. If a catalyst (possibly unsuspected) is present it may increase greatly the rate of areaction, and an inhibitor (negative catalyst) may stop the reaction, a t least far a time (the induction period). The basic eouioment needed to effect mometer to record the temperature and a method of controlling it within suitable limits. Where heating is necessary to supply the energy of activation t o thereage&: the heating mantle or bath must have a suitable energy regulator tocontrol heat input. If the reaction exothem is expected to be large, the mantle or bath must be arranged so that it can be rapidly removed and if necessary replaced by a cooling bath. When the energy of activation is law little or no heating will be required, hut suitably large cooling capacity may be needed for a highly exothermic reaction. When reaction control is effected by the rate of addition of one of the reaeentr. dill>-
thermic reaction A66 / Journal of Chemical Education
Well-documented reaction procedures, sueh as those in "Organic Syntheses" or "Inorganic Syntheses" usually contain details of control procedures appropriate to the energies involved in particular reactions. Where a novel reaction or experimental procedure is to he undertaken, it is necessary to try to establish beforehand, both from available literature and from one or more preliminary carefully conducted smnll-scale experiments, what are the kinetic and thermochemical characteristics of the novel reaction system before any sizeable preparation is attempted. Or, more briefly, "look before you leap." These factors are considered in greater detail with examples in a recent laboratory manual (11) which also contains a guide t o the relationship between chemical structure and reactivity or instability in various groups of eompounde The suhiects of toxicitv and taxicoloev ... of chemioali, uhwh i n w w rr\pecu!,arenot y r develqed r u rhe snme r x r r n t as the contrnl ~ rri w r t i m hnmrdr, o r r also cuvrrcd in the same manual, as well as in other reference works (13, 14).
The Way Ahead The farce of legislation has now been added to existing moral obligations to promote safe working in chemical laboratories, hut this goal wiil only be more nearly attained when improved attitudes and motivation have been better developed in both tutors and pupils by continued and determined use of existingand new edueatianl techniques (15). The means to safe laboratory working are largely to hand: the need to improve the application of these means to the residual problem remains.
Literature Cited I11 Howard H. Faweeft pmvidd much ofthe information on the early course of US safety develo~menf. I21 Bailar, J. H. Editor. "Com&hensi& Inorganic Chemistry," Pergamon, Oxford. 1973. Val. 22. p. 17R1
131 Eulenberg, H., "Die Sehddiiehr und Ciltigen Case,'' Rninrwick ,886. I41 Thelmier, I . A,, " D ~ Amidsno s dons les Lobomloires du Chimi*." Paris. 1866. (51 Willard, H. (Editor). "Gatterman's Labor Pmxisdor Orgonischr Chemia. de Gruytor, Berlin, 19th edn.
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,976
I61 Faw&t,H. H., Chem. Ene. News. 30.258SI19521. (71 Fawcett, H. H., "The Literature ofChemical Safety," JLCHEM. EDUC.42.A BlS,AS97 119651. 18) "Manual of Hazardous Chemical Reactions," 491 M, Boston, National Fire Protection Association, 5th edn., 1975. I91 Bretherick, L., "Handbook of Reactive Chemical Hazards, London, ButfeworLhs, London, 1975 (new edition in press1. 110) Loleu. J., Hiactions chimigum dsngereuses, serial quarterly publication in Cohier* da Notes documntairea. Paris, InstitutdeRechercheSecurite.1972 to dale. I111 Muir.G. D. IEditorl. "Hasordsin theChemicolLoburoiury,"The Chemicai Society, London 3rd edn., 1977. I121 Preliminary report in Chrm. Eng. News. 55 1471. 19 119771. I131 Steers, N. V. (Edilarl. "Handbook of Laboratory Safety," Chemical Rubber Co., Cleveland, Ohio ed., 1971. I141 Windhnk M. lEdilorl."TheMerekInddd,"Morckand Co. Ine., Rahway INJI. 9th ed.. 1976. I161 The%*were reuiewpd in this Joumnl. 1978, MarehApril issues
