An Introduction to HAZOP A Hazard and Operability Technique Inherent Problems The fundamental cause of this thermal instability of organic oxidant salts is that their crystal lattices contain a t a molecular level the powerfully oxidant anions (in the present eases permanganate) closely juxtaposed to the cations containing hydrocarbon substituents. Like any other intimate mixture of fuel and oxidant. once theenerev c.f nerivntic,n become* available (by heating. frictim, Imparr. ere.,, uxidntion of the org a n i ~catimc b" the anions will brain and accelerate, perhaps eventually to explosion, because the liberated heat energy cannot escape rapidly from the solid matrix. At first sight, therefore, i t seems unlikely that any resolution of this paradoxical problem may be possible.
Posslble Solutlon It is, however, remotely possible that, in view of the greater stability of the C-F bond (93 kcsllmal, 389 kJ/mol) ascompared t o the C-H bond (87 keallmol, 364 kJImol), oxidant salts derived from fully fluorinated quaternary ions might show a sufficiently increased margin of thermal stability over their nonfluorinated analogs t o allow use of the former as oxidants with agreater margin of safety than currently appears possible with the latter. A cursory examination of recent issues of the Chemical Abstracts molecular formula indices shows that several fully fluorinated tertiary amines are well
[311-89-7jj. However, no exampl& of the perfluoro quaternary ions derived from these tertiary perfluoro amines could be found in the same indices, so i t is not yet clear whether such fully fluorinated quaternaryoxidant salts are in fact capable of existence. If they are capable of existence but are not sufficiently stable, the formation of significant amounts of highly toxic earbonyl fluoride on thermal decomposition seems a distinct possibility, arising from oxidation of the CFz fragments. So the solution of one problem may raise another in its place.
Literature Cited L. Goldstein. N.;
Ragle. J. N. J . Chsm. Phys.
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5. Fuote.C.S. Photocham. Phofobiol. 1978,28,718. 6. Solomon, I. J.; Kscrnarek, A. J.: MeDonough. J. D.: Hatlori, K. J.Amzr.Chern.Soc. 1960.82.5640. 7. Udupa, M. R. Propellants Exploa. P y r o t ~ c h .1962, 7, 155. 8. Mell".. J. W. "Comprehensive Treatise on Inorganic and Theoretical Chemistry", 2nd ed.: Longmans: London, ,945 Vol11, p 358. 9. Sala, T.:Sargent, M. V. J. Chom. Soc., Chern. Comm. 1978.253. 10. Morris, J.A.: Mi1ls.D. C. C h ~ m . I n d 1978.446. . 11. Schmidt. H.-J.: Schafer. H. J. Angeu. Chem. (Intern.
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hedron Lett. 1980,21,2261. 14. Grade, J.: Rienackcr, R. Angem.
Martin J. P i i Depaltment of Chemical Engineering. University of Leeds. U.K.
HAZOP is a technique developed by ICI, and extensively used in the U.K. chemical industry to find unanticipated dangers, and help in controlling them'. The following notes are intended to give educationalists some idea of chemical safety practices in industry and toshow how the technique can be aoolied in the lahoratorv. Properly applied, HAZOP is a team exercise, requiring time and good management. There is much a t stake, so considerable effort and a deal of experience are needed to deal with complex plants and processes. However, it is possible far an individual to make use of the idea in "thinking through" an exoeriment. A tvoical team is three tosix . :ndividuals, each possessine une or more of the idlowing rhnmrtrrirtica \after 1.ihuu-J:
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(1) The Designer or someone very familiar - with the item under studv. who can answer questions but who may be too close to the problem to recognize some of the dangers. (2) The Experienced Person-someone who is familiar with the technology and its problems but has not been involved with this item. (3) The Naive Questioner-someone who is either inexperienced or from another field and who is not afraid to ask a foolish question. (4) The Seeretogv-someone who will make sure that important points are noted, so that action can be taken. (5) The Choirmon-preferably someone experienced in the technique who can keep the discussion in order and watch out for misunderstandings or omissions.
Thus e minimum team of three might be madefrom, say, achemist (as the Designer), his Safety Officer (as Chairman and Experienced Person) and someone from another lab (as Secretary and Naive Questioner). Industrially, one might expect a young chemical engineer to start off as Secretary and progress to Naive Questioner and ultimately to the other roles.
Purpose The purpose of a HAZOP study is to consider how some equipment or process operates and how it might deviate from the normal condition. The consequences of such deviations are examined t o determine whether they would be trivial, inconvenient, or dissstrous. Having recognized both deviations and conseouences. a decision can he made as t o what action is reauired. For ex-
Chem. (Intern. Ed.)
1983.23.625.
15. Karsrnan. H.: Ban"", R. J ; Roben.on,B. E.; k , D . G.rl Org. Chrm. 1984.49.4SW.
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Journal of Chemical Education
it is fairly probable, whereas action may be
taken against a remote possibility with catastrophic consequences. HAZOP does not of itself quantify risk nor replace good judgment. I t is merely a technique to ensure that as far as humanly possible no dangerous circumstance is overlooked. It does this hy requiring that certain questions be asked, and this is the essence of the technique.
Method The first step is t o make a complete description of the item under study. For a chemical plant, this will normally he based on a flow diagram, but in the laboratory a simple (but complete) sketch will probably suffice. In fact, i t is possible to use a photograph or even simply t o view the equipment far simple laboratory setups. In all cases the picture should be supplemented by a written brief description of the operations earried out and the materials involved. This is normally the task of the Designer. The group then studies the information, and questions the Designer to ensure that they understand it correctly, and that nothine has been omitted (far examole. a nitroe e i ~ u r-e.e )Onlv . then can a critkalanalvsis rnkr place. Actually, thisexercw of making n 11111 dtwriptiun may oi itreli help rhr l)esigner to recognize some flaws or simple improvements that could he made. After thisvitalpreliminary, thechairman steers an orderly discussion of the apparatus and the process, piece by piece and operation by operation. As the discussion proceeds. the Seeretarv marks off items on the diagram and the notes toensurr that everyIhing is rcmwlered. For this purpose it is worth making a list 01 rtrms and of operations, for example: mantle, flask, condenser, funnel, vent; charging, mixing, boiling, addition of reagent, reflux, evaporation, etc. The question for each topic is "What is supposed to happen, and how can it go wrong?" The HAZOP technique is t o check off a series of guide words. For example, the guide word NO is applied to the flow of water to the condenser, and the consequences (release of vapor, flask boiling dry, etc.) are considered. The guide word OPPOSITE may be similarly applied (reverse flow, water hoses connected wrongly, etc.). Probably the consequences are unimportant in this ease, but there areother cireumstances where reverse flow is both possible and dangerous-for example, a vent "sucking back" liquid from a seal. In the same way, MORE flow of cooling water is just wasteful, but the same guide word applied to the addition of acatalyst or reagent could indicate the oossibilitv of owrheatine and a runauay renrtim. T h r word .\LSO suggests sumethlnc nddirimnl ro what is Lntendcd; the w r d OTHER means that sumeth~ng happens instead
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