mfety In the
edited by MALCOLM M. RENFREW Univer~ityof ldaho Moscow. ldaho 83843
Safety in the Analytical Laboratory Galen W. Ewingl New Mexico Highlands Unlversity, Las Vegas, NM 87701 I t muat he dear to all readers of this series that many of the safety rules apply to all chemistry laboratories, including those devoted to analytical work. The present section is therefore devoted to those features that are unique to the analytical laboratory or especially important there. Poor techniques that endanger only the validity of analytical results I do not consider "safety" hazards, hence I will usually not treat them. However, I will include practices that are unsafe in that they endanger expensive apparatus and instruments, whether or not the operator is endangered. I must give special attention to eye protection. I have had students refuse to wear their protective goggles, for instance, when using the analytical balance; it may he un-
likely that a spattered chemical will he encountered in the balance room, hut you never know what fool thing your neighbor may do! If a separate room is set aside for computer terminals, all chemicals should be strictly outlawed, and perhaps the eye protection can he dispensed with. Ass general exhortation, let me quote the old saying: "Familiarity hreeds contempt." There is a tendency, in the chemistry lab as elsewhere, to become careless about safety rules. One says, in effect, "I have been doing chemistry for such a long time without any accidents that I now have a 'feel' for what is acceptable procedure, and hence I will automatically do things the right way without thinking about it, and accidents will not
happen to me.'' Famous last words! Hazardous Reagents Many chemical reactions ofanalyrical importance involve the use of potentially dangerous reagents, and with these careful adherence to safety rules are mandatory. Examples include the following: The use of strong acids is required in the dissolution of many refractory or inert samples. Stainless steels and other alloys may require concentrated mixtures of HzSOnor HCIOl with H3P04. Noble metals such as platinum can only he dissolved by mixed concentrated HNOl and HC1 (aqua regia). Such procedures should he carried out in all-glass vessels (no rubber stoppen!) in a well-ventilated fume hood, with a protective shield in place, as well as the usual personal orotection afforded hv safetv elasses and laboratory aprons or theu equi\alent. Perchlorle acrd mwt he used only m an appnr. pr~ntelgdesigned fume hood devoted exrlu. sively to this service. Concentrated perchloric.acid, especially, should he treated with the utmost caution. Used under ideal conditions it is safe, but it should never he heated in contact with any organic matter, including alcoholic solutions. Even traces of stopcock grease may cause a disastrous explosion. Another acid sometimes called for, particularly in the dissolution of silica-containing samples, is aqueous HF. The hazard here is not the possibility of explosion, hut rather the toxicity of hydrofluoric acid and many of its salts. A drop of H F solution on the skin will produce a painful lesion that is very slow to heal and requires special medical attention. I speak from personal experience. Some analytical procedures involve the use of gaseous or volatile reactants that may he toxic. These include H2S, SOn, Brz, and HCN. amone others. Thev should alwavs be handled in closed fume hood. ~ & oft these substances have disagreeable odors that help to announce their presence, hut in some instances they are toxic in small enough concentrations that their odors may not he noticeable (CO has no odor!). Reliance should not be placed on odor, especially as individuals vary widely in their ability to detect odors. H B is particularly dangerous in that it deadens the sense of smell when the concentration hecomes relatively high, justwhen this warning ismost needed.
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Transfarrlng S a m p l e s Analysts frequently need to transfer a
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Journal of Chemical Education
small, accurately measured, portion of a solution from a volumetric flask or other such vessel to another container, normally done with a volumetric pipet. In former times, this was done by mouth, sucking up the liquid into the pipet to some level above the etched mark, then allowing it to drain out slowly until the mark is just reached. The danger in this procedure is that the tip of the pipet may not be immersed far enough into the solution, and as the level is lowered by removal of liquid, air will be pulled into the pipet. This effectively blows liquid that is already in the pipet well past the desired terminal level. often out of the too of the nioet entirelv: This is esmeiallv iikelv " to happen if one is applying auction by the lips directly at the pipet, hecause then the position of the apparatus is such tbat the operator cannot see what is going on. Of course in this situation the liquid that overflows the top of the pipet ends up in the analystk mouth, a distinctly unpleasant and unhealth" event. I t is true tbat some solutions are bmign, but it highly ilnmse to try to d~tferentiatebetween toxicand nontoxic solut~onr:o 1 u . a ) ~treat them ar though they were known poisons. This overflow can also occur, of course, when a safety pipet filler (such asa ruhher bulb) isused in place ofthe lips, but in this event the hazard is to the correctness of analytical results, without personal danger to the operator. Transfer by pipet is particularly difficult with volatile liquids such as methanol or bromine, and special care must he taken. Transfer of liquids by pouring from a reagent bottle also has its dangers. Spattering is always possible, especially if the reagent is being added to another solution with which it reacts exothermieallv. The usual warnine about adding acid to water, not water to acid, is a h a ) %valid when concentrated scids are involved, but [he same principle ex. tends t o other systems than acidlbase. Sometimes it may not be immediately evident which reagent should he added to which, but in general one can say that the more concentrated or more hazardous should be added slow& to the less concentrated or hazardous. Thus any spattering that may occur will involve droplets of a more dilute and less dangerous material.
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Cleaning Apparatus After using glass apparatus, it is always wise to clean it before storing it away for future use. There are many methods of cleaning, and some of them are hazardous. One of the most effective procedures, also one of the most dangerous, is to soak the apparatus in a solution of "chromic acid" made by adding potassium dichromate to concentrated sulfuric acid. This is highly effective a t removing grease and uneharacterized "gunk". But it is also effective at removine,. fineers .. and makine hales in clothing. (In addition, it involves the use of a carcinogen ) In the analyriral latwratory the type of reridurn lrkely to be present in used glassware almost neuer requires the use of this material, and it should he outlawed. Much safer is the use of soap or a laboratow detergent, which offers minimal hazard. Often it is better not to use any cleaning solution; I have seen students "clean" with detergent and vigorous application of a brush, aflask that has held only dilute HCI; (Continued on page A160)
Volume 67
Number 6
June 1990
A159
rinsing with distilled water would have been just as effective and much less work. Similar rules apply to cleaning crucibles and other porcelain ware.2 A special problem is encountered in cleaning glass (or quartz) cuvettes for spectrophotometers. The difficulty here is due to the small size, which makes it difficult to avoid dropping. More than once I have seen a student wash the outside of e cuvette with soap, then while his fingers were still slippery, hold it under the tap, whereupon the force af flawing water swept it to destruction. And these cuvettes are expensive! A detail here: if a quartz cuvette is to he used in the ultraviolet, fingerprints must be avoided, because they can absorb some of the UV; wiping the optical surfaces with a piece of filter paper wetted with alcohol or acetone should take care of it.
Eye Protection Besides the usual protective goggles, precautions must often be taken against optical damage to the eyes, especially from highintensity ultraviolet radiation from a xenon lamp or welding equipment, for examples, or from laser beams. Light from any of these sources can cause acute discomfort in the eyes, often not evident until several hours after the exposure. When working with such sources, safety goggles or face masks are essential. Sufficient light may be reflected from shiny surfaces to be harmful, even whenit reaches the eye from the side, so that side shielding is necessary. Ordinary sunglasses are not adequate. Manufacturers of lasers are required to label their products with warnings against eye contact, identifying the specific filters needed for protection. Such warnings should always be taken most seriously. ULtraviolet lasers do not produce any visible light, as most other UV sources do, sothat it is not easy to know whether they are turned on or not. I might mention here other poasible side effects of ultraviolet radiation, particularly the accompanying production of ozone, which is toxic. I once had occasion to carry out a prolonged photochemical experiment requiring 2537-A radiation from a mercury lamo. The exueriment was run unattended overnight to avoid eye problems, but in the morning it was discovered that the lahorato. ry was flooded. Rubher hoses carrying cooling water had deteriorated by the action of ozone to the point where they could not withstand the water pressure. ~~~~
Equlpment Damage Analytical instruments are easily damaged by misuse. In the first place, instruments should he located in a separate room, preferably air-conditioned, and no chemical ~roeedures(includiue such annarentlv behe carried out in the inslmrnent room. The only exception co this rule should be made for instruments that perform on-line operations. There is no way, for instance, that a stopped-flow spectrometer could be operated at a laeation remote from the associated chemical equipment. But great care should be taken to avoid any spillage of chemicals,
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Journal of Chemical Education
especially solutions, into or onto any instrument. This applies to cups of coffee and bottles of soft drinks. I was once given an infrared spectrometer that had been completely ruined because a coffee maker that had been set on top of it had overflowed! In normal use, no well-designed instrument should be damaged by incorrect settings of the controls. (If you are using a homemade instrument, however, this may not always he true.) roubles shooting should always be left to an experienced person, and this applies to 8eemindy simple repairs, such as installing anew lamp in a spectrophotometer if the old one fails to light; some lamps must be handled with special precautions, and some require special focusing procedures. Replacing a lamp with a different type may result in burning out a power supply or in creating mare heat than the cooling system is designed to handle. If a fuse blows, it is not wise merely to replace it; there must have been a reason for its failing, and a replacement is likely to burn out immediately. The source of trouble should be identified first. If this proves illusive, then-"If all else fails read the direetiona!" Actually, this directive should not be taken too Literally. It is hoped that you will have studied the directions carefully before "all else fails". Electrical safety rules must always be followed carefully, especially with apparatus that has heen constructed (or repaired) by amateurs, often including professors. Equipment assembled by students should, if possible, take their power only from batteries. If power-line connections are unavoidable, the line cord should always be of the three-wire type, with the third wire (the "ground" wire) connected solidly to the chassis of the instrument. This makes electrical accidents much less likely, though it cannot entirely prevent them. A fault in the internal wirine" or in external connections to other laboratow eauioment is much ~ more ~ , likely to shunt the power off harmlessly to ground through the third wire thancopassit through the higher resistance route, including the operator's body, to ground. High-voltage equipment must be used for some experiments, and require special precautions. Photomultiplier tubes operate a t 1 to 2 kV, hut only draw a few milliamperes of current. This is enough voltage to result in a painful shock. If you have to work with a eource like thia out of its normal environment, be sure that the power is turned off and that all capacitors in the unit are discharged, usually by clipping a wire across their terminals. When working with these sources, it is wise to keep one hand behind your back since the results of a shock current passing through your body from one hand to the other is much more severe than from one finger to the next on the same hand. Power supplies for certain types of lasers and other high-powered lamps (xenon lamps, for instance) are designed to supply several nmoeres a t a few thousand volts. These are much more hazardous than~the photomultiplier supplies, and should be repaired nnly by experienced service personnel. ~~
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' Emeritus Professor of Analytical Chamlsby. 'Some itemsare not wolm cleaning. A test tube !hat has been used in me destructive distillation of wood or coal is likely to oe COV~IM internally wlm black carbon. When a student asks me what solvent will clean it out. I tell him or ner that caroon s only soluble in molten imn Galm W. Ewlw received his BS degree at me College of Willlam and Mary in 1936 and his PhD at the Unlversity of Chicago In 1939. His graduate specialty was in physlcai chemistry, but his work b a defenserelated laboratory during World War II sacn changed his interests to analytical chemlsby wlth panicular emphasis on electronic insfrumentation. His fist teaching was at Blackburn College, then (after the war) at Union College and New Mexico Highlands University. He lefl Highlands in 1964 for Seton Hall Unlversity where he taught for 15years. retirlng in 1979. Hethen returned to New Mexiw Highlands as adjunct prcfessor, wlth a year as visiting professor at Carleton College. His research interests have been in various fields of elechoanalyilcal and spsctroswpic lnstrumentation. Ewing has wrinen several textbooks. including lnslrumentai Methods of ChemC mi Anaipis (Mffiraw-~iii) and (wim B. H. Vassos) Analog and Digital Eiecfronics fw Scientists (Wiley).His most recent work is as editor of a Handbook of Anaifllcal b sm,mentation, now in press with Dekker. Readers may recall h t ha edited for 12 years a monthly column entitled Chemical instrumentation in this Jownal.
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