Chemical instrumentation Edited by GALEN W. EWING, Seton Hall University, So. Orange, N. J. 07079
These articles are intended to serue the readers of THIS JOURNAL by calling attention to new developments in the theory, design, w availability of chemical laboratory instrumentation, or by presenting useful insights and explanations of topics that are of practical importance to those who use, or Leach the use of, modern instrumentation and instrumental techniques. The editw invites correspondence from prospective contribulors.
LVI. Nuclear Quadrupole Resonance Spectroscopy.
Part TWO-instruments
J. A. S. SMITH,
School of Molecular Sciences, University of Warwick, Coventry CV4 7A1 England
resonance spectroscopy, the frequencies of nuclear quadrupole resonance depend Part I of this series appeared in the on the nature of the molecule of which January, 1971 issue of THIS JOURNAL, the quadrupolar nucleus is part, and can page 39. Additional portions will conrange in practice from a few hundred stitute the March and April TOPIC8 colkHz to over 1000 MHz for some of the umns. The entire series will be reprinted heavier nuclei. No single spectrometer together; limited numbers of reprints will a t the present time spans a frequency he available from the author or from the rmge of 13 octaves, so that the design column editor. of the instrument depends very much on the frequency range to he investigated. G. W. E. As a. rough generalization (to be discussed further in the fallowing pages), below 5-10 MHz one uses s mt~rginal INTRODUCTION TO oscillator or some kind of limited oscillator, whereas above 10 MHz and up to at INSTRUMENTAL METHODS least 700 MHz the super-regenerative The present article is concerned with oscillator is most used, pmticolmly when recent developments in the kinds of wide frequency sweeps are necessary, alinstrument that can be used to detect though rf bridge methods have recently and record nuclear quadrupole resonance been used over narrow frequency ranges. signals in the solid state. At the present Because of it3 widespread application, we time, these methods (together with the therefore discuss the super-regenerative related measurements of quadrupole split oscillator in some detail. ting in nuclear magnetic resonance) furnish The majority of measurements of nuthe most accurate values of quadrupole clear qorsdrupole resonance frequencies in coupling constants in solids, the resolving solids has been made with this instrupower in general heing a. factor of 10' ment. The reasons for its popularity will greater than that obtained in Miissbauer he analyzed shortly, hut it is perhaps spectroscopy. worth commenting that it is a relatively Two different instrumental methods will easy oscillator to build, hut extremely he described. In the &st, the principle difficult to control. I t is therefore the objective of the experiment is to measure simplest and cheapest kind of radio frefrequencies and if possible line-shapes with quency spectrometer to huild p~ovidedone the maximum svaihble sen~itivity;the has the fairly limited objective of detecting predominrlnt detector in thin group is the strong signals d l lying in a narrow fresuper-regenerative oscillator, although quency range; some detail will therefore other kinds of oscillittors me important. be given of the construction of a simple In the second group of methods, the spectrometer working in the range apobjective is to measure the way in which propriate to many jSC1 frequencies (viz., the system responds to bursts of radio25-45 MHz). At the same time, we will frequency power, i.e., the relaxation discuss hrieflv the kinds of modification properties of the nuclei; the important instruments in this group use pulse techniques. control, and automatic frequency calibraMETHODS OF MEASURING tion. The super-regenerative oscillator was NUCLEAR QUADRUPOLE the first instrument to he used in the RESONANCE FREQUENCIES detection of nuclear quadrupole resonance in solids by Dehmelt and Kriiger in 1950 I n sharp contrast to nuclear magnetic Mitor's Noh
Dr. J. A. S. Smith, who at present, is Render i n hIu1crnl:rr Srie~lces;rt tho ilnivemity of M'nl.wicl\, Coventry. Englnad and h a recently been appointed to a Chair of Chemistry at Queen Elizabeth College in the University of London, graduated and took his doctor's degree n t the Unversity of Oxford. IIe is co-inventor of an nutornntio nuclear oundruoole resonance spectrometer whieh is now being manufactured commercially, 2nd has a grent interest not only in npplications of this kind of speotroseopy to physical and inorganio chemistry, but also to the study of molecular eleetronio structure and the way in which it is modified in crystals. He also works in the fields of X-ray crystallography, inelastic neutron scattering, and pulsed nuclear magnetic resonance, as part of his general interest in .moleeulnr structure and moleoulnr motion in the solid state, in which field he has contributed over fifty papen in the ehemioal and physical literature.
(SO), after an earlier unsuccessful search by Pound ($1) in 1949. Much of the later development of the instrument was due to Dean (bb), whose work in particular laid the basis from which s, fully controllable instrument could he huilt. In order to discuss the important features of this instrument, we must first discuss the way in which it is believed to work. Oddly enough, the instrument was used for many y e a s before a completely satisfactory account of its mode of operation was presented! Super-regenerative oscillators work intermittently, the rf train being interrupted s t regular intervals by an internal or external quenching mechanism, corresponding to a quench frequency lying usnl~lly in the range of one hundredth to one thousandth of the rf frequency. The rf envelope therefore appears as in Figure 7 which shows (a) the quench waveform and (below) the rf envelopes of the oscillator working in the so-called logarithmic mode, in which each rf wave-train is allowed to build up to its limiting value before the quench action commences. In (b), the (Continued on page A78)
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Chemical Instrumentation first rf pulse dies away completely before the next is initiated by noise, the so-called incoherent mode; in (c), the second pulse is initiated by the trail of the preceding one. The super-regenerative oscillator has the almost unique feature among oscillators of variable coherence and several different kinds of rf power spectrum can be obtained from the instrument according to the pulse-frequency or alternatively to tom the time for which the quenching pulse is ( a ) QUENCH WAVEFOW
(b) INCOHERENT Leading edge diffuse since oscillations build up from noise.
( c ) COHERENT
may distinguish the fundamental f, and sidebands spaced a t intervals of f,, the quench frequency. In the completely coherent made, the power spectrum consists of a set of frequencies separated by f,, the maximum intensity being a t f., and this would be the pattern observed in a rsdio receiver placed close to the oscillator. Note that the width of each of this set of frequencies is variable according to the degree of incoherence. It may be useful at this stage to describe a circuit for a super-regenerative oscillator. Among the first to be given in the litere,
+
(d) COHERENT and with large input signal. Figure 7.
Oscillmtion emelope of a super-regeneratire orcillmtor.
a. INCOHERENT
Figure 8.
Power spectrum of
0
off (which is just half the reciprocal of the pulse frequency when the pulse train has unity mark-space ratio). Three selected states are illustrated in Figure 8; st (a), we have the fully incoherent mode, when the spectrometer transmits a. broad band of frequencies centered on the fundamental frequency of the oscillator, fa. As tom is shortened, the oscillator moves into the coherent mode; sharper peaks appear in the power spectrum, among which we
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mper-regenerative oscillabr.
ture for the detection of W l quadrupole resonance frequencies, which mostly lie in the range 4-70 MHz, was that quoted in Das and Hahn's book (ref. 4, p. 90) which was devised by Dean, who has also given a simplified version ($3) of the circuit suitable for beginners. Most later workers have used modifications of Dean's original circuit. Several versions have been developed in the author's laboratory (Continued un page A80)
very suitable for demonstrating the henomenan of nuclear quadrupole resomoe. The circuit is a quenched Colpitts icillator, the quenching action either zing governed by an ezternal quench
square-wave, with mark-space ratio of about unity, note that the coherence will depend critically on the quench frequency, since this governs tom. The sample is contained within a small induction coil L shown on the lefbhhand side of the circuit, which serves to generate the rotating
oltage applied to the grid of V1 or interallv by replacing the 27 k resistor on the rid by 8 fixed 22 k fallowed by a variable M to earth (varying the latter changes
magnetic field which as we have seen excites the transitions. The coil is tuned by the large tuning capacitor C; the var(Continued on page d82)
?4), one of which, shown in Figure 9,
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Chemical lnstrumentation actor diode D then enables one to sweep the frequency at (say) 50 or 60 Hz by application of an sudio-frequency sinusodid or sawtooth voltage across the two terminals marked S (note the reverse biasing of D). The width of this f r e quency range is governed by the applied alternating voltage and the 20-pf capacitance connected toD;for asweepvoltageof 10 V and a suitable hias on SS to prevent forward conduction of D, the frequency variation will be a small fraction of the fundamental frequency of the oscillator. If, for example, we are studying pdichlorahenzene a t room temperature (vp near to 34.27 MHz), the depth of frequency modulation might he zt50 to 100 kHz. Tuning C to within 50 kHz of 34.27 MHz then means that the oscillator is driven "through" the nuclear quadrupole resonance frequency of the sample a t a rate determined by the sweep frequency. At resonance, the system of nuclear spins and the radiation field of the coil will interact; omitting for the moment the precise way in which this interaction operates, we conclude that the presence of the nuclear quadrupole resonance signal introduces into the oscillator an additional amplitude modulation. If this is amplified by an audio-freqnency amplifier (a suitable circuit for which is shown in Fig. 9) and the output resented to the Y-plates of s cathode-ray oscilloscope, the X-plates of which are fed from the same source used for the frequency sweep, a stationary
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Photograph of an oscillo~copetroce of ' T I resonance in KC103 ot r w m temperature,
Figure 10.
picture of the nuclear quadrupole resonance signal may he obtained. If, for example, one uses a sawtooth frequency modulation (and many oscilloscopes have a, direct output from the time base which is suitable for this purpose), then the horizontal displt~cement on the oscilloscope may he linear ((or nearly so) in frequency, the absorption line appearing as a peak in the trace, usually superimposed on a more slowly varying hackground produced by amplitude modulation alwavs mesent in the circuit. Firmre 10 shows such a trace for 'Cl resonance in "
A
KCIOs at room temperature; the fund* mental frequency is near 28.2 MHz. Before discussing the precise way in which this circuit is believed to operate, we give R few hints on the construction and operation of the circuit and a suitable choice of ssmples. The rf oscillator section should follow good high-frequency wiring practice, with short Iiads from the tube base to all componenk of the oscillator; it is in fact sdvisahle to place all companents in a copper (or, less advisably, an aluminum) box with a coaxial connection (Continued on page A84)
to the rf coil, which should be as short as possible. The tube V1, marked as a 6C4, could equally well be an EC90 or half of a 12AU7; once a signal has been found, it is advisable to try several tubes of the same kind and select the one which gives the best signal-to-noise ratio. D is a variable capacitance diode; several types are suitable here, particularly the low-noise varieties, the important condition being to keep the diode always reverse biased and not to exceed the maximum rated reverse voltage (which is 30 V for the BA110). The sweep voltage may he derived, as stated previously, from the oscilloscope time brse or if this is not available from a mains transformer s u p plying (say) up to 20 V; in either case, it may be necessary to supply the reverse bias by means of a small battery. C, the main tuning element, should be a good quality tuning capacitor with an equally reliable slow-motion drive. The highvoltage supply should be reasonably stable, and free as far as possible from hum; batteries are, of course, the simplest way of derving such a voltage, but prohably not the cheapest in the long run. Immediately following the anode load come the filters which remove quench components from the anode waveform; from there, the signal goes to the preamplifier shown in Figure 9; this has no critical constructiond features but should
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scope--or the hesdphones which may be substituted for it. The best samples to try at first are probably carbon-chlorine compounds with a good proportion of chlorine; one of the best in practice is p dichlorobenzene, which shows a strong signal (together with the sideband responses) near 34.27 MHz at room temperature. The material should be carefully recrystallized, dried, and packed as densely as possible into a 12 or 14 mm sampletube with as thin wtslls as possible (some manufacturers supply egg-shell glass which is very suitable for this purpose). The ooil may he made from about 5 turns 18 swg varnished copper wire wound fairly tightly on the sample tube with a spacing equal to one wire diameter between turns; it is advisable to fix the coil to the tube with an adhesive (of low dielectric loss) to reduce microphonics (see Fig. 12 for some commercial rf probes). The depth of sample in the tube should be sufficient to overreach the two ends of the coil by several millimeters. From the chemist's point of view, nuclear quadrupole resonance is clearly rather demanding in the size of sample required. Usually a t least 2-3 g. are required when a search is being carried out, but there artre many compounds which give strong sign& from as little as 0.1 g. Once the sample has been attached to the oscillator, for example by s coaxial plug and socket, the whole unit should be left for 10 min or so before s serious search is made, in order to reduce the effect of inhomogeneities in temperature across the srtmple produced by han(Continued o n page A86)
dling (most nuclear quadrupole resonance frequencies are highly sensitive to temperature, as we will discuss in the third article). C is then adjusted to bring the oscillator frequency near to 34.27 MHz, either by picking up the frequency, on a. radio receiver or by injecting a signal of this frequency from a signal generator. In a. receiver, one detects the frequency spectrum shown in Figure 8c, and the loudcst beat note may he assumed to be the fnndamentd. The coherence is next adjusted to give a. noise pattern on the oscilloscope intermediate in strength between that for complete coherence and that for complete incoherence; the same adjustment may be made with the help of a radio receiver, when one listens far a reasonahly.sharp set of sidebands rather than the broad spectrum of noise obtained in the incoherent made. Careful adjuse ment of C should then bring the signal onto the oscilloscope, and, once found, the best signal-to-noise is sought by small adjustments of the quench frequency. If the oscillator is found to have "deadspots" in which oscillations cease, the fault may lie in the wrong choice of B rf choke in the cathode circuit, and another should be tried. Unfortunately, the oscillator is also liable to give spurious responses arising for example from internal resonances or interference from radio stations. To eliminate these, one simply removes the sample, and returns C to the original rf frequency, when the "signals" should
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disappear. Alternatively, one may use the sensitivity of the quadrupole resonance frequency to small magnetic fields; as we have discussed in the first article, the field produces a splitting of the line, the separations being dependent on the orientation of the crystal with respect to the applied field. In a poIycryslalline specimen, s range of splittings is produced, so that the line is broadened and if the magnetic field is strong enough will eventually disappear into noise. To test whether an observed response is a. nuclear quadrupole resonance or not, one therefore brings up to the coil and sample a. small bar magnet. The line should broaden and eventually disappear if i t is a true signal, but note that too close a proximity of the metal magnet may also shift the frequency. A third method is to change the sample temperature, e.g., by immersion of the coil and sample in a suitable refrigerant, when the frequency will also change, moving usually to higher frequency at low temperature. If the coil is attached by s. short length of coaxial cable (say 10-20 cm) to the coaxial plug, it may be possible to immerse the sample in liquid nitrogen and so observe spectra at a. ssmple temperature of 77'K (liquid oxygen or liquid air must NOT he used in contact with organic samples). Resonance signals may then be seen in compounds which are liquids at roam temperature; for example, a t 77OK, CHCb gives two strong signals (with sidebands) at 38.254 and 38.308 MHz. The a phase of hexachlorooyclopentadiene, CsClr gives (Continued on page A88)
Chemical Instrumentation an excellent spectrum with six lines a t 36.952, 37.279, 37.283, 37.452, 38.812, and 39.082 MHz, the second and third lines heing resolved as s closely-spaced doublet (4 kHz) if the frozen sample is left to
"mature" for half-an-hour or so. (It may be necessary to "pre-cool" the sample in solid COz in order to get this spectrum.) If the liquid nitrogen is allowed to evaporate, the nuclear quadrupole resonance frequencies will decrease as the temperature rises and vanish altogether as the melting-point of the sample is approached. In all these examples, one sees on the oscilloscope hoth the fundamental and several ~idebands,usually well separated sinoe line-widths (1-5 kHz) are less than the usual quench frequencies (30-50 kHz). One way of distinguishing the fundamental response from sidebands is to vary the quench frequency; the fundamental will not change its position on the oscilloscope screen hut any sidebands will move to and fro in synchronixn with thk variation. Unfortunately varying the quench frequency also varies the gain of the oscillator, so that in practice this procedure is sometimes difficult to perform satisfitctorily. We now return to the problem of how the super-regenerative oscillator works in detecting signals, and this in turn will lead us to wnsider recent improvements in its design which have lead to the production of almost automatic spectrometers. We may consider the super-regenera-
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tive oscillator to act in two WBYS:Iirstly, as a detector of nuclear qusdrupole resonance signals, and secondly as an ezcitor of such signals. In its first role, what we know about the oscillator is consistent with the following picture. From the moment when the application of the quench waveform stops oscillations, the rf envelope begins to decay at a rate governed largely by G,/CI where Gois the effective conductance in parallel with the tank circuit during the off-period and C, is the total tank circuit cappacitance. In the wherent mode, the tail of this pulse initiates the next; in the presence of a nuclear quadrupole resonance signal, however, there will be sn additional component arising from the nuclear magnetization, so that the amplitude of the exponential decay will be slightly larger and the next pulse is initiated at a slightly earlier point in time. In Figure 7d, the oscillator envelope in the presence of a signal is therefore larger than in its absence (Fig. 7c), so that the presence of a signal changes the auerage anode current of the oscillator tube and produces an additional voltage across the mode impedance. The output voltsge, VOUT,of the circuit operating under these conditions will be proportional to Jq in (Va/Vt) where V* is the rf voltage in the pulse tail in the presence of 8. signal and V, that in its absence, and J, is the quench frequency; hence by making VI as smdl as possible, we get a high signal response and n sensitive detector of nuclear quadmpole resonance sign& We should add that the above relation is slightly modified when we wme to consider the efficiency of
the oscillator as an excitor of nuclear quadrupole resonance signals, hut our basic wnclusions remain unaltered. The modified equation for the gain of the system, Vou~/Vs,where Vs ia Lhe amplitude of that conlponent of the nuclear magnetization which is in phase with the ~ u l s tail, e is VoUT = -
Vs
CtfQ(l- J g t o ~ ~ ) e x(GDto~~/2Cd p (43)
The gein is seen to depend on hoth quench frequency and C. the total tank circuit capsoitmce; since i t is the latter that we vary when we wish to change our operating rf frequency, i t is clear that the gain will depend critically on frequency and the instrument would need frequent readjustscans. To ments durine laree freauencv . make the instrument into a workable spectrometer, some form of automatic gain control is necessary. Two such systems have been described in the literature, hoth stemming from Dean's pprpwal ($9) that the overall gain for a resonance signal can be wntrolled by maintaining the noise output of the spectrometer constant. The control signal will therefore be obtained from the oscillator by amplifying and rectifying noise voltages in the approximate frequency range of (say) 2 to 7 kHz (with suitable filtering from any modulation frequency comp&ents, or any harmonics thereof, and any quench frequency com~onents). The two svstem differ in the &ay in' which this kntrol voltage,
.
derived from noise, is used. In the first, due to Peterson and Bridenbaugh ((86), the oscillator is self-quenched and the control voltage adjusts gain by changing f, via the grid time-constant. This control system is incorporated into the spectrometer manufactured by the Wilks Scientific Corporation.* In the second, due to Smith and Tong, ((88), the control voltage changes t o m and, when necessary, Go,and forms the basis of the spectrometer manufactured by Ileces.*' This method of control dso enables the spectroscopist to remove the quench sideban&, to which we hrwe referred earlier, using a method first suggested by Dean and Pollak ((88). They that one should modulate the quench frequency s t a rat,e fast compared with the recording time constant bnt slow compared with the modulation frequency; the sidebands then vary in frequency and are unable to get through to the recorder. To put Dean and Pollak's suggestion into practice, one needs therefore to keep the gain constant, but change f,, and this can be done by using a quench waveform of constant tom but variable puke repetition frequency. The automatic gain control then takes care of the small changes in gain ~raducedby the vmietion of j, according to equation (43). Figure 11 shows a. photograph of the Decc* spectrometer; the oscillittor is a t the left of the photograph above the box containing the Dewar system and the magnetic modulation coils which provide the modu'South Narwdk, Connecticut, U.S.A. **Wdton-on-Thames, Surrey, England.
~ ~ s u r 1e1 . The Decco refononce spectrometer.
nuclear
quodrvpole
lation of (Ire signal when a permanent record is required. The central unit contains the control systems, modulation generators, frequency markers, and power supplies. The recorder is tracing out part of the complex lBline pattern of W l resonance in CCI. a t 77'K. Some typical rf probes with sample coils and containers are shown in Figure 12.
Super-regenerative oscillators hrwe been operated up to at least 800 MHz, and there seems no reason why automatic gain eontrol systems should not function over the whole of this range. Below 10 MHa, however, the gain of super-regenerative oscillators with respect to nuclear quadrupole resonance signals begins to fall, and some of their advantages s t high frequencies (such as a high effective rf level) cease to be of such importance. For "N resonance signals, which lie below 5 MHz, one therefore turns to mrtrginal or limited oscillators for sensitive signal detection. Two well-known circuits have been in common use far many yeamone due to Pound, Knight, and Watkins (87) and the other due to Robinson (88)and their performance and cha~acteristics are clearly described in the references quoted. References (20) DEXUELT, H.G., and KRUOER,H.. N a l w wissenschojlcn. 37,11 (1950). (21) Poulm,R. V., Phys. Rsu., 79, 685 (1950). (22) D e m , C., reported in Ref. 4, p . 90; DEAN C.. and PoL>*K. . M.., Rev. sei. Indrum.. I: DEAN, C . , Re". Sci.
968): DIXON, M.. Thesis, Univ. of ,>oem
(25) PETER~ON. G . E., and B r n n s ~ e ~ uP. o ~M.. , Re". Sci. In&um., 35, 698 (1964); 36, 702 (1965). CON., D. A,. J . S C ~ .
(1968).
:NIOXT.
W . D.. RN.
Figure 12. Typicol rf probe. used in nuclear qwdrupole resonance spectroscopy.
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in the Chemical laboratory Edited by N O R M A N V. STEERE, 140 Melbourne Ave., S.E. Minneapolis, Minn. 5541 4
LXXII.
Accident Facts in Two Clinical LaboratoriesA Ten Year Study GRACE M A R Y EDERER, M.P.H., Associate Professor, Department of Loboratory Medicine, Division of Medical Technology, University of Minnesota, Minneopolis, Minnesota 55455 B A R B A R A TUCKER, B.S., Chief Administrative Technologist, Northwestern Hospitol Division of Abbott Northwestern Corporotion, Minneapolis, Minnesota 55407 A l J A V I K M A N I S , B.S., formerly Assistant to the Director, Division of Clinical Laborotories, Deportment of Laboratory Medicine, University of Minnesoto Hospitals, Minneapolis, Minnesota 55455
...a
a ! D
feature
Council (i, 5, 4). The US. Buret~uof Labor statistics for olinioal laboratories studied in 1963 were used for comparison (5, 4 ) Unplanned consequences of unsafe acts in combination with other circumstances, which caused a harmful effect or an effect questionably harmful, were reported as accidents. These were counted and evaluated to orovide an insirht, into the mfetv trends kithin the two problems of the two institutions. They were compared with the accident experience of a previously reported study (8)in these institutions since these facts were not available on a national basis.
Abstract
Methods
Results
The accident experience during 19601969 in the clinical laboratories of a university hospital and a private hospital were compsred. The frequency rates per million man hours for disabling injuries was 2.21 and the severity rate was 14.1 in the university hospital laboratory. These two rates were zero in the private hospital. Minor accidents which did not cause loss of time were also reviewed. In both lsboratories the personnel most frequently involved in minor accidents were medical technologists. The areas of the body most frequently affected were fingers, hands and arms. Improper handling of glass was the major cause of these minor accidents.
Acoident facts were collected in two clinical laboratories, an 850-bed university hospital laboratory and s. 400-bed private hospital laboratory. Definitions for counting the events were estahlished. Disabling injuries were counted as those injuries which prevented the person from performing any-of his usual duties for a. full day or more beyond the day of the aocident. The injury frequency rate was determined per million man hours of exposure. The severity rate was established according to the number of days charged for work injuries per million mawhours of exposure. These definitions and calculations for frequency rates were in agreement with those of the U S . Bureau of Labor and the National Safety
The disabling injury frequency rates and severity rates of the two hospitals for the period 1960-1969 are shown in Table 1. There were no accidents which involved loss of time beyond the day of the accident in the private hospital. The disabling injury frequency rate of 2.21 for the university hospital for this 10 year experience compares favorably with the weighted experience of over 5000 hospitals surveyed in 1963. The disabling injury frequency rate for all hospitals was 8.3 in 1963 and for d l clinical laborat,ories was 3.1 (4). The severity rates published for 1963 of 313 and 141 for hospitals and clinical laboratories respectively are far more then those of the university hospital laharstory over a ten year period (4). The average severity rate for industry for 1968 was 665 (I),which was far more than that of total hospital experience in 1963. The disabling injuries of university laboratory personnel were incurred during four of the ten years. The data concern-
There have been countless articles about safety programs and safety me* Table 1. Frequency rates for sures in clinical laboratories published disobling injuries 1960-1 969 during the last ten years. There &re, University Private however, only a few publications which Ibtes deal with acoident facts in this area (8,5,4). The purpose of this paper is to present Injury frequency 2.21 0 ing these accidents is shown in Table 2. the accident experience of the last ten Four of the disabling injury-producing ratell, 000,000 years, 1960-1969, in two clinical laboraman hours accidents occurred in the supportive tories. These facts are presented to Severity rate/14.1 0 personnel group and three in the profesprovide 8. point of reference for hospital 1,000,000 man sional medicd technologist group. Four hours and laboratory administrators to use in accidents involved sprains; three of these evaluating the accident experience and effectiveness of safety programs under Table 2 . Classification of Iaborotory employee, days lost ond type of their management. The importance of accident in the universitv hos~itolloboratow objective evdustion of accident and Yea Classificrttian I h v s lost Tvoe of accident injury frequenoy rates is great since the hazard potentials are numerous in the 1961 Supportive personnel 3 Sprained wrist loading clinical laboratory. The costs to bosdish-washing machine pitals for compensation, medical services Supportive personnel 1 Sprained back lifting six 1-liter bottles and the replacement of damaged equipSu~oortive~ersonnel 2.5 Cut hand on broken ment for accidents and injuries of all glass personnel amounted to over eleven 1966 Supportive personnel 20 Burned leg, hot media, million dollars in 1963 (4). This fact bottom fell out of Z alone provides strong motivation for liter flask introspective study. The need to protect 1967 Medical technologist 10 Frozen hand, propane each worker, however, provides the loaG .greatest incentive to look a t the facts Medical technologist 2 Sprained beck lifting 5 in order to find the major causes of gal carboy 1968 Medical technologist 6 Sprained ankle on chair minor accidents so that efforts can be 7 em~lovees 44.5 davs Total directed towa~d eradication of minor accidents in order to bring disabling in(Continuedm page A98) jury frequency rates to zero.
..
LU*..
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