Appendix 1 - Electrical current and the human body

There is a rather large inter-individual difference in the susceptibility for effects of electrical

current, as is illustrated in Table 1 by the difference in current inducing ventricular fibrillation in

5% and 50% of all persons. A similar variability is seen in the “let-go” current, which in women

varies between about 8 mA (5%) and 13 mA (95%), in men between 12 mA (5%) and 20 mA

(95%), with median (or 50%) values of about 11 mA and 16 mA, respectively [10] (the “let go”

current is the maximum current at which it is still possible to voluntary remove one’s hand from

a live part one is holding in his hand. Values higher than this are called “freezing” currents).

Currents through the chest above the “let-go” threshold may cause asphyxia, unconsciousness

and death if they are not interrupted in time. Induction of ventricular fibrillation forms the

greatest risk for a fatal outcome of electrical shock, however.

Small, seemingly innocent shocks can induce unintended, life threatening movements of the

sufferer. Larger currents may jolt the victim away from the apparatus due to strong, involuntary

muscle contractions. Severe muscular stimulation can cause ruptures of tendons and muscles and

even the fracture of bones.

Some factors affecting the magnitude and physiological consequences of an electrical current

through the human body are:

- The resistance met by the current. The resistance between the two hands is between about 1

and 10 kΩ, depending on contact area and skin wetness. Hand-foot values are 10% to 20%

lower than corresponding hand-hand resistances.

- The path of the current. The risk is especially high when part of the current passes through

the heart. Currents in the heart as low as 50 μA may cause ventricular fibrillation (the safe

1

limit is as low as 10 μA). The heart is most susceptible during cardiac repolarization (the T-

wave phase in the electro-cardiogram). Generally, fibrillation can only be ended by another

brief, strong electric shock that arrests the complete heart, allowing a synchronized restart.

- Shape of voltage. The thresholds for different levels of risk of fibrillation are somewhat

higher for full- and half-wave rectified currents (rms) from transformers than for the

corresponding unrectified currents. Table 2 illustrates this for situations in which contact lasts

several seconds. Thresholds for pulsed voltages (their amplitude, not the rms value) as

generated by an inductor are also shown in Table 2.

- The frequency of the source of electricity. The sensitivity is highest around 50 – 60 Hz, but

the IEC assumes a constant risk within 15 – 100 Hz. The threshold for fibrillation increases

with frequency, e.g., at 300 Hz it is about five times higher than at 60 (or 50) Hz, and at 1000

Hz about 14 times higher [11]. For DC-voltages the risks are also somewhat less than for 15

– 100 Hz AC-current, e.g. the threshold currents for ventricular fibrillation are about 3 times

higher than indicated in Table 1 when contact duration is between 1 to 10 seconds. For 10 ms

and 100 ms contacts, the thresholds are similar to those in Table 1.

As X-ray systems require high-voltage in addition to some primary source of “low voltage”

electricity, greater risks come into play. High-voltages (defined by the National Electrical Code

as > 600 V [10]) puncture the skin, lowering the resistance between two contacts on the body.

For the hand - foot resistance holds according to [10]: 5% of all persons have a resistance below

460 Ω, 50% of less than 620 Ω and 95% of less than 840 Ω. These numbers apply to AC- and

DC-current and are virtually independent of the size of the contact area. Depending on the

electrical power of the supply, high-voltages can induce very large currents (e.g., already 10 A to

2

20 A at 10 kV in case of a sufficiently powerful high-voltage source) causing severe damage to

tissues (e.g. to nerves, muscles and blood vessels) and subcutaneous burns.

A discharge may pass through the air, turning an insulating track of air into a conducting path

of rather low resistance. Fig. S1 shows the distance between sharp points high-voltage may

bridge in air through a discharge [13], which is taken as the minimum distance that should be

observed to prevent injury from a spark.

Fig. S1 Estimate of maximum distance a spark can bridge in air. It gives an indication of the

3

0 20 40 60 80 100 120 140 160020406080100120140160180200220240260280

Peak voltage [kV]Max

imum

spa

rk le

ngth

[mm

]

minimum distance that must be maintained from live parts of an X-ray system [13]. At 100 kV,

this is, for example, already 15 cm.

Appendix 2 - High-voltage power supplies used in X-ray systems

Static generators

Static generators based on the influence principle were already well developed in 1895

[16]. As they provided sufficiently high DC voltages for the production of X-rays, they found

immediate application in radiology. The early static models had the advantage of being run by

hand, and the continuous DC output eliminated the problem of “reverse current” that occurred

with induction coils after closure of the interrupter. Reverse current limited the life of the tube

and could cause X-rays to be generated at an unwanted place.

Static systems had disadvantages as well as they only produced small currents and

functioned poorly if the air was humid. Improved models, mainly variations of the Töpler, Holtz

and Wimshurst systems [17], soon became available [9,15], but the old problems were never

completely solved. When Leyden jars were used to achieve the desired high-voltage, these would

discharge through the tube once the discharge potential had been reached, resulting in a pulsed

X-ray beam much like induction coils produced.

Type (manufacturer) Diameter Plate[cm]

Numberof platesa

Speed of rotation[s-1]

Current[mA]

Wimshurst [17] 55 2 “max” 0.085Wimshurst [17] 55 8 “max” 0.21Wommelsdorf (Wehrsen) [18]

55 2 “max” 0.3 – 0.35

Toepler-Holtz (Wagner) [19] 71 4 30 1.3Toepler-Holtzb 71 100 30 10 - 20

Table S1 Current to be drawn from static machines

a a single element of any static machine consists in principle of 2 platesb very large system that was probably too expensive, complicated and noisy for common use from R.V. Wagner, Chicago, USA [20,21]

4

The manufacturers of static systems generally provided limited information on their

systems. Typically, they provided some construction details specific to their apparatus and the

maximum spark length. From this spark length the high-voltage, of the order of 50 – 150 kV,

could be deduced (Fig. S1). The current a system could deliver was usually unspecified. With a

few exceptions, we only found measured values in scientific publications, e.g., in the chapter

“Elektrisiermaschinen und Apparate” by Schmidt in Graetz’ books on physics [17] and in the

work by Wommelsdorf [22]. Some of this data is shown in Table S1. The maximum current of

the commonly used systems likely did not exceed 1 mA. When these static generators were

effectively short-circuited, e.g., by a person of low impedance touching both output terminals,

the current was not much higher as the system behaved as a current-source. Personal risks were,

therefore, small.

Because of the low maximum output current and the problematic nature of static

machines, most radiological professionals considered the more expensive induction coil superior.

Both slowly lost their place once the high-voltage transformer became available in 1907.

Induction coils

Like static generators, induction coils predated the discovery of the x-ray. [23]. Early

induction coils were mostly low power devices. For example, the Gerhardt, Bonn, system we

tested before was rated at 100 Watt, corresponding to an upper limit of the average secondary

current of 1 mA at 100 kV (in practice rather a few tenths of a mA) [42]. The new application of

inductors in generating X-rays prompted the development of more powerful systems.

Table S2 gives an overview of data for a few commercial products. Manufacturers of

inductors provided few specifications in the early years, which explains the many empty cells in

the Table.

5

Table S2 Power specifications of some induction coils (maximum high-voltage ≥ 100 kV)a

Application / manufacturer Year Primary power

(max) [kW]

Secondary power[kW]

Secondary currentb

(max.) [mA]

Diagnosis (and other purposes) Gerhardt, Bonn [42] <1896 0.1 1 Siemens & Halskec, Berlin 1901 2 Max Kohl, Chemnitz [24] 1902 3.3 Siemens & Halskec, Berlin 1908 15 45d

American X-ray, New York [45] 1915 6.6 2 20Therapy RGSe, Erlangen 1913 0.75 RGSe, Erlangen 1919 0.36 RGSe, Erlangen 1922 0.57

a All specifications from manufacturers, except for the Max Kohl coilb Time averaged currentc From Siemens MedArchiv (personal communication)d Estimated assuming an efficiency of 30% (see text)e RGS = Reiniger, Gebbert & Schall (Siemens MedArchiv, personal communication)

When the efficiency of an induction coil is known, the secondary current can be

estimated from the primary power. Salomonson performed such efficiency measurements for a

12-inch (30cm) spark induction coil from Max Kohl, Chemnitz [24]. The efficiency was between

35 – 54% when a rectifier was inserted to block the negative lobe of the output pulse and the

losses caused by the interrupter (likely a mercury interrupter) were taken into account.

According to Armagnat, the efficiency for a Wehnelt interrupter might still be lower, 20% or

even less [23]. These figures are similar to the efficiency calculated from the primary and

secondary ratings of the American X-ray coil as listed by the manufacturer [45], which was 30%

(Table S2).

6

Assuming an efficiency of 30%, the system with the highest primary power of 15 kW

(Siemens & Halske) would produce 4.5 kW at its output. At a high-voltage of 100 kV, the

corresponding time averaged output current would be 45 mA maximum. This was an impressive

output as Morton noted in 1915, “with a modern tube and powerful apparatus, a current of ten

milliamperes is quite ordinary.” [25].

In therapy the power used was generally lower than in diagnostic applications as

prolonged exposures were not a problem and low power had the advantage of sparing the tube.

However, the high-voltage for deep therapy was higher (180 – 250 kV) than for imaging or

superficial therapy (up to 100 – 150 kV). The replacement of coil systems was slower in deep

therapy than in diagnostic radiology because coil systems were easier to make for higher

voltages than transformers. Even around 1920 several authors still doubted that transformers

would overtake induction coils [24,26-28].

The frequency of the pulsed high-voltage supply is relevant for its physiological effect.

Typical frequencies are shown in Table S3. Most frequencies fall within the most dangerous

range of 15 – 100 Hz, except coils with Wehnelt interrupters which mostly worked at higher

frequencies. After 1903 the Wehnelt system and the mercury jet interrupter were the favorite

interrupters for many users, though they were far from perfect [28-31].

Table S3 Frequency of HV-pulses from induction coils with various interrupters [29,30]Type of interrupter Frequency [Hz] RemarksClassical hammer-on-spring, Pt-contacts, Wagner, Neefs 15 - 20 Low power, low voltageMechanical interrupter, with Pt-contacts, Deprez 15 - 40 Low power, low voltageMotor mercury interrupter with dipping contact 20 - 30 Larger coilsMotor mercury interrupter with double dipping contacts 40 - 50 Larger coilsMercury-jet interrupter ≈ 100 Large coils, up to 240 V inputElectrolytic interrupter, Wehnelt 300 – 400a High power

a Typical frequency range, but frequencies could be as high as 5 kHz

7

What happened if a person came into contact with the secondary circuit of an induction

coil X-ray system? It was common to leave the secondary, including the X-ray tube, electrically

floating, i.e. no point was connected to earth. A person touching a live part of such a system

received a shock, but one with little risk (see the discussion below in Appendix 7, “Types of

electrical accidents”, points 1 and 2). When contact was made with both poles of the secondary,

or equivalently with the anode and cathode of a powered tube, more severe shocks were possible.

The time-averaged currents given in Table S2 are unsuitable for estimating risk according

to IEC [11]. Peak currents are required, and these can be assessed from information on inductors

from Rühmer [32] and basic theory of inductors [23,33]. The maximum current in the secondary

after break, Ismax, is equal to I0/M, with I0 the primary current just before break, and M the

transformer ratio of the inductor [23,33]. Some information on a series of typical induction coils

from the Allgemeine Elektrizitäts Gesellschaft (AEG, Berlin) is given in Table S4 [32]. To have

such coils produce their rated spark length, using a mercury interrupter at a frequency of 18 Hz

with equal closure and opening times, the average primary current had to be about 3 A.

Assuming the primary current increased approximately linearly between closure and break, the

maximum current at break (I0) must have been about 12 A. Table S4 then shows the peak-peak

currents that might flow in the secondary in case of a short-circuit.

An approximation of the upper limit of the short-circuit current from these coils might be

calculated in the following way. Rühmer specified the maximum power the inductors could

transfer continuously when they were used as a normal transformer [32]. Although inductors

were not used to generate X-rays in this manner, we assumed the same maximum power in the

calculation of the short-circuit current for conventional interrupted DC. We further presumed

220 V DC-mains was available from which the power could be taken (Table S4).

8

Table S4 Typical properties of inductors [32] and the currents in a short-circuited secondary

Spark length 33 cm 43 cm 54 cm 65 cmWeight 42 kg 58 kg 70 kg 103 kgInductor used as transformer for normal AC as from mains Transformer ratio M, assuming 80% efficiency 240 300 350 420 Maximum power continuously allowed 600 W 900 W 1300 W 1900 WSettings for rated spark length (at 18Hz)a

Voltage (DC) 20 V 24 V 28 V 32 V Primary current I0 before break 12 A 12 A 12 A 12 A Estimated max. secondary short-circuit currentb Ismax = I0/M 50 mA 40 mA 34 mA 29 mAMax. power. 220 V-DC; frequency and current set for max powera,c

Frequency of interrupter 44 Hz 33 Hz 25 Hz 20 Hz Primary current I0 before break 11 A 16 A 24 A 35 A Estimated max. secondary short-circuit currentb Ismax = I0/M 45 mA 55 mA 68 mA 82 mA

a Mercury interrupterb Currents are peak-peak valuesc For 110 V-DC, frequencies would be halved, currents doubled, assuming M remained the same

When a Wehnelt interrupter was used instead of a mercury interrupter, the frequency was

likely in the range of 300 – 400 Hz, and the threshold for the induction of fibrillation increased

by a factor of about 5.

In practice the power supply was adjusted in such a way that a specific gas X-ray tube

received the optimized combination of voltage and current for a specific task. This adjustment

was usually done in the primary circuit by choosing one of several separate primary coils

available in inductors for use with mercury and Wehnelt interrupters, through the adjustment of

rheostats, and sometimes through the introduction of a coil for additional inductance. Thus, in

many cases Ismax would have been less than the estimates presented at the bottom of Table S4.

Comparison with the thresholds for fibrillation in Table 2 shows that the risks generally must

have been small. However, current settings presenting greater risk were possible.

High-frequency coils

9

X-ray systems using high-frequency inductors (often called Tesla coils) as high-voltage

power supply were rather popular in the US, but their specifications were hard to find.

A high-frequency coil generally used the output of an induction coil as its input. The

output consisted of high-voltage bursts of high-frequency oscillations. Specially constructed gas

tubes that suppressed reverse current were required so that only one polarity of the high-voltage

would generate X-rays. The high-voltage and current were of a similar magnitude as those of

commonly used induction coils (the quality of the X-rays was likely similar). The efficiency of a

Tesla coil could be high. A typical frequency might have been about 500 kHz, a high frequency

with low likelihood for causing muscular contraction and ventricular fibrillation. In case a person

short-circuited the output of a high-frequency system the most important effect of the electrical

current was heating of the tissue, implying that burns were possible. Note that the so-called skin-

effect is still negligible for tissue at the frequency mentioned.

Transformers

What is commonly called a transformer differs from an induction coil in that a

transformer’s iron core is normally closed, e.g. often has a rectangular or circular shape. The

core of an induction coil was generally linear and open. The transformer was normally fed by a

sinusoidally shaped AC-voltage, for instance from the mains power supply, and was well suited

for high power applications. The negative lobe of the sinus of the high-voltage had to be

eliminated for the gas tube, so some form of rectification had to be applied. For this purpose

Snook introduced a mechanical rotating rectifier in 1907, along with his transformer [9,15].

Later, suitable rectifying tubes (valves) were developed, and with the advent of the Coolidge

vacuum hot cathode X-ray tube, the X-ray tube itself could be used as rectifier for low power

10

applications. To give an idea of the behavior of a transformer when it is short-circuited, we did

some tests with a simple 220 V (50 Hz), 24 V and 20 VA transformer. The maximum allowable

current is (20/24) = 0.83 A, but when it was short-circuited the output current increased to 5.1 A,

i.e. it became more than 6 times higher. To illustrate the difference in risk between using a

resistor network and an autotransformer for setting the voltage, the primary voltage was

(arbitrarily) set to 150 V for a secondary load current of 0.6 A using each method. When the

transformer was subsequently short-circuited, the current increased to 1.46 A for the resistor

network and 3.56 A for the autotransformer, showing a higher current (corresponding to a higher

risk) of the autotransformer. Although the tested transformer was not of the high-voltage type, it

might serve to illustrate the typical behavior of transformers.

In 1919 a complete X-ray unit in an oil-filled tank, the CDX (Coolidge Dental X-ray

unit), was developed at General Electric based on a patent obtained by Waite [34]. It only

required a low voltage mains connection, and as no voltage carrying parts could be touched, it

was electrically shockproof. Its current, however, was low, 5 or 10 mA at 60 kV. High power

systems were necessarily more voluminous. A few manufacturers built large structures with all

components within one shielded container, sometimes with the power supply outside the

examination room [9]. More flexible high-power systems only became shockproof after the

shielded flexible (rubber) high-voltage cable was developed at the end of the 1920s [51]. Tubes

and power supplies, often submerged in oil, were shielded in separate housings and connected to

each other with the new cable, yielding completely electrically shockproof systems. Philips

introduced such a system, the Metalix Junior, in 1928 [35]. Siemens-Reiniger-Veifa introduced

their TUTO fully shockproof system in 1931 [Siemens MedArchiv; personal communication].

11

Appendix 3 – Table S5 Specifications of the allowed load of some X-ray tubes

Application / manufacturer Year Current & Time the current was allowedGas tubes Fluoroscopy Radiography Therapy Crookes nr. 9 [42] Early 1896 0.1 – 0.2 mA & minutesa

Green & Bauer [40] About 1910 ≈10 mAb & 30 s RGS*, Erlangenc 1915 2 mA & ? 40 mA – 60 mA & ? Philips, type R Id 1923 5 mA & some minutes 40 mA & 5 s Philips, type R II Momentd 1923 70 mA & 0.5 s; 30 mA &10 s

Philips, type T IId 1923 2 mA & 60 min (130 kV) Philips, type T IIId 1923 2.2 mA & 60 min (155 kV)

Hot cathode (Coolidge) tubes GE [43] 1913 26 mA & cont. (70 kV) GE, Universal broad focus [41] 1924 5 mA & cont. (140 kV) 80 mA & 5 s (100 kV) RGS*, Erlangenc 1922 10 mA 20 mA Philips, Metalix Type Dd 1927 6 mA & cont. (120 kV) 100 mA & 0.5 s (70 kV) RGS*, Erlangenc 1925 10 mA & cont. (65 kV) 150 mA & 0.5 s (50 kV) Philips, Rotalixd 1929 2 mA & cont. (100 kV) 230 mA & 0.04 s (100 kV)

6 mA & 10 s (100 kV) SRV, Goliathc 1929 555 mA & 0.1 s (50 kV)

86 mA & 5 s (100 kV)

Philips, Metalix Type Fd 1925 4 mA & contin. (220 kV) SRV, T III/4c 1926 7 mA & contin. (165 kV)

4 mA & contin. (220 kV)a Estimate [42]b Assuming coil efficiency of 50%c from Siemens MedArchiv (personal communication)d Philips (personal communication)

12

Appendix 4 - Safety recommendations and regulations

The American Röntgen Ray Society established a committee to investigate electrical

hazards and provide recommendations to improve safety in 1920 [55]. The results were

published in 1923 [56]. Some of the recommendations were: high ceilings, dry rooms, insulating

floors, no footswitches, quick acting automatic circuit breakers acting on a 20% overload (in

addition to fuses), easily accessible operating switches, overhead high tension conductors at

sufficient height made of tubing not less than half an inch in diameter and firmly mounted,

strong high tension wire on automatically winding reels to connect the X-ray tube to the

overhead tubing and to keep the wires straight, insulating patient table and the application of

sufficient insulation material and distance between persons (both patients and operators) and live

parts.

In the US new rules were provided in the 1931 “National Electrical Code” (NEC)

regulations [7], with revisions in 1933 and 1937. Even in 1936 US legislation did not yet require

that newly installed systems be of the shockproof type [57]. Today’s requirements are laid down

in the 2011 edition of the National Electrical Code NFPA 70, with articles 517 (medical) and 660

(non-medical) dealing with X-ray installations.

In Germany DIN RÖNT I was issued in 1930, providing rules to increase electrical safety

(DIN stands for Deutsches Institut für Normung). It distinguished several classes (A – D) of

systems depending on the degree to which the various parts were shielded with an earthed

conductor [8]. The rules are too detailed to summarize here. The document included a class of

apparatus, A, with all live parts fully protected by an earthed conductor, but such electrically

shockproof systems were still rather exceptional at that time. Electrically shock- proof systems

have been legally required in Germany since 1954.

13

Appendix 5 – Fatal electrical accidents with X-ray systems

Case Approximate Name Age Profession Country (state)

No. date

1 18-Sep-1906 Murphy MF 58 Patient, financier USA, Pennsylvania

2 1-Nov-1917 Clapp AM 41 MD USA, Massachusetts

3 6-May-1919 Fishpaugh RS 21 Private (soldier) USA, Maryland

4 28-Nov-1919 Jaugeas F 39 MD France

5 16-Jul-1920 Cope CL 29 MD, Dentist USA, Indiana

6 11-Nov-1920 Ilg C 35 Dental patient USA, New Jersey

7 16-Aug-1921 Bagley W ?? Demonstrator, nurse USA, Illinois

8 20-Oct-1921 Bryant WE 21 Assistant USA, Massachusetts

9 10-Mar-1922 Law IT ?? MD USA, Florida

10 21-Oct-1924 ?? ?? MD Finland

11 21-Oct-1924 ?? ?? Helper, female Finland

12 1925 Remy E ?? MD USA, Ohio

13 15-Oct-1925 Farago S 30 MD Hungary

14 23-May-1927 Matevich L 38 Father of patient USA, Illinois

15 9-Jun-1927 Cardona A 32 X-ray technician France, Algeria

16 5-Jan-1927 Klubien E 48 MD Denmark

17 6-Feb-1928 Bolton AT 49 MD USA, Ohio

18 7-Jun-1928 Steuer H 35 MD USA, Ohio

19 18-Dec-1928 Laverack D 8 Patient, girl UK

20 6-Feb-1929 Ledon P ?? X-ray technician France

21 8-Mar-1929 Robb HJ 40 MD USA, Montana

22 5-Sep-1930 Yancey BA 25 MD USA, Missouri

23 20-Sep-1930 Chadwick B 22 Nurse USA, Iowa

24 26-Oct-1930 Nyitrai B 36.5 MD Hungary

14

25 2-Mar-1931 Lemire WA 53 MD USA, Michigan

26 1931 ?? ?? Patient Italy

27 29-Oct-1931 K., Lissy ?? Patient Germany, Ostpreussen

28 28-Mar-1932 ?? 46/48 Patient Italy

29 2-Jul-1932 Magnusson HV 65 MD USA, California

30 16-Nov-1932 Eberle JD 52 MD Swiss

31 19-Jan-1933 Davis DD 32 MD USA, Iowa

32 16-Dec-1933 Barnes D 26 Nurse UK

33 5-Sep-1934 Berger S 55 Patient USA, New York

34 20-Mar-1937 Coates WM 29 Physicist USA, New York

35 27-Jun-1937 Thane BJ 51 MD USA, Montana

36 24-Sep-1937 Tracy HM 24 Electrical engineer USA, Illinois

37 2-Oct-1939 Kostas G 10 Patient, boy USA, Idaho

38 18-Jul-1940 Pompa M 29 Patient USA, Connecticut

39 24-Oct-1940 Brixey HH 45 MD, Dentist USA, California

40 17-Dec-1940 Cummings RE 56 MD USA, Pennsylvania

41 24-Sep-1941 Walker H 36 MD, Dentist USA, Illinois

42 11-Mar-1948 Kellet EG 23 X-ray repair man USA, Maryland

43 7-Nov-1949 Mandula I ?? Doctoral candidate Hungary

44 27-Jun-1951 Roderick J 24 X-ray technician USA, Pennsylvania

45 25-Jul-1951 Rius JM ?? MD Spain

46 3-Nov-1955 Walton PK 28 Mother of patient Australia

47 5-May-1956 Esclangon 40 MD?, Professor France

48 21-Jul-1959 Frehner A 6 Child in shoe shop Swiss

49 14-Jun-1962 Jones RJ 80 Patient USA, California

50 1919- 1933 ?? ?? Excited kin of patient Germany (?)

51 1919-1933 ?? ?? MD Germany (?)

15

Appendix 6 - Serious but non-fatal electrical accidents with X-ray systems

Case Approximate Name Age Profession Country (state)

No. date

1 22-Feb-1908 Maloney JJ ?? MD USA,

2 20-Dec-1910 Gaze WH ?? MD Australia

3 5-May-1913 Dr. R. ?? MD (lecturer) Austria

4 1-Oct-1921 ?? ?? Patient Germany ?

5 22-Jan-1922 Dr. B. ?? MD Austria

6 21-Oct-1924 ?? ?? Patient Finland

7 19-Nov-1924 ?? ?? Nurse Germany ?

8 13-Aug-1925 ?? ?? Patient Germany ?

9 15-Dec-1925 Dr. H. ?? MD Austria ?

10 18-Dec-1925 ?? ?? Nurse Austria ?

11 29-Jun-1926 Pike CM ?? Father of boy patient USA, Pennsylvania

12 28-Feb-1928 Matthews A ?? Nurse, student - USA, Iowa

13 8-Mar-1929 Waite ?? Nurse USA, Montana

14 27-Mar-1930 Sidenberg SS ?? MD USA, Ohio

15 27-Mar-1930 Hahn WF ?? Custodian children's ward USA, Ohio

16 27-Mar-1930 ?? ?? Patient, baby/child USA, Ohio

17 1930 ?? ?? MD, intern USA, Missouri

18 7-Aug-1931 Robinson WW ?? MD USA, Washington

19 29-Oct-1931 ?? ?? MD Ostpreussen

20 28-Mar-1932 Gortan M 59 MD Italy

21 28-Mar-1932 D'Este ?? MD Italy

22 28-Mar-1932 ?? ?? MD Italy

23 25-Sep-1933 Geering ?? Fire brigade officer USA, Pennsylvania

24 21-Feb-1934 Selby H ?? MD UK

25 12-Dec-1934 Bethune P ?? Hospital porter Australia

26 11-May-1936 Ratner I 33 Nurse USA, New York

27 25-Oct-1936 Coats EB ?? MD USA, Montana

16

28 17-Dec-1936 Russell 23 MD Australia

29 13-Jun-1939 Speirs RB ?? MD Australia

30 24-Jun-1939 Epstein ?? MD Australia

31 1940 Bonnie (pseudonym) ?? Radiographer UK

32 14-Dec-1944 Barron WH ?? MD USA, Texas

33 1919-1922 Hemler WF ?? MD USA

34 1919-1922 ?? ?? Orderly USA

35 1919-1933 ?? ?? ?? Germany ?

36 1921 ?? ?? Nurse Germany ?

37 1922-1927 ?? ?? Patient Germany ?

38 1922-1927 ?? ?? MD Germany ?

39 1928 Pansdorf H ?? MD Germany

40 1919-1922 ?? ?? Patient USA

41 1919-1922 Dr. F.V.M. ?? MD USA

42 1919-1933 ?? ?? MD Germany ?

43 before 1929 ?? ?? Assistant Germany ?

44 1919-1933 ?? ?? Patient Germany ?

45 1919-1933 ?? ?? MD Germany ?

46 1919-1933 ?? ?? MD Germany ?

47 1919-1933 ?? ?? Engineer Germany ?

48 1919-1933 ?? ?? Nurse Germany ?

49 before 1922 Hemler WF ?? MD USA

50 before 1922 Dr. S.C. ?? MD USA

51 before 1922 ?? ?? Anesthesist USA

52 before 1934 ?? 35 Patient USA

53 1928 Clarke BLW ?? MD Australia

54 before 1918 Thimgan D ?? Father of patient little girl USA

55 2-Mar-1920 Nixon SF ?? Patient USA, Pennsylvania

17

56 before 1926 Pugh-Grant EM ?? Nurse, test-patient USA, Texas

57 before 1928 Curley E ?? Patient USA, Massachusetts

58 before 1929 Ragin ?? Patient USA. California

59 1-Dec-1933 Kelly ?? Mother, helped USA, Pennsylvania

60 before 1944 Rabasco ?? Father of a child patient USA, New York

61 before 1944 McLaughlin ?? Patient USA, Arkansas

62 2-Mar-1955 Sinatra ?? Patient USA, New Jersey

18

Appendix 7 - Types of electrical accidents

We will restrict our evaluation to accidents with transformers as we assume that they

were responsible for nearly all accidents (merely two cases clearly involved coils). Only the most

common accidents will be addressed; more complicated sequences of events and additional

information are found in the work of Grossmann [38,39] and in Grashey’s Chapter 4 of [37].

1. By its construction, the secondary coil of a transformer was normally floating, i.e. not

connected to earth at any point. In this configuration both poles had a similar variation in

potential with respect to earth. For instance, if the secondary voltage was 70 kV peak-to-

peak, each pole’s potential would approximately vary between -35 kV and +35 kV with

respect to ground, and both poles would momentarily have opposite potential. If a person

who was well isolated from earth touched one pole of the secondary, a small current may

have flowed through corona discharges. In addition, a very small current would have been

present as the person and the other pole were both capacitively coupled to ground, forming a

closed circuit of high impedance. These currents would have posed negligible risk. Note that

static machines and induction coils normally had a floating output when used for generating

X-rays as well.

2. If the person was grounded when he touched a floating secondary, e.g., because he was in

contact with a grounded part of the X-ray stand or was standing on a good conducting floor,

the point of contact of the secondary would effectively obtain ground potential. The charge of

the parasitic capacitive system that the secondary circuit forms with earth would change,

leading to a brief current through the person that was felt as a shock. Though it may have

19

been painful, it was likely harmless. In addition, a small continuous current ran as mentioned

above.

3. There was a risk at higher potentials when a grounded person touched a floating secondary. If

one pole of a formerly floating secondary was grounded, the other pole’s potential varied

between plus and minus the full potential, e.g., between – 70 kV and +70 kV for a 70 kV

peak-to-peak output. A transformer, and other parts of the X-ray system, designed to

withstand half of the full potential as was sufficient under normal conditions, could not

necessarily do so with the full potential. If it led to a shortcut, e.g., in the transformer, or to a

discharge to a grounded part, a closed current loop was formed from the contacted pole,

through the person and earth, to the other pole whose isolation failed. The risk of serious

injury or death was high in such an occurrence.

4. To ascertain that the full potential was indeed equally distributed over both poles of the

secondary, some manufacturers grounded the middle of the secondary. These systems were

the most dangerous even if one was exposed to only half of the full potential. If a grounded

person touched one of the poles, a closed circuit was immediately in existence: contacted

pole of secondary, person, earth, middle of secondary.

5. The last type of severe hazard to consider occurred when someone came into contact with

both poles, for instance during repositioning a tube by taking the anode in one hand and the

cathode in the other while the high-voltage was on. Alternatively, another person could also

inadvertently switch the power on, or the victim himself could mistakenly step on the foot

switch intended for fluoroscopy. It was not necessary to make physical contact with a live

part; coming close to it might have had the same effect, although an air gap somewhat limited

the magnitude of the current. It also appeared that in several cases the path of the current was

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considerably more complicated than discussed above. It was not uncommon for metal parts

or several persons to come in series in the path of the current. In an accident of type 5, for

instance, two persons were standing directly next to (or against) each other, and one took the

cathode of the X-ray tube in his hand and the other tried to take the anode while the high-

voltage was on. The current passed through both persons, and both were killed [60]. The

footswitch was a dangerous device because a misstep could turn on the high voltage. It

provided also an effective connection to earth, because either the housing was grounded, or

the electrical wires inside were well within sparking distance when a “hot” foot was on it

(Fig. 1). These wires generally had some connection with mains voltage, and mains voltage

has a low impedance connection to earth.

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