CSSC_Barriers_PIW_Hazard_Letter_Report_21Jan11.pdf

ERDC/CERL LR-11-XXX January 2011

SEPT 2009 ELECTRIC FIELD STRENGTH ANALYSIS OF THE CHICAGO SANITARY

AND SHIP CANAL ELECTRIC BARRIER SYSTEM

Michael McInerney, Brianna Aubin, Jonathon Trovillion, Carey Baxter, Vincent Hock, Charles Shea

US Army Engineer Research and Development Center Construction Engineering Research Laboratory

PO Box 9005 Champaign, IL 61826-9005

ERDC/CERL Letter Report LR-11-XXX January 2011

ENGINEERING ANALYSIS OF THE CHICAGO SANITARY AND SHIP CANAL

ELECTRIC FISH BARRIER: ELECTRIC FIELD STRENGTHS

BACKGROUND

The US Army Corps of Engineers (USACE) - Chicago District is safely operating an electric field-based aquatic nuisance species dispersal barrier project in the Chicago Sanitary and Ship Canal (CSSC), Romeoville, Illinois. The barriers were constructed by Smith-Root Inc, sole licensees of the U.S. patent (Smith 1988), to prevent the movement of invasive species, such as the Asian Carp (Rasmussen 2001), between the Mississippi River and Great Lakes basins. The barrier project consists of two distinct parts:

the demonstration barrier (Barrier I) and Barrier II. Barrier I, which consists of steel cables fastened to the bottom of the canal, sends a low-voltage, pulsing direct current (DC) through the water in order to repel invasive fish. Barrier II is also a pulsed DC barrier and is located 800 to 1,300 feet downstream of Barrier I. Barrier II is able to generate a more powerful electric field over a larger area and consists of two sets of electrical arrays and control houses, known as Barriers IIA and IIB. Each control house and set of arrays can be operated independently. Currently only Barrier IIA is in operation. Barrier IIB is in the final stages of construction and operational testing. Figure 1 shows the relative locations of Barriers I, IIA and IIB.

Previously completed in-water electric field strength mapping and safety testing at the barrier project is described in detail in:

Engineering Analyses of the Chicago Sanitary and Ship Canal Electric Fish Barrier: Electrical Effects on Barges and Tow Vessels. U.S. Army Corps of Engineers, Engineering Research and Development Center Construction Engineering Laboratory. May 2005.

Engineering Analyses of the Chicago Sanitary and Ship Canal Electric Fish Barrier: Electrical Effects on Personnel in the Waster. U.S. Army Corps of Engineers, Engineering Research and Development Center Construction Engineering Laboratory. February 2006.

Dispersal Barrier IIA Electric Field Strength and Sparking Potential Testing. U.S. Army Corps of Engineers, Chicago District and Engineering Research and Development Center Construction Engineering Laboratory. 24 October 2006.

Dispersal Barrier IIA Sparking Potential and Electric Field Strength Testing to Determine the Optimal Operating Configuration. U.S. Army Corps of Engineers, Chicago District and Engineering Research and Development Center Construction Engineering Laboratory. 11 June 2007.

Demonstration Dispersal Barrier and Dispersal Barrier IIA Sparking Potential and Long Tow Testing to Determine Safety Considerations. U.S. Army Corps of Engineers, Chicago District and Engineering Research and Development Center Construction Engineering Laboratory. 12 May 2008.

Evaluation of Risk That Electric Fish Barriers Pose to Human Immersion in the Chicago Sanitary and Ship Canal. U.S Navy Experimental Diving Unit. June 2008.

Prior to August 2009, Barriers I and IIA were operating at maximum in-water field strength at the water surface of 1 Volt/inch (V/in) with five pulses per second (a frequency of 5 hertz (Hz)) and each pulse 4 milliseconds (ms) in duration. USACE and Smith-Root are engaged in an ongoing research program to identify the most effective combination of electric field strength, pulse frequency, and pulse duration for deterring all sizes of carp. After environmental DNA (eDNA) monitoring indicated that Asian Carp may have migrated closer to the barrier system than previously thought, the operating parameters at Barrier IIA were increased in August 2009 to levels recommended based on the research completed at that time: a maximum in-water field strength at the water surface of 2 V/in with a pulse rate of 15 Hz and a pulse duration of 6.5 ms. Increasing the Barrier IIA operating parameters raised concerns about conducting barge and boat operations safely and the potential hazards to a person who fell into the water. During preliminary discussions between ERDC-CERL, the Coast Guard, and the Chicago District, it was emphasized that it is crucial to identify and understand the risks associated with the new operating parameters.

ERDC-CERL supported the Chicago District by completing various tests to establish the risks posed by the new operating parameters to assist in the determination of appropriate safety guidelines. These tests were conducted over three time periods: August 17 and 18, 2009; September 2 and 3, 2009; and September 23 and 24, 2009. The following tests were completed:

1. Determination of whether sparking will occur between barges during typical fleeting operations at the Midwest Generation docks.

2. Measurement of the voltage potential differences between barges during the sparking potential testing to attempt to determine the level of potential differences that can lead to sparking.

3. Determination if the operation of Barrier IIA will affect the corrosion potential of barges moored in the fleeting area.

4. Evaluation of voltages and currents a person could be subjected to if, while traversing Barrier IIA, they touch two metal objects in contact with water (e.g. metallic hull penetrations) that are not electrically bonded. For this test protocol, a vessel with no common ground was used.

5. Examination of the possibility of ignition of gasoline stored on board a vessel traversing Barrier IIA. This test evaluated the energy of measured voltages and currents for sparking potential.

6. Determination of the possibility of damage to electronic (e.g. propulsion control, navigation, radio) equipment on a vessel traversing Barrier IIA. This test evaluated whether the barrier has any effect on the quality of the power distribution of the vessel.

7. Evaluation of voltages and currents a person would be subjected to while in the water in the barrier area.

8. Determination of the possibility of electric shock to a person in a barge or boat by measuring the voltages and currents between fixed and moving barges in the fleeting area and the dock.

9. Determination of the barge sparking potential by measuring the voltages and currents between barges passing through the barrier area and in the fleeting area.

This report covers Test 7 only. Data from the other tests has previously been shared with the U.S. Coast Guard. USACE is also preparing a summary compilation report of the results of the other tests.

APPROACH

Task 7 - Determine the Electrical Hazard to a Human in the Water

Experimental Approach

Tests were conducted on 24 September 2009 to determine the electrical hazard to a human who falls into the water. Refer to Figures 2 through 5 for information on the barrier physical configuration, measurement setup, and testing protocol. Measurements were acquired to simulate voltages and currents across a body immersed in the water. Measurements of voltage (1) between horizontal electrodes spaced one-foot apart were used to simulate voltages across the chest and feet, (2) between horizontal electrodes spaced six-feet apart were used to simulate voltages through a body floating prone in the canal, and (3) between two vertical electrodes spaced five-feet apart were used to simulate voltages across an upright body. Measurements of current (1) through a 100-ohm (Ω) resistor between two horizontal electrodes spaced one-foot apart simulated current flow through the chest, (2) between a 500-Ω resistor between two horizontal electrodes spaced six-feet apart simulated voltages through a body floating prone in the canal, and (3) through a 500-ohm resistor between two vertical electrodes spaced five-feet apart simulated current flow through an upright body. Voltages and currents were measured using separate sets of sensing electrodes, located adjacent to each other. Data was collected along three pathways in the canal (Figure 5). Each path covered a minimum distance of at least from the Midwest Generation fleeting area to the aerial pipeline arch. This extended the data collection region well beyond Barrier I and Barrier IIA.

Barrier IIA was operated in the recommended physical configuration and testing was done only at that configuration (Figure 2). Barrier IIA was operating at a maximum in-water field strength at the water surface of 2 V/in, with a 6.5 ms pulse width, and a 15 Hertz frequency. Ambient temperature, humidity, and water conductivity measurements were recorded throughout all testing. The platform used was a 22-foot Guardian Boston whaler owned by USACE.

Details on the instrumentation used for data collection and the data reduction procedures are presented in Annex 1.

Analysis of Data

The Navy Experimental Diving Unit (NEDU) report, “Evaluation of Risk That Electric Fish Barriers Pose to Human Immersion in the Chicago Sanitary and Ship Canal” was used as the basis for computing the range of harmful physiological effects from the measurements. The NEDU based their threshold voltage levels for harmful effects on International Electrotechnical Commission (IEC), Publication 60479-1, “Effects of Current on Human Beings and Livestock - Part 1: General Aspects.” Table 13 of the IEC publication (reproduced as Table A-1 in Annex 2 of this report) defines four zones of physiological effects to the human body due to DC current pulses. The zones are differentiated by duration of current pulse and body current. The most harmful effects occur in Zone DC-4 and include cardiac arrest, breathing arrest, and burns or other cellular damage.

The NEDU computation is for the worst-case effect: current through the chest of a body upright over the barrier. For this scenario, the measurements of the open circuit voltage with one-foot electrode spacing at approximately one foot below the surface, V12, are used.

Minimum electric field strengths required to induce physiological effects were derived using the formulas and methods given in the NEDU report. Details of the analysis are presented in Annex 2. Table A-2 summarizes the results of this analysis. A worst-case value of 0.05 V/in was determined to be the threshold for harmful effects. Voltage gradient data collected in the field was then analyzed to find the points where the field exceeded this limit.

RESULTS

Environmental data collected during the field testing is summarized in Table 1.

Electrical field strength data for V12 from runs 1 through 9 is presented in Figures 6 through 13. The zero point on the x-axis of these figures is centered between Barrier IIA’s two northern-most sets of electrodes (see Figure 16). This is where the electric field strength of Barrier IIA is the strongest.

Figures 14 and 15 show the threshold for harmful effects, ±0.05 V/in, overlaid on top of the electric fields measured over Barrier IIA and Barrier I in run 1. These figures are representative as to how each run was analyzed to determine the range of harmful effects. The areas where the peaks of the electric field extend beyond ±0.05 V/in are the areas where it is potentially dangerous for a person to be in the water.

Isolated “spikes” in the voltage gradient beyond the main “humps” of voltage gradient created by the barriers are due to electrical noise and are not harmful. Previous testing has shown that these spikes due to electrical noise are detected in the canal even when the barriers aren’t operating (see the other testing reports referenced in the Background section of this report).

Tables 2 and 3 present the range of voltage gradients sufficient to cause harmful physiological effects for each run completed over each barrier. These values were obtained by examining the electric field plots and estimating where the voltages crossed the threshold limit lines for harmful effects. The greatest extent of the harmful effects for Barrier IIA is 522 feet (ft) (159 meters (m)), between 246 ft (75 m) downstream and 276 ft (84 m) upstream of the center of Barrier IIA’s two northern-most sets of electrodes. The greatest extent of the harmful effects for Barrier I is 322 ft (98 m), between 1089 and 1411 ft (332 to 430 m) upstream of the center of Barrier IIA’s two northern-most sets of electrodes.

CONCLUSIONS

Figure 16 shows the areas of likely harmful effects with Barrier IIA operating at a maximum in-water field strength at the water surface of 2.0 V/in with a 15 Hz pulse frequency and 6.5 ms pulse duration and Barrier I operating at a maximum in-water field strength at the water surface of 1.0 V/in with a 5 Hz pulse frequency and 4 ms pulse duration.

When Barrier IIB is activated and at any time that the operating parameters of a barrier are changed, the electric field strengths in the water must be mapped again to determine the areas of harmful effects.

However, the approach laid out in Annex 2 and the Results section of this report will still be applicable and can be used to evaluate the new field mapping results.

REFERENCES

“Effects of Current on Human Beings and Livestock - Part 1: General Aspects,” International Electrotechnical Commission (IEC), Publication 60479-1, 4th ed (Geneva, Switzerland: IEC, 2005).

“Evaluation of Risk Posed by Electric Fish Barriers to Human Immersion in the Chicago Sanitary and Ship Canal,” Navy Experimental Diving Unit, LT 07-05, NEDU TR 08-01, June 2008.

Rasmussen, J.L. 2001, The Cal-Sag and Chicago Sanitary and Ship Canal: A Perspective on the Spread and Control of Selected Aquatic Nuisance Fish Species, U.S. Fish and Wildlife Service, 4469 - 48th Avenue Court, Rock Island, IL 61201, 26 pp.

Smith; David V., Fish repelling apparatus using a plurality of series connected pulse generators to produce an optimized electric field, United States Patent 4,750,451 June 14, 1988.

ACKNOWLEDGEMENTS

ERDC-CERL is grateful for the assistance of the Chicago District during the field exercises, including providing the Boston Whaler and pilot for the field mapping exercises.

Chicago District Corps of Engineers field testing team Jeff Zuercher, Project Manager Sinko Higgins, Whaler Pilot

TABLES

Table 1. Environmental Conditions During Testing

Date Time Mean Temperature (°F)

Average Humidity

Precipitation (in)

Water Temperature

(°F)

Water Conductivity

(µS/cm)

Water Resistivity (mhos-cm)

24 September 2009 14:10 636 1572 15:15 79.3 55 0 17:35 72.0 73 0 73.4

Table 2. Locations of Barrier IIA Voltage Gradients (≥0.05 V/in) Sufficient to Cause Harmful Physiological Effects

Run Location in Canal Range in ft (m) Downstream Distance with respect to IIA in ft

(m)*

Upstream Distance with respect to IIA in ft (m)*

1 East Wall 443 (135) ‐230 (‐70) +213 (+65)

2 West Wall 522 (159) ‐246 (‐75) +276 (+84)

3 Center 420 (128) ‐171 (‐52) +249 (+76)

4 Center 351 (107) ‐92 (‐28) +259 (+79)

5 East Wall 440 (134) ‐203 (‐62) +236 (+72)

6 West Wall 354 (108) ‐85 (‐26) +269 (+82)

7 Center 410 (125) ‐151 (‐46) +259 (+79)

8** West Wall ‐ ‐ ‐

9 East Wall 472 (144) ‐217 (‐66) +256 (+78)

Greatest Extent 522 (159) ‐246 (‐75) +276 (+84)

* Distances are from a zero point at the center of Barrier IIA’s two northern-most sets of electrodes. This point is shown on Figure 16.

** Electric field measurements not included due to inaccurate GPS measurements.

Table 3. Locations of Barrier I Voltage Gradients (≥0.05 V/in) Sufficient to Cause Harmful Physiological Effects

Run Location in Canal Range in ft (m) Downstream Distance with respect to IIA in ft

(m)*

Upstream Distance with respect to IIA in ft (m)*

1 East Wall 223 (68) 1089 (332) +1312 (+400)

2 West Wall 308 (94) 1102 (336) +1411 (+430)

3 Center 262 (80) 1096 (334) +1358 (+414)

4 Center 295 (90) 1096 (334) +1391 (+424)

5 East Wall 256 (78) 1096 (334) +1352 (+412)

6 West Wall 295 (90) 1109 (338) +1404 (+428)

7 Center 269 (82) 1122 (342) +1391 (+424)

8** West Wall ‐ ‐ ‐

9 East Wall 276 (84) 1109 (338) +1385 (+422)

Greatest Extent 322 (98) 1089 (332) 1411 (430)

* Distances are from a zero point at the center of Barrier IIA’s two northern-most sets of electrodes. This point is shown on Figure 16.

** Electric field measurements not included due to inaccurate GPS measurements.

FIGURES

Figure 1. Relative Locations of Barriers I, IIA, and IIB

Figure 2. Barrier IIA Operating Configuration During Testing

Figure 3. Placement of Electrodes on Test Frame for Field Mapping Measurements

5 feet 10 feet6 feet

Water Surface

Measurements V12 (open circuit) I12 (100 ohm) V13 (open circuit) I13 (500 ohm) V14 (open circuit) I14 (500 ohm) V45 (open circuit

1 foot

3 feet

6 feet

1 2 3

4 5

5 feet 10 feet6 feet

Water Surface

Measurements V12 (open circuit) I12 (100 ohm) V13 (open circuit) I13 (500 ohm) V14 (open circuit) I14 (500 ohm) V45 (open circuit

1 foot

3 feet

6 feet

11 22 33

44 55

Figure 4. Frame Mounted on Whaler During Testing

Figure 5. Field Measurement Paths in Canal

Figure 6. Plot of voltage gradient (V12) for run 1. Zero point reference is shown on Figure 16.

Figure 7. Plot of voltage gradient (V12) for run 2. Zero point reference is shown on Figure 16.

Figure 8. Plot of voltage gradient (V12) for run 3. Zero point reference is shown on Figure 16.

Figure 9. Plot of voltage gradient (V12) for run 4. Zero point reference is shown on Figure 16.

Figure 10. Plot of voltage gradient (V12) for run 5. Zero point reference is shown on Figure 16.

Figure 11. Plot of voltage gradient (V12) for run 6. Zero point reference is shown on Figure 16.

Figure 12. Plot of voltage gradient (V12) for run 7. Zero point reference is shown on Figure 16.

Figure 13. Plot of voltage gradient (V12) for run 9. Zero point reference is shown on Figure 16.

Figure 14. Example of minimum field strength sufficient to cause harmful effects shown on a plot of a Barrier IIA field strength measurement run (run 1, V12). Areas above or below the red lines are areas where the electric field strength is sufficient to be harmful.

Isolated spikes above these lines which occur outside the main area of the barrier electric field are due to electrical noise and are not harmful. The zero point reference is shown on Figure 16.

Figure 15. Example of minimum field strength sufficient to cause harmful effects shown on a plot of a Barrier I field strength measurement run (Run 1, V12). Areas above or below the red lines are areas where electric field strength is sufficient to be harmful.

Isolated spikes above these lines that occur outside the main area of the barrier electric field are due to electrical noise and are not harmful. The zero point reference is shown on Figure 16.

Figure 16. Relative locations of areas of likely harmful effects with Barrier IIA operating at a maximum in-water field strength at the water surface of 2.0 V/in, 15 Hz, 6.5 ms pulse duration and Barrier I operating at a maximum in-water field strength at the water surface of 1.0 V/in, 5 Hz, 4 ms pulse duration.

ANNEX 1 – Instrumentation and Data Reduction

Data Acquisition Equipment

A Pacific Instruments 6000 Series Data Acquisition System was used to continuously measure and record the voltage differentials. This system was chosen because of its multiple independent channel capabilities and its high sampling rate. The data acquisition system was connected to a laptop computer through a GPIB interface and the data was immediately transferred to the computer for storage. Because of the high sample rate and long scan times, barrier pulses were easily captured. When interpreting the Pacific data, the individual pulses and the ‘envelope’ (overall trend of the peak values) of the waveform may both be examined.

The Pacific Instruments 6000 Series Data Acquisition System is a high performance transducer signal conditioning, digitizing, and control system. The system is modular to accommodate applications of different size and transducer types. For this data collection, the Pacific Instruments Model 6033 8-channel strain gage transducer digitizing boards were used. These boards were configured for differential voltage measurements. The input to these boards has an impedance of 50 Megaohms shunted by 1000 picofarads. Measurements were taken using a sampling frequency of 10,000 samples/second for all testing. The unit has a 24-channel capability and the noise per channel is 200 microvolts (μV) peak-to-peak.

Tektronix P5200 High Voltage Differential Probes were used to attenuate the voltage signal level at the input and to isolate the Pacific Instruments 6000. The Tektronix Differential Probe has a 25 megahertz (MHz) bandwidth and an input impedance of 4 Megaohms with a common mode rejection ration of 80 dB at 60 Hz. The maximum voltage input at the 1/50 attenuation setting is 130 V. The maximum voltage input at the 1/500 setting is 1300 V.

GPS Data Collection with ike 300 and ike 304.

Throughout the project all moving electrical measurements were collected and referenced with geospatial coordinates to aid in mapping and determining the extent and nature of the electrical field. Multiple Global Positioning Systems (GPS) were used to record the data. These were placed on the bow of the Boston Whaler. Minimal margins of error for GPS accuracy was recorded at +/- 1 meter. Data for testing runs that exceeded the minimal accuracy were excluded from analysis.

The GPS recorded its position every two seconds. Because the data acquisition instruments recorded voltages at millisecond intervals, in order to georeference the electrical data a linear interpolation of the GPS data was required. The electrical measurements were georeferenced by using the barrier array as a marker. Because the maximum electrical measurement values occur over the barrier, the time values of the measurement files were georeferenced by synchronizing the time of the maximum values with the time of the location of the barrier arrays in the GPS files.

Data Reduction

In order to match the electrical data with the georeference data, the electrical data was downloaded into Matlab, along with the georeference data. The georeference data was broken down by run into separate files. The known GPS coordinates for the center of Barrier IIA were matched up with the largest absolute voltage value contained within each run for the electrical data, and the electrical data for each run matched up with the GPS data for that run via the time logs for each data set. Because the electrical data contained far more readings per minute than the georeference data, linear interpolation was used to infer the GPS coordinates for the voltage readings which occurred between GPS readings, thus providing an approximate GPS position for each reading contained within the electrical data. These newly combined files were then saved according to run number.

ANNEX 2 – Computation of Hazardous Electric Field Levels

The analysis of the effects of the measured voltages and electric field gradients and the resultant body current on a human immersed in the CSSC near the barriers is complex. While many studies of the effects of electrical shock to animals and humans are published in the scientific literature, almost all investigate bodies in air, not immersed in water, and with single current burst shocks from 50 to 60 Hz alternating current (AC). The same is true for electrical safety standards and codes. In addition, many continuously changing environmental and physiological variables characterize the situation.1

The Navy Experimental Diving Unit (NEDU) reviewed electric shock studies as well as appropriate electrical safety specifications and codes in the scientific literature to determine conservative, relevant physiological effects likely to occur in humans exposed to electric shock while immersed in the water, with water conductivity and electric field strengths over the range found in the CSSC.2

Following conservative methods and assumption, NEDU used measured field strength data, together with generally accepted body resistance values, to evaluate the maximum electrical body currents likely to be experienced by a person immersed in the CSSC. The safety and possible physiological effects of derived maximum body currents were evaluated using research studies available in the open scientific literature as well as national and international electrical safety specifications and codes.3

Figure A-1 and Table A-1 are from the International Electrotechnical Commission (IEC) time-current zones of effects of a DC current pulse. They show that to remain below the threshold where patho-psychological effects, such as cardiac arrest, breathing arrest, and burns or other cellular damage, may occur the current through the body must be ≤ 500 milliamperes (mA) DC for each pulse. The region where patho-physiological effects may occur is identified as region DC-4 in this figure. The minimum value of body current to pass into area DC-4 (the c1 curve in Figure A-1), is 500 mA for durations of current flow less than 10 ms. The c1 curve appears to transition to vertical for pulse duration less than 10 ms, so the 500 mA value is valid for both Barrier I’s 4 ms and Barrier IIA’s 6.5 ms pulse widths.

Figure A-1 and Table A-1 can also be used to evaluate the current bursts induced by repetitive pulse shocks. However, the threshold for ventricular fibrillation applicable to the second current burst can be as low as 65% of the threshold current applicable to the first burst. Each succeeding pulse reduces the threshold current appropriate for the preceding burst for ventricular fibrillation by another ≈35%, until a minimum threshold of ≤10% of the single pulse threshold is reached for ≥7 bursts. Since a person immersed in the CSSC near a fish barrier will experience 5 or 6.5 pulses per second for an indefinite period, the value of the threshold current appropriate for evaluating the risk for ventricular fibrillation posed to such a person is ≤10% of the threshold current for a single pulse DC shock4 Reducing the threshold to 10% of the single-pulse current value (as is appropriate for the continuously repeated fish

1 “Evaluation of Risk That Electric Fish Barriers Pose to Human Immersion in the Chicago Sanitary and Ship Canal,” Navy

Experimental Diving Unit, LT 07-05, NEDU TR 08-01, June 2008, page v.

2 Ibid, page 3.

3 Ibid, page 4.

4 Ibid, page 38.

barrier pulses) dramatically changes the fibrillation threshold to a < 50mA pulse for a <5% risk of fibrillation (c1 curve, FigureA-1 and Table A-1).5

Therefore, to identify the areas in the CSSC where it is likely harmful to be immersed in the water, it is necessary to be able to calculate the areas where an immersed person would develop a current through the body greater than 50 mA. This can be done using the demagnetizing factors technique.

In a swimmer not wearing an insulative garment, current can flow into the person through all areas of the body’s surface. In addition, the field within the body can be significantly altered from that which was in the volume of water before the body was immersed. The degree of alteration is strongly influenced by the relative electric resistivity of the water compared to that of the immersed body. ERA Technology Limited, Stoner, and Osborn present a technique that represents the body as an ellipsoid and calculates the ratio of the current density in the body to that in the water before the body is immersed. It solves the problem by “analogy with a corresponding magnetic problem, namely that of determining the magnetic flux density inside a magnetic ellipsoid when introduced into a uniform magnetic field. Solutions to this problem are well known and expressed in terms of ‘demagnetizing factors.’”6

The demagnetizing factors technique reveals that the most severe physical orientation in low resistivity (and thus high conductivity) water is that in which a person is upright, with the electric field oriented in the direction from chest to back (Case A). For high resistivity (and thus low conductivity) water, the most severe exposure orientation occurs when a person’s body is horizontal to the water surface, with the direction of the field oriented along the body length (Case S).7

In order to determine the worst-case electric field value (minimum electric field strength that might produce harmful physiological effects), four combinations of worst-case resistivities and body orientations were analyzed.

Water conductivity data collected by the Metropolitan Water Reclamation District of Greater Chicago at CSSC river miles 304.7 and 296.2 from October 1998 to April 2010 was used in the analysis. Resistivity is the inverse of conductivity. Mean resistivity was 10.19 Ω-m with a minimum of 2.13 Ω-m and a maximum of 20.45 Ω-m. The transition from low to high resistivity occurs around 10 Ω-m. Therefore, the mean value of 10.19 Ω-m could be considered either low (Case A) or high (Case S) resistivity and was evaluated for each case.

The computation of the minimum electric field strength likely to cause harmful effects can be done using equations from the NEDU report “Evaluation of Risk That Electric Fish Barriers Pose to Human Immersion in the Chicago Sanitary and Ship Canal.”

The variables used in the computations are:

k – (water resistivity)/(body resistivity)

5 Ibid, page 38.

6 Ibid, pages 25-26.

7 Ibid, page 26.

Ib – current density in the body once it is immersed

Io – current density in the water before the body is immersed

IB – current produced through the chest area by body current density Ib ρ – resistivity

E – electric field strength

The assumptions used in the computations are:

1) Water resistivity(taken from October 1998 through April 2010 data) o minimum value of 2.13 Ω-m o mean value of 10.19 Ω-m o maximum value of 20.45 Ω-m

2) Body resistivity is 3.75 Ω-m8

3) Cross sectional area of chest is 0.08 m29

4) IB ≤ 50 mA (0.05 A) DC to avoid harmful effects (as explained above)

The computations for the four combinations of worst-case resistivities and body orientations are shown below. References to equation numbers and pages refer to pages in the NEDU report. The results are summarized in Table A-2. The lowest value where harmful effects are likely, and therefore the worst case, is approximately 0.05 V/in.

Low Resistivity Case A k = 2.13 Ω-m / 3.75 Ω-m = 0.57 (Assumptions 1 and 2)

(Ib/I0) = k/(1+[k-1] x 0.566) (Equation for Case A, page 26)

(Ib/I0) = 0.57/(1+[0.57-1] x 0.566) = 0.75

Ib = 0.75 x I0

IB = Ib x 0.08 m2 = 0.75 x I0 x 0.08 m2= 0.06 m2 x I0 (Equation 2, page 27 and assumption 3)

I0 = IB/0.06 m2

I0 ≤ 0.05 A/0.06 m2 (Assumption 4)

I0 ≤ 0.833 A/m2

8Ibid, page 26.

9 Ibid, page 27.

E = I0 x ρ (Equation page 39)

E ≤ 0.833 A/m2 x 2.13 Ω-m (Assumption 1)

E ≤ 1.77 V/m (0.54 V/ft) Threshold for low resistivity Case A

Midrange Resistivity Case A k = 10.19 Ω-m / 3.75 Ω-m = 2.72 (Assumptions 1 and 2)

(Ib/I0) = k/(1+[k-1] x 0.566) (Equation for Case A, page 26)

(Ib/I0) = 2.72/(1+[2.72-1] x 0.566) = 1.38

Ib = 1.38 x I0

IB = Ib x 0.08 m2 = 1.38 x I0 x 0.08 m2= 0.11 m2 x I0 (Equation 2, page 27 and assumption 3)

I0 = IB/0.11 m2

I0 ≤ 0.05 A/0.11 m2 (Assumption 4)

I0 ≤ 0.455 A/m2

E = I0 x ρ (Equation page 39)

E ≤ 0.455 A/m2 x 10.19 Ω-m

(Assumption 1)

E ≤ 4.64 V/m (1.41 V/ft) Threshold for midrange resistivity Case A

Midrange Resistivity Case S k = 10.19 Ω-m / 3.75 Ω-m = 2.72

(Ib/I0) = k/(1+[k-1] x 0.034) (Equation for Case S, page 26)

(Ib/I0) = 2.72/(1+[2.72-1] x 0.034) = 2.57

Ib = 2.57 x I0

IB = Ib x 0.08 m2 = 2.57 x I0 x 0.08 m2= 0.21 m2 x I0 (Equation 2, page 27 and assumption 3)

I0 = IB/0.21 m2

I0 ≤ 0.05 A/0.21 m2

(Assumption 4)

I0 ≤ 0.238 A/m2

E ≤ 0.238 A/m2 x 10.19 Ω-m

E ≤ 2.43 V/m (0.74 V/ft) Threshold for midrange resistivity Case S

High Resistivity Case S k = 20.45 Ω-m / 3.75 Ω-m = 5.45

(Ib/I0) = k/(1+[k-1] x 0.034) (Equation for Case S, page 26)

(Ib/I0) = 5.45/(1+[5.45-1] x 0.034) = 4.73

Ib = 4.73 x I0

IB = Ib x 0.08 m2 = 4.73 x I0 x 0.08 m2= 0.38 m2 x I0 (Equation 2, page 27 and assumption 3)

I0 = IB/0.38 m2

I0 ≤ 0.05 A/0.38 m2 (Assumption 4)

I0 ≤ 0.132 A/m2

E ≤ 0.132 A/m2 x 20.45 Ω-m

E ≤ 2.70 V/m (0.82 V/ft) Threshold for high resistivity Case S

TABLE A-1. Time-Current Zones for Physiological Effects of Single-Pulse DC Shock for Hand-to- Feet Pathway

(Summary of Zones on Figure A-1)

A) Information in this table is reproduced from Table 13 of IEC Publication 60479-1.

Table A-2. Minimum Electric Field Strengths (Voltage Gradients) Sufficient to Cause Harmful Physiological Effects

Water Resistivity (Ω-m)

Body Orientation* Minimum Electric

Field Strength (V/ft)

Minimum Electric Field Strength

(V/in)

2.16 A 0.54 0.05

11.34 A 1.41 0.12

11.34 S 0.74 0.06

26.32 S 0.82 0.07

* A – low water resistivity, electrical field is oriented in direction from chest to back

S – high water resistivity, body is oriented horizontally to the water’s surface with the direction of the field oriented along the body’s length

Figure A-1. Time-Current Zones of Effects of DC Currents (figure 22 of IEC 60479-1).