[Hallb-engineering] Fwd: Lesson Learned "PHY-16-0829 Employee Shocked While Using a JLG Manlift- No Injuries"
tilles at jlab.org
Wed Nov 30 11:49:27 EST 2016
----- Forwarded Message -----
From: "Tina Johnson" <cjohnson at jlab.org>
To: "Tina Johnson" <cjohnson at jlab.org>
Sent: Tuesday, November 29, 2016 5:00:09 PM
Subject: Lesson Learned "PHY-16-0829 Employee Shocked While Using a JLG Manlift- No Injuries"
Jefferson Lab Lessons Learned : Print Lesson
PHY-16-0829 Employee Shocked While Using a JLG Manlift- No Injuries
Statement of Lessons Learned
1. Improper use of GFCI protection may lead to a lessened level of protection from an electrical shock. It was later determined that the wall outlet used to power the JLG 120 volt cord was not powered from a gfci protected circuit.
If the JLG manlift was plugged into a GFCI protected receptacle initially, then the employee would have benefitted from both let-go protection and protection against fibrillation because of the 4-6 milli-amp trip limit on a class A GFCI.
2.Technicians need to know whether their test tool has a low input impedance or a high input impedance. Technicians also need to understand the advantages and disadvantages of each.
Discussion of Activities
On August 29, 2016 around 10:00 AM a worker in Hall A was using a portable band saw that was plugged into an electrical outlet on the JLG-manlift when he felt a slight shock in his forearm. The employee notified his supervisor and reported to Occupational Medicine. He was determined to be uninjured and was permitted to return to work.
The man lift was tested and it revealed approximately 48 volts AC (VAC) from the structure of the man lift to an earth ground. The connection to the manlift 120 volt circuit was locked and tagged out. There was no indication of damage to the manlift or the electrical system. Facilities Management and Logistics subcontractors inspected the equipment on August 30, 2016 and it was determined by process of elimination using a volt/ohm meter that the internal power cord must be damaged. When the internal power cord was plugged in to 120 volts AC wall power, there was a repeatable 48 VAC between the body of the man lift and earth ground and then when power was removed from the internal power cord the 48VAC disappeared. Discussions with hall staff and the Facilities Management and Logistics subcontractors determined that the internal cord had leakage to the body of the man lift. The internal cord was replaced.
The JLG manlift contractor replaced the integrated 120 volt power cord on the Hall A manlift. The contractor also replaced the internal 120 volt power cord on the Hall C manlift, as a precautionary measure, since this lift was of similar style and age.
Following the repair the Hall A personnel checked the manlift using a digital Fluke 77 multimeter and measured approximately 30 VAC to an earth ground.
A check of the Hall C manlift was also checked since the internal power cord was also replaced and it also was exhibiting ~30 VAC to earth ground when the manlift was powered through a 120 volt wall receptacle.
Observing that some voltage issue still appeared, the following subsequent testing took place to determine the source of the voltage:
1) The man lift was relocated from outside the Hall A enclosure and then powered by another 120 volt wall receptacle (the thought was possible noise on a ground loop within the Hall enclosure).
2) A measurement was taken between the JLG frame and an earth ground separate from the lab electrical grounding system; a metal pipe embedded in the ground, near where the JLG was parked, was used (the thought was to use an even more remote ground point) .
3) The JLG was powered by a portable generator (the thought was to eliminate any connection to the lab electrical distribution system by using a separately derived source of power).
All of the three test setups above still showed ~30 VAC between the JLG frame and a grounding point. At the time of test measurements different models of multimeters (Amprobe-20 and Fluke 77) were used because of availability. During one of the measurements of the setups above it was noticed that the JLG was no longer recording a voltage reading. This specific voltmeter (Amprobe-20) was then rechecked at the wall power receptacle and it read 120 VAC. Then when used on the JLG again it read 0 VAC again. At this point a second meter (Fluke 77) arrived and it measured ~30 VAC between the JLG and a ground. At this point in time the meter (Amprobe-20) that was reading 0 volts was thought not to be working correctly and all other measurements were taken with the Fluke 77 voltmeter.
After further follow up investigation it was determined that the 30 VAC may be from what the industry refers to as a "Ghost" voltage. Ghost voltages occur from having energized and non-energized wiring located in close proximity to each other, such as in the same conduit or raceway. This condition forms a capacitor and allows capacitive coupling between the energized wiring and the adjacent unused wiring. In the case with the JLG, the 120 volt internal cord is ran alongside and bundled with other cords and hydraulic lines.
Most digital multimeters available and used today have an input impedance that is high enough to show the capacitively coupled voltage, giving a false impression of a voltage measurement. Having a high input impedance means that when the digital multimeter is placed across a circuit for a measurement, it will have little effect on circuit performance. This is the desired effect for most voltage measurement applications and is especially important for sensitive electronics or control circuits. The main advantage of low impedance input test tools is that they are not susceptible to "Ghost" voltage as they do not pick up stray magnetic fields.
With thought of this phenomenon, a new test set up was made using two different styles of multimeters. Meter #1 (Amprobe-18) had a high input impedance of 10 Megohms and meter #2 (Amprobe-20) had a low input impedance of 750 Kilo-ohms. The results of the test were that both meters displayed 120 VAC at the wall outlet but when the JLG was measured with respects to ground the high input impedance meter read 30.* VAC and the low input impedance meter read 0 VAC.
With the suspicion of a "Ghost" voltage being measured, another test was sought out to further verify this new conclusion. A Fluke SV225 "Stray Voltage Eliminator" adapter was purchased and used with the high input impedance meter (meter #1). With the combination of the SV225 and meter #1, 120VAC was measured at the wall outlet, 0.167 VAC (basically 0 VAC) was measured between the JLG and an earth ground, and then 120VAC was measured at the wall outlet a second time. The SV225 Stray Voltage Eliminator is a digital multimeter accessory that allows measurements in circuits which may be subjected to stray voltages encountered from adjacent energized wiring. The adapter provides an approximate 3,000 ohm load to the measured circuit, desensitizing the meter to low energy, spurious sources of interferences.
The final disposition is the ~30 VAC being measured is a "Ghost" voltage that is capacitively coupled from the energized internal power cord and that was being recorded with a high input impedance multimeter. Since the "Ghost" voltage is a physical phenomenon involving very small values of capacitance, it cannot energize a load or cause physiological damage to a person.
Root Cause: Equipment failure- It was initially thought that the JLG manlift's internal power cord failed which presented the shock hazard (~45 VAC).
Failure to plug the JLG into a GFCI protected outlet within the Hall. Locating GFCI protection at the beginning of a circuit provides the maximum benefits (a gfci device only protects the downstream circuitry and not any portion of circuitry that is placed before the gfci device).
The inspection checklist is LTA and does not cover all the necessary items to consider the equipment fully inspected. Although an inspection of equipment was complete prior to its use, the semi-annual inspections do not involve testing of the GFCI and the function of the internal power cord.
Extent of condition: Check all the other manlifts that are similar to this JLG manlift to ensure that the built in power cord is in good working condition.
1. Have the contractors inspect, diagnose and fix the failure in the defective man lift.
2. ISM poster to increase awareness of the requirement and proper use of GFCI protection when using extension cords to supply power to equipment used by a worker.
3. Have the contractor add inspection of the 120 volt integrated power cord circuit within their JLG inspection checklist for the lab. At a minimum this should include a visual check of accessible portions of the power cord and an operational check of the 120 volt gfci receptacle in the man basket. The operational check of the receptacle should include a test of the gfci receptacle and verification that the receptacle outlet has the correct polarity and continuity; all to which can be done with a handheld gfci/circuit tester.
4. Send communication to all JLG/Scissor lift owners that they need to ensure that all lifts are plugged into a GFCI wall outlet.
5. Retest the electric bandsaw tool with using one of the lab's "CLARE Safe Check 5" safety checkers. This unit will perform the following test -> ground-bound, short-to-case, short-to-line, and a leakage test.
JLab Preventive Measures
See above mentioned corrective actions
11/29/2016 3:46:47 PM by Johnson, Tina
SME reviewed and approved. Please share these lessons within your work groups.
Summary Lesson ID: 978
Safety Related: NO
Originator: Johnson, Tina
Issued: 11/22/2016 11:21:24 AM
Approved By: Johnson, Tina
Approved On: 11/29/2016 3:46:47 PM
Source: TJNAF NE
Contact: Tina Johnson
Queued Emails: 0
Sent Emails: 0
Viewings: 15 times Attachments
* Material Handling Equipment
* Cranes & Hoists - Ordinary or Pre-Engineered
* SAF300: AERIAL WORK PLATFORM
* SAF301: AERIAL WORK PLATFORM SUPERVISOR ORIENTATION
* SAF302: AERIAL PLATFORM/MANLIFT OPERATION
* SAF303: SCAFFOLD SAFETY
* SAF304: WIRE ROPE INSPECTION TRAINING
* SAF401: CRANE SUPERVISOR ORIENTATION
* SAF402: CRANE OPERATION AND RIGGING
* SAF402-1: CRANE OPERATOR TRAINING
* SAF405: MASTER RIGGING WORKSHOP
* SAF500: SUBCONTRACTOR FORKLIFT TRAINING
* SAF501: FORKLIFT OPERATOR SUPERVISOR TRAINING
* SAF502: FORKLIFT OPERATOR
* SAF603: SAF603A FPA-70E BASIC ELECTRICAL TRAINING
* SAF603A: ELECTRICAL SAFETY AWARENESS
* SAF603N: NFPA-70E BASIC ELECTRICAL SAFETY
* SAF702J: QUALIFIED JOURNEYMAN RIGGER
* SAF702M: QUALIFIED MASTER RIGGER
* SAF303A: BAKER TYPE SCAFFOLDING SAFETY TRAINING
* SAF303B: TUBE AND COUPLER TYPE SCAFFOLD TRAINING
* SAF303C: TUBULAR WELDED FRAME SCAFFOLD SAFETY TRAINING
* SAF403: Overhead Crane Operator Qualification
* SAF302A: AERIAL PLATFORM EQUIPMENT ORIENTATION-RE-QUALIFICATION
* SAF604: HIGH VOLTAGE IN R&D
* SAF502B: FORKLIFT ATTACHMENTS
* SAF603S: Switching of Electrical Equipment
* SAF603M: NFPA-70E for Managers
* SAF112Q: Qweak Target Operation
* SAF404: 2000# Capacity Hoisting and Lifting
* SAF603N1: ARC FLASH:LIVE to TELL! (ELE016EFV)
* SAF603N2: Electrical Safety:Beware of the Bite (ELE5EFV)
* SAF603N3: Electrical Safety for the Qualified Worker (ELECEFV)
* SAF403X: Overhead Crane Operator Qualification-Extension
* *Division Safety Officers (DSOs)
* *Safety Wardens
* *DOE Notification
* *ESH&Q Liaisons
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