Water Well Journal

April 2016

Water Well Journal

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to review the location of the power lines and the steps that will be taken to prevent encroachment or electrocution. If tag lines are used, they must be non-conductive, mean- ing they can't become energized. Tag lines are a rope (usually fiber) attached to a lifting load for controlling or stabilizing a bucket or magnet during material handling operations. One end of the tag line is attached to the load and the other end is held by a worker who controls the load's motion by exerting force on the line. If the equipment or load were to contact a power line while an employee is holding a tag line that can conduct electricity, the employee would be electrocuted! Requiring the tag line be non-conductive is designed to protect against such an event. Under dry conditions, non-metallic fiber rope typically satis- fies the definition of non-conductive. Workers need to set up and maintain an elevated warning line, barricade, or signs in view of the operator—equipped with flags or high-visibility markings. These need to be 20 feet from the power line or at the minimum distance under Table A. Barricades can be temporary fencing or equipment or stor- age containers placed at the minimum distance barrier to pre- vent equipment movement within the encroachment zone. Such boundaries must still be marked with flags, a warning line, or signs that limit all crane movement. Important too: If the crane or equipment operator is unable to see the warning line, a dedicated spotter must be used. Other safety measures include a proximity alarm, range control device, range of motion limiting device, or an insulat- ing link. Other safety controls include insulated sleeves at- tached directly to power lines and boom-cage guards—which are non-conductive cages surrounding the boom of the crane. All these measures and controls may further prevent and protect against contacting power lines. But the measures dis- cussed earlier must still be observed if any part of the equip- ment or load could get closer than the minimum approach distance permitted in Table A. What to Do If You Hit a Line Power line contacts involving mobile cranes generally don't result in injuries to the crane operator. Injuries and death are often suffered by the riggers or workers standing near the equipment. The reason for fewer injuries to operators is equip- ment design. If a contact occurs, the operator is at the same voltage potential as the equipment is. When the operator is isolated in the crane cab and contacts a line, the operator should wait in the crane and all other workers should stay away from the equipment. The line should be de-energized by the power company before the op- erator leaves the crane cab or until contact between the boom and the power line is broken. Only under extreme circum- stances, such as fire, should the operator leave the equipment. If the operator must leave the equipment, the operator must jump from the equipment and land feet together. Care must be taken to not touch any part of the crane and the ground at the same time. The operator must then shuffle his or her feet in very small steps (or bunny hop) away from the crane. After contact with a power line, the current flows outward from the point of contact through the soil in a ripple pattern. Areas of high and low potential circle the energized equip- ment—just like ripples in a pond after a stone hits the surface. If a person steps from an area of high potential to an area of low potential, electricity can flow through their legs, causing injury or death. The current flowing through the ground is also why other workers in the area of the energized equipment must stay away. The Bottom Line Contact with overhead power lines continues to be the most common cause of crane-related fatalities. Overhead power lines should be identified before any equipment arrives on site by conducting an assessment inside the work zone. If the assessment shows the crane could get closer than 20 feet for lines rated up to 350 kV, measures must be taken to pre- vent encroachment or electrocution. The first consideration should be to have the power lines de-energized and visibly grounded. If this is not doable, then other safety precautions must be taken to make sure the mini- mum clearance distance for power lines is maintained. For power lines less than 50 kV, the boom and all parts of high-reaching equipment must be kept at least 10 feet away. For power lines with higher voltages, the minimum clearance distance is increased. SAFETY from page 33 DACUM Codes To help meet your professional needs, this column covers skills and competencies found in DACUM charts for drillers and pump installers. DO refers to the drilling chart. The letter and number immediately following is the skill on the chart covered by the article. This article covers: DOA-4; DOC-5, 9, 12; DOD-4, 5, 6, 8; DOI-3; DOK-8, 9 More information on DACUM and the charts are available at www.NGWA.org. 29 CFR 1926.1408 Table A Voltage Minimum Clearance Distance Up to 50 kV 10 feet Above 50-200 kV 15 feet Above 200-350 kV 20 feet Above 350-500 kV 25 feet Above 500-750 kV 35 feet Above 750-1000 kV 45 feet Above 1000 kV (As established by the utility owner/ operator or registered professional engineer who is a qualified person with respect to electrical power trans- mission and distribution) waterwelljournal.com 34 April 2016 WWJ Figure 1. OSHA's minimum clearance distances.

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