Cranes and Overhead Power Lines
In a recent four-year review of work-related crane fatalities, 312 people died and only 30 of these were crane operators. The other unfortunate people were working on or near the crane-laborers, riggers, welders, iron workers, carpenters or truck drivers. 72 people, or 23%, died when the crane contacted an energized overhead power line.
Power lines can be hard for the crane operator to see. They sometimes appear to be either further away or much closer than they really are. It is difficult for the human eye to accurately judge the clearance between the crane’s boom or line, and a power line. Fellow workers can help assure that safe clearances are being maintained between the crane, the line, the load and the overhead power line. The table below shows basic clearance minimums, which apply to all areas around the power line-above, below or to either side:
What can you do to help ensure safe operations around energized power lines?
- Help pre-plan the work. Before the crane comes to the project, determine where it will sit and where it will travel. Avoid areas with power lines if possible, de-energize if possible, or mark and flag the area as a last resort.
- Consider any overhead line “hot” until the owner or utility company verifies that it is not energized and is visibly grounded. The line must be “cold” if minimum clearance cannot be met.
- Look carefully before the boom is moved, particularly in congested areas of poor visibility. Get additional workers to help with the move if a clear view of all areas is not possible.
- Place a visual marker, such as a florescent line or flagging to mark off the danger zone.
- Never store materials that must be accessed by a crane beneath a power line.
- If you are on the crane when contact is made, stay with the crane. If you must get off, jump as far from the crane as possible, keep your legs together and “hop” away from the area.
Cranes vs. power lines only have one winner – THE POWER LINES!
Electrical Safety on Construction Sites
Assured Grounding Programs and Ground Fault Circuit Interrupters
Electric shock, and too often fatalities, occur on construction jobsites when temporary power systems are in use. All construction workers who operate power tools should receive training in the systems which safeguard them from electrical hazards.
1. What is the difference between an “Assured Equipment Grounding Program” and GFCI?
• An Assured Equipment Grounding Program is a scheduled system for testing construction site electrical tools and extension cords to assure their proper grounding, polarity and resistance.
• A Ground Fault Circuit Interrupter (GFCI) is equipment that serves as a circuit breaker if it senses a 5 milliamp or greater difference in current between the hot and neutral sides of the circuit.
2. Under what conditions must Ground Fault Circuit Interrupters (GFCI) be used on a worksite?
• When electrical tools and extension cords are used in connection with the process of construction or alteration — and
3. Under what conditions are GFCI’s not required?
• When the company has an established, implemented Assured Grounding Conductor Program that systematically tests for continuous circuitry on electrical tools being used on the worksite.
• When employees are instructed NOT to use any equipment that does not meet the requirements of the Assured Grounding Program.
• When 120-volt, single-phase, 15-20 ampere receptacle outlets are being used, which are not a part of the permanent wiring of buildings or structures.
4. When must electrical tools and extension cords be tested for grounding and continuity of the circuitry?
• Before first use.
• When returned to service following repairs.
• At least every three months on a scheduled basis.
5. What types of defects should workers continually look for?
• Deformed or missing pins, insulation damage and indications of possible internal damage.
6. What does the Assured Grounding two-color coding system identify?
• The first color (usually colored tape applied to the cord) identifies the quarter in which the equipment was last tested; the second color identifies the month within the quarter when the last test took place.
7. What equipment is excepted from Assured Grounding tests?
• “Double insulated” tools, which are clearly marked and identifiable as a double insulated tool usually by a “D in a square”. These tools should nevertheless be inspected by workers, before each use, for cord damage or case damage and may also be taped for inclusion in the overall program.
8. What kind of records are kept on an Assured Equipment Grounding Program and who keeps them?
• The color coding system must be maintained as part of the company’s written safety program. A log of the items inspected and date of the test must be kept by an authorized person who is competent to recognize electrical hazards.
9. When there are general and subcontractors on a job site, who is responsible for the assured grounding or GFCI program?
• Each subcontractor on a job may use his own individual program, but general and sub- contractors alike are responsible for having a program in place — preferably coordinated. (Good generals insist on a coordinated program to avoid mishaps, cross color-coding and to help maintain enforcement. The code colors within a “test period” are often displayed in a visible location by the inspector, for all workers to see.)
• Unless the general provides GFCIs for central power and all portable power stations at jobsite locations, subcontractors must provide their own GFCIs or Assured Equipment Grounding Program for all temporary power use.
10. When should Assured Grounding or GFCI training be provided to construction workers and what should be included in the training?
• All new employees to the jobsite, who use electrical tools, should receive training or a review of this electrical safety program.
Training should at least include:
./ The purpose of these electrical safety measures;
./ The color code system in operation;
./ How to identify electrical hazards;
./ Procedures for reporting electrical hazards;
./ GFCI uses and limitations;
./ How to troubleshoot a GFCI “trip.”
The following rules apply only to electrical installations used on the jobsite, both temporary and permanent:
1. Extension cords used with portable electrical tools and appliances shall be of three-wire types. Grounds are never to be removed from the extension cords.
2. Temporary lights shall be equipped with guards to prevent accidental contact with the bulb. Guards are not required when the reflector is constructed in such a way that the bulb is deeply recessed.
3. Temporary lights shall not be suspended by their electric cords unless cords and lights are designed for this means of suspension.
4. Splices shall have insulation equal to that of the cable.
5. Electrical and extension cords or cables are not to be laid on floors, in walkways, etc., unless it is impractical to do otherwise. They should be suspended or secured in such a way as not to block or hang in walkways, doorways or work areas.
6. Panel boxes shall have a cover on them at all times, except when being serviced and when a temporary cover is in place it should be marked “HOT” to denote live current.
7. Explain to the employees which ground fault system is being used, either GROUND FAULT CIRCUIT INTERRUPTERS OR ASSURED EQUIPMENT GROUNDING CONDUCTOR PROGRAM.
With electricity we are dealing with something that cannot be seen and is still the
most useful power controlled by man. It is useful but can be a very destructive power to both man and material if the proper precautions are not taken. The danger is always there and we must know what means of protection can be used to eliminate the hazards.
Portable Power Tools
In construction portable power tools with defective wiring cause many injuries. The following safe practices are recommended:
1. Use tools with three wire plug and make sure connections are tight.
2. Check tool, equipment and cables frequently for safe condition.
3 .Disconnect tool before making adjustments or repairs.
4. When using power tools in a wet area, use caution. The shock hazard is increased.
5. Selection of protective systems
BEFORE USING – make a safety check for loose cable connections, bare wires, cracked outlets and missing or damaged face plates.
WHEN USING – be sure plug fits firmly and check for any signs of heating caused by faulty connections.
TO REMOVE CORD – GRAB AT PLUG
Yanking a cord from an outlet can:
- Break cord insulation and wires
- Pull loose wire connections
- Bend plug prongs
- Spread clips inside outlet
ABOUT THE THREE (3) PRONG PLUG
Guard it! It is your shock LIFEGUARD. Never cut off the third prong to fit an older two-hole outlet. Never use a two-wire extension cord with this three prong plug. If using an adapter at a two-hole outlet, be sure the pigtail is attached to face plate screw.
(NOTE: Screw must be tested for known “ground source”.)
What is lockout/tagout?
What must be locked or tagged out
Electrical controls, equipment and circuits
Although lockout/tagout is mentioned in the construction rules at these few places, those rules can be applied to all electrical and mechanical lockout/tagout situations at your worksite. It would be foolish to just apply them to electrical and concrete work.
The best approach to take is to follow the general industry lockout/ tagout rule at 29 CFR 1910.147 and put together a written program to cover all lockout/tagout situations at your worksites.Power Line Contacts in Construction
Each year, fifty-five construction workers are killed by electrocution from contact with overhead power lines.
Over 90 percent of the contacts involved overhead distribution lines. These are the same lines that run in the alleys behind our houses and through our job sites.
There are distinct patterns to these fatalities. The most obvious is apathy. We all grew up around power lines. Since they are so common to us, they seem harmless. This serious mistake is fueled by two common misconceptions: the belief that some overhead lines don’t carry enough power to kill, and the belief that power lines are well-insulated. Both are dead wrong.
The leading category of contact involves heavy equipment– cranes, drilling rigs, concrete pumps, aerial buckets, and backhoes. Of all heavy equipment contacts, cranes–either mobile or boom trucks– account for 57 percent of electrocutions. The type of crane most likely to kill the operator is the boom- truck. Contact typically occurs with the rig’s boom or load line. Boom trucks are designed with the controls located on the side of the truck chassis, or in some cases attached to a tether. With both designs the operator is in direct contact with the ground. When contact occurs between the equipment and the power line, the electricity looks for the shortest distance to ground. The operator is almost always in this path, and is electrocuted. But when a mobile crane contacts a power line, it is usually the rigger or ground worker who is electrocuted. Unlike the operator sitting in the cab, they are not isolated from the ground. If a contact occurs while the rigger is attaching a load, or guiding it with a tag line, electricity passes through the load line to the worker on the ground.
Drilling rigs, aerial buckets, backhoes, concrete pumps, and other high-reaching equipment account for another 29 percent of power line contacts. Fatalities associated with high-reach aerial baskets usually occur when the basket makes direct contact with the power line. Accidents involving drilling rigs, however, usually affect the ground workers. With most equipment, the largest number of contacts happen during machinery movement, and not during the setup or take-down phase. The exception is concrete pumps, when incidents tend to occur during the take-down phase. Apparently, during setup and use of the pump operators are more careful. But when the work is completed, they use less caution retracting and storing the boom. The use of metal extension ladders around power lines is also a frequent cause of fatalities. One study on ladder electrocutions found that virtually all fatalities involved metal ladders. Ladder contacts usually occur during erection, lowering or relocation of the ladder.
Protect yourself from live power lines; look around your work area and identify the location of all power lines before you move or erect any equipment. Make certain that no part of any equipment can come within a minimum of 10 feet from the power line. And remember, this distance is greater for voltages above 50kV. Don’t operate equipment around overhead lines unless you are authorized and trained to do so.
Contrary to what many people think, overhead power lines do carry enough voltage to kill and most are not insulated.