Does your crew know how to prevent electrocutions from contact with overhead power lines?
By Jerome E. Spear
Contacting energized power lines can result in fatal electrocutions, if not serious burns or damaged equipment. Contact with overhead power lines is the most common cause of deaths involving cranes or other high-reaching equipment.
Reviewing causes of crane-related deaths in construction from 1992-2006, electrocutions accounted for almost onethird (32%) of crane-related fatalities. Half of all the electrocutions occurred when the crane boom or cable contacted an overhead power line. The rest involved a power line coming into contact with parts of the crane (McCann et al. 2008).
Some years ago, the Occupational Safety and Health Administration revised its requirements for working around overhead power lines. These revisions were contained in OSHA’s Final Rule for Cranes and Derricks in Construction (29 CFR Part 1926) and published in the Federal Register in 2010.
OSHA determined a more systematic, proactive approach to preventing contact with power lines was needed. We will discuss these measures to prevent contact with an overhead power line, as well as what to do if contact is made.
Assess the Hazard
Before beginning operations, a hazard assessment inside the work zone must be performed. The hazard assessment must:
- Identify the work zone and assess it for power lines. Determine how close the crane or any high-reaching equipment could get to the lines. The employer has an option of assessing the area the entire 360 degrees around the crane or assessing a more limited area.
- If the assessment shows the crane could get closer than 20 feet for power lines up to 350 kilovolts (kV) or 50 feet for lines over 350 kV—then requirements for additional action are triggered.
Eliminate the Hazard
If operations involving cranes or drilling rigs will be performed near overhead power lines and the minimum clearance distances specified by OSHA, shown later, cannot be maintained, the first option is to de-energize and visibly ground the power lines. By eliminating the source, the hazard of electrocution is eliminated.
De-energizing the lines has to be coordinated with the utility company or owner of the line. The line owner may need several weeks to comply with the request, so the work should be planned appropriately. Only authorized personnel may de-energize a power line. All power lines shall be presumed energized unless the utility owner or operator confirms the power line has been, and continues to be, de-energized and visibly grounded at the worksite.
If the power line cannot be de-energized for the duration of the work, another option is to move the line the minimum clearance distance it can be maintained. Like de-energizing the line, only the company who owns the line may move it. Again, the line owner may need several weeks to comply with the request.
Keep Your Distance
OSHA’s requirements regarding working near overhead power lines with cranes and other high-reaching equipment are straightforward. For lines 50 kV or less, the operator must keep all parts of the crane or other equipment at least 10 feet away from all power lines. For lifting equipment, this also includes any load being carried.
This minimum clearance distance is a buffer zone that must be kept between the equipment and overhead lines. In other words, minimum clearance is the minimum distance that is allowed from any part of a crane or other high-reaching equipment to an overhead power line.
If the lines have a voltage higher than 50 kV, the line’s minimum clearance distance must be increased according to Table A of 29 CFR 1926.1408, Power Line Safety— Equipment Operations (see Figure 1).
Distribution lines are typically 50 kV or less, whereas transmission lines are typically higher than 50 kV. Distribution lines are the most common lines used by utilities. To determine the voltage rating of the power line, contact the utility company. If you still cannot determine the voltage range, you must keep at least 45 feet away.
Preventing Encroachment or Electrocution
If any part of the crane, equipment, or load (including rigging and lifting accessories)—while operating up to the maximum working radius in the work zone—could get closer than the minimum approach distance permitted in Table A, a number of precautions should be followed.
Conduct a planning meeting with the operator and other workers who will be in the area of the equipment or the load 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, meaning 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 satisfies 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 storage containers placed at the minimum distance barrier to prevent 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 insulating link. Other safety controls include insulated sleeves attached 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 discussed earlier must still be observed if any part of the equipment 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 equipment 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 operator leaves the crane cab or until contact between the boom and the power line is broken. Only under extreme circumstances, 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 equipment— 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 prevent 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 minimum 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.
Added safety measures can be taken to prevent contacts with overhead power lines. However, the bottom line is always this: Keep your distance!
McCann, M., J. Gittleman, and M. Watters. 2008. Crane-Related Deaths in Construction and Recommendations for Their Prevention. Silver Spring, Maryland: CPWR, The Center for Construction Research and Training.
Occupational Safety and Health Administration. 2010. Cranes and Derricks in Construction; Final Rule. The Federal Register.
Jerome E. Spear, CSP, CIH, is president of J.E. Spear Consulting and has more than 22 years of experience helping organizations prevent injuries and illnesses, control losses, and achieve regulatory compliance. He held the positions of technical, services manager with XL Specialty Risk Consulting and corporate industrial hygiene manager for Chicago Bridge and Iron Co., a worldwide steel fabricator and construction company.