Solution Summary: Using Overhead Powerline Proximity Warning Devices for Heavy Equipment
Using overhead powerline proximity warning device for heavy equipment is a work practice that can warn and immobilize heavy equipment when it reaches a certain height or unsafe distance from overhead power lines. This can reduce safety risks that might occur if the operator or spotter is distracted and the equipment is tracking into live lines.
Construction workers suffer from electrocution more than any other industries, primarily due to workers and materials accidentally contacting power lines (Figure 1). Warning devices are designed to be installed on any mobile construction equipment – e.g., cranes, trucks, etc. – at risk of coming in contact with high-voltage power lines. These devices have sensors that detect the presence of live current close by and use audio and/or visual warning signals to alert the operator before getting dangerously close to the live lines.
Figure 1. Schematic of a power line contact (Adapted from Homce et al. 2001, Sacks et al. 2001, and www.cplso.org)
A proposed solution for these risks is to use proximity warning devices to alert operators when they approach too close to live lines. Examples of powerline proximity warning devices are provided in Figure 2. These warning devices include an electric field sensor, which is mounted on the heavy equipment. The sensor is designed to sense the electric fields around the overhead power line and to warn when the operator when the equipment passes the preset safe distance from the power line. Further, these detection devices are flexible and can also be placed anywhere safety is concern such as the load itself and on boom arms or any other heavy equipment extension.
Although these devices are reported to be effective in many applications, the manufacturers caution against over-reliance on them, encouraging users to consider supplementary and comprehensive safety strategies (www.osha.gov). Moreover, insulating links must be attached to the crane’s hook and/or boom to prevent the flow of electricity if the equipment accidentally makes contact with energized power lines.
Figure 2. Examples of powerline proximity warning device (Source: www.pipelinemachinerycat.wordpress.com)
In addition, some of these warning devices are used to accurately monitor the equipment’s vertical movement (Figure 3).
Figure 3. Heightwatch 6 to monitor vertical distance of construction equipment from live powerlines.
Contact with electric current is a major cause of injury and death among construction workers (Janicak 2008). In 2012, the Census of Fatal Occupational Injuries (CFOI) data produced by the Bureau of Labor Statistics (BLS) indicated that contact with electric current was the fourth leading cause of work related deaths—after falls, transportation incidents, and contact with objects and equipment (BLS 2012). Electricity can cause electric burns, electrocution, shock, arc flash/blast, fires and explosions.
Electrical hazards may happen due to contact of mobile construction equipment – i.e. boomed vehicles with their extended – with live power lines. Based on the federal regulations in 2002, no part of a crane or suspended load is allowed to come within 10 feet of a 50kV line. If the construction equipment contacts high-voltage powerlines, it might lead to fatal injuries and death, not only for equipment operators, but also for other crews nearby (Figure 4). Poor lighting conditions, poor training, and human error in estimating safe distance may be among the causes of accidental contact with live lines. Therefore, the risk of working near cables must be assessed and controlled.
Figure 4. Potential damage that can occur when a vehicle contacts with a powerline (Source: www.semrad.com.au)
IMPORTANT: Even if the equipment has to pass beneath overhead lines, barriers should be assembled to create a passageway (Figure 5).
Figure 5. Passing underneath overhead lines
Therefore, if construction equipment gets too close to overhead power lines, the electricity will be conducted to earth. This can cause an explosion, electrocution, electric shock, and burns to operators or any other ground workers nearby. Overhead live lines do not need to touch to cause electrocution since the electricity can arc across small gaps.
How Risks are Reduced:
In 2010, OSHA published new regulations and standards for cranes that consider overhead power lines as potential hazards to both operators and ground workers working near equipment with booms or other extension elements that have a potential of reaching high-voltage powerlines. The most effective way to prevent contact with live lines is to use proximity warning devices. These devices can help operators who may be distracted and unable to see the overhead power lines and can prevent fatalities. These warning devices are designed to detect and warn the workers or operators about the risk of shock and electrocution by sensor if mobile equipment moves within some preselected minimum distance of an energized overhead electrical power line.
Effects on Productivity:
Even making contact with less dangerous utilities can cause various risks and damages, which could result in huge costs and reduced productivity. Using warning devices on mobile construction equipment – e.g., trucks, cranes, booms, etc. – can increase productivity by minimizing the risk of accidental contact with overhead powerlines during construction activities.
Other prevention techniques include de-energizing power lines in order to work nearby, using spotters to warn operators of imminent contact, and providing barriers to impede physical contact with live lines [29 CFR 1910.333(c)(3) and 29 CFR 1926.550(a)(15)]. However, these techniques require more field personnel and the expenses associated.
In most cases, the minimum distance will be dictated by occupational safety regulations. For example, the OSHA standards require a clearance of at least 10 ft (3.0 m) for powerlines at voltages up to 50 kV (29 CFR 1926.550). The warning devices should not alarm outside the desired minimum clearance distance since these false alarms may cause the operator to question the effectiveness of the sensor and thereby ignore it completely. The study that has been conducted by Centers for Disease Control and Prevention (CDC) in 2008 on the performance of warning devices suggested to test the performance of warning devices, before initiating crane operation, using small changes in boom length (less than ± 5 ft (1.5 m) and boom elevation angle (less than ± 8°).
It must be noted that warning devices cannot completely prevent accidents. However, if they are properly installed, they would decrease the risk of accidents. The operator needs to set up the minimum distance and check the performance of sensors before operating the heavy equipment on the jobsite.
Sogand Hasanzadeh - University of Nebraska- Lincoln
Behzad Esmaeili, Ph.D. - University of Nebraska- Lincoln
Atlas Polar- HiVolt Alert™ Proximity Warning System
To obtain information, visit http://www.atlaspolar.com/ or contact 1-888-799-4422
Pipeline Machinery International (PLM)- Powerline Proximity Alarm
To obtain information, visit http://www.plmcat.com/ or contact 1-713-939-0007
Sigalarm High Voltage Power Line Warning Device
To obtain information, visit https://sigalarminc.com/ or contact 1-407-321-0722
ProxyVolt Safety Pty Ltd (Distributorship available for North America)
To obtain information, visit http://www.proxyvolt.com.au/ or contact +61-7-3722-6499