Temporary protective grounds create a secure path to ground for induced voltage on de-energized power lines, which otherwise could produce great risks to workers.
Hazard Analysis — Electrical shocks, burns and/or electrocution
Problem:Workers that install and repair high voltage lines, transformers and switches may face hazards from electrical shocks, burns and/or electrocution.
An electric shock is the passage of an external electrical current between parts of the body or through the body which can cause injury or death. Coming in contact with electrical currents may result in shocks and electrical burns, and potentially cause death if a worker is exposed to a lethal amount of electrical energy. High voltage systems can also form a plasma in air that can cause death or dismemberment.
The electrical stimulation from shocks can sometimes cause muscles to contract. This "freezing" effect makes the person unable to pull free from the circuit which increases the length of exposure to the electricity. This current can cause skin blisters which in turn can reduce the body's resistance thereby increasing the dose of the current. The longer the exposure, the greater the risk of serious injury.
Shock-related injuries can lead to three different types of burns:
- Electrical burns, among the most serious burns, occur when an electrical current flows through tissues or bones. This passage of current can generate enough heat to cause internal burns which can lead to tissue damage.
- Arc or flash burns result from high temperatures caused by an electric arc or explosion near the body. An arc flash occurs when electrical equipment explodes and causes a burst of radiant energy outwards.
- Thermal contact burns result when the skin comes into contact with hot surfaces of overheated electric conductors, conduits, or other energized equipment. Moreover, they can also be caused when clothing catches on fire through the ignition of an electric arc.
The term "electrocution" is used for electrical shocks that results in death. For an electrocution to occur, the human body must become part of an active electrical circuit, having a current capable of over stimulating the nervous system or causing damage to internal organs, usually by internal burns.
Working near high voltage systems may also expose workers to arc flashes which are conditions associated with the possible release of energy by an electric arc or explosion. An arc flash hazard occurs when energized electrical conductors or circuit parts are exposed, or when they are within an electrical equipment that produces an electric arc (i.e. when the equipment shorts) in a guarded or enclosed condition.
Level of Risk:
There is limited data of non-fatal electrical injuries specifically related to the construction sector. However, nonfatal electrical injury rates in the utility industry increased from 1.3 per 10,000 workers in 2003 to 1.7 in 2007. The rise in injury rates in the utility industry was driven mainly by an increased number of electrical shock-related burns that includes electrical, arc/flash and thermal contact burns. The utility industry reported 120 nonfatal injuries from electric shock and 450 from electrical burns.
According to the U.S. Bureau of Labor Statistics, electrocution was the fourth leading cause of death in construction in 2005 (after falls to a lower level, transportation injuries, and being struck by objects and equipment). Also in 2005, electrocutions caused 9% of 1,243 construction deaths. For the general construction industry from 2003-2005, electrocution caused 1.1 deaths per 100,000 full-time workers (Chart A). The rates of death was 30 times that of the average construction worker (among electrical power installers and repairers). Power installers are a subset of electricians who work with live high voltage systems.
By stratifying the same data from 2003-2005 by types of workers, we see a difference in the distribution of causes of electrocutions between electrical and non-electrical workers, Graph A and B, respectively. Among electrical workers, the main cause of electrocutions was contact with energized, or "live," equipment and wiring accounting for 44%. As for non-electrical workers, the main cause of electrocution was contact with overhead power lines accounting for 57% of 238 deaths. Moreover, only one-fifth of these overhead power line electrocutions in non-electrical workers were attributed to direct contact of the worker's body with the live power line; the rest resulted when workers contacted objects or machinery with the power line.
In a 2008 study conducted by Janicak, he found that the proportion of electrocutions is significantly higher for young workers, in the 16 to 19 years old age group, which the main attributal cause was frequent contact with overhead power lines. In comparison, the causes for electrocutions in older workers were mainly attributed to contact with electrical wirings, transformers and other related equipments.
Brett Brenner, James C. Cawley. EHS Today. New York: May 2009. Vol. 2, Iss. 5; p. 47
Janicak, Christopher, A. . "Occupational fatalities due to electrocutions in the construction industry." Journal of Safety Research. 39:6 p.617.
U.S. Bureau of Labor Statistics, Table A9 (Accessed November 2007)
U.S. Bureau of Labor Statistics,Table R64 (Accessed November 2007)
U.S. Bureau of Labor Statistics, 2003-2005 Census of Fatal Occupational Injuries. Calculations by Michael McCann, CPWR.
An energized, or "live," conductor may not appear any different than a dead conductor. For that reason, electrical hazards are usually not apparent. Assessment of electrical contact hazards should be an integral part of the site safety planning process. If someone contacts a source of electricity, the extent of injury depends on these factors:
- The magnitude of the current (affected by the voltage and resistance)
- The pathway of the current through the body
- The flow duration of the electrical current
- The confinement or pathway followed by the plasma in case of an arc
To assess the exposure to potential electrical contacts and arc flashes, it is important to determine:
- If electrical tools are free from wears and tears or any other defects due to normal use and the rugged nature of construction tasks; double-insulated tools usually add more protection.
- If there are warning or danger signs posted when electrical hazards are present; some signs will specifically indicate the approximate voltages.
Here is an example of an electrical hazard checklist.
Assessing Overhead Power Lines Contact Risk
Many construction occupations require workers to perform their job tasks near overhead power lines. Although by no means comprehensive, here is a list of equipment that can be energized if contact occurs to reduce the risk of electrocution from overhead power lines:
- Aerial Work Platforms
- Metal building materials
- Metal ladders
Here is a list of personnel-related considerations to reduce the risk of electrouction from overhead power lines:
- Can the employees 1) competently recognize the hazards of working near overhead power lines and 2) learn how to use the proper procedures in eliminating or minimizing the hazards?
- Are employees cautious when operating vehicles and working with equipments such as ladders, scaffolds and other types of tools and materials that can potentially come within 10 feet of power lines?
- Are there trained and qualified employees ("spotters") on site that can observe the clearance of tall vehicles operating near power lines when it is difficult for the operators to judge and maintain the required distance.
- Are there electronic warning devices installed on cranes, vehicles or other equipments that can help alert operators if the equipments come close to energized power lines.
- If possible, are the overhead power lines are de-energized, insulated and/or grounded prior to the start of work (utility companies or owners of overhead power lines usually have that information)
Regulations & Standards:
Federal OSHA Standards are enforced by the U.S. Department of Labor in 26 states. There are currently 22 states and jurisdictions operating complete State plans (covering both the private sector and state and local government employees) and 5 - Connecticut, Illinois, New Jersey, New York and the Virgin Islands - which cover public employees only. If you are working in one of those states or jurisdictions you should ensure that you are complying with their requirements.
Assessing Effectiveness of Electrical Safety Programs
In order to assess whether electrical safety programs are effective , here are some important elements that employers should keep into consideration to better reduce the risk of electrical contacts. The programs should:
- Be comprehensive; when necessary, revise existing programs to thoroughly address the area of electrical safety in the workplace.
- Be in compliance with existing OSHA regulations (see below "Regulations & Standards").
- Be in compliance with the National Electrical Code and the National Electrical Safety Code (see below "Regulations & Standards").
- Provide adequate training in the identification and control of the hazards associated with electrical energy in their workplace for the employees.
- Provide additional specialized electrical safety training to the employees working with or around exposed components of electric circuits. This training should include, but not be limited to, training in basic electrical theory, proper safe work procedures, hazard awareness and identification, proper use of PPE, proper lockout/tagout procedures, first aid including CPR, and proper rescue procedures. Provisions should be made for periodic retraining as necessary.
- Have proper procedures to control hazardous electrical energy which include lockout and tagout procedures and ensure that employees follow these procedures.
- Have safety meetings at regular intervals.
- Have scheduled and unscheduled safety inspections at work sites.
- Actively encourage all workers to participate in workplace safety.
- Have jobsite surveys before starting any work in order to identify any electrical hazards, implement appropriate control measures, and provide training to employees specific to all identified hazards.
- Ensure that proper personal protective equipments are available and worn by employees where required (this includes fall protection equipment).
- Have job hazard analyses of all tasks that might expose workers to the hazards associated with electrical energy and implement control measures that will adequately insulate and isolate workers from electrical energy.
- Have Identify potential electrical hazards and appropriate safety interventions during the planning phase of construction or maintenance projects. This planning should address the project from start to finish to ensure workers have the safest possible work environment.
Using cover-up equipment properly cover the live power lines to protect line workers from accidental contacts with energized conductors.
Insulating line hose provides a protective barrier to prevent accidental contact with high-voltage lines.
LOTO devices reduce the risk of an unexpected equipment start-up by ensuring that an unauthorized worker cannot energize that equipment.